I looked at what the RIN contribution of the sqrtInv sensor is by locking the arms individually on IR using POX and POY.  I then took spectra of the sqrtInv channels.  For the Xarm, I had forced the triggering so that the QPD was being used as the transmission PD, while the Yarm was using the regular Thorlabs PD.  I also had the green lasers locked to the arms, and took beatnote spectra to see what the sensing noise of the beatnotes is, all at the same time.

For the sqrtInv channels, I used the Optickle calibration from elog 10187. For today's plot, I am using the calibration at about 1nm, since that is about where we are when we transition to the sqrtInv Thorlabs signal usually.

For the ALS channel, I was using the _FINE_PHASE_OUT signal, which is in units of degrees of phase for a single green wavelength.  So, since k * x = phi, I want the phase data to be converted to radians (2*pi/360), and use k = 2*pi / lambda_green.  So, doing some algebra, this gives me x = phi_degrees * lambda / 360 for my calibration. 

What I see in the plot is that the ALS sensing noise is pretty bad compared to the sqrtInv channels, so maybe we don't have to work so hard on the ISS this next week.  Also, the Thorlabs PD is much better than the QPDs, which maybe isn't so surprising since we have them set so that they have good SNR at higher power.

Anyhow, here's the plot:

Also, here is the Thorlabs PD only, with single arm locked on RF, with the noise calibrated to different CARM offsets:

Your calibration of the ALS signal should be revised.

The phase for the ALS is not an optical phase of the green but the phase of the phase tracker servo output.

The calibration of the phase tracker depends on the cable length of the delay line in the beat box.
It seems that we are based on this calibration. Which gives up ~19kHz/deg.

Or, equivalently, use C1:.....PHASE_OUT_HZ instead.

Patient One for this new system will be the MC servo card. The DCC number is D1400242. Currently, v1 is just the original drawing with no modifications. I've updated the DCC document tree at E1400326 accordingly.

It looks like we can use Jenne's information in 40m:9892 to deduce the modifications that have been made (alternatively, someone can just pull the board and examine it on the bench).

 Purpose

The idea was to measure the profile of the light coming out of the fiber, so we could have knowledge of it for further design of measurement apparatuses, for characterization of the fibers' properties.

Methods

The method was the same as the last time I tried to measure the fiber mode.

This time I moved the beam profiler in a wider range along the z-axis.

Additionally, I adjusted the coupling until it gave ~1mW through the fiber, so the signal was high enough to be reliably detectable.

Measurements were taken in both X and Y transections of the beam.

The range of movement was limited by the aperture of the beam profiler, which cuts off at 9mm. My measurements stop at 8.3mm, as the next possible measurement was beyond the beam profiler's range.

Analysis

I entered my data into A La Mode, which gave me a waist of 5um, at a location of z = -0.0071 m, that is to say, 7.1mm inside the fiber.

Note that in the plot, data points and fits overlap, and so are sometimes hard to distinguish from each other.

Code is attached.

Moving Forward

Using this data, I will begin designing setups to measure fiber characteristics, the first of which being Polarization Extinction Ratio.

Eventually, the data collected from these measurements will be put to use in the frequency offset locking setup.

Interlock closed valve V1, V4, V5 and VM1 when the nitrogen supply run out. The IFO pressure rose to P1 1 mTorr

In order to recover Vacuum Normal valve configuration I did the following:

Replaced both nitrogen cylinders. Confirmed pneumatic nitrogen pressure 70 PSI.   Opened valves V4 and V5

At P2 < 1 mTorr, Maglev rotation 560 Hz , V1 was opened.

VM1 was opened when CC1 pressure dropped below < 1e-5 torr

Please  take a look at the N2 cylinders pressure on Friday to insure that there is enough for the week end.

The daily consumption is 600-700 PSI

The autolocker claimed it was running and blinking, but not doing anything (i.e. lock bit was not updating and no switches or sliders being touched)

After stopping and starting it a number of times, it began working again, through no real changes of my own. I'm a little mystified as to what the problem was... keep an eye out.

 Edit

The previous data were flawed, in that they were taken in groups of three, as I had to move the micrometer stage which held the beamscan between holes in the optical table.

In order to correct for this, I clamped a straightedge (ruler) to the table, so I could more consistently align the profiler with the beam axis.

These data gave a waist w_o = 4um, located 6mm inside the fiber. While these figures are very close to what I would expect (3.3um at the end of the fiber) the fitting still isn't as good as I would like.

The fit given by ALM is below.

Moving Forward

I would like to get a stage//rail so I can align the axes of the beam and profiler more consistently.

