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ID Date Author Type Category Subject
  1975   Mon Apr 29 13:53:31 2024 PacoLab InfrastructureOpticsSetting up NeoVAN

Late log from 04/24

[JC, Paco]

We replaced the O-rings on pretty much all connections and ran the leak test successfully, (no leaks). Next is fix the lines to the ground, protect them and manage the cables around the floor.

Next steps:

  • Seed (NPRO = 100 mWs or Mephisto = 1 mWs?) beam shaping and injection through the amplifier.
  1974   Fri Apr 19 20:24:22 2024 PacoLab InfrastructureOpticsSetting up NeoVAN

Late log from 04/16

[JC, Paco]

Now that the last optics including the two PPLN crystals have arrived for the initial SFG experiments we started commissioning the high power laser amplifier in the lab. The amp is a NeoVAN, and we have a controller and head both of which have to be water chilled. The thermofischer chiller we borrowed from the QIL meets the requirements both in cooling power and flow speed for the system, so we started setting it up.

The Attachments below show photos of the reorganization that took place to accommodate the chiller unit, the laser AMP, and the tools/optics cabinets. Furthermore we got a small 19 inch rack to place all the relevant electronics for the Amplifier and the seed (an Innolight NPRO).


Chiller Test

We ran the chiller in a closed loop with no load to (a) check that the cooling is working and (b) test for any leaks at the level of the chiller alone. For the first test, we filled the reservoir to half using deionized water and setup a closed loop of tubing and a setpoint of 17.5 C. The chiller started pumping and after < 10 minutes overshot to ~ 16.1 C so we declared the test done. For the second test we simply placed the cooling lines and their joints on a bucket and verified no leaks were present upon running the first test.

We then installed the full chiller + NeoVAN controller + NeoVAN amplifier unit cycle. For this, we removed some of the screws in the smaller optical table and ran the tube up and into the push-to-connect valves. The inlet is usually in the right hand side and the outlet is at the left. Similarly, we split and ran the inlet and outlet lines for the controller. This time, turning the chiller on at a setpoint temperature of 20.0 C we noticed a small leak at the controller's outlet port. Upon closer inspection we realized an o-ring acting as a seal was broken and quite worn down. JC ordered some O-rings and we hope to be able to replace this soon.

Attachment 1: PXL_20240416_181850082.MP.jpg
PXL_20240416_181850082.MP.jpg
Attachment 2: PXL_20240416_181855136.MP.jpg
PXL_20240416_181855136.MP.jpg
Attachment 3: PXL_20240416_183010539.MP.jpg
PXL_20240416_183010539.MP.jpg
Attachment 4: PXL_20240416_210919538.MP.jpg
PXL_20240416_210919538.MP.jpg
Attachment 5: PXL_20240416_210923834.MP.jpg
PXL_20240416_210923834.MP.jpg
  Draft   Fri Apr 5 13:53:46 2024 Aaron Goodwin-JonesMisc  
  1972   Thu Mar 7 11:27:28 2024 PacoLab InfrastructureLaserTesting Lightwave controller after capacitor replacement

[JC, Masaya, Paco]

After JC replaced the power supply capacitor (400 V, 100 uF), we hooked up a faulty laser head borrowed from CTN, but didn't succeed in even turning the controller on. We made sure the interlock was correct, the laser head was also connected to the unit, and even tested with two different power cords but no success.

  1971   Tue Jan 30 12:48:18 2024 JCMiscOpticsBorrowing Lab Equipment

Shruti and I went to DOPO lab to search for a base, or post to raise the Waveguide to a 5in height. While we weren't able to find a base that was suitable, we found a nice stage to hold the waveguide with a 40X Collimater. We've decided to take this and use it for the WOPA Experiment.

Attachment 1: IMG_7941.jpeg
IMG_7941.jpeg
Attachment 2: IMG_7940.jpeg
IMG_7940.jpeg
  1970   Fri Dec 22 16:44:29 2023 murtazaSummary Triple Suspension Damping

I've posted a summary and attached the plots comparing the damping filters in the new and old configuration in this alog. Additionally, I've added the filter design for SR3 using the same design principle. (Bandstop from 10-20Hz, then move poles and zeros around)
Some thoughts and next steps:
- SR2 and SR3 can be tested next; each DOF section is tweaked differently. BS needs some redesign since the same filter section cannot be copied across all DOFs.
- Make the names of the new filter section consistent across all optics. 10SB20 sounds like a good label
- Write a script that can handle the switching off and switching on of the filter sections in an automated fashion
- Write a script that can inject noise in increasing orders of magnitude at the coils and find the contribution to the DARM signal. Some preliminary work is done here in ChecksForSite
- Test the scripts on a virtual environment, eg rtsfreenrun or the test stand before doing any tests at the site
- For future loop designs to reduce noise in a particular bandwidth, the following figures of merits can be added to the existing ones: rms motion in the bandwidth of interest, closed loop Qs of the damped modes and ASC loop measurements for the closed loop system

  1969   Tue Dec 5 17:42:16 2023 murtazaSummarySUSLIGO Triple Damping Loops

- I checked the elliptical filter files; The gain factor of 1.25 was indeed to make the DC gain = 1. I restored the gain value
- Notches are bandstops in this context to filter out the noise in the 10-20Hz range.
- Done.
- Done.

Quote:

Thanks for the summary

  •  elliptic bandstop filters: Make sure that they have a DC gain of 1, not something like 1 dB or 0.1 dB.
  • notches - can you explain what these are for? Do you really mean notches or just some low pass or bandstop?
  • maybe rename FM2 as 'lead filter'
  • absorb the gain of 1/4x or -4 or whatever into FM0. No need for an extra gain module. We just want to NOT change the gain field when trying out new filters. We just swap in new filters without overwriting anything that's in use. Then we can revert when the test breaks things. i.e. let's not have to load a new filter file to transition back to the existing stable config.

 

  1968   Tue Dec 5 11:51:45 2023 ranaSummarySUSLIGO Triple Damping Loops

Thanks for the summary

  •  elliptic bandstop filters: Make sure that they have a DC gain of 1, not something like 1 dB or 0.1 dB.
  • notches - can you explain what these are for? Do you really mean notches or just some low pass or bandstop?
  • maybe rename FM2 as 'lead filter'
  • absorb the gain of 1/4x or -4 or whatever into FM0. No need for an extra gain module. We just want to NOT change the gain field when trying out new filters. We just swap in new filters without overwriting anything that's in use. Then we can revert when the test breaks things. i.e. let's not have to load a new filter file to transition back to the existing stable config.
  1967   Mon Dec 4 18:04:44 2023 murtazaSummarySUSLIGO Triple Damping Loops

EDIT(12/05/2023):
-Renamed RCVR_PH_L as Lead_Filter_L
- Absorbed the gain factors to FM0.(To make the overall gain = -1 compensating for the GAIN field in the filter design. For L, GAIN = -4. To make it equal to -1, I add a gain of 1/4 in FM0)
- The gain of 1.25 in the elliptical filter design  for bounce and roll was to make the DC gain equal to 1. I've restored it.


tldr: Converted the damping filters to foton from matlab (Attachment 2). The changes are to the following modules:
SRM_M1_DAMP_L, SRM_M1_DAMP_T, SRM_M1_DAMP_V, SRM_M1_DAMP_Y, SRM_M1_DAMP_P, SRM_M1_DAMP_R

The transfer functions for the filters in matlab and foton agree with each other in the {+-0.5dB, +-1degree} range on average at the frequencies I arbitarily picked (1Hz, 8Hz) where all the funny business can potentially happen.
I am accounting for these small differences due to numerical errors while obtaining the poles and zeros from the transfer function. (The filter designs in matlab for notches and bumps assign the parameters to the coefficients in the rational functions; factoring them can cause the numerical errors).
(Attachment 1 shows the comparison of the transfer functions which are arranged in the following order: {L, T, V, Y, P, R}, {Foton, Matlab}. Apologies for the poor labelling no, this is just for reference if something ends up being messy for later).
I overwrote some of the filter sections {0, 1, 2, 3, 4, 5, 6, 8}; the DAMP filters are arranged in the text file as follows (example given for L, follows similarly for all DOFs):

  Number Name Description

0 rolloff_L Velocity Damping with 2 poles and 1 zero

1 RG0.67 Resonant Gain to bump 0.67Hz

2 LEAD_FILTER_L Recover Phase Margin by adding a small bump ahead of the Last Unity Gain Crossing at the cost of a small Gain Margin

3 SUPP_NOISE_L Notches from 10Hz-20Hz to suppress sensor noise from feedback
  4 ELEC_GAIN Electronics Gain accounted to match the model (Only used to compare filters in matlab with foton, no need during site implementation)
  5 Plant Plant Model

 

6    

 

7 0:20 ???????
8 BR Filtering of the bounce and roll modes. Interestingly, for the same parameters for the Elliptical Filter function in Foton as compared to Matlab, the suppression is comparatively lower. (~100dB larger suppression in Matlab. I've left the parameters unchanged for now, this just means slightly better phase and gain margins in the filter design in Foton than in simulation in Matlab)
  9 ELP9R

????????

Some Notes:
- The filters sections with are requierd to be active
- I'm not sure what's the purpose of filter sections 7 (looks like velocity damping) and 9 (looks like noise suppression) exactly are (they are active at the sites). However, the filter shapes are fairly similar for the filters currently in use vs the ones designed; I'm guessing I'm capturing similar features with the new design.
 

