Clean up some multiple sockets

I tidied up the power supply of the absorption measurement system because it was too messy. There were a lot of unnecessary multiple sockets connected in series (which is bad for the electrical grounding), especially under the stairs (all covered by dust). So, I rearranged the multiple sockets and put the unneeded ones on a shelf in the first floor, see the picture.

Try to adjust the beam height

I rotated the dichroic mirror in order not to block the green beam for next step. For easy understanding, the first picture shows how I did the rotation. Before I did the rotation, we tried for very long time to do the mode matching, but there are always two beams, and no matter how we changed the two mirrors and the position of the cavity, it did not get better, and the misalignment seems in the horizontal direction. But after I rotated the dichroic mirror for 90 degree, which I think will not effect the transmitted beam, the mode I saw now are all vertical modes. I found a mode with round shape which is likely to be the TEM00, but I am not pretty sure that is the real fundamental mode or just some coincidence that the two beams overlap.I found its peak from the spectrum, and tried to make it larger with adjustment of the two mirrors, but it did not have an obvious change. For now the misalignment is in the vertical direction and it is true that now the beam is a little bit lower than the cavity, it maybe better to higher the beam, since we have four mirrors before the cavity, it seems not very hard to higher the beam and recover it parallel to the table. Then I will check again if I got the TEM00.

Progress of 16th and 17th

We found out the beam we are looking at is not clear enough, it will be harder to do the alignment with that, so I adjusted the camera and also the beam path. From the first picture, it is the beam path that if we want to look at the beam directly with CCD, I lower the camera instead of bending the holder which will make the situation more complicated. The second picture shows what we have now with CCD. It seems the higher order beam is in horizontal direction but the mode is a liitle bit strange. And before if we use the camera with the camera lens, and use the camera to look at the card, the beam is quiet small. So I changed the lens to make the beam larger and have more details of the beam. But then I found out that instead one beam, there were two separate spots on the card.( I didn't get very good picture to show this.) And first I thought it may be the TEM01 mode, but if it is, the pattern should be like one round spot cutting into two, but what I saw it two round spots and there is some distance between them. The other guess is that it is the reflection in the cavity, which means that the beam path inside the cavity is not overlap with the line between the center of miniscope and crystal.But when I drove the PZT, the distance between the two spot seems not change. So I am not sure where the two spots came from.

Alignment of the SHG

I did the alignment SHG cavity for some days. For now, the first picture in the attachment shows the spectrum from the PD. At the beginning, the mode I got are all Laguerre modes. So I moved the position of the cavity to get better waist position matching. After that, I removed the mirror, let the transmitted beam from the cavity go directly to the CCD, in the second picture shows the situation of the optical bench now. Then from the screen that connected to the screen, I got the mode visually. Since the height of the camera mount is too high, so I bend the holder for 90 degree, so from the third picture although it seems like the misalignment is in the vertical direction, actually it is in the horizontal direction. The third picture only shows one of the mode I saw, but the others are all like this, and there are also some others too weak to see.During the adjustment I did on Friday, with adjusting the two mirror before the cavity in horizontal direction, did not make the situation better. I'll keep trying.

Current version of the VIs to control the large translation stage

I upload the front panels and diagrams of the current version of the VIs and subVIs that I made with the help of Sakai-san.

The main VIs are "Translation Stage Map.vi" and "Translation Stage Scan.vi"

I don't upload the diagrams of subVIs that belong the SR830's and the Zaber motors' libraries.

Adjustment of the telescope and other progress

According to the conclusion we got before holiday (the detailed report of the work we did before the holiday will be uploaded later), I did some adjustment of the telescope today to get the beam waist we need as about 52 micrometer. At first, I changed the position of the lens little by little, but since the starting point is the beam waist less than 40, so after three times changing, the size was still far from the goal. So I recalculate the parameters of the telescope, found one of the result with the same lens we used before. According to this result and many times tiny adjustment, I got the needed waist size. The position of each lens list below( still the origin is at the output of the EOM):

L1: 37 cm
L2: 46 cm
L3: 55 cm

the final beam waist is 52.7 micrometer and the position is at 82.2 cm.
The first picture shows what we have on the optical bench before holiday, it is only for doing the measurement, so the dichroic mirror is not in the right gesture. So today I flipped the dichroic mirror, and put the SHG housing in the right position and direction, according to the result showed in the last paragraph. Aligned the inject beam and the reflection beam, got the transmission beam after the SHG and the reflection beam at the back side of the mirror after EOM. I tried to find some mode but did not get any. I will try to do it tomorrow.
Another problem is that I thought the stage we are using now is broken...in one of the direction, it can only move one way, but it can still be used.

