[Jenne, Yuta]

Summary:
  We tried to see the Yarm length change using Yarm green beat note. The beat note is still puny, so we put an extra amplifier. We saw something, but still can't control the arm length with ALS.

What we did:
  1. Aligned Y arm and PSL green optics as usual.

  2. By changing the temperature of the PSL laser with C1:PSL-FSS_SLOWDC, we find small beat note when

  PSL laser temperature on display: 30.59 deg C (PSL HEPA 100%)
  C1:PSL-FSS_SLOWDC = 5.2100
  Y end laser "T+": 34.049 deg C
  Y end laser "ADJ": 0
  Y end laser measured temperature: 34.68 deg C (*)
  C1:GCY-SLOW_SERVO2_OFFSET = 29425

 (*) Measured using diagnostic output on the back of the laser controller(Lightwave 125/6-OPN-PS) - between pins 2(GND) and 4. Calbration factor is 10 degC/V.

  3. The peak height right after the amplifier on the Y green beat PD was ~ -48dBm, so we put another amplifier (and attenuator) because the beat note which goes into the frequency divier should be -30 dBm to +7 dBm. After we put the amplifier, the peak height was ~ -23 dBm.

  4. We could see the C1:ALS-BEATY_COARSE_I_ERR ringing down, when opening and closing the control room door, which may introduce Y arm length change(screenshot of dataviewer below). But we are still not sure if we are actually getting the Y arm length signal because closing and opening Y end green shutter doesn't make difference on C1:ALS-BEATY_COARSE_I_ERR. The ring down was seen when we turned on the unWhiten filters in C1:ALS-BEATY_COARSE filter modules.



  5. Tried to hold Y arm length with ALS, but couldn't.

Current setup:
  Red ones are the ones we added or changed.



Note:
  Dataviewer is so slow and flakey now.

Summary:
  Y arm green transmission to the PSL table improved from ~ 20 uW to 61 uW. Improvement was done by adjusting steering mirrors before and after the faraday on the Y end table.
  But 61 uW is not enough!

What I did:
  1. The incident power to the faraday for the green beam on the Y end table was 1.4 mW, but the transmission was 1.2 mW. So, I adjusted the steering mirrors and the transmission increased to 1.4 mW.

  2. I found that adjusting the steering mirrors to the faraday also increased alignment of the green beam to the Y arm. We always adjusted only the steering mirrors after the faraday for the alignment. I adjusted the alignment using both steering mirrors this time. Reflection of the green beam on the ETMYT camera seems more reasonable now and more frequently lock to TEM00 when closing and opening the Y end green servo loop.

  3. For the adjustment, I tried to utilize PD at the reflection port, or the transmission port. However, I couldn't do that because they fluctuates too much. I don't know why.

  4. Measured the green transmission to the PSL table, The transmitted power was ~20 uW, but after the aligning, it improved to 61 uW.

Current green power:
  I measured the green beam power at various places using Newport power meter (Model 840) with its filter on.



  Incident green power to the Y arm is ~ 1 mW (more than 1 mW because the aparture of the power meter was smaller than the beam size) and Y arm transmission is designed to be 55%. So, if the alignment and mode matching are perfect, the transmission to the PSL table should be ~ 600 uW. The measured value 61 uW seems too small. Kiwamu says it was 140 uW when he did Y arm.

Next:
  I will find the beat note again tonight and check if the beat PD is working correctly and if the mode matching of the two beams at the PSL table is good.

I found the big big Y green beat. Details will be posted later.

[Koji, Yuta]

Summary:
  We improved the Y arm green transmission to the PSL table. It is now 197 uW.
  The improvement was done mainly by adjusting the Y arm green servo gain.

What we did:
  1. Fine-adjusted steering mirrors after the faraday on Y end table by monitoring Y arm green transmission (used Thorlabs PDA36A as a PD, C1:GCV-GREEN_TRY as a channel). We decided which way to adjust the mirrors by just pushing/pulling its mount.

  2. The output of the reflection PD on the oscilloscope seemed like the Y end frequency servo was oscillating. So, we reduced the amplitude of the frequency modulation from 2.83 V to 0.13 V.

  3. We noticed there were two TEM00, one is brighter and the other is dim. We thought this came from a mode-hopping or something. So, we changed the Y end laser temperature from 34.68 deg C to 34.13 deg C (measured). This reduced dim TEM00 and the main one got brighter. C1:GCY-SLOW_SERVO2_OFFSET was changed from 29425 to 29845.

  4. Fine-adjusted the position of the mode-matching lens by reduing LG modes.

Current green power:
  Current measured green power values are as follows.



  Calculated value for the Y arm green transmission is ~ 600 uW, but we think we are almost at the maximum we can get. So, we have about 70% loss from the Y end table to the PSL table. There may be large loss in windows. The beam shape of the transmitted beam seems OK, but there may be some clipping.

To do:
  - Fine tune the Y end frequency servo loop. Reducing the amplitude of the frequency modulation for reducing the gain is not a very good idea.

Summary:
  I found the big green beat note for the Y arm. The alignment of the green optics on the PSL table was crappy.

What I did:
  1. By adjusting PSL laser temperature, I found tiny beat note when

  PSL laser temperature on display: 31.35 deg C (PSL HEPA 100%)
  C1:PSL-FSS_SLOWDC = 1.75

and

  PSL laser temperature on display: 33.21 deg C (PSL HEPA 100%)
  C1:PSL-FSS_SLOWDC = -6.82

Y end laser temperature settings are fixed as follows during the measurement.

  Y end laser "T+": 34.049 deg C
  Y end laser "ADJ": 0
  Y end laser measured temperature: 34.13 deg C (*)
  C1:GCY-SLOW_SERVO2_OFFSET = 29845

Bryan's formula (swapped one; see elog #6746),  suggests the paring

  (Yend laser temp, PSL laser temp) = (34.13 deg C, 31.09 deg C).

  2. Checked that beat PD is working by swapping the beat PDs for Y arm and X arm.

  3. Checked that the mode-matching of the two beams, one from Y arm and the other from PSL, is OK by moving mode-matching lens and measuring the beam spot size at near/far field are the same.

  4. When checking the beam spot size at far field(~ 1 m from the BS), I noticed the relative beam tilt by ~ 1 mrad. We aligned them few days ago, but I think the green beam from the Y arm has shifted. Of course we align IR to the Y arm first, but we difinitely need dither servo or A2L for the arm, too.