Attachment 1: Filter_Check_SRM.pdf
Filter_Check_SRM.pdf Filter_Check_SRM.pdf Filter_Check_SRM.pdf Filter_Check_SRM.pdf Filter_Check_SRM.pdf Filter_Check_SRM.pdf Filter_Check_SRM.pdf Filter_Check_SRM.pdf
Attachment 2: L1SUSSRM.txt
# FILTERS FOR ONLINE SYSTEM
#
# Computer generated file: DO NOT EDIT
#
# MODULES SRM_DITHERINF_P SRM_DITHERINF_Y SRM_LKIN_P_DEMOD_I SRM_LKIN_P_DEMOD_Q
# MODULES SRM_LKIN_P_DEMOD_SIG SRM_LKIN_Y_DEMOD_I SRM_LKIN_Y_DEMOD_Q SRM_LKIN_Y_DEMOD_SIG
# MODULES SRM_M1_COILOUTF_LF SRM_M1_COILOUTF_RT SRM_M1_COILOUTF_SD SRM_M1_COILOUTF_T1
# MODULES SRM_M1_COILOUTF_T2 SRM_M1_COILOUTF_T3 SRM_M1_DAMP_L SRM_M1_DAMP_P
# MODULES SRM_M1_DAMP_R SRM_M1_DAMP_T SRM_M1_DAMP_V SRM_M1_DAMP_Y SRM_M1_DITHER_P
# MODULES SRM_M1_DITHER_Y SRM_M1_DRIVEALIGN_L2L SRM_M1_DRIVEALIGN_L2P SRM_M1_DRIVEALIGN_L2Y
... 1341 more lines ...
  1966   Fri Dec 1 19:07:12 2023 murtazaSummarySUSLIGO Triple Damping Loops

Anamaria said that they would like the text files with the filters.
 In the process of converting the filters from Matlab to Foton, I've hit a roadblock.
The notch filter design which I've been using in matlab takes 3 parameters for which the code is attached. (Attachment 1)

To recreate this with the Notch filter design in foton, it takes the same 3 parameters, (f0, Q, atten). Note: this takes the attenuation in dB; which is not a problem. Easy to go from absolute magnitude to dB. 
However, I cannot understand the mapping between the Q factors in matlab and foton. With the same Q numerically, they have different widths (Attachment 2). This suggests a different algorithm for the filter design in foton compared to matlab (or something else).
I can add the zpk values or the coeffiicient values of the transfer function in foton that correspond to a filter in matlab manually, but it would be super nonintuitive for someone looking at the filter designs in foton in the future. So I don't want to do that.
Finding a mapping would be the best (same for bump -> ResGain as well).

EDIT (12/03/23): Brett pointed me towards Quack: https://dcc.ligo.org/DocDB/0076/G1101245/002/G1101245_autoquack_description.pdf; I'll take a look at it.
EDIT (12/04/23): I checked the documentation for AutoQuack, it seems confusing to me and I don't think it will solve the issue I am currently facing.
EDIT (12/04/23): I reached out to Brian Lantz who authored the code; he said there's still no good way to convert matlab filters to foton. I am moving ahead with using the poles and zeros for those filters for now. But it's cumbersome and can be done more systematically in the future.

Attachment 1: notch.m
function [sys]=notch(f0,Q,atten)
%NOTCH builds a bogus notch filter
%[sys]=notch(f0,Q,attenuation);
%f0 is the center freq, Q and atten control the width and depth
%
% see notch2 for the old version
%
% Brian Lantz Jan 23, 2003

top=1/Q;
... 8 more lines ...
Attachment 2: foton_matlab_comp.png
foton_matlab_comp.png
  1965   Thu Nov 30 18:53:04 2023 murtazaSummarySUSLIGO Triple Damping Loops

​Saturation Check with CoilOut Filters

tldr: no saturation observed with the CoilOut Filters in the chain for 1um or 1urad impulse given at the same time.
Building up on the arbitrary saturation check, I added the CoilOut Filters and their analog counterparts before and after the saturation blocks. The filters modules were obtained from the sites for the ones actively used.
Since these CoilFilters were for the individual coils, a proxy method of checking this was as follows:
As we go from the Euler to the OSEM Basis, the actuators are shared between the respective DOFs given by the EUL2OSEM Matrix (Attachment 1).
Since each OSEM drives a fraction of it's respective DOFs, the one with the highest "gain" element for the particular OSEM will saturate first assuming that the actuation required is the same
(This is again a very coarse approximation, since the signals are stochastic, and this matrix takes a linear combination of those signals and feeds it to the coils, it doesn't necessarily hold true.)
Thus, the factors are chosen to be the maximum, rowwise between all the contributing coils for a particular DOF.

Next, the saturation limits are specified by the DAC response. Since the DAC is 20bits with 1 bit for sign, we have 2^19 counts as the maximum limit. The counts to Newton calibration is taken as 0.72cts/uN.
Thus, the maximum force that can be applied by each coil is given by 2^19*0.72*1e-6 = 0.7282N.
Under this limit, for the given impulse response, we see no saturation (Attachment 2 shows the signals compared between the saturation block and after)
The ringdown is shown in Attachment 3.

(The output from the damping filters actuate at <~0.01% of the actuator limits, which seems very small and makes me think I'm missing something here. Hope someone catches it).

Attachment 1: SR2_M1_eul2osem.png
SR2_M1_eul2osem.png
Attachment 2: Screenshot_2023-11-30_at_7.45.36_PM.png
Screenshot_2023-11-30_at_7.45.36_PM.png
Attachment 3: impulse_response_coilout.png
impulse_response_coilout.png
  1964   Thu Nov 30 10:04:20 2023 murtazaSummarySUSLIGO Triple Damping Loops

tldr: ODE45 relative tolerance was the issue with the weird behavior with the longitudinal DOF. I set the relative tolerance to 1e-9 which solved the behavior. The output from the damping filter rings along with ~50% saturation (Attachment 1) still leads to a decent ring down (Attachment 2). Attachment 3, 4 shows the same plots respectively with no saturation
A small detail that I missed in the previous elog; this test is to see how the filters behave qualitatively under some saturation. The motion of the mirrors is assumed to be 1um/1urad and the saturation limits are arbitariliy set such that the net saturation in the Euler basis is ~50%. The goal was to understand if the closed loop system can still damp out respectfully under this saturation.
For this test, I gave an "impulse" of 1um or 1urad (combination of step responses) instead of a step to be consistent with the tests I've ben doing previously. The saturation on the output of the damping filters were set as follows:
L - 5e-6N
T - 3e-6N
V - 2e-6N
Y - 2e-6N
P - 2e-6N
R - 2e-6N

The Long Story
There was something funny happening with the step response of the Longitudinal DOF in the previous elog which I wanted to figure out. Although the motion in L was damping out fairly (m3_disp_L), the output of the damping filter was not ringing down in proportion (here). 
-I first tried increasing the step size until I saw the effect go away. At a step size of around 1, this wasn't seen anymore. But then, as I begain decreasing the step size, this effect started creeping in. So I compared the ins and outs of different blocks to see where this fuzzy behavior was arising.
- The "culprit" was the damping filter, the comparison of the input to the filter and the output are shown in Attachment 5. This did not make any sense though; Although it looks like high freqeuncy oscillations, I was not sure where this would potentially come from. I plotted an ASD of this data to determine if there was something I was missing (Attachment 6).
- The low frequency peak was expected, but the higher frequency content was confusing; especially since the gain at the freqeuncies was very small (suppression expected). 
- I then compared this with the filter used at the sites to see if this was due to poor filter design on my end. But the same issue persisted with the site filters as well.
- I stared at the screen.
- Some more staring. 
- I then remembered the ODE45 situation from the previous day so I went in to double check if something changed there. And there I found the solution; the relative tolerance was set at 1e-3 which, for a 1e-6m impulse would be too large. I decreased the tolerance arbitarily to 1e-9. This worked finally!
 

Attachment 1: DF_OUT_rel_tol.png
DF_OUT_rel_tol.png
Attachment 2: ringdown_rel_tol.png
ringdown_rel_tol.png
Attachment 3: DF_OUT_rel_tol_no_sat.png
DF_OUT_rel_tol_no_sat.png
Attachment 4: ringdown_rel_tol_no_sat.png
ringdown_rel_tol_no_sat.png
Attachment 5: df_in_out.png
df_in_out.png
Attachment 6: asd_m1_dsip_l.png
asd_m1_dsip_l.png
  1963   Wed Nov 29 17:14:46 2023 murtazaSummarySUSLIGO Triple Damping Loops

The step response for a small step size (1um for longitudinal DOFs, 2urad for angular DOFs) are as follows.

The actuator saturations are shown in Attachment 1
The step response is shown in Attachment 2

Rings down pretty well in-spite of saturations, about 50% saturation on the actuators for all DOFs.

Attachment 1: DF_OUT_Saturation_small_step.png
DF_OUT_Saturation_small_step.png
Attachment 2: step_response_small_step.png
step_response_small_step.png
  1962   Wed Nov 29 11:14:56 2023 ranaSummarySUSLIGO Triple Damping Loops

there's no way that we have a 5 ms delay in our systems; its more like 1.5 ms in the 2 kHz systems.

I bet the phase lag is due to some high frequency anti-aliasing. Maybe something in the SUS system has a ~800 Hz AA filter for a 2048 sample rate.

But approximating this by a Pade time delay seems like a fine approach for testing.

  1961   Tue Nov 28 22:46:47 2023 murtazaSummarySUSLIGO Triple Damping Loops

tldr:
-Bounce and Roll mode notches added to the filters (same as the ones used at the sites) for all triple suspensions. Minor adjustments made to filters to achieve margin requirements.
-Damping consistent even under actuator saturation for HSTS. Checked with a step response of magnitude of 1unit (meters, radians as applied)
EDIT(11/28/2023): Checked for BS and HLTS as well, F_max for HLTS is 0.2016N, could not find the electronics chain for BS, assumed the same as HLTS; behaves similarly

To check the effect of actuator saturation, I built a quick simulink model (Attachment 1)  for the closed loop system. The actuators saturations were placed in front of the output of the damping filters with limits set as follows:

I suspected the actuator limits that could be set digitally or through the DAC. I first checked the digital limits, but they were set to 0 for all filters for SR2, which suggests that it's not used at the sites. 
To check the DAC limits, I referred the electronics chain for HSTS from the DCC: https://dcc.ligo.org/DocDB/0008/T1000061/007/HSTSElectronics_T1000061-v7.pdf
From the BOSEM Coil Electronics Chain, it can apply a force of 0.963 N/A, the current to volt conversion given by 11.9mA/V. Since the voltage limits are +-10V, the maximum force that can be applied by each coil is given by:

|F_max| = 0.963*11.9*1e-3*10 = 0.1145N
Since the basis change from OSEM to Euler basis distributes the required force to each OSEM such that the fractional force exerted by each individual add up to the net forv (taking the geometry of the mass into account for angular DOFs), this force is used as the actuator limit for all degrees of freedom.
I then used a step response of step size 1 to check the effect of actuator clipping.
(Maybe: For better completeness, I thought about using the maximum displacement that could be measured by the BOSEMS: From the same electronics chain document, the PD has the follow readout characteristic: 95uA/mm -> 240k V/A; for a 40Vpp, the maximum displacement that can be read would be (40/2)/(95*1e-6*240*1e3) = |0.877mm|. 
EDIT (11/29/2023): Brett later pointed me towards the BOSEM sensitivity curve which is linear for a range of 0.7mm (Attachment 7) which gives 0.35mm on either side, which is lower than the estimate from raw calculations.
I tried giving a 1mm step but it showed no clipping on the output of the damping filters, so I reverted to using a larger magnitude for the step size).

