Found the possible reason for high frequency oscillation

The first check we did today is to install a PD on the after the first BS mirror to look at the infrared beam came out from the laser,so the first picture is the error signal when the output power of the laser about 500mW, and the second is the signal from the new-set PD which shows that the infrared signal from the laser somehow also has the high frequency oscillation. And the situation are same with or without the green.

Then we increased the power a little bit, do the alignment again, then the error signal and the infrared signal shows in the third picture. There is a flashing spot in the infrared signal.

But the changing part is when we lock the cavity, the 500mW situation has the oscillation also(picture 4), but the second seams not.(pic 5)

According to this circumstance, we at least got one conclusion is that the high frequency oscillation has nothing to do with the green.

Then we rethought the polarization again, found out no matter s or p polarization reflect back, it is should stopped by the Faraday Isolator, but now it seems not.

We decided to check the polarization again from the beginning. Firstly one thing for sure is that, the input infrared beam to the cavity is in p polarization, and the reflect infrared beam is also p polarization.

Then we try to put another FI and half wave plate after the BS mirror and before the telescope to cancel the reflect infrared beam from the cavity. We use the same FI as we used before, but found out the two polarization cube point to different direction of the original one. Then the new put FI did reflect out the reflection beam, and get rid of the oscillation.

Then we guess that the original FI did not do its job maybe because the two wave plate before it did not clean the polarization as they should do.So we put a PBS after the first quarter wave plate and second wave plate, found out exactly what we suspected, so we adjusted them firstly then the Faraday and the other two half wave plate, got pure p polarization inject into the cavity.

Now the oscillation seems not there but the efficiency of green beam is only about 10%, so we tried to increased the alignment, but it seems we should do it from the start. After we make a progress in the alignment, we can check again if the oscillation really disappear. Then we can be sure that it is caused by the polarization problem.

Beam goes into the chamber

The table leg arrived on Friday, so we install them under the original leg, increase the bench to the height we want. Show in the first and second picture.

After doing this, we remove all the tall mounts for infrared and do the alignment again both in the infrared and green path. During the alignment, we found out maybe the cavity itself is a little bit tilt up, with one mirror we recover the beam to the right height.

Then we inject both the green and infrared beam into the chamber.

Firstly, adjust the position of G1 mirror in the picture try to get the green beam in the middle of it in horizontal direction. Then use adjust it slightly to get the reflection beam goes to the GR mirror.

Then we adjust the infrared beam, use the last two mirror on the bench in infrared path to adjust the infrared go through the Faraday Isolator, reflect by the R2 mirror and also goes to the GR mirror.

Then after the GR mirror we try to do our best to overlap the infrared and green beam and get a good result, next step is let these two beams goes into the BS chamber and try to overlap them there.

Then we installed the RP1 mirror, this is a mirror with high reflection with 0 zero degree. Then also install the RP2 mirror, this is the mirror has high reflection in P polarization. With this two mirror we got the p polarization reflection of the infrared beam and it arrives about the right position in the bench.

Comment to Status of magnets and stand-off of PR telescope mirror (Click here to view original report: 421)

This morning I have removed the support of the standoff glued on saturday. This time it has remained attached to the mirror and it looks ok.

Status of magnets and stand-off of PR telescope mirror

This morning I went to check the status of the magnets and stand-off we glued on thursday on the telescope mirror. 

While removing the jigs, a stand-off came off. We probably put to much glue on it and it overflowed a bit on the support causing the stand-off to remain attached to the support.

After removing it, I have cleaned the mirror and the support and glued it again paying more attention to avoid overflow.

Matteo gently touched the other 3 stand-offs and they seem to be well glued. We did not touch the magnets but they also look good.

Some pictures taken by Matteo are attached.

A special thank to Yuefan who woke up at 10 a.m. to prepare the glue!

Picomotors check for suspension in BS chamber

Today we checked the picomotors in the BS chamber.

BS suspension picomotors

The out-of-vacuum connector is connected to the flange named PO 4 (see first attached picture)

There are two cables (with 6 pins) coming out from the connector, that I labelled BS ALIGNMENT and BS LENGTH. 

Here what we found:

BS ALIGNEMENT

• A:   PITCH
• B:   YAW
• C:   

BS LENGTH

• A:  Z
• B:  X
• C: should be Y  but doesn't work!

We checked the connections and they seem to work, so it is probably the picomotor itself which doesn't work although the screw can be rotate by hand. 

2'' telescope mirror picomotors

The not-suspended 2" telescope mirror will be equipped with 3 picomotors (pitch, yaw and a translation). See picture 2.

I have checked that the 3 picomotors can work and I prepared a cable for the out-of-vacuum connection.

I re-used a former cable used for PO1 in the PR chamber adding 2 pins for controlling the translation picomotor. The pinout of the modified, cable labelled TELESCOPE 2", is shown in figure 3.

