Eleonora, Raffaele, Yaochin and Yuhang

Yesterday night we came to TAMA and improved especially the matching and alignment from OPOtra to filter cavity. We moved the lens position and also tried to align a bit the steering mirror. After this work, the matching level is estimated as following

TEM00: 460

TEM10: 108

LG10: 108

offset: 100

So the mis-matching level is about 5%

This matching level is better than the measurement of locking accuracy of last time. And we think the matching level will also influence the locking accuracy. So we characterize the locking accuracy again. This time we used the same setting as last time. The AOM was scanned with a modulated sine wave. The modulation is 2000Hz/s. We measured the PDH signal and use it for calibration. The measured PDH signal pk-pk is 234mV with a seperation of 118ms.

So the calibration is 2000/(2*234/118) Hz/V

We measured the demodulated BAB reflection spectrum, the locking accuracy is integrated as 5Hz. But now we have some new peaks.

Today, the spacer for cryogenic cavity was delivered and I did brief inspection of it with half inch flat mirror.
I just checked whether the reflected beam can pass through the output hole of the spacer or not.
The reflected beam could pass through, but there is a undesirable feature due to my mistake of design.
Fortunately it can be easily removed by an additional machining.
I will ask the company to do it.

The measurement of CC2 loop opto-mechanical transfer function, CC2 open loop tranfer function and CC2 error signal spectrum is attached as attachement.

The good news is that the OMTF is very flat.

The first obvious oscillation we could find is ~23kHz(the last attachement). While we could see from the error singal spectrum, we have two narrow peaks at ~15.5kHz and ~22kHz.

Aritomi, Eleonora, Yaochin and Yuhang

We found that fc tra is more than 3000 counts. And this is more than we had, so we did the following check. And it shows that the more green power seems to be from a higher conversion efficiency of SHG.

green before EOM 268mW

before AOM 48.4mW

before MZ 198mW

AOM frequency 109.03575MHz

AOM amplitude 2.5dbm (then go through zhl-2 amplifier to AOM)

[Aritomi, Yuhang, Yaochin, Eleonora, Matteo, Raffaele]

First we aligned IR into filter cavity. Current mode matching is around 95.8%.

Then we succeeded in locking CC2 with filter cavity with new phase shifter. This time CC2 testmass feedback worked well and CC2 correction signal and IRMC reflection became more stable. Gain of testmass feedback is -2.

We measured FDS at 600Hz and CC2 phase noise (Pic.1,2). CC2 demodulation phase is as follows. CC2 error signal is 76mVpp. At high frequency, we had 3dB squeezing, but the spectrum was not clean. Below 100Hz, there was large bump.

After this measurement, we found that DC balance of LO was bad. We measured frequency independent squeezing before/after DC balance (Pic.3). After DC balance, squeezing spectrum and squeezing level got better, but still not clean as before.

Then we measured FDS again with/without testmass feedback (Pic.4). Low frequency bump became lower down to 60Hz and it doesn't change with/without testmass feedback. It seems that DC balance improved low frequency bump.

I roughly investigated the transmittance of fused silica mirrors which will be used for input and output couplers.
I measured transmitted beam power for 2 of 4 mirrors.
The trasmitted power was 1.8uW for both of them with respect to 10mW incoming power.
This value corresponds to T=0.018% and R=99.982% assuming no loss in mirrors.
Then the finesse can be estimated as 1.7*10⁴.
This value is reasonable since the designed finesse was 1.5*10⁴.

I gonna construct FP cavity with these mirrors and try to lock TEM00.

I removed the gauge from the chamber.

Baking time today (11/26): 9:30-10:30 (1 hour)

After the temparature settled, I opened the gate valves for the TMP. The pressure was decreased from 1x10^-6 mbar to 2x10^-7 mbar.

[Eleonora, Federico, Matteo]

The zero-detect board of the rampeatuo (Pic1) reads a signal (usually the cavity transmission) and compares it with a treshold signal in order to engage the lock. The threshold signal can be manually set with a potentiomenter and goes from -15 V to 15 V. Pierre installed a probe to monitor this threshold some times ago.

