We found that the issue of not being able to move END yaw is similar as in elog 2995, namely the sign of H3 is flipped...

Also, we now have about 2mm range for the pitch picomotor in one direction but it should be enough for our offload.

[Takahashi, Marc, Rishabh]

We opened the chamber to investigate the suspension in the west end.

• All actuator magnets are still on the mirror.
• There is no rubbing point.
• The pitch-yaw motion of the mirror with the picomotors looks fine.
• We found that the OpLev beam hits the cables for the actuator coils. We treated the cables so as to avoid the beam.

Using the power meter in reflection I saw that the mode matching of IRMC was > 95%.

Flipping the INV/NON INV switch makes the IRMC lock to the mode with output power up to 1.01 mW (/1.68 mW input = 60%). So that works now. Actually, I did the same thing for SHG previously when it was showing similar behaviour...

Adjusting the gain on the IRMC servo shows very little change in the transfer function. For gain increase from 1.1 to 7, the unity gain frequency increases to a rather underwhelming 15 Hz. Now that I think about it, the IRMC PD (Thorlabs PDA05CF2) is specified for a -3dB bandwidth of 150 MHz (75 MHz linewidth). 

IRMC error signal has a DC offset of 150 mV for some (probably not good) reason (figure 1). Green mode cleaner error signal suddenly went to about 60% of what it was yesterday (figure 2).

[Marc, Rishab, Shalika]

TLDR :

PR and BS are offloaded and fine ; INPUT need offload ; END can not move in yaw

cameras are fine ; can not connect to pico server or 2nd target

First we wanted to do suspension healthcheck but had again time-out issue.

It was solved by restarting the standalone pc. We found out that the BS response was really strange (eg fig 1) and that a END had a too low magnitude (fig2).

We went to tried to realign BS (even though was already good enough for the previous measurement) and went to END room where we found that the oplev gain was 10 instead of 100.

We put the proper gain and also realigned slightly the END oplev.

Before, we were not able to see camera image from 2nd target or end room in central building so we confirmed that END room cameras are working properly.

In central building, we restarted the quad camera board that solved this issue.

We could see green flash on GR transmission.

We then offloaded PR by keeping the GR beam on second target and acting on picomotors to make the coils offset go to 0.

We did the same for BS. However, at first both pitch and yaw of coils moved in diagonals in the camera. We found out that once the coils offset absolute value is below 200 this coupling is removed.

Now both PR and BS are working fine and offloaded.

We have to do the same for END (but now yaw coil offset is 0 and it seems far off good alignment and coils do not work) and INPUT.

We found that the ethernet cable that connect the picomotors pc to the switch was squash below a monitor. We replaced the cable but still are unable to connect to picomotors nor 2nd target...

Rishabh, Michael

We intended to go and tweak the IRMC control loop gain for better control bandwidth and stability, as well as measuring the GRMC/MZ transfer functions. But there were a few problems.

The IRMC seems a bit misaligned. We only have about 0.33 mW/1.66 mW = 19.9% transmission. We tried unlocking and relocking several times. Trying to view the free spectral range on the IRMC reflection PD showed some weird jagged spectrum with not very high amplitude. Power meter showed nothing, although Marc later said this is because the bandwidth of the power meter needs to be set to High. Perhaps the PLL alignment process affected the IRM alignment again. The injection and reflection power are basically the same as when it was working properly though.

On the green path after the SHG, the 90/10 green beamsplitter sends reflection to the filter cavity green AOM, which was optimised as per recent elog entries. Accordingly, due to optimisation of the 90/10 BS reflection alignment, there will be a small amount of change in the transmitted path length to the GRMC and MZ. Indeed, some change in the mode spectrum could be seen in the GRMC transmission (figure 1). We used the steering mirror after MZ and now the mode matching is (1.25/(1.25+0.40)) = 96.9% (figure 2, 3). We also tweaked a bit the PDH error signal - the phase was adjusted from 164.993 to 185 degrees (DDS2 Channel 2 GRMC Demod), so the error signal looks a bit more symmetrical (figure 4).

