NAOJ GW Elog Logbook 3.2
EleonoraCapocasa, YuhangZhao - 23:21, Thursday 18 January 2018 (631)
Attempt to align the IR beam
Today we have tried to recover the IR alignment.
1) We have checked the references on the PR viewport. According to the attached scheme, they come from the transmission of the first and the second PBS of the Faraday.
We have observed that when the beam transmitted by the Faraday is well centerd on the cross on the plastic film out of the wieport, the other reference beam is slightly hitting the edge of the second PBS of the Faraday and this makes the beam to have a quite irregular shape on the cross. Since the irregurity is not so evident we wondered if it was like this also when the reference was done or if it a sign that the beam is not well aligned.
2) We have put a camera to look inside the BS and we coud spot the beam on the 2 inch telescope mirror. We did it by moving the steering mirrors on the bench in order to make it hit the edge of the mirror and we have verfied that it is reasonably circular.
3) Then twe continued to follow the beam path: we have looked at the PR mirror with a camera and we have done a scan in the horizontal direction. We could see a dim shape hitting the leg of the PR suspension and we could see it moving on the leg on the other side of the suspension while performing the scan.
4) We have out a camera to look at the input mirror but we coudn‘t see any light even when scanning the beam position in the two direction.
5) Finally we have used the camera to look at the first target. We coud observe a very irregular light shape, much larger than the expected beam. At the beginning we thought it was the light diffracted by the beam hitting the pipe but when we moved the PR we observed that the shape was mooving accordingly. (You can see a video here). It probably suggests that the beam is reaching the target but it is clipped along its path before the BS.
6) As reported in entry 630, we have also cheked the dimension of the beam on the bench, finding a difference of about a factor two with the value measured previously by Yuefan. Since the main laser has been mooved, it is likely that the the telescope has to be retuned. i don‘t know how much this discrepancy can contribute to the strange effect we observed.
We have also measured the power of the references, wich gives a lower limit on the losses of the Faraday. For an input power of 15.7 mW we found that the transmission of the fist BPS of the Farady is 270 uW and while that of the second one is 120 uW. We have verified that changing the IR polarization from s to p most of the light is transmitted by the the first PBS.
1) We have checked the references on the PR viewport. According to picture 1, they come from the transmission of the first and the second PBS of the Faraday. We have checked that when the beam
transmitted by the Faraday is wel centerd on the cross on the plastic ï¬ÂÂÂlm out of the wieport, the other reference beam is slightly hitting the edge of the second PBS of the Faraday and this makes the
beam to have a quite irregular shape on the cross. Since the irregurity is not so evident we wondered if it was like this also when the reference was done or if it means that the beam is not well aligned.
2) We have put a camera to look inside the BS and we coud spot the beam on the 2 inch telescope mirror. By mooving the steering mirrors on the bench we moved it in order to make it hit the edge of
the mirror and we have veriï¬ÂÂÂed that it is reasonably circular.
3) Then twe continued to follow the beam path: we have looked at the PR mirror with a camera and we have moved the beam. We coud see a dim shape hitting the leg of the PR suspension and we
could see it moving on the leg onother side of the suspension.
4) We have out a camera to look at the input mirror but we coudn‘t see any light even when mcoving the beam.
5) Finally we have used the camera to look at the first target. We coud observe a strange, irregular light shape, much larger than the expected beam. At the beginning we thought it was the light
diffracted by the beam hitting the pipe but when we moved the PR we observed that the shape was mooving accordingly. (You can see a video here). It probably suggest that the beam is reaching the
target but it is getting clipped along its path.
6) As reported in entry. we have also chech the dimension of the beam on the bench finding a difference about a factor two with the value measured previously by Yuefan. Since the laser has been
mooved. it is likely that the the telescope has to be retuned. i don‘t know how much this discrepancy can contribute to the strange effect we observed.
We have also measured the power of the referencies. wich give a lower limits on the losses of the Faraday. For an input power of we find that the translission of the fist BPS of the Farady is and the
second one is. We have veryfled that chaging the IR polarization from s to p almost all the light is transmitted by the the first PBS
1) We have checked the references on the PR viewport. According to picture 1, they come from the transmission of the first and the second PBS of the Faraday. We have checked that when the beam
transmitted by the Faraday is wel centerd on the cross on the plastic ï¬ÂÂÂlm out of the wieport, the other reference beam is slightly hitting the edge of the second PBS of the Faraday and this makes the
beam to have a quite irregular shape on the cross. Since the irregurity is not so evident we wondered if it was like this also when the reference was done or if it means that the beam is not well aligned.
2) We have put a camera to look inside the BS and we coud spot the beam on the 2 inch telescope mirror. By mooving the steering mirrors on the bench we moved it in order to make it hit the edge of
the mirror and we have veriï¬ÂÂÂed that it is reasonably circular.
