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ID Date Author Type Categoryup Subject
  4873   Thu Jun 23 23:54:29 2011 KojiOmnistructureEnvironmentWe are saved

Sonali, Ishwita, and another anonymous SURF saved the long-lasted water shortage of the 40m

  5451   Sun Sep 18 16:42:00 2011 KojiBureaucracyEnvironmentClean up your mess

Mess in the lab is increasing. Kiwamu and I had to clean up some stuffs to continue our work.
(i.e. some components were disturbing to open the lid of the tables.)

Basically the tools/equipments/component/cables/digital cameras/lens caps/IR viewers
you have used for the day should be cleaned up at the end of the day.

If one likes to leave a temporary stuff, leave a note to indicate by whom, for what, how long
it will be kept like that, and when one is going to back there with contact info like the cell phone #.

  5650   Tue Oct 11 15:19:17 2011 ranaHowToEnvironment40m map

The Kinemetrics dudes are going to visit us @ 1:45 tomorrow (Wednesday) to check out our stacks, seismos, etc.

40mLabMap.png40mLabMap.jpg

I put these maps here on the elog since people are always getting lost trying to find the lab.

  5651   Tue Oct 11 17:32:05 2011 jamieHowToEnvironment40m google maps link

Here's another useful link:

http://maps.google.com/maps?q=34.13928,-118.123756

  5924   Thu Nov 17 11:51:14 2011 JenneUpdateEnvironmentIncandescent vs. fluorescent lights?

I'm just on an elog roll this morning...

Again while poking around inside the IFO room, I noticed that they have replaced all of our incandescent lights with CFLs.  Do we care?  The point of having the incandescent lights on a separate switch from the big fluorescent lights was so that we could have only 60Hz lines, not wide-band noise if we want the lights on while locking. 

I'm not sure that we actually care, because more often we just turn off all the lights while trying to do serious locking, but if we do care, then someone needs to ask the custodial staff (or someone else?) to undo the change.

  5988   Wed Nov 23 14:47:14 2011 JenneConfigurationEnvironmentAC in the IFO room was off

I turned it back on, maybe around 11am?  Definitely a little while before the 12:30 meeting.

EDIT by KI:

 Sorry, it's me. I was checking if AC was doing something bad on the ALS noise.

  6081   Wed Dec 7 09:56:14 2011 rana imitation of steveOmnistructureEnvironmentTelephone Map

 This is the fone storree 

we should turn off 3977,3979 and 2351 has no function

 

Edit, JD:  x8925 is at the Visitor desk, and isn't on the map.

  6383   Wed Mar 7 23:28:41 2012 Lab Cleanup CrewHowToEnvironmentTrue Beauty....

Or, how a lab should look at the end of every day.

Clean_40m_Electronics_Bench.jpg

Beat that, Bridge kids!

  6497   Fri Apr 6 16:22:15 2012 DenUpdateEnvironmentseism box

I've changed R2 resistor in the seism box for the VERT 1 channel from 464 Ohm to 1051 Ohm to reduce the gain of this channel by a factor of 2. This should help the GUR1Z signal not to be corrupted inside the AA box, so we can use it in the adaptive filtering.

  6511   Mon Apr 9 17:03:38 2012 DenUpdateEnvironmentLms vs Wiener

I tried to figure out why offline LMS filter subtract seismic noise much better from MC_F then the Wiener filter. I did the calculations twice - with my codes and with Matlab in-build functions, the results are the same. So this is not a code error.

The coherence between GUR 1, 2 and MC_F is still poor. Wiener filter is linear and its performance is confined to the frequency ranges where we see coherence. Lms filter is non-linear and it may be possible to subtract the noise even if non-linear effects are present in the system.

gur12_mcl.png

I've checked seismometer readout box again. I've soldered 50 Ohms to plus and minus inputs to VERT 1,2 N/S 1,2, E/W 1,2 - GUR 1 and 2 use these channels. Then I put the box back and connected it to the ADC.

seismboxnoise.png

The plot shows that the readout box noise is below the ADC noise. It is possible that amplifiers introduce non-linear effects. To check this I plotted the coherence between OSEM sensors and GUR1X signal:

gur1_osem.png

The coherence between OSEM sensors and GUR1X is pretty good, so may be witness path is not responsible for low coherence at 0.1 - 0.5 Hz between MC_F and GUR 1,2. IT seems that MC_F is bad at low frequencies. I terminated the input to the Channel 1 of the Pentek Generic board, where MC_F is plugged in.

mcl_noise.jpg

ADC is also good. Something else is wrong.