I would also like to use an aperture the more precisely align the profiler aperture with the beam axis.

Once these measurements have been made, I can begin assembling the setup to measure the Polarization Extinction Ratio of the fiber.

The attached zip file has a modified schematic of the MC servo card (011/MC), as deduced from Jenne's photos. Someone should go through and verify that the schematic is correct. Then it can go on the DCC as D1400242-v2.

To modify the schematic, I used Inkscape (the svg files for each sheet are included in the zip file). Then to generate the pdf, I ran

for i in sheet*.svg; do inkscape -A "${i/svg/pdf}" "$i"; done

pdftk sheet*.pdf cat output D1400242

Using the modified schematic (40m:10250), I've made a plot of the TFs I expect for G_IN1 = G_VCO = 0 dB, taking into account our 50 Ω loading of the board.

Evidently I'm somehow missing a factor of 2 in the gain of the overall TF, but the shapes of the expected vs. measured magnitudes agree quite well.

At 1 MHz, I expect we should have accumulated about 80 degrees of phase going through the servo board. In reality, we appear to have lost more like 105 degrees.

 ITMY oplev was nearly clipping in yaw, causing wonky behavior (POY lock popping in and out frequently). I recentered it and the arm is locking fine now. 

I repeated this process once more, this time using the computer controlled stage that the beam profiler is designed to be mounted to.

These data//fitting appears to be within error bars. The range of my measurements was limited when the beam width was near the effective aperture of the profiler.

This latest trial yielded a waist of 4um, located 2.9 mm inside the fiber for the X profile, and 3.0mm inside the fiber for the Y profile.

Code is attached in fiberModeMeasurement4.zip. Note that the z=0 point is defined as the end of the fiber.

 The Past Week

I spent the past week coupling NPRO light into the fibers, and subsequently measuring the fiber mode profile using the beam profiler.

The Next Week

In the next week, I plan to at least do measurements of the Polarization Extinction Ratio of the fibers.

Materials

My current optical setup, plus an additional polarizing beam splitter (have it).

 Work Done:

• Created a Channel Access Server on the Raspberry Pi  to write data from the FC into EPICS Channel.
• Completed characterization and noise estimation of the FC counter with improved timing.
• Started installation of FC inside the 40m.

Plans for this Week:

• Testing how well the FC can replace the spectrum analyzer which is in the control room. For this I have asked Steve to order  an RF adder/combiner to see how frequency counter responds to two RF signals at different frequencies(much like the RF signal fed to the spectrum analyzer) .
• Complete the installation of FC insode the 40m and start initial testing.
• Characterization of the Temperature Actuator and initial PID loop design.

Inside the 40m Lab:

• I will have to go inside the 40m lab this week for routing the RF mon cables to the FC box(in detail:http://nodus.ligo.caltech.edu:8080/40m/10163) .
• Also to setup for characterization of the temperature actuator, I will be required to go inside the lab in this week.

As Koji pointed out, I messed up the calibration.  However, fixing it doesn't change things that much.

From this calibration by Yuta, the Xarm ALS calibration is 54 deg / MHz, or 19.17 kHz / deg.  So, I multiply my data which is in these degree units by 19.17e3 to get Hz.  Then I use delta_f / f = delta_L / L to convert to meters.  f = c / lambda_green, and L = 37.5 meters. 

This only changes the calibration by about 10-15%.  It still looks like the ALS noise is well above the RIN level of the sqrtInv signal.

Quad processor 2 & 3 were replaced.

To do:

1. Measure and calibrate out  attenuation and phase changes due to RF cables in the PDFR system.
2. Create a database of canonical plots for comparison each time new data is acquired.
3. Vector fitting or LISO fitting of transimpedance curves.

Does not require time from a lab expert.

 As a part of installation of two(X-ARM and Y-ARM) frequency counters in the 40m, I have tested their performance when using them both on a single Raspberry Pi. The timing plots are attached. There are almost no timing issues in this configuration and it can be said that there is no harm using both of the FCs on the same platform.

We will be installing the FC box inside the lab and carry out few tests with RF mon beat note inputs.

Alone with the IFO. Started from some conversation with it.

Some ALS trials: Found the Y-end green alignment was terrible. In fact the end green set up is terrible.
Unfixed optics, clipping/fringing in the faraday, unstable suprema mounts which is unnecessarily big.

Eventualy I stopped touching the end alignment. Run ALS to see the stability of the things.
This is a performance confirmation after some touching of the ALS electronics by Manasa/SURFs

The sensing noise levels of the ALSs looks the same as before.

The intensity noise of the transmission was also checked. They are not RIN but very close to RIN
as the DC was the unity for both arms.