We couldn't lock the GRMC though. According to a previous entry from Yuhang regarding this issue, we looked at several troubleshooting points:

0. grmc has a good alignment.
97% mode matching (figure 2, 3)

1. PDH signal has 316mV pk-pk checked from EPS1.
120 mV pk-pk (figure 4)

2. grmc has loop sign of INV, which is as design.
Yes

3. The RF source phase is reloaded. The phase of RF source is 125deg. When it is changed to 35deg, the signal around resonance becomes flat. This indicates the RF signal phase is still a good one.
Due to the change of EOM the DDS phase is different, but we flipped by 90 degrees and saw that the signal around resonance became zero so indeed the error signal and DDS configuration are fine.

4. There is a switch which has +/- sign. This doesn't decide the sign of control loop. But when we use this type of servo for CC1/2 controls, we need to flip this switch. I tried to flip this switch, but it doesn't help to close loop.
I tried this but no change

5. grmc transmission is checked to have 1.13V peak. This is two times smaller than the value written by Pierre.
The main peak reads 1.25V from the PD signal (figure 3)

6. Loop gain is 3 as usually used.
Yes. Likely this will need to be changed later though due to the EOM change.

7. Threshold for peak identification is -0.55V. This is as required.
The threshold knob was set to 3.3 but I tried changing it to a few values and didn't get any lock.

8. The GR power reaching AOM is measured to be 44mW, whose nominal value is 50mW.
We have 47 mW reaching the AOM

We have good mode matching and a good error signal shape. So the alignment, transmission PD, DDS configuration and PZT are all fine. It seems like the issue is coming from the servo module, or perhaps the amplitude of the error signal. Hopefully it's just to do with the settings and not something for which we have to take the board outside of the cleanroom.

[Marc, Michael, Rishabh, Shalika]

We tweaked the last mirror on green injection into PR and recovered targets on PR tank.

We moved PR coils and recovered BS target. Actually, the gate valve between BS and INPUT is open so we could not use it to fine tune this alignment.

However, we found out that centering the beam on the 2inch mirror inside BS chamber was also a good way to have the beam centered on the first target.

We tried to control the 2nd target and look at its camera from remote but we could not connect to them. Maybe related to the on-going fiber installation in the arm?

We went to 2nd target and could recover alignment by moving BS pitch and PR yaw. It now seems that at least one of the yaw magnet of BS fall down as the beam is not moving properly.

Then we tuned END to recover the back-reflection on the 2nd target. However, it also seems that END yaw is not working properly..

We tweaked a bit INPUT and the green beam is now back to the injection FI.

We will have to offload several suspension using pico-motors as current coil offset is quite large for several dofs.

I checked the alignment to the green AOM (FC first stage length control).

Initially the following signal was applied to the AOM: 109.036 035 615 MHz, 5 dBm signal generator amplitude + 18 dB RF amp, 24V 0.5A power supply to RF amplifier

I used the " BSN10 GR 90/10" (as it is labelled) to move the beam into the AOM, then kept going to align the first order diffracted beam into the iris (figure 1). The following power levels were measured:
Power from SHG: 270 mW
Power into AOM: 47.0 mW
Power after AOM (no signal): 46.0 mW
Power after iris (23 dBm signal): 22.0 mW

(c.f. reference levels 2764: 48.6 mW in, 24.3 mW out)

I took a few different measurements of the first order power for different RF signal amplitude - not really a comprehensive characterisation, just a quick check. Seems roughly consistent with old measurements (531 1679), but I wasn't trying to be too precise for now. I didn't rotate the AOM at all though.
22 dBm -> 18.6 mW (40%)
23 dBm -> 22.0 mW (47%)
24 dBm -> 26.0 mW (55%)
25 dBm -> 30.0 mW (67%)
26 dBm -> 33.2 mW (70%)

The green beam is roughly aligned close to the PR targets (figure 2). There shouldn't be too much adjustment needed, though it is a 2 person job.