  6515   Tue Apr 10 13:42:54 2012 JenneUpdateEnvironmentPlumbing guys are here

I don't know why, but they're looking around on the roof, and inside our ceiling above the bathrooms.

  6519   Wed Apr 11 14:34:48 2012 JenneUpdateEnvironmentPlumbing guys are here

Quote:

I don't know why, but they're looking around on the roof, and inside our ceiling above the bathrooms.

 Bob tells me that the carpenter is going to move the nitrogen bottles to the other side of the outside door, so that the plumbers can install a safety shower / eyewash right outside our door.

Also, the carpenter just mounted a new glass door cabinet from Bob's lab in the IFO room, so we have some new storage space.

  6523   Wed Apr 11 22:48:39 2012 ranaUpdateEnvironmentBLRMS

seis_blrms.png

  6524   Thu Apr 12 00:16:38 2012 JenneUpdateEnvironmentEarthquake - moderate

 


M4.7 - Santa Isabel, Mexico 2012-04-12 06:48:38 UTC

Mode Cleaner doesn't want to stay locked.  Seismic is coming down from an earthquake ~20min ago.  

We're in the process of measuring IPPOS, so this is obnoxious.

EDIT:  Followed by a 6.2 and a 7.1 at 07:06UTC and 07:15UTC in the same area.

We're following the tried and true tradition of going home when there's an earthquake big enough that the MC won't stay locked.

Several optics have rung up, PRM is the only one which has tripped so far, because the side sensor has the extra gain, but the watchdog threshold is set for the face OSEMs.

  6792   Mon Jun 11 16:08:58 2012 JenneUpdateEnvironmentRattling in the HEPA

There is an intermittent rattling sound coming from the HEPA in the NE corner of the PSL table (right above the PMC, all of our input optics).

Steve says it might be a bad bearing, but he'll check it out in the morning and get it fixed.

  6793   Mon Jun 11 21:35:55 2012 JenneUpdateEnvironmentRattling in the HEPA

Quote:

There is an intermittent rattling sound coming from the HEPA in the NE corner of the PSL table (right above the PMC, all of our input optics).

Steve says it might be a bad bearing, but he'll check it out in the morning and get it fixed.

 MC was having a hard time staying locked, with no discernable reason from the control room (i.e. no big seismic, no PMC PZT railing).    The HEPA was on 100%, so I turned it down to 50% to hopefully reduce the rattling, if that was what was wrong. 

  6975   Fri Jul 13 19:48:56 2012 JenneUpdateEnvironmentRocks - very loud

I assume it's the rock tumbler, although it could be something else, but the MC has had trouble staying locked yesterday and today (yesterday Yaakov and I went over there and they were doing stuff almost constantly - it's super loud over there), and today even the PMC has fallen out of lock twice.  I just relocked it again, since it went out of lock just after Journal club started.

Anyhow, I think this will be good data for Masha, and then also for the Masha+Yaakov triangulation project.

  7110   Tue Aug 7 23:30:58 2012 ranaUpdateEnvironmentNearby EQ

 Just felt an EQ. Impulse moved some vertical blinds by several mm.

Tue Aug 07 23:26:06 2012 

  7111   Tue Aug 7 23:33:34 2012 DenUpdateEnvironmentNearby EQ

Quote:

 Just felt an EQ. Impulse moved some vertical blinds by several mm.

Tue Aug 07 23:26:06 2012 

 All optics except MC2 and ETMX are crazy

watchdogs.png      mc1.png    gur.png

  7113   Wed Aug 8 09:46:29 2012 MashaUpdateEnvironmentETMX EQ

[Sasha, Masha, Liz, Eric]

 

A bunch of surfs in the lab just noticed that ETMX is going crazy (laser is shifting everywhere) due to a 4.5 EQ that just hit LA. The optic is already shut down according to the watchdogs.