The X arm has worse ALS noise level and RIN.
Although I forgot to turn off the HEPA flow at the south bench during the measurement. Gurrr.

The plots in the previous Elog includes delay and a little attenuation by RF cables and the RF mux.

Today I separately calculated the delay and attenuation for an RG405 cable (550 cm) and the RF mux(using really small RF cables). These delays should be accounted for when fitting the transfer function of Demodulator boards and transimpedance of PDs.

The plots are in both semilogx and linear.

 Purpose

We wanted to improve the coupling into the fibers, because it's very rarely good enough to take measurements with, as the beam is obscured by random noise.

Additionally, we want to add some things to the current setup in order to better measure Polarization Extinction Ratio.

What Was Done

After flailing for several hours, Koji helped me couple the NPRO light into the fiber, using the fiber illuminator for alignment. The coupled optical power immediately jumped from 0-1uW to 5.6mW (around 11% coupling).

Q and I discussed the setup for measuring PER. In addition to the current setup, we added a half wave plate to control the angle of the polarization, in addition to the existing quarter wave plate, which corrects the beam for ellipticity.

Once everything was coupled, I started minimizing S-Polarization coming out of the first polarizing beam splitter, and maximizing the P-Polarization entering the fibers.

I did this by first varying the Quarter Wave plate to eliminate as much S Polarization as possible, and then, maintaining a constant differential in angle between QWP and HWP, I rotated them both to maximize power coupled into the fibers.

I measured 0.2 mW of S-Polarization, and 54.3 mW of P-Polarization.

At this point, a locking effort started, and I had to leave the 40m.

Moving Forward

Tomorrow, I would like to finish the setup of the PER measurement design. That is to say, add a collimator to the other end of the fiber, and align it with the second PBS.

And, of course, take a measurement of the Polarization Extinction Ratio of the fiber.

To eventually be implemented in Frequency Offset Locking.

 A time delay can be modeled as the exponential transfer function :  e^(-sT_d)  as seen HERE . Therefore the slope of the phase gives us the time delay.

A RG405 coaxial cable, exactly 5.5 meters in length, was fit to an ideal delay function e^(-sT_d) , with T_d = 150 ns.

The plots shows the actual data, fit data and data after correction using the ideal model stated above.

Conclusion:

Delay in RG405 cables is approximately 27.27 ns per meter. This value can be used to correct the phase in measurements of transimpedance for each PD by dividing out the ideal transfer function for time delay.

[EDIT: This looks like we have about 12 % the speed of light inside the RF cables. Too small to be true. I will check tomorrow if the Network analyzer itself has some delay and update this value.]

The varying attenuation of about 1dB due to the cable is not compensated by this. We need to separately include this.

Things to do:

1) Get the length of RF cables that is being used by each PD, so that the compensation can be made.

2) Calculate the attenuation and delay caused by RF multiplexer and Demodulator boards. Include these in the correction factor for transimpedance measurements. 

A time delay can be modeled as the exponential transfer function :  e^(-sT_d)  as seen HERE . Therefore the slope of the phase gives us the time delay.

The transfer function of RF multiplexer in rack 1Y1 (NI PXI-2547) was fit to an ideal delay function e^(-sT_d) , with T_d = 59 ns.

The plots shows the actual data, fit data and data after correction using the ideal model stated above.

Conclusion:

Delay the RF Multiplexer is approximately 59 ns. This value can be used to correct the phase in measurements of transimpedance for each PD by dividing out the ideal transfer function for time delay.

 [Koji, ericq]

We were working on getting back into the locking groove tonight.

The POP2F and REFL3F demod angles needed some tuning to lock the PRC reliably. The green alignments were mostly fine, the X end PZT ASS works reasonably well. Suspensions, especially the ITMs, seemed to be drifting a fair deal; today was fairly hot out, I guess.

We only got to the point of attempting the SqrtInv handoff once (which failed because I forgot to check the filter bank offsets). This was because the Mode Cleaner refused to stay locked longer than ~5-10 minutes at a time. We adjusted the MC and FSS servo offsets by the usual means, but this didn't make a difference.

We discussed and decided that the time is right to roll up our sleeves and dig into the MC loop, and try to figure out why these intermittent times of unreliability keep cropping up. We will check out the servo board, and see if we can find the missing phase than Evan observed, as well as characterize the FSS/PZT crossover, and investigate what kind of conditions we may create that cause the PC to saturate.

 Here's a fun fact: since the great computer failure of June2014, the PRM Oplev gains have been ZERO.

arrrrggggh

I've restored the gains to their old values, and measured the loop TFs.

