You could use some remote "smart" PDUs as done in virgo.

See as example

https://tds.virgo-gw.eu/?content=3&r=15139

(the name of the PDU is ENERGENIE EG-PMS2-LAN, see attached PDF file)

Based on the measurement we did before, we have dark noise of CC PD. We use this PD to lock the green pump phase, at the same time, we have bandwidth lower than 80Hz. So we could use this dark noise to evaluate the phase noise we have for coherent control loop 1. The calibration method is to use pk-pk value when we scan the green phase, which corresponds to radians of pi/2. In the case of that entry, 25mV corresponds to pi/2. The estimated phase noise(RMS) is attached as follows.

While it will be better to measure the spectrum and do RMS integration. And according to Emil thesis, this 200mrad of phase will degrade ~15dB of squeezing to ~5dB. And it seems to be close to the squeezing situation we saw in the past few days.

[Aritomi, Eleonora P, Yuhang]

Today we replaced a green phase shifter with a new thick phase shifter (picture 1). After re-alignment of GRMC, we got good mode matching (picture 2) and succeeded in locking of GRMC with lower gain. Green power is 146mW before GRMC and 90mW after GRMC when MZ is maximized. So transmission of GRMC is 62% which is good.

Lock of green phase with BAB transmission seems stable with this new phase shifter.

We'll measure transfer function of green phase lock loop with new green phase shifter tomorrow.

Eleonora P, Yuhang, and Aritomi

By keeping green always locked, we measured the power of all the higher order modes we could see from camera. The reason to keep green locked is that we have 'two different FSR' for IR. We found a lot of higher order modes. But the main higher order mode is HG10. This means our alignment needs to be improved for yaw direction. The power for each mode is reported as follows.(picture attached insequence without HG10 and TEM00)

Some modes I didn't write name seem so-called ince-gaussian modes. Maybe it comes from the combination of yaw misalignment and mode-mismatch.

We found the second HG10 at 109.4313MHz, which means FSR is 0.499MHz which is in agreement with our expectation.

We will do alignment of yaw for the next step.

Akutsu-san, Tanioka-san, Simon

It has been a long time since I wrote something in this logbook!

Anyway, we (that means AOS) are now relocating the scatterometer, which is still in one of JASMINE's laboratories at the ATC, to our lab on the first floor of ATC.
The reason is mainly that the JASMINE group needs the space in their lab and removed some desks which we used for the scatterometer's PC.

On the other hand, all of our optics-related stuff is more or less already in that lab where we are going to put the scatterometer in (including the back-scatterometer). So, it seems logical to relocate it there.

The first step in this week was therefore to find a suitable place in the lab, and we decided to use Torii-san's former space for that.
So, we cleaned it up and moved a theoretically usable clean-booth (still without walls) into the free space and a black-painted optical table underneath that booth (see pictures).

By doing all the cleaning-up thing, we discarded a lot of old carton-boxes and plastic garbage.
Now, it looks much more usable.

Next step will be to move the actual scatterometer.

The day before yesterday, we found a water leakage point in the middle station of TAMA arm (north, the arm we are using). See entry #1403. Yesterday I found it was filled fully by the leaked water.

Eleonora P, Yuhang, Matteo, and Aritomi

Several months ago, we have already found the channel for AOM amplification was broken. And the work we did yesterday was without AOM working. Fortunately, Eleonora C remembers where is the old RF amplifier. And today we first implemented the old RF amplifier(ZHL-2). The amplification factor of it is 16dBm. The optimal RF signal for AOM should be 27dBm(while it converts too much to the first order). so usually, we use a lower value. So I give 7dBm from the signal generator and amplify it by 16dBm to have totally 23dBm of driving signal to AOM. The conversion efficiency is about 80% now.

Then, for sure, we need to do the alignment for green again. And then also for IR.