This is where I got stuck for half the day: SIMULINK WAS USING AN ODE15 SOLVER WHICH WAS PRODUCING AN UNSTABLE SYSTEM WHEN I INTRODUCED THE DAMPING FILTERS IN THE SIMULINK WORKSPACE (IT DIDN'T MATTER IF THE LOOP WAS CLOSED, IF THE DAMPING FILTER WAS LOADED IN THE SIMULINK MODEL, IT WOULD LEAD TO THE ROLL DOF BLOWING UP. LOST ATLEAST 5 HAIR OVER THIS. ATTACHMENT 2 FOR REFERENCE).

I eventually used the ODE45 solver and things were stable with it. 

The step responses along with the damping filter outputs saturating are shown in Attachment 3, 4
The step responses with no saturations enforced and damping filter outputs are shown in Attachment 5, 6

Visually, the ringdowns show a very small difference with/without saturation (maybe a few seconds) for all DOFs and there are no instabilities arising in the system with saturations. 

EDIT(11/29/2023): I wanted to test out which DOFs start saturating first so I decreased the step sizes starting from 1unit progressively until I saw clipping disappear. I thought about doing them individually first, but since the DOFs are coupled, there was no good way to tease them apart. So I maintained a constant step size of "x units" for all DOFs (the length and angular DOFs should ideally be different magnitudes), but this was easier to check since there is coupling between the DOFs. I don't think it provides any useful information as a whole, but just putting it out there if required later.
Observations:
- At 0.1 units (meters/radians), we have no clipping. This is way beyond (~300 times) the sensor sensitivity.
- At 0.2 units (meter/radians), L and T start clipping. Again, way beyond the sensitivity.

Attachment 1: Screenshot_2023-11-28_at_9.33.54_PM.png
Screenshot_2023-11-28_at_9.33.54_PM.png
Attachment 2: image.png
image.png
Attachment 3: step_response_w_saturation.png
step_response_w_saturation.png
Attachment 4: DF_OUT_Saturation.png
DF_OUT_Saturation.png
Attachment 5: step_response_wout.png
step_response_wout.png
Attachment 6: DF_OUT.png
DF_OUT.png
Attachment 7: bosem_characteristics.png
bosem_characteristics.png
  1960   Mon Nov 27 15:40:04 2023 murtazaSummarySUSLIGO Triple Damping Loops

Triple Suspension Model Discrepancy

Anamaria Effler pointed out a phase difference > 8Hz in the undamped model and the measured transfer functions of the plant for some of the triple suspensions. She provided code with the model and measurement of the plant for SR2 which I've used here as a reference.

I started with M1 (L -> L) which is shown in Attachment 1.The phase drops with an increase in frequency which (as Brett pointed out), could be a posiible time delay (or something else). To test the time delay hypothesis, I calculated the time delay at ~10Hz, ~ 20Hz and ~30Hz given by 

timeDelay = phaseLoss/(360*frequency)

10Hz - 5.1ms
20Hz - 5.5ms
30Hz - 5.7ms

This does not look like a constant time delay, but for now, it can work as a fair enough approximation for the discrepancy. Cosidering the timeDelay thus at 10 Hz, the phase loss at UGF (~3.2Hz) would be ~5.5degrees. Given the current requirements of phase margin for the trial filter design (35 degrees), it is well accounted for.  
Using this model, for the remaining degrees of freedom, the "timeDelay" at ~10Hz is as follows:

L - 5.1ms
T - 6.1ms
V - 6.2ms
Y - 6.1ms
P - 6.3ms
R - 6.0ms

I can add this time delay to the damping filters to "simulate" this discrepancy and get the minimum stability margins in simulation later. However, for now; considering a consistent phase loss of 6 degrees is a a good enough approximation.

Attachment 1: M1_L2L_comparison.png
M1_L2L_comparison.png
  1959   Mon Nov 27 15:08:48 2023 murtazaSummarySUSLIGO Triple Damping Loops

Next Steps:

I had a conversation with Anamaria Effler (Livingston) and Brett earlier today to get a better understanding of the situation on ground. She had a few pointers which I am hoping to address:

- The measured plant transfer functions have a phase difference with the model which starts becoming noticable above ~8Hz. She provided some matlab code that shows this difference for SR2. I'll check it out and find a way to incorporate it. [DONE]

- The bounce and roll peaks unfortunately couple to other modes in the true system and thus needs aggressive filtering in all DOFs (Although I can get away with having a higher Q factor to avoid losing a large phase margin around the UGFs). I will proceed to add those the filter designs. 

- From the projection data, I can rank the OSEMs and thus DOFs according to their contributions to DARM noise. Cosequentially, the damping filters can be prioritized which needs finer tuning.

- At the sites, a phase margin of 20-25 degrees for local damping is considered sufficient; I won't change the requirements set earlier (35 degrees) for now, but those extra 5-10 degrees can be useful in adding things like the bounce roll notches and so forth.  

  1958   Wed Nov 22 14:41:21 2023 murtazaSummarySUSLIGO Triple Damping Loops

TRIPLE SUSPENSIONS DAMPING LOOPS SUMMARY

tldr:
- Comparison of noise performance at 10, 20Hz and ringdown periods for small suspensions, large suspensions and the beamsplitter. (The comparisons are against the filter banks currently in use at Livingston (taking into account the site filters for SRM and PR2 updated on 11/17/2023), site noise asd was produced using a timeseries obtained from 11/22/2023, 12am PST for a duration of 1 hour to reflect the changes in this alog)
- Scripts to run the simulation now parked on the 40m Git: https://git.ligo.org/40m/triple-suspension-simulation
(The scripts needs some comments, restructurization and so forth)
- The small filters are designed using SR2 as a baseline.
- There are some redundancies in this elog from the previous ones (large triple remains the same, however I wanted to have filter metrics for all triple suspensions on the same page).

 

Small Triple Suspensions
(NOTE: If the noise reduction on PRM is too high, we can use the filter design for PRM from the previous elog and use the filter designed against SR2 for the optics (SR2, PR2 and SRM})

Noise Performance (Factor of Reduction vs Sites)

  L T V Y P R
  10Hz 20Hz 10Hz 20Hz 10Hz 20Hz 10Hz 20Hz 10Hz 20Hz 10Hz 20Hz
PRM 55.5 55.3 55.5 51.6 86 55.5 62.0 51.6 60.4 56.3 44.3 53.5
PR2 12.7 10.1 12.3 9.7 18.9 10.4 13.1 9.7 11.2 10.4 10.4 10.1
SRM 12.7 10.1 12.3 9.7 18.9 10.4 13.1 9.7 11.2 10.4 10.4 10.1
SR2 12.7 10.1 12.3 9.7 18.9 10.4 13.1 9.7 11.2 10.4 10.4 10.1

Ringdown Period (seconds)

  L T V Y P R
Trial Filter Design 2.84 1.81 0.96 1.23 3.76 29.25
PRM 1.31 1.3 0.87 0.84 3.67 52.85
PR2 1.31 1.31 0.87 0.84 3.68 57.42
SRM 1.31 1.31 0.87 0.84 3.68 57.42
SR2 1.31 1.31 0.87 0.84 3.68 57.42

Large Triple Suspensions

Noise Performance (Factor of Reduction vs Sites)

  L T V Y P R
  10Hz 20Hz 10Hz 20Hz 10Hz 20Hz 10Hz 20Hz 10Hz 20Hz 10Hz 20Hz
PR3 11.0 12.1 11.0 10.3 10.2 10.7 10.5 10.3 9.8 10.1 9.6 10.2
SR3 12.8 10.2 3.2 3.1 16.4 13.6 140.9 24.7 67.3 17.6 2.8 14

Ringdown Period (seconds)

  L T V Y P R
Trial FIlter Design 10.38 5.53 2.59 4.38 1.85 8.50
PR3 11.07 5.7 2.17 5.86 1.79 4.73
SR3 13.37 8.15 3.93 1.84 1.82 17.04

Beamsplitter

Noise Performance (Factor of Reduction vs Sites)

  L T V Y P R
  10Hz 20Hz 10Hz 20Hz 10Hz 20Hz 10Hz 20Hz 10Hz 20Hz 10Hz 20Hz
BS 10.1 10.7 9.9 10.0 10.2 9.4 11.2 11.9 12.1 10.8 11.3 10.3

Ringdown Period (seconds)

  L T V Y P R
Trial FIlter Design 3.31 3.28 3.97 2.39 19.01 1.40
BS 2.17 3.42 2.57 4.78 14.58 0.73

 

  1957   Wed Nov 22 13:58:13 2023 murtazaMiscNoise BudgetLIGO Triple Damping Loops

Small Triple Suspension Trial Filter Design (SR2 Baseline)

tlpr: Referencing the triple noise breakdown from this alog , SR2 has the highest noise amongst the smaller suspensions. I had designed the trial filters eariler using PRM as a baseline, but since the optics couple against DARM loop differently, I am switching to this new baseline
While designing for SR2, I used the site noise asd (seismic noise + sensor noise = DAMP_IN*(1 + OLG)) given as input to the controller instead of using white noise while desinging them. I had to lose out on the ringdown times this time, still doing comparable to the sites. Phase and gain margins almost at design criterion now.
I've also added bumps to account for the "SECRET COSTS" at low frequencies; however, since I had to reduce the gain on the damping filters, they're relatively lower in magnitude than the site filters (most of these peaks are around the mechanical resonances at the lower frequencies; getting similar features in the ringdown could be a good measure of these bumps doing the job although being lower in magnitude, maybe :$).
The site noise asd was produced using a timeseries
obtained from 11/22/2023, 12am PST for a duration of 1 hour
The design objectives that were met are as follows:

  • Lower noise by a factor ~10 in the 10-30Hz bandwidth or better
  • Achieve similar ringdowns for the impulse response
  • Have phase margins of ~30 degrees and gain margins of ~3dB or better

The same design principles were used for SR2 as for PRM (explained in this elog). Here’s the filter design for each DOF. (The electronics gain has not been accounted for here, it must be added to the filter design). The filters work with negative feedback with a gain of 1. 
 