Measurement of the ROC of the 4" telescope mirror

Participants: Capocasa, Flaminio

We checkd the ROC of the 4" telescope mirror. To do that we used the mirror to focus the
image of a lamp placed at distance D1 and measured the distance D2 of the image from the mirror.
When the two distances are made equal D1 = D2 = 6.05 m = ROC of mirror.
The error of the measurement is about +/- 2 cm.
The specification was 6 m +/- 0.3 m. Looks good.

Opening of the BS vacuum chamber

Participants: Ishizaki, Marchio, Guo, Capocasa, Tacca, Flaminio

Wednesday, March 15th, 2017

We opened the top of the BS vacuum chamber.
Apart from the BS suspension and the corresponding cables for the coils and the
picomotors, there is no additional cable in the vacuum chamber.
There are two masses that were used as counter masses to balance the PO suspensions.

Opening of the PRM chamber and installation of the Faraday Isolator

Participants: Ishizaki, Marchio, Guo, Capocasa, Tacca, Flaminio

Tuesday, March 14th, 2017

Morning
We close the MC vacuum chamber.
We move the clean-booth around the PRM vacuum chamber.
We opened the PRM vacuum chamber. Then we installed the clean-booth ceiling and run the clean air flux.
We clean the vacuum chamber as well as the floor around the PRM vacuum chamber.

Afternoon
We installed the Faraday-Isolator inside the PRM vacuum chamber.
While doing that, we moved the two steering mirrors equipped with picomotors from
the Faraday Isolator platform on two independent posts so to place them at the right positions
(drawing and pictures will be added later).
The mirrors are mounted on 7" tall posts so to have the mirrors center at the
correct height i.e. 120 cm from the ground and 21.3 mm from the optical bench which
is the same height as the suspended mirror.

Opening of MC chamber and removal of the Faraday Isolator

Participants: Ishizaki, Marchio, Guo, Capocasa, Tacca, Flaminio

Monday, March 13th, 2017

Morning
We moved the PRM clean-booth around the MC chamber.
We open the top of the MC vacuum chamber and protected the inside of the
vacuum chamber with a plastic sheet.
We then install the clean-booth ceiling and operate the air flux.

Afternoon
We remove the Faraday-Isolator as well as the two steering mirrors from the MC chamber.
The two steering mirrors are equipped with picomotors.
Together with the Faraday-Isolator block we removed the corresponding four
beam dampers (pictures will be added later).
We left the cable used to drive the picomotors inside the MC vacuum chamber.

Add some pictures

The first picture is what the high frequency oscillation shows in the oscilloscope.

The second one is the green path on the bench now.

The third one is the infrared path, we increase the beam height.

Problems and progress

Now we have two problems with green beam that we haven’t figure out why:

1.There is some high frequency oscillation when the alignment is better, efficiency reach around 40%(Output power of the laser is 500mW). Even if we reduce the power to only 50mW output from the laser, the oscillation still there. We try to change the temperature and increase the power, find out the oscillation disappear, but under this situation, the alignment is not very good, so we need to find out which is the reason that make the oscillation disappear.

2. When we change the PZT output with hand to get near the resonance from one side, the high frequency oscillation will increase first, but then it starts to reduce, when we reach the resonance, we are not at the maximum of the oscillation.

2.We find out there are two TEM00 mode, one is more powerful then the other.

Now we can lock the cavity with 500 gain, and it is stable.

We installed the simple version of the green path, without the EOM, AOM and MZ, just to send the green beam to the chamber to check the position, and for the infrared beam which should go together into the chamber with the green, we increase it to the right height( the height we will reach after we increase the table leg) and align it to let it go through the Faraday Isolator and reflected by a mirror, goes to the direction to the BS chamber.

Picomotors cabling of the steering mirrors in the PR chamber

Today we checked the picotmotors and the cabling of the 2 steering mirrors in the PR chamber. They both work fine.

The connections has been done in order to have two cables exiting from the flange, labelled SM PITCHS and SM YAWS. (See first attached picutre)

According to the hand-pad convention (A, B, C),  the connections are the following:

SM PITCHES:

• A: Pitch SM1
• B: Pitch SM2
• C:  

SM YAWS

• A: Yaw SM1
• B: Yaw SM2
• C: 

 

Where SM1 is the steering mirror closer to the suspension (on the path of the green beam) and SM2 is the mirrror further from the suspension (on the path of the IR beam). See  second attached picture.

NB: cables for the steering mirror picomotors are connected to the flange closer to the optical table( which has also the coils cables), those for the control of the suspension are connected to the opposite one.

Transmission spectrum of Crystalline coating

I used the SolidSpec3700 spectrophotometer at ATC to measure the transmission spectrum of the Crystalline coating from CMS.

We have 2 samples, one is AlGaAs transferred on a silica substrate and the other one is transferred on a sapphire substrate.

The settings of the instrument are: 

- Slit width = 2nm

- Sampling = 0.5nm

- Range 1400nm - 600nm

- Lamp switch point: 840nm

There are some little differences between the two samples:

- they are shifted by about 3nm 

- silica substrate sample has larger side oscillations

Picomotors check for suspension in PR chamber

Today we checked the picomotors of the suspension in the PR chamber (a part of the filter cavity telescope).

