Marc Matteo

We removed FC from the AZTEC #3.

Note that the imaging unit black cover was modified so that we don't need anymore to disconnect the cables.

We checked the bulk reference sample and measured R = 0.5794 cm/W with Pin = 27.67 mW and Pt = 15.06 mW.

It is still consistent with previous estimation so we installed the AZTEC #3 on the translation stage.

We did a long z scan and estimated the 2 surfaces at z = 26.05 and 114.5 mm so that z_center = 70.275 mm

We started XY measurement at Z_center.

From the long z scan, absorption seems promising.

Marc, Matteo

Today we removed AZTEC #2 and installed the bulk reference sample.

We measured R = 0.5780 cm/W which is compatible with previous measurement within 5%.

This is reasonable so AZTEC #2 measurements are fine.

We used again first contact on the AZTEC #3 as there was some remained of the previously applied first contact and peeled.

Note for future to never use the sticky tape given by first contact.

We also applied first contact on the second surface of the 1.5 inch sapphire used for calibration.

We cutted holes in the black box covering the imaging unit in order to avoid to have to remove the cables every time we want to intall/remove KAGRA size substrates.

We started measurement of AZTEC #1 at exactly the same position as before (XY map at Z center).

Measurement is on-going but preliminary results seems compatible with previous measurements meaning that they should be fine.

Report of AZTEC #2 absorption measurements.

For reference the arrow is on top pointing towards the imaging unit.

Absorption is larger than AZTEC #1 and we can also quite clearly see the growing seed on the xy2 map (fig 2 that is measured at the z center of the substrate)

Two photos (under gluing and after gluing) are attached.

[Takahashi, Aritomi, Marc]

We opened PR chamber and fixed one falling magnet of PR mirror and released the suspension. During this work, we noticed the oplev laser was hitting off center of PR mirror. We aligned the oplev laser to make it center of PR mirror. Currently the oplev beam is not reaching the PD and we need to align it.

We will open BS chamber on Friday next week (5/27).

Date: 2022/5/13

With Homare Abe and Takayuki Tomaru

At KAGRA

• We took pictures of 2 sapphire samples with a green injection laser beam:
  • One of them showed a green scattering light
  • The other one showed a red scattering light
• We also took pictures of ITMY mirror with the same green injection laser beam:
  • The results showed a green scattering light

Analysis will be performed.

Pictures: klog

Aritomi, Marc, Michael

We installed the new picomotors drivers. They worked fine for PR picomotor but did not work for BS picomotor.

We need to open BS chamber to check the picomotors.

With PR picomotors, we recovered the old reference in BS chamber (eg in elog 2794). In that configuration (and maybe BS in a 'random' position, the green beam is hitting quite below the gate valve window between BS/input but at least we don't have anymore clipping).

However, the PR oplev laser is now hitting the edge of the steering mirror before the PSD. It means that the PR reference at BS chamber that we are using might not be valid anymore for the current alignment inside the PR chamber.

We realigned PR and END oplevs and ran the coil health check codes.

All magnets of PR, INPUT and END mirrors are fine except PR H2 and we can not assess BS situation as the oplev PSD is broken as reported in elog2775.

We found a spare PSD inside the cleanroom and tested its dark noise (see attached figure where red and blue curves are the dark noise).

It is fine so we plan to replace it after the recovery of BS picomotors.

Since the beam spot at GV between BS/input depends on both PR and BS, we should align PR and BS at the same time by using the GV between BS/input and the first target as references.

[Aritomi, Michael]

We found that one of the green references at PR chamber was not aligned as shown in Fig. 1, which means we need to align the green injection beam. We removed the cover of the optical bench and aligned the green injection beam as shown in Fig. 2.

Then we aligned PR to make the green beam at the center of GV between BS/input. However, in this situation, the green beam at PR reference in BS chamber is clipped by a mirror behind the BS as shown in Fig. 3,4.

Marc, Matteo

Following the recovery of the PCI, we installed the AZTEC #2 sample.

First we measured X_center = 400.735 mm, Y_center = 122.105 mm.

We did a long z scan and got the 2 surfaces at z = 26.28 mm and 119 mm meaning that Z_center = 72.64 mm.

We have incident power = 7.69W  and transmitted power = 6.636W.

We started a XY measurement at Z_center and hope to finish all 5 maps by monday.

Marc Matteo

This entry summarizes these past days activities.

We found a mistake in the fitting code (the wavelength was hard coded to 633 nm instead of 1064 nm making the previous estimation wrong by a factor sqrt(1064/633))

To avoid this issue, we coded a more flexible function 'fit_blade.m' that is saved in the PCI scripts folder on the desktop

With this function, we could finally tuned the pump beam telescope and recover Manuel's parameters (fig 1)

We also check the vertical and horizontal angle of incidence to be -0.2 deg and 2.5 deg respectively.

We also checked the probe beam parameters by placing a power meter in front of the absorption PD.

We also got same parameters as Manuel (fig 2)

The angle of incidence is 3.47 deg meaning that the relative angle between the probe and pump beam is also correct.

We installed the surface reference sample and tried to maximize the R coefficient by changing both the translation stage and imaging unit z positions.

While doing these motions, we could find the expected maximum at x = 35 mm and z_iu = 68 mm.

However, R = 14 /W meaning that we still had not optimal conditions.

After investigating other possible issues (chopper frequency, laser power, pd, lock-in are all fine) and repeating several times this calibration, we could not improved this value by much...

