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ID Date Author Type Category Subjectup
  15603   Tue Sep 29 17:07:25 2020 gautamUpdateGeneralLab visit for inventory location

I was in the lab from 1630-1830. I have located and visually inspected all the parts required for the magnet regluing / optic cleaning parts of the planned vent, except the fresh batches of scpectroscopic grade solvents. I was in the cleanroom part of the clean and bake lab from 1630-1700.

  1231   Fri Jan 16 11:28:54 2009 YoichiUpdateComputersLab. laptop needs wireless lan driver update
One of the lab. laptops (belladonna) cannot connect to the network now.
I guess this was caused by someone clicked the update icon and unknowingly updated the kernel, which resulted in the wireless lan driver malfunctioning.
It was using a Windows driver through ndiswrapper.
Someone has to fix it.
  14533   Thu Apr 11 01:10:05 2019 gautamUpdateALSLarge 2kHz peak (and harmonics) in ALS X

These weren't present last week. The peaks are present in the EX PDH error monitor signal, and so are presumably connected with the green locking system. My goal tonight was to see if the arm length control could be done using the ALS error signal as opposed to POX, but I was not successful.

Attachment 1: EX_PDH_2kNoise.pdf
EX_PDH_2kNoise.pdf
  14548   Wed Apr 17 00:50:17 2019 gautamUpdateALSLarge 2kHz peak (and harmonics) in ALS X no more

I looked into this issue today. Initially, my thinking was that I'd somehow caused clipping in the beampath somewhere which was causing this 2kHz excitation. However, on looking at the spectrum of the in-loop error signal today (Attachment #1), I found no evidence of the peak anymore!

Since the vacuum system is in a non-nominal state, and also because my IR ALS beat setup has been hijacked for the MZ interferometer, I don't have an ALS spectrum, but the next step is to try single arm locking using the ALS error signal. To investigate whether the 2kHz peak is a time-dependent feature, I left the EX green locked to the arm (with the SLOW temperature offloading servo ON), hopefully it stays locked overnight...

Quote:

These weren't present last week. The peaks are present in the EX PDH error monitor signal, and so are presumably connected with the green locking system. My goal tonight was to see if the arm length control could be done using the ALS error signal as opposed to POX, but I was not successful.

Attachment 1: EX_PDHnoise.pdf
EX_PDHnoise.pdf
  14549   Wed Apr 17 11:01:49 2019 gautamUpdateALSLarge 2kHz peak (and harmonics) in ALS X no more

EX green stayed locked to XARM length overnight without a problem. The spectrogram doesn't show any alarming time varying features around 2 kHz (or at any other frequency).

Attachment 1: EX_PDH_specGram.pdf
EX_PDH_specGram.pdf
  4338   Tue Feb 22 14:37:24 2011 steveUpdateSAFETYLarisa received 40m safety training

Larisa Thorne received 40m lab specific, basic safety training. She will attend P. King's Basic Laser Safety Training Session tomorrow.

 

  3588   Mon Sep 20 10:33:21 2010 josephbBureaucracyComputersLarry stopped by - GC machine had conflicting IP

Larry stopped by today and had to disconnect the m25 machine (this is the 1st GC machine on the left as you walk into the control room) because its IP was conflicting with a machine over in Downs.  Do not use 131.215.115.125 as the IP on this machine as this is already assigned to someone else.  They couldn't figure out the root password to change it which is why it is not currently plugged into the network, and is not to be until an appropriate IP is assigned.

They've asked that whoever set the machine up to please contact them (extension 2974).

  6500   Fri Apr 6 19:40:57 2012 Mike J.SummaryGeneralLaser Emergency Shutoff

I accidently shut off the laser at 19:34 with the emergency shutoff button while trying to tap into a video line for the Sensoray device.

  6501   Fri Apr 6 20:05:12 2012 JamieSummaryGeneralLaser Emergency Shutoff

We reset the interlock and restarted the PSL.  The end AUX lasers seem to have come back online fine.  PMC and mode cleaner locked back up quickly.

  1465   Thu Apr 9 23:11:27 2009 robSummaryLockingLaser PM to PO-DC transfer functions at multiple CARM offsets

I've plotted some transfer functions showing the response at POB DC to laser frequency (phase) noise.  There are transfer functions for multiple CARM offsets.  Basically, the transfer function looks like the DARM transfer function when the CARM is at zero offset, and is super-wonky elsewhere.  POB-DC is not a good CARM signal for intermediate stages of lock acquisition in a dual-recycled interferometer.  We should look into switching back to REFL-DC.

 

Attachment 1: CARMoffs1.png
CARMoffs1.png
Attachment 2: CARMoffs2.png
CARMoffs2.png
Attachment 3: CARMcarpet.png
CARMcarpet.png
  1466   Thu Apr 9 23:20:35 2009 robSummaryLockingLaser PM to REFL-DC transfer functions at multiple CARM offsets

Quote:

I've plotted some transfer functions showing the response at POB DC to laser frequency (phase) noise.  There are transfer functions for multiple CARM offsets.  Basically, the transfer function looks like the DARM transfer function when the CARM is at zero offset, and is super-wonky elsewhere.  POB-DC is not a good CARM signal for intermediate stages of lock acquisition in a dual-recycled interferometer.  We should look into switching back to REFL-DC.

 

 Here are the corresponding transfer functions for REFL-DC.

Attachment 1: CARMoffs1_r.png
CARMoffs1_r.png
Attachment 2: CARMoffs2_r.png
CARMoffs2_r.png
Attachment 3: CARMcarpet_r.png
CARMcarpet_r.png
  1468   Fri Apr 10 03:10:08 2009 ranaSummaryLockingLaser PM to REFL-DC transfer functions at multiple CARM offsets

I hereby award the previous rainbow transfer functions the plot innovation of the month award for its use of optical frequency to denote CARM offset.