The suspesion is equipped with 5 picomotors and 2 piezo.

Starting from the top (see attached picture):

1° stage:  

• YAW (orizontal)  + piezo 
• PITCH (vertical) + piezo

2° stage:

• Y (defined as the vertical translation of the mirror)

3° stage:

• Z (defined as traslation along the beam axis ( perpendicular to the mirror))
• X (the left one)

In order to control the picomotor we have used as out-of vacuum cable the original cable used for the double pendulum suspension in NM1.

Pinout: http://tamago.mtk.nao.ac.jp/tama/ifo/www_suspension_install_status/burndy.jpg (we are not sure that our definitions of X, Y, Z agree with that reported in this link)

There are two cables (with 6 pins) coming out from the connector, repectively named EF ALIGNMENT and EF LENGTH. We have connected them to the picomotor driver and checked the degree of freedom controlled by each of them.

NB: each cable can move 3 picomotors, which using the hand-pad convention are named A, B, C.

Here what we found:

EF ALIGNEMENT

• A:   PITCH
• B:   YAW
• C:   

EF LENGTH

• A:  Z
• B:  X
• C:  Y

We checked that all the picomotors work in both directions.

Vent of the MC line

The MC line (MC1, MC2, and 10m tube) was vented on the 3rd in March.

- The pressure was 1.2 Torr before vent.
- The GV in the mid point is opened.
- The TMP and the Drypump can work.

Metallic coated 5mm half ball glued on 1

I checked the gluing test with the uncoated half ball (elog entry http://www2.nao.ac.jp/~gw-elog/osl/?r=390).

I pushed a bit the half ball and I couldn't remove it, so the gluing is successful.

Therefore I could proceed with the gluing of the coated one.

I made a hole in a plastic cap to hold the coated half ball.

Put some glue on the border oh the central hole of a 1" metal plate

Took the glued plate and attached on the half ball.

Used the plastic cap to adjust the position.

Now I wait for the glue to dry and to cure.

Picomotors updates

PICOMOTORS CONTROL

Today we completed the test on picomotor motion succeding in moving a test picomotor using "old" picomotor Multiaxis driver 8732 (see picture1) controlled by pc.

A recap of the different option we tested to move the picomotrs:

1) by using "new" newfocus 8753 picomotor controller, connected to the pc by ethernet connection and controlled using labview (MCL commands). See picture 2.

2) by using Multiaxis driver 8732 controlled by hand-pad.

3) by using Multiaxis driver 8732 conected to the computer by GPIB (using GPIB-USB -HS cable) and custom labview VI.

 

PICOMOTORS CABLING

Several progress today

From yesterday, we found there are strange shape near the peak on the cavity scan, like there is some high frequency oscillation, so when we try to lock the cavity, the green beam also flash very speedily. We did some test, change the temperature of the cavity to not produce green, and we did no see these things then. So we guess that this is caused by the green maybe reflected back and sent into the laser.

But if everything works well, the Faraday Isolator should stop the reflect beams. So we checked the polarization again, try to get pure p or s polarization at the place we want. After that, the situation gets better, the peak looks normal, and the green stopped flashing. But the error signal sometimes still have some high frequency oscillation.(To further check tomorrow)

Before the two steering mirror, one of them is dichoric mirror and the other is normal mirror, for get rid of the green reflection, we changed the normal mirror with a second dichoric mirror.

Then we check the power everywhere, we have about 490mW at the output of the laser, 350 after the EOM and 230mW enter the cavity. So now nearly half of the power reach the cavity. With not very good alignment, we got 95mW in green finally, so now the green efficiency is 35%-40%. We try to measure the power reflect back after one of the dichoric mirror, 5% of green power is reflected.

Silica substrate roughness PSD

I have 3 sets of roughness measurement data from LMA. It is a sample of silica substrate used to transfer crystalline coating on it. The sets are taken at different points and surfaces of the same sample. I plot the measurement after tilt and curvature removal. I plot the PSDs of the roughness. Result is that the roughness is uniform on the sample. RMS=1nm

How to glue magnets and stand-off to the mirrors

Participants: Eleonora, Yuefan, Manuel, Matteo Tacca, Raffaele, Tatsumi-san

Today Tatsumi-san gave us a practice class about how to glue magnets and stand-off ( a.k.a wire braker or spacers) to the mirrors.

Pictures showing the procedure can be found in the following link

https://www.dropbox.com/sh/ggpodec805a30k3/AAB0Bd2UBSd00-coYK7Wp5QYa?dl=0

In the attached file you can find the instruction to make the glue. The glue can be used up to 1 hour after its preparation and the glued parts has to wait for at least 24 hours.

 

The procedure for Kagra mirror  (which is not so different) can be found here

 

http://gwdoc.icrr.u-tokyo.ac.jp/cgi-bin/private/DocDB/ShowDocument?docid=4248