  7114   Wed Aug 8 10:15:13 2012 jamieUpdateEnvironmentAnother earthquake, optics damped

There were another couple of earthquakes at about 9:30am and 9:50am local.

earthquake.png

All but MC2 were off the watchdogs.  I damped and realigned everything and everything looks ok now.

Screenshot-Untitled_Window.png

  7866   Thu Dec 20 19:46:20 2012 ranaConfigurationEnvironmentControl Room Projector

 Needs

StevePurple.JPG

  8268   Mon Mar 11 14:10:05 2013 JenneUpdateEnvironmentMC suspensions moved by this morning's earthquakes

None of the suspensions All suspensions were tripped (edited by Manasa; see elog 8271) by this morning's earthquakes, but the MC suspensions are in a different place than they were a day ago.  The big symptom here is that the MCWFS are pulling the mode cleaner slightly out of alignment.  When it first locks, the reflected light is ~0.5, but when the WFS are engaged it goes up to ~0.8.  I'm going to put the MC optics back where they were (according to SUSpit and SUSyaw), and tweak up the MC from there. Probably other optics are affected, but I was going to work on continuing to center the beam on the Yarm optics, so I'll deal with the rest of the IFO in a minute.

Note re: lower plot - the mxstream was down on c1sus and c1ioo, so no fast channels on those computers were recorded for almost a day.  (The plot is one day 4 days long).  I was going to plot the seismic blrms along with the suspension pointing values, but there's no data saved, so there's no point.  Jamie tells me he thinks this spontaneous loss of the mxstream is fixed in the next RCG upgrade, and that we can talk about upgrading the RCG after the LSC meeting, so this data loss is no longer an issue.

EQ.png

MC-SUS-kicked-EQ.png

EDIT:  Plot with 4 days of trend, rather than just 1.  The MC alignment (as measured by MC refl) has been very bad for several days.  I'm going to move the suspensions back to their last good place.  Also, Manasa realigned the MC after the EQ, so I don't actually know where the suspensions got kicked to this morning.

  8271   Mon Mar 11 17:18:00 2013 ManasaUpdateEnvironmentEarthquake: Suspensions tripped and MC realigned

I found all suspensions including the MC suspensions tripped this morning after the earthquake.

I damped all the optics and realigned MC mirrors to lock at refl 0.57.

PRM and SRM tripped a couple of times due to the aftershocks that followed; but were damped eventually.

  12828   Tue Feb 14 10:43:06 2017 gautamBureaucracyEquipment loanEquipment to Cryo Lab

PZT Buzzer Box (Thorlabs HV Supply + Manual + 2*PZT Buzzers) ---> Cryo Lab (Brittany + Aaron)

  13324   Wed Sep 20 16:14:17 2017 gautamUpdateEquipment loanImpedance test kit borrowed from Downs

I borrowed the HP impedance test kit from Rich Abbott today. The purpose is to profile the impedance of the NPRO PZTs, as part of the AUX PDH servo investigations. It is presently at the X-end. I will do the test in the coming days.
 

  14170   Mon Aug 20 14:04:53 2018 johannesBureaucracyEquipment loanTwo C30642G PDs removed

EDIT: After discussing with Koji and checking the existing M2ISS PDs I put the two C30642G back and took two C30665GH (active diameter: 3mm) diodes. Only one of this type remains in storage.

I removed two C30642G photodiodes from the stash for the new M2ISS hardware and updated the wiki page accordingly.

  14174   Tue Aug 21 17:32:51 2018 awadeBureaucracyEquipment loanOne P-810.10 Piezo Actuators element removed

I've taken a PI Piezo Actuator (P-810.10) from the 40m collection. I forgot to note it on the equipment checklist by the door, will do so when I next drop by.

  14565   Wed Apr 24 11:22:59 2019 awadeBureaucracyEquipment loanBorrowed Zurich HF2LI Lock in Amplifer to QIL

Borrowed Zurich HF2LI Lock in Amplifer to QIL lab Wed Apr 24 11:25:11 2019.

  14616   Fri May 17 10:12:07 2019 AnjaliSummaryEquipment loanBorrowed component

I borrowed one Marconi (2023 B) from 40 m lab to QIL lab.