The attached movie here shows the sensing matrix (minus MICH) as a function of CARM offset. There are 3 CARM signals plotted:

GREEN - tonights starting CARM signal - REFL_DC

RED - my favorite CARM signal - REFL 166 I

CYAN - runner up CARM signal - POX 33 I

  1636   Mon Jun 1 13:56:52 2009 AlbertoUpdatePSLLaser Power after fixing the laser chiller

The laser power seems to have become more stable after fixing the laser chiller. The power is lower than it used to be (MOPA amplitude 2.5 versus 2.7) but, as shown in the attchement, it became more steady.

Attachment 1: MOPAtrend.jpg
MOPAtrend.jpg
  1639   Mon Jun 1 15:01:31 2009 ranaUpdatePSLLaser Power after fixing the laser chiller: more traces
If you look at the correlation between RMTEMP and HTEMP, you see what we knew: namely that there
was a 1:1 correlation before. After the chiller fix, I can see no correlation between the room and
amplifier temperature at the resolution of 10:1. So the chiller loop has a gain > 10 at 24 hour time
scales.

I don't understand why the PMC looks more stable.
Attachment 1: Picture_7.png
Picture_7.png
  552   Mon Jun 23 15:22:04 2008 ranaBureaucracySAFETYLaser Safety Walkthrough today
Attachment 1: Walkthrough08.jpg
Walkthrough08.jpg
  16024   Tue Apr 13 20:45:16 2021 YehonathanUpdatePSLLaser amplifier

{Yehonathan, Rana}

We unpacked the content of the amplifier crate in front of the water fountain (see attachments). Inside we found:

1. Amplifier head. (attachment 1)
2. Amplifier electronics and pump diodes (attachment 2).
3. Optical fiber (attachment 3).
4. 2 Long water hoses (~2m) and 2 short ones.
5. Network cable.
6. A wooden plate.
7. Cable sleeve (attachment 2)?
8. Some manuals will be uploaded to the wiki soon.

Please don't move/touch any of that stuff

Things that we need to consider/obtain:
1. A suitable power cable (attachment 4) with suitable power ratings (800W according to the amplifier specs). The connector head is C19 I believe.
2. A chiller. Rana says Aidan knows where to find one. Should we chill the amplifier head as well?
3. A mounting plate for the amplifier head with good thermal conductivity.
4. The pump wavelength is 808nm, we need to get suitable safety goggles.
5. Where to put the big electronics box. Preferably on 1X1 or 1X2.
6. How do we arrange the different components on the table? We also need to mode match the beam into the amplifier.

 

Attachment 1: 20210413_204721.jpg
20210413_204721.jpg
Attachment 2: 20210413_203300.jpg
20210413_203300.jpg
Attachment 3: 20210413_204940.jpg
20210413_204940.jpg
Attachment 4: 20210413_205549.jpg
20210413_205549.jpg
  16032   Wed Apr 14 19:48:18 2021 gautamUpdatePSLLaser amplifier

A couple of years ago, I got some info about the amplifier setup at the sites from Terra - sharing here in case there is some useful info in there (our setup will be rather different, but it looked to me like our Amp is a 2017 vintage and it may be that the performance is not the same as reported in the 2019 paper).

collection of docs (table layout in 'Proposed....setup') : https://dcc.ligo.org/LIGO-T1700046

LVC 70W presentation: https://dcc.ligo.org/LIGO-G1800538 

I guess we should double check that the beam size everywhere (in vacuum and on the PSL table) is such that we don't exceed any damage thresholds for the mirrors used. 

  16034   Thu Apr 15 09:46:24 2021 YehonathanUpdatePSLLaser amplifier

Some more relevant documents provided by Matt:

Phase III:70W amplifier integration at LIGO

70W amplifier External Shutter

aLIGO PSL high power attenuator

 

  16044   Fri Apr 16 18:21:36 2021 YehonathanUpdatePSLLaser amplifier

I surveyed a bit the 1X1/2 area to plan for the installation of the laser amplifier.

There is a vacancy at the bottom of 1X2 (attachment 1). I measured the dimensions of the diode box (DB) and it should fit. The optical fiber bundle is 75m long and should reach the amplifier head on the table easily.

According to the specs, the maximum power consumption of the DB is 800W (typically 600W), it should probably have its own circuit breaker. It can easily draw more than a few amps. The rack power strips are connected to this 4 socket box (attachment 2), is this just another power strip? It is connected to a circuit breaker with a 30A rating. How do we proceed from here?

In any case, we will need at least 2 meters of power cable.

I also tried to find a suitable place for a water chiller. A few suggestions are in the attachments. Basically either between the electronics shelves and the small rack next to 1X2 or next to the small rack close to the optical table. Maybe put it where the ladder sits and find another place for the ladder. Other options?

We would also need a windows machine running the Beckhoff software. The idea is that all the different laser components (DB, chillers, interlocks, switches) are connected to the EtherCat (over the ethernet infrastructure) so that the Beckhoff code can recognize a failure and switch off everything.

The things that are monitored:

1. Is the NPRO on?

2. Is the flow rate from the chillers enough?

3. Is the temperature of the diodes in the normal range?

4. Is one of the interlocks open?

5. Was one of the emergency buttons pushed?

6. Was the key switch on the DB turned to OFF?

The DB is EtherCat ready but the rest of the signals need to be interfaced somehow. Do we have to buy these EtherCAT terminals?

 

 

Attachment 1: 20210416_143642.jpg
20210416_143642.jpg
Attachment 2: 20210416_145408.jpg
20210416_145408.jpg
Attachment 3: 20210416_145448.jpg
20210416_145448.jpg
Attachment 4: 20210416_181324.jpg
20210416_181324.jpg
  16046   Sun Apr 18 21:29:55 2021 ranaUpdatePSLLaser amplifier
  • Ideally, we put the chiller outside of the interferometer area. The PSL chiller used to be in the control room near the door by IMC REFL. We could also put it in the drill press room.
  • Once we figure out a couple of places where the Diode Box can go, we can ask facilities to make the appropriate power connections. They will have to eval the situation to figure out if the main power to the lab needs to be shut down.
  • Can we put the laser diode box in the drill press room too? Then the hoses can be short. Perhaps less EMI getting into our sensitive places.
  16062   Wed Apr 21 11:09:57 2021 yehonathanUpdatePSLLaser amplifier

I went to the TCS lab to take a look at the chillers lying around. I spotted two chillers:

1. Thermoflex1400 (attachment 1,2). Spec sheet.

2. Polyscience Recirculator 6000 series (attachment 3,4). Manual.

The Thermoflex has various communication ports. The Recirculator doesn't have any communication ports, but it is connected to a flow meter with what seems to be an electronic readout (attachment 5). Manual.