DOF

UGF

Velocity Damping

Notches

Bumps

Elliptical

Longitudinal

3.1

zpk(0, -2*pi*pair(150, 80), 1)

 

notch(10,10,9),

notch(15,10,9),

notch(20,10,8)

bump(0.67, 5, 10),

bump(4.5, 3, 11)

 

 

Transverse

3.3

zpk([0], -2*pi*pair(80, 30), 1)

notch(10,12,4), notch(10,12,3),

notch(15,12,10),

notch(20,12,4), notch(20,12,5)

bump(4.5, 5, 3),

bump(0.674, 5, 6)

 

Vertical

3.2

zpk([0], -2*pi*pair(100, 70), 1)

notch(10,12,5), notch(10,12,5),

notch(15,12,10),

notch(20,12,10), notch(25,12,10)

bump(0.678, 5, 5),

bump(6, 5, 5)

ellip(6, 3, 30, 2*pi*[24, 30],'stop', 's')

Yaw

3.6

zpk([0], -2*pi*pair(100, 70), 1)

notch(10,12,4), notch(10,12,4),

notch(15,12,10),

notch(20,12,5), notch(20,12,5)

bump(1.98, 5, 3),

bump(5, 5, 3)

 

Pitch

4.25

zpk([0], -2*pi*pair(100, 50), 1)

notch(10,10,5), notch(10,10,5),

notch(15,10,5),

notch(20,10,5), notch(20,10,6)

bump(1.006, 10, 6),

bump(7, 10, 8)

 

Roll

2.6

zpk([0], -2*pi*pair(100, 50), 1)

notch(10,10,3), notch(10,10,2),

notch(15,12,4),

notch(20,12,3), notch(20,12,4)

bump(1.52, 7, 18),

bump(4, 5, 5)

ellip(6, 3, 50, 2*pi*[35, 45],'stop', 's')

 

The pdf has been arranged as following for each DOF. (Comparisons are between the existing site filter design and the trial filter design (sticking to this terminology, psych).

  • Figure 1 shows a comparison of the sensor noise ASD (DOF sensor noise on M1 to DOF Displacement on M3) in the bandwidth of interest and ringdown periods for the impulse response. (FOR Longitudinal DOF, the impulse input was ground, for the remaining DOFs, the input was at M1). 
  • Figure 2 shows a comparison of the filter designs in the bandwidth of interest
  • Figure 3 shows the open loop transfer function (P(s)*C(s)) with phase and gain margin (minimum stability margins)
  • Figure 4 shows a comparison of the open loop transfer functions (P(s)*C(s)).
Attachment 1: Small_Triples_Filter_Design_1122.pdf
Small_Triples_Filter_Design_1122.pdf Small_Triples_Filter_Design_1122.pdf Small_Triples_Filter_Design_1122.pdf Small_Triples_Filter_Design_1122.pdf Small_Triples_Filter_Design_1122.pdf Small_Triples_Filter_Design_1122.pdf Small_Triples_Filter_Design_1122.pdf Small_Triples_Filter_Design_1122.pdf
  1956   Mon Nov 20 14:46:10 2023 murtazaSummarySUSLIGO Triple Damping Loops

tldr:
- Comparison of noise performance at 10, 20Hz and ringdown periods for small and large suspensions. (Filters for PR2, SRM updated to reflect changes in https://alog.ligo-la.caltech.edu/aLOG/index.php?callRep=68331)
- Scripts to run the simulation now parked on the 40m Git: https://git.ligo.org/40m/triple-suspension-simulation
(The scripts needs some comments, restructurization and so forth)
- I did a quick visual scan at the text filter files for PR2, SR2 and SRM and they look pretty similar; thus similar performances. Additionally, there is an existing notch for them in the 10-20Hz range which is why the noise performance is better only by a factor of ~2.

Small Triple Suspensions

Noise Performance

  L T V Y P R
Factor of Reduction 10Hz 20Hz 10Hz 20Hz 10Hz 20Hz 10Hz 20Hz 10Hz 20Hz 10Hz 20Hz
PRM 10.1 10.6 13.3 9.9 9.9 10.1 10.3 9.7 10.2 10.5 10.4 9.7
PR2 2.3 2.0 2.9 1.8 2.2 1.9 2.2 1.8 1.9 1.9 2.4 1.8
SRM 2.3 2.0 2.9 1.8 2.2 1.9 2.2 1.8 1.9 1.9 2.4 1.8
SR2 2.3 2.0 2.9 1.8 2.2 1.9 2.2 1.8 1.9 1.9 2.4 1.8

Ringdown Period (seconds)

  L T V Y P R
Trial Filter Design 1.43 1.81 0.88 1.20 3.27 37.43
PRM 1.31 1.3 0.87 0.84 3.67 52.85
PR2 1.31 1.31 0.87 0.84 3.68 57.42
SRM 1.31 1.31 0.87 0.84 3.68 57.42
SR2 1.31 1.31 0.87 0.84 3.68 57.42

Large Triple Suspensions

Noise Performance

  L T V Y P R
Factor of Reduction 10Hz 20Hz 10Hz 20Hz 10Hz 20Hz 10Hz 20Hz 10Hz 20Hz 10Hz 20Hz
PR3 11.0 12.1 11.0 10.3 10.2 10.7 10.5 10.3 9.8 10.1 9.6 10.2
SR3 12.8 10.2 3.2 3.1 16.4 13.6 140.9 24.7 67.3 17.6 2.8 14

Ringdown Period (seconds)

  L T V Y P R
Trial FIlter Design 10.38 5.53 2.59 4.38 1.85 8.50
PR3 11.07 5.7 2.17 5.86 1.79 4.73
SR3 13.37 8.15 3.93 1.84 1.82 17.04
  1955   Fri Nov 17 14:24:06 2023 murtazaSummarySUSLIGO Triple Damping loops

BS Suspension Trial Filter Design

tldr: While designing for BS, I used the site noise asd (DAMP_IN*(1 + OLG)) given as an input to the controller instead of using white noise while designing them.
The design objectives that were met are as follows:

  • Lower noise by a factor ~10 in the 10-30Hz bandwidth or better
  • Achieve similar ringdowns for the impulse response
  • Have phase margins of >35 degrees and gain margins of >6dB or better

The same design principles were used for BS as for PR3 (explained in this elog). Here’s the filter design for each DOF. (The electronics gain has not been accounted for here, it must be added to the filter design). The filters work with negative feedback with a gain of 1. 
Note: As the edit mentions in the previous elog, "Highest UGF" denotes the highest frequency where the gain crosses 0dB (In some places on the internet, they call this frequency as the Unity Gain Frequency if there are multiple 0dB crossings, although the sources are debatable)

 

DOF

Highest UGF

Velocity Damping

Notches

Bumps

 

Longitudinal

2.0

zpk(0, -2*pi*pair(150, 80), 1)

 

notch(10,10,9), notch(15,10,7), notch(20,10,8),

notch(20,10,5) 

bump(1.09, 15, 2), bump(0.467, 15, 5),

bump(4, 5, 2)

 

 

Transverse

3.35

zpk([0], -2*pi*pair(80, 60), 1)

notch(10,12,5), notch(10,12,8), notch(15,12,8), 

notch(20,12,8), notch(20,12, 7)

bump(7, 5, 4)

 

Vertical

4.2

zpk([0], -2*pi*pair(100, 30), 1)

notch(10,12,5), notch(10,12,4), notch(15,12,9),

notch(20,12,12), notch(20,8,12), notch(17.5,80,6)

bump(6.8, 5, 12)

 

Yaw

2.3

zpk([0], -2*pi*pair(100, 30), 1)

notch(10,12,3), notch(15,12,8), notch(20,12,7),

notch(20,12,6), notch(15,12,4)

 

 

Pitch

1.7

zpk([0], -2*pi*pair(100, 50), 1)

notch(10,10,3), notch(10,10,2), notch(15,10,15),

notch(20,10,5), notch(20,10,5)

bump(1.05, 5, 6), bump(0.418, 15, 8),

bump(3.5, 10, 6)

 

Roll

3.65

zpk([0], -2*pi*pair(100, 50), 1)

notch(10,12,4), notch(15,12,8), notch(20,12,9),

notch(20,12,9), notch(25.966,80,20)

bump(1.05, 5, 2), bump(6, 5, 3)

 

The pdf has been arranged as following for each DOF. (Comparisons are between the site filter design and the trial filter design (need to come up with a better terminology for this)).

  • Figure 1 shows a comparison of the sensor noise ASD (DOF sensor noise on M1 to DOF Displacement on M3) in the bandwidth of interest and ringdown periods for the impulse response. (FOR Longitudinal DOF, the impulse input was ground, for the remaining DOFs, the input was at M1). 
  • Figure 2 shows a comparison of the filter designs in the bandwidth of interest
  • Figure 3 shows the open loop transfer function (P(s)*C(s)) with phase and gain margins (minimum stability margins)
  • Figure 4 shows a comparison of the open loop transfer functions (P(s)*C(s)).
Attachment 1: BS_ASDnRD1115.pdf
BS_ASDnRD1115.pdf BS_ASDnRD1115.pdf BS_ASDnRD1115.pdf BS_ASDnRD1115.pdf BS_ASDnRD1115.pdf BS_ASDnRD1115.pdf BS_ASDnRD1115.pdf BS_ASDnRD1115.pdf
  1954   Fri Nov 17 12:14:44 2023 ranaSummarySUSLIGO Triple Damping loops

its looking pretty good. just looking at the HSTS (lets ignore HLTS for now), it seems like you've lowered the feedback gain a lot in those regions where the existing loops have wide gain humps.

I think people probably put those there to reduce some troubling noise peak which is not captured in our "cost function" so far. If you re-insert those gain humps, can you still get good 10 Hz noise performance?

  1953   Thu Nov 16 18:46:27 2023 murtazaSummarySUSLIGO Triple Damping loops

I made some tweaks to the existing filters to meet the gain margin of >6dB and phase margin of >35degrees requirement, surprisingly, didn't really need to lose out much on noise performance on any (still meeting the factor of ~10 mark).
(Which means that an optimal solution to designing against these objectives must exist, need to find it someday).
EDIT (11/17/2023): The gain margin and phase margins that I have used as a design criterion are the minimum stability margins (there would be multiple crossover freqeuncies where the magnitude corsses 0dB and the phase crosses 180 degrees; designing aginst the minimum margins should take care of the remaining margins)

Large Triple Suspension (Attachment 1)

Degree of Freedom Phase Margin Gain Margin
L 37.2 8.95
T -37 12.8
V 38.2 8.55
Y 37.9 12.9
P 36.9 7.11
R 43.5 10.4

Small Triple Suspension (Attachment 2)

Degree of Freedom Phase Margin Gain Margin
L 41 8.13
T -55.5 7.13
V 37.7 8.27
Y 38.7 7.34
P 36.8 8.08
R 39 9.31
Attachment 1: large_6db_35deg.pdf
large_6db_35deg.pdf large_6db_35deg.pdf large_6db_35deg.pdf large_6db_35deg.pdf large_6db_35deg.pdf large_6db_35deg.pdf large_6db_35deg.pdf large_6db_35deg.pdf
Attachment 2: small_6db_35deg.pdf
small_6db_35deg.pdf small_6db_35deg.pdf small_6db_35deg.pdf small_6db_35deg.pdf small_6db_35deg.pdf small_6db_35deg.pdf small_6db_35deg.pdf small_6db_35deg.pdf
  1952   Thu Nov 16 14:48:08 2023 murtazaHowToSUSLIGO HSTS Damping loops

In general, it has been difficult to save phase/gain margins for Pitch for both suspension types. Making note of the current phase and gain margins for the large and small suspensions.

