After I did this replacement, I found there is a new peak appeared. Compared with the alignment Chien-ming did for GRMC, this additional peak has a much higher height.

Today I use a camera to check this peak and it shows shape like the attached figures.

But I think this is not a big issue since we just need to lock on TEM00. But we will lose some power.

In the past days Pierre and Yuhang noticed that the level of the LO to the fiter cavity mixer was not the one required by the mixer, so they amplified it. After this change we were not able to lock the cavity on the TEM00 peak anymore. We went back to the previous configuration but still we could not lock properly. It seemed that we were locking on a sidebands and, strangly enough, we could lock on the top of TEM00 only by switching off the rampeauto power supply. But of course in this configuration the gain was much lower and the lock was not stable.

We found that the problem was that the sign of the lock had changed (even after going back to the original configuration). 

Note that the sign inverter on the rampeauto doesn't change the error signal sign, the only way to change the sign is by shifting the demodulation signal sent to the mixer of 180 deg. We did it and the cavity could lock again.  

We also learnt that swiching off the reampeauto power supply somehow changes the sign of the correction that it provides.

Matteo, Simon

After the little desaster today with the ETMY substrate, we confirmed that the absorption bench was not damaged and continued to do the absorption measurements with the ETMX substrate from GT. We confirmed that this sample has approximately the same thickness as the ETMY one and set it into the sample-holder in the same way.

We learned our lessons today and did the alignment settings of the substrate without the IR-laser, just with the probe-laser.

The absorption-map is now being taken and the measurement should be finished by tomorrow (fingers crossed!).

Matteo, Simon

In order to measure absorption maps of the Sappire substrate from the "GT" company, we started to take the ETMY substrate. For this purpose, we carefully opened the container of the mirror and took-out the sample This was actually a tricky part as the sample is quite heavy and not only there were some placeholder-columns in the container which we could not remove and made it difficult to pick-up the sample, but also we realized that the sample already has the "ears" attached.

Somehow we succeeded to put the sample inside the mirror-holder and confirmed that it has a reproducable position in it by using a horizontal alignment of the ears. We can furthermore report that close to the edge, we recognized several defects which we, however, do not consider as being a problem.
Also, due to a repolishing measure which has been done after bKAGRA-phase1 (the substrates were already been used as KAGRA mirrors before), the thickness is reduced compared to the Shinkosha#7 sample (150 mm → 143 mm)

Once we set the substrate together with its holder inside the transition stage, we adjusted a little bit the position of the imaging-unit (6.7 mm → 9.7 mm) due to the reduced thickness. After that, the DC-signal was adjusted and the pump-laser power maximized.

Main Issue:

At that point we could start setting the basic limits for the transition stage with the respective LabView program.
However, the initial (default) values for the stage-position put the holder into the beam-path of the pump-laser while at maximum power!!!
→ That burnt a hole into the mirror-holder
→ Parts of the burnt hard-plastic could be found also on the sample surface

Of course, we immediately blocked the laser-power and removed the sample and its holder for inspection:

• It seems that the sample itsel is not damaged but dirty on one surface now
• With an air-blower, we removed the largest parts of the dirt), while the sample-holder has a hole on the outer side. No further damage could be reported (the sample holder is still usable).
• We put the sample back into the container-frame and put first-contact on it

Let's hope this will clean the surface enough for continuing the measurements (we will see next week...).

Pierre, Aritomi, Eleonora, and Yuhang

After we used the new base plate for mirror mount, we measured the optomechanical transfer function yesterday. (Later we realize that we lock with a bandwidth of only around 100Hz. We saw ~1kHz resonance oscillation when we tried to increase gain)

Today, Pierre designed the new CC1 locking servo. While we have the same problem of ~1kHz oscillation. We could only lock with a bandwidth of 200Hz which is reasonable. I realize only now that we should have this 1kHz oscillation problem. With the locking bandwidth of 200Hz, we could measure the open loop transfer function. The measurement result is shown as attached figures.

There is no particular explanation of why we have this new 1kHz peak. And this peak height is around 20dB. This height of peak makes the system very unstable.

