Manuel (remote), Marc

Recently Manuel is helping me to try to restore the translation-stage v3 and v4 VI.

Yesterday, Manuel found out that the problem of v3 is that the left panel to choose all z values for the scans are overwriting the z value in the usual panel (same one as v2).

So it is needed to put first the z values on the left panel, then start the vi and and then everything works properly.

Aritomi, Marc, Matteo, Simon

Yesterday, we started by aligning back the ir beam on the 2 lenses [ before I wasn't thinking about the fact that adjusting the beam position by acting on these lenses will introduce astigmatism...]

Then we used the pinhole to characterize the ir beam.

The beam waist was too far (~60mm) so we moved the first lens after the periscope closer to the periscope.

I discovered that previous fits were wrong because i was trying to fit at the same time beam waist [um] and position [mm]. I corrected this and results are presented in figure 1 (red is red beam, blue is ir).

The situation is :

- crossing position is roughly matched to the 2 beam waists

- ir waist roughly 2 times too large -> need to move the second lens after the periscope closer to the periscope by ~1mm

- ir beam is not horizontal -> higher than red beam (larger z corresponds to smaller height)

Marc, Michael

On Wednesday we started the FC recovery.

First we checked the OpLev spectra and it seemed fine (no extra peaks indicating touching).

The PR references are good meaning that the squeezer alignment were good.

We moved PR picomotors to recover the reference on BS chamber.

We started to move BS picomotors to recover the beam on the 2 targets. But at some point the pitch picomotor stopped moving..

We did ~2000 steps for pitch.

We checked the OpLev spectra again and seemed fine so no touching.

I measured again the red beam when passing through the pinhole and extracted waist size and position (from power transmitted by a circular aperture) and the propagation directions (fig.1 in red).

The goal is to have the ir beam crossing the red beam at their waists with angle between their propagation directions of 0.1 rad (in fig 1 it corresponds to Y direction).

The corresponding ir propagation direction is shown in blue in figure 1.

I placed the pinhole at 2 positions (extracted from the figure) and acted on the 2 lenses after the periscope to maximize the power transmitted by the pinhole.

However, the ir beam was quickly clipped on the last lens before the translation stage.

Also, I wanted to use a small rail to more precisely control the first lens position and therefore the waist position.

However, the lens mount is too large and it is not possible to use the rail with this mount.

Marc, Matteo

Yesterday we tried to shift the ir beam using the pinhole at 2 positions.

However, after some back and forth between these positions, the power transmitted started to have a steep decrease...

Recentering the power-meter did not help.

We tried to remove the pbs and the waveplate between the 2 lenses as the beam started to get misaligned on these optics.

It did not change the power level.

Then I did several scan of the position of the imaging unit to check which is the good distance of the imaging unit with the new lens position. Before each measurement I tried to maximize both AC and DC.

I recorded both AC and DC and in figure 1 you can see the AC/DC in function of the imaging unit distance.

It seems that 74 mm corresponds to the maximum (previously it was 70 mm). Also, at this position there was a maximum of R~14 (goal is 18) maybe due to a better alignment compared to the other measurement?

I also preformed scan at each of these positions which still show umbalanced peaks.

Now I'll try to check again the beams propagation direction and the ir waist position as it might have changed again due to the removing of the pbs and waveplate...

If this does not work I'll try to remove the 2 lenses and start from scratch.

Today I tried to put the new Shinkosha sample (1'' thickness) into the new holder for this thickness.

No problems on this side.

Yuhang and Michael

The vertical alignment of the beam reflection from the pase shifter was improved. We can see that the incident and reflected beams stay at the same height for a long distance (figure 1).

Afterwards, the pitch efficiency of the IRMC was checked. In 2424, the phase shifter was given a DC voltage in order to cause mode mismatch in the IRMC. Much more light went into TEM01 than TEM10 at high offset - at 70V offset on the high voltage driver, the ratio of TEM01 to TEM00 was approximately 23%, as seen in figure 2 of 2424. This time, we did a quick measurement of the reflection spectrum at 70V offset and obtained 544 mV in TEM00, 132 mV in TEM01 and 32 in TEM10, corresponding to 18.6% power into TEM01. Which is improved but still not optimal.

