This is nice. Can we test this idea with POP22 + a razor blade?

Just to take transfer functions in PRMIsb between the PRM angle to POP QPD/POP22+razor blade
as well as the noise spectrum measurement are already useful.

We want to figure out the requirement for the 2f QPD.
(Transimpedance / Noise level / Beam size / etc)

Depending on the requirement we'll see if we need demodulation or just a power detector.

 In addition to the simulation described in my previous elog, I simulated the signal on a quadrant photodetector demodulated at 2F. The input laser beam is modulated at 11MHz up to the fifth order. There is no additional 55 MHz modulation.

The QPD demodulated at 2F shows good signals for PRC control for all CARM offsets, as expected from the previous simulation.

Last Week

Took first round of PER measurements after a long setup.

Started setting up to take measurement of the other polarization--ran into issues with mounts again. (Spinning of their own free will again.)

Devised a new scheme for taking more robust measurements of PER--still in progress.

Next Week

Finish data analysis of these latest PER measurements

Hopefully finally move on to frequency noise characterization

Materials Needed

None for PER

Unknown for frequency noise

The ALS system is iffy tonight.

After putting the cable back to the RF spectrum analyzer (it had been taken to test the frequency counter setup, and not put back), I had a good Yarm beatnote, but again this evening the Xarm beatnote is small.  I touched up the PSL table alignment (very, very little needed, but it did double my peak height).  I *think* that this is happening because we haven't settled into a good IFO alignment place, so the arm pointing keeps changing very slightly, which means that the PSL ALS alignment needs touching.  Anyhow, even after alignment the Xarm beatnote is only -36 dBm at 81 MHz.  It should be at least -25 dBm or so, although I haven't seen it any larger than about -35 dBm since the IFO beam was lost last Friday.

I am not able to hold ALS lock long enough to scan the arms and find the IR resonances.  The only optics that I am actuating on this evening are the 2 ETMs.  When I lose lock and look at the watchdogs, the ETMs are the only optics that have largeish numbers, which comes from the ALS lockloss.  So, I don't think I am suffering from the ITM suspension kicks tonight.  Rather, I think that it's that the ALS system isn't tuned up nicely.

I think that it is past time we tuned up and checked out the ALS PDH setup.  Q:  Can you please measure the loop TFs for both of the ALS PDH boxes tomorrow?  At the very least we want to know what we're working with. 

Evan:  What is the status with the ISS? 

I am going to try tomorrow to look at the suspensions, and see if I can track anything down.  I feel like I see the kicks more often when the arms are locked, i.e. we are sending an LSC signal to them.  The LSC POS signal is a factor of a few hundred larger than the damping SUSPOS signal is.  Are we saturating something somewhere?  Why is this a new thing?  We certainly do see kicks when the LSC is not engaged, so this may not be the right path, but it is something concrete to look at.

 Today I and EricQ went inside the lab and set up the cables running from the a DAC channel into  PZT input so that we can use the PID controller to tune in the PZT offset to maintain the beat note within a detectable range (This is plan B as the main plan of actuating on the laser temperature can be achieved only after the fiber setup with the PSL is ready). I obtained all the poles and zeroes of plant and started designing a PID loop to test it with the existing system.

I will put in my PID values into the already existing PERL controller code (that is used for controller design in the 40m) and run tests with the PID loop while actuating on the PZT offset. 

 Finally,  the efforts put in the Frequency Counter paid off . I tested the working of both the FC and EPICS channels that I created by displaying the beat note on MEDM screens. EricQ helped me locking the X arm ( Y arm free) thus acquiring only the X arm beat note from the frequency counter. We plotted the beat note on MEDM and clearly could see a stable beat note when the arm was locked. Now it can be said that the FC(two of course) can replace the spectrum analyzer outside and also get the beat-note frequencies  into EPICS channels. The channel names of these two beat note frequencies are:

X Arm:          C1:ALS-XBEAT_FREQ_MHZ

Y Arm:          C1:ALS-YBEAT_FREQ_MHZ

(Note: There are many problems in alignment of the arms and we could have beat note only for some time after putting a lot of effort).