 The PRM sus gains checked OK

All other suspension oplev gains setting were checked out OK

Today, I encountered a problem with the stage that holds the coupler, in that its ability to rotate unchecked causes coupling to degrade over time due to torsion in the fibers. Our solution was to stress-relieve the fiber with a clamp.

Unfortunately, this also meant losing coupling completely. It was re-coupled at up 72% efficiency. (Subsequent changes in the setup have decreased that to ~24%)

When I took preliminary measurements of the PER, it was significant, which was unexpected. Upon further discussion with Q, we concluded that since the fiber's fast axis hadn't been aligned with the light's polarization, I was getting multiple polarizations out the end of the fiber.

Subsequent measurements of the power contained in the two polarizations of the output light gave about 0.8% S-Polarization introduced by the fiber.

Tomorrow

I would like to find another collimator holder, to hold the output side of the fiber.

Also, I will spend more time aligning the fiber axes, and the second PBS in order to get a better (read: more reasonable) measurement of PER.

 As a part of temperature actuator characterization, today Eric Q and I made some measurements for the open loop TF of both the X-arm and Y-arm  thermal actuators. 

For this, we gave an input  of random excitation for the temperature offset input( since we faced some serious issues when we gave in Swept sine yesterday) and observed the PZT actuation signal keeping the arm to be locked all the time of our measurements and ensuring that the PZT signal doesn't saturate.

The  channels used for the measurement were  C1:ALS-X_SLOW_SERVO2_EXC as the input and C1:ALS-X_SLOW_SERVO1_IN1  as the output.

The random noise used for the measurement :

Y-ARM:  Gain- 6000;  Filter - butterworth-first order - band-pass filter with start frequency= 1 Hz stop frequency = 5 Hz.

X-ARM: Gain -3000; Filter - butterworth- first order- band-pass filter with start frequency 3 Hz and stop frequency = 30 Hz and  notch(1,10,20).

The Y-ARM measurement was stable but for the X-ARM, the PZT was saturating too often so Eriq Q went inside the lab and placed a 20dB attenuator in the path of the  X-ARM PZT signal readout to carry out the stable measurements.

The units of the TF of these measurements are not calibrated and are in count/count. I will have to calibrate the units by measuring the PZT count by changing the cavity length so that I can get a standard conversion into Hz/count. I will elog the calibrated TFs in my next elog after I take the cavity length and PZT TFs.

The attached are the bode plots for both the X-ARM and Y-ARM thermal actuators(non-calibrated). I will work on finding the poles and zeroes of this system once I finish calibration of the TF measurements.

 Purpose

We're putting together a box to go into the 1X2 rack, to facilitate the frequency counters, and Raspberry Pi that will be used in FOL.

Separately, I am working on characterizing the Polarization Extinction Ratio of the PM980 fibers, for further use in FOL.

What's Been Done

The frequency counters have been mounted on the face of the box, and nylon spacers installed in the bottom, which will insulate the RPi in the future, once it's finally installed.

In regard to the PER setup, there is an issue, in that the mounts which hold the collimators rotate, so as to align the axes of the fibers with the polarization of the incoming light.

This rotational degree of freedom, however, isn't "sticky" enough, and rotates under the influence of the stress in the fiber. (It's not much, but enough.)

This causes wild fluctuations in coupled power, making it impossible to make accurate measurements of PER.

What's Next

In the FOL box's case, we've ordered a longer power cable for the raspberry pi (the current one is ~9 inches long).

Once it arrives, we will install the RPi, and move the box into its place in the rack.

In the case of the PER measurement, we've ordered more collimator mounts//adapters, which will hopefully give better control over rotation.

 I succeeded in creating a new channel access server hosted on domenica ( R Pi) for continuous data acquisition from the FC into  accessible channels. For this I have written a ctypes interface between EPICS and the C interface code to write data into the channels. The channels which I created are:

C1:ALS-X-BEAT-NOTE-FREQ

C1:ALS-Y-BEAT-NOTE-FREQ

The scripts I have written for this can be found in:

db script in:     /users/akhil/fcreadoutIoc/fcreadoutApp/Db/fcreadout.db

 Python code:  /users/akhil/fcreadoutIoc/pycall

C code:          /users/akhil/fcreadoutIoc/FCinterfaceCcode.c

I will give the standard channel names(similar to the names on the channel root)once the testing is completed and confirm that data from FC is consistent with the C code readout. Once ready I will run the code forever so that both the server and data acquisition are in process always.