  14618   Fri May 17 16:07:25 2019 gautamSummaryEquipment loanBorrowed component

ZHL-3A (2 units) —-> QIL

Quote:

I borrowed one Marconi (2023 B) from 40 m lab to QIL lab.

  14753   Thu Jul 11 17:58:38 2019 gautamUpdateEquipment loanTT suspension --> Downs

Arnaud has taken 1 TT suspension from the 40m clean lab to Downs for modal testing. Estimated time of return is tomorrow evening.

  14822   Thu Aug 1 13:55:34 2019 DuoBureaucracyEquipment loanGpib module taken to QIL lab

vanna --> QIL.

gautam 20190804: The GPIB module + power supply were returned to me by Duo ~5pm today at the 40m.

  15529   Mon Aug 17 15:18:26 2020 gautamUpdateEquipment loanBeam Profiler + peripherals --> 40m

Gabriele left the DataRay beam profiler + peripherals (see Attachment #1) in his office. I picked them up just now and brought them over to the 40m.

  15561   Sun Sep 6 14:17:18 2020 JonUpdateEquipment loanZurich Instruments analyzer

On Friday, I grabbed the Zurich Instruments HF2LI lock-in amplifier and brought it home. As time permits, I will work towards developing a similar readout script as we have for the SR785.

  15678   Mon Nov 16 16:00:19 2020 gautamUpdateEquipment loanLB1005-->Cryo lab

Shruti picked it up @4pm.

  15728   Thu Dec 10 16:24:13 2020 gautamUpdateEquipment loanNoliac PZT --> Paco

I gave one Noliac PZT from the two spare in the metal PMC kit to Paco. There is one spare left in the kit.

  15879   Mon Mar 8 12:54:54 2021 gautamUpdateEquipment loan40m-->Cryo
  1. Busby box
  2. SR554 transformer preamplifier
  16176   Wed Jun 2 17:50:50 2021 PacoUpdateEquipment loanBorrow red cart

I borrowed the little red cart 🛒 to help clear the path for new optical tables in B252 West Bridge. Will return once I am done with it.  

  16180   Thu Jun 3 17:49:46 2021 PacoUpdateEquipment loanBorrow red cart

Returned today.

Quote:

I borrowed the little red cart 🛒 to help clear the path for new optical tables in B252 West Bridge. Will return once I am done with it.  

 

  16226   Fri Jun 25 19:14:45 2021 JonUpdateEquipment loanZurich Instruments analyzer

I returned the Zurich Instruments analyzer I borrowed some time ago to test out at home. It is sitting on first table across from Steve's old desk.

  14518   Fri Apr 5 11:40:57 2019 AnjaliUpdateFrequency noise measurementFrequency noise measurement of 1 micron source
  • Attachment #1 shows the present experimental setup. The photodiode is now replaced with PDA255. The farther end of the fiber (output of the delayed arm) is coupled through a collimator and aligned such that the beam from the delayed path fall on the detector along with the undelayed path of MZI. We tried to measure the frequency noise of the laser with this setup, but we didn’t get anything sensible.
  • One of the main draw backs of the measurement was the polarisation was not aligned properly in the setup. So, then the next step was to identify the polarisation at different locations in the beam path and to maximise the polarisation to either S or P component.

  • So, we introduced HWP at the input beam path after isolator as shown in attachment #1. Also, the polarisation was tested at positions P1, P2, P3, and P4 shown in attachment #1 by placing a polarisation beam splitter at these locations and then by observing the transmitted (P component) and reflected light (S component) using power meter.

  • The observations at different locations are as the follows

Position Input power (mW) P component (mW) S component (mW)
P1 279 145 123
P2 255 113 137
P3 129 67 58
P4 124 66 53

 

  • These observations show that the P and S components are almost equal, and this is not a good polarisation arrangement. At this point, we also had to check whether the incoming beam is linearly polarised or not.

  • To test the same, the PBS was placed at position P1 and the P and S components were observed with power meter as the HWP is rotated.Attachment # 2 shows the results of the same, that is the variation in P and S component as the HWP is rotated.