The PDFR system now has the capability to automatically run vectfit3.mat using a wrapper script named vectorfitzpk.m

This is done via a shell script being called from inside python that inturn runs the matlab script.

After aligning the arms to IR, I aligned the Y green beam to the arm.  Also, the X green beatnote was very small, so I aligned the PSL green for X.

Q is working on fixing the "save offsets" script for the ASS, because that has lost me my alignment two more times in the last few hours.  But, right now I have both arms locked with transmitted powers of about 0.9!  To get this, I ran the ASS scripts, and hand-tweaked the bias sliders of some of the optics to relieve the ASS outputs.  Then I turned the ASS gain to zero, and by-hand turned off the oscillators.  So, the ASS outputs are just frozen. 

I haven't seen IMTX suspension kicks, I think since Q did the front end reboot earlier. There has been ITMY activity, however. I think I'm going to be bold, and try locking ALS.

TRX and TRY communication were recovered by doing a simultaneous reboot of all of the frontends.

Working with the interferometer has been extremely frustrating today. Having transmission values let us lock and ASS, but that has been less helpful than you would hope.

Saving the ASS offsets has repeatedly resulted in an overall bad change in alignment, moving the TTs and other things off randomly.

ITMX continues to be kicked. ITMY intermittently wanders away. It has not been possible to maintain IFO alignment for a reasonable length of time.

Also, the wall IOO striptool shows the MC2 Trans QPD Yaw having large step-function features. The MC is having an ok duty cycle, but this just may mean that the WFS are able to absorb what is happening to the MC suspensions.

The suspensions are really misbehaving. We need to get to the bottom of this, or else we are going to keep losing time to alignment.

 ITMX is kicked up periodically.  ITMX_PD_MAX_VAR is lowered to 500 from 1350

It started at Friday morning 8-1

It's great that you guys found the beam.
Yes, ITMX kick and lost communication for TRY were the motivation of my CDS rebooting.

[ericq, Jenne]

We both happened to come by today to fix things up.

When I arrived, the PMC was locked to a 01 mode, which I fixed. The PMC transmission is still worryingly low. MC locked happily. 

ETMX was getting odd kicks, the kind where a DC shift would occur suddenly, and then go away a few moments later. I turned off all dynamic coil outputs, and looked at the MON output of the SOS driver with a scope to try and see if the DAC or dewhitening was glitching, but didn't see anything... Meanwhile, Jenne fiddled with the TTs until we got beams on POP and REFL. (EDIT, JCD:  Useful strategies were to put an excitation onto TT2, and move TT1 until the scattered beam in the chamber was moving at the excitation frequency,  Find the edges of TT2 by finding where the scattered light stops seeing the excitation, and center the beam on TT2.  By then, I think I saw the beam on the PRM face camera.  Then, put a temporary camera looking at the face of PR2.  Using TT2 to center here got us the beam on the POP camera.)

We then walked PRM and the TTs around to keep those two camera beams and get the PRM oplev beam back on its QPD. At this point, ITMX was misaligned (by us), and ITMY aligned to get some recycled flashes into the Y-arm. Y-arm was locked to green, and we poked TTs to get better IR flashes. Misaligning PRM, we had Y-Arm flashes of ~0.7. From there, the michelson and then X-arm were roughly aligned. Both arms were seeing flashes of about 0.7, and the MICH fringes on the AS port look nice.

Frustratingly, the SUS->LSC communication for TRY and TRX isn't working, and could not be fixed by any combination of model or front-end restarting... Thus we haven't been able to actually lock the arms and run ASS. THIS IS VERY FRUSTRATING. 

Additionally, at the point where we were getting light back into the Yarm, the ITMX that were seen on Friday were happening again, tripping the watchdog. Also, something in the Yarm cavity is getting intermittently pushed around, as can be seen by the green lock suddenly wandering off. All of these suspension shenanigans seem to be independent of oplev damping. 