Yesterday, when I set out to test the channel, I faced few serious issues in booting the raspberry pi. However, I have backed up the files on the Pi and will try to debug the issue very soon( I will test with Eric Q's R Pi).

To run these codes one must be root ( sudo python pycall, sudo ./FCinterfaceCcode)  because the HID- devices can be written to only by the root(should look into solving this issue). 

Instructions for Installation of EPICS, and how to create channel server on Pi will be described in detail in 40m Wiki ( FOLL page).

Koji said that the method we used for X-arm thermal actuator TF measurement was not correct and suggested us to make measurements separately for high and low frequencies( ensuring coherence at those frequencies is high).

(Edit by KA: The previous measurements for X/Y arm thermal actuators were done with each arm individually locked. This imposes the MC stability to the arm motion. The MC stability is worse than the arm stability due to shorter length and more number of the mirrors. Thus the arm motions were actually amplified rather than stabilized. The correct configuration was to stabilize MC using the other arm and control the measurement arm with the arm cavity length.)

So I and Eric Q took some improved TF measurements last night for the X-arm. The input excitation and the filters used were similar to that of the previous measurement . The attached are the TF plots showing two different frequency measurements.The data was saved and will be used to generate a complete TF. The attached (TFX_new.pdf)shows the independent TF measurement for X-arm temperature actuator. The black legend shows the TF at high frequencies(>1 Hz) and the red at low frequencies(<1 Hz). The final TF plots( from the data) will be posted in my next elog. 

We also made the measurements needed for calibration of these actuator Transfer functions. For this we gave some excitation for the arm length( separately for X arm and Y arm) and measured the PZT response. I will eLog with the details of the measurement and results shortly.

controls@rossa|~ 2> ls /users/akhil/fcreadoutIoc
ls: cannot access /users/akhil/fcreadoutIoc: No such file or directory
controls@rossa|~ 2> 

This code should be in the 40m SVN somewhere, not just stored on the RPi.

I'm still confused why python is in the mix here at all.  It doesn't make any sense at all that a C program (EPICS IOC) would be calling out to a python program (pycall) that then calls out to a C program (FCinterfaceCcode).  That's bad programming.  Streamline the program and get rid of python.

You also definitely need to fix whatever the issue is that requires running the program as root.  We can't have programs like this run as root.

controls@rossa|~ 2> ls /users/akhil/fcreadoutIoc
ls: cannot access /users/akhil/fcreadoutIoc: No such file or directory
controls@rossa|~ 2> 

 I tried making these changes but there was a problem with R pi boot again.I now know how to bypass the python code using IOC.I will make these changes once the problem with the Pi is fixed.

The NDS2 server on megatron was unresponsive for what i think was the last couple of days.

The NDS the log file (~nds2mgr/logs/nds2-201407151045.log) started reporting "Stage: parser output queue is full." at 2014.7.24 14:47:54 also there are 16 connections still not closed with LindmeierLaptop.cacr.caltech.edu (131.215.146.102) with 15 of them in CLOSE_WAIT. 

To identify these zombie sockets we use "netstat -an | grep 31200"

The server was in a condition that /etc/init.d/nds2 stop didn't work and the process had to be manually kill -9'ed and then about 3 or 4 minutes later the zombie sockets were gone at /etc/init.d/nds2 start was used to restart the server.

The LindemejerLaptop was using pynds to get a bunch of channels at once to test drive a streaming visualization code for glitches.  It's unclear whether this bumped into a server limitation.  We have seen similar states in ldvw that seem to be the result of errors which result in client-server connections not being closed properly, leaving data in an output buffer causing Linux to wait for the other side to empty the buffer.

 I used vector fitting to fit the transfer functions between RF input and PD RF MON of demodulator boards. These fittings can certainly do a lot better on LISO, but for the time being I will assume these to be good enough and change the main PDFR scripts to calibrate out this factor and get a decent reading of PD transimpedance. Then it will just be a matter of changing the transfer function parameters. A lot of work needs to be done on the PDFR interface and plot features.

Attached: The plots showing data and fits.

 To calibrate the measured TFs and characterize the thermal actuator for the FOL loop, we [ Me, Eric Q, Koji ] made the TF measurements of PZT response by giving a  disturbance to the position of  each of X and Y arm ETM  and ITM.

In order to make reasonable conclusions, the measurements were done at frequencies greater than 20 Hz (assuming the PZT response to be flat till a few KHz), which is out of the  bandwidth of the control loops operating for other noises at low frequencies, so that we can get the response only( mainly) due to the disturbance of the masses. 