Through the time I was in the cleanroom the SHG unlocked a few times, maybe once every 45 minutes or so.

I measured the OLTF of the SHG and IRMC using the old spectrum analyser. I used two methods:

1) In FFT instrument mode, apply white noise to Perturb IN, measure Ch2/Ch1 (EPS1/EPS2) frequency response and coherence using a range of noise injection levels. The noise -> FFT method is fast but less precise when it comes to measuring characteristics about peaks.
2) In swept sine instrument mode, apply swept sine to Perturb IN, measure Ch2/Ch1 frequency response and cross spectrum (swept sine doesn't have coherence option)

In the case of white noise injection, lock at 500 mVpk was a bit temperamental but the spectrum could still be measured. Swept sine worked for an initial injection level of 20 mVpk. For values higher than that, it would unlock when the measurement reached ~ 100 Hz (it starts at the max frequency and goes downward).

Magnitude, phase and coherence for the two cavities are plotted for various excitation levels (fig 1-6), and the best result is collected in a 3x1 image (fig 7, 8)

SHG has a somewhat low unity gain of 600 Hz, nearly 100x lower than previous (50 kHz). Phase margin is about 50 degrees. Maximum coherence is obtained for about 200 mVpk noise injection.

IRMC is very low. It seems a bit strange actually. UGF is around 10 Hz and coherence is quite bad for excitation < 500 mVpk, but it also unlocks really easily when excited at this level.

[Marc, Shalika]

Yesterday we checked again DDS3 outputs and got similar results as last time (3178).

We opened the box to check the +12V/GND provided to each amplifiers. We found that DAC0 and DAC3 were not receiving the expected voltage.

DAC3 +12V cable got easily disconnected and we found that DAC0 +12V pin was extremely tilted..

We removed DAC0 amplifier and soldered a new one. We also resoldered DAC3.

Our guess is that all the +12V/GND cables have a strong strain and twist due to the limited space in the board. So we replace the connection to the board output from a SMA female to female connector to a about 5cm length SMA cable.

All the ouputs of the board are now as expected :

DAC0 8.8dBm

DAC1 9 dBm

DAC2 8.6 dBm

DAC3 8.6 dBm

Maybe the strong twist of DAC0 amplifier +12V pin was the reason for all our issue?

Also the board inside is now quite messy. If we want to tidy it we should prepare some custom length SMA cables.

Marc, Shalika, Michael

We looked a bit at SHG transfer function using the new spectrum analyser (Source -> Perturb IN, Ch1 -> EPS2 Out, Ch2 -> EPS1 Out). Just a quick check using FFT with white noise injection showed that the gain of the loop is somewhat lower than before. The frequency response Ch2/Ch1 in the reference level is flat at 20 dB until 10 kHz, but now we drop off fairly fast at about 100 Hz. Switches are set to NON INV, 1/F3, DIF OFF, SIGN -

I found the SHG wouldn't lock properly even though the servo light was green. First I checked the power compared to reference levels. Input IR was fine (~700 mW) but reflected green was very low, < 1 mW. Next I tried checking the mode spectrum but it didn't show anything at all. After flicking the lock switch a few more times I noticed the green power actually dropped when it locked, so based on that I turned the INV switch to NON INV and now it locks as it should (270 mW green). Basically, we have to do some tweaking of the servo because of changing the EOM

We recently purchased a new Stanford Research SR785 Dual Channel Signal Analyser to be used in the FC cleanroom.

It is a bit complicated. One of the main features is that the measurement is independent of the display. This allows us, for example, to have a really precise measurement but with a really rough display, among other things. It can also save a lot more data into its internal buffer in one go, so we can then transfer to disk without having to redo a measurement.

By default it had a really irritating alert message that sounds like a phone ringing, so I turned it off in "Preferences -> Alarm noise -> Quiet". There is another menu option which says "Alarms -> off" but that controls the display of error messages. Very strange UI in my opinion.