It troubles me that this whole situation is fairly similar to the last time we lost the input pointing (ELOG 10088)

In any case, we feel that we have gotten the IFO alignment to a lockable state.

I was investigating several issues on the IFO. As many of you noticed and not elogged, ITMX had frequent kicking without its oplev servo.
Also I had C1:LSC-TRY_OUT flatted out to zero even though I could see some fringes C1:SUS-ETMY_TRY_OUT.

Restarted all of the realtime models (no machine reboot).

Now I don't find any beam on REFL/AS/POP cameras.

If I look at BS-PRM camera, I can see big scattering, the beam is in the BS chamber.
I jiggled TT1 but cannot find neither a Michelson fringe nor POP beam.

So far I can't figure out what has happened but I'm leaving the lab now.

IMC is locked fine.
I can see some higher order mode of the Yarm green, so the Y arm alignment is no so far from the correct one.

 The PZT actuation on the laser frequency in MHz/V ( assuming the previous calibration here of the PZT count/V) is :

X- arm: 33.7 MHz/V

Y- arm: 14.59 MHz/V

This number seems to be wrong by a factor of 10. 

So we[I and EricQ] decided to trace the cables that run into the ADC from the PZT Out. We found a black LEMO box in the path to ADC,which is  an anti-aliasing filter for each input channel. However,in theory the response of this filter should be flat up until a few kHz i.e. for  the DC gain it should be 1. But we will manually test it and look at the DC gain of the LEMO box.

Koji and Evan have both brought up a good point that we may not be backing up the svn and ELOG properly.

I have modified the rsync.backup script that nodus' cron runs every night that backs up /cvs/cds to what I presume are the tape backups at ldas-cit.ligo.caltech.edu.

Specifically, I added two rsync commands that grab the svn and elog directories from /export/home and copy them to their old locations in /cvs/cds/caltech. This way, the old locations are updated, and the tape backups stay current.

Reasoning to choose the current parameters:

FSS Common: 18dB
FSS Fast: 20dB

Attachment 1:
Openloop transfer function of the IMC loop with the nominal gain setting. The UGF is 176kHz and the phase margin is 48 deg.
This is about 3 time more bandwidth than the previous setting. (Good)

It is visible that the TF has sharp roll off around 1MHz. I wonder if this comes from the demodboard LPF and/or the PMC cav pole.
In fact, according to Manasa, the PMC has the ringdown of 164.6ns which corresponds to the cavity pole of 967kHz. So this must
be there in the OLTF.

From the plot, the order of the low pass is about 5. Subtracting the slope by the cavity pole, the order is four. If I look at the TF of the minicircuits
LPFs (this entry), the phase delay of the filter at 1/10 of the cut off freq is ~30deg. And the order of the filters are maybe 6th elliptic?
So it's not yet clear if the LPF is causing a significant phase delay at 180kHz.

More significantly, the gain margin at ~1MHz is way too small. This is causing a big servo bump at that frequency as seen in Attachment 2.

In total, my recommendation is to move the LPF freq up by x2 or x3, and give a mild LPF above 500kHz.
This requires some modeling as well as try and error.

Attachment 2:

This figure is to explain how the common FSS gain was set. By increasing the gain, the UGF is increased and we can enjoy more supression (from red to purple).
The more gain, however, the more servo bump we observe above the UGF. The gain was chosen so that the total PC feedback does not exceed 3V.

Attachment 3/4:

This figure explains how the fast FSS gain (namely crossover frequency between fast and PC) was set. When the fast is low (red) the phase margin between two loops
are plenty and therefore the openloop TF is smooth. But the PC's frequency domain is large and has to work more (in rms). As the fast gain is increased, the actuation
by the PC is offloaded to the fast PZT (that's good). But eventually the phase margin is not enough and the dip start to show up (purple). This dip cause worse closed loop TF,
as seen in Attachment 4, or even an instability of the loop eventually. So the fast gain was set somewhere in between (green).

The comparison between the new and old MC servo (FSS part) was attached.

