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ID Date Author Type Category Subject
11797   Sun Nov 22 12:07:09 2015 KojiUpdateIOOIMC fix

TO DO

Done (Nov 23, 2015) - Check if the attenuator is still there in the input chain

Done (Nov 23, 2015) - Check if the actual LO levels at the 17dBm mixers are reasonable.

- Check if the actual LO levels for the LSC demods are OK too

11798   Sun Nov 22 12:12:17 2015 KojiUpdateIOOIMC OLTF

Well. I thought a bit more and now I think it is likely that this is just the servo bump as you can see in the closed-loop TF.

 Quote: 6. Broad feature from 40kHz to 200kHz. The IMC loop is adding the noise. This is the frequency range of the PC drive. Is something in the PC drive noisy???
11802   Mon Nov 23 22:12:10 2015 KojiUpdateIOOLO level check for the IMC demod board

In order to check the proper LO level, the IMC demod board was checked. As a short summary, -8dBm is the proper input for the IMC demod board. This was realized when the variable attenuator of the RF AM Stabilizer was set up be -7dB.

Initially, I tried to do the measurement using the extender board. But every board had the issue of +15V not working. After several extender boards were tried, I noticed that the current draw of the demod board burned the 15V line of the extender board.

Then I moved to the work bench. The signals were checked with the 10:1 probe. It's not properly the 50Ohm system, exactly to say.

I found that the LO signals at the mixers have huge distortion as it reaches the nominal 17dBm, and I wondered if ERA-5s were gone. Just in case I replaced the ERA-5s but didn't see any significant change. Then I thought it is due to the mixer itself. The mixer was removed and replaced with a 50Ohm SMD resister. Then the output of the last ERA-5 became sinusoidal, and the level was adjusted to be ~17dBm (4.52 Vpp) when the input power was measured to be -7.7dBm with the RF power meter. Once the mixer was reinstalled, it was confirmed that the waveform becase rectangular like, with the similar amplitude (4.42Vpp).

Now the module was returned to the rack. The RF level at the LO input was adjusted to be -8dBm by setting the attenuator level to be 7dBm.

Once the IMC is locked with this setting, the open loop transfer function was measured. The optical gain seemed almost unchanged compared with the recent nominal. The UGF and PM were measured to be 144kHz and 30deg.

Attachment 1: IMG_2137.JPG
Attachment 2: IMG_2138.JPG
11807   Wed Nov 25 04:24:21 2015 ranaUpdateIOOLO level check for the IMC demod board

Hmmm. Very non-standard demod. From the photo, looks like someone did some surgery with the attenuators (AT1, AT2, AT3) in the LO path. (might be me from a long time ago).

-8 dBm input to a circuit is a not a low noise situation. It would be best to remove the amplifiers in the I&Q paths and just have a single amplifier in the main path. Ideally we want the LO to never go below -3 dBm and certainly not below 0 dBm while outside of the board.

I doubt that all of the LSC demods were modified in this way - this one ought to get some sharpie or stickers to show its difference.

11808   Wed Nov 25 10:07:10 2015 KojiUpdateIOOLO level check for the IMC demod board

I didn't finish making the DCC entry for this module yet.

But the attenuators are
- AT1: 10dB. There is a sign that it was 3dB before ---  a 3dB chip was also attached on the boardnext to 10dB.
- AT2/3: Removed. They were replaced with 0Ohm resistors.

Currently the input is -8dBm. The input and output of the first ERA-5 are -17dBm and +7dBm, respectively.
Then the input and output of the second ERA-5 are -2dBm and 17dB, respectively.

In order to remove the second amplification stage, the first stage has to produce 26dBm. This is too much for either ERA-5 or any chips that fits on the foot print. If we use low gain but high output amp like GVA-81 (G=10dB, DF782 package), it is doable

Input 0dBm - [ATTN 3] - -3dBm - [ERA-5 G=20dB] - +16~+17dBm - [Circuits -9dB] - +7dBm - [Attn 0dB] - +7dBm - [GVA-81 G=10dB] - +17dBm

I think we should check the conditions of all the LSC demods.

11811   Wed Nov 25 16:46:10 2015 KojiUpdateIOOLO level check for the IMC demod board

Awwww. I found that the demod board has the power splitter (PSCJ-2-1) with one output unterminated.
This power splitter should be removed.

https://dcc.ligo.org/D1500443

Attachment 1: D990511-40m_151123.pdf
11812   Wed Nov 25 20:07:35 2015 ranaUpdateIOOLO level check for the IMC demod board

Perhaps we can replace T1 with a mini-circuits hybrid 0-90 deg splitter and then remove the trim caps. (JSPQ-80, JYPQ-30, SCPQ-50)

11885   Wed Dec 16 10:22:14 2015 SteveUpdateIOOthis morning

c1sus and c1ioo were restarted. PMC locked.

