CC2 error signal with/without test mass feedback

We took a movie of CC2 error signal when test mass feedback is engaged (blue line in attached movie). Test mass feedback is engaged around 12s in the movie. CC2 seems better with test mass feedback. Attached picture shows CC2 correction signal with gain 0 (red line) and gain -1 (blue line). 

CC2 free running phase noise when turbo pump is ON/OFF

During this measurement, filter cavity is locked.

Alignment of IR with green and IR overlapping

[Aritomi, Yuhang, Yaochin]

First, we found that IR transmission was only 450 and it was due to optimal p pol PLL frequency changed. Current optimal PLL frequency with 60mW green is 150MHz. After this change, IR transmission became 2500.

Then we aligned IR with two steering mirrors on the bench to make green and IR overlap at first and second target.

Current mode matching is as follows. Mode matching is improved a bit and 93.5% now.

Mode	IR transmission
TEM00	2000
HG10	120
HG01	180
IG20	120
offset	94

Although green and IR should overlap, IR transmission is still fluctuating. Attached picture shows spectrum of IR transmission.

Off resonance reflectivity is 79-81%. On resonance reflectivity is 44-54%. Note that p pol PLL is 305MHz without green and current BAB power before OPO is 186mW.

Check the overlap of GR and IR

[Aritomi, Yuhang, Yaochin]

We could find green and infrared beam from the first and second targets. We draw a circle of beam edge (as shown in attached pictures) on the screen and compared the profile of green beam and IR beam.

In the end, we confirmed both IR and GR overlapped very well.

Attached picture 1 and 2: IR and GR on the first target (before overlap)

Attached picture 3 and 4: IR and GR on the second target (after overlap)

Note: In entry 1709, we couldn't see IR on the first target. This time we could see IR on the first target, the reason is figured out that the iris inside the camera was closed too much. After the fully open of it, we solved the problem.

First trial of input test mass feedback of CC2 correction signal

[Aritomi, Yuhang, Yaochin]

First we checked CC2 correction signal. Correction signal is 8.2 Vpp (Pic. 1). As you can see from the picture, it is saturating. This may be saturation of servo.

Then we injected this correction signal to ADC CH13 directly and tried to feedback to input test mass. We just set the gain -0.5 for filter. Surprisingly, the test mass feedback worked well without any filter. Pic. 2 shows CC2 correction signal when gain is 0 (blue), -0.5 (green), -1 (red). CC2 correction signal is suppressed when the loop is closed. CC2 control is more or less stable with test mass feedback now. We will improve CC2 with proper filter. Pic. 3 is CC2 in loop phase noise when CC2 is stable with test mass feedback (CC2 error signal is 56.4 mVpp). Note that free running phase noise and in loop phase noise are measured at different day. Turbo pump was ON.

Comparison of the absorption map between SHINKOSHA#5 and SHINKOSHA# 6

[Simon, Pengbo]

Attached to this report are the XY maps and distribution histograms of the absorption coefficient from the Shinkosha #5((shown in the attached figure 1 and 2), and Shinkosha #6(shown in the attached figure 3 and 4), the color bar scale for the two maps is the same.

As can be seen, sample #6 has better absorption than sample #5, and we think this is due to the inhomogeneous of the absorption along the z-axis of the samples.

For these two samples, we choose the center of the z-axis. We can check our assumption by doing another XZ maps.

Measurement of microphone spectrum of CC2 phase shifter

Aritomi, Yaochin, and Yuhang

For CC2 phase shifter, we could always hear the sound around it and we wanted to check what is the frequency of this sound. So we used a sound spectrum analyzer and it shows only one frequency component which is 6.9kHz. Note that we couldn't see this oscillation from the oscilloscope. 

We checked the squeezing spectrum and found that this frequency appears in the spectrum of squeezing. Also in the squeezing spectrum we could find the peak at ~23kHz. These peaks come from the resonance of CC2 phase shifter.