From finesse simulation and experimental results, we theorize that the pitch misalignment is coming from bending of the piezo element controlling the phase shifter. In this case, there may be a static bending in the pitch direction causing misalignment when the piezo is excited. Ideally we only want longitudinal motion of the piezo. Yuhang also simulated the effect of phase shifter misalignment versus the phase shifter proximity to the beam waist, and found that the noise is reduced as the beam waist is brought closer to the phase shifter. In the previous arrangement, the beam waist after the 250 mm lens was located approximately two breadboard holes from the phase shifter (see 2393 for a screenshot of the relevant optical table layout). Now, the beam waist is located approximately one breadboard hole after reflection from the phase shifter, and we see a corresponding reduction in pitch noise from the measurements in 2407 compared to 1904.

Following this, we will move the phase shifter to the beam waist position. However, there isn't enough space on the optical table to move the phase shifter one hole backwards, so the IRMC mode matching lens setup may need to be reworked.

Comment on the characterisation of ATC cleanroom laser.

The beam profiler output shown in attached figures. We can see the beam position on the profiler for each measurement. The number on Gaussian -> 13.5% is taken as the beam diameter. V is the vertical axis and W is the horizontal axis.

Michael and Yuhang

When IR phase shifter (IRPS) is driven, an obvious misalignment could be found in the IRMC scanning spectrum. In this elog, we report the detail of misalignment when IRPS is given different level of high voltage.

Experimental setup: IRMC is scanned to have two TEM00 peaks within one slope of ramp signal. The IRPS is located before IRMC and given an 75V high voltage at the beginning. We changed the high voltage level and took scanning spectrum accordingly. The measurements were done with the following high voltage

We got scanning spectrum as attached figure 1. It is clear from figure 1 that almost only TEM01 mode appears after IRPS is given different high voltage.

According to the peak values in figure 1, we extract the percentage of power goes to TEM01 as figure 2.

Aritomi, Marc

Following the discovery of the not fixed lens on the IR path, we started to realign this beam.

First, I fixed by hand this lens at a position where the AC signal with the surface reference sample was ~0.08 (to compare to the previous ~0.25 and expected 0.36).

Then, we made sure the beam was horizontal after the 2 lenses using the pinhole at 45 and 27 mm on Z.

This allowed us to measure the beam power transmitted by the pinhole at various Z position.

From this measurement, it was possible to extract the waist size (~70um ) and position (~34 mm).

I took 2 points for the red beam to find the crossing point of these 2 beams.

And it can be seen (fig 1) that the ir beam has to be shifted horizontally by 232 um to have the crossing point at the the ir waist.

I started to move the ir beam using again the pinhole at 2 positions but it was required to move this beam both horizontally and vertically.

I'll finish this alignment this morning.

Note that compared to the previous situation, the crossing point is 3 mm closer towards the periscope.

Yuhang and Michael

We refer to the previous logbook entries:

1904 - Reference measurement to IRPS jitter noise

2393 - First entry on this topic describing the new layout of the phase shifter to orient in perpendicular incidence and jitter noise

2407 - Previous entry on IRPS replacement, with measurement of X and Y channels of PSD 

This time, we performed a series of measurements of the X and Y channels on the PSD, divided by the T (total) channel (i.e. frequency response 2/1 in spectrum analyser). This was motivated by the entries 1904 and 2407, where after discussion we determined it was ambiguous whether or not we were measuring jitter or amplitude noise - since we were measuring past the IRMC, we are taking the transmission of the mode cleaner, the power output of which is affected by the alignment of the input beam. This also motivated Yuhang to simulate the effect of beam waist positioning on the noise at the PSD past the IRMC.