Attachment 1: PMClocked.png
11896   Tue Dec 22 16:23:33 2015 gautamUpdateIOOInput alignment to PMC tweaked

When I came in this afternoon, I saw that the PZT voltage to the PMC had railed. Following the usual procedure of turning the servo gain to zero and adjusting the DC offset, I got the PMC to relock, but the PMCR level was high and the alignment looked poor on the control room monitor. So I tweaked the input alignment on the PSL till I felt it was more reasonable. The view on the control room monitor now looks more like the usual state, and the "REFL (V)" field on the PMC MEDM screen now reads 0.02-0.03 which is the range I remember it being in nominally.

11998   Thu Feb 18 02:52:27 2016 ericqUpdateIOOSome housekeeping

I manually aligned the IMC. Spot positions are all < 1.5mm. PMC trans of ~0.74, MC2 Trans of ~15400, MC Refl ~0.4, which is better than its been for some time now.

Somehow the WFS DC offsets were off, which made it look like it was impossible to center the beam on WFS2. The script for setting these wasn't working so I fixed it, ran it. WFS and MC2 trans offsets were set, WFS are back on and have been holding MC REFL nice and low for ~3 hours.

Arms were dither aligned, wrote the offsets to SDF files. Oplevs need centering. No further daqd crashes.

12021   Fri Mar 4 13:52:41 2016 ericqUpdateIOOPSL Laser Opened

PSL Table doors were open, and the laser shutter was closed.

Doors have been closed, laser has been opened.

12022   Sat Mar 5 10:37:48 2016 ranaUpdateIOOPSL Laser Opened

Sorry, that was me; taking some photos of the PSL and EX mirrors.

 Quote: PSL Table doors were open, and the laser shutter was closed. Doors have been closed, laser has been opened.

12032   Sat Mar 12 22:23:37 2016 ranaSummaryIOOPMC relocked

Found it locked on TEM01 mode.

Sweets in the fridge for non-PhD holders, courtesy of the highest levels of Caltech.

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
12041   Tue Mar 22 14:12:18 2016 SteveUpdateIOOLaser is turned back on

The 2W Innolight was turned on.

Attachment 1: off-onAgain.png
12042   Tue Mar 22 21:30:15 2016 KojiUpdateIOOPMCIMC aligned, WFS offset adjusted

The alignment of the PMC adjusted on the PSL table: Trans 0.737->0.749

The alignment of the IMC adjusrted on the sliders: Trans 14300->15300

WFS offset has been reset by /opt/rtcds/caltech/c1/scripts/MC/WFS/WFSoffsets

Attachment 1: 08.png
12072   Tue Apr 12 22:41:00 2016 KojiUpdateIOOPMC/IMC aligned, WFS offset adjusted

Did it again.

PMC Trans ~0.739
IMC Trans ~15000

12214   Sun Jun 26 15:27:28 2016 ranaFrogsIOOPMC /MC lopced

Found PMC unlocked for many hours so I relocked it. IMC relocked by itself, but the input switch seems to be flickering to fast. Also the Keep Alive bit is not flashing.

12639   Wed Nov 23 17:48:16 2016 rana, kojiUpdateIOOHow bad is the McWFS?

Medium.

Previous elog entries on this:

12640   Wed Nov 23 20:08:51 2016 Koji, ranaUpdateIOOMC WFS Demod/Whitening boards removed from the IOO rack

We removed one set of the MC WFS demod board and whitening board from the IOO rack for the investigation.
The MC WFS servo loops are disabled with the EPICS screens.
Let us know when you need the MC WFS boards to be returned to the rack.

This is to investigate the signal chain and fix some issues. We ramped down the -100 V supply for the WFS QPD bias (why is it so big?), but everything else is still on. Koji is doing demod board. Rana will upload a marked up WFS whitening board schematic soon.

12641   Sat Nov 26 19:16:28 2016 KojiUpdateIOOIMC WFS Demod board measurement & analysis

[Rana, Koji]

1. The response of the IMC WFS board was measured. The LO signal with 0.3Vpp@29.5MHz on 50Ohm was supplied from DS345. I've confirmed that this signal is enough to trigger the comparator chip right next to the LO input. The RF signal with 0.1Vpp on the 50Ohm input impedance was provided from another DS345 to CH1 with a frequency offset of 20Hz~10kHz. Two DS345s were synced by the 10MHz RFreference at the rear of the units. The resulting low frequency signal from the 1st AF stage (AD797) and the 2nd AF stage (OP284) were checked.

Attachment 1 shows the measured and modelled response of the demodulator with various frequency offsets. The value shows the signal transfer (i.e. the output amplitude normalized by the input amplitude) from the input to the outputs of the 1st and 2nd stages. According to the datasheet, the demodulator chip provides a single pole cutoff of 340kHz with the 33nF caps between AP/AN and VP. The first stage is a broadband amplifier, but there is a passive LPF (fc=~1kHz). The second stage also provides the 2nd order LPF at fc~1kHz too. The measurement and the model show good agreement.