It can write data to USB, however, due to weird stuff, it won't recognise storage devices over 8GB. This seems to be a common issue with making old tech forward compatible with FAT32 USBs. The grey USB drive in the FC cleanroom works fine and I already formatted it.

The spectrum analyser formats the USB to pretend that it is several hundred 1.44MB floppy disks. But unfortunately Windows only recognises the first "disk" in the sequence (labelled 000 in red digits on the front panel of the device next to the USB port), so it still runs out of space. Also at one point the spectrum analyser would refuse to re-format the USB, so I had to Full Format on Windows (slow...) and then re-format on the analyser. Shalika says that apparently you can program it to send data over wifi to the computer, which would be better. The manual talks about cable connections only (RS232 and GPIB) but maybe we can find a wifi attachment.

To do: Figure out a good way to remotely import data from the analyser using programmable commands, and then batch convert into some convenient data format. Personally I want to separate headers and data, and the delimiter doesn't matter to me. MATLAB also seems to not mind this operation. But maybe others also have preferences for dealing with data.

Objective: [In continuation to elog 3177]

1. Measuring ringdown decay time

Details:

1. The new RF switch's output was attached to AOM. The diffraction efficiency remained the same as noted previously, i.e. 57% (as mentioned in 3131)

2. The PD used at the transmitted path is  PDA20CS-EC (see elog 3139 for properties). The PD at the transmitted beam is set with a 10dB attenuator.

3.  The amplitude of TEM00 mode in the transmitted signal was 4V. The demodulation phase was set to 185º. The mode matching was observed to be 4.88/(4.88+1.82)=72%

4. The filter cut-off frequency was 3 Hz and the gain was 100. 

5. The laser temperature was 8400±20. The offset voltage varied from -1 to -0.8. 

6. The cavity was able to lock the TEM00 mode (see Fig 1). The voltage of the RF switch control was set to low to cut off the input to AOM. The possible fitting obtained gives a decay time of 1.45 µs (see Fig 2)

[Marc, Shalika]

We removed the 3 broken amplifiers from DDS3 (ie the ones connected to DAC1,2,3).

We confirmed that the ground and +12V were correctly provided.

We soldered the DAC1 amplifier, brought it to TAMA to test the output and measured the expected 9dBm.

We then soldered the 2 remaining amplifiers.

We then measured :

DAC0 -> 6.5dBm

DAC1 -> 9dBm

DAC2 -> 9.6 dBm

DAC3 -> -23 dBm

Because we did not remove DAC0 amplifier before installing the new amplifiers, we suspected that some bad connections could explain the too low output of DAC3.

We tighten better the connections of all amplifiers and this time we got

DAC0 -> -20 dBm while all other outputs were same...

We tried to untighten a little the connection and this time DAC0 -> -36 dBm (other unchanged)..

We need to investigate the reason for this drop (maybe same as what happened before that `broke` the amplifiers?)

Objective: [In continuation to elog 3145]

1. Testing the new RF switch HSWA4-63DR+

Details:

1. The new RF switch has 4 RF terminals (which can behave as both input and output) and 3 control terminals. The RF common port can behave as output or input depending on how we treat the RF terminals.

2. The RF switch was supplied a voltage (using voltage supply) and control voltage to two control terminals (using DC offset from function generator). The RF common port was treated as input and was connected to the output of the RF driver. The output of switch was collected at RF1. All the other ports were terminated using a 50 Ohm terminator. I also made sure that it didn't touch the table top as RF switches are sensitive to electrostatic discharge and commonly this disrupts the output. The output of the RF switch was seen at the RF1 port, in the oscilloscope. See Fig 1 for RF switch setup. 

The input was provided as mentioned in the table

3. The control terminal behaves as a TTL(Transistor-Transistor logic) and can switch on or the output depending on their state. The logic of the control for RF1 is as follows:

Although there are 3 controls for this switch, we can leave control 3 unconnected. 