 For this measurement , a Sine sweep excitation was given as an input to one of the test mass and PZT actuation signal was monitored. The channels used for the measurement are: 

Input( Mirror displacement):

ITMX- C1:SUS-ITMX_LSC_EXC

ETMX- C1:SUS-ETMX_LSC_EXC

ITMY- C1:SUS-ITMY_LSC_EXC

ETMY- C1:SUS-ITMX_LSC_EXC

Output ( PZT Response):

C1:ALS-Y_SLOW_SERV_IN1

The units of the TF of these measurements are not calibrated  and are in count/count. For this I will use the ITMX and ITMY calibration values from Izumi's Elog. I will also make some calculations and post in the calibrations of ETMX and ETMY in a separate elog.

I am now estimating the calibrated Thermal Actuator TF and will estimate the location of poles and zeroes to build the PID loop. I will elog the final calibrated TFs in my next elog.

The attached are the Bode Plots  for ETM and ITM for X and Y arms.

 Purpose

We want a measurement of the fiber modes at either end, with the collimators, because these will be the modes that we'll be trying to match in order to couple light into the fibers, for FOL and/or future projects.

Measurement

In order to measure these modes, I used the beam profiler (Thorlabs BP 209-VIS) to take measurements of the beam diameter (cut off at 13.5% of the amplitude) along the optical axis, for each of the fiber ends.

The ends are arbitrarily labelled End 1 and End 2.

For each measurement, the fibers were coupled to roughly 30%, or 25mW at the output.

Regarding the issue of free rotation in the collimator stages: while End 1 was relatively stable, End 2 tended to move away from its optimal coupling position. In order to correct for this, I chose a position where coupling was good, and repositioned the stage to that coordinate (124 degrees) before taking each measurement.

The data were then entered into A La Mode, which gave waist measurements as follows:

End 1--- X Waist: 197um at Z = 4.8mm       Y Waist: 190um at Z = 13.6mm

End 2--- X Waist: 192um at Z = 7.4mm       Y Waist: 190um at Z = 6.0mm

A La Mode code is attached in .zip file

Moving Forward

These are the types of profiles that we will hopefully be matching the PSL and AUX lasers to, for use in frequency offset locking.

More characterization of the fibers is to follow, including Polarization Extinction Ratio.

We also hope to be testing the overall setup soon.

 [Akhil, Harry]

Work Completed :

 Frequency Counter:

• Interfacing with the Raspberry Pi

• Characterization of the FC:          

                                   - Transfer Function 

                                   - Quantization Noise Estimation

Temperature Actuator:

• Measurement of the Transfer Function

EPICS and Channel Readout:

•  Creating a new Channel Access Server(SoftIOC)
•   Piping data from FC into created channels.              

Frequency Offset Locking(FOL) Box Design and Plan:

• Planning and selection of place for installation.
• Preparation of the box and routing cables.

Work Plan for Upcoming Weeks:

• Calibration of the Thermal Actuator TF and PID loop design.
• Channel Testing after installation of the FOL box inside the 40m.
• Optics:
  • Measure beam profiles of AUX lasers and PSL.
  • Design coupling telescope, given space constraints at end tables
  • Couple lasers into fibers
  • Connect fibers from lasers to fiber coupled Beam Combiner and Photodiode.
• Testing of FOL loop after installation of the complete system.

ETMX sus damping restored

The MC openloop gains were measured with several conditions
- MC fast/PC crossover was measured to be ~30kHz.
- No feature found in the fast path above 10kHz.

=====

I have been making a circuit to test the crossover between the PZT and PC paths.
This was supposed to allow us to inject a test signal as well as the 5V necessary to offset the voltage for the HV amp.
So far this attempt was not successful although the circuit TF looked just fine. I was wondering what was wrong.

I now suspect that the noise of the circuit was too big. It has ~65nV/rtHz noise level. This corresponds to the external
disturbance of 1~2Hz/rtHz. This is ~10 times larger noise level than the freerun frequency noise.

In the control band the circuit noise is suppressed (cancelled) by the feedback loop.
This is OK when the loop is dominated by the PZT loop. However, if the loop is dominated by the PC path,
the PC path has to work for this compensation.

So what I should do is to remove the low pass filter in the FSS and move it to the downstream of the HV amp.
This way we may be able to reduce the PC path actuation as the noise of the HV amp is also reduced by the LPF.

=====

For the meantime, I used another approach to characterize the MC crossover. I could manage to lock the MC without the PC path.
The openloop was measured with and without the PC path in this low gain setup. In fact the loop was oscillating at 6kHz
due to the low phase margin. Nevertherless, this comparison can let us find where the crossover. The loop gain was also
measured with the nominal condition.

