[Aritomi, Yuhang]

Today we found WFS1 optimal demodulation phase changed again. The optimal demodulation phase for WFS1 is changed from 107.5deg to 127.5deg.

We tried to decouple pitch and yaw in WFS1 I by changing the rotation matrix of pitch and yaw in WFS1 (elog2149). When the rotation angle is 20deg, 11Hz BS pitch peak in WFS1_I_YAW minimized.

Then we injected a 12Hz line to INPUT/END PIT/YAW and measured sensing matrix again (previous measurement). Although 11Hz BS pitch peak and 12Hz INPUT PIT peak are decoupled in WFS1, coupling in WFS1 for INPUT YAW and END PIT got worse and coupling in WFS1 for END YAW is still bad.

[Aritomi, Yuhang]

[Aritomi, Yuhang, Matteo, Eleonora]

We measured RF peaks in QPD2 input1. This is the same measurement as elog2111, but this time the green is reflected from FC and galvo is engaged and there is no 32dB amplification. Setting of spectrum analyzer is the same as elog2111. Green power at QPD2 was 2.3 mW. 

Measured RF peak values are as follows. Note that 62.8 MHz and 93.2 MHz peaks are beatnotes of 15.2MHz and 78MHz.

Green injection to FC: 20 mW

Gain of FC servo: 9

UGF: 13 kHz (attached picture)

To investigate more about the optical losses in our set-up and have idea how to reduce more about optical losses, the measurement about half-wave plate (HWP) losses was done.

The test used the infrared beam before IRMC, which is directly from main laser. By measuring infrared beam power with power meter before and after HWP, the optical losses was evaluated. The power meter was fixed in this measurement while the HWP was taken away or put back several times. Therefore, for each HWP, there were several measured data. The difference between each measurement is that beam is hitting on HWP with different angle and different position.

Three HWP were tested: Two used CVI HWP (being used for SQZ reflected from FC, being used before injection to filter cavity), a new CVI HWP, a new thorlab HWP.

The result of optical losses measurement is listed in the following table:

[Matteo, Yuhang , Eleonora]

The problem was solved just by replacing the LAN cable that connects the desktop PC to the router. Note that the light at the LAN cable connection is still yellow/red and blinking. Probably it doesn't need to be green.

We checked CC1 error signal with 25 mW green power (attached picture) and found that peak to peak value of CC1 error signal is smaller than before.

The CC1 error signal also has offset. Currently we don't know the reason.

Today we found we cannot access to remote desktop (first attached picture).

Then we found the computer next to standalone cannot connect to network. Even after we restart the PC, it cannot connect to network. Second attached picture shows LAN cable connection to the PC. 

ps -ef | grep firefox

then kill the grepped number

Though I did ringdown measurement, the sampling rate was not enough to estimate the decay time...
I will modify it next time.

Anyway, I can lock the cavtiy at least 120 K.

I have added a rotation matrix to combine pitch and yaw WFS RF signals in order to compensate a possible physical rotation of the sensor (see entry #2144).

See attached the screenshot for model (pic1) and medm (pic2) modification. For the moment I didn't modify the DC part.

Takahashi-san, Tanioka

Takahashi-san kindly helped me to introduce He gas into the cryostat chamber.
This work is to prepare for the power outage scheduled on weekend.

Now the temperature is rising.

What I did

As the temperature became enough low, I tried to lock the laser to the cryogenic cavity and measure the finesse.
First, I scanned the laser frequency to measure the linewidth.
In addition to the linewidth, I could see the splitting peak probably due to the difference of polarization.
Then I did ringdown measurement several times.

Next step

I will analyze the obtained data.

Notes

As there will be a power outage work on next Sunday, I turned off the refrigerator to raise the temperature.
I will cool down to 10 K next time after improving the alignment.

This issue is originated by the fact that the servo galvo and the DGS are following two different convention for the WFS segment order:

The galvo servo from initial TAMA is following the convention in pic 1 (take from this document), while the DGS is following the convention on pic 2 (KAGRA convention).

The cables from the WFS DC segments have been connected into the galvo servo followig the convention from KAGRA/DGS and this resulted in a swap between X and Y error and correction signals.

We decided to keep the current configuration to be coherent with the DGS beam position monitor. Note that for WFS1 the cable for the correction signal for X and Y were originally inverted by mistake.

[Aritomi, Yuhang, Eleonora]

First we changed the demodulation phase for WFS1 from 17.5 deg to 107.5 deg in order to have all signals in I phase.

Then we measured spectrum of WFS signals (attached picture). As you can see, 11Hz BS pitch peak appears in WFS1_I_YAW which means there is large pitch and yaw coupling in WFS1. Eleonora will make rotation matrix to rotate WFS1 I pitch and yaw.

[Aritomi, Yuhang]

We measured closed loop transfer function (G_CL) of galvo by measuring ADD_OUT/ADD_IN in galvo servo. From G_CL, open loop transfer function (G_OL) can be calculated as follows.

G_OL = -1+1/G_CL

Note that sign of formula (3) in the attached galvo document should be opposite.

We measured OLTF of QPD2 DC pitch (X) (attached figure). UGF is 800Hz and phase margin is 30 deg. Compared with design (figure 8 in the galvo document), shape is similar, but UGF is smaller (design is 2kHz).

Today I measured the finesse of the cavity at room temperature by using ringdown method.
I also measured by cavity scan.
The results will be reported tomorrow or day after tomorrow...

Then I turned on the refrigerator and started cooling down the cavity.

As they will do works which involve a power outage on next Sunday, the target temperature is 120 K at this moment.

[Aritomi, Yuhang]

First we found that optimal demodulation phase for WFS1 has changed. It was 20 deg, but today it is 17.5 deg after we optimized it.

We measured sensing matrix by injecting a line to INPUT PIT/YAW and END PIT/YAW (attached pictures). The line frequency is 12Hz and the amplitude is 2000.

In the attached pictures, the left peak is BS pitch 11Hz peak and the right peak is the 12Hz injected line.

We have to think about how to decouple pitch and yaw in driving/sensing.

When we have test timed-out in DGS, we need to restart standalone.

This is a memo for restart of standalone.

1. take snapshot

2. turn off the power button of standalone

3. turn on the power button of standalone

4. restore snapshot