Large Triple Suspension

Degree of Freedom Phase Margin Gain Margin
L 25 7.82
T 32.1 10.9
V 28.5 7.81
Y 33 12.5
P 26.1 5.71
R 43.5 10.4

Small Triple Suspension

Degree of Freedom Phase Margin Gain Margin
L 41 8.13
T -55.5 7.13
V 31.1 6.51
Y 38.7 7.34
P 30.9 6.72
R 29 9.41

I'll proceed to tweak the DOFs in marked in red at the cost of noise margins at 10, 20Hz.

  1951   Thu Nov 16 14:08:47 2023 ranaHowToSUSLIGO HSTS Damping loops

I think we want >6 dB of gain margin and > 35 deg of phase margin. Its not necessary to do this for all loops in all systems, but the suspensions get thrashed a lot and so we want them all to be pretty stable.

If you cannot meet the 10-20 Hz noise requirements with this, we can back off, but I think this would be a good design criterion.

Also, the loops are AC coupled so we need to consider all of the UGFs, not just the highest frequency one.

 

  1950   Thu Nov 16 13:15:06 2023 murtazaMiscNoise Budgettriples

Small Triple Suspension Trial Filter Design

tldr: From the Damp_OUT spectrum of the small suspensions, PRM had a relatively larger magnitude in the 10-30Hz bandwidth. I thus choose to design filters for them using PRM as a reference.
While designing for PRM, I used the site noise asd (DAMP_IN*(1 + OLG)) given as input to the controller instead of using white noise while desinging them.
The design objectives that were met are as follows:

  • Lower noise by a factor ~10 in the 10-30Hz bandwidth or better
  • Achieve similar ringdowns for the impulse response
  • Have phase margins of ~30 degrees and gain margins of ~3dB or better

The same design principles were used for PRM as for PR3 (explained in this elog). Here’s the filter design for each DOF. (The electronics gain has not been accounted for here, it must be added to the filter design). The filters work with negative feedback with a gain of 1. 
Note: I had an an interesting time designing the Roll Mode, bumping the peaks to increase damping on them after setting the UGF at 2.75 would increase the ringdown period. I reverted to using a similar overall "magnitude" that they used at the sites and added notches for reducing noise in the required bandwidth. The new filter still better on the ringdown (15 seconds lesser) so I'll leave it at that for now and make changes if required later. 

 

DOF

UGF

Velocity Damping

Notches

Bumps

Elliptical

Longitudinal

3.5

zpk(0, -2*pi*pair(150, 80), 1)

 

notch(10,10,5), notch(15,10,9), notch(20,10,11)

bump(4.5, 3, 2)

 

 

Transverse

3.5

zpk([0], -2*pi*pair(80, 30), 1)

notch(10,12,5), notch(15,12,6), notch(20,12,7)

bump(4.5, 5, 3.5), bump(0.674, 5, 5)

 

Vertical

3.8

zpk([0], -2*pi*pair(100, 70), 1)

notch(10,12,6.5), notch(15,12,9), notch(20,12,11), notch(25,12,5)

bump(5.5, 2, 1.5)

ellip(6, 3, 30, 2*pi*[24, 30],'stop', 's')

Yaw

3.8

zpk([0], -2*pi*pair(100, 30), 1)

notch(10,12,5), notch(15,12,8), notch(20,12,15)

bump(4.5, 5, 1.4), bump(4, 6, 7)

 

Pitch

4.5

zpk([0], -2*pi*pair(100, 50), 1)

notch(10,10,3), notch(15,10,7), notch(20,10,10)

bump(1.006, 10, 6), bump(6.5, 10, 2)

 

Roll

2.75

zpk([0], -2*pi*pair(100, 50), 1)

notch(10,10,3), notch(15,12,5), notch(20,12,5.5)

bump(1.51, 5, 10), bump(4, 5, 2)

ellip(6, 3, 50, 2*pi*[35, 45],'stop', 's')

 

The pdfs have been arranged as following for each DOF. (Comparisons are between the site filter design and the trial filter design (need to come up with a better terminology for this)).

  • Attachment 1 shows a comparison of the sensor noise ASD (DOF sensor noise on M1 to DOF Displacement on M3) in the bandwidth of interest and ringdown periods for the impulse response. (FOR Longitudinal DOF, the impulse input was ground, for the remaining DOFs, the input was at M1). 
  • Attachement 2 shows a comparison of the filter designs in the bandwidth of interest
  • Attachment 3 shows the open loop transfer function (P(s)*C(s)) with phase and gain margin (minimum stability margins)
  • Atttachment 4 shows a comparison of the open loop transfer functions (P(s)*C(s)).
Attachment 1: L_smallASDnRD1115.pdf
L_smallASDnRD1115.pdf L_smallASDnRD1115.pdf L_smallASDnRD1115.pdf L_smallASDnRD1115.pdf L_smallASDnRD1115.pdf L_smallASDnRD1115.pdf
Attachment 2: L_smallFilter1115.pdf
L_smallFilter1115.pdf L_smallFilter1115.pdf L_smallFilter1115.pdf L_smallFilter1115.pdf L_smallFilter1115.pdf L_smallFilter1115.pdf
Attachment 3: L_smallComBodeOL1115.pdf
L_smallComBodeOL1115.pdf L_smallComBodeOL1115.pdf L_smallComBodeOL1115.pdf L_smallComBodeOL1115.pdf L_smallComBodeOL1115.pdf L_smallComBodeOL1115.pdf
Attachment 4: L_smallBodeOL1115.pdf
L_smallBodeOL1115.pdf L_smallBodeOL1115.pdf L_smallBodeOL1115.pdf L_smallBodeOL1115.pdf L_smallBodeOL1115.pdf L_smallBodeOL1115.pdf
  1949   Wed Nov 15 09:48:05 2023 ranaMiscNoise Budgettriples

Can you explain how you calibrated the control signals into displacement units? It would be fine to start if you could just plot them with the y-axis in counts/rHz for now, unless you have good confidence in the calibration.

  1948   Tue Nov 14 22:18:15 2023 murtazaMiscNoise Budgettriples

The spectra for damp out for the following optics
- small triples {PR2, PRM, SR2, SRM} (Attachment 1)
- large triples {PR3, SR3} (Attachment 2)
- beamsplitter {BS} (Attachment 3)

For pwelch(), I was not taking into account the DC offset which is why I was getting funky plots (spectral leakage). I corrected for it, no more interpolation anymore!

Edit: I have changed the yaxis label for all plots to counts/rHz for now since I do not know the exact calibration

Attachment 1: Small_Triples_DAMP_OUT_Spectra.pdf
Small_Triples_DAMP_OUT_Spectra.pdf Small_Triples_DAMP_OUT_Spectra.pdf Small_Triples_DAMP_OUT_Spectra.pdf Small_Triples_DAMP_OUT_Spectra.pdf Small_Triples_DAMP_OUT_Spectra.pdf Small_Triples_DAMP_OUT_Spectra.pdf
Attachment 2: Large_Triples_DAMP_OUT_Spectra.pdf
Large_Triples_DAMP_OUT_Spectra.pdf Large_Triples_DAMP_OUT_Spectra.pdf Large_Triples_DAMP_OUT_Spectra.pdf Large_Triples_DAMP_OUT_Spectra.pdf Large_Triples_DAMP_OUT_Spectra.pdf Large_Triples_DAMP_OUT_Spectra.pdf
Attachment 3: BS_DAMP_OUT_Spectra.pdf
BS_DAMP_OUT_Spectra.pdf BS_DAMP_OUT_Spectra.pdf BS_DAMP_OUT_Spectra.pdf BS_DAMP_OUT_Spectra.pdf BS_DAMP_OUT_Spectra.pdf BS_DAMP_OUT_Spectra.pdf
  1947   Tue Nov 14 16:14:11 2023 ranaMiscNoise Budgettriples

we only care about PRM, PR2, PR3, BS, SR3, SR2, SRM, so you should eliminate all other optics from the plots.

Then just plot the HSTS to get started and we can see how they compare.

  1946   Mon Nov 13 17:39:12 2023 murtazaSummarySUSTriple Suspension Simulation

Triple Suspension Test Mass Displacement Spectrum (Livingston)

[WIP] (need to think some more about what's happening differently between the small and large suspensions)

tldr: Test Mass Displacement spectrum for all triple suspensions at Livingston for true (seismic_motion + sensor_noise).
 

Method:
- DAMP_IN1 ASD was obtained as described in the previous elog.
- The sum of seismic motion and sensor noise can be estimated such that, seismic_motion(s) + sensor_noise(s) = (1 + OLG)*DAMP_IN1.
- This ASD is then given as an input to the damping filters (DOF_IN) and propogates through to the test mass displacement (m1_disp) which is shown in the plots

 

 

 

Attachment 1: M1_Disp_ASD.pdf
M1_Disp_ASD.pdf M1_Disp_ASD.pdf M1_Disp_ASD.pdf M1_Disp_ASD.pdf M1_Disp_ASD.pdf M1_Disp_ASD.pdf
  1945   Mon Nov 13 14:52:29 2023 murtazaSummarySUSTriple Suspension Simulation

Triple Suspension DAMP_OUT Spectrum (Livingston)

tldr: DAMP_OUT spectra for all triple suspensions at Livingston. For each DOF, in the 10-30Hz range, the feedback signals with comparatively large magitudes (visually) are as follows:

L: PRM, MC2
T: PR3, MC2
V: PRM, MC1, MC2, MC3
Y: MC2
P: PRM, SR3, MC1, MC2, MC3
R: PRM, PR3, SR3, MC1, MC2, MC3

 

Method:
- Damping filters were obtained for each optic from svn: l1:filter files in python using foton and exported them to matlab
- The timeseries for each optic were obtained for DAMP_IN1 channels (256Hz) using gwpy for the time interval of 1 hour (1382893218, 1382896818). The asd were calculated from the timeseries with a window length of 8s and overlap of 4s. This asd along with it's corresponding freqeuncies were exported to matlab
- Since there was no way to change the frequency resolution over which it was calculated in gwpy, it was interpolated in matlab using the interp1 function to match the frequency resolution that was used in matlab.
- The DAMP_OUT spectra was thus calculated as [*DAMP_OUT = (Damping_Filter)x(*DAMP_IN1)]

Attachment 1: DAMP_OUT_Spectra.pdf
DAMP_OUT_Spectra.pdf DAMP_OUT_Spectra.pdf DAMP_OUT_Spectra.pdf DAMP_OUT_Spectra.pdf DAMP_OUT_Spectra.pdf DAMP_OUT_Spectra.pdf
  1944   Thu Nov 9 12:56:10 2023 murtazaSummarySUSTriple Suspension Simulation

DATA ACQUISITION (FILTER MODULES) FROM LIVINGSTON

tldr: the filter files (active modules) for all the triple suspensions at Livingston were obtained.