  • This result clearly shows that the input beam is linearly polarised. The HWP was then adjusted such that the P component is maximum and coupled to the MZI. With this orientation of HWP, the polarisation observed at different positions P1, P2, P3, and P4 are as follows.

Position Input (mW) P component (mW) S component (mW)
P1 283 276 5
P2 248 228 7
P3 126 121 2
P4 128 117 1
  • This shows that the polarisation is linearly polarised as well as it is oriented along the P direction (parallel to the optical table).

  • We have the polarisation maintaining fiber (PM 980) as the delay fiber. The polarisation of the light as it propagates through a PM fiber depends on how well the input beam is coupled to the axis (slow or fast) of the fiber. So, the next task was to couple the light to one of the axes of the fiber.

  • The alignment key on the fiber is a good indication of the axis of the fiber. In our case, the alignment key lines up with the slow axis of the fiber. We decided to couple the light to the fast axis of the fiber. Since the incoming beam is P polarised, the output fiber coupler was  aligned such that the fast axis is parallel to optical table as possible.

  • A PBS was then introduced after the fiber output collimator . There is a HWP (marked as HWP2 in attachment 1) in front of the input coupler of the fiber as well. This HWP was then rotated and observed the P and S component from the PBS that is now placed after the output coupler with a power meter.The idea was , when the light is coupled to the fast axis of the fiber, we will see the maximum at the P componet at the output

  • Attachment # 3 shows the observation. 

  • In this way I tried to find the orientation of the HWP2 such that the P component is maximum at the output. But I was not succeeded in this method and observed that the output was fluctuating when the fiber was disturbed. One  doubt we had was whether the fiber is PM or not . Thus we checked the fiber end with fiber microscope and confirmed that it is PM fiber. 

  • Thus, we modifed the setup as shown in attachement # 4.The photodetector (PDA55) was monitoring the S component and the output of the detector was observed on an oscilloscope. We rotated the HWP2 such that the S component is almost minimum. At the same time, we were disturbing the fiber and was observing whether the output is fluctuating. The HWP2 angle was tweaked around the minimum of S component and observed the output with disturbing the fiber. This way we found the orientation of HWP2  such that the light is coupled to the fast axis of the fiber and the output was not fluctuating while we disturb the fiber. We tested it  by heating the fiber with a heat gun as well and confirmed that the output is not fluctuating and thus the light is coupled to the fast axis of the fiber.

  14520   Sat Apr 6 02:07:40 2019 AnjaliUpdateFrequency noise measurementFrequency noise measurement of 1 micron source
  • The alignment of the output beam from the delayed path of MZI to the photodetector was disturbed when we did the polarisation characterisation yesterday. So, today we tried to align the output beam from the delayed path of MZI to the detector .
  • We then observed the beat output from the detector on oscilloscope.We initialy observed a dc shift . We then applied a frequency modulation on the input laser and observed the output on oscilloscope. We expected to see variation in output frequency in accordance with variation of input frequency modulation. But we didnt observe this and we were not really getting the interference pattern. 
  • We tried to make the alignment better. With a better alignment, we could see the interference pattern. We also observed that the output frequency was varying in accordance with variation in the input frequency modulation. We would expect a better result with proper mode matching of the two beams on the photodetector.
  14529   Wed Apr 10 00:33:09 2019 AnjaliUpdateFrequency noise measurementFrequency noise measurement of 1 micron source
  • Attachement #1 shows the input (ch4-green) modulation frequency and the photodiode output (ch1-yellow) when the modulation frequency is about 100 Hz
  • Attachement #2 shows the input (ch4-green) modulation frequency and the photodiode output (ch1-yellow) when the modulation frequency is about 30 Hz
  • The output frequency is varying in accordance with variation in modulation frequency. It is observed that, for a given modulation frequency also, the output frequency is fluctuating. There could be multiple reasons for this behaviour. One of the main reasons is the frequency noise of the laser itself. Also, there could be acoustic noise coupled to the system (eg, by change in length of the fiber).
  • The experimental setup is then modified as shown in attachment #3. The thick beam spliiter is replaced with a thinner one. The mount is also changed such that the transmitted beam can be now coupled to an other photodiode (earlier  the transmitted light was blocked by the mount). One more photodiode (PDA55) is introduced .So now the two photodiodes in the setup are PDA520 and PDA 55. 
  • We then applied frequency modulation on the input laser and observed the output of the two photodiodes. But we didn't get the results as we expected and observed earlier (shown in attachment #1 &2). Looks like, the problem is poor mode matching between the two beams. 
Quote:
  • The alignment of the output beam from the delayed path of MZI to the photodetector was disturbed when we did the polarisation characterisation yesterday. So, today we tried to align the output beam from the delayed path of MZI to the detector .
  • We then observed the beat output from the detector on oscilloscope.We initialy observed a dc shift . We then applied a frequency modulation on the input laser and observed the output on oscilloscope. We expected to see variation in output frequency in accordance with variation of input frequency modulation. But we didnt observe this and we were not really getting the interference pattern. 
  • We tried to make the alignment better. With a better alignment, we could see the interference pattern. We also observed that the output frequency was varying in accordance with variation in the input frequency modulation. We would expect a better result with proper mode matching of the two beams on the photodetector.
  14540   Fri Apr 12 01:22:27 2019 AnjaliUpdateFrequency noise measurementFrequency noise measurement of 1 micron source