<<Measuerement condition>>

No PC
MC IN1 Gain: +19dB
VCO Gain: +3dB
Boosts: No boost / No super boost
FSS Common Gain: +13dB
Fast Path Gain: +21.5dB
The PC path disconnected.
(Note that the loop was almost oscillating and the apparent gain may look lower than it should have been)

WIth PC
MC IN1 Gain: +19dB
VCO Gain: +3dB
Boosts: No boost / No super boost
FSS Common Gain: +13dB
Fast Path Gain: +21.5dB
The PC path connected.

Nominal
MC IN1 Gain: +19dB
VCO Gain: +15dB
Boosts: Boost On / Super boost 2
FSS Common Gain: +13dB
Fast Path Gain: +21.5dB
The PC path connected.

The ultimate goal of characterizing the temperature actuator turned to be fruitful in obtaining the calibration values for ETMX and ETMY (Calibration of ITMs were done previously  here but not for ETM). In this process, I measured the PZT response by  displacing one of the test masses in the frequency range of 20 Hz and 900 Hz  and measured the transfer functions in counts/counts. 

ETMX = [12.27  x 10 ^-9/ f² ] m/count

ETMY = [14.17  x 10 ^-9/ f²] m/count

I calculated these calibration values from the measurements that we have taken( in detail : elog)  and did the following calculations: 

The measurements I made were :PZT count/ Actuator Count separately for all the test masses.

PZT count/ Actuator count = [PZT count/ arm cavity displacement(m) ]*[ displacement of a test mass(m) / Actuator Count]

For a same laser and assuming flat response of the PZT, the term [PZT count/ arm cavity displacement(m) ] remains for all the test masses.

The fitting was done on the gain plots of the PZT Response vs Test mass displacement and a function G * f ^-2 was fitted. The resulting G values were:

ETMX: 8.007* f ^-2 

ITMX: 3.067* f ^-2

ETMY :11.389* f ^-2

ITMY : 3.745* f ^-2

To calculate the calibration of ETMX:

 [PZT count/ Actuator count : ETMX ] / [ displacement of a test mass(m) / Actuator Count :ETMX] =  [PZT count/ Actuator count : ITMX ] / [ displacement of a test mass(m) / Actuator Count :ITMX]

putting the values from the above fitting and Kiwamu's elog,

the calibrated value was calculated to be [12.27 * 10^-9 /f^-2 ]m/count.

A similar calculation was done for ETMY.

The attached are the fitting plots for the measurements taken.

 Now using these and the previously measured calibrations, I will get the complete calibrated TF of the thermal actuator.

//edit Manasa//  Harry will update this elog with before/after pictures of the table and power of the 1064nm rejected beam from the SHG.
While making these measurements, I reduced the Y end laser power (decreasing the current) so that we could use the beam profiler without burning anything and then brought it back up to the nominal power after the measurements were done.

Purpose

We wanted to take measurements of "waists" of the PSL and AUX (Y-Arm) so I can then design a telescope to couple both into fibers for use in FOL.

Measurements

For both lasers, PSL and AUX, I measured the profile of the dumped red (1064nm) beams coming out of the second harmonic generators, as this is the light that we will be using in FOL.

The power in the beam I measured from the PSL was 87.5 mW, and the power in the measured beam at the end table was 96 mW (when reduced from nominal power).

I used the beam profiler to take measurements of spot size at multiple points along the optical axis of both lasers.

An issue with these measurements was space constraints. In other words, there was no room on either table for a translation stage to hold the Profiler. I used a tape measure to determine Z-Coordinates. However, especially in the case of the AUX laser, parallax error caused uncertainty in my position measurements, which I would estimate at plus and minus 1.5cm.

I then fit these data using ALM to determine waist size and location for use in telescope design.

Z = 0 in the PSL graph is the face of the first mirror in the beam path, and in the AUX graph Z = 0 is the face of the SHG.

My measurement of the PSL gave:

X Waist = 43um at z = 6.8mm, as measured from the face of the SHG.

Y Waist = 44um at z = 6.8mm, as measured from the face of the SHG.

AUX Measurements gave:

X Waist = 44um at z = -3.1mm from the SHG face

Y Waist = 36um at z = -3.6mm from the SHG face

Find attached alm files in .zip

Movement on the Tables

In order to facilitate the measurements, we needed to move some things around, as pictured below.

On the PSL table, we installed a steering mirror after the Green filtering mirror, which is immediately after the SHG output, in addition to appropriate beam dumps.

before       after   

At the end table, we removed some unused optics, as well as a PD, which were in the way . //edit// manasa: We removed IPANG (which has no light on it) and the associated steering optics.

before      after   

Moving Forward

Either tonight or tomorrow morning, I will use these data to design coupling telescopes for the PSL and AUX light.