The previous time I obtained the damping filters from the site, it was very messy and manual. I spent some time cleaning the scripts to get the filter module switch status, gains and so forth along with the filters.
Here's random bits of information and some progress update along the way.

- A handy place to obtain channel names: https://cis.ligo.org/

- To obtain the filter module switch status, you look at the channel name ending in SWSTAT which returns a decimal value. You convert it to binary and look at the first 10 digits from the right. 0-OFF, 1-ON.

- I was having trouble using gwpy to get the filter status from the Livingston site. The error looked as follows:
NDSWarning: unique NDS2 channel match not found for 'L1:SUS-PR3_M1_DAMP_T_SWSTAT' warnings.warn(error.split('\n', 1)[0]

I needed a machine that could use foton (obtain filter files) and nds2utils(obtain filter module status ON/OFF) on the same machine.
Paco advised against installing nds2utils on the 40m PCs so I used the conn method from nds2. Here's a nice script that shows how to use the method -> https://git.ligo.org/40m/measurements/-/snippets/164
(Be careful, chann_buffers is a shared_pointer. For example, if you pass a list of 6 channels and want to access the data from the 3rd channel, you use

my_data = chann_buffers[2].data

It has multiple methods if you want to access things like time, etc.)

- Instead of connecting to the 40m host, I connected to the Livingston (L1) host. Here's a list of hosts for future reference.

(None, ('nds.ligo.caltech.edu', 31200)),
('H1', ('nds.ligo-wa.caltech.edu', 31200)),
('H0', ('nds.ligo-wa.caltech.edu', 31200)),
('L1', ('nds.ligo-la.caltech.edu', 31200)),
('L0', ('nds.ligo-la.caltech.edu', 31200)),
('V1', ('nds.ligo.caltech.edu', 31200)),
('C1', ('nds40.ligo.caltech.edu', 31200)),
('C0', ('nds40.ligo.caltech.edu', 31200)),
('K1', ('k1nds0.kagra.icrr.u-tokyo.ac.jp', 8088)

- For the triple suspensions at Livingston, I will be obtaining the data for the following triple suspensions (https://dcc.ligo.org/DocDB/0033/T1100073/004/T1100073-v4_suspensions_by_chamber.pdf)
from DAQSVN (The document mentions IMC1, IMC2, IMC3 but since its from 2013, I'm hoping that the naming convention has changed for them to MC1, MC2, MC3)
 

HLTS - PR3, SR3
HSTS - PRM, PR2, SRM, SR2, MC1, MC2, MC3

The connection kept timing out yesterday intermittently , I'll try again today.

ERRNO: read_server_response_wait: Timed out: errno: 62 - Timer expired

Update: I kept trying it at hourly intervals, I managed to grab the data cool

  1943   Fri Nov 3 16:43:26 2023 murtazaSummarySUSTriple Suspension Simulation

PR3 Trial Filter Design

tldr: PR3 (Livingston, HLTS) filters redesigned with the following goals.

  • Lower noise by a factor ~10 in the 10-30Hz bandwidth
  • Achieve similar ringdowns for the impulse response
  • Have phase margins of ~30 degrees and gain margins of ~3dB

This was the first time I’ve designed damping filters => I’ll be verbose in the explanation. The ASD shows noise reductions at 10Hz and 20Hz between the site filter design and the trial filter design (assuming that the natural roll off makes 30Hz noise low enough). The filters were designed individually (with the remaining DOFs damping turned off).

The basic philosophy for designing filters for each DOF has been the following. 

  • Velocity damping with a zero at 0 and a pair of complex poles. The zero at 0 is what gives viscous damping and the pole pair provides filtering of noise and gives a finite actuation size. Having complex part for the poles helps recover some phase margin while inducing some oscillations in the signal (which is assumed to be okay).
  • Instead of manually setting the gain for the filters, the UGF for open loop transfer function can be manually set where we want it to be. (For newbies like me, the bode plot crosses the the 0dB or unity gain mark multiple times, the UGF is the frequency where it crosses that point the last time. The intuition behind setting the UGF is as follows:
    1) For feedback, all frequencies are fed back to the system, however the ones above the 0dB mark in the OLTF are significant.
    2) Mechanical resonances can usually be at any frequency, however in this case, the first order modes usually occur at lower frequenices. 
    3) Mechanical systems naturally roll off (magnitude steadily decreases) at higher frequencies
    4) From 3), you can set the UGF at higher frequencies for faster damping (more gain on the peaks), but that will also lead feeding back the sensing noise into the system. Thus, it’s a tradeoff.
  • Once a UGF has been picked appropriately, add bumps at the frequencies where the peaks are not high enough in the OLTF. This ensures they are damped well.
  • Add notches in places where you want a reduction in sensor noise entering the system by looking at the ASD of the sensor noise on M1 to Test Mass displacement.
  • Add elliptical filters (bandstop in this case) for aggressive filtering of the modes that have considerable peak in the noise ASD due to bounce and roll (stretching of the wire) at higher frequencies. This means that there is virtually no damping on these modes (with the goal being to reduce the sensor noise at these modes). 6th order filters are used usually and in this case, the attenuation used was 40dB for the filter. (This is specifically for the vertical and roll modes, the metric was to do slightly better on the noise performance than the sites at these ringup frequencies).
  • Most SISO loops after all this had decent gain margin but sucked with phase margin. Adding a small bump in front of the UGF (f0 + df) helps recover sizable phase margin at the cost of some gain margin. 

 

With these following toolsets, here’s the filter design for each DOF. (The electronics gain has not been accounted for here, it must be added to the filter design). The filters work with negative feedback with a gain of 1. 

 

DOF

UGF

Velocity Damping

Notches

Bumps

Elliptical

Longitudinal

3.2

zpk(0, -2*pi*pair(150, 80), 1)

 

notch(10,10,10), notch(15,10,7), notch(20,10,7), notch(10,10,8), notch(15,10,7), notch(20,10,8)

bump(6, 5, 8), bump(0.66,15, 3.5)

 

 

Transverse

3.88

zpk([0], -2*pi*pair(80, 30), 1)

notch(10,12,5), notch(15,12,6), notch(20,12,7)

bump(4, 5, 3.5), bump(0.68, 20, 20)

 

Vertical

3.75

zpk([0], -2*pi*pair(100, 40), 1)

notch(10,12,4.5), notch(10,12,4.5), notch(15,12,8.5), notch(20,12,6), notch(20,8,5.5)

 

bump(1.07, 10, 5), bump(4.5, 5, 3.5)

ellip(6, 3, 60, 2*pi*[24, 30],'stop', 's')

Yaw

3.40

zpk([0], -2*pi*pair(100, 30), 1)

notch(10,12,7), notch(15,12,8), notch(20,12,8), notch(10,12,7), notch(15,12,5)

 

bump(0.989, 10, 5), bump(4, 6, 7)

 

 

Pitch

3.62

zpk([0], -2*pi*pair(100, 30), 1)

 

notch(10,10,8), notch(10,10,9), notch(15,10,7), notch(20,10,4), notch(22,10,6)

bump(0.745, 10, 1.8), bump(4.5, 10, 4), bump(0.66, 10, 1.8)

 

 

 

Roll

3.79

zpk([0], -2*pi*pair(100, 50), 1)

notch(10,12,4), notch(15,12,5), notch(20,12,5), notch(20,12,5), notch(35,12,7)

 

bump(5, 5, 5), bump(1.98, 10, 5), bump(0.692, 10, 5)

 

ellip(6, 3, 100, 2*pi*[40, 48],'stop', 's')

 

The pdf has been arranged as following for each DOF. (Comparisons are between the site filter design and the trial filter design (need to come up with a better terminology for this)).

  • First figure shows a comparison of the sensor noise ASD (DOF sensor noise on M1 to DOF Displacement on M3) in the bandwidth of interest and ringdown periods for the impulse response. (FOR Longitudinal DOF, the impulse input was ground, for the remaining DOFs, the input was at M1). 
  • Second figure shows a comparison of the filter designs in the bandwidth of interest
  • Third figure shows the open loop transfer function (P(s)*C(s)) with phase and gain margins
  • Fourth figure shows a comparison of the open loop transfer functions (P(s)*C(s)).
Attachment 1: PR3_Final_Design_1103.pdf
PR3_Final_Design_1103.pdf PR3_Final_Design_1103.pdf PR3_Final_Design_1103.pdf PR3_Final_Design_1103.pdf PR3_Final_Design_1103.pdf PR3_Final_Design_1103.pdf PR3_Final_Design_1103.pdf PR3_Final_Design_1103.pdf
  1942   Tue Oct 31 14:14:52 2023 murtazaSummarySUSTriple Suspension Simulation

PR3 Livingston Filter Design (PITCH DOF)

tldr: meeting noise reduction requirements, meeting ringdown time requirements, doing okay on the phase margins (~20 degrees for the minimum stability margins)

Filter Design: Using the same design philosophy for the longitudinal DOF, I proceeded to design the pitch damping loop

1. zpk(0, -2*pi*pair(100, 75), -1) (Damp the pitch DOF on M1)
2. bump(0.66, 15, 9) (Damp the natural frequency of M1 at 0.75Hz)
3. bump(3.75, 5, 3.5) (Recreating the accidental bump from the longitudinal filter, adding a small bump slightly ahead of where I want to set my UGF does well for the noise performance).
3. notch(10,12,8)*notch(15,12,5)*notch(20,12,7)*notch(10,12,5)*notch(15,12,7) (Suppress the noise from 10->20Hz, used a single notch at 20Hz exploiting the natural roll off of the system)
The UGF was then set at 3.62Hz.