First, we took the measurements of X/T and Y/T using a PSD just past the homodyne detector's flipping mirror, shown in figure 1 and 2. In the X/T (Yaw) case, the relative contribution of the X and T channels changes very little with the amount of excitation. The noise floor is similar to no excitation with the difference of a broad peak at about 2.3 kHz, which could correspond to the beam vibration frequency of the PZT element supporting the phase shifter mirror. In the Y/T case (pitch), the contribution of the Y channel actually decreases with respect to T. However, we saw in 2407 that the absolute value of the Y noise is quite high. This indicates that there is quite a lot of amplitude noise introduced on the Y channel. Yuhang's simulation indicates that this amplitude noise may be caused by the phase shifter being offset from the beam waist. The results motivate us to do the following two measurements, prior to adjusting the relative position of waist/phase shifter: 1 - measure the X, Y/T noise induced by the phase shifter excitation, with the PSD before the IRMC, and 2 - measure the spectrum of the IRMC when changing the voltage sent from its high voltage driver, specifically looking at the behaviour of higher order modes as the IRMC is mismatched. 

So far, we have taken measurements of the jittering before the IRMC. A sketch is shown in figure 3. Measurements are shown in figures 4-6 (some traces at certain values of excitation are missing due to data corruption) In this layout, we are definitely measuring more angular deflection now. In all cases,the contribution of X and Y increases relative to T with increased phase shifter excitation, and is also higher in relative magnitude, often above 0 dB. By contrast, the X, Y/T do not go above 0 dB after the IRMC. This increased noise may also be due to some other broad resonances at about 12 kHz and 30 kHz.

Yuhang and Michael

We will assemble the new OPO in the ATC cleanroom. We wanted to see if the laser beam set up in the corner is collimated. We measured the beam using the beam profiler from TAMA FDS cleanroom, with z = 0 being the position of the last lens that was fixed on the bench as we got here (figure 1).

Using curve fitting, we find the following fit of the beam size (figure 2), where blue refers to the horizontal axis and orange the vertical axis. The beam is not collimated and also a bit astigmatic. The fitting on the horizontal size also is quite distant from the data point closer to z = 0.

Yesterday I acted on the 2 lenses on the ir path to shift the beam vertically and superpose it to the red.

I placed the pinhole on the translation stage and moved it back and forth along the optical axis to maximize the power on the power-meter.

Then I did a scan of the surface reference sample that showed little improvement (R~12.5).

Matteo noticed that the crossing of the 2 beams did not correspond to the ir waist position.

I wanted to move the lenses on the ir path lateraly to shift the beam.

However, I found out that the first lens was not fixed at all : the mount got easily out of the fork and I had to unscrew the fork to fix the lens...

I tried my luck to recover a good position of this lens by hand but it is too sensitive (even though for a brief instant I could see R~18 which is the expected value, it was not possible to fix it at this position alone) so I'll have to restart the ir alignment...

Marc, Michael, Yoichi, Yuhang

Due to the earthquake reported in elog2416, we had issue of PR/BS pico-motors. To fix this problem, we opened PR/BS chambers today.

In the end, we fixed problems of PR/BS position and pico-motors. PR/BS chambers have been closed. But the air was not evacuated. Probably, we can evacuate on tomorrow.

While PR/BS chambers are open, we found issues as following:

1. PR pitch pico-motor is close to the end of range. (Figure 1)

2. BS mirror is too low, which makes the upper horizontal earthquake stop not useable.

3. BS earthquake stop is too far from mirror. The distance was reduced to be around 1mm now.

We can send infrared light from input-coupler side. After that, we take reflection and transmission power. By doing ring-down measurement, we can extrapolate well information of P0, P1, r1, t1.

P0 is power coupled to OPO cavity, P1 is power not-coupled to OPO cavity, r1 is amplitude reflectivity of input coupler, t1 is amplitude transmissivity of input copuler.

I did a calculation with the ideal parameters of OPO, which tells us decay time of ~4us.

To measure this decay, we should be able to lock OPO and switch off incident laser faster than ~100ns. To do this we need to use signal generator to send a square wave to an AOM which is before OPO. According to the spec of MT110-A1.5-1064, the rise time can be smaller than 100ns if the beam size is smaller than 0.6mm (diameter). We will design a small enough beam to make this rise time small enough to measure ring-down.

The expected ring-down for reflection and transmission is attached as figure 1.

Using measurements of entry 2391 I could compare the IR and red beams propagation directions as in the attached figure (axis unit in mm):

• the angle the 2 beam : ~0.07rad
• the height difference between the 2 beams : ~ 100 um (might explain the difficulties to align)

I'll try to use the pinhole to shift the IR beam height to the red beam one.

