NAOJ GW Elog Logbook 3.2
I did some tests with the 633nm probe on the LMA samples that I already measured some years ago with the original setup. elog entry: http://www2.nao.ac.jp/~gw-elog/osl/?r=141
SCANS
calibration 633nm: z=34.5mm power 33mW; AC=0.2017V; phase=-103.8deg; DC=3.38V freq=375Hz filename=Fri, Jun 08, 2018 6-20-48 PM.txt
median filter order 5, average filter order 5
lasr current 1.3A, angle maximum IPC
lma15033 power=960mW z=34.5; AC=0.000651 phase=-104; DC=4.52V freq=375Hz filename=Tue, Jun 12, 2018 11-22-12 AM.txt
absorption = 16.4ppm (nominal 12.8ppm)
lasr current 4A, angle maximum IPC
lma15033 power=5090mW z=34.5; AC=0.00305 phase=-105; DC=4.62V freq=373Hz filename=Tue, Jun 12, 2018 3-46-17 PM.txt
absorption = 14.2ppm (nominal 12.8ppm)
lma15032 power=5130mW z=34.5; AC=0.001407 phase=-105; DC=4.7V freq=378Hz filename=Tue, Jun 12, 2018 4-12-54 PM.txt
absorption = 6.4ppm (nominal 4.5ppm)
median filter order 20, average filter order 20
lma15034 power=5130mW z=34.5; AC=90uV phase=-110; DC=4.28V freq=375Hz filename=Tue, Jun 12, 2018 4-49-39 PM.txt
absorption = 0.47ppm (nominal 0.65ppm)
laser current 7.5A
lma15034 power=10W filename= Tue, Jun 12, 2018 5-18-22 PM.txt
absorption = 0.44ppm (nominal 0.65ppm)
MAPS
lma15033 power=960mW filename = Tue, Jun 12, 2018 11-46-14 AM.txt
mean (std) on the map = 15.3 +/- 1 ppm
lma15034 power=10W filename = Tue, Jun 12, 2018 6-08-48 PM.txt
mean (std) on the map = 0.43 +/- 0.08 ppm
Participants : Yuhang, Eleonora
By sending the fiber output to the collimators (PAF-X-7-C) and (PAF-X-11-PC-C) we got the output beam and we could adjust the z of the collimator to make the beam collimated, and x and y to make it go straight.
We used beam profiler to measure the dimension of the collimated output beam:
- PAF-X-7-C has a diameter of 2000um
- PAF-X-11-PC-C has a diameter of 3300um
We put a label on the collimator holders to specify the beam diameter that we measured (that is the dimension of the collimated beam that they need in input).
They are now well aligned and should not be touched.
More info on the collimator mechanics and aligment procedure can be found here:
Useful tip to adjust the z of the collimator: if the beam is diverging the z screws should be turned counter clock wise, if it is converging they should be turned clockwise.
This spare screw has been used in place the broken one and the collimator has been riassembled and it seems to work.
Partecipants : Yuhang, Marco, Eleonora
During the auxiliary lasers installation performed in the past week the green beam got a bit misaligned and the filter cavity was not locked since then.
Today, in order to recover the lock, we have at first realigned the green beam, than we have zeroed the error signal for the local control of the input mirror since the stanford was saturating.
Note that the last time we had to zeroes the local control was more than 2 month ago.
The SHG temperature control was set to 3.175 kOhm and we injected about 8.5 mW of green light into the viewport.
The local control offsets for the optimal alignment were found to be
| pitch | yaw | |
| BS | 0.3 | -0.07 |
| PR | -0.76 | -0.34 |
| IM | -0.95 | 0.45 |
| EM | -1.73 | 2.82 |
The transmitted power is about 1.6 V.
The IR beam on the other hand is not aligned anymore, since we are going to take a pick off to be used to the aux lasers PLL.
Participant: Eleonora, Marco, Yuhang and Matteo
Input beam: waist of 192e-6 m at a distance -0.2 m from the laser head. Characterized here.
The input power is 232mW. After put two waveplates, the power becomes 228mW.