Both chillers have similar capacity ~ 4 gallons/minute. Thermoflex has 2 times more reservoir capacity than the Recirculator.

None of them seem to be Bechkoff-ready.

I guess we can have interlock code handling mixed signals Beckhoff+Non beckhoffs?

Attachment 1: 20210420_171606.jpg
20210420_171606.jpg
Attachment 2: 20210420_171621.jpg
20210420_171621.jpg
Attachment 3: 20210420_171611.jpg
20210420_171611.jpg
Attachment 4: 20210420_171629.jpg
20210420_171629.jpg
Attachment 5: 20210420_171702.jpg
20210420_171702.jpg
  16080   Thu Apr 22 17:28:34 2021 YehonathanUpdatePSLLaser amplifier

According to the aLIGO 70W amplifier interlock concept the flow rate of the chiller should be between 5 and 40 l/min. The chillers I found in the TCS lab both have around 15 l/min flow rate so we should be fine in that regard.

Assuming that the power consumption of the diode box is ~800W and that the optical output power of the diode is ~ 300W of optical power, the chillers need to be able to remove the remaining power. At room temperature, they both have enough cooling capacity according to their specs.

As for the idea to put the chiller and diode box in the drill room: There are not a lot of options here. The only viable place is the SW corner (attachment 1). I was told this place is used sometimes for liquid nitrogen dewar. Alternatively, if possible, we can move the fire extinguishers to the SW corner and use the NW corner. In that way, we don't have to clear all the junk from the SW corner, as long as the extinguishers are still accessible.

I made a sketch (attachment 2) showing a possible setup for a diode box + chiller rack. The fiber and network cable can go through the hole in the wall that already exists for the N2. It will have to get bigger though (attachment 3). The rack would also need to host some Acromag unit to convert the communication channel of the chiller/flow meter to Ethernet. The Acromag on 1X7 has no spare channels.

The only power socket in the room, to which the drill is connected, is circuit #36 which is connected to panel L in the lab. The breaker's ampacity seems to be 20A if I'm reading the number on the breaker correctly.

 

Attachment 1: 20210422_124940.jpg
20210422_124940.jpg
Attachment 2: DrillRoomSchematics.pdf
DrillRoomSchematics.pdf
Attachment 3: 20210422_125240_1.png
20210422_125240_1.png
  1003   Mon Sep 29 01:19:40 2008 ranaSummaryPSLLaser chiller running a little hot
I looked at it some last night and my suspicion was the ISS. Whenever the ISS switch came on the FAST got a kick.

We should try to disable the MC locking and ISS and see if the FSS/PMC/MZ are stable this way. If so this may be
a problem with the ISS / Current Shunt.
  1005   Mon Sep 29 13:23:40 2008 robSummaryPSLLaser chiller running a little hot

Quote:
I looked at it some last night and my suspicion was the ISS. Whenever the ISS switch came on the FAST got a kick.

We should try to disable the MC locking and ISS and see if the FSS/PMC/MZ are stable this way. If so this may be
a problem with the ISS / Current Shunt.


My entry about the laser chiller got deleted. The PSL appears to be running with the ISS gain at -5dB, so that's good, but the
chiller is still showing 21+ degrees. It should be at twenty, so there's something causing it to run out of
headroom. We'll know more once Yoichi has inspected the ISS.

In the deleted entry I noted that the VCO (AOM driver), which is quite warm, has been moved much closer to the MOPA.
This may be putting some additional load on the chiller (doubtful given the amount of airflow with the HEPAs on,
but it's something to consider).
  3417   Thu Aug 12 23:49:04 2010 nancyUpdateEnvironmentLaser chiller temp raised

Since the laser is off, Jenne and I rasied the chiller-chiller (small AC in the Control Room) set point temperature to 73 degree F (from 68F) to save people from shivering.

  1568   Sat May 9 00:15:21 2009 YoichiUpdatePSLLaser head temperature oscillation
After the laser cooling pipe was unclogged, the laser head temperature has been oscillating in 24h period.
The laser power shows the same oscillation.
Moreover, there is a trend that the temperature is slowly creeping up.
We have to do something to stop this.
Or Rob has to finish his measurements before the laser dies.
Attachment 1: laser.png
laser.png
  1569   Sat May 9 02:20:11 2009 JenneUpdatePSLLaser head temperature oscillation

Quote:
After the laser cooling pipe was unclogged, the laser head temperature has been oscillating in 24h period.
The laser power shows the same oscillation.
Moreover, there is a trend that the temperature is slowly creeping up.
We have to do something to stop this.
Or Rob has to finish his measurements before the laser dies.


How's DTEC doing? I thought DTEC was kind of in charge of dealing with these kinds of things, but after our laser-cooling-"fixing", DTEC has been railed at 0, aka no range.

After glancing at DTEC with Dataviewer along with HTEMP and AMPMON (my internet is too slow to want to post the pic while ssh-ed into nodus), it looks like DTEC is oscillating along with HTEMP in terms of frequency, but perhaps DTEC is running out of range because it is so close to zero? Maybe?
  1570   Sat May 9 15:19:10 2009 ranaUpdatePSLLaser head temperature oscillation
This is 8 days of 10-minute trend.

DTEC is just the feedback control signal required to keep the NPRO's pump diode at a constant temperature.
Its not the amplifier or the actual NPRO crystal's temperature readout.

There is no TEC for the amplifier. It looks like to me that by opening up the flow to the NPRO some more
we have reduced the flow to the amplifier (which is the one that needs it) and created these temperature
fluctuations.