  5. As soon as aligning the PSL green optics near the BS, I found a large beat note. The measured amplitude was ~ -26 dBm, without any amplifiers after the PD.

  Currently the measured green beam power onto the beat PD from Y end is 75 uW and from PSL is 92 uW. So the calculated beat amplitude will be ~ -10 dBm (see calculation in elog #6746). So there is about 84% loss. Anyway, I will go on to the mode scan.

I coarsely stabilized Y arm length to off resonance point for IR using ALS.
Currently, ASL servo loop is unstable and oscillates so much that I can't hold the length to the resonance point.
We need more investigation on the servo loop before doing the mode scan.

Below is a snapshot of ALS medm screens and time series data of the error signal for ALS coarse loop (C1:ALS-BEATY_COARSE_I_ERR) and IR transmission for the Y arm (C1:LSC-TRY_OUT) when I turned the servo on.

Note:
  I took off amplifiers right after the beat PD on PSL table.
  Also, I reverted the gain change Jenne made last night (elog #6750), because they no longer show overload lights.

Yes. The end PDH servo should be checked more carefully.

The end PDH seems to have insufficient gain at around 100Hz.
The attached is the ALS noise budget calculated with the simulink model for the green locking paper.

The residual error of the end AUX laser (green) is contributing to the final ALS signal (black).
In particular, the residual AUX frequency noise, which is shown as the blue, is contributing to the noise above 100Hz.

In the model I also confirmed that the servo still has a room for improvement.

By having more suppression of the AUX frequency noise, we will be able to increase the ALS servo bandwidth
without increasing the ALS residual RMS by a servo bump. This will give us the improvement of the seismic
noise suppression at 10Hz (i.e. more suppression of red).

Laser temperature settings for Y arm green work today are;

  PSL laser temperature on display: 31.38 deg C (PSL HEPA 100%)
  C1:PSL-FSS_SLOWDC = 1.68
  Y end laser "T+": 34.049 deg C
  Y end laser "ADJ": 0
  Y end laser measured temperature: 34.13 deg C (*)
  C1:GCY-SLOW_SERVO2_OFFSET = 29845

Green transmission from Y end and PSL green power on the beat PD are;

  P_Y = 28 uW
  P_PSL = 96 uW

P_Y decrease from its maximum we got (75 uW, see elog #6777) is because the alignment for Y arm green is decreased. I can see the decrease from the green reflection on ETMT camera, but I will leave it because we already have enough beat.

I aligned PSL optics, including the mode-matching lens to maximize the beat note. The beat note I got is about 26dBm.
The calculated value is -14 dBm, so we have about 75 % loss.
I measured the reflection from the PD window and its reflectivity was about 30%. We still have unknown 45% loss.

Summary:
  We need I-Q frequency deiscriminator to control the arm length fine and continuously.
  I checked the beatbox (LIGO-D1102241-v4; see elog #6302) and it was working.

What I did:
  1. Measured some transferfunctions with a network analyzer (Aligent 4395A) and checked the cabling is correct.

  2. Put 30 m/1.5 m delay line and checked I-Q outputs are actually orthogonal. I did this by sweeping the frequency of RF input to the beatbox. See attached picture. You can see nice circle on the oscilloscope.

Some measurement results:
  - Gains of the transferfunctions(@ 10-100MHz) between;

   RF in -> RF mon: -25 to -20 dB
   RF in -> fine delay out: -50 to -40 dB
   RF in -> coarse delay out: -50 to -40 dB
   RF in -> LO of mixer RMS-1: ~ +4 dB  (RMS-1 needs +7 dB LO)
 
  - 30m delay line(RG-142B/U) had -2 dB loss.

Note:
  - RF input must be larger than about -3 dBm to get enough LO to the mixer. Otherwise, you won't get I-Q outputs.
  - The comparator, whitening filter and differential DAQ outputs are not installed in the current beatbox.
  - Current beatbox only has electronics for the one arm.
  - The print on the board D1102241 says +15V and -15V, but they are actually opposite. Cabling is swapped in order to supply correct power to the ICs.

[Jenne, Yuta]

We aligned Y arm to the Y end green incident beam.
We noticed two TEM00, bright and dim, so we decreased Y end laser temperature to 34.13 deg C.
It doubled the transmission of the green, and now the transmission to the PSL table is 178 uW, which is close to the maximum(197 uW) we got so far.

Current settings for Y end laser is;

  Y end laser "T+": 34.049 deg C
  Y end laser "ADJ": 0
  Y end laser measured temperature: 34.13 deg C
  C1:GCY-SLOW_SERVO2_OFFSET = 31025
  Y end slow servo: on (was off)

We aligned IR beam to the Y arm by mostly adjusting PZTs and got the transmission, C1:LSC-TRY_OUT ~ 0.9.

We tried to calculate the mode-matching ratio for IR by taking TRY data while ITMY and ETMY are swinging (without ALS), but it was difficult because we see too many higher order modes.

Tomorrow, we will (1) connect the beatbox to ADC, (2) edit c1gcv model, (3) scan the arm using I-Q signals.

Yuta added channels so we can get the Q phase of all the beat PDs to the c1gcv model.  I showed him how to recompile/install/start.

During the install, it couldn't find: Unable to find the following file in CDS_MEDM_PATH: LOCKIN_FILTER.adl

On all the screens (ALS and SUS), lockin parts are white.  Someone changed something, then didn't go back to fix the screens.

Otherwise, things look to be working fine.

[Jamie, Yuta]

We recompiled c1gcv because the order of the channels were confusing. We found some change in the phase rotation module when we did this.

I did some cabling and checked each signals are actually going to the right channel. I labeled all the cables I know, which go into the AA chasis for ADC1 of c1ioo machine.

Below is the list of the channels. If you know anything about "unknown" channels, please let me know.

Current channel assignments for ADC1 of c1ioo machine:
  Red ones were added today. Green ones existed in the past, but channel assignment were changed.

Memorandum for me:
  Recompiling procedure;

ssh c1ioo

rtcds make c1gcv
rtcds install c1gcv
rtcds start c1gcv

[Mengyao, Yuta]

Yes!! We have I-Q signals for the beat!!

What we did:
  1. Aligned Y arm to the Y end green incident beam. The transmission to the PSL was about 195 uW.