- The new servo has the same DC range as before.
  Even though there is 1/2 gain in the chain now, the previous range of the FSS box was 0 to 10V.
  Now it is +/-10V. So we did not lose the range.

- The new servo has x3.2 larger range above 100Hz.

- x1.6 enhancement of the FSS Box output noise above 10Hz.

- The noise of the HV amp (and the summing amp) is x300 and x2600 more filtered at 10kHz and 100kHz respectively.

The summing amp is prepared to allow up to use bipolar full range of the FSS box output

This means that the FSS fast PZT output is now nominally 0V and can range +/-10V.

- FSS Box has the output range of +/-10V

- Thorlabs HV amp MDT694 accepts 0V ~ +10V

- This circuit add an offset of +5V while the main signal is attenuated by a factor of 2. The offset voltage is produced from the voltage reference IC AD586.

- In addition, a summing node and voltage monitors before and after the summing node are provided. They are useful to test the crossover frequency of the fast/PC loops.

- The output noise level at 10kHz was ~60 nV/rtHz. The transfer function of the circuit was measured and flat up to 100kHz. The phase delay is negligible at 10kHz and less than 3deg at 100kHz

- Although the schematic was drawn in Altium, the board is a universal 1U eurocard and all wires were hand soldered.

It seems that the MC auto locker and the FSSSlow PID servo survived a night.

PC Drive is still angry occasionally. We want to know what this is.

- Put the circuit diagram of the sum amp on/in the circuit enclosure and associate it with an elog [done].
- Update the circuit diagram of the pomona box [done]
ALL DONE

To make MC auto locker running correctly, mcdown and mcup were revised

I tried it by unlocking MC several times. It seems OK. Let's see how it works.

Nominal gains for locking (to be taken care by mcdown)

C1:IOO-MC_REFL_GAIN
was 16 and is 19 now.

C1:IOO-MC_VCO_GAIN
was 9 and is 9 now too.

C1:PSL-FSS_MGAIN
was missing and now +13

C1:PSL-FSS_FASTGAIN
was +23.5 and is now +20.0

Nominal gains for operation ( to be taken care by mcup.

C1:IOO-MC_REFL_GAIN
was 19 and is 19 now too.

C1:IOO-MC_VCO_GAIN
was 25 and now uses ezcastep (ezcastep C1:IOO-MC_VCO_GAIN=9 +1,16 -s 0.1)

C1:PSL-FSS_MGAIN
C1:PSL-FSS_FASTGAIN

ezcawrite C1:PSL-FSS_MGAIN `ezcaread -n C1:PSL-STAT_FSS_NOM_C_GAIN`
ezcawrite C1:PSL-FSS_FASTGAIN `ezcaread -n C1:PSL-STAT_FSS_NOM_F_GAIN`

C1:PSL-STAT_FSS_NOM_C_GAIN`  is +18
C1:PSL-STAT_FSS_NOM_F_GAIN`   is +20

- PMC suddenly refused to lock.

- Investigated what's wrong

- Finally, I touched RF Output Adjust (C1:PSL-PMC_RFADJ). Then it started locking.

- C1:PSL-PMC_RFADJ was set to 2.0 by rana when we looked at the PMC LO issue.
  Now PMC does not lock with this value. I set it to 6.0 so that the lock is robust.

- Right before I lost PMC locking, I had some difficulty in locking IMC. Of course,  the robustness of the PMC is related to the robustness of the IMC.
  We definitely need to investigate this. (RF powers, open loop TF, etc)

FSS Slow set point to be zero

op340m:FSS>cat FSSSlowServo
#!/usr/bin/perl -w

# PID Servo for PSL-FSS (Slow)
# Tobin Fricke 2007-01-09

use strict;
#use Scalar::Util qw(looks_like_number);

sub looks_like_number {
    return ($_[0] =~ /^-?\d+\.?\d*$/);  #FIXME
}

use EpicsTools;

# Parameters
my $process  = 'C1:PSL-FSS_FAST';
my $actuator = 'C1:PSL-FSS_SLOWDC';
#my $setpoint = 5.5;
my $setpoint = 0;
my $blinkystatus = 0;
 

op340m:scripts>/opt/rtcds/caltech/c1/scripts/PSL/FSS/FSSSlowServo > /cvs/cds/caltech/logs/scripts/FSSslow.cronlog &

The main IFO modulation frequency was adjusted to match with the FSR of the IMC.