The alignement was disturbed after the replcement of the beam splitter. We tried to get the alignment back . But we are not succeeded yet in getting good interfernce pattern. This is mainly because of poor mode matching of two beams. We will also try with the spooled fiber.

Quote:

 

  • The experimental setup is then modified as shown in attachment #3. The thick beam spliiter is replaced with a thinner one. The mount is also changed such that the transmitted beam can be now coupled to an other photodiode (earlier  the transmitted light was blocked by the mount). One more photodiode (PDA55) is introduced .So now the two photodiodes in the setup are PDA520 and PDA 55. 
 
 
  14544   Mon Apr 15 22:39:10 2019 gautamUpdateFrequency noise measurementAlternate setup with PSL pickoff

[anjali, gautam]

just main points, anajli is going to fill out the details.

To rule out mode-matching as the reason for non-ideal output from the MZ, I suggested using the setup I have on the NW side of the PSL enclosure for the measurement. This uses two identical fiber collimators, and the distance between collimator and recombination BS is approximately the same, so the spatial modes should be pretty well matched. 

The spooled fiber we found was not suitable for use as it had a wide key connector and I couldn't find any wide-key FC/PC to narrow-key FC/APC adaptors. So we decided to give the fiber going to the Y end and back (~90m estimated length) a shot. We connected the two fibers at the EY table using a fiber mating sleeve (so the fiber usually bringing the IR pickoff from EY to the PSL table was disconnected from its collimator). 

In summary, we cannot explain why the contrast of the MZ is <5%. Spatial mode-overlap is definitely not to blame. Power asymmetry in the two arms of the MZ is one possible explanation, could also be unstable polarization, even though we think the entire fiber chain is PM. Anjali is investigating.

 


We saw today that the Thorlabs PM beam splitters (borrowed from Andrew until our AFW components arrive) do not treat the two special axes (fast and slow) of the fiber on equal footing. When we coupled light into the fast axis, we saw huge asymmetry between the two split arms of the beamsplitter (3:1 ratio in power instead of the expected 1:1 for a 50/50 BS). Looking at the patch cord with an IR viewer, we also saw light leaking through the core along it. Turns out this part is meant to be used with light coupled to the slow axis only.

  14547   Wed Apr 17 00:43:38 2019 gautamUpdateFrequency noise measurementMZ interferometer ---> DAQ
  1. Delay fiber was replaced with 5m (~30 nsec delay)
    • The fringing of the MZ was way too large even with the free running NPRO (~3 fringes / sec)
    • Since the V/Hz is proportional to the delay, I borrowed a 5m patch cable from Andrew/ATF lab, wrapped it around a spool, and hooked it up to the setup
    • Much more satisfactory fringing rate (~1 wrap every 20 sec) was observed with no control to the NPRO
  2. MZ readout PDs hooked up to ALS channels
    • To facilitate further quantitative study, I hooked up the two PDs monitoring the two ports of the MZ to the channels normally used for ALS X.
    • ZHL3-A amps inputs were disconnected and were turned off. Then cables to their outputs were highjacked to pipe the DC PD signals to the 1Y3 rack
    • Unfortunately there isn't a DQ-ed fast version of this data (would require a model restart of c1lsc which can be tricky), but we can already infer the low freq fringing rate from overnight EPICS data and also use short segments of 16k data downloaded "live" for the frequency noise measurement.
    • Channels are C1:ALS-BEATX_FINE_I_IN1 and C1:ALS-BEATX_FINE_Q_IN1 for 16k data, and C1:ALS-BEATX_FINE_I_INMON and C1:ALS-BEATX_FINE_I_INMON for 16 Hz.