What we need to do is choke down the needle valve and ream out the NPRO block.
Attachment 1: Picture_2.png
Picture_2.png
  13414   Wed Nov 8 00:28:16 2017 gautamUpdateLSCLaser intensity coupling measurement attempt

I tried measuring the coupling of PSL intensity noise by driving some broadband noise bandpassed between 80-300Hz using the spare DAC channel at 1Y3 that I had set up for this purpose a couple of weeks ago (via a battery powered SR560 buffer set to low-noise operation mode because I'm not sure if the DAC output can drive a ~20m long cable). I was monitoring the MC2 TRANS QPD Sum channel spectrum while driving this broadband noise - the "nominal" spectrum isn't very clean, there are a bunch of notches from a 60Hz comb and a forest of peaks over a broad hump from 300Hz-1kHz (see Attachment #1).

I was able to increase the drive to the AOM till the RIN in the band being driven increased by ~10x, and saw no change in the MICH error signal spectrum [see Attachment #1] - during this measurement, the RFPD whitening was turned on for REFL11, REFL55 and AS55, and the ITM coil drivers were de-whitened, so as to get a MICH spectrum that is about as "low-noise" as I've gotten it so far.

I tried increasing the drive further, but at this point, started seeing frequent MC locklosses - I'm not convinced this is entirely correlated to my AOM activities, so I will try some more, but at the very least, this places an upper bound on the coupling from intensity noise to MICH.

Attachment 1: PSL_RIN.pdf
PSL_RIN.pdf
  13353   Tue Oct 3 01:32:39 2017 gautamUpdateLSCLaser intensity noise coupling to MICH (simulated)

GV Oct 6: This coupling is probably not correct - Finesse outputs TF magnitude in units of W/W, and not W/RIN

Since I was foiled (by lack of DAC) in my attempt to measure the coupling of laser intensity noise to MICH in the DRMI (no arms) configuration, I decided to try understanding the effect with a simulation.

For this purpose, I used my DRMI Finesse model - this had mirror positions tuned for locking and photodiode demod phases tuned to give a sensing matrix model that wasn't too far from an actual measurement (within factor of a few). So the model seems okay for a first pass at estimating this coupling.

Measuring transfer functions in Finesse is straightforward - use the fsig command to modulate some quantity (in this case the input beam intensity), and use the pd2 detector to demodulate the effect of this modulation at the port of interest (in this case AS55_Q).

**Note that to apply a modulation to an input beam (i.e. Laser) in Finesse, the keyword for the "type" argument given to fsig is "amp" and not "amplitude" as the manual would had me believe. In fact, there seem to be quite a few such caveats. The best way to figure this out is to go to the pykat installation directory, find the file components.py, and look for the fsig_name for the component of interest. It is also indicated in the same file, via the canFsig argument, if that property of the component can be modulated for transfer function measurements.  

Attachment #1 shows the result of such a sweep.

To estimate what the actual contribution to the displacement noise is, I used the DQ-ed MC transmission (recorded at 1024Hz) from the DRMI lock, computed the ASD using scipy.signal.welch, divided by the nominal MC transmission of ~15,000 counts to convert to RIN/rtHz. The RIN was then multiplied by the above calculated coupling function, and divided by the sensing matrix element for AS55_Q (in units of W/m) to give the curve shown in Attachment #2. If we believe the simulation, then Laser Intensity Noise shouldn't be the limiting noise between 10Hz-1kHz. 

I will of course measure the actual coupling and see how it lines up with Attachment #1 - would be a nice additional validation of the Finesse model. I will also try using the Finesse model to estimate some other coupling transfer functions (e.g. Laser Frequency Noise, Oscillator Noise).

Quote:

The absence of evidence is not evidence of absence.

 

Attachment 1: MICH_intensityNoiseCoupling.pdf
MICH_intensityNoiseCoupling.pdf
Attachment 2: MICH_intensityNoiseASD.pdf
MICH_intensityNoiseASD.pdf
  14978   Fri Oct 18 18:13:55 2019 KojiUpdatesafetyLaser interlock looks OK

I've checked the state of the laser interlock switch and everything looked normal.

  1256   Wed Jan 28 19:08:50 2009 YoichiUpdatePSLLaser is back (sort of)
Yoichi, Peter, Jenne

Summary:
We found that the chiller water is not going to the NPRO base. It was hot whereas it was cold when I touched it a few months ago.
I twisted the needle valve on the water line to the NPRO base. Then we heard gargling noise in the pipe and the water started to flow.
The laser power is now climbing up slowly. The noisiness of the MOPA output is reduced.

I will post more detailed entry explaining my theory of what actually happened later.
Attachment 1: Improving.png
Improving.png
  1257   Thu Jan 29 13:52:34 2009 YoichiUpdatePSLLaser is back (sort of)
Here is what I think has happened to the laser.

After the chiller line to the NPRO base clogged, the FSS slow slider went down to keep the laser frequency constant.
It is evident in the attachment 1 that the behavior of the slow slider and the DTEC (diode temp. stabilization feedback signal) are almost the same except for the direction. This means the slow servo was fighting against the increased heat caused by the lack of the cooling from the bottom.
DTEC was doing the same thing to keep the diode temperature constant.

Even though the slow actuator (a Peltier on the crystal) worked hard to keep the laser frequency constant, one can imagine that there was a large temperature gradient in the crystal and the mode shape may have changed.

Probably this made the coupling of the NPRO beam to the PA worse. It may also have put the NPRO in a mode hopping region, which could be the cause of the noisiness.

Right now, the MOPA power is 2.7W.
The FSS, PMC, MZ are locked. At first, the PMC locked on a sideband. I had to twiddle the phase flip button of the PMC servo to lock the PMC. Probably this is another sticky channel, which needs to be tweaked after a reboot of c1psl. I added a code to do this in /cvs/cds/caltech/scripts/Admin/slider_twiddle.