Tomorrow, I will couple both lasers to fibers, and hopefully finish assembling the optics for FOL

The PDFR system's interface and scripts have been updated to include quite a few more features.

On the interface side, there are buttons to open the previous plot for each PD and also a single button to run the scans on all PDs sequentially. The previous plot buttons actually open a softlink that is updated each time a measurement is taken.

Running a scan now pops up a terminal window to show messages that help understand whats going on.

In the background, the script now takes in the transfer function of the demodulator board in ZPK format and calibrates it out of each measurement. The parameters are given .dat files making it easier to replace the transfer function. (Remember my last elog which showed that the fitting of transfer functions were not really great and that I am going to use it anyway to get the script updated.)  Also, the script now takes the delay in the RF cables and calibrates out that as well. So we no longer have the huge phase variations and the phase related to transimpedance are visible.

A test run was conducted today. Plots attached.

NOTE: The test can be conducted only on REFL 11,33,55,165 , AS55, and POX11.

POY11 has an optical fiber routed from this system, but there is no space to actually illuminate this PD. So it is currently not included in our system, even though there is a button for this.

POP22 has a fiber illuminating it, but its a unknown broadband PD. I do not know it's DC transimpedance or other values. Its just of matter of updating a few files that feed it's parameters into PDFR.

However, for the above PDs, the demodulator boards have been fit to a transfer function and the script is ready to go as soon as the above problems are fixed.

Conclusion: The plots look noisy. But, the transimpedance now resembles the one on 40-m wiki for all the PDs, both the shape and values.

There will be some errors that are induced because of improper demodulator TF fitting. This has to be taken care of eventually.

Work remaining: Create a canonical set of plots for each PD and set them as the baseline. These canonical plots will be plotted along with each measurement for easy comparison.

A well documented manual for the whole system clearly explaining where and how it takes all the parameters into account so that anybody can easy update just the essential information.

 The Past Week

In the past week, I have improved the coupling in the fiber testing setup on the SP table to up to ~45%

I also measured the input/output modes of the fiber with collimators.

Manasa, Q and I have designed, and redesigned a setup to measure Polarization Extinction Ratio introduced by fibers.

I have also partially assembled the box that will hold the frequency counters and RPi for FOL.

Today (Tuesday) I measured waists of PSL and AUX, at dumped light from the SHG's for use in designing coupling telescopes for FOL.

Next Week

In the next week, I will design and couple light from PSL and AUX (Y arm) into fibers for use in testing FOL.

Once that's done, I will continue testing fiber characteristics, starting with Polarization Extinction Ratio.

Items Needed

Power cord for Raspberry Pi (ordered)

AD9.5F collimator adapter (ordered)

 Xarm Green Steering Mirror Upgrade

Nick and I did the upgrade for the green steering mirror today. We locked in the TEM00 mode.
We placed the shutter and everything. We move the OL, but we placed it back. Tonight, I'll be doing a more complete elog with more details.

That was super fast! Great job, Andres and Nic!

A heads up to anyone using SVN with computers on the Martian network:

When we moved the svn repository on nodus to /export, we set it up such that the internet-facing svn URL was unchanged. However, it turns out that the martian network machines (i.e. Stuff mounted on the NFS share) were still pointing to the old svn files in /cvs/cds/caltech/svn, and thus not seeing new revisions made in /export/home/svn. If your martian network svn'd files got weird, this is why. 

I'm relocating the root svn URLs on the martian machines' checkouts to point to the nodus https address as I find them, to make them robust against future local movement of the svn files. 

Peoples' user files should be fine, this looks like it'll only really affect things such as scripts and medm screens, etc. 

I used an oscillator and an oscilloscope to measure the open loop transfer function at higher frequency than 100kHz.
(I remember that I tried to use Agilent 4375A for this and failed before ... due to low input impedance???)\

Here is the update. It seems that the gain margin is not so large. We should apply low pass to prevent too large servo bump.

From old 40m elog 5-29-2007

Hello Steve, 

I’ve received some fan pictures from our manufacturing center. Your system will have one of the two fans pictured. Please contact manufacture company   for more information.

http://www.sunon.com/index.php

Best Regards,

Agustin (TJ) Tijerina

Commercial Product Support Center

Coherent, Inc.

5100 Patrick Henry Dr., Santa Clara, Ca. 95054

Product Support: (800) 367-7890

product.support@coherent.com

www.coherent.com

 Finally we got it!

The fans are ordered.