4. RF driver : First I checked the output of RF driver. The RF driver is given a 9.71 V tuning voltage (to make 80Mhz for the AOM) and 1 V input. The output of 80 Mhz frequency is as seen in Fig 2. (When I made the setting of oscilloscope to 50 Ohm impedance, I couldn't change the scale of channel beyond 1 V and so couldn't see the signal in the frame. When I tried the autoset setting, it made the impedance to 1MOhm. This is the only oscilloscope I had which had 50Ohm option but uses a floppy disk and so I had to use the 1MOhm impedance option)

5. RF switch : The output of RF switch is as expected, and is the same as the RF driver output. See Fig 3 for the ON state and Fig 4 for the OFF state. 

Next Step:

1. Connect the output of the switch to AOM

2. Lock the cavity and measure the ringdown appropriately. 

Items Borrowed: I took 3 cables and a 50Ohm terminator required for this setup from elec shop. I have returned the multimeter that I borrowed previously to elec shop. I apologize for any inconvenience I may have caused.

[Shalika, Marc]

Objective: Recover PLL alignment

Details:

1. We tuned the mirror alignment to increase the main laser and auxiliary laser coupling. For AUX1 and AUX2 the mirrors circled in red and blue in Fig 1 were tuned respectively. (The output of the PD was observed in the oscilloscope but it was fluctuating a lot and so the tuning was done with all lights off)

2. The coupling status is as follows 

3. We did face trouble during tuning optics for AUX1. One possibility could be that after we changed EOM in the main laser path, the new EOM introduced a change in beam shape due to its wedge shape, and now it's difficult to focus the beam into the fiber. 

4. Also, HWP was kept before mirrors (circled in red in Fig1) to investigate polarization issues. The effect of its rotation was not observed at the AUX1 output and left the output unchanged. 

Next Step:

1. Soldering the amplifiers for the DDS3 board and doing connections. 

[Marc, Takahashi-san]

There is a clean booth close to BS chamber hosting a small optical table and microscope.

As it is too close to the LC optical table, we moved it on the other side of the vacuum tube.

The several TAMA optics (BS, TM) were placed on the bottom left drawer of the large dessicator. Note that one TM has several chips..

There were also 2 boxes that are now in the west arm.

[Marc, Nishino, Shalika]

Today's goal was initially to recover the 2 PLLs alignment.

However, we found out that one of the newly installed steering mirror to recover the beam tilt because of the wedge of the new EOM was quite miscentered.

We realigned this mirror but then also had to realign several optics afterwards..

This meant that both PLL and IRMC alignment got destroyed.

For the PLL part, we tried to recover the coupling of Main Laser to the fiber as in elog 1200.

Luckily, we still had transmitted beam after the single mode fiber.

After some tweaking we got:

[Shalika, Marc]

Overview: The Labview interface for the temperature controller, voltage controller, and polarimeter camera has been completed. 

1. For temperature controller: We can switch on/off, enable/disable channel, set temperature, choose the sensor type to be interfaced, and various other kinds of features can be accessed. (see Fig 1 and Pdf 1 attached for the front and back panels respectively)

2. Fopr voltage controller: we can switch on/off, enable/disable, set desired voltage, and sweep for any number of iterations desired. For the birefringence characterization of the KAGRA size sample, we might need more than 100000 iterations. and it can be done easily. (see Fig 2 and Pdf 3 attached for the front and back panels respectively)

3. For the Camera, we can see the azimuth, ellipticity, and power of the beam incident. (We would like to integrate the Poincare sphere, and visuals of the Polarization axis to make it better and the same as Thorlabs software. (see Fig 3 and Pdf 3 attached for the front and back panels respectively)

For all the 3 Interfaces, almost all the features offered by Thorlabs software have been integrated with the new labview interface. 

Next Step:

1. Integrate all the VI in one. Also, the GUI can be resized or components can be moved for feasibility during the experiment. 

2. Try to take real-time measurements.