2. The output noise levels of the 1st and 2nd stages were meausred and compared with the noise model by LISO.
Attachment 2 shows the input referred noise of the demodulator circuit. The output noise is basically limited by the noise of the first stage. The noise of the 2nd stage make the significant contribution only above the cut off freq of the circuit (~1kHz). And the model supports this fact. The 6.65kOhm of the passive filter and the input current noise of AD797 cause the large (>30nV/rtHz) noise contribution below 100Hz. This completely spoils the low noiseness (~1nV/rtHz) of AD797. At lower frequency like 0.1Hz other component comes up above the modelled noise level.

3. Rana and I had a discussion about the modification of the circuit. Attachment 4 shows the possible improvement of the demod circuit and the 1st stage preamplifier. The demodulator chip can have a cut off by the attached capacitor. We will replace the 33nF caps with 1uF and the cut off will be pushed down to ~10kHz. Then the passive LPF will be removed. We don't need "rodeo horse" AD797 for this circuit, but op27 is just fine instead. The gain of the 1st stage can be increased from 9 to 21. This should give us >x10 improvement of the noise contribution from the demodualtor (Attachment 3). We also can replace some of the important resistors with the thin film low noise resistors.

Attachment 1: WFS_demod_response.pdf
Attachment 2: WFS_demod_noise.pdf
Attachment 3: WFS_demod_noise_plan.pdf
Attachment 4: Screen_shot_2011-07-01_at_11.13.01_AM.png
12645   Tue Nov 29 17:45:06 2016 KojiUpdateIOOIMC WFS Demod board measurement & analysis

Summary: The demodulator input noise level was improved by a factor of more than 2. This was not as much as we expected from the preamp noise improvement, but is something. If this looks OK, I will implement this modification to all the 16 channels.

The modification shown in Attachment 1 has actually been applied to a channel.

• The two 1.5uF capacitors between VP and AN/AP were added. This decreases the bandwidth of the demodulator down to 7.4kHz
• The offset trimming circuit was disabled. i.e. Pin18 of AD831 was grounded.
• The passive low pass at the demodulator output was removed. (R18, C34)
• The stage1 (preamp) chip was changed from AD797 to OP27.
• The gain of the preamp stage was changed from 9 to 21. Also the thin film resistors are used.

Attachment 2 shows the measured and expected output signal transfer of the demodulator. The actual behavior of the demodulator is as expected, and we still keep the over all LPF feature of 3rd order with fc=~1kHz.

Attachment 3 shows the improvement of the noise level with the signal reffered to the demodulator input. The improvement by a factor >2 was observed all over the frequency range. However, this noise level could not be explained by the preamp noise level. Actually this noise below 1kHz is present at the output of the demodulator. (Surprisingly, or as usual, the noise level of the previous preamp configuration was just right at the noise level of the demodulator below 100Hz.) The removal of the offset trimmer circuit contributed to the noise improvement below 0.3Hz.

Attachment 1: demod.pdf
Attachment 2: WFS_demod_response.pdf
Attachment 3: WFS_demod_noise.pdf
12647   Tue Nov 29 18:35:32 2016 ranaUpdateIOOIMC WFS Demod board measurement & analysis

more U4 gain, lesssss U5 gain

12661   Fri Dec 2 18:02:37 2016 KojiUpdateIOOIMC WFS Demod board measurement & analysis

ELOG of the Wednesday work.

It turned out that the IMC WFS demod boards have the PCB board that has a different pattern for each of 8ch.
In addition, AD831 has a quite narrow leg pitch with legs that are not easily accessible.
Because of these, we (Koji and Rana) decided to leave the demodulator chip untouched.

I have plugged in the board with the WFS2-Q1 channel modified in order to check the significance of the modification.

WFS performance before the modification

Attachment 1 shows the PSD of WFS2-I1_OUT calibrated to be referred to the demodulator output. (i.e. Measured PSDs (cnt/rtHz) were divided by 8.9*2^16/20)
There are three curves: One is the output with the MC locked (WFS servos not engaged). The second is the PSD with the PSL beam blocked (i.e. dark noise). The third is the electronics noise with the RF input terminated and the nominal LO supplied.

This tells us that the measured PSD was dominated by the demodulator noise in the dark condition. And the WFS signal was also dominated by the demod noise below 0.1Hz and above 20Hz. There are annoying features at 0.7, 1.4, 2.1, ... Hz. They basically impose these noise peaks on the stabilized mirror motion.

WFS performance after the modification

Attachment 2 shows the PSD of WFS2-Q1_OUT calibrated to be referred to the demodulator output. (i.e. Measured PSDs (cnt/rtHz) were divided by 21.4*2^16/20)
There are three same curves as the other plot. In addition to these, the PSD of WFS2-I1_OUT with the MC locked is also shown as a red curve for comparison.