Cavity locked and got the beam size

Member: Matteo,Yuefan
This week we increased the height of the crystal instead of lower the miniscope. But after the increase, we still cannot get rid of the higher modes. We guessed it is because of the mismatch of the beam waist size. Since the increase of the crystal was reached with putting a spacer under the 'L' part which used to fix the crystal, the wire of the thermal sensor and the peltier are also connected to this part, we cannot push too much on the crystal,so now when we touch the wire outside the housing, the position of the crystal will change slightly. Another problem is that we found out the first turning mirror is too closed to the beam waist focused by the first lens of the telescope, and this caused the optical damage of the mirror coating, since the power density at the beam waist is too high when we use the full power of the laser. So we decided to move the the easily damaged turning mirror one hole closed the first lens, and do the same change with all the other component of the telescope without changing the distance between them. Then according to the new version optical scheme, we changed the dichroic mirror into the one transmit green and reflect red. In this case, we can use this dichroic mirror and the last mirror of the telescope to adjust the beam, things became easier. As I mentioned before, we guess the reason of the higher mode existence is because of the mismatch of the beam size. So we turned the cavity again,inject the beam from the back side of the housing, tried to lock the cavity and get the exact beam waist size we need. Give the EOM 15.235MHz modulation and use the PD to get the error signal. With the demodulation board found in TAMA, and the Stanford as a low pass filter, we locked the cavity, but cannot get rid of the offset. The lock last for more than two hours until we swtiched off everything and left. During the lock, we measure the beam size and got the beam waist size the cavity need is 54.1 micrometer. So the next step is the adjust the telescope again to get the beam waist size given by this locking.

Picomotors status

Picomotors of the 4 suspended mirrors (2 of filter cavity and 2 of telescope) need to be put in operation.

 

The cables that connect the picomotor to the the chamber flange inside the chamber should be already in place for the 4 suspension (to be checked)

 

Takahashi-san provided driver for the picomotor (fig 1) to be connected to a cable (fig 2) to the extern part of the flange. This device were used to control picomotors of TAMA SAS.

 

The drivers can be controlled by a joystick and by remote using a labview software that Takahashi-san will provide

 

Some more information:

 

1- Picomotors drivers are 3 (IM1 IM2 NM3), NM2 could not be found. We checked in both end rooms without success.

 

2- We need 4 cable to connect them too the  4 chambers. For the moment we have only 2. (Again we checked in both the end rooms).  According to Takahashi-san the missing two cable can be built using spare connectors like that in figure 2 and spare suitable cables I already found in TAMA. Takahashi-San can also provide the suitable tool to connect pins in the connector.

 

3- All this material is temporarily stored in a box under my desk in TAMA

NIM-modules to filter and amplify optical lever signals

In the past days with the valuable help of Matteo L. we realised 4 NIM-modules able to filter an input signal with a lowpass filter of 2 order (cut frequency at 100 Hz) and to amplify it of a factor 100.

 

The scheme of the circuit, using a multiple feedback (MFB) filter, drawn with the software LTSpace is shown picture 1 and its transfer function in picture 2. 

 

Each module can process two channels, so in total we have 8 available filters+amplifiers.

 

A picture of the circuits and the module are shown in attached files 3 and 4.

 

They will be used to filter and amplify the output signal of the PSD  used for the filter cavity optical levers, replacing the stanfords that have been doing this job up to now.

Progress in SHG

Since we found a spare PSD in TAMA, we used that PSD to make the alignment of the crystal optical axis with the beam. We changed the stage under the SHG housing, for two reason: take less space, let the center of the crystal to be the exact the same height with the beam. With the available component in TAMA, in the attachment I put the picture of the present stage we made. At first step, we use the PSD to get the total power and the power in two directions. Then put the SHG housing on the new stage, but with 180-degree turning compare to the final position of the housing, in this way we can make sure that the beam really goes along the optical axis of the crystal. After getting almost the same power value compared to the first step, which means the crystal has been put into the right position, we installed the miniscope, try to find some modes. But finally we found out we need to lower the miniscope to get better result,the reduce of the height probably can be finished in NAOJ. So the question for now is how much we want the engineer to make the reduction. For now we have two kinds of spacer,one is 50 micrometer, the other is 150 micrometer.

Optical scheme changed

We finished the alignment of the beam, kept the reflection beam and transmission beam at almost the same height as the input(76cm) and got the green. According to the new optical scheme, we need to change to a different kind of dichroic mirror(reflect infrared and transmit green), which we don't have in lab now. And also the present transfer stage we are using for SHG housing take too much space. If we do not change it, it will be hard to realize the new optical scheme. In the attachment, I put the picture of the stage.

Alignment of the beam hight

Member: Matteo, Eleonora, Yuefan
Today we restart the alignment from the first beginning. Firstly, with the power meter, measure the input and output of the EOM, adjust the transfer stage until almost the same power value. Then for the component, try to adjust them until the beam shine on the middle of everyone. With the tilt angle of the mirror, adjust the beam height as 76cm at both the near field and far field. Finally, we found out the transfer stage under the SHG housing is too high for present beam height.So we remove the bottom layer, got the transfer beam and the reflection beam, but the green is weak. The possible reason may be:1.Low input power 2.During the adjust process, the position of the lens may change,leading to the change of the waist position, so the input beam size of SHG crystal is too large 3.The polarization 4. The misalignment of the beam height and the crystal height. We will check all the possible reason tomorrow.