Currently the ISS is unstable. Kakeru and I are now taking OPLTF of the servo.
Looks like the phase margin at the lower UGF is too small.
Attachment 1: SlowDC.pdf
SlowDC.pdf
  12035   Tue Mar 15 10:31:58 2016 SteveUpdateIOOLaser is turned back on

It's may be the janitor's doing.

I noticed that the HEPA filers were off. They are turned on at 20%
 

Attachment 1: 2WlaserOff-On.png
2WlaserOff-On.png
  12041   Tue Mar 22 14:12:18 2016 SteveUpdateIOOLaser is turned back on

The 2W Innolight was turned on.

 

Attachment 1: off-onAgain.png
off-onAgain.png
  9255   Mon Oct 21 09:46:12 2013 SteveUpdatePSLLaser just turned on

I have just turned on the PSL Innolight laser. The laser shut down  with unknown reason a day ago.

Attachment 1: laserTurnedON.png
laserTurnedON.png
  10102   Wed Jun 25 17:13:10 2014 NichinUpdateElectronicsLaser power check - PDFR system

[Nichin, Manasa]

I wanted to make sure Alex's system of Diode laser + laser controller + optical splitter was working fine and then make a manual measurement for AS55 PD. Manasa was supervising my work and helping me with unhooking the fibers and taking power meter readings. I have tuned on the power to REF DET from under the POY table.

I switched on the laser sitting in the 1Y1 rack and turned up the driving current to 240mA. On checking the laser power readings at AS55 (AS table) and REF DET (POY table) simultaneously, we got readings of 1.6mA and 2.4mA respectively. This much difference in readings was not expected and I did not continue taking the readings for transimpedence measurement.

I will rectify if this unequal splitting of power by the 1x16 optical splitter is going to cause any difficulties for the automated PDFR system measurement technique and resolve it if needed.

 

  1034   Wed Oct 8 19:17:55 2008 YoichiConfigurationPSLLaser power is slowly recovering
This afternoon we (rich, steve, yoichi) shutdown the laser for the DC-DC converter installation.
(we decided not to do so. Detail will be posted soon.)
After we turned on the laser again,the laser power has been recovering but very slowly.
At the time of writing, the laser power is 2.6W (MOPA_AMPMON).
I think it is because the chiller temparature has not yet settled down (it went up to 25C and slowly coming down, now at 22C).
It will take some hours until the power fully comes back.
Right now I confirmed that at least the MC locks.
  12083   Tue Apr 19 18:37:29 2016 gautamUpdateendtable upgradeLaser swap + optical layout

Summary of work done over the last two days

  1. Lightwave NPRO + controller moved to PSL table
    • ​​The interlock is not connected to the controller
    • Controller is not powered
  2. Innolight NPRO + controller installed at endtable
    • ​​​​Interlock has been connected
    • For initial alignment purposes, I'm running it at an injection current of 1.000A (~50mW of IR out of the NPRO)
    • Temperature of crystal set to 31.66 degrees in anticipation of operation in the nominal state
  3. Laying out optics
    • ​​Given that the mode out of the NPRO is different from that from the Lightwave, the mode-matching had to be re-done
    • Attachment #1 shows the mode-matching solution being implemented
    • Current state - I've placed all the optics up to and including the doubling crystal + oven. Alignment through IR Faraday is pretty good, QWP+HWP angles optimized to maximize transmission through the Faraday (<10% loss). Oven has been hooked up to temperature controller, and is currently set to 36.3 degrees. Coarse alignment into doubling crystal done at lower power. Even with the low IR power, I am able to see some green. It remains to turn the injection current up and do the fine alignment + lens position tweaking to maximize the green power from the doubling crystal - with ~1W of power, assuming 2%/W SHG efficiency, we should be seeing 20 mW of green (which is probably way too much)

Immediate next steps:

  1. Some optimization to be done with regards to beam dumps for rejected beam from IR Faraday. Also double check to make sure that the reflected beam from L1 doesn't go back directly to the laser (at the moment it doesn't, is there a standard way to do this? I was trying to have the lens as close to normal incidence as possible, but I may not have been entirely successful which is why the reflected beam is not going straight back at the moment).
  2. Optimize mode-matching into the doubling crystal
  3. Once the desired green mode is obtained, continue with the rest of the layout
  4. Update CAD drawing to reflect new layout

 

Attachment 1: IR_modematch_19April2016_2.pdf
IR_modematch_19April2016_2.pdf
  12017   Thu Mar 3 01:25:50 2016 gautamUpdateGreen LockingLaser swap - 2 IR + 1 green beatnotes found

[ericq, gautam]

Summary of work done tonight:

  • The PDH setup at the Y-end has been restored after I had pulled the whole thing apart some weeks ago to see that nothing was obviously wrong with the uPDH box
  • Adjusted the temperature of the Y-end laser such that a beatnote was obtained - I did this using the IR beat (the end laser temp wasn't updated after the PSL temp was changed recently)
  • The Y green beatnote was found easily, there was no alignment on the PSL table necessary, though there is room to improve this situation (beatnote amplitude was ~ -35dBm though we are used to more like -25dBm)
  • The X green beat remains elusive - I played around with the alignment onto the green beat PD at the PSL table for some time, and the two beams are aligned as far as I can tell given the constrained area available in that area. It may be that I have to clear some optics, do a rigorous near-field/far-field alignment of the two beams and then try again
  • Since we had two strong (-5dBm for Y, -9dBm for X) IR beatnotes, we decided to take the ALS noise spectra for these. So as to not overload the amplifiers, a -10dB attenuator (-6dB) was placed directlty after the Y (X) IR beat PDs, before routing these signals through the usual green beat signal chain. Attached is the measured spectrum. The new values of the temperature sliders at which beatnotes can be found are : 1700 for X and -5990 for Y (spectra taken at these values).

