Katsuki-san, Marc

Today we removed the AZTEC sample in order to prepare the absorption and birefringence measurement of the TAMA T1 sample.

We reinstalled the steering mirror in the injection part to dump the sample reflection (see fig1)

We installed a flipping mirror before the birefringence readout to redirect the pump beam to the high power power meter (see fig2).

We reconnected the absorption photodiode to the lockin amplifier.

We installed the surface reference sample and with z = 42.3mm and zIU = 66 mm we got R_surf = 18.72 /W

We installed the bulk reference sample with z = 40.95 mm  and zIU = 65.7 mm and got R_bulk = 0.6679 cm/W.

We installed the TAMA T1 and using DC values could find Y_center = 121.92 mm and X_center = 326.74 mm.

We increased the pump laser current to 6A (beforehand we changed the HWP angle that control the power to 9 deg that corresponds to the min pump power) which gave Pt ~6.1W.

We realigned the DC at the previous z_center (62.4mm) and did long z scan but could not find clear surfaces absorption neither on the AC nor the phase.

This seems to confirm that this sample absorption is quite low ( previously measured at 18 ppm).

Because it is the first time using such high power with all the birefringence optical component we turned off the laser today and will start the absorption measurement tomorrow morning.

Katsuki-san, Marc

Today we checked the relationship between the input polarization angle and the AZTEC sample polarization angle.

We confirmed that thanks to the realignment the maximal power of both photodiode is reached without sample.

Further analysis to follow.

Here are the figures.

During the week-end we took birefringence measurements of the AZTEC sample rotated by 180 deg and back to same orientation as the absorption measurement (ie 0 deg).

Due to some mistakes it was not possible to perform too many measurements (once labview is exited it reset the lockin amplfiier to absorption measurement)..

To avoid confusion I report here the measurement with 180 deg rotation.

Recently, it is found that GRMC loop cannot be closed. To check what is the problem, I disconnected the slow scan of MZ and put MZ PZT offset to a value that GRMC transmission is the highest. After that, according to the original setting, I have done following checks

0. GRMC has a good alignment.

1. PDH signal has 316mV pk-pk checked from EPS1.

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

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.

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.

5. GRMC transmission is checked to have 1.13V peak. This is two times smaller than the value written by Pierre.

6. Loop gain is 3 as usually used.

7. Threshold for peak identification is -0.55V. This is as required.

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

These checks show little issues but they should not prevent the GRMC locking. More investigation is required.

After the earthquake on 7th this month, we confirmed the normal operation of vacuum system, mirror suspension system. Especially, the filter cavity alignment was recovered and mirror's oplev shows usual spectra.

However, we found already that the driving of BS has problem. The problem is when we try to move yaw or pitch, the beam reflected by BS moves diagonally.

To confirm if there is any issue for magnets, I took a photo of BS magnets. Attached photo shows this check. Two red boxes indicate the location of four coil-magnet actuators. An arrow points to the magnet which seems to be broken. This magnet may be knocked during earthquake and get tilted. So the coil cannot drive it properly.

Katsuki-san, Marc

In order to mitigate the misalignment induced by the sample, we decided to move the 2 PDs closer to the waist.

For that, we also needed to change the ODs mounts for a smaller one.

We confirmed that with the realignment the maximal power of s or p polarizations with sample is smaller than the maxima without sample.

We started measurement with s polarization at input and the AZTEC sample rotated by 180 deg

Just to clarify :

There is some input polarization angle for which the the s polarization power is higher with sample than the maximum without sample.

This hints for either scattered light but more probably some misalignment (maybe the beam hits the side of the PDs that fakes strong power?)

Shinkosha evaluation plate # 10 is available inside PCI clean room.

Documentation is below the PC.

After spending time trying to use another PC, another usb hub, another usb cable and others Kinesis version that all failed I installed a spare motorized HWP and confirmed that it worked perfectly fine.

It is now possible to control perfectly fine the 2 motorized HWPs at the same time.

Michael and Yuhang

We checked filter cavity alignment yesterday. The pico-motor of PR/BS and END mirrors are moved. The movement of PR is to recover its reference on BS chamber. The movement of BS is to recover its reference in filter cavity transmission camera. The movement of END mirror is to recover the flash.

After these movement, we checked the oplev spectrum as attached in this elog. They look fine. So this time, no touching issue of mirror was found.

Katsuki-san, Marc

This morning we went to PCI to check the ATEC sample.

We found out that the peak visible in the polarization angle measurement is likely due to a dust so we removed it. Except that the sample seems perfectly fine.

We brought a laptop with Kinesis installed and connected it to the motorized HWP.

We got the same issue as with the PC (only jog by 1 deg).

We tried to home it and will check after lunch.

If problems persist we will contact Thorlabs and switch the 2 motorized HWP as the other is working fine.

This entry reports the birefringence measurement of the AZTEC sample with no rotation,

Note that a quite strong earthquake happend right after the measurement with input polarization = 0 deg...

Note that in that case the input polarization angle of 0 deg is made with hwp angle = 346 deg..