  2. Aligned IR beam to the Y arm by adjusting PZTs and got the transmission, C1:LSC-TRY_OUT ~ 0.86.

  3. Aligned green optics on the PSL table to get the beat signal. The beat was found when;

  PSL laser temperature on display: 31.41 deg C
  C1:PSL-FSS_SLOWDC = 1.43
  Y end laser "T+": 34.049 deg C
  Y end laser "ADJ": 0
  Y end laser measured temperature: 34.14 deg C
  C1:GCY-SLOW_SERVO2_OFFSET = 29950
  Y end slow servo: off (was on)

  4. Connected the beat PD output to the beatbox.

  5. Kicked ETMY position to change the cavity length and while the ringdown, we run pynds to get data. We plotted C1:ALS-BEATY_FINE_I_ERR vs C1:ALS-BEATY_FINE_Q_ERR, and C1:ALS-BEATY_COARSE_I_ERR vs C1:ALS-BEATY_COARSE_Q_ERR (below). We got nice circle as expected.



Current setup:
  Only AA filers are put between the output of the beatbox and the ADC.

I stabilized Y arm length by using only I phase coarse signal from the beat(C1:ALS-BEATY_COARSE_I_ERR).
I sweeped the arm length by injecting 0.05Hz sine wave from C1:ALS_OFFSETTER2_EXC.
Below is the plot of TRY and the error signal(ideally, Y arm length) while the sweep.



I couldn't hold the arm length tight, so you can see multiple peaks close to each other.
We need to
  - adjust offsets
  - adjust rotation phase of I-Q mixing
  - adjust servo filters
to hold the length tighter.

Also, I couldn't sweep the Y arm length very much. I need to calibrate, but to do the modescan for many FSRs, we need to
  - introduce automatic phase optimizing system
There were sin/cos function in the CDS_PARTS, so I think we can feedback I_ERR to control rotation phase of I-Q mixing.

 That sounds goofy.

With the delay line technique, you can get a linear signal over 50 MHz with no phase shifting. What is with all this I/Q stuff?

Linear range df of the delay line technique is about df ~ c/(2D). So, the linear range for the fine signal(delay line length D=30m) is about 5 MHz.
Arm cavity FSR = c/(2L) = 3.7 MHz.
So, I think we need phase shifting to do mode scan for more than 2 FSRs by holding the arm length finely with fine servo.
For the coarse (D=1.5m), the linear range is about 100 MHz, so if we can do mode scan using coarse servo, it is OK.

In any case, I think it is nice to have linear signal with fixed slope even if we don't adjust the phase every time.

You can easily calculate whether or not the coarse readout will work by thinking about the scan resolution you need given the ADC dynamic range and the whitening filter that you use.

[Jenne, Yuta]

We put 0 dBm sine wave to the RF input of the beatbox and linear-sweeped frequency of the sine wave from 0 to 200 MHz using network analyzer (Aligent 4395A).
(We first tried to use 11 MHz EOM marconi)

Whlile the sweep, we recorded the output of the beatbox, C1:ALS-BEATY_(FINE|COARSE)_(I|Q)_IN1_DQ. We made them DQ channels today. Also, we put gain 10 after the beatbox before ADC for temporal whitening filter using SR560s.

We fitted the signals with sine wave using least squares fit(scipy.optimize.leastsq).
Transision time of the frequency from 200 MHz to 0 Hz can be seen from the discontinuity in the time series. We can convert time to frequency using this and supposing linear sweep of the network analyzer is perfect.

Plots below are time series data of each signal(top) and expansion of the fitted region with x axis calibrated in frequency (bottom).





We got

C1:ALS-BEATY_COARSE_I_IN1_DQ = -1400 sin(0.048 freq + 1.17pi) - 410
C1:ALS-BEATY_COARSE_Q_IN1_DQ = 1900 sin(0.045 freq + 0.80pi) - 95

C1:ALS-BEATY_FINE_I_IN1_DQ = 1400 sin(0.89 freq + 0.74pi) + 15
C1:ALS-BEATY_FINE_Q_IN1_DQ = 1400 sin(0.89 freq + 1.24pi) - 3.4

(freq in MHz)

The delay line length calculated from this fitted value (supposing speed of signal in cable is 0.7c) is;

  D_coarse = 0.7c * 0.048/(2*pi*1MHz) =  1.6 m
  D_fine = 0.7c * 0.89/(2*pi*1MHz) = 30 m

So, the measurement look quite reasonable.

FINE signals looks nice because we have similar response with 0.5pi phase difference.
For COARSE, maybe we need to do the measurement again because the frequency discontinuity may affected the shape of the signal.

[Jenne, Koji, Yuta]

We tried to scan of the Y arm but we couldn't scan for more than 1FSR.
In principle, we can do that because the error signal we are using, C1:ALS-BEATY_COARSE_I_IN1, has the range of ~ 40 MHz, which is about 10FSR (see elog http://nodus.ligo.caltech.edu:8080/40m/6815).

ALS stays for more than 10 min when we don't do the scan. If we put some offset gradually from C1ALS-OFFSETTER2, the lock breaks.
We monitored PZT output of the Y end laser, C1:GCY-SLOW_SERVO1_IN1, but it stayed in the range when scanning. So, there must be something wrong in the ALS loop.

Current in-loop arm length fluctuation is about 0.1 nm RMS (0.5 counts RMS).
Below is the spectrum of the error signal when the ALS is off(green) and on (pink,red). Below ~ 50 Hz, the measurement of the Y arm length is limited by ADC noise (~ 2uV/rtHz).

[[Requirement]]
 Arm cavity FWHM for IR is

  FWHM = FSR / F = c/(2LF) = 8 kHz.

 In cavity length, this is

  L/f * FWHM = 40m/(c/1064nm) = 1.2 nm

 So, to do mode scan nicely, arm length fluctuation during resonant peak crossing should be much less than 1.2 nm.


[[Diagram]]
 Let's consider only ADC noise and seismic noise.


* S: conversion from Y arm length to the beat frequency

  dL/L = df/f

 So,

  S = df/dL = f/L = c/532nm/40m = 1.4e7 MHz/m


* W: whitening filter

 We set it to flat gain 50. So,

  W = 50


* D: AD conversion of voltage to counts

 D = 2^16counts/20V = 3300 counts/V


* B: frequency to voltage conversion of the beatbox.