The new frequency is 11.066128 MHz. This corresponds to the IMC round-trip length of 27.0910 m

This has been done by looking at the peak at 25.845MHz (5* fmod - 29.5MHz) in the MC REFL PD mon.

Did this break "netgpibdata"?

I couldn't download data from SR785. Downloading from AG4395A was OK.

The cause seemed the module for SR785

-rw-rw-r-- 1 controls controls   24225 2014-07-30 18:36 SR785.py

I had a local copy of this file and replaced it with mine. Now netgpibdata start working.
The old one is named SR785.py_bak

-rwxr-xr-x   1 controls staff      12944 Jul 31 23:08 SR785.py

The file size is significantly different from the one we had.

Don't leave your food on tables and desks!

Also I put the souvenir chocolates in the microwave, just in case.

Oh, this is cool! Thanks!
I could not figure out how to place robot.txt as it was not so obvious how elogd handles the files in the "logfile" directory.

Quick note:

Migration of the 10Hz pole from the output stage of the FSS to the pomona box was successful.
This also allowed me to insert my offsetting/summing point circuit.

Trial 1:

- Remove C63 (1uF cap) of the FSS

- Short 500 Ohm in the pomona box

This removed 10Hz pole in FSS and 32 Hz zero in the pomona box.
In total we obtain the gain and range of 3.2 for the fast PZT path.

3x10^2 to 3x10^3 times more filtering of the HV amp noise between 10kHz and 100kHz.

The current maximum gains of the FSS is

Overall +19dB (prev. +13dB)
Fast     +30dB (prev +21.5dB)

Trial 2:

- Insert a summing amplifier between the FSS box and the HV amp.

- This amplifier attenuate the input by a factor of 2, and add 5V. i.e. +/-10V input => 0~10V output.

- This just worked fine.

Trial 3:

- Now the fast gain is nominally +30dB.

- In order to provide more room to play with the fast-PC cross over, I moved the pole freq from 2.9Hz to 9.9Hz
  This was done by replacing a 5kOhm in the pomona box by a 1.5kOhm.

Trial 4:

- I just noticed that the output impedance of the FSS (15.8kOhm) and the input impedance of the summing amp (10k Ohm)
  interfere and gives additional 1/2.58 attenuation in addition to the attenuation in the summing amplifier.
  This yields the output range of the HV amp between 45-105V, instead of 0-150V. This is not nice.

- The output impedance of the FSS box (R46 15.8kOhm) was replaced with 100Ohm.

- Now the PMC unlocks very frequently. This might have come from the PMC locking issue or too much gain of the IMC

Trial 5 (final):

- I suspected that the PMC unlock is caused by too much actuation at the high freq. So I decided to revert the  pomona box change

Yesterday elog was excruciatingly slow, and bingbot was the culprit. It was slurping down elog entries and attachments so fast that it brought nodus to its knees. So I created a robots.txt file disallowing all bots, and placed it in the elog's scripts directory (which gets served at the top level). Today the log feels a little snappier -- there's now much less bot traffic to compete with when using it.

We might be able to let selected bots back in with a crawl rate limit, if anyone misses searching the elog on bing.

 Purpose

We wanted to measure the PER of the polarization maintaining fibers, so we could say to what extent they are truly polarization maintaining.

Setup

The experimental setup of this measurement includes: The NPRO, quarter and half wave plates for tuning ellipticity and orientation of the resultant polarization, attenuating optics, two steering mirrors for coupling, a polarizing beam splitter before and after the laser coupled fibers, the coupling assembly and fiber, and a powermeter.