However, we found there was also a clear peak at 16kHz. And we found this peak when we measure OLTF of CC2. So it seems this peak comes from servo? Maybe we can consult with Pierre.

Recovery of IR alignment

[Aritomi, Yuhang, Yaochin]

Last Friday, we lost IR alignment, but the IR alignment could be easily recovered by moving one steering mirror on the bench. I moved both pitch and yaw, but especially pitch was misaligned. Now mode matching went back to ~90% as before.

Measurement of microphone spectrum of CC2 phase shifter

Aritomi, Yaochin, and Yuhang

For CC2 phase shifter, we could always hear the sound around it and we wanted to check what is the frequency of this sound. So we used a sound spectrum analyzer and it shows only one frequency component which is 6.9kHz. Note that we couldn't see this oscillation from the oscilloscope. 

We checked the squeezing spectrum and found that this frequency appears in the spectrum of squeezing. Also in the squeezing spectrum we could find the peak at ~23kHz. These peaks come from the resonance of CC2 phase shifter.

However, we found there was also a clear peak at 16kHz. And we found this peak when we measure OLTF of CC2. So it seems this peak comes from servo? Maybe we can consult with Pierre. (figured out later this 16kHz if from mechanics)

Check of IR and GR overlap on First target/Second target/IR camera

Aritomi, YaoChin and Yuhang

To have a feeling of IR and GR overlap. We checked three points.

1. First target(shown in the attached figure 1 and 2). In the first figure, IR is actually in the center. When I was checking it, I could see the difference if Aritomi-san blocks or unblock the IR beam. In the second figure, there is GR. But it is difficult to tell the overlap level.

2. Second target(shown in the attached figure 3 and 4): It seems IR is higher and a bit left.

3. End camera(shown in the attached figure 5 and 6): It seems IR is also higher and a bit left. 

Diagonalization of length control matrix for Input mirror

Eleonora, Yaochin, and Yuhang

Firstly, we tried to excite FC length by using H1 and H3 coil. But we found H1 is not working(because we sent excitation to H1 only but the mirror couldn't move accordingly). So we checked if we were sending the signal and whether the signal is reaching the coil driver. We found the signal is reaching the coil driver but with some noise. The frequency of this noise is measured as 700kHz.

So we decided to excited FC length by using H2 and H4 coil. The method we used to diagonalize is to measure the response of the mirror optical lever signal. We sent excitation to channel K1:FDS-INPUT_Z_CORR_fil_EXC with a frequency of 4Hz and amplitude of 4000. We set the matrix index for H2 as 1 and measured the spectrum of K1:FDS-INPUT_Y_fil_IN1. There was a peak of 126.9 at 4Hz. Then we set the matrix index for H4 as 1 and measured the spectrum of K1:FDS-INPUT_Y_fil_IN1. There was a peak of 173.4 at 4Hz. So we decide to put index 1 for H2 while index 0.73 for H4 to make the coupling to yaw to be zero.

In the end, we measured the transfer function from the excitation of the INPUT mirror length to FC correction. There should be a response. We also measured the TF from the excitation of INPUT mirror length to INPUT mirror yaw optical lever. There should be not a response. Also the coherence of the above two. The result is shown in the attached figure 1. We have a response from the FC correction signal 10 times larger than the response from the yaw optical lever. Also, the coherence is better for FC correction. This can be a good start for the implementation of the feedback for CC2 phase noise.

Filter cavity GR_tra DC dropped again and its recover

Eleonora, Pengbo, Yaochin, and Yuhang

We found green transmission DC dropped to ~600 counts at the beginning of today's work.

First, we checked the GR higher-order modes we have for the filter cavity.(As shown in the last figure) It was fine.

Then we went to the end room and found the GR_tra PD was tilted almost by 45deg. We think the PD cables have been accidentally pulled during the work to repair air conditioner which took place this morning in the end room. After we correct the angle of this PD, we found the signal went back to ~2700 counts.