Telescope
First lens (f = 50) at a distance 13.5 cm from the laser head.
after the lens we measured a beam with a waist of 33.6e-6 m at z = 0.188 m from the laser head
Second lens (f=175) at a distance 39 cm from the laser head.
after putting the second lens, we adjust it and make it collimated. The beam diameter now is 3800e-6m.
Faraday isolator: input power 227mW output power: 202 mW Throughput 89%
Semireflective mirror: input: 180 mW reflection: 174 mW trransmission 2.7 mW
Fiber collimator: input power 2.6 mW output power 2* 0.88 mW. Power coupled 68%
In this report the first part of the assembly of the OPO cavity. For the drawing refer to file "assiemepdopov3asm.pdf". The pictures have been uploaded on drive at the following link: https://drive.google.com/open?id=1bjSdCoMSOHeWpJarAu0ZhKGuFZZME19h
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Step 1: check peltier (21) hot/cold side. In order to check which side of the peltier is the hot or cold one, the peltier has been powered up and the sides have been checked manually to determine which is the hot and which is the cold one. For this particular type of peltier, the cold side is the one with text (XF29) while the hot one is blank. See picture 1 and 2. Since we need the peltier to heat our crystal up, the cold side has been mounted in contact with the OPO assembly baseplate (6) while the hot one will be mounted in contact with the copper lower L (8). In order to ensure a good thermal contact between the components, a sheet of 0.1mm indium has been placed in between the peltier and the copper L.
Step 2: mount the thermometers (24) on the copper lower L (8) with the retainer (22, 23). See picture 3 and 4. After mounting the thermometers, bend the wiring of the thermometers and ensure the wires go in the groove, see picture 5.
Step 3: apply indium on the copper lower L and on the macor upper L (9). See picture 6.
Step 4: place the PPKTP crystal (7) in position. See picture 7. The PPKTP crystal mounted is the one with part number 7-11159316418, see picture 8. The crystal has a black dot on one side. I suppose this indicates the HR side, so the crystal has been mounted accordingly, see picture 9.
Step 5: assemble the lower and upper L on the peltier element and close the assembly with the POM bridge (5), see picture 10. Before doing this step, make sure the two POM tipped set screw (27) have been completely relased. While mountin the POM bridge be very careful about the crystal positioning. During this part one issue has been found and solved, see "Problem 1" part.
Step 6: fix the crystal position acting on the POM tipped screws. See picture 11. On this step be very careful not to brake the crystal. Alternate acting on X and Y screws, starting from the Y one. If you see the macor L starts tilting up, while acting on X, act on Y to fix the tilt. The final position of the assembly is when the peltier, and both the lower and upper L touch the left side of the POM bridge.
Step 7: mount the crystal holder retiner (25). See picture 12.
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Problem 1: during the step 5 of the assembling procedure an issue has been found. The Hexagon Socket Low Head Cap Screws (26) was not a "Low head cap screw", therefore this screw was interacting in a bad way with the POM tipped screw for X alignment, and was preventing the complete relese of this screw, necessary to start step 5 (see picture 13). This problem has been solved substituting this screw with a different screw with lower head cap (see picture 14 and 15). This solution allowed the release of the POM tipped screw for X alignment without problems.
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List of picture:
01 - peltier cold side
02 - peltier hot side
03 - copper lower L, thermometers and retainer before assembling
04 - copper lower L, thermometers and retainer after assembling
05 - lower L with thermometers in place and termometers wires bended
06 - indium applied to the lower and upper L
07 - crystal on the lower L
08 - crystal part number
09 - black dot on the crystal side indicating the HR (??) side
10 - POM bridge assembled
11 - crystal positioning using the POM tipped screws
12 - part 1 of OPO assembly finished
13 - problem with compenetrating screws
14 - new screw compared to old one
15 - compenetrating screw problem solved
NOTE: if you look for the collimator into the Thorlabs site the part number is PAF2P-11C. Thorlabs changed very recently the part number of this item from the one written on top of the collimator to this new one.
This spare screw has been used in place the broken one and the collimator has been riassembled and it seems to work.