To do:

  • For both ends, find the three temperatures at which we have beatnotes, and choose the middle one
  • PM characterization of AUX X laser - it may be that the excess noise in the X spectrum is due to sub-optimal PDH
  • Align the Y green better at the endtable, also take an OLTF measurement for the Y PDH loop
  • Re-check the alignment onto the green beat PD for the X beat

Remarks:

  • The Lightwave laser controllers differ from the Innolight ones in that it is not possible to directly set the signal to the SLOW control BNC to 0, and have that as the new reference point. Rather, there seems to be some setpoint which is saved as a reference, and the moment any signal is applied to the SLOW control BNC, it adjusts the actual temperature w.r.t. this saved setpoint. I believe it is possible to update this setpoint (it is also possible to update the calibration of the power readout, this is an additional issue at the X end), but since this wasn't critical, I've left it as is for the moment...
  • The ALS nosie spectrum for the Y arm IR beat is surprisingly good!
Attachment 1: IR_beat_20160303_2.pdf
IR_beat_20160303_2.pdf
  12012   Fri Feb 26 01:52:44 2016 gautamUpdateGreen LockingLaser swap - Green PDH OLTF

I spent some more time today trying to optimize the modulation frequency and amplitude for the X end PDH, and the alignment/mode-matching of the green to the arm. Some notes:

  1. After my best efforts to tweak the alignment and mode-matching into the arm by using the two lenses on translational stages, I was able to get the green TRX up to about 0.06. As mentioned in a previous elog, this is much lower than what we had with the old setup, even though we have more green power going into the arm now. However, the mode looks pretty bright and clean on the monitors. Could the large ellipticity in the beam is the limiting factor now?
  2. I measured the transfer function (attachment #1) of the PDH loop once I had settled on a modulation frequency and amplitude that I judged to be optimal (indicated on the plot). The UGF is ~7kHz. The PDH error signal as viewed on the oscilloscope is comparable to what we had with the Innolight. All this optimization was done empirically, I have yet to do the PM measurement. I can't seem to get more than 0.2 mW of IR arriving at the fiber coupler, the number I found in some older elogs is 2mW with the old setup.
  3. I did some alignment of the PSL green and the X arm green onto the beat PD on the PSL table. After the power glitches, the doubling ovens do not automatically turn on, I had turned on the end ovens earlier, and today I turned on the PSL oven. I noticed some strange behaviour initially - though the setpoint was 36.9 deg C, when I enabled the heater, there was a large overshoot (it went to almost 50deg C). I disabled the heating at this point, and re-enabled it once the oven had cooled down to ~35 deg C. I didn't observe anything like this while turning on the end ovens. But the PID parameters at the PSL table are very different, so perhaps this large overshoot and ringing is to be expected. In any case, I managed to get this working. But I was not able to find a beatnote tonight. 

To do:

  1. Verify that the two beams are aligned on the beat PD - I think I've done this carefully by checking the near and far-field, but I will double check.
  2. Find the beat note and look at the ALS noise performance with this new setup to see if it is usable even though GTRX is only 20% of what it used to be..
  3. Fix the coupling of the IR pickoff into the fiber at the endtable. Once this is done, I can do the PM measurement, and finding a beatnote may be easier given the IR beat PDs have a much wider bandwidth...
Attachment 1: X_PDH_OLTF_20160225.pdf
X_PDH_OLTF_20160225.pdf
  12009   Wed Feb 24 19:29:13 2016 gautamUpdateGreen LockingLaser swap - Green PDH locked

After the discussion at the meeting today, I decided to try and lock the green by sweeping through PZT dither frequencies in the vicinity of 200kHz without worrying about the AM/PM ratio for now. I was able to lock the PDH loop relatively quickly, at an empirically determined PZT dither frequency of 213.873kHz, 2Vpp (the amplitude was copied from the value at the Y-end). For today's efforts, I borrowed the sum+HPF pomona box from the Y-end, I will make a replica given that we are using Lightwave lasers at both ends now. After adjusting the PZT sliders and lenses on the translational stages at the endtable to maximize the green transmission as best as I could, I was able to get GTRX up to about 0.07 - this is far off from the value of ~0.25-0.3 I seem to remember us having with the old setup, even though we have more green light into the arm cavity. I will take a measurement of the loop transfer function to see what sort of bandwidth we have...

  12006   Tue Feb 23 23:01:16 2016 gautamUpdateGreen LockingLaser swap - Green PDH locking

Given that we were seeing green flashes in the arms, I tried to see if I could get the green locked to the arm in a nice mode. For a start, I tried hooking up the PDH box and LO using the same settings as was being used previously. However, this did not work. I suppose we will have to do the whole AM/PM measurement for the Lightwave as well before we can determine what would be a suitable frequency for the LO. The AM measurement was relatively straightforward, I just repeated the same steps as detailed here. The two attachments show the AM response (one from 10kHz to 5MHz, the other for a narrower range of 100kHz to 1MHz, both with an excitation amplitude of 0dBm). To see if I could guess some sweetspot for operation, I tried setting the LO frequency to the two marked notch frequencies but was unsuccessful in getting the PDH lock going. At the moment, the alignment for the optics that picks off the IR after the doubler and routes it to the fiber are ccompletely misaligned, I will align these and do the PM measurement tomorrow and then we should conclusively be able to say what the appropriate frequency is to actuate on the PZT.


Unrelated to this work: the KEPCO high voltage power supply that drives the green steering mirror PZTs was switched off - I suppose this has been the case since the power outage last week. I turned it back on and reset it to the nominal settings: Vout = 100V, and Imax_out = 10mA, the driver board is currently drawing ~7mA which I judged to be consistent with the values labelled on the unit.

Attachment 1: AM_scan.pdf
AM_scan.pdf
Attachment 2: AM_scan_zoomed.pdf
AM_scan_zoomed.pdf
  11999   Fri Feb 19 00:42:19 2016 gautamUpdateGreen LockingLaser swap - beam ellipticity from laser?