3) Then twe continued to follow the beam path: we have looked at the PR mirror with a camera and we have moved the beam. We coud see a dim shape hitting the leg of the PR suspension and we
could see it moving on the leg onother side of the suspension.
4) We have out a camera to look at the input mirror but we coudn‘t see any light even when mcoving the beam.
5) Finally we have used the camera to look at the first target. We coud observe a strange, irregular light shape, much larger than the expected beam. At the beginning we thought it was the light
diffracted by the beam hitting the pipe but when we moved the PR we observed that the shape was mooving accordingly. (You can see a video here). It probably suggest that the beam is reaching the
target but it is getting clipped along its path.
6) As reported in entry. we have also chech the dimension of the beam on the bench finding a difference about a factor two with the value measured previously by Yuefan. Since the laser has been
mooved. it is likely that the the telescope has to be retuned. i don‘t know how much this discrepancy can contribute to the strange effect we observed.
We have also measured the power of the referencies. wich give a lower limits on the losses of the Faraday. For an input power of we find that the translission of the fist BPS of the Farady is and the
second one is. We have veryfled that chaging the IR polarization from s to p almost all the light is transmitted by the the first PBS
CONCLUSION: we suspect that the beam is clipped somewhere in its in vacuum pathhave been working on the IR aligment.
1) We have checked the references on the PR viewport. According to picture 1, they come from the transmission of the first and the second PBS of the Faraday. We have checked that when the beam
transmitted by the Faraday is wel centerd on the cross on the plastic ï¬ÂÂÂlm out of the wieport, the other reference beam is slightly hitting the edge of the second PBS of the Faraday and this makes the
beam to have a quite irregular shape on the cross. Since the irregurity is not so evident we wondered if it was like this also when the reference was done or if it means that the beam is not well aligned.
2) We have put a camera to look inside the BS and we coud spot the beam on the 2 inch telescope mirror. By mooving the steering mirrors on the bench we moved it in order to make it hit the edge of
the mirror and we have veriï¬ÂÂÂed that it is reasonably circular.
3) Then twe continued to follow the beam path: we have looked at the PR mirror with a camera and we have moved the beam. We coud see a dim shape hitting the leg of the PR suspension and we
could see it moving on the leg onother side of the suspension.
4) We have out a camera to look at the input mirror but we coudn‘t see any light even when mcoving the beam.
5) Finally we have used the camera to look at the first target. We coud observe a strange, irregular light shape, much larger than the expected beam. At the beginning we thought it was the light
diffracted by the beam hitting the pipe but when we moved the PR we observed that the shape was mooving accordingly. (You can see a video here). It probably suggest that the beam is reaching the
target but it is getting clipped along its path.
6) As reported in entry. we have also chech the dimension of the beam on the bench finding a difference about a factor two with the value measured previously by Yuefan. Since the laser has been
mooved. it is likely that the the telescope has to be retuned. i don‘t know how much this discrepancy can contribute to the strange effect we observed.
We have also measured the power of the referencies. wich give a lower limits on the losses of the Faraday. For an input power of we find that the translission of the fist BPS of the Farady is and the
second one is. We have veryfled that chaging the IR polarization from s to p almost all the light is transmitted by the the first PBS
CONCLUSION: we suspect that the beam is clipped somewhere in its in vacuum path
Images attached to this report
iManuelMarchio - 18:52, Wednesday 17 January 2018 (628)
Status of 633nm probe alignment
we found the pd DET10A for the 633nm probe didn't give any output. Replacing the power supply with a 12V battery solved the problem. We checked the power supply with a multimeter and it looks fine (9V of output). We figured out that it's the adaptor bad contact. We continue working using the battery.
We made a scan of the surf ref sample and maximized the AC signal adjusting the pump alignment.
Current experimental parameters:
Laser current 1.3A Power meter value: 31mW (without sample)
DC signal: 3.26 (with sample) (3.4V at the max of the scan)
AC signal max: 0.2V
Images attached to this report
AkihiroTomura, YuhangZhao - 13:41, Tuesday 16 January 2018 (627)
SHG characterization
We measured the output power of SHG (green) with respect to the LiNb temperature and the input power (IR). A figure attached shows a result. The x-axis of the right graph remains to be converted to actual temperatures (we don't know the name of the thermistor we are using at this moment).
Images attached to this report
Comments related to this report
I did the SHG output power vs input power measurement again. I used HWP and FI pair after the main laser to change the input power in order not to get mode-hops. During the measurement, the current value of the main laser was 2.004 A. The SHG crystal temerature was 3.170 kOhm.