I measured the beam power at all the pertinent locations, shown in the figure below. Note that dots represent S polarization, and orthogonal line segments represent P polarization.

Methods

I first assembled this, coupling the output to a fiber coupled powermeter, in order to adjust the coupling.

Then I needed to couple the fibers to the NPRO, which I did to 39.8%. This gave me enough output power to have a coherent, visible beam. (Visible to non-fiber coupled power meter, and on the viewer card). It was important to be sure that the fast axis of the fiber was aligned in some known orientation. Mine was aligned to the horizontal, using the key on the fiber as an indicator. This is to be certain that the output polarization is consistent with the input.

Once everything was coupled and collimated, I began tuning the polarization of the beam at different points.

Immediately after the NPRO, I used the quarter and half wave plates to first eliminate as much ellipticity as possible, and then turn the polarization to align it with the beam splitter and the fiber axis. I then tuned the first PBS to reflect as little as possible. At the output, I installed the second PBS. Since there was no fine adjustment for the angle of this one, I tuned it using the yaw controls of the 6-axis mount the collimator was held in.

Once all this tuning was done, I took power measurements (displayed above) using the unfiltered, Orion/PD power meter.

Results

From a theoretically completely P-polarized input, the Polarization Extinction Ratio, calculated at 10*log(P/S), was  -24.26 +/-  0.43 dB.

These results can be effected by environmental conditions, such as high tightly wound the cable it, its length, etc.

Moving Forward

The next measurement to make would be to characterize the frequency noise introduced by the fiber.

In addition to this measurement, the setup of the beat note system for FOL can be done as soon as we have more collimator adapters.

These measurements may be important in FOL, and in future experiments that may use these types of apparatuses.

 The PZT seems to saturate at around +/- 3500 counts. So for the Y arm, I excluded the saturated points and fitted the data points again.

As for the calibration number, we expect the 3276.8 count/V for +/- 10 V range of a 16 bit ADC but the number is ~800 count/V. I couldn't figure out a reason why the number is so different.

The new calibration values are :

X- arm PZT : [146.3 +/- 2.37 ]  counts/Volt   (with a 20 dB attenuator included in the path)

Y- arm PZT :  [ 797 +/- 3.6]    counts/Volt  

I will get the calibration in MHz/V of PZT actuation and check whether these numbers make any sense.

1) Don't be brainless. Redo the fitting of the Y arm. Obviously the fit is not good.

2) How can you explain the value from the ADC bit and range?

e.g. +/-10V range 16bit ADC => 2^16/20 = 3276.8 count/V

The Transimpedance plots of PDFR now have a reference plot or baseline plot along with the current measurement, for easy comparision.

Current Work: Getting Matlab's vectfit3 to work simultaneously on the transimpedance readings and print the zeros and poles alongside the plots. 

 Koji asked me to get the calibration of the PZT counts to Volts for the the X and Y ends. Yesterday, I went inside the lab and took some measurements from the digital readout of the PZT by giving in a DC offset(-5 to +5 volts) to PZT_Out and read out from these channels:

For X-end:  C1:ALS-X-SLOW_SERVO1_IN1

For Y-end:  C1:ALS-Y-SLOW_SERVO1_IN1

Since a 20dB attenuator was placed in the path of X-arm readout while taking the Transfer functions(Detail), I did the calibration measurements without removing it from the path. However, for the Y arm there was no attenuator in the readout path.

The obtained calibration values are :

X- arm PZT : [146.3 +/- 2.37 ]  counts/Volt 

Y- arm PZT :  [ 755.1 +/- 3.6]    counts/Volt

The attached are the fit and data plots for the above calibration.

 Last night, I poked around to try and see if I could reproduce the sketchy MC behavior by exciting MC2 in a way that may be similar to what we do when using it as a CARM actuator. 

The short of it is that at frequencies under 1k, the MC lock didn't mind MC2 position excitations up to 8000 counts. However around 4-5k, a 1000 count excitation would induce a good deal of low frequency (2-5Hz) activity in the MC trans power, causing it to fluctuate by thousands of counts before unlocking. If I turned the excitation off before the unlock, it would eventually settle back down, but not immediately. 