While the mean value of the polarization angle measurement seems reasonable, there is now a strange 'peak' on the top right of the sample...

We'll go to PCI to check if the sample is fine.

In order to further investigate the effects of the input beam incident angle we mesured the polarization angle as a function of the input beam polarization angle.

Data are attached to this entry.

Note that :

There are input polarization angle for which the s polarization power transmitted with sample is higher than transmitted s polarization power without sample..

The minimum s polarization seems to be reached for hwp  angle = 71 deg (ie 26 +45 deg) and using this polarization to normalize our signals means that the hwp angle = 341 deg that was assumed to be fully s polarization is in fact 10 deg polarization angle...

We also measured extra polarizations and results are attached to this entry.

Furthermore, I also computed the relationship between the input polarization angle and the polarization angle of the sample (see last figure).

Yuhang and Michael

After discussion in the TAMA filter cavity meeting on the 29th of September, we realigned the OPO, noting the following points:

• The OPO assembly position with respect to the rotation stage has been set up so that rotating one of the upper screws results in OPO yaw rotation, and rotating both upper screws results in X translation (horizontal direction perpendicular to propagation axis). Likewise, rotating one of the lower screws results in OPO pitch rotation, and rotating both lower screws results in Y translation. See figure 1.
• We confirm that the first stage of the OPO alignment starts with the beam entering the curved HR side (figure 2). This was noted with the black dot in figure 4 of 2682, which is closer to the flat faced side of the plastic holder (i.e. the incoupling mirror is mounted on the opposite side of the assembly from the periscope). The rationale is described in Matteo's thesis with respect to the SHG. We do it this way to ensure that the optical axis and OPO central axis are coincident before placement of the incoupling mirror. After placing the incoupling mirror, the cavity can be scanned for removal of higher order modes. Then, when the alignment of OPO/incoupler is confirmed, the assembly can be turned around for the finesse measurement.
• The beam size of the CC/p-pol beam entering from the HR surface of the OPO in the TAMA experiment is nominally 36 um (Marc 936)
• The distance of the beam from the f = 75 mm lens to the beam waist is measured to be 125 mm (2515). It is estimated that the OPO should be about 57 mm from the top of the periscope (figure 3). Note that there is a mistake in the figures of that elog entry - the predicted waist size of 20 um is with the lensing action of the meniscus (incoupler). Without the incoupler, the beam waist should be 25 um, as measured. However, as noted above, this beam size is setup for the OPO cavity finesse measurement, which is performed after the alignment of the incoupler.

The OPO has been aligned by using the camera to make a reference point (figure 4), placing the OPO, then ensuring that the incident and reflected beams overlap. We confirmed reflection/incidence overlap at the AOM exit port and Faraday Isolator. The beam is also centered on the target as indicated by the camera. In the future, we should take note to have the modulators and FI be further away from the OPO cavity for easier alignment of the reflected beam.

One of the wires detached from the DSub unit (figure 5). It appears to be the positive end coming from the OPO thermistor.

Katsuki-san, Marc

After investigating the effect of the AZTEC sample rotation, we decided to try to act on the imaging unit part.

We removed the OD (2 and 3) in front of the PBS in the imaging unit and added similar OD in front of each PD.

We tried to tweak the alignment as best as we could but because we installed the OD with a quite large angle to try to mitigate effects of scattering we don't have a balance powers on the 2 PD.

In order to have a beam small enough on the PDs we had to replace the lens before the PBS by one from the FC Newport lens box (f = 125 mm)

Anyway we started measurement in this new configuration.

In order to investigate the reason of the seemingly uniform theta distribution, we decided to start new measurements with the AZTEC sample rotated.

I marked the position of the holder, rotated the sample and measured an arc length of 3 cm that corresponds to a rotation of the sample by 34.4 deg (radius is 5 cm).

I took several measurements that are reported in the attached figures.

An important thing to notice is that I found I made mistakes in the use of the code.

Starting from the code available in the PC the modifications for our current setup are :

DC gain = 10

AC gain = 1000

DC is s - pol

AC is p pol

While the gain were correct, the previous figures were made with inverted AC and DC !

Also, the incident polarization angle was wrongly estimated (ie no normalization).

Note that to estimate the delta_n distribution it has to be multiplied by 1e6 to properly compute variance and mean.

Now all these modifications have been implemented for these figures.

Furthermore, the HWP working condition could be recovered a bit and all the reported measurements are made with the HWP between 341 deg ( s-pol) and 26 deg (p pol).

As a brief summary of the results :

- s0 and s1 absolute values are now similar

- delta n and theta increase with the incident polarization angle

Raffaele suggested to put time series together with spectrum of BAB PDH signal. The spectrum was measured in elog2573.

The last time of FC aligned was about one month ago. However, the alignment work took less than 20min today. In addition, the BAB alignment to FC didn't drift away too much. Although I didn't check higher order modes, the BAB transmission was about 430 counts.

After optimizing BAB transmission to about 460 counts, I took time series and put together with spectrum as attached figure.

There are now 4 SHINKOSHA evaluation plates inside the PCI clean room.

I marked the 7,11 and 14 on the side close to the ingot position marking.