We also checked green power at two points(shown in the attached picture 1) in today's situation (the green injected power is 12mW). The first point is just before GR_tra PD and it is 45uW(shown in the attached picture 2 and measured as shown in the attached picture 3). The second point is just after the green BS and it is 1mW(shown in the attached picture 4).

Recalculation of Absorbance for the Sapphire Calibration Samples

Simon

I recalculated the absorbance values to take into account the small transmittances we got from the spectra taken at the ATC for all colored Sapphire samples.

The new spectra, now also with reference values at 633nm, can be found in the attachement.

Absorption Measurement on Small Sapphire Smaple from Shinkosha

Pengbo, Simon

We removed the OSTM and packed it again. It is now located in the small shelf inside the clean room.

After that, we recalibrated the system.
The calibration values are:

R_surf = 17.86 1/W
(AC = 0.54V, DC = 4.58V, P_in = 0.030W, abs_surfref = 0.22)

R_bulk = 0.8 cm/W
(DC = 0.105V, AC = 5.42V, P_in = 0.030W, abs_bulkref = 1.04/cm)

Then, we exchanged the calibration sample with the first of the 5 small Shinkosha Sapphire samples: S5 (2" x 20mm)
We located the center of the sample as [X,Y,Z] = [327.25, 122, 33.5].
The transmittance of the sample is T ~ 0.85

Since we cannot set 10W as an input power and leave it as it is while moving the sample into the beam and out again (the sample holder will cut the beam otherwise), we set the power to its minimum trough the polarizer while it is feeded with 7A current and used the beam-shutter for moving the sample holder. In the center position, we set the power to maximum. The transmitted beam power has been measured to be 8.4W.

Now the map is being taken with 15mm radius.

Test of bias for AA's quadrant

Aritomi and Yuhang

We found the problem of the small RF signal of the AA's quadrant (elog1670). Matteo T suggested checking the bias. We turned on the button on the quadrant box and measured the voltage at the end of the power cable.  We checked with multi-meter and it shows 150V reached quadrant.

So bias seems not to be a problem.

Installation of Mirrors

I installed 3 steering mirrors for HOMs beam paths to roughly decide where to put PDs for intensity stabilization.
2 HOM-beams are roughly alinged into STMs which are for the alignment for cryogenic cavity.

Attached is the picture of current situation of optical table.

Summary of current issues

• fluctuation of IR transmission from filter cavity (entry 1701)
• large CC2 phase noise from filter cavity (entry 1695)
• large bump in shot noise spectrum at low frequency (entry 1529)

IR alignment with dithering

[Aritomi, Yuhang]

We measured mode matching when filter cavity is aligned with pitch dithering. The result is as follows. Mode matching was around 90%. We found that when pitch dithering was engaged, pitch misalignment became less, but yaw misalignment became more.

Mode	AOM frequency (MHz)	IR transmission
TEM00	109.03607	3000
HG10	109.43128	350
HG01	109.43219	200
IG02	109.8288	115
offset		94

IR TEM00 transmission was fluctuating even when dithering was engaged (attached movie). Time scale of the movie is 2s and DC offset is 94.

We measured BAB reflection when BAB is on/off resonance. Off resonance reflectivity is 82% and the reflection might be still cutted.

Preparation for CC2 feedback to the INPUT mirror

I modified the simulink model to include the possibility to feedback the CC2 correction signal to the length d.o.f. of the input mass.

The ADC channel where to inject the CC2 signal is the n 13 in the top BNCtoDsub converter in the clean room (named ADC0 Ch16-32).

I modified the medm screen accordingly. Next step will be to optimize the length driving of the input mirror.

Time-out error on diaggui.

On Wed 02/10 we had another timed-out error on diaggui. It was solved by restarting the standalone. It happened ~13 days after the previous one. (entry #1650).