In the current configuration the rampeauto sums the transmission signal and the threshold and engages the lock if this sum is > 0. This means that if we don't connect the transmission signal, the cavity gets locked when we set the threshold above 0.  

By connecting the transmission and keeping the threshold below zero we can assure the the lock is engaged only when the transmission is higher than the absolute value of the treshold. This means that we can prevent the servo from locking on HOMs. In the current configuration, the cavity transmission (when it is locked and well aligned) is ~1.5 V. The threshold is set at -0.5 V so that the lock is engaged only when the transmission is higher than 0.5. 

In order to remotely control the lock, we used a stanford to subtract an offset (generated by the recenty installed DAC) to the transmission signal, before the rampeauto. If such offset is 0 the cavity stays locked, if it is larger than 1 V the trasmission signal sent to the rampeauto is lower that 0.5 V and the servo stops the lock. We set the offset at 1.5 V and we verified that the cavity lock can be controlled by adding and removing it.

I added a button on the main MEDM screen to control such offset (pic 2). From now on please try to use remote lock of the filter cavity as much as possible and keep the threshold knob where it is.

The attached figure shows the remained peaks in the squeezing/anti-squeezing spectrum.

In the anti-squeezing spectrum, we could see that all the peaks appear at a harmonics of 50Hz.

In the squeezing spectrum, the peaks appear mainly at harmonics of 50Hz. Only 3 out of 14 peaks are not harmonics of 50Hz but they are close.

Eleonora and Yuhang

After Takahashi-san glued the PZT on the new mount. We soldered the PZT to a BNC connector and replaced it with the old IR phase shifter. (attached figure 1)

The alignment to IRMC was recovered. Then we locked it and tried to see the effect of scanning IR phase shifter. We sent a sine wave to IR phase shifter from 25-125V, which is almost the same output range of our servo. Then we found IRMC transmission is modulated by almost 12% in the pitch direction. (attached figure 2)

The reason why pitched is mainly modulated is guessed as that the mirror on top of PZT is a bit heavy so it has some pitch tilt, the PZT motion creates mainly pitch misalignment. Also, the beam is tilted hitting on IR phase shifter is tilted in the pitch direction.

FC IR TRA channel (ADC CH1) is not working well. We used ADC CH16 (FDS-SEISM_Z_IN1) for FC IR TRA instead.

Pengbo, Simon

Today, with the very much appreciated help from Manuel, we could start the translation-scans of the razor blade in horizontal direction at different Z-values in order to analyze the beam-profile automatically.
For the measurements itself, the powermeter is connected via a BNC cable to the DC-port of the LabView program.

Pengbo has written a Python-script to fit several of those scans at once so that we can easily get the results.

The laser-power of the pump beam is set to be ~110 mW for the entire measurements.

We started with our measurements actually in the area where the waist of the beam is supposed to be (Z-distance = 2mm, dZ = 0.1 mm, Zcenter = 74.1).
The next set of measurements will be over a wider range in Z further away from the waist.

Baking time today (11/25): 14:00-17:00 (3 hours)

[Tomaru-san, Tanioka]

Today, we investigated the problem of the vacuum gauge.
Tomaru-san cleaned the inside of it, then I installed it to the chamber.
We checked the behavior by pumping down, but the situation was not improved.
Around 1.2*10^-2 Pa, the vacuum gauge showed an error related to the sensor.

We will send it to the company and ask for repairing or buy a new one.

I found that the TMP in south end was failed. The TMP controller showed red indication but the LCD was disappeared.

Similar to the case in BS, oil vapor went from the RP to the TMP. Therefore the RP was replaced to the dry pump from the MC.

The TMP controller was replaced to the other one from the BS. The TMP is under baking to remove the contamination due to the oil vapor.

I tried to compute a rough calibration for the cavity mirrors actuation in DC.