At some point I'd like to reclaim this setup for ALS, but meantime, Anjali can work on characterization/noise budgeting. Since we have some CDS signals, we can even think of temperature control of the NPRO using pythonPID to keep the fringe in the linear regime for an extended period of time.

  14571   Thu Apr 25 03:32:25 2019 AnjaliUpdateFrequency noise measurementMZ interferometer ---> DAQ
  • Attachment #1 shows the time domain output from this measurement. The contrast between the maximum and minimum is better in this case compared to the previous trials.
  • We also tried to extract the frequency noise of the laser from this measurement. Attachment #2 shows the frequency noise spectrum. The experimental result is compared with the theoretical value of frequency noise. Above 10 Hz, the trend is comparable to the expected 1/f characteristics, but there are other peak also appearing. Similarly, below 10 Hz, the experimentally observed value is higher compared to the theory.
  • One of the uncertainties in this result is because of the length fluctuation of the fiber. The phase fluctuation in the system could be either because of the frequency noise of the laser or because of the length fluctuation of the fiber.  So,one of the reasons for the discrepancy between the experimental result and theory could be because of  fiber length fluctuation. Also, there were no locking method been applied to operate the MZI in the linear range.
  • The next step would be to do a heterodyne measurement. Attachment #3 shows the schematic for the heterodyne measurement. A free space AOM can be inserted in one of the arms to do the frequency shift. At the output of photodiode, a RF heterodyne method as shown in attachment #3 can be applied to separate the inphase and quadrature component. These components need to be saved with a deep memory system. Then the phase and thus the frequency noise can be extracted.
  • Attachment #4 shows the noise budget prepared for the heterodyne setup. The length of the fiber considered is 60 m and the photodiode is PDA255. I also have to add the frequency noise of the RF driver and the intensity noise of the laser in the noise budget.
Quote:
  1. Delay fiber was replaced with 5m (~30 nsec delay)
    • The fringing of the MZ was way too large even with the free running NPRO (~3 fringes / sec)
    • Since the V/Hz is proportional to the delay, I borrowed a 5m patch cable from Andrew/ATF lab, wrapped it around a spool, and hooked it up to the setup
    • Much more satisfactory fringing rate (~1 wrap every 20 sec) was observed with no control to the NPRO
  2. MZ readout PDs hooked up to ALS channels
    • To facilitate further quantitative study, I hooked up the two PDs monitoring the two ports of the MZ to the channels normally used for ALS X.
    • ZHL3-A amps inputs were disconnected and were turned off. Then cables to their outputs were highjacked to pipe the DC PD signals to the 1Y3 rack
    • Unfortunately there isn't a DQ-ed fast version of this data (would require a model restart of c1lsc which can be tricky), but we can already infer the low freq fringing rate from overnight EPICS data and also use short segments of 16k data downloaded "live" for the frequency noise measurement.
    • Channels are C1:ALS-BEATX_FINE_I_IN1 and C1:ALS-BEATX_FINE_Q_IN1 for 16k data, and C1:ALS-BEATX_FINE_I_INMON and C1:ALS-BEATX_FINE_I_INMON for 16 Hz.

At some point I'd like to reclaim this setup for ALS, but meantime, Anjali can work on characterization/noise budgeting. Since we have some CDS signals, we can even think of temperature control of the NPRO using pythonPID to keep the fringe in the linear regime for an extended period of time.