 We measured BWD(elog #6815). When we measured this, W was 10. So, the calibration factor at 0 crossing point(~ 50 MHz) is

  B = 1400*0.048/10/D = 0.0021 V/MHz


* A: actuator transferfunction

 I didn't measure this, but this should look like a simple pendulum with ~ 1 Hz resonant frequency.


* n_ADC: ADC noise

 ADC noise is about

  n_ADC = sqrt(2*LSB^2*Ts) = sqrt(2*(20V/2^14)**2*1/64KHz) = 1.6 uV/rtHz


* n_seis: seismic noise

 We measured this by measuring C1:ALS-BEATY_COARSE_I_IN1. This is actually measuring

  D(WBSn_seis + n_ADC)

 Calibrated plot is the red spectrum below.


* F: servo filter (basically C1:ALS-YARM)

 We need to design this. Stabilized arm length fluctuation is

  x_stab = 1/(1+G)*n_seis + G/(1+G)*n_ADC/(WBS)

 where openloop transferfunction G = SBWDFA.
 Below ~ 50 Hz, n_seis is bigger than n_ADC/(WBS). We don't want to introduce ADC noise to the arm. So, UGF should be around 50 Hz. So, we need phase margin around 50 Hz.
 We also need about 10^3 DC gain to get the first term comparable to the second term.

 Considering these things, openloop transferfunction should look like the below left. Expected error signal when ALS on is the below right. I put some resonant gain to get rid of the peaks which contribute to the RMS (stack at 3.2Hz, bounce at 16.5 Hz).
 Inloop RMS we get is about 0.3 nm, which is only 4 times smaller than FWHM.




[[Discussion]]
 We need to reduce RMS more by factor of ~ 30 to get resolusion 1% of FWHM.
 Most contributing factor to the RMS is power line noise. We might want comb filters, but it's difficult because UGF is at around this region.

 So, I think we need more fancy whitening filters. Currently, we can't increase the gain of the whitening filter because SR560 is almost over loading. Whitening filter with zero at 1 Hz might help.

[Jenne, Yuta]

We couldn't scan the Y arm for 1FSR last night because the ALS servo breaks while sweeping.
We thought this might be from the amplitude fluctuation of the beat signal. The amplitude of the beat signal goes into the beatbox was about -5 dBm, which is not so enough for the beatbox to get good LO. So, we put an amplifier (and attenuators) and the amplitude became +1 dBm. The range beatbox can handle is about -3 dBm to +3 dBm, according to our calculation.

This increased stability of the lock, and we could scan the arm for 1FSR. Below is the plot of scanned ALS error signal (blue), Y arm IR PDH signal (green) and TRY (red).



For each slope, we can see two TEM00 peaks, some higer order modes(may be 01, 02, 02) and sidebands (large 11MHz, small 55MHz?).

We couldn't scan for more. This is still a mystery.

Also, we need to reduce residual Y arm length fluctuation more because we get funny TRY peak shape.

Scan speed:
  For C1:ALS-BEATY_COARSE_I_IN1, 1 count stands for 0.21 nm(see elog #6817). We sweeped 4000 peak to peak in 50 sec. So, the scan speed is about 17 nm/sec.
  This means it takes about 0.06 sec to cross resonant peak.
  Cavity build up time is about 2LF/(pi*c) ~ 40 usec. So, the scan is quasi-static enough.
  Characteristic time scale for the Y end temperature control is about 10 sec, so Y end frequency is following the Y arm length change with temperature control.

  Currently, sampling frequency of DQ channels are 2048 Hz. This means we have 100 points in a TRY peak. I think this is enough to get a peak height.

Next step:
  - Reduce RMS. We are trying to use a whitening filter.
  - Find why we can't scan more. Why??
  - ETMY coil gains may have some unbalance. We need to check
  - Characterize Y end green frequency control. Koji and I changed them last week (see elog #6776).
  - Calculate positions of RF SBs and HOMs and compare with this result.

I scanned Y arm for 5FSR (below).
I could done this after I put a whitening filter.
Currently, whitening filter between the beatbox and AA filter is made of

  Ponoma blue box(passive filter with zero at 1 Hz, pole at 10 Hz) + SR560(flat gain 100)

I couldn't do more than 5FSR because SR560 overloads. I checked it by staring at the indicator during the scan.
Reason why we kept loosing lock last night was the overload of  SR560. Mystery solved!

Anyway, 5FSR is enough.
Our next step is to reduce residual arm length fluctuation.

Also, I increased the alingnment of IR. So, the higher order modes are less than the last scan.

Interesting. It seems for me that there is a dependence of the noisiness as the beat frequency is scanned.

As you increase (or decrease?) the offset, C1:ALS-BEATY-COARSE_I_IN1 becomes bigger and more crisp.
The resulting out-of-loop stability also seems to be improved as you can see from the crispness of the PDH signal.

Do you find why this happens? Is this because the beat S/N depends on the beat frequency due to the PD noise?

ADC noise is not a limiting noise source in a current ALS setup.

Below is the calibrated spectrum of C1:ALS-COARSE_I_ERR when
  Y arm swinging with just damping (red; taken last night)
  terminated before AA (green)
  blocked PSL green beam (blue)

Blue and green curve tells us that noise from the beat PD to ADC is not contributing to the Y arm length sensing noise.

[Mengyao, Yuta]

Last night, I used 1.5 m delay line COARSE and got 5FSR mode scan. The range 5FSR was limited by the range of SR560.
So, this time, we used 6.4 m(21 feet) cable as a delay line for FINE servo. This should increase the sensitivity by factor of 4. But the range will be 4 tmes smaller, ~ 1.3FSR.

Below is the plot of the mode scan.
You can see the peak height difference between TEM00s, but it's just from the resolution of pixels.

You still can see noisiness goes up when blue plot goes down. But this time, 2000 stands for 27 MHz and -2000 stands for 15 MHz in the beat frequency because we flipped the filter gain this time.
Last night, the top of the triangle was about 40 MHz and bottom was about 60 MHz.




We are going to derive mode-matching and some cavity parameters using this plot.

Is that time stamp really correct? I wanted to look at the signal closely to see if I could get any feeling for why it would look so different when positive vs. negative, but I do not see a triangle anywhere near this time (1023780144)...