Another very important thing is the amplification of BAB(after OPO transmission). In the beginning, we were thinking to lock it with the same method for CC locking. But we observed noise level brought by the beat between BAB and CC. And this noise is almost 200 times larger than the coherent control error signal we have. So it is not possible to lock with CC beam. By following Matteo's suggestion, we used the leakage power from OPO s-pol transmission through PBS and to p-pol locking PD. Then we feedback this signal after giving an offset. And then we can basically lock the green phase and have a more stable IR beam going inside the filter cavity.

After all the work above, we could lock both green and IR again by changing the AOM driving frequency. We found make higher order modes and they are listed as follows.

The task of tomorrow will be to maximize the TEM00 by moving the last two steering mirrors on the bench for IR. And measure the height of each higher order modes. Also, maximize mode matching. We will follow the entry.

EleonoraP, EleonoraC and Yuhang

We achieved the matching of the BAB (IR probe beam co-aligned with squeezing) into the filter cavity.

In order to align BAB into the FC, we mainly followed the IR alignment procedure we did more than one year ago (entry #646). The main steps of this procedure are to align the cavity for the green, recover the reference on PR chamber, maximize IR reflection from the input mirror, not to look for the beam on the first target and check instead the second target and the end camera.

However, since BAB is only 250uW, it is too weak to see. So we used the green pump to amplify it. The maximum green we can give is obtained setting the offset on the MZ control servo at 4.3 and at that time we have roughly 30mW of IR going to FC. This measurement of power is done while we scanned the green pump phase. So actually we are sending a repeated segment of a sine wave.

By using this 30mW and following the procedure above, we found the flashes of IR. Check attached video.

As you can see in the video, this beam is too bright so, in order to avoid saturation, we decide to reduce the power to around 10mW. In this case, we need to use temperature of 7.202 for OPO, MZ offset of 4.1 and lock p-pol PLL on 150MHz.

After achiving the alignment with the amplified BAB we confirmed that flashes cannot be seen without amplification. (BAB power ~250 uW)

Next steps are to optimize the matching and to use AOM to make green and IR both resonant.

I used one of the few ADC channels still availabe to acquire the filter cavity green transmission. Channel name is K1: FDS-FC_GR_TRA

For the moment it is recorded as an epic channel, since I wanted to display it on the medm screen.

The attached picture show today's lock streches (Even it doesn't seem so, no realigment has been done during this period and the lock was stopped on purpose)

Since the trasmission PD is actually a PSD, I plan to acquire also the X and Y signals in order to  possibly correlate beam motion to suspesion resonances and understand what we should improve.

As entitled. 

It is probably due to the heavy rain of these days. You can check the video. We put a bucket to collect the water.

As reported in entry #1267 we could not setup the new DGS computer wtith gentoo linux HDD, as it was not able to detect the USB.  We bought a PCI express board to be used as USB driver.

Last week I installed it but I still couldn't make the PC to detect USB. I think the board might not be compatible with linux. We should look for another one or consider to change PC.

[Eleonora P, Yuhang]

We installed the IR injection telescope on the bench and we pre-installed the reflection telescope (putting all the optical mounts on the bench without fixing them).

We used the two 750 mm focal length lenses present in the lens box in the lab. Since we saw the beam focusing before the cavity, after the telescope, we thought one of the two focal lengths to be wrong. In fact the second one was actually wrong and it was replaced by another lens of 750 mm focal, located in the lab (Newport KPX121AR.18, PCX LENS, BK 7).

We put HR Laser Line mirrors, BK 7, ALTECHNA Co. Ltd.

In fig 1 the photo of the injection telescope on the bench. We used two of the new small mirror mounts.

We notice that the pipe of the rotary pump close to BS was directly touching the vacuum pipe, transmitting a lot of vibrations.  We have moved the pump of  few centimeters so that the pipe was not touching anymore.

The vibration of BS in the region of 20 Hz seems improved. (See pic 1)

EleonoraP and Yuhang

Today we checked the PBS and the two following mirrors for OPO transmission. PBS has a transmission of 0.2% while we measured reflection more than incidence.  And the two mirrors are fine as well. We didn't use wrong coating components or they have some issues.