This figure tells us that the measured PSD below 20Hz was dominated by the demodulator noise in the dark condition. And the WFS signal is no longer dominated by the electronics noise. However, there still are the peaks at the harmonics of 0.7, 1.4, 2.1, ... Hz. I need further inspection of the FWS demod and whtening boards to track down the cause of these peaks.

Attachment 1: WFS_demod_noise_orig.pdf
Attachment 2: WFS_demod_noise_mod.pdf
12662   Sat Dec 3 13:27:35 2016 KojiUpdateIOOIMC WFS Demod board measurement & analysis

ELOG of the work on Thursday

Gautam suggested looking at the preamplifier noise by shorting the input to the first stage. I thought it was a great idea.

To my surprise, the noise of the 2nd stage was really high compared to the model. I proceeded to investigate what was wrong.

It turned out that the resistors used in this sallen-key LPF were thick film resistors. I swapped them with thin film resistors and this gave the huge improvement of the preamplifier noise in the low frequency band.

Attachment 1 shows the summary of the results. Previously the input referred noise of the preamp was the curve in red. We the resistors replaced, it became the curve in magenta, which is pretty close to the expected noise level by LISO model above 3Hz (dashed curves). Unfortunately, the output of the unit with the demodulator connected showed no improvement (blue vs green), because the output is still limited by the demodulator noise. There were harmonic noise peaks at n x 10Hz before the resistor replacement. I wonder if this modification also removed the harmonic noise seen in the CDS signals. I will check this next week.

Attachment 2 shows the current schematic diagram of the demodulator board. The Q of the sallen key filter was adjusted by the gain to have 0.7 (butter worth). We can adjust the Q by the ratio of the capacitance. We can short 3.83K and remove 6.65K next to it. And use 22nF and 47nF for the capacitors at the positive input and the feedback, respectively. This reduces the number of the resistors.

Attachment 1: WFS_demod_noise.pdf
Attachment 2: demod.pdf
12668   Tue Dec 6 13:37:02 2016 KojiUpdateIOOIMC WFS Demod board measurement & analysis

I have implemented the modification to the demod boards (Attachment 1).
Now, I am looking at the noise in the whitening board. Attachment 2 shows the comparison of the error signal with the input of the whitening filter shorted and with the 50ohm terminator on the demodulator board. The message is that the whitening filter dominates the noise below 3Hz.

I am looking at the schematic of the whitening board D990196-B. It has an VGA AD602 at the input. I could not find the gain setting for this chip.
If the gain input is fixed at 0V, AD602 has the gain of 10dB. The later stages are the filters. I presume they have the thick film resistors.
Then they may also cause the noise. Not sure which is the case yet.

Also it seems that 0.7Hz noise is still present. We can say that this is coming from the demod board but not on the work bench but in the eurocard crate.

Attachment 1: demod.pdf
Attachment 2: WFS_error_noise.pdf
12669   Tue Dec 6 16:47:40 2016 KojiUpdateIOOIMC WFS whitening filter investigation

The whitening board saids it is Rev B, but the actual component values are more like Rev. C.

The input stage (AD602) has an input resistor of 909 Ohm.
This is causing a big attenuation of the signal (x1/10) because the input impedance of AD602 is not high. And this screws up the logarithm of the gain.
I don't think this is a right approach.

Attachment 1: D990196-C.pdf
12670   Tue Dec 6 17:54:08 2016 KojiUpdateIOOIMC WFS whitening filter investigation

The input resistor 909Ohm of AD602 was shorted. I've confirmed that the gain (= attenuation by voltage division) was increased by a factor of 10.
This modification was done for WFS2-I1 and WFS2-Q1. Also the thick film resistors for the WFS2-I1 channel was all replaced with thin film resistors.

Attachment 1 shows the comparison of the noise levels. The curves were all calibrated referred to the response of the original whitening filter configuration.
(i.e. measurement done after the gain change was compensated by the factor of 10.)

Now the AF chain is not limited by the noise in the whitening filter board. (Brown)
In fact, this noise level was completely identical between I1 and Q1. Therefore, I don't think we need this resistor replacement for the whitening filter board.

We can observe the improvement of the overall noise level below 10Hz. (Comparison between green and red/blue)
As the signal level goes up, the noise above 100Hz was also improved.

Now we need to take care of the n x 0.7Hz feature which is in the demod board...

Attachment 1: 34.png
12671   Tue Dec 6 22:41:49 2016 KojiUpdateIOOIMC WFS whitening filter investigation

I have implemented the same modification (shorting the input resistor of AD602) to the two whitening boards.