I was able to reproduce this a handful of times before it decided to stop locking altogether, perhaps because of its random mood swings, or perhaps because this kind of disturbance is related to the mood swings...

- ALS X/Y arm stability was checked by IR locked arms.

- Basically the stability looks same as before.

Q sez: here are some ALS ASDs (in Hz/rtHz). 

The reference plots are with the arms locked on CARM/DARM with ALS. The main traces are with the arms locked on POX/POY. Alignment affects these traces a fair amount.

The X arm ALS seems no worse for the upgrade, and the PZT actuators do look pretty orthogonal when we play around with the alignment. 

- The cable for the beat note was disconnected from the frequency counter and reconnected to the spectrum analyzer.

- PMC/IMC had not been locked for 8 hours. 

- PMC was relocked.

- IMC got immediately relocked. Today IMC relocks very fast.
C1:IOO-MC_REFL_OFFSET -0.238
C1:PSL-FSS_INOFFSET -0.94

- Went to the ETMX table. Aligned the oplev beam on the QPD

- The X end green beam was realigned to the cavity.
I can feel that the two mirrors provides quite independent alignment adjustment. VERY NICE.
Green TRX: without PSL Green - 0.612, with PSL green - 0.725

I can clearly see that the mode matching is not ideal. All the higher modes are LG modes!
The input mode is very round.

- Arm cavities were aligned by ASS

- Tested ASX. PZT2 Pitch/Yaw servos run with the previous setting. We still can maximize the transmission by touching PZT1.

- Now Eric joined the activity.

-  Once the beam is aligned what we could lock was LG00/10/20/30.
   We measured the power in LGn0 modes
   LG00: 0.588
   LG10: 0.154
   LG20: 0.053
   LG30: 0.020

   This suggests that the mode-matching ratio is something like 70%

- Q is aligning the PMC. PMC transmission prev 0.783. Basically we could not improve it.
We thought this number can go up to ~0.82 or even ~0.84. We wonder if this comes from the decay of the laser power or reduced visibility?

In fact there is a pomona box between the HV amp and the laser.
It is expected that the combination of the box and the laser PZT (2.36nF by Elog #3640) provides poles at 2.9Hz and 148kHz and a zero at 32Hz.
Basically, the gain of this stage is 0.1 at 10kHz. So the injected noise is reduced by factor of 10. It is just barely OK.
I need a bit more careful design of the output stage for the MC servo.

 Purpose

These telescopes will be used to mode match//couple the dumped SHG light from both PSL and AUX (Y-Arm) lasers into PM fibers for use in FOL.

Methods

Using the waist measurements I made yesterday (29/7/14) as seed waists, I used a la mode to design coupling telescopes.

These are designed to match the output mode of the fibers with collimators.

ALM files are attached in .zip file.

Moving Forward

Once the fibers are coupled, I will continue in assembling the Y-Arm FOL setup, using fiber coupled beam combiner and photodiodes.

I will also do the same procedure for the X-Arm, access permitting.

 The goal of the measurements we made ( my previous 3 elogs) was to characterize the laser frequency thermal actuator that is a part of the FOL- PID loop.

For this we made indirect TF measurements for the thermal actuator by looking at the PZT response by 1)arm cavity( ETM ,ITM) displacement  and 2) temperature offset excitation. The goal was to do something like getting G1=TF3/TF1 and G2=TF3/TF2 and ultimately dividing G2/G1 to get TF2/TF1 with correct calibration. The final TFs obtained are the X and Y arm TFs for Laser frequency response vs temperature offset in(HZ/count). The calculations  in detail are:

Obtained    G1 = PZT response/ Temperature Offset (count/count): (in detail here )

Obtained    G2 = PZT response/  X and Y arm displacement( count/ count) : (in detail here)

Calibrated G2 to count/m ( in detail here)