 Yes. I used pyNDS to get data, but here's a screenshot of dataviewer playing back 300 seconds from GPS time 1023780144.

Calibrating error signal to beat frequency;
  I injected 0 dBm RF sine wave into the beatbox and sweeped the frequency(just like we did in elog #6815).
  This time, we have different whitening filters. I sweeped the frequency from 0 to 100 MHz in 200 sec.
  The length of the delay line is ~1.5 m for COARSE.


Y arm length;
  Here, I think we need some assumption. Let's assume wavelength of IR lamb_IR = 1064 nm and Y end green frequency is nu_g = 2*nu_IR.
  There is a relation
    dnu_g / nu_g = dL / L
  So,
    dnu_g / (dL/lamb_IR) = 2*nu_IR * lamb_IR / L = 2c/L
  We know that dL/lamb_IR = 1/2 for difference in beat frequency between TEM00s. Therefore, slope of the dnu_g vs dL/lamb_IR plot gives us the arm length L(figure below, middle plot).

  Error estimation is not done yet, but I think the COARSE_I_IN1 error signal to the beat frequency calibration has the largest error because it seems like the amplitude of sine wave changes ~10% day by day.

Calibrating beat frequency to Y arm length change;
  I used L = 32.36 m (figure above, bottom plot).
    dnu_g / dL = c / lamb_g / L = 1.74 MHz/m

Wow. This is way too short.

You don't need to use Albertoo's arm length as his measurement was done before the upgrade.

I know!
But I think there's some error (~ 10% ?) in calibrating the beatbox. In elog #6815, slope near zero crossing point is about 68 counts/MHz, but now, its 60 counts/MHz. Also, zero crossing point in elog #6815 was 47 MHz, but now, its 45 MHz. 5FSR scan was done between these two calibration measurement.

I analyzed mode scan data from last week.
Mode matching ratio for Y arm is 86.7 +/- 0.3 %. Assuming we can get rid of TEM01/10 by alignment, this can be improved up to ~ 90%.

Peak search, peak fitting and finnesse calculation:
  I made a python script for doing this. It currently lives in /users/yuta/scripts/modescanresults/analyzemodescan.py.
  What it does is as follows

  1. Read mode scan data(coarse5FSRscan.csv, fine1FSRscan.csv). Each column in the data file should be

[time] [some thing like C1:ALS-BEAT(Y|X)_(COARSE|FINE)_(I|Q)_IN1] [C1:LSC-POY11_I_ERR] [C1:LSC-TRY_OUT]

Each separated by comma. Currently, this script uses only TRY, but it reads all anyway

  2. Find peak in TRY data. For the peak search, it splits data in 1 sec and find local maximum. If the local maximum is higher than given threshold, it recognize it as a peak. If two peaks are very close, it uses higher one. This sometimes fails, because mode scan data we have is not so nice.

  3. Fit each peak with Lorentzian function,

TRY = a*b/(4*(t-c)^2+b^2) + d  (a>0, b>0)

  where a/b is a peak height, b is a linewidth (FWHM), c is a peak position in time, and d is a offset.
  I don't like this, but currently, a/b+c is fixed to the maximum value of TRY data used for fitting. This is because sometimes TRY data is so bad and I couldn't get the peak height correctly. Each points of TRY data doesn't have same error because cavity length is fluctuating and relation between cavity length and TRY is not linear. I think I should use some weighting for the fit, but currently, I just use least squares.

  4. Find TEM00 and calculate FSR in "seconds". I just used "seconds" assuming we did a linear sweep. This script recognize TEM00 from the given threshold.

  5. Calculate finesse using FSR and linewidth of the closest TEM00.

  Below are the result plots from this analysis. Calculated finesse looks quite high (~1000). I think this is from non-linearity in the sweep and error in "measured" line width.



Higher order modes and RF sidebands:
  Assuming the curvature of ITMY/ETMY are flat/57.5 m, Y arm length is 38.6 m(FSR 3.9 MHz), positions of HOMs and RF sidebands(11/55 MHz) in frequency domain should look like the plot below.
  The script for calculating this currently lives in /users/yuta/scripts/modescanresults/HOMRFSB.py, inspired by Yoichi's script for KAGRA


Mode-matching ratio:
  By comparing mode scan data and HOM/RF SB positions in a sophisticated way, you can tell which peak is which.



  From COARSE 5FSR measurement, peak heights are

TEM00 0.884, 0.896, 0.917, 0.905, 0.911
TEM01 0.040, 0.037, 0.051, 0.054, 0.062
TEM02 0.083, 0.078, 0.079, 0.071, 0.078
TEM03 0.018, 0.015, 0.013, 0.015, 0.014

  So the mode-matching ratio is

MMR = 86.2 %, 87.3 %, 86.5 %, 86.6 %, 85.5 %

  From FINE 1FSR measurement, peak heights and mode matching ratio is

TEM00 0.921
TEM01 0.031
TEM02 0.078
TEM03 0.014

MMR = 88.2 %

  Assuming each measurement had same error, mode-matching ratio from these 6 values is

MMR = 86.7 +/- 0.3 %  (error in 1 sigma)

  This can be improved by ~5% by alignment because we still see ~5% of TEM01/10. Study in systematic errors on going.

[Koji, Jenne, Yuta]

Summary:
  We put phase tracker in FINE loop for ALS. We checked it works, and we scanned Y arm by sweeping the phase of the I-Q rotator.
  From the 8 FSR scan using FINE (30 m delay line), we derived that Y arm finesse is 421 +/- 6.

What we did:
  1. We made new phase rotator because current cdsWfsPhase in CDS_PARTS doesn't have phase input. We want to control phase. New phase rotator currently lives in /opt/rtcds/userapps/trunk/isc/c1/models/PHASEROT.mdl. I checked that this works by sweeping the phase input and monitoring the IQ outputs.

  2. We made a phase tracker (/opt/rtcds/userapps/trunk/isc/c1/models/IQLOCK.mdl) and included in c1gcv model. Unit delay is for making a feed back inside the digital system. Currently it is used only for BEATY_FINE (Simulink diagram below). We edited MEDM screens a little accordingly.



  3. Phase tracking loop has UGF ~ 1.2 kHz, phase margin ~50 deg. They are enough becuase ALS loop has UGF ~ 100 Hz. To control phase tracking loop, use filter module C1:ALS-BEATY_FINE_PHASE (with gain 100). Sometimes, phase tracking loop has large offset because of the integrator and freedom of 360*n in the loop. To relief this, use "CLEAR HISTORY."