12676   Tue Dec 13 17:26:42 2016 KojiUpdateIOOIMC WFS whitening filter investigation

Rana pointed out that this modification (removal of 900Ohm) leave the input impedance as low as 100Ohm.
As OP284 can drive up to 10mA, the input can span only +/-1V with some nonlinearity.

Rather than reinstalling the 900Ohms, Rana will investigate the old-days fix for the whitening filter that may involve the removal of AD602s.
Until the solution is supplied, the IMC WFS project is suspended.

12678   Thu Dec 15 03:46:19 2016 ranaUpdateIOOIMC WFS whitening filter investigation

https://dcc.ligo.org/LIGO-D1400414

As it turns out, its not so old as I thought. Jenne and I reworked these in 2014-2015. The QPD whitening is the same as the IMC WFS whitening so we can just repeat those fixes here for the IMC.

 Quote: Rana pointed out that this modification (removal of 900Ohm) leave the input impedance as low as 100Ohm. As OP284 can drive up to 10mA, the input can span only +/-1V with some nonlinearity. Rather than reinstalling the 900Ohms, Rana will investigate the old-days fix for the whitening filter that may involve the removal of AD602s. Until the solution is supplied, the IMC WFS project is suspended.

12679   Mon Dec 19 22:05:09 2016 KojiSummaryIOOPMC, IMC aligned. The ringdown PD/Lens removed.

PMC and IMC were aligned on Friday (16th) and Today (19th).

The PD and lens for the ringdown experiment were removed as they were blocking the WFS.

12680   Wed Dec 21 21:03:06 2016 KojiSummaryIOOIMC WFS tuning

- Updated the circuit diagrams:

IMC WFS Demodulator Board, Rev. 40m https://dcc.ligo.org/LIGO-D1600503

IMC WFS Whitening Board, Rev. 40m https://dcc.ligo.org/LIGO-D1600504

- Measured the noise levels of the whitening board, demodboard, and nominal free running WFS signals.

- IMC WFS demod phases for 8ch adjusted

Injected an IMC PDH error point offset (@1kHz, 10mV, 10dB gain) and adjusted the phase to have no signal in the Q phase signals.

- The WFS2 PITCH/YAW matrix was fixed

It was found that the WFS heads were rotated by 45 deg (->OK) in CW and CCW for WFS1 and 2, respectively (oh!), while the input matrices were identical! This made the pitch and yaw swapped for WFS2. (See attachment)

- Measured the TFs MC1/2/3 P/Y actuation to the error signals

Attachment 1: DSC_0142.JPG
12682   Thu Dec 22 18:39:09 2016 KojiSummaryIOOIMC WFS tuning

Noise analysis of the WFS error signals.

Attachment 1: All error signals compared with the noise contribution measured with the RF inputs or the whitening inputs terminated.

Attachment 2: Same plot for all the 16 channels. The first plot (WFS1 I1) shows the comparison of the current noise contributions and the original noise level measured with the RF terminated with the gain adjusted along with the circuit modification for the fair comparison. This plot is telling us that the electronics noise was really close to the error signal.

I wonder if we have the calibration of the IMC suspensions somewhere so that I can convert these plots in to rad/sqrtHz...?

Attachment 1: WFS_error_noise.pdf
Attachment 2: WFS_error_noise_chans.pdf
12683   Fri Dec 23 20:53:44 2016 KojiSummaryIOOIMC WFS tuning

WFS1 / WFS2 demod phases and WFS signal matrix

Attachment 1: DSC_0144.JPG
Attachment 2: DSC_0145.JPG
12684   Fri Dec 23 21:05:56 2016 KojiSummaryIOOIMC WFS tuning

Signal transfer function measurements

C1:SUS-MC*_ASCPIT_EXC channels were excited for swept sine measurements.

The TFs to WFS1-I1~4, Q1~4, WFS1/2_PIT/YAW, MC2TRANS_PIT/YAW signals were recorded.

The MC1 and MC3 actuation seems to have ~30Hz elliptic LPF somewhere in the electronics chain.
This effect was compensated by subtracting the approximated time delay of 0.022sec.

The TFs were devided by freq^2 to make the response flat and averaged between 7Hz to 15Hz.
The results have been summarized in Attachment 3&4.

Attachment 4 has the signal sensing matrix. Note that this matrix was measured with the input gain of 0.1.

Input matrix for diagonalizing the actuation/sensor response

Pitch

$\begin{pmatrix} -1.58983 & -0.901533 & -5592.53 \\ 0.961632 & -0.569662 & 1715.12 \\ 0.424609 & 1.60783 & -5157.38 \end{pmatrix}$

e.g. To produce pure WFS1P reaction, => -1.59 MC1P + 0.962 MC2P + 0.425 MC3P

Yaw

$\begin{pmatrix} 1.461 & -0.895191 & -4647.9 \\ 0.0797164 & 0.0127339 & -1684.11 \\ 0.223054 & -1.31518 & -4101.14 \end{pmatrix}$

Attachment 1: IMC_WFS_segment_TF.pdf
Attachment 2: IMC_WFS_channels_TF.pdf
Attachment 3: IMC_WFS_161221_table1.pdf
Attachment 4: IMC_WFS_161221_table2.pdf
Attachment 5: IMC_WFS_161221.xlsx.zip
12685   Sun Dec 25 14:39:59 2016 KojiSummaryIOOIMC WFS tuning

Now, the output matrices in the previous entry were implemented.
The WFS servo loops have been engaged for several hours.
So far the REFL and TRANS look straight. Let's see how it goes.