Notice: we could measure open loop transfer function with servo and network analyzer again. The reason is we connect network analyzer power with ground floated.

When I connect it with the same power with rack, the 50Hz noise becomes even higher!

Another thing to be noticed is that when I use SR560 as servo, and inject noise from network analyzer to SR560, there is no 50Hz noise!

With Manuel's help I managed to change the sensitivity initialization of the lock-in. Now it is set at 5mV/mA.
I restarted the measurement around 23:45 after measuring the stability of the pump laser: dP/P < 2.5% (see attached fig.1)

I logged in to monitor the measurement and found that the labview crashed. I tried to restart the measurement but the computer was unbearably slow so I reboted it.
The crash of the labview and subsequent restart resetted the LockIn parameters, therefore the measurement now seems unfeasible.

We will investigate tomorrow how to solve this problem.

Pierre, Aritomi and Yuhang

We found that when we just connect the source port of network analyzer to servo, the error signal presents a very very large 50Hz noise.

Today at 20:15 I checked the status of the map and found that the computer rebooted (apparently due to some windows updates even if the auto-update was switched off).
Luckily the laser was still operating at the previously set value, so I restarted the map at 20:17.

Matteo, Eleonora, Simon

With the alignment set yesterday and the day before (see log entries 1448 and 1445), we were able to start with inserting a sapphire mirror (SHINKOSHA, No. 7). We are using this mirror as a kind of a test-sample to check whether the system is giving reliable data since this sample has been measured already in the past.
 

• We removed the silica mirror from the mirror-holder (that one is now stored in the small shelf inside the clean-room - be very careful when moving around as it is easy to hit!!!)
• We took the sapphire mirror from its container and put it inside the mirror-holder (see attached pictures)
• For placing the mirror-holder inside the transition-stage, we removed the protection-shield around the detector-bench, relocated the imaging units of both red and IR (red -> 6.7mm), and moved the translation-stage to a convenient position
• Then, we placed the mirror-holder on the translation-stage
• After that, we put the protection shield

Note: In order to have enough clearance for the mirror (thickness ~15cm), we removed the IR imaging-unit later on

Once the mirror was set, we started a checkup measurement to compare our setup with measurements from the past:

• Setting the border-limits to define where the mirror starts and ends in Y and X direction
• Readjusting the imaging-unit to have a maximum in DC
• Run horizontal measurements to obtain the coordinates of input and output surface with ~1W of input power in the center
• Run horizontal measurements with 10.47 W of input power to check all initial settings (see screenshot)

With the results, we confirmed an absorption coefficient of ~130 ppm/cm which is in agreement with Manuel's measurements (~119 ppm/cm mean value over an entire map)

Then, in the afternoon, we started to take a X-Y absorption map in the center of the mirror (anticipated duration ~14h). That should be finished by tomorrow.

Pierre and Yuhang

Since Matteo designed the new base plate for the new mirror mount (RadiantDyes), I replaced the old base plate with this new one. This new one has two holes in the plate, so we expect it to have a better performance.

After the replacement, I tried to lock again with the new MZ/GRMC servo realized by Pierre. But at that moment, we didn't succeed. The reason was found out that somehow GRMC transmission was reduced. Now the highest power we can have for GRMC transmission is around 55mW.

Then we tried to find the coherent control error signal for CC1. But we failed. We will try to figure out the reason tomorrow.

Eleonora, Pierre, Aritomi, Yuhang

Recently we found 50 Hz presents everywhere. In the attached figures, we can see some examples of these 50Hz noises.