Eric and I spent some time yesterday night trying to recover the green in the arm after the laser swap. The problem essentially was that though I was getting ~800uW of green out of the doubling oven, the mode wasn't clean, and hence, the beam profile looked really messed up just before entering the arm cavity.We got to a point where we thought we were getting a good mode out of the doubling oven (as judged by propagating this beam onto the wall with the help of a mirror). But we were only getting ~400uW of green power. I tried tweaking the alignment of the oven on the 4 axis stage for a while, but was not able to improve the situation much. So I decided to start from scratch:

  • First, I made sure that the IR beam from the laser was hitting the first steering mirror approximately at the center (see here for the optical layout). 
  • Then I used the two steering mirrors immediately after the laser to make sure that the IR beam was hitting the first lens and the HWP before the IR faraday roughly at their center. 
  • Next, I propagated the beam through the IR Faraday, again using SM1 and SM2 to do the steering - initial alignment through the Faraday was done by eye, and I did  some fine adjustment by maximizing the power coming out of the Faraday. We have 252mW of IR going into the IR Faraday, and 225mW coming out. I judged that these numbers were reasonable, and compared favourably to what we had with the Innolight.
  • Keeping the downstream alignment, I used SM1 and SM2 to hit the second lens roughly at its center. I then re-measured the distance from this lens to the center of the doubling oven, and tweaked this slightly to match my mode-matching calculation. 
  • I then tried to carefully play with this lens and the alignment of the doubling oven using the four axis stage. After (many) iterations, and with some luck, I managed to find what I judged to be a good alignment. Using the mirror-on-a-stick to reflect the green beam out of the doubler onto the wall nearby (see Attachment #1, all photos taken using my phone camera), the mode looks reasonably clean. I was also able to get 1mW of green power out of the doubler, an efficiency of ~2%/W. The doorknob should give some sense of scale, but at this point, the mode looks pretty clean (this was not the case previously).
  • I then aligned the post doubler optics to send the beam through the green Faraday (~0.85mW of green out of the green Faraday) and through the two irides I had put in before swapping the lasers. As the beam propagates, however, some ellipticity in it becomes more and more apparent - especially after the f=-100mm lens between the two piezo mirrors. Attachment #2 shows the beam immediately after this lens, while Attachment #3 shows the beam on the iris just before it is sent into the arm cavity. 

I am beginning to wonder if this ellipticity is inherent from the IR beam from the laser? My beamscan results suggest that the beam is more divergent in the "P direction" as compared to the "S direction", which is borne out by these photographs. And if this is indeed the case, do we need to add cylindrical lenses to correct this?


Unrelated to this work: The ITMX Oplev seems to have wandered off so the X arm won't lock. I am not realigning the Oplev for now, but am turning the ITMX Oplev servo off for the night. 

Perhaps related to my work on the endtable: The ETMX oplev MEDM readings seemed to be frozen, though there was red light on the QPD on the endtable. Checking the CDS overview screen, I saw that all models on c1iscex had crashed. I sshed into c1iscex and restarted all the models, but the IOP block remained red. I checked the datetime, and found that this was wrong - so I followed the instructions here, but the "Diag Word" block remains red. I am shutting down the watchdog for ETMX and leaving this as is for now... This seems to have happened before...

Attachment 1: IMG_6287.JPG
IMG_6287.JPG
Attachment 2: IMG_6288.JPG
IMG_6288.JPG
Attachment 3: IMG_6286.JPG
IMG_6286.JPG
  12019   Fri Mar 4 01:11:41 2016 gautamUpdateGreen LockingLaser swap - both green beatnotes found

The good news: both green beatnotes have now been found. The problem was alignment on the green beat PD on the PSL table which I fixed. They are about -40dBm in amplitude (compare to -25dBm we used to see). But looking at the phase tracker Q output seems to suggest that there is adequate signal...

The bad news: the ALS noise still looks bad (see attachment)- I think the IR beat for the Y was perhaps marginally better. The beat amplitude for the X beat was optimized on the PSL table with the help of the oscilloscope. There may be some headroom for improvement with the Y beat.

I also did the AM/PM measurement for the replaced lightwave, chose an LO frequency based on this, and took the loop OLTF, plots to follow...

To do: 

  • Check Y-end PDH loop OLTF
  • Optimize beat note amplitude of Y beat
  • Align Y-green better to the arm using steering mirrors on the endtable.
  • Double check calibration of PM/AM measurement and that I've picked the correct LO frequency/ I don't have any other ideas for improving the situation with the X beat though
Attachment 1: IR_beat_20160303_green.pdf
IR_beat_20160303_green.pdf
  11988   Fri Feb 12 17:05:40 2016 gautamUpdateGreen LockingLaser swap - green light recovered but no flashes in the arm

After carefully tweaking the mode-matching of the IR into the crystal and the four-axis translation stage on which the doubling oven is mounted, I managed to recover 800uW of green power going into the green Faraday. Considering we have ~225mW of IR power coming out of the IR faraday (and roughly that amount going into the SHG crystal), I'd say this is pretty consistent (if not slightly better) with a recent power budget I had made for the X end. The amount of green power we get out of the doubling crystal is very sensitive to the alignment of the crystal to the beam axis. I suspect we could improve the situation slightly if the mode-matching lenses were mounted on translational stages so we could tweak their position, but the current situation on the X endtable does not provide space for this. In any case, I'd say we are at least as good as we were before, and so this should be an adequate fix until the new end-table is installed (though I don't know why we aren't seeing the predicted SHG conversion efficiency of 3-4% as predicted by Kiwamu's calculations, we are getting more like .36% conversion efficiency)...

Because the alignment of the beam before the doubling oven had changed, I had to adjust the steering mirrors to make the green beam go into the green faraday. I had placed a couple of irides for the green beam as a reference of the old path into the arm, and I used these to adjust some of the green mirrors to center the green beam on these. However, I did not observe any flashes in the arm. I will check if we are still mode-matched to the arm, and if the lenses downstream of the doubling oven need to be moved....

  11989   Fri Feb 12 19:07:52 2016 KojiUpdateGreen LockingLaser swap - green light recovered but no flashes in the arm

800e-6 / 0.225^2 = 0.016

=> 1.6%/W

I thought Kiwamu had roughtly 2%/W.