 

Attachment 1 shows a comparison of the ASD and the ringdown times.
Attachment 2 shows a comparison of the filter designs
Attachemnt 3 is the open loop transfer function for M1 (P DOF) with the minimum stability margins. The current phase margin is ~21 degrees 
Attachment 4 shows a comparison of the OLTFs for M1 (P DOF). 

Attachment 1: 10_31_PASDandRD_comparison.png
10_31_PASDandRD_comparison.png
Attachment 2: 1031_pitch_filter_comparison.png
1031_pitch_filter_comparison.png
Attachment 3: 1031_OLTF_BodeWMargins_P.png
1031_OLTF_BodeWMargins_P.png
Attachment 4: 1031_OLTF_comparison_P.png
1031_OLTF_comparison_P.png
  1941   Mon Oct 30 12:08:35 2023 murtazaSummarySUSTriple Suspension Simulation

PR3 Livingston Filter Design (LONGITUDINAL DOF)

tldr: meeting noise reduction requirements, meeting ringdown time requirements, doing okay on the phase margins (~20 degrees for the minimum stability margins)

Filter Design:

1. zpk(0, pair(-2*pi*100, 75), -1e6) (Damp the longitudinal DOF on M1)
2. bump(0.75,30, 10) (Damp the natural frequency of M1 at 0.75Hz)
3. bump(3.2, 5, 1.5) (I was trying to get some damping on the 3Hz peak, although it didn't improve the impulse response as compared to without the bump, it recovered 10 degrees of phase margin and improved the noise performace by a factor of ~5).
3. notch(10,10,7)*notch(15,10,7)*notch(20,10,7)*notch(10,10,5)*notch(15,10,5)*notch(20,10,5) (Suppress the noise from 10->20Hz)
The UGF was then set at 3Hz.

 

Attachment 1 shows a comparison of the ASD and the ringdown times.
Attachment 2 shows a comparison of the filter designs
Attachemnt 3 is the open loop transfer function for M1 (L DOF) with the minimum stability margins. The current phase margin is ~20 degrees 
Attachment 4 shows a comparison of the OLTFs for M1 (L DOF). 

Attachment 1: 10_30_ASDandRD_comparison.png
10_30_ASDandRD_comparison.png
Attachment 2: 1030_longitudinal_filter_comparison.png
1030_longitudinal_filter_comparison.png
Attachment 3: 1030_OLTF_BodeWMargins.png
1030_OLTF_BodeWMargins.png
Attachment 4: 1030_OLTF_comparison.png
1030_OLTF_comparison.png
  1940   Sat Oct 28 22:46:55 2023 PacoLab InfrastructureEquipmentLoanThorlabs HV pzt driver

I took the Thorlabs PZT driver to the 40m for use with the BHD OMC.

  1939   Fri Oct 27 01:00:37 2023 murtazaSummarySUSTriple Suspension Simulation

With the following goals:

- 10x lower noise magnitude than the current filter design in the 10-20Hz range
- 10s ringdown time 

After gaining some intuition from Brett, I started designing the filter. The New design current contains the following components
- Velocity damping: zpk(0, [10, 10], 1e6). Zero at 0 to prevent feeding back the DC offset, Poles at 10Hz to low pass freqeuncies over 10Hz, Gain arbitarily chosen to achieve feedback.
- Notches at 10Hz and 15Hz balancing the magnitude to prevent sufficient loss in phase margin
- Bump at 0.745Hz to suppress the peak at the same frequency
 

The comparisons are made with just having the Longitudinal DOF filter active in the loop between the filter used at the site and the new design

Attachment 1 shows a comparison of the ASD and the ringdown times.
Attachment 2 shows a comparison of the filter designs
Attachemnt 3 is the open loop transfer function for M1 (L DOF) with the minimum stability margins. The current phase margin is ~22 degrees (Aiming for 30 degrees)
Attachment 4 shows a comparison of the OLTFs for M1 (L DOF). 

This in no way acheives the objectives, the next steps for tuning are:
- Tune parameters for the current filter design
- Add lead/lag compensators
- Compare the performance between notches and elliptical filters 

Attachment 1: 1027_ASDandRD_comparison.png
1027_ASDandRD_comparison.png
Attachment 2: 1027_longitudinal_filter_comparison.png
1027_longitudinal_filter_comparison.png
Attachment 3: 1027_OLTF_BodeWMargins.png
1027_OLTF_BodeWMargins.png
Attachment 4: 1027_OLTF_comparison.png
1027_OLTF_comparison.png
  1938   Mon Oct 23 16:52:54 2023 murtazaSummarySUSTriple Suspension Simulation

A velocity damping filter with of the following form: zpk(0, 2*pi*[-20, -20], 100) was applied to the Length DOF while the remaining filters were set to 0. The following Attachements are comparisons betwen the Active Filters at Sites vs Velocity Damping Filter

Attachment 1 shows the Bode Plot comparisons

Attachment 2 shows the Ringdown Period comparisons

Attachment 3 shows the ASD comparisons for M3_L

Attachment 1: Screenshot_2023-10-23_at_5.10.21_PM.png
Screenshot_2023-10-23_at_5.10.21_PM.png
Attachment 2: Screenshot_2023-10-23_at_5.02.45_PM.png
Screenshot_2023-10-23_at_5.02.45_PM.png
Attachment 3: Screenshot_2023-10-23_at_5.04.01_PM.png
Screenshot_2023-10-23_at_5.04.01_PM.png
  1937   Fri Oct 20 12:13:00 2023 murtazaSummarySUSTriple Suspension Simulation

I made some changes to the plots
tldr:
 - collected the linear and angular DOFs sensor noise contributions from M1 in a single plot
- added some meaningful titles and legends
- changed the limits of the plots

The plots were zoomed in with the following limits.
- x-limits [0.5 - 20Hz]
- y-limits [1e-18, 5e-9]

The x-limits were with the following rationale:
lower limit -> arbitarily chosen to incorporate the peaks <1Hz
upper limit -> the detection band begins from 10Hz, with the spectrum rolling off steeply and being 3 orders of magnitude lower than the peaks

The y-limits were with the following rationale:
lower limit -> arbitarily chosen, do not know the floor which is significant for detection. 5 orders of magnitude seemed reasonable
upper limit -> All peaks lower than 5e-9, thus no need of space above it.

 

Attachment 1: m1_sens_to_m3_disp.pdf
m1_sens_to_m3_disp.pdf m1_sens_to_m3_disp.pdf m1_sens_to_m3_disp.pdf m1_sens_to_m3_disp.pdf m1_sens_to_m3_disp.pdf m1_sens_to_m3_disp.pdf m1_sens_to_m3_disp.pdf m1_sens_to_m3_disp.pdf
  1936   Thu Oct 19 18:22:21 2023 murtazaSummarySUSTriple Suspension Simulation

Jeff Kissel: 

In short — above 10 Hz, the number that’s typically tossed around verbally for displacement noise floor is 5e-11 [m/rtHz].

Using this (with the assumption that it is white), I proceeded to estimate the displacements in M3 DOFs due to the sensor noise in M1 DOFs. The OSEM configuration/dimensions were obtained from https://dcc.ligo.org/DocDB/0002/D070447/002/D070447-v2_HLTS_OSEMLeverArmMeasurements.pdf

noise = 5*10^{-11} m/\sqrt{Hz}

The noise in each DOF was estimated by taking the quadrature sum of the contribution of each sensor used for the DOF measurement (eg, for L, since there are 2 sensors measuring the same value, it would be  \sqrt{(0.5*noise)^{2} +(0.5*noise)^{2} }
I looked at the OSEM2EUL matrix for PR3 to get the change of basis. The matrix elements for the angular basis agrees with the small angle approximations using geometry to obtain the magnitudes (Attachment 1).
Attachment 2 has the individual as well as the combined ASD for the estimate Range [0.5 - 100 Hz]

Pages 1,2 are the positional and rotational ASD of m3 displacements respectively taking the quadrature sum of the sensor noise contribution to each DOF in m1.
Figures 4-9 are arragned showing the contribution of the individual DOFs of m1 to displacements of m3.
Noticable sensor noise in m1_disp were observed for the following:


m3_L ------> m1_L, m1_P
m3_T ------> m1_T, m1_R
m3_V ------> m1_V
m3_Y ------> m1_Y
m3_P ------> m1_L, m1_P
m3_R ------> m1_T, m1_R

 

Attachment 1: 5CF0AAFE-354E-43B6-B40B-F457A7A7E83C.jpg
5CF0AAFE-354E-43B6-B40B-F457A7A7E83C.jpg
Attachment 2: asd_m1sens_to_m3.pdf
asd_m1sens_to_m3.pdf asd_m1sens_to_m3.pdf asd_m1sens_to_m3.pdf asd_m1sens_to_m3.pdf asd_m1sens_to_m3.pdf asd_m1sens_to_m3.pdf asd_m1sens_to_m3.pdf asd_m1sens_to_m3.pdf
  1935   Wed Oct 18 11:51:55 2023 murtazaSummarySUSTriple Suspension Simulation

Closer look at the damping siutation.
tldr: Corrected electronics gain, Signs of filters flipped, AND THE CORRECT MODEL (HLTS) WAS USED.

- I looked around the SVN to find the recent electronics gain. To begin with, the gains applied previous to the simulation were incorrect (MC1, 2012, e_k = 34.1). This was corrected to (PR3, 2023, e_k = 1.5404)https://svn.ligo.caltech.edu/svn/sus/trunk/HLTS/L1/PR3/SAGM1/Results/2023_07_20_1100_L1SUSPR3_M1_ALL_TFs.pdf

- With the new gain, the system was unstable. I wanted to check the closed loop behavior of each individual filter to see where the instabilty was rising from. I checked the matlab and simulink simulations for each filter turned on individually and flipping signs of feedback sequentially.

(0 = unstable, 1 = stable)

Active Filter M, S M, S
  -ve feedback +ve feedback
L 0, 1 1, 1
T 0, 1 1, 1
V 0, 1 1, 1
Y 0, 1 1, 1
P 0, 1 1, 1
R 0, 1  1, 1

While writing this elog, I realized that PR3 was a large suspension and I needed to use the HLTS model instead of the HSTS model. I updated the model and poof, the closed loop system is stable. Matlab and simulink agree with each other now so I'll proceed with using Matlab now.