Chien-Ming and Yuhang

After the last very good measurement of squeezing, we start to think about improving coherent control 1 PD. Then we measured squeezing again. The result is attached in figure 1 and 2. As you can see the low frequency is covered by classical noise while high frequency seems fine. However, the squeezing level was only 4.9dB at that moment.

Then Chien-ming suggested cleaning optics. And then we checked optics together. We found optics are tremendously dirty. Especially one of the lenses is very dirty on one side of the surface. And for others, there are lots of dust on the surface of the mirror. However, after the cleaning of optics, the balance of BS is destroyed. After the alignment of this BS, we measured squeezing again. However, we didn't improve the squeezing. We observed squeezing level almost the same with last time. See attached figure 3 and 4.

There is some consideration after this measurement:

1. The fluctuation of measurement is about 4dB pk-pk. Is this coming from the measurement device?  

2. The low-frequency noise of the second measurement of squeezing is much higher than the first one. We also know that for the second measurement, the balance of the SQZ part is very bad. The unbalance signal on PD is about 50mV. Although we know this balance is not as important as the balance of local oscillator, we still need to make it stay at a decent level.

3. To keep a clean clean room is really important for squeezing to avoid some potential losses.

4. We also tried to change coherent control power, but we noticed that after we decrease coherent control power we may also increase phase noise. This measurement is better done when we have a better coherent loop. Also with some characterization of the coherent control loop.

[Yuhang, Eleonora]

Today we temporarily swiched off both the rotary and turbo pump in the central area (close to BS).

The attached plot show the comparison of the spectra of the suspensions in the central area, with pumps on and off.

We see that BS is strongly affected by the pumps vibration while PR and INPUT seem not.

[Note that at the time when I developed local control for the first time, the pump where swiched off].

The pumps have been switched off for about 3 hours ( from 5PM to 8PM).

Yuhang, Aritomi, EleonoraP, and EleonoraC

On 5th of June 2019, we locked the filter cavity again after almost half a year we haven't done this. We checked several references including irises on the bench, target on the film of PR chamber, target on the film of BS chamber, the first and second target inside the filter cavity vacuum tube. To recover these checking points, we used pico-motors with almost no failures. But it seems there are still some problems with end mirror pico-motor. Also, we observed some large mirror motion after we moved pico-motor of BS. But it went back to static after several minutes.

The alignment is also done with the standard procedure. It is first to misalign input mirror and find filter cavity transmission. Then center it on the screen. Then bring back input mirror and make injection and reflection overlap. Finally, align end mirror to have TEM00 dominant. After the lock, change the control point of each mirror to see if the transmission goes up to maximize.

Power:

Signal:

The demodulation phase for filter cavity locking is 65deg.

The setting of FC locking servo:

Today suddenly DAC died. Since I was working around the DGS I supposed I accidentaly disconnect some cables, but I check carefully and everything seemed fine.

We rebooted the standalone computer and the problem was solved. Note that in order to switch it on we had to disconnect and reconnect the power cables and to disconnect the timing singnal (pic 1). Timing cable was reconnected after the restart.

We observed that connecting end room picomotor driver to the power line in the same mupliple socket of OPLEV laser and PSD brings a HUGE 50 Hz in the signals.

Since picomotors are only used temporarily we have now disconneted them. We may try to connect them to another socket next time that we need them.

Local control on END mirror were implemented.

Pic 1 Pitch TF

Pic 2 YawTF

Pic 3 Comparison between open and closed loop spectra.

Pic 4, 5 photon model and damp for pitch  

Pic 6, 7 photon model and damp for yaw

I found a minimum of the sensing coupling when input signals (pitch and yaw) are rotated of -0.06 rad. So I updated accordingly the rotation matrix.

I used the following driving matrix  (pitch, yaw -> coils)   [0, 1, 0, 1; 1 0 -1, 1].  Note that the coil disposition is not the usual one!

For a comparison with the old control check entry #238.