 

  12026   Mon Mar 7 23:51:36 2016 gautamUpdateGreen LockingLaser swap - some improvement
Quote:

 

Next steps in recovering ALS and trying to lock again

  • Having set the PDH modulation frequency to 256.62kHz, I took the spectrum of ALS noise using the IR beat (i.e. by piping the IR beat signal through the electronics the green beats usually go through - 6dB and 10dB attenuators were placed immediately after the beat PDs for the X and Y arms respectively, to make the signal levels compatible with the electronics), Attachment #5 unfortunately suggests that the noise performance is still poor, and I suspect the situation will be similar using the green beat (though I have not measured this yet).
  • The modulation depth could be sub-optimal for the X-end PDH, I have to measure this and check that it is at an acceptable level. This will also tell me if I need to change the sum+HPF pomona box used to send the PDH control signal + piezo dither signal to the laser PZT. In order to do this, I need to know what the input impedance to the FAST control BNC is - the manual isn't very helpful, it just says the piezo has a capacitance less than 10,000pF. I suppose I will have to actually measure this.
  • PDH loop OLTFs have to be re-measured for both ends to check that the servo gain's are appropriately placed.
  • We know that the mode-matching into the arm for the X end is poor (I have yet to quantify this) - I suspect that the beam ellipticity is the main culprit. However, the DC transmitted power levels at the PSL table are comparable to (even slightly better than) the Y arm numbers, and so this cannot be the sole reason why the X-arm ALS noise is so much worse... I will continue my investigations next week...

Attachment #1

Since I could not determine how many volts at the LO input of the pomona box input corresponds to how many volts at the laser PZT, I measured the transfer function between these points using the Agilent network analyzer. The measured TF suggests that for a function generator output of 2Vpp, we get approximately 75mrad of phase modulation, which compares reasonably well with the value of 120mrad reported here. I did not attempt to further increase the LO output signal to push this number closer to 120mrad, as with 2Vpp from the function generator we get +7dBm at the mixer, which is what it wants - so I wanted to avoid any attenuators etc...

Attachments #2 and #3

After ensuring that we have appreciable phase modulation, I set out to measure the PDH OLTFs and adjust the gain on the uPDH boxes accordingly. The X end gain is at 6.0, and the Y end gain is at 4.0. Before measuring the Y-end OLTF, I adjusted the steering mirrors to increase GTRY to ~0.45. GTRX remains a paltry 0.05... But the UGFs seem satisfactory..

Attachment #4

Finally, I took the ALS noise spectrum for the green beats. The beat note amplitudes on the network analyzer in the control room are still puny compared to what we had, -40dBm for Y and -45dBm for X. But the phase tracker Q values are ~1000 and ~3000 for X and Y respectively, which are pretty close to what these were if memory serves me right. There may still be some room for optimization of the PDH loop gains etc, and we could perhaps look at lowering the gain of the REFL PD at the X end? I also have yet to do the sweep for the 3 temperatures at which we can find a beatnote and park at the middle one...

These spectra suggest we could even possibly try locking? We are approximately a factor of 3 above the reference for X and on par with the reference for Y....

Unrelated to this work: I also realinged the PMC, PMC transmission is now 0.730V up from ~0.65V.

Attachment 1: PomonaTF.pdf
PomonaTF.pdf
Attachment 2: XPDH.pdf
XPDH.pdf
Attachment 3: YPDH.pdf
YPDH.pdf
Attachment 4: greenbeat_20160307.pdf
greenbeat_20160307.pdf
  12027   Tue Mar 8 18:22:20 2016 ranaUpdateGreen LockingLaser swap - some improvement

Why is the transmission of X green so low? Perhaps you can phase lock the IR and then scan the X frequency, using the X arm as the analyzer. i.e. put a slow ramp into MC2 to pull the PSL frquency and thus the green frequency. You can record a movie of the scan using the framegrabber and record the green transmission peaks to see how big the mode match is exactly (which modes are so big)

  12016   Wed Mar 2 17:42:19 2016 gautamUpdateGreen LockingLaser swap - some progress

[Koji, Johannes, gautam]

With Koji's and Johannes' help, I managed to resolve the coupling the pick-off IR beam into the fiber at the X end. I will put up a more detailed elog about how this was done - but in summary, we have about 31% coupling efficiency into the fiber, which isn't stellar, but I felt this was adequate to find a beatnote. Koji also pointed out that the collimation telescope attached to the fiber at the X-end is poorly mounted - this is something to fix when we swap endtables, but this was not addressed right now because if we were to adjust this, we would also have to adjust the mode matching into the fiber.

I then attempted to tune the temperature to find the IR beatnote. While doing so, I noticed some strange features of the controller - there are essentially two display modes relevant to laser crystal temperature, one which allows us to change the setpoint and one which is an actual readback of the temperature (this one can't be adjusted). While tuning the temperature, I noticed that the latter display ("LT") did not change in value. On a hunch, I disconnected the "SLOW" control BNC on the front panel, and voila, I was able to tune the setpoint and observe the measured temperature shift accordingly. I was thus able to find a reasonably strong IR beatnote (-9dBm) at T ~ 44.6 deg C (the beat PD was set to 0dB attenuation, i.e. high gain mode). However, the moment I reconnected the SLOW control BNC, the beatnote vanished (it gradually shifted out of range of the HP network analyzer), and the same thing happens if I terminate the SLOW control BNC connector! I don't understand this behaviour, as the manual says that the range of voltages accepted to this input is +/-10V, so I would assume 0V means do nothing, but clearly this isn't the case, as the beatnote is being shifted in frequency by > 1GHz, and the tuning coefficient is listed as 5GHz/V in the manual. This situation needs further investigation.

Since I had a reasonable IR beatnote setup, I returned the HP analyzer to the control room and tried to see if a green beatnote was present as well - I first ran ASS, then maximized the green transmission using the PZT mirrors, but no beatnote is evident. The contrast isn't great, the ratio of AUX power to PSL power on the green beat PD is something like 5:1, so this probably requires some tuning as well. I will update this elog after today evening's activities...

ELOG V3.1.3-