We installed the bulk reference sample and got R = 0.5536 cm/W.

Both surface and bulk calibration are 10 % lower than expected but the reason is still not clear to us...

We decided to use the 1.5 inches sapphire that Manuel used to check the setup calibration (eg check entry 1132).

We did the exact same measurement and got similar values (fig 3)  : mean absorption ~ 40 ppm/cm.

However, the sample was really dirty so it we cleaned this sample by wiping alcohol on it and repeated the measurement that gave identical result (fig 4)

It means that despite some issue with the setup, our calibration gives us reasonable results and can be considered to be working again.

Today I installed the razor blade that cuts the beam vertically and measured the pump beam parameter.

The blade is at 90 mm from the edge of the breadboard and I used about 100 mW of input power.

I measured a waist size of 22 um at 58 mm (in Manuel's unit) while we expect 36 um at 61 mm.

I started the tuning of the telescope but it is not concluded yet.

I subtracted the dark noise from the locking accuracy measurement done in elog2864. I calculated sqrt(locking accuracy^2-dark noise^2). In the point where the dark noise is larger than the locking accuracy, the subtraction is set to 0. The rms after the subtraction is almost the same as one before subtraction.

We have two iris inside filter cavity arm to check the direction of green laser beam. To make sure the beam can arrive at the filter cavity end mirror, we need to make the green beam hit on a point checked in the past when filter cavity is aligned.

Remember that, for the first step, we should make the green beam hit on several reference points on PR and BS chambers.

The first attached picture shows the beam position on the first iris. In this case, the iris needs to be rotated so that the stick is not visible (hidden on the back side of iris). At this moment, the beam position should be just above the hole.

For the first iris, when the stick is visible, the situation is shown in Fig. 2. At this moment, the beam is above the hole and located a bit the left side.

If the beam hits on the first iris like what is shown here, it should be not diffcult to find the green beam on the second iris. If not visible on the second iris, we should move the green beam around with little adjustment. Then what we need to do is to just make the green beam go through the hole of it.

Information

Date: 14th Apr 2022

Members: Dan Chen, Satoru Ikeda

Place: Kamioka Hokubu-kaikan 1F meeting room

Background

The mirror substrates made for KAGRA O5 may have high internal scattering, and we are developing a simple measurement method for this purpose.
The idea is using a camera to take a picture.
At first we used a laser pointer (Green, 1mW) as a laser beam source and a sapphire sample from Mitaka to check the measurement principle.

Result

ASI camera (ASI224MC) is not suitable for this measurement because of the noise.
The reason can be the insufficient noise reduction in the camera or poor lens we used or both.

A digital camera (Canon EOS Kiss M2) successfully captured the scattered light from the sapphire sample with 61s exposure time and ISO6400.

Detail

Laser source

Model: UC-S1
Wave length: 532nm
Max power: 1mW

ASI camera

Camera: ASI 224MC
Lens: CCTV LENS 2.1mm 3MP
Application: Planetary Imager

Result: we tried several conditions for exposure time and gain, but the scattered light in the sample was not clear because of noise.

Digital camera

Camera: Canon EOS Kiss M2
Lens: EF-M15-45 F3.5-6.3 IS STM
Exposure time: 61s
ISO: 6400
Color temperature: 6000K
F: 16
Focus length: 45mm
Recorde image quality: best (about 15MB/picture)
Output image format: jpeg

Result:
With the above condition, the scattered light was observed. In order to make it clear, we took a picture with the Green laser ON and OFF, then we made a diff image using "imageJ". The diff image shows the internal scattered light clear.

What we learned:
Because the scattered light we want to measure is very faint, we need to avoid environmental light and stray/scattered light generated outside of the sapphire sample interfering with the measurement.

Additional maps.

Here the position and average.
Z=105.3, mean absorption: (61.6 +/- 13.95)
XZ map, mean absorption: (50.1 +/- 18.1)
YZ map, mean absorption: (56.8 +/- 19.1)

[Aritomi, Michael]

After opening the gate valves between input/end and arm, we tried to recover FC. We centered the PR reference and first target, but we could see only the scattered light at second target... We checked that the green beam is roughly center of the gate valve between BS/input with the PR reference.

Note: After the gate valve between BS/input is used as PR reference, don't forget to open the gate valve.

In elog2865, it is reported that the RF amplifier (ZHL-2) for AOM stopped outputting. I checked the output of the RF amplifier and confirmed that it is working. I injected the input of 5.5dBm and the output of the amplifier is 23.4dBm, which is reasonable.

I opened the gate valves between input/end and arm. Before I opened the gate valve between input/arm, the pressure of input and arm were 1.2e-6 mbar and 3.7e-8 mbar, respectively. After I opened the gate valve, both of them became 1e-6 mbar. Before I opened the gate valve between end/arm, the pressure of end and arm were 2e-7 mbar and 1.5e-7 mbar, respectively. After I opened the gate valve between end/arm, the pressure of end and arm became 4e-7 mbar and 5.4e-7 mbar, respectively. 

[Aritomi, Michael]

We started the evacuation of input/end chambers. After evacuation with a rotary pump, we opened small gate valves close to input/end chambers. The current pressure of end chamber and arm are 3.7e-4 mbar and 3.4e-8 mbar, respectively. The current pressure of input chamber and arm are 4.1e-4 mbar and 3.1e-8 mbar, respectively. We will open small gate valves close to arm, and large gate valves between input/end and arm next week.