  14573   Thu Apr 25 10:25:19 2019 gautamUpdateFrequency noise measurementHomodyne v Heterodyne

If I understand correctly, the Mach-Zehnder readout port power is only a function of the differential phase accumulated between the two interfering light beams. In the homodyne setup, this phase difference can come about because of either fiber length change OR laser frequency change. We cannot directly separate the two effects. Can you help me understand what advantage, if any, the heterodyne setup offers in this regard? Or is the point of going to heterodyne mainly for the feedback control, as there is presumably some easy way to combine the I and Q outputs of the heterodyne measurement to always produce an error signal that is a linear function of the differential phase, as opposed to the sin^2 in the free-running homodyne setup? What is the scheme for doing this operation in a high bandwidth way (i.e. what is supposed to happen to the demodulated outputs in Attachment #3 of your elog)? What is the advantage of the heterodyne scheme over applying temperature feedback to the NPRO with 0.5 Hz tracking bandwidth so that we always stay in the linear regime of the homodyne readout?

Also, what is the functional form of the curve labelled "Theory" in Attachment #2? How did you convert from voltage units in Attachment #1 to frequency units in Attachment #2? Does it make sense that you're apparently measuring laser frequency noise above 10 Hz? i.e. where do the "Dark Current Noise" and "Shot Noise" traces for the experiment lie relative to the blue curve in Attachment #2? Can you point to where the data is stored, and also add a photo of the setup?

  14576   Thu Apr 25 15:47:54 2019 AnjaliUpdateFrequency noise measurementHomodyne v Heterodyne

My understanding is that the main advantage in going to the heterodyne scheme is that we can extract the frequecy noise information without worrying about locking to the linear region of MZI. Arctan of the ratio of the inphase and quadrature component will give us phase as a function of time, with a frequency offset. We need to to correct for this frequency offset. Then the frequency noise can be deduced. But still the frequency noise value extracted would have the contribution from both the frequency noise of the laser as well as from fiber length fluctuation. I have not understood the method of giving temperature feedback to the NPRO.I would like to discuss the same.

The functional form used for the curve labeled as theory is 5x104/f. The power spectral density (V2/Hz) of the the data in attachment #1 is found using the pwelch function in Matlab and square root of the same gives y axis in V/rtHz. From the experimental data, we get the value of Vmax and Vmin. To ride from Vmax to Vmin , the corrsponding phase change is pi. From this information, V/rad can be calculated. This value is then multiplied with 2*pi*time dealy to get the quantity in V/Hz. Dividing V/rtHz value with V/Hz value gives  y axis in Hz/rtHz. The calculated value of shot noise and dark current noise are way below (of the order of 10-4 Hz/rtHz) in this frequency range. 

I forgor to take the picture of the setup at that time. Now Andrew has taken the fiber beam splitter back for his experiment. Attachment #1 shows the current view of the setup. The data from the previous trial is saved in /users/anjali/MZ/MZdata_20190417.hdf5

 

Quote:

If I understand correctly, the Mach-Zehnder readout port power is only a function of the differential phase accumulated between the two interfering light beams. In the homodyne setup, this phase difference can come about because of either fiber length change OR laser frequency change. We cannot directly separate the two effects. Can you help me understand what advantage, if any, the heterodyne setup offers in this regard? Or is the point of going to heterodyne mainly for the feedback control, as there is presumably some easy way to combine the I and Q outputs of the heterodyne measurement to always produce an error signal that is a linear function of the differential phase, as opposed to the sin^2 in the free-running homodyne setup? What is the scheme for doing this operation in a high bandwidth way (i.e. what is supposed to happen to the demodulated outputs in Attachment #3 of your elog)? What is the advantage of the heterodyne scheme over applying temperature feedback to the NPRO with 0.5 Hz tracking bandwidth so that we always stay in the linear regime of the homodyne readout?

Also, what is the functional form of the curve labelled "Theory" in Attachment #2? How did you convert from voltage units in Attachment #1 to frequency units in Attachment #2? Does it make sense that you're apparently measuring laser frequency noise above 10 Hz? i.e. where do the "Dark Current Noise" and "Shot Noise" traces for the experiment lie relative to the blue curve in Attachment #2? Can you point to where the data is stored, and also add a photo of the setup?

 

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