Divided G2/G1 to get X and Y arm displacement/ Temperature Offset( m/ count) to get G3

Did these calculations:

dL/ L = dF /F

F = c/lambda ;Lambda = 532 nm  ; L = 

X arm length = 37.79 +/- 0.05 m

Y arm length = 37.81 +/- 0.01 m

TF: Laser Freq/ Temperature Offset = G3 *F/L       (HZ/Count)

The calibration coefficients for the ends  are :

X End:  [23.04 +/-  0.23 ]* 10^3  (HZ/Count)

Y End:    [18.71 +/-  0.2 ]* 10^3 (HZ/Count)

For the TFs of the temperature actuator on laser frequency I used ITMs for both the arms. The bode plots for the calibrated( HZ/Temp Count) are attached.

 For the X-Arm Thermal Actuator, I calculated the TFs at two different frequency ranges and combined the results where the coherence is high(>0.7). At 1 Hz the coherence was not as good as the other frequencies(due to the suspension resonance at 0.977 Hz).

The poles and zeroes are estimated after fitting this data using Matlab vectfit tool.The  graphs showing fit and measured values are attached.

Y arm Thermal Actuator:

5th order TF fitted: 

Gain: 9000

Zeroes:

z1 = -0.9799;

z2 = 2.1655; 

z3 = -2.9746- i * 3.7697

z4 = -2.9746+ i * 3.7697

z5 =  95.7703 + 0.0000i 

Poles:

p1 = -0.0985- i* -0.0845

p2 = -0.0985+ i* -0.0845

p3 = -0.6673- i* -0.7084

p4 = -0.6673+ i* -0.7084

p5 = -8.7979.

X-arm Thermal Actuator:

5th order TF fitted: 

Gain = 20

Zeroes:

z1= -305.7766

z2 =   -18.2774

 z3 =  -16.6167

 z4 =   -1.2486

 z5 =   28.1080

Poles:

p1  = -0.1311 - 0.1287i

p2 =  -0.1311 + 0.1287i

 p3  =  -8.3797 + 0.0000i

 p4 =  -4.0588 - 7.5613i

  p5 = -4.0588 + 7.5613i

I will use get the poles and zeroes from these fitted  bode plots and use it to build the PID loop.

 Plan for the week:

• PID loop design and testing with the Green laser beat note by actuating the arm cavity length.
• Beat note readout on MEDM screens and Strip tool.
• Calibration of the laser frequency response to PZT signal in MHz/V using a test DC input(Koji assigned me this task because this calibration has not been done and is very useful).

Inside the Lab:

• Placing the FOL box sometime in the afternoon today(with supervision of Manasa / EricQ).
• Calibration of the PZT(Today or tomorrow).

Green Steering Mirror Update

Yesterday, Nick and I completed the green steering mirrors upgrade. I attached the file that contained the procedure that we plan before we did the upgrade. We placed an iris at the input of the OL and we place another iris before the harmonic separator. We did not use the beam scanner because someone was using it, so what we did was to assume that the cavity is well align and place the iris so that we can recover the alignment. We used the measuring tape to approximate as close as we could the position where the lenses were supposed to go. I did a measurement of the derivative of the waist size in terms of the position of the lens and the derivative of the waist Position in terms of the lenses position at the optimum solution that a la mode give us. Because of this plot, we decide to mount lens 3 and lens 5 into translational stages. After mounting each lenses and mirrors we worked on the alignment of the beam into the cavity. We were able to align the green into the cavity and we were able to locked the cavity to the TEM00 mode. We started to work on the optimization of the mode matching. However, the maximum mode matching that we got was around 0.6, which we need to work a little bit more on the tuning of the mode matching. We leave the iris mounted on the table. I took a picture of the table, and I attached below. For the OL, we just make sure that the output where somehow hitting the QPD, but we didn't really I aligned it. We need to work a little bit more on the alignment of the OL and the tuning of the mirror to maximize the green mode matching.

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.

From old 40m elog 5-29-2007

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.

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. 

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

 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.

 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)