  4. Locked Y arm using C1:ALS-BEATY_FINE_PHASE_OUT as an error signal. It worked perfectly and UGF was ~ 90 Hz with gain -8 in C1:ALS-YARM filter module.

  5. Swept phase input to the new phase rotator using excitation point in filter module C1:ALS-BEATY_FINE_OFFSET. Below is the result from this scan. As you can see, we are able to scan for more than the linear range of FINE_I_IN1 signal. We need this extra OFFSET module for scanning because BEATY_FINE_I_ERR stays 0 in the phase tracking loop, and also,  error signal for ALS, output of PHASE module, stays 0 in ALS loop.


  6. We analyzed the data from 8FSR scan by FINE with phase tracker using analyzemodescan.py (below). We got Y arm finesse to be 421 +/- 6 (error in 1 sigma). I think the error for the finesse measurement improved because we could done more linear sweep using phase tracker.

Next things to do:
  - Phase tracker works amazingly. Maybe we don't need COARSE any more.
  - Install it to X arm and do ALS for both arms.
  - From the series of mode scan we did, mode matching to the arm is OK. There must be something wrong in the PRC, not the input beam. Look into PRC mode matching using video capture and measuring beam size.

For those of you who want to see plots from slower scan.

I very badly forgot to log about this in the crush of surfs.

I removed Koji's proto-beatbox RF comparator amp from the X arm ALS setup.  I was investigating hacking it onto one of the discriminator channels in the new beatbox, now that Yuta/Koji's Yuta/Koji's phase tracker is making the coarse beatbox path obsolete.  Upon further reflection we decided to just go ahead and stuff the beatbox board for the X arm, and use the proto-beatbox to test some faster ECL comparators.  This will be done first thing in the morning.

In the meantime the old amp is in my cymac mess on the far left of the electronics bench.

[Yuta, Koji, Jenne]

Lots of small things happened tonight, in preparation for having both arms' ALS working simultaneously.

1. Xarm aligned in IR

     1.1 ETMX oplev centered

2. Xgreen coarsely aligned to Xarm

3. X beat setup on PSL table resurrected. 

     3.1 Steering optics for both X and Y green (before PBS) were touched to fix clipping Xgreen on some of the first mirrors after the light exits the chambers.

     3.2 Xgreen aligned to beat PD

     3.3 PSL green waveplate rotated so ~half of the light goes to X beat, other ~half goes to Y beat (recall we had rotated the polarization so we had max light on the Y beat PD a few weeks ago).

          3.3.1 Now we have ~80uW of PSL green going to each beat PD.

     3.4 PSL green aligned to X beat PD

          3.4.1 Replaced mount for mirror between PBS (which splits PSL green light) and BS (which combines PSL green and X green) so that I could get the alignment correct without having to use the full range of the knobs on the mount.

     3.5 Realigned (coarsely) Ygreen to Y beat PD - the mirrors just after the chambers had been touched, so Y green was no longer directly on the PD.  This will need to be done more finely when we're ready to lock the Yarm again.

     3.6 Dedicated cables for the DC of each beat PD were put in place, so we have those in addition to the DC transmission PDs which we are putting in temporarily each time we align the green to the cavities.  Some mystery unused cables that were running under the PSL table were removed.  The power for the X beat PD was rerouted so that it's much closer to the actual diode, and out of the way. 

4. Better alignment of X green to X arm.

     4.1 Put Green Transmission camera into place

     4.2 Noticed that the X green spot on the transmission camera is not nearly as steady as the Y green.  Increased the gain of the X green refl PD on the end table to see if it helped the spot be more steady, but it's still very wiggly.  We reverted the gain to what it was.  We need to fix this!!!!

    4.3 Removed camera, looked at X transmission DC (PD is temporarily in front of the beat PD), tried to increase the transmission.

     4.4 Aligning the green to the X arm has been really tough - there were a few more iterations of camera then DC PD.

     4.5 Measured X green power on the PSL table - 02 mode was ~150uW.  The 00 mode is still not very stable, which is frustrating, although we have a reasonable amount of power transmitted.   

     4.6 The X end green shutter was moved out of the beam path since the green beam was clipping while going through the shutter.  We need to put it back now that the beam is pretty much aligned.  The beam size and the aperture are roughly the same, so we should look to see if there is a different place on the table where the beam is a little smaller, where we can put the shutter.

5. Whitening filters (Pomona box-style) made for the Xarm I and Q channels - these are the same as the whitening for the Y arm.

6. 30m SMA cable made to be used for 2nd delay line.

     6.1 Steve reminded me this morning that we returned one of the fancy spools of cable that was purchased for the delay lines, since it was defective.  We didn't get it replaced because there was debate as to what is the best kind of cable to use.  We need to come to a conclusion, but for now we have a regular RG-405 cable.

7.  Jamie has started work on modifying the beatbox so that we can have 2-arm ALS.  Hopefully that will be done soon-ish, because we're otherwise pretty close to being ready.

I've reinstalled the beatbox in the 1X2 rack.  This improved version has the X and Y arm channels stuffed, but just one of the DFD channels (fine) each.

I hooked up the beat PD signals for X and Y to the RF inputs, and used the following two delay lines:

• X: 140' light-colored cable on spool
• Y: 30m black cable

The following channel --> c1ioo ADC --> c1gcv model connections were made:

• X I  --> SR560 whitening --> ADC 22 -->  X fine I
• X Q --> SR560 whitening --> ADC 23 --> X fine Q
• Y I --> SR560 whitening --> ADC 24 --> Y fine I
• Y Q --> SR560 whitening --> ADC 25 --> Y fine Q

The connections to the course inputs on the ALS block were grounded.  I then recompiled, reinstalled, and restarted c1gcv.  Functioning fine so far.

[Yuta, Jenne]

We locked both arms using the ALS system simultaneously!  Hooray!

Video of spectrum analyzer during lock acquisition of both beats is attached.

Jamie is super awesome, since he fixed us up a beatbox speedy-quick.  Thanks Jamie!! 