12686   Mon Dec 26 12:45:31 2016 KojiSummaryIOOIMC WFS tuning

It didn't go crazy at least for the past 24hours.

Attachment 1: IMC_REFL_TRANS_26hrs.png
Attachment 2: IMC_TRANS_P_Y_26hrs.png
12688   Thu Dec 29 13:22:21 2016 ranaSummaryIOOIMC WFS tuning
• For the rough calibration below 10 Hz, we can use the SUS OSEM cal: the SUSPIT and SUSYAW error signals are in units of micro-radians.
• It seems from the noise plots that the demod board is now dominating over the whitening board noise.
• If the RF signals at the demod input are low enough, we can consider either increasing the light power on the WFS or increasing the IMC mod. depth.
• We should look at the out-of-lock light power on the WFS and re-examine what the 'safe' level is. We used to do this based on the dissipated electrical power (bias voltage x photocurrent).

At Hanford, there is this issue with laser jitter turning into an IMC error point noise injection. I wonder if we can try out taking the acoustic band WFS signal and adding it to the MC error point as a digital FF. We could then look at the single arm error signal to see if this makes any improvement. There might be too much digital delay in the WFS signals if the clock rate in the model is too low.

12689   Thu Dec 29 16:52:51 2016 KojiSummaryIOOIMC WFS tuning

Koji responding to Rana

> For the rough calibration below 10 Hz, we can use the SUS OSEM cal: the SUSPIT and SUSYAW error signals are in units of micro-radians.

I can believe the calibration for the individual OSEMs. But the input matrix looked pretty random, and I was not sure how it was normalized.
If we accept errors by a factor of 2~3, I can just naively believe the calibration factors.

> If the RF signals at the demod input are low enough, we can consider either increasing the light power on the WFS or increasing the IMC mod. depth.

The demod chip has the conversion factor of about the unity. We increased the gains of the AF stages in the demod and whitening boards. However, we only have the RMS of 1~20 counts. This means that we have really small RF signals. We should check what's happening at the RF outputs of the WFS units. Do we have any attenuators in the RF chain? Can we skip them without making the WFS units unstable?

12690   Thu Dec 29 21:35:30 2016 ranaSummaryIOOIMC WFS tuning

The WFS gains are supposedly maximized already. If we remotely try to increase the gain, the two MAX4106 chips in the RF path will oscillate with each other.

We should insert a bi-directional coupler (if we can find some LEMO to SMA converters) and find out how much actual RF is getting into the demod board.

Attachment 1: Screen_Shot_2017-01-03_at_5.55.13_PM.png
12691   Thu Dec 29 21:48:32 2016 ranaUpdateIOOMC AutoLocker hung because c1iool0 asleep again

MC unlocked, Autolocker waiting for c1iool0 EPICS channels to respond. c1iool0 was responding to ping, but not to telnet. Keyed the crate and its coming back now.

There's many mentions of c1iool0 in the recent past, so it seems like its demise must be imminent. Good thing we have an Acromag team on top of things!

Also, the beam on WFS2 is too high and the autolocker is tickling the Input switch on the servo board too much: this is redundant / conflicting with the MC2 tickler.

12723   Mon Jan 16 21:03:47 2017 ranaSummaryIOOMCL / MCF / Calibration

Oot on the streets and in the chat rooms, people often ask, "What is up with the MC_F calibration?".

Not being sure of the wiring in the c1ioo model, I have formed this screencap of today's model and put it here. The MC_LENGTH and MC_FREQ are the filter banks which would calibrate these channels. In the filter banks there were various version of a 'dewhite' filter. They were all approximately z=150, p=15, g =1 @ DC, but with ~1% differences. I don't trust their provenance and so I've enforced symmetry and fixed their names to reflect what they are (150:15). I have also turned on one filter in MC_FREQ so that now the whitening of the Pentek Interface board is compensated.

Why is this TF 1/f? It should be -20 dB/decade if MC_F is in units of Hz* and MCL is a pendulum response. Perhaps its because the combination of the Koji summing box, the Thorlabs HV driver, and the Pomona box forms an additional 1/f ? IF so, this would explain the TF we see. Once we get confirmation from Koji, we can load the TF into the MC_FREQ filter bank and then MC_F will be in units of Hz (as will the summary pages).