 (m1->drive->DOF -------> m1->disp->DOF) 
- Bode Plots: Attachment 1
- Step Responses: Attachment 2

Attachment 1: Screenshot_2023-10-18_at_12.26.44_PM.png
Screenshot_2023-10-18_at_12.26.44_PM.png
Attachment 2: Screenshot_2023-10-18_at_12.28.13_PM.png
Screenshot_2023-10-18_at_12.28.13_PM.png
  1934   Tue Oct 17 22:11:21 2023 murtazaSummarySUSTriple Suspension Simulation

I attempted a matlab simulation for closing the loops on the triple suspensions. The system (hsts) was imported from https://git.ligo.org/jenne-driggers/SUS.
The active damping filters were read for the PR3 optic at LLO. 
There were a few glitches which were accounted for. 

- The complex pairs of poles and zeros differed ever so slightly in their conjugate parts. An example is given in Attachment 3. The real and imaginary values were rounded off to the 10th place
- The closed loop system was unstable. Brett suggested accounting for the electronic gains which were obtained from https://svn.ligo.caltech.edu/svn/sus/trunk/HSTS/L1/MC1/SAGM1/Results/2012-05-08_1700_L1SUSMC1_M1_ALL_TFs.pdf. A factor of 34.1 was accounted for all DOFs.
- The matlab version uses connect for closing the loops. Even after accounting for the gain, there were a few RHP poles (smaller now). 
- A simulink version for the system was created which essentially did the function of "connect" in matlab and it was simulated. This closed loop system was stable. A comparison of the Bode plots (m1->drive->DOF -------> m1->disp->DOF) is given in Attachment 1.
(forgot to wrap the phase for the Bode plots, will change to the corrected version tomorrow)
- The step responses fo the simulink plant for (m1->drive->DOF -------> m1->disp->DOF) were generated (Attachment 2).

Next Steps:

- Need to check for the inconsistencies between the two simulation methods
- Can proceed to add ports for noise inputs
- Need to verify the current electronic gain calibrations at LLO for the optic (if available)
 

Attachment 1: Screenshot_2023-10-17_at_9.52.29_PM.png
Screenshot_2023-10-17_at_9.52.29_PM.png
Attachment 2: Screenshot_2023-10-17_at_10.10.38_PM.png
Screenshot_2023-10-17_at_10.10.38_PM.png
Attachment 3: Screenshot_2023-10-17_at_5.31.06_PM.png
Screenshot_2023-10-17_at_5.31.06_PM.png
  1933   Mon Sep 25 15:56:17 2023 PacoLab Infrastructure1418 nm AUX ECDL2nd ECDL housing assembled

I assembled the second ECDL with a 19XX SAF gain chip (all pins remain disconnected), and a 14XX nm angle facet plate with a grating.

Attachments #1-4 show the final state of the housing along with the thorlabs current and temperature drivers. The remaining spare components (including screws, angle facet plates for the gratings and two SAF gain chips, one for each wavelength) are stored in a single box in the right top cabinet on the north end.

Attachment 1: PXL_20230925_223237259.MP.jpg
PXL_20230925_223237259.MP.jpg
Attachment 2: PXL_20230925_223622837.MP.jpg
PXL_20230925_223622837.MP.jpg
Attachment 3: PXL_20230925_222547746.MP.jpg
PXL_20230925_222547746.MP.jpg
Attachment 4: PXL_20230925_223541276.MP.jpg
PXL_20230925_223541276.MP.jpg
  1932   Thu Jul 20 12:57:38 2023 aaronMiscEquipmentLoanAOM to cryo lab

I returned the Gooch & Housego R26035-2-1.55-LTD AOM (SN 216939) from DOPO table

  1931   Thu Jan 12 11:51:49 2023 KojiLab InfrastructureGeneralHow to move the large engine hoist through the narrow door

How to move the large engine hoist through the narrow door

See http://nodus.ligo.caltech.edu:8080/Mariner/122

  1930   Tue Jan 10 23:40:17 2023 KojiLab InfrastructureGeneralHeavy item transport - preparation 

See http://nodus.ligo.caltech.edu:8080/Mariner/121

  1929   Thu Jun 23 16:34:46 2022 PacoLab InfrastructureDOPORelocated DOPO setup

Following Koji's request, I took some time to clear the area surrounding the crackle chamber so it can be migrated to the former TCS lab.

I moved the DOPO setup which was sitting on a breadboard for easy transportation (Attachment #1) and placed into the other table in the lab. Attachments #2-3 shows the cleared area. Several instruments from the DOPO experiment still remain around the other side of the crackle chamber, if they need to be relocated I can move them as well.

Attachment 1: PXL_20220623_222426584.jpg
PXL_20220623_222426584.jpg
Attachment 2: PXL_20220623_223623414.jpg
PXL_20220623_223623414.jpg
Attachment 3: PXL_20220623_224259785.jpg
PXL_20220623_224259785.jpg
  1928   Tue Mar 8 09:32:56 2022 PacoDailyProgress1418 nm AUX ECDL1418nm ECDL Frequency noise

[Paco, Radhika]

Beatnote recovery

Restarted ECDL characterization last Friday. After some lab cleanup, and beatnote amplitude optimization we borrowed Moku Lab from Cryo lab to fast-track phase noise measurements. Attachment #1 shows a sketch of our delayed self-heterodyne interferometer. The Marconi 2023A feeds +7 dBm to a  ZHA-3A amplfier which shifts the frequency of the laser in one of the arms using a free space AOM. The first order is coupled back into a fiber beamsplitter to interfere with a 10 m delay line beam.

Improved beatnote detection

The 38.5 MHz beatnote was barely detectable before when using PDA20CS2 because at unity (lowest) gain stage, the bandwidth was only 11 MHz... We instead switched to an FPD310-FC-NIR type which has a more adequate high-frequency response. Attachment #2 shows the beatnote power spectrum taken with Moku Lab spectrum analyzer. The two vertical lines indicate (1) the heterodyne beatnote frequency and (2) the "free spectral range" indicating the actual delay in the MZ arms, which is calibrated to c\tau/n = 9.73 m (using 1.46 for n, the fused silica fiber index).

Phase meter and freq noise calibration

We then tried using the phase meter application on the Moku. The internal PLL automatically detected the 38.499 MHz center frequency and produced an unwrapped RF phase timeseries (e.g. shown in Attachment #3). The MZ interferometer gives an AC signal

I_{\rm AC} = I_0 \cos(\Omega_0t + \phi(t + \tau) - \phi(t))

oscillating at \Omega_0 , i.e. the angular beatnote frequency. The delay (calibrated above) characterizes the response of the MZ relating the RF phase noise spectrum to the optical phase noise spectrum. The RF phase obtained through the phase meter has a fourier transform

\tilde{\phi}_{\rm RF}(\omega) = \tilde{\phi}(\omega) e^{-i \omega \tau} - \tilde{\phi}(\omega)

So the optical phase spectral density is related to the rf phase spectral density by a transfer function H(\omega) = e^{-i \omega \tau} - 1  Then, the RF & optical phase power spectral densities are related by S_{\phi_{\rm RF}}(\omega) = |1 - e^{-i \omega \tau}|^2 S_{\phi}(\omega)  or

S_{\phi}(\omega) = \frac{S_{\phi_{\rm RF}}(\omega) }{ 4 \sin^2(\omega \tau /2) }

Then, because the instantaneous laser frequency is 2 \pi \nu = \dot{\phi},  in fourier domain \tilde{\nu} = \frac{i\omega}{2 \pi} \tilde{\phi} the frequency and phase PSDs are related by the magnitude square of this transfer function like

S_{\nu}(\omega) = f^2 S_{\phi}(\omega)

Following this prescription, we compute an estimate for the frequency noise ASD (square root of the PSD) shown in Attachment #4. The frequency noise estimated by this method has several contributions and *does not* necessarily represent the free-running ECDL frequency noise.


Next steps

  • Noise budgeting (experiment)
  • Control loop (open/closed) models
Attachment 1: schematic.png
schematic.png
Attachment 2: raw_bn_spectrum.png
raw_bn_spectrum.png
Attachment 3: phase_timeseries.png
phase_timeseries.png
Attachment 4: ecdl_freqnoise.png
ecdl_freqnoise.png
  1927   Tue Oct 19 13:52:03 2021 RadhikaDailyProgress1418 nm AUX ECDL1418nm ECDL Frequency noise

Attachment 1 is a diagram of the current setup for measuring ECDL frequency noise. Since the last update, I have fed the beat note signal to a mixer, using a 35 MHz LO sourced from the Marconi. The resulting demodulated signal is passed to a low-pass filter, removing the 2f sinusoidal term (any trace of the frequency difference) and leaving behind a low-frequency term containing frequency noise information of the original beam (accumulated over the length of delay line).

I took spectra of the resulting signal using the SR785 (Attachment 2). Note that these units are still in V/rtHz, since the signal has not been calibrated to the appropriate units for frequency noise, Hz/rtHz. Finding the calibration term will involve study of delay line frequency discrimination. 

Attachment 1: ECDL_diagram.pdf
ECDL_diagram.pdf
Attachment 2: ECDL_FNM_13-10-2021_151524.pdf
ECDL_FNM_13-10-2021_151524.pdf
  1926   Mon Oct 4 17:44:34 2021 RadhikaDailyProgress1418 nm AUX ECDLFree space AOM

[Paco, Radhika]

Last Friday we received a new lens to direct the AOM 1st-order beam from free space into a fiber cable. We mounted the lens and connected a fiber cable into the photodiode, and tried to align the lens and see a jump in the oscilloscope. We were not able to do so and wrapped up for the day.

Today we continued aligning the lens with the fine adjustment on the mount, and eventually saw signal on the scope! Hooray, done with free space. We then prepared for eventually taking a heterodyne beat note measurement and hooked up the appropriate inputs/outputs to the beamsplitters. We added in the 50-50 beamsplitter that takes in the 1st order diffracted beam along with the beam from the delay line as inputs. We passed one of the outputs to the photodiode and had to retweak the freespace-to-fiber lens until we recovered signal on the scope, and we saw the beatnote signal.

Next, while Paco is out of town I will continue to work towards making a frequency noise measurement. We made a roadmap today:

I will demodulate the beat note using a mixer and a 35 MHz LO sourced from the Marconi. The result will be a 2f cosine term, along with a much lower frequency term which encloses the frequency noise information. This will be passed through a low-pass filter to get rid of the first high-frequency term. The remaining time-domain signal will be passed to the SR785 to obtain a spectra of the frequency noise. Calibration will need to be performed to obtain the right units for the spectra, Hz2/Hz (or Hz/rtHz). 

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