 Details:

1:  Aligned PSL green optics

     1.1:  We added an amplifier of ~20dB after the X beat PD (more Xgreen power on the PSL table so the signal was ~3dB higher than Y, so required less amplification).  The ~24dB amplifier is still in place after the Y beat PD.  Both beat signals go to a splitter after their amplifiers.  One side of each splitter goes to one of the channels on the beatbox.  The other side of each splitter goes to a 3rd splitter, which we're using backwards to combine the 2 signals so we can see both peaks on the spectrum analyzer at the same time.

2:  Found both beat notes

     2.1:  Y beat was easy since we knew the temps that have been working for the past several days

     2.2:  X beat was more tricky - the last time it was locked was the end of February (elog 6342)

         2.2.1:  We found it by adjusting the PSL laser temp nearly the full range - DC Adjust slider was at 8.8V or so (Y beat was found with the slider at ~1.1V tonight)

          2.2.2:  We then walked the beat around to get the PSL temp back to "normal" by moving the PSL temp, then compensating with the Xend laser temp, keeping the beatnote within the range of the spectrum analyzer.

          2.2.3:  Fine tuned the temps of all 3 lasers until we had 2 peaks on the analyzer at the same time!!

               2.2.3.1:  Yend - measured Temp=34.14 C, thermal Out of Slow servo=29820

               2.2.3.2:  Xend - displayed temp=39.33 C, thermal Out of Slow servo=5070

               2.2.3.3: PSL - displayed temp=31.49 C, Slow actuator Adjust=1.100V

3:  Locked both arms using ALS!!

     3.1:  We were a little concerned that the Xarm wasn't locking.  We tried switching the cables on the beatbox so that we used the old channels for the Xarm, since the old channels had been working for Y.  Eventually we discovered that the input of the filter module for ETMX's POS-ALS input was OFF, so we weren't really sending any signals to ETMX.  We reverted the cabling to how it was this evening when Jamie reinstalled the beatbox.

          3.1.1:  We need to sort out our SUS screens - Not all buttons in medm-land link to the same versions of the SUS screens!  It looks like the ALS screen was modified to point the ETMY button to a custom ETMY SUS screen which has the ALS path in the POS screen, along with LSC and SUSPOS.  There is no such screen (that I have found) for ETMX.  The regular IFO_ALIGN screen points to the generic SUS screens for both ETMY and ETMX, so we didn't know until Yuta searched around for the filter bank that the ALS input for ETMX was off.  We just need to make sure that all of the screens reflect what's going on in the models.

     3.2:  See the video attached - it shows the beat peaks during locking!!! (how do I embed it? right now you have to download it)

          3.2.1:  First you will see both peaks moving around freely

          3.2.2:  Then X arm is locked briefly, then unlocked

          3.2.3: Y arm is locked, steadily increasing gain

          3.2.4:  X arm is locked, so both arms locked simultaneously

          3.2.5:  Yuta clicked a button, accidentally unlocking the Xarm

4:  The transmission of the X arm was not so great, and both of our green beams (although X green especially) were no longer nicely aligned with the cavities.  Yuta tried to align the X arm to the X green, but it's bad enough that we really need to start over with the whole IFO alignment - we leave this until tomorrow.  Since we didn't have any good IR transmission, we didn't bother to try to find and hold the Xarm on IR resonance using ALS, so we didn't measure a POX out of loop residual cavity motion spectrum.  Again, tomorrow. 

Are these correct?

1. It is a nice work.

2. This is not locking, but stabilization of the both arms by ALS.

3. We now have the phase trackers for both arms.

4. There is no coarse (i.e. short) delay line any more.

5. The splitters after the PDs are reducing the RF power to Beat-box.
Actually there are RF monitors on Beat-box for this purpose, but you did not notice them.

6. c1ioo channel list
https://wiki-40m.ligo.caltech.edu/CDS/C1IOO%20channel%20list
has to be updated.

7. Video can be uploaded to Youtube as Mike did at http://nodus.ligo.caltech.edu:8080/40m/6513

Answers to questions from Koji.

Are these correct?

1. It is a nice work.

Correct, of course!

2. This is not locking, but stabilization of the both arms by ALS.

Correct.

3. We now have the phase trackers for both arms.

Correct.

4. There is no coarse (i.e. short) delay line any more.

Correct. No coarse, only fine delay line (30m) with the phase tracker.

5. The splitters after the PDs are reducing the RF power to Beat-box.
Actually there are RF monitors on Beat-box for this purpose, but you did not notice them.

Oh, yes. But distance between beatbox and spectrum analyzer in the control room is longer than distance between BBPD on PSL table and the spectrum analyzer. We were too lazy to do cabling, but maybe we should.

6. c1ioo channel list 
https://wiki-40m.ligo.caltech.edu/CDS/C1IOO%20channel%20list
has to be updated.

Yes, we will.

7. Video can be uploaded to Youtube as Mike did at http://nodus.ligo.caltech.edu:8080/40m/6513

We didn't, but we can.

[Yuta, Jenne, Koji]

We stabilized the Xarm using the ALS and took a spectrum of POX as our out of loop sensor.  We used the calibration from elog 6841 to go from counts to meters.

We find (see attached pdf) that the RMS is around 60pm, dominated by 1Hz motion.

In other, related, news, I took out the beam pipe connecting the AP and PSL tables and covered the holes with foil.  This makes it much easier and faster to get to the X beat setup for alignment.  Eventually we'll have to put it back, but while the AUX laser on the AP table is not being used for beating against the PSL it'll be nice to have it out of the way.

X arm finesse is 416 +/- 6, mode-matching ratio is 91.2 +/- 0.3%

I did mode scan for X arm just like we did for Y arm (see elog #6832)

Servo design:
  Servo filters are as same as Y arm.
  UGF and phase margin of X arm ALS are 100 Hz and 14 deg.
  For phase tracking loop, they are 1.5 kHz and 56 deg.