- Since the pump is now at 2° incidence, the reflection from the sample was hitting the mount of the periscope. Without moving the periscope, I collected the reflection with a mirror and I redirected it outside with another mirror through a hole in the enclosure. Then I put a blackhole damper to absorb the power. I decided to bring the power outside to avoid heat generation inside the enclosure that may cause temperature fluctuations and noise at low frequency on the absorption signal.
- I also added a shutter after the chopper, to be able to close the pump for few seconds (not more otherwise the shutter melts) and be able to move the sample away from the pump path without burning the sample mount.
- The pump path at the ground level of the optical table was covered with a black paper enclosure. I replaced it with black anodized aluminum panels to reduce the generation of dust.
In order to solve the problem of the pattern on the surface reference sample I had to move the pump probe by 2°. The resulting path was outside the periscope mirror, so I had to move the periscope. It also went outside the chopper, so I had to move the chopper as well. First I aligned the pump beam without the focusing lens and measured the transmitted peak from the pinhole at different Z
Y Z
121.384100 55
120.684361 35
119.984621 15
angle 0.034987rad = 2.004deg
Then I put the focusing lens again and after putting the lens maximize the AC signal on the surf ref sample. Then measured again the transmitted peak position:
Y Z
121.923354 55
121.28 35
120.57 15
angle = 1.94deg
and moving the pinhole around the crossing point I maximized the transmitted power of both pump and probe at the following coordinates:
X 327.432
Y 121.255
Z 34.900
this is the new position of the crossing point
The first screenshot is the surface reference scan along Z.
The second screenshot is the surface reference scan along Y, that shows that the pattern amplitude is now of about 5%
The third screenshot is the bulk reference scan along Z.
I also made a map of the surface reference sample
Please note that the map Absorption[ppm] axis is not calibrated.
Manuel, Eleonora
I checked the pump power vs laser current with the power meter PM100D with the head S145C ( Integrating Sphere Photodiode Power Sensor, InGaAs, 800 - 1700 nm, 3 W ).
It doesn't work with the chopper modulation, so I turned off the chopper. The angle of Input Power Controller (IPC) is set around the minimum of transmitted power because the power meter head has 3W of range.
Result: see the first plot.
Every time the current is changed, the laser needs some time (about 20 min) to stabilize. Since I changed the current without waiting for this time, the plot is noisy.
Then I set the laser current to 1.5A and rotated the angle of the IPC to change the power in a more stable way. I measured the power for different angles, without the chopper modulatoin, with two power meters: the PM100D-S145C and the Ophir-Vega (that has a larger range). Then we repeated the measurement with the chopper on and measured it with the Ophir-Vega to check if the ratio with and without chopper is 0.5.
Participant : Eleonora, Marco, Yuhang and Matteo.
After put the first lens(f = 62.9mm), I checked the beam diameter by beam profiler. The result is 101um and 88um. According to the simulation, it should be 88um. It looks fine, so I procced.
For Faraday:
1. Rotate lambda/4 to find the maximum, then rotate 180 degree, compare to find a better angle.(146 degree)
2. Rotate lambda/2 to find the maximum.(279 degree)
3. Before FI the power is 272mW, after FI the power is 253mW. The coupling is 93%.
After putting the second lens, we measured the beam is collimated and has a beam diameter as 2500um.
Then we rotate the half wave plate(163.5 degree), we have s-polarization 202mW while p-polarization 100uW. Means we have 99.95% s-polarization.
After put the 98:2 beam splitter, we got 1.9mW as transmission and 217mW as reflection. The ratio between them becomes 99 : 1. The ratio change is because of the polarization.
For the purpose of having 2.4mm collimated beam in diameter(as required by entry 801), we did the design.
This is for AUX 1, the laser that will be used for the coherent control. A first characterization was done and reported in entry 666. It seems compatible with the new measurement.