A part of noise level was identified that it comes from of ground loop between circuit and measurement device. This is identified by changing the power supply of the oscilloscope to different places. But we cannot eliminate this noise totally. (From figure 5 to figure 2, the change is the change of oscilloscope power supply)

We also identified that the 50Hz noise for GRMC transmission signal comes from the DDS board. At that moment, only DDS board output is connected to mixer and mixer IF channel is connected to the oscilloscope. We tried to change the connection with and without a lot of other components, and we found only DDS board gives this 50Hz noise.  (Figure 3)

We see a different shape with normal measurement 50Hz noise for GRMC transmission signal, so we think this noise coupled into control loop and affects the phase locking of GRMC a lot. (Figure 2)

Pierre, Yuhang

After the design/talk/discuss with Matteo, Eleonora and us, Pierre redesign the circuit and we implemented it. Now the procedure is just to press 'reset' button and then MZ and GRMC will be locked in sequence. Please also remember to use 'auto' mode of GRMC and 'man' mode of MZ and put them both in 'lock' state.

Then we measured the open loop transfer function of MZ.

[Matteo, Simon]

Today we switched on the 1064nm pump laser for the first time after four months. We had some problem identifying the correct COM port (COM11) but solved that the laser could be successfully switched on and controlled from the PCI computer. One thing to be noticed is that the power cord of the pump laser seems to have connection instabilities, please remember to be careful and never touch the plug in into the power supply.

After the successful result on the pump laser we switched on the probe laser (633nm). No problems on that. We had to install a variable OD filter in front of the probe laser not to saturate the photodiode on the imaging unit. We aligned the probe on the imaging unit without any reference sample to have about 4V of DC output as read by the lock in. We then installed the surface reference sample and performed some z scan. NOTE: the written part present on the sample is facing the imaging unit. At this stage we aligned again the probe beam into the imaging unit photodiode maximizing the DC to compensate for the misalignment introduced by the reference sample, we then aligned the pump beam to maximize the AC signal at the crossing point.

MEMO: to align the probe on the IU photodiode we used the IU lens translation stage; to align the IR beam we used the translation stage on the last lens before the sample area.

Attached (1) the screenshot of the absorption measurement for surface reference sample (try one).

After speaking with Manuel, he told us that the written part of the surface reference sample should be facing the pump side and not the IU side. We flipped the surface reference sample and optimized again the alignment and performed again the z scan. Result is in attached figure (2).

In the end we substituted the surface reference sample with the bulk reference sample and measured the z scan. Result is in the attached figure (3).

From measurements shown in (2) and (3) we can obtain the calibration of the system.

R_surf = AC_surfref/(DC_surfref*P_in*abs_surfref) = 16 [1/W]
where AC_surfref = 0.42V, DC_surfref = 3.85V, P_in = 0.031W and abs_surfref = 0.22

R_bulk = AC_bulkref/(DC_bulkref*sqrt(T_bulkref)*P_in*abs_bulkref) = 0.604 [cm/W]
where AC_bulkref = 0.067V, DC_bulkref = 4.64V, T_bulkref = 0.55, P_in = 0.031W and abs_bulkref = 1.04/cm

The two calibration values are compatible with old calibrations.

[Pierre, Aritomi]

Pierre fixed RF amplifier and measured amplification factor for AOM which is 34dB. Since we should have 23dBm for AOM, RF signal before RF amplifier should be -11dBm.

I replaced IR phase shifter with a new one (Pic 1) and aligned IRMC and locked it with Pierre's servo. Tomorrow we'll measure transfer function of CC2.

[Aritomi, Yuhang, Eleonora, Matteo]

Recently we had a problem that when BAB is injected into filter cavity, we cannot lock green phase with p pol leakage of BAB transmission. Today we found that back reflection of IR from filter cavity makes green phase error signal unstable. When we block IR injected into filter cavity, green phase error signal is stable, but when we open it and IR is aligned to filter cavity, green phase error signal fluctuates a lot. We guess that back reflection of IR from filter cavity goes back to OPO and amplified and becomes p pol leakage.

To reduce back reflection, we put faraday (IO-3-1064-VHP) after OPO on the bench (Pic 1,2). BAB transmission without green before faraday is 103mV and 100mV after faraday, which means transmissivity is 97%. 

After installation of faraday, IR is totally misaligned. We'll try to align faraday tomorrow.

To connect the DGS remote desktop from cleanroom, please use Remote Desktop Connection, not Microsoft Remote Desktop. I put Remote Desktop Connection to taskbar in computer in clean room.