Earth quake happened on 20210320 18:09, which was quite strong and long.

We checked the oplev signal of all suspended mirrors (attached figure 2). The watchdog of BS and END mirrors were switched off. However, since we didn't give large offset, we can just use the oplev signal to check how much mirror drifted. We could see these change

Pierre and Yuhang

To investigate if SNR can be improved by an improved photo detector design, we conducted TAMA resonant PD simulation by using two simulation tools. One is a python code called 'zeros', the other is a Texas Instrument software 'TINA'.

The configuration is based on the scheme in this link. In the real case, we have modified this scheme, which results in two cases. One case is using the same op-amp with R1 10Ohm and R2 100Ohm. The other case is using op-amp LMH6624 with R1 1kOhm and R2 10kOhm.

To measure PD noise, we used a 32dB amplifier to make sure the PD noise is well above the instrument noise. The use of this amplifier has been considered also in the simulation software. In the first attached figure, there are electronic noise measurement and simulation results. We could see that python code simulates well the floor noise. However, the noise around 14MHz is better simulated by TINA.

We anticipated a signal of 0.11uA from CCFC field. To compare signal and noise, we divided the voltage noise from figure one by the PD gain. Then we get the current input noise as the attached figure 2. This DC value of signal is much higher than the noise level at 14MHz. From the python simulation, LMH6624 has better performance. However, simulation of TINA tells us that AD8057 has better performance.

To compare, we put here also a measurement of PD noise budget (figure 3). From this noise budget, TINA simulation is closer with the real measurement.

Figure 4 and 5 show the SNR of different PD configurations with TINA simulation

Marc, Yuhang

Following the End mirror OpLev check (entry 2412) and the measurement with the sensing matrix of entry 2411 we decided to use a 4x4 matrix to try to remove the coupling of unwanted degrees of freedom on the reconstructed signals from the 2 QPDs.

• We locked the FC and only close End mirror length control.
• Tune the phases : We found out that all the phases changed by ~40 degrees. So we used time series of all segments and maximized the I signals
• We sent a line at 2 Hz on Input and End pitch and yaw. Using the calibration of entry 1877 we injected a 3.78 mrad line for every dof. Namely

  	Pitch	Yaw
  Input	600	172
  End	727	141

• We measured the amplitude of the injected line (removing the background level noise) on each QPDs.
• We computed the driving matrix and had to modify the medm configuration (outmatrix.adl) to allow to use the 4x4 matrix

• 	QPD1 pitch	QPD2 pitch	QPD1 yaw	QPD2 yaw
  Input pitch	6	-5	-0.5	-1
  End pitch	-5	10	0.5	1
  Input yaw	1	-2	4	-3
  End yaw	2	-4	-4	12

• We checked each QPDs signals as in entry 2412 but coupling was still visible.
• We checked the demodulation phases and they seem to have moved by ~-40 degrees back to the previous phases...
• We checked possible reasons for this phase changes :

1. We aligned the FC to another position : no phase changes
2. We tried to put the optical bench to the ground (before putting the electronics inside of a clean room the optical table was connected to the nim racks ground) : no changes

• We putted back the 2x2 matrix of entry 2412 and tried to tuned the coupled coefficients by hand to remove coupling. It could approximatively work but during this tuning we could also see that the level of coupling increases or decreases sometimes without noticeable reasons...

Marc, Yuhang

We went to check to End mirror OpLev : All optics seemed well fixed.

We tuned the beam height to be identical on the injection and detection windows.

We moved vertically the lens on the detection window to have the beam centered.

Unfortunately it didn't change the coupling of pitch to yaw visible in the figure 1 of the parent entry.

We can see that pitch couples to yaw but not yaw to pitch.

This seems to indicate that the sensing matrix of OpLev is not the culprit.

Furthermore, when we inject a line on the End mirror pitch, we can indeed see the beam on the FC transmission camera moving in pitch but not in yaw. Even if the OpLev yaw senses this line...

On input mirror we can see both pitch and yaw lines on pitch and yaw signals from the oplev so it could be solved by finer tuning of the oplev rotation matrix.