(along the way I've also turned off the craaaazzzy servo input enable tickling that gets put in the MC AutoLocker every April Fool's leap year - resist the temptation)

Since we have a frequency counter system here and some oscillators, I wonder if we can just calibrate the MC_L and MC_F directly using a mixer lashed up to one of the counters. If so, and we can get the stabilized laser frequency noise down below 10 mHz/rHz, maybe this is a viable alternative method to the photon calibrators. Counting zero crossings is more honest than counting photons.

Attachment 1: c1ioo_zoom_MCLF.png
Attachment 2: MCL.pdf
12732   Wed Jan 18 12:34:21 2017 ericqSummaryIOOMCL / MCF / Calibration
 Quote: In the filter banks there were various version of a 'dewhite' filter. They were all approximately z=150, p=15, g =1 @ DC, but with ~1% differences. I don't trust their provenance and so I've enforced symmetry and fixed their names to reflect what they are (150:15).

The filters were made in response to a measurement of the pentek whitening boards in 2015 (ELOG 11550), but this level of accuracy probably isn't important.

12748   Tue Jan 24 01:04:16 2017 gautamSummaryIOOIMC WFS RF power levels

Summary:

I got around to doing this measurement today, using a minicircuits bi-directional coupler (ZFBDC20-61-HP-S+), along with some SMA-LEMO cables.

• With the IMC "well aligned" (MC transmission maximized, WFS control signals ~0), the RF power per quadrant into the Demod board is of the order of tens of pW up to a 100pW.
• With MC1 misaligned such that the MC transmission dropped by ~10%, the power per quadrant into the demod board is of the order of hundreds of pW.
• In both cases, the peak at 29.5MHz was well above the analyzer noise floor (>20dB for the smaller RF signals), which was all that was visible in the 1MHz span centered around 29.5 MHz (except for the side-lobes described later).
• There is anomalously large reflection from Quadrant 2 input to the Demod board for both WFS
• The LO levels are ~-12dBm, ~2dBm lower than the 10dBm that I gather is the recommended level from the AD831 datasheet
 Quote: We should insert a bi-directional coupler (if we can find some LEMO to SMA converters) and find out how much actual RF is getting into the demod board.

Details:

I first aligned the mode cleaner, and offloaded the DC offsets from the WFS servos.

The bi-directional coupler has 4 ports: Input, Output, Coupled forward RF and Coupled Reverse RF. I connected the LEMO going to the input of the Demod board to the Input, and connected the output of the coupler to the Demod board (via some SMA-LEMO adaptor cables). The two (20dB) coupled ports were connected to the Agilent spectrum analyzer, which have input impedance 50ohms and hence should be impedance matched to the coupled outputs. I set the analyzer to span 1MHz (29-30MHz), IF BW 30Hz, 0dB input attenuation. It was not necessary to turn on averaging to resolve the peaks at ~29.5MHz since the IF bandwidth was fine enough.

I took two sets of measurements, one with the IMC well aligned (I maximized the MC Trans as best as I could to ~15,000 cts), and one with a macroscopic misalignment to MC1 such that the MC Trans fell to 90% of its usual value (~13,500 cts). The peak function on the analyzer was used to read off the peak height in dBm. I then converted this to RF power, which is summarized in the table below. I did not account for the main line loss of the coupler, but according to the datasheet, the maximum value is 0.25dB so there numbers should be accurate to ~10% (so I'm really quoting more S.Fs than I should be).

WFS Quadrant Pin (pW) Preflected(pW) Pin-demod board (pW)

## IMC well aligned

1 1 50.1 12.6 37.5
2 20.0 199.5 -179.6
3 28.2 10.0 18.2
4 70.8 5.0

65.8

2 5 100 19.6 80.0
6 56.2 158.5 -102.3
7 125.9 6.3 11.5
8 17.8 6.3

119.6

WFS Quadrant Pin (pW) Preflected(pW) Pin-demod board (pW)

## MC1 Misaligned

1 1 501.2 5.0 496.2
2 630.6 208.9 422
3 871.0 5.0 866
4 407.4 16.6

190.8

2 5 407.4 28.2 379.2
6 316.2 141.3 175.0
7 199.5 15.8 183.7
8 446.7 10.0 436.7

For the well aligned measurement, there was ~0.4mW incident on WFS1, and ~0.3mW incident on WFS2 (measured with Ophir power meter, filter out).

I am not sure how to interpret the numbers for quadrants #2 and #6 in the first table, where the reverse coupled RF power was greater than the forward coupled RF power. But this measurement was repeatable, and even in the second table, the reverse coupled power from these quadrants are more than 10x the other quadrants. The peaks were also well above (>10dBm) the analyzer noise floor

I haven't gone through the full misalginment -> Power coupled to TEM10 mode algebra to see if these numbers make sense, but assuming a photodetector responsivity of 0.8A/W, the product (P1P2) of the powers of the beating modes works out to ~tens of pW (for the IMC well aligned case), which seems reasonable as something like P1~10uW, P2 ~ 5uW would lead to P1P2~50pW. This discussion was based on me wrongly looking at numbers for the aLIGO WFS heads, and Koji pointed out that we have a much older generation here. I will try and find numbers for the version we have and update this discussion.