The expected beam diameter for our case is calculated like this:
D = 4*lambda(1064nm)*f(11mm)/(pi*MFD(6.2um)) = 2.4mm
We also received some suggestions from Tomura-san,
1. Check to meet the NA's requirement. (Tomura-san told us basically that is all)
NA of lens: lambda/(pi*(MFD/2)) = 0.11
NA of fiber(HI-1060-Flex): 0.14 (from manual)
From this point of view, we are fine.
2. He also thinks we need to notice if we damage the fiber, if we bend it too much. Our complicated collimator (more complicated than Tomura-san's) can make couple more difficult.
Since we find the beam parameter changed because we change the laser power, we did the beam parameter measurement again. Now the power of laser is 277mW.
|
from laser head cm |
beam diameter1 um | beam diameter2 um |
|---|---|---|
| 34 | 1975 | 1848 |
| 29 | 1801 | 1683 |
| 24 | 1643 | 1527 |
| 19 | 1421 | 1371 |
| 14 | 1274 | 1194 |
result 1: 183um at -0.19m
result 2: 201um at -0.20m
mean: 192um at -0.195m
This is for AUX 1, the laser that will be used for the coherent control. A first characterization was done and reported in entry 666. It seems compatible with the new measurement.
Seris number: BM-3 UV.
Without filter, it is 0.1W/cm2.
With filter, it is 20W/cm2.
After check everything is fine, I proceed to put 98:2 and total reflect mirror.(As attached Fig. 1)
1. I checked the beam parameter, we want beam raidus as 1450um. But we have only 1100um now. (See Fig. 2) I am wondering why it doesn't match the simulation in e-log 791. Here the power should not influence a lot. Because I just increase it from 10mW to 30mW. This is confusing.
2. I tried to align the beam to fiber. I got only 30uW (total is 11mW), means only 0.3% couple. I have tried my best. On the multi-meter, the shown number is very stable(I didn't use 50Om). But the shown number on the power meter is changing a lot. (See Fig3 and 4)
Improved the simulations. Instead of calculating the temperature at fixed times, I calculated the real part and the imaginary part of the temperature. In this way, the time dependence is given by the rotation of the phasor on the complex plane.
Then I calculated the propagation of the probe through the real part an through the imaginary part of the temperature distribution. These two separate propagations give two values on the photodetector. One is the real part of the signal and one is the imaginary part. Putting these two values together in the complex plane we get the modulus and the phase of the signal. Doing this for each position of the sample we get the scan of the AC signal and of the phase. See the plot.
In the plot there is the comparison of two scans of the same sample, same thickness, same absorption rate, same incident power, but made of different materials: Silica and Sapphire. The sapphire sample looks shorter because the angle inside the sample is smaller (snell's law). The AC signal is smaller because the sapphire diffusivity is higher. The ratio between the two AC signals is 3.7. The phase difference is 33°.
After found a half waveplate in TAMA(it is a square one as in attached Fig.1), I used it to rotate the polarization of the output of FI.
After increasing laser power around 300mW,
I checked the power before and after FI(see Fig.2 and Fig.3). The ratio is 90.55%(=280.8mW(detect after FI)/310.1mW(detect after the first lens)).
The light comeing from the side of FI is really not a point. So it is very diffcult to detect it. Roughtly there is 7mW coming out from output side port, 3mW from input side port.
I checked the p-polarization portion is 113.4uW, s-polarization portion is 235mW.(The total power sending to PBS is 245.9mW, this means we lose a lot of light by half waveplate and focal lens)
The maximun power we can reach for our laser is around 600mW.
Today I check the beam shaking at another place, as shown in attached Fig. 1. I compared it with the calculation I did with ABCD matrix.(Fig. 2 The result is 0.00059) However, the result doesn't match the measurment(Fig. 3 this value should ccrrespond to 0.000142). I will try to find why my code is wrong.
I also measured the noise spectrum in low frequency, as shown in Fig. 4 and 5. As told by Matteo, our loop can sense the beam shaking as a length shaking. So we can see the noise level is increased.
So I decided to take the video of this shaking on the first iris in the vacuum tube between IM and EM.
(Video is here)https://drive.google.com/open?id=1jNG-MD1ATfqfCkNuEixQux5IXnzmwJTk