I injected an offest of 10.000 counts in pitch and yaw, in INPUT and END mirrors, one at a time, and record the change seen by OPLEV.

Then I used the calibration reported in entry #1874 to convert it in urad:

Pitch is stiffer than yaw. There is a difference of 15/20% beetween INPUT and END that can come from both errors in OPLEV calibration and actuation unbalance. Also It is a bit strange to me that for the same amout of injected counts pitch motion is larger for INPUT and yaw motion is larger for END.

[Federico, Matteo, Eleonora]

In the past few days we had many troubles with our DACs. Several channels were not working and moreover the issue seemed somehow "non stationary": some channels stopped working, than worked again, etc..

After we veryfied that the connections and the hardware have no evident problems, we decided to change the old DAC board with a new one. This seems to have fixed the problem. We also installed the cable to connect the second DAC board to the timing box and test the signal chain. We had to deal with several issues:

1) Dsub to BNC board installed in the cleanroom had a strange behaviour. We found some jumpers were missing inside and we soldered them (we could't find proper jumpers in the elec-shop). Now it is OK.

2) The AI board has only 8 channels (instead on 16)  but only channels 2-3-4 seem to work fine. Channel 1 has a large offset and the signal is very much attenuated, channels 5-6-7-8 show crazy things.

3) In general both the dsub to BNC boards show an oscillation at about 1 MHz, with amplitude of volts, when the output is probed with a long cable. This issue was also observed in KAGRA. (Entry #6266 of Klog). According to our expert electronician this is due to the cable impedence which induces an auto-oscillation of the last op-amp. This could have been solved by inserting a resistence before the output. Note that we are currently sending such dirty signals to our coil-drivers. Hopefully the oscillation frequency is so high that they don't really care? Note that most but not all the channels show this behaviour. 

Federico, Yaochin, and Yuhang

1. Test of small size beam with different power (attached figure 1 and 2)

power varies from 5mW to 12mW.

2. Test of 12mW light with a different beam size (attached figure 3 and 4)

3. The test of the large beam with different power (attached figure 5 and 6)

varies from 0.5mW to 12mW.

Note: According to the AA telescope design, the beam size is ~260um. The available power we can send to QPD is 2mW, the power distributed to rach quarter is 0.5mW.

I summarize the calibration for the OPLEVs.

For the conversion from counts to Volts, I used the following value:  1 V = 1638 counts  ->  cal =  6.105e-4 [V/count].

Note that for BS and PR we use TAMA PSD and no lens for shift/tilt decoupling. 

PR (entry #276)  --- SUM:  11 V  

Yaw:   0.24+/-0.03 [mrad/V]  = 0.146+/-0.02 [urad/count]

Pitch:  0.33+/-0.03 [mrad/V]  = 0.21+/-0.02 [urad/count]

NB: for geometrical reasons pitch is multiplied by a factor sqrt(2) (see attachment in entry 276)

BS (entry #337)  --- SUM: 13.4 V

Yaw:   0.37+/-0.03 [mrad/V]  = 0.25+/-0.02 [urad/count]

Pitch:  0.37+/-0.03 [mrad/V]  = 0.25+/-0.02 [urad/count]

NB: Since in this case the incident angle is almost normal the factor sqrt(2) can be neglected.

INPUT (entry #278 and pag 168 of my Phd thesis)  --- SUM: 3.2 V

Yaw:   0.038 [mrad/V]  = 0.027 [urad/count]

Pitch:  0.062 [mrad/V]  = 0.038 [urad/count]

NB: We considered a factor 100 coming from SR560 amplifiers 

END (entry #278 and pag 168 of my Phd thesis)  --- SUM: 4.45 V

Yaw:   0.030 [mrad/V]  = 0.018 [urad/count]

Pitch:  0.043 [mrad/V]  = 0.026 [urad/count]

NB: We considered a factor 100 coming from SR560 amplifiers 

It would be good to implement real time calibration for OPLEV channels.