Misc:

1. For the sake of completeness, the LO levels are ~ -12.1dBm for both WFS demod boards (reflected coupling was negligible)
2. In the input signal coupled spectrum, there were side lobes (about 10dB lower than the central peak) at 29.44875 MHz and 29.52125 MHz (central peak at 29.485MHz) for all of the quadrants. These were not seen for the LO spectra.
3. Attached is a plot of the OSEM sensor signals during the time I misaligned MC1 (in both pitch and yaw approximately by equal amounts). Assuming 2V/mm for the OSEM calibration, the approximate misalignment was by ~10urad in each direction.
4. No IMC suspension glitching the whole time I was working today

Attachment 1: MC1_misalignment.png
12757   Wed Jan 25 18:18:08 2017 KojiSummaryIOOMCL / MCF / Calibration

jiSome notes on the FSS configuration: ELOG 10321

12759   Fri Jan 27 00:14:02 2017 gautamSummaryIOOIMC WFS RF power levels

It was raised at the Wednesday meeting that I did not check the RF pickup levels while measuring the RF error signal levels into the Demod board. So I closed the PSL shutter, and re-did the measurement with the same measurement scheme. The detailed power levels (with no light incident on the WFS, so all RF pickup) is reported in the table below.

IMC WFS RF Pickup levels @ 29.5MHz
1 1 0.21 10.
2 1.41 148
3 0.71 7.1
4 0.16 3.6
2 1 0.16 10.5
2 1.48 166
3 0.81 5.1
4 0.56 0.33

These numbers can be subtracted from the corresponding columns in the previous elog to get a more accurate estimate of the true RF error signal levels. Note that the abnormal behaviour of Quadrant #2 on both WFS demod boards persists.

12818   Fri Feb 10 13:04:32 2017 ranaUpdateIOOMC AutoLocker hung because c1iool0 asleep again

c1iool0 was down again. Rather than key the crate, this time I just pushed the reset button on the front and it came back.

As move towards the wonderfulness of AcroMag, we also have to buy a computer  to handle all of these IOCs. Let's install the new c1iool0 over by the SUS computer.

12857   Tue Feb 28 21:05:44 2017 ranaSummaryIOOMC Length offset changes MCWFS offsets

The input offset on the MC length servo board changes the lock point of the length loop (by how much? need to calibrate this slider into meters & Hz).

The SUM signal on the MC WFS is ~few 1000. This is several times larger than the pit/yaw signals. This is bad. it means that the TEM00 mode on the WFS (or what the WFS interperets as a TEM00) is larger than the TEM01/10 that its supposed to measure.

So if the beam moves on the WFS head it will convert this large common mode signal into a differential one.

We moved the MC Servo offset around from -3 to +3 V today and saw that it does affect the transmitted light level, but we need to think more to see how to put the offset at the real center of the resonance. This is complicated by the fact that the MCWFS loops seem to have some several minutes time constant so things are essentially always drifting.

1. Characterize and juice up the WFS loops.
2. Figure out how to set the MC length loop offset. Is this bad offset changing the zero point of the MC WFS loops?
3. If so, it may be a source of excess jitter noise in the interferometer.

I changed the McREFL SMOO to make it easier to use this noisy channel to diagnose small alignment changes:

caput C1:IOO-MC_RFPD_DCMON.SMOO 0.1

12878   Thu Mar 9 20:38:19 2017 ranaConfigurationIOOMC lock acquisition settings changed; no more HOM locks

The MC was sort of misaligned. It was locking on some vertical HOMs. So I locked it and aligned the suspensions to the input beam (not great; we should really align the input beam to the centered spots on the MC mirrors).

With the HOMs reduced I looked at the MC servo board gains which Guatam has been fiddling with. It seems that since the Mod Depth change we're getting a lot more HOM locks. You can recognize this by seeing the longish stretches on the strip tool where FSS-FAST is going rail-to-rail at 0.03 Hz for many minutes. This is where the MC is locked on a HOM, but the autolocker still thinks its unlocked and so is driving the MC2 position at 0.03 Hz to find the TEM00 mode.

I lowered the input gain and the VCO gain in the mcdown script and now it very rarely locks on a HOM. The UGF in this state is ~3-4 kHz (I estimate), so its just enough to lock, but no more. I tested it by intentionally unlocking ~15 times. It seems robust. It still ramps up to a UGF of ~150 kHz as always. 'mcdown' commited to SVN.

ELOG V3.1.3-