Raw data from the mode scan:



Fitted peaks and finesse:


By taking the average,

F = 416 +/- 6 (error in 1 sigma)
(For Y arm, it was 421 +/- 6. See elog #6832)


Mode matching ratio:
 From X arm 8FSR measurement using phase tracker, peak heights are

TEM00 0.834, 0.851, 0.854, 0.852, 0.876, 0.850, 0.855, 0.878
TEM01 0.031, 0.031, 0.017, 0.017, 0.009, 0.014, 0.009, 0.011
TEM02 0.053, 0.052, 0.057, 0.058, 0.061, 0.060, 0.061, 0.059
TEM03 0.011, 0.010, 0.010, 0.007, 0.006, 0.005, 0.006, 0.005

 So, the mode-matching ratio is

MMR = 89.7%, 90.1%, 91.0%, 91.2%, 92.0%, 91.4%, 91.8%, 92.1%

 By taking the average,

MMR =  91.2 +/- 0.3 (error in 1 sigma)
(for Y arm, it was 86.7 +/- 0.3 %. See elog #6828)


Discussion:
 - Mode matching ratio for both X and Y arm is ~90%, which is not so great, but OK. It seems like there's no huge clipping or mode-mismatch from MC to ITMs. I think we should go next for PRMI investigation.

 - Measured finesse seems too low compared with the design value 450. If we believe power transmission of ITM and ETM are 0.0138 and 1.37e-5, the measured finesse tells you that there's ~0.1% loss(F = 2*pi/(T_{ITM}+T_{ETM}+T_{loss})). We need some evaluation for the linearity of the sweep, before concluding that there's 0.1% loss for each arm. Using FINE_I/Q signal for calibration, or installing frequency divider for monitoring actual beat frequency would help.


Things to do for the beat setup:
 - Amplifiers after beat PDs shouldn't be on the PSL table. Move them near the beatbox.
 - Install DC PD (and camera?) at un-used port of the beat BS for monitoring green transmission power.
 - Make nice MEDM screens for our new phase tracking ALS.
 - Make a script to sweep arm length with ALS and find IR resonance.
 - Look into X end table. Beam spot of the X green transmission is wiggly when X end table is opened and there's air flow.

I moved amplifiers for beat PD at PSL table to 1X2 rack. Current beat setup from PD to ADC is shown below. Setup for X beat and Y beat are almost the same except for minor difference like cable kind for the delay line.

Currently, DC power for amplifiers ZHL-1000LN+ is supplied by Aligent E3620A.
I tried to use power supply from the side of 1X1 rack, but fuse plug(Phoenix Contact ST-SI-UK-4) showed red LED, so I couldn't use it.
Measured amplification was +25 dB for 10-100 MHz.

Measured gain from RF input to monitor output of the beat box was ~ -1 db for 10-100 MHz.

To get the feeling of the master of IFO, I;

1. Stabilized both arm length using ALS.

2. Ran findIRresonance.py for both arms and find what offset gives me IR resonances.

3. Holded X arm to IR resonance, holded Y arm to IR resonance, and released both arms.

Below is the time series data of what I did.



Issues:
 - Currently ALS is not stable enough. It only stays for about few minutes. I think it is because of the bad alignment of green from each end.
 - We can't tell end green frequency is higher or PSL green frequency is higher. So, the sign of the servo filter sometimes flips.
 - Wobbliness of X end green transmission beam spot was from the ETMX oplev. When the oplev servo is on, it got more wobbly when X end table is opened. But when the oplev servo was off, wobbliness was same even if the presence of air flow.
 - MICH contrast in plot above seems like it somehow got better when two arms are at resonance by ALS. I think this is not real because reflection from both arms at AS port was not well aligned and beam was clipped. Koji and I measured contrast of FPMI and MI(ETMs misalined), and they were 99.6 % and 99.9 % respectively. Beam clipping seems like it comes from some where between BS to AS port. We need to figure out where and fix this.

Things need to be done to make ALS more concrete:
 - Align Y end green beam!
 - Look into Y end green frequency servo
 - How do we hand-off servo using ALS to IR lock?
 - Noise budgeting for new phase tracker scheme
 - Linearity check of the beat box and phase tracker

We have received the dichroic optics from Laseroptik.  The coatings are:

HR:

• 532nm: T(s+p) > 97%
• 1064nm:  R(p) > 99.9%

AR:

• 532nm: R(s+p) < 1%
• 1064nm: R(p) < 2%

We got two sets with these coatings:

• 6x: 50 x 9.5mm, 2 degree wedge
• 8x: 25 x 6.35mm, 2 degree wedge
• 1x: 25 x 3mm, witness

I put them in the "visible optics" drawer of the newish, metal optics cabinet with the thin drawers down the Y arm.

I locked MI while both arm length are stabilized at IR resonance. This could be done using DC READOUT, in other words, use AS_DC as MICH error signal.
Lock using RF signals are still not successful.

Yuta and I bought some new BS mounts so that we could use the 4th port of the beamsplitters which are combining the PSL green and the arm transmitted beam, just before the Beat PD for each arm.  I just placed the Yarm one, and have aligned the light onto both the Beat PD and the Trans DC PD. 

I'll do the Xarm after lunch.

Jamie and I were doing some locking, and we found that the Yarm green wasn't locking.  It would flash, but not really stay locked for more than a few seconds, and sometimes the green light would totally disappear.  If the end shutter is open, you can always see some green light on the arm transmission cameras.  So if the shutter is open but there is nothing on the camera, that means something is wrong.

I went down to the end, and indeed, sometimes the green light completely disappears from the end table.  At those times, the LED on the front of the laser goes off, then it comes back on, and the green light is back.  This also corresponds to the POWER display on the lcd on the laser driver going to ~0 (usually it reads ~680mW, but then it goes to ~40mW).  The laser stays off for 1-2 seconds, then comes back and stays on for 1-2 minutes, before turning off for a few seconds again.

Koji suggested turning the laser off for an hour or so to see if letting it cool down helps (I just turned it off ~10min ago), otherwise we may have to ship it somewhere for repairs :( 

 I turned the Yend laser back on....it hasn't turned itself off yet, but I'm watching it.  As long as we leave the shutter open, we can watch the C1:ALS-Y_REFL_DC value to see if there's light on the diode.

The end sus models (c1scx and c1scy) both contain some ALS stuff.  This stuff could maybe be moved to their own models, but whatever.

The stuff at X and Y were identical, but were code copies (BAD!).  I made a new library part for the ALS end controls: ${userapps}/isc/c1/model/ALS_END.mdl

It contains just some filter modules for the ALS end laser control, and a monitor of the ALS end REFL PD DC.  I also added a DQ block for the recorded channels (see screen shot).

When I added this new part to c1scx and c1scy I made it so the channel names would be more sensible.  Instead of "GCX" and "GCY", they are now "ALS-X" and "ALS-Y".  They will now all show up under the ALS subsystem.