Cavity alignment

Member: Matteo, Eleonora, Yuefan
Last Friday, we installed the mirror part of the cavity,tried to align it. For doing this, firstly we add 20 kiloohm resistance to the present photo diode to increase the sensitivity at the cost of reducing the bandwidth(200 kHz). At the first try,we got multiple modes.With two mirrors and the lens, we tried to rule out higher modes and get the TEM00 one, but found out that there is misalignment in the vertical direction. After adding some piece under the mirror block, this problem has been solved, but still we cannot get rid of the effect of TEM02(TEM20) mode. We will restart the alignment again today, try to make some progress.

Update of the relationship between the SHG crystal temperature and the green light power

Member: Matteo, Eleonora, Yuefan
Yesterday I uploaded three figures, the first one is the green light power as a function of resistance, since we can only get the resistance from the thermal controller. Today we took smaller step of resistance changing, got better shape of the curve,and finished the convert from the resistance to temperature. The final figure shows in the attachment. We still need to do some modification of the beam to get more symmetric result.

Green light

Member: Matteo, Eleonora,Yuefan

We did the clean-up of the SHG housing today, installed the crystal, mounted the harmonic beam splitter and SHG housing, and finally we got the green light. But during the process of finding the green light, we installed another half-wave plate between the second and third lens of telescope, because of the design of the SHG housing, the polarization is not we thought it should be. In the attachment you can find the situation of the optical bench now. The installation of other two harmonic beam splitter is for the power measurement of the pure green light instead of the mixture of the green and infrared.
We did three groups of measurement:
1.The relationship between the resistance(temperature) and the green light power. Since the thermal controller we are using now cannot show directly the temperature of the SHG, it can only shows the resistance. During this measurement, the diode current of the laser is 1.996A and the temperature of laser crystal is 23.63 degree. From the figure, you can find out that when the resistance is about 3.375, the power reach its peak. According to the manual of the thermal sensor, 3.011 kilo ohm response to 60 degree and 4.147 response to 50 degree. So the phasing matching temperature of the crystal is lower than what we thought it should be at 65 degree.
2.The relationship between the laser crystal temperature and the green light power. Under the circumstance with resistance setting to 3.375 kilo ohm. Since this kind of laser can have two modes in the same time at some temperature which will increase the power of green light to 1.5 times, these temperature points are where we should avoid. The red circle with plus marker in the figure is the temperature we used before. It is in the middle of two unexpected point, so we can still set the temperature there.
3.The last one is to show the linear relationship between the power of infrared and green, since they both linear dependent with diode current of the laser.

1310nm probe beam laser profile measurement

Members [Manuel, Matteo L.]

I measured the divergence of the 1310nm laser. Since the beam profiler doesn't work over  1100nm, I used the DET10N-InGaAs Detector to measure the time-dependent intensity while the beam is cut by the chopper. On the oscilloscope, I measure the rising time from 10% to 90% of the gaussian integral and calculate the waist and the divergence. I repeated for several chopper positions along the beam axis.

divergence = 1.0 ± 0.1 mrad.

waist = 420±40 um

Telescope for SHG has been finished

Member: Matteo, Yuefan, Eleonora

The design of the telescope did with some Matlab code, double checked with the JamMT program and it gave out a visually simulation of the telescope, showing in the attachment.During the mounting of the telescope, the maximum power of the Laser has been used. The detail of the practical telescope shows as below:
Focal length
F1--50.2mm
F2--62.9mm
F3--125mm
Distance:(Set the output of EOM as origin)
L1--37.5cm
L2--47.5cm
L3--58.5cm
Final beam waist--82.5cm
Final beam size(radius)--44.0854 micrometer

During the last check, I found out the distance between the Beamsplitter and the first turning mirror is 5cm longer the optical scheme shows, caused by my counting error of the holes.But since behind this part there are some space left, so I thought maybe we can leave it like this.

Radiation-shield and window-holder for the inner chamber of NAOJ's cryostat

Today, the machine-shop of the ATC finished the manufacturing of the radiation shield and the window holder which are going to be attached to the inner chamber of our cryostat in the ATC. I took some photographs of the item(s). The next step would be to actually install it in the cryostat but before that I have to order some coated windows to make use of the window holder...

Setup-drawings for the length-sensing OpLevs of BS, PR2, and PR3

I finished the drawings of the setup of the OpLevs on the optical table for the BS, PR2, and PR3 mirror of KAGRA. They can be found on the JGW document server.

New Laser for JASMINE arrived

The new laser for the JASMINE scatterometer arrived. However, it seems that we still need some more preparations to use this instrument as no heat sink or ON/OFF switch was delivered together with the laser.