Images attached to this comment
YuhangZhao, EleonoraCapocasa - 23:02, Monday 15 January 2018 (626)
Recovery of the cavity lock after Christmas break
Today I and Eleonora have aligned and locked the cavity again. We found that the beam was pretty misaligned (not reaching any of the two in-vacuum targets) and the range of the optical levers was too small to recover the alignement. So we had to move PR picomotor to send the beam at 300 m and INPUT mirror picomotor to superpose the reflected beam on the incoming one.
After doing that we have put to zero the local control error signals and we have closed all the local controls loops. Then, we could fine tune the alignment with the local controls and lock the cavity stably.
We took pictures of each local control panel while the cavity was locked (See figure from 1 to 4: END, INPUT, BS, PR). The lock can last for more than 30 minutes (we had to unlock on purpose before going away). See figure 5 for the transmitted beam during the lock. We took photos of the oscilloscope showing the transmitted power just after achieving the lock (pic 6) and after 30 min of locking (pic 7). In the best alignment condition it is about 1 V.
After doing that we have put to zero the local control error signals and we have closed all the local controls loops. Then, we could fine tune the alignment with the local controls and lock the cavity stably.
We took pictures of each local control panel while the cavity was locked (See figure from 1 to 4: END, INPUT, BS, PR). The lock can last for more than 30 minutes (we had to unlock on purpose before going away). See figure 5 for the transmitted beam during the lock. We took photos of the oscilloscope showing the transmitted power just after achieving the lock (pic 6) and after 30 min of locking (pic 7). In the best alignment condition it is about 1 V.
Images attached to this report
YuhangZhao - 23:16, Friday 12 January 2018 (625)
Second time testing of grating with infrared
After talking with Matteo, I found the last measurement was needed to be improved. Firstly, the rotation direction should make sure that the incident direction is against the arrow direction marked on the edge of grating. Secondly, to find a good place to do measurement with enough times. Thirdly, to check the polarization of infrared beam. Fourthly, we also need to know the diffraction angle.
So I did experiment today. Fortunately, I found a PBS without costing a lot of time. Although yuefan told me that the most consuming part of job in TAMA is finding something.
Then I improvised the testing set-up. I found most of the light is reflected by the PBS. However, I didn't know the ratio between s and p polarization should be around 1000, which I learnt from Matteo latter on. But this can explain why the energy doesn't conserve if I put half-wave plate in-between. You can refer to attached picture 1. I will take the picture of weak light and measure it next time. As Matteo suggested, the weak signal will have less fluctuation which is important for measurement.
The power evolution is shown as attached picture 2. The attached picture 3 is about the diffraction angle.
I will do the measurement of green soon and compare it with this one. Before that we will refine the alignment of some wave plates.
So I did experiment today. Fortunately, I found a PBS without costing a lot of time. Although yuefan told me that the most consuming part of job in TAMA is finding something.
Then I improvised the testing set-up. I found most of the light is reflected by the PBS. However, I didn't know the ratio between s and p polarization should be around 1000, which I learnt from Matteo latter on. But this can explain why the energy doesn't conserve if I put half-wave plate in-between. You can refer to attached picture 1. I will take the picture of weak light and measure it next time. As Matteo suggested, the weak signal will have less fluctuation which is important for measurement.
The power evolution is shown as attached picture 2. The attached picture 3 is about the diffraction angle.
I will do the measurement of green soon and compare it with this one. Before that we will refine the alignment of some wave plates.
Images attached to this report
YuhangZhao - 00:47, Friday 12 January 2018 (624)
Test of grating for infrared
These days I tested the grating we will use for separating green and infrared.
I use the holes on the bench to estimate the incident angle. The test are divided by two sorts. For the first one, the incident beam is aligned with the arrow on the grating. For the second one, it is opposite.
I also test it by using a wave plate. It is used to see if polarization can affect the diffraction and if so, how it can affect.
I use the holes on the bench to estimate the incident angle. The test are divided by two sorts. For the first one, the incident beam is aligned with the arrow on the grating. For the second one, it is opposite.
I also test it by using a wave plate. It is used to see if polarization can affect the diffraction and if so, how it can affect.
Images attached to this report
AkihiroTomura - 01:07, Wednesday 10 January 2018 (623)
Comment to Mode cleaner telescope 1 (Click here to view original report: 613)
This is a correction of the entry 613.
In the entry 613, I made a miscalculation. This entry is a correct one.
I re-calculated optimal lens pairs for a telescope for the mode cleaner (green) with accurate dimensions (see here for the drawing). Figures attached show lens pairs that seem acceptable and the parameters I used.
In the case of the first figure, the mode matching factors are 99.718% and 99.601% for vertical and horizontal axes, respectively.
In the case of the second figure, the mode matching factors are 100% and 99.727% for vertical and horizontal axes, respectively.
The lens with 75.6 mm focal length that we already have is one without any surface coating thus low transmissivity. So I think the first case is preferable.
In the entry 613, I made a miscalculation. This entry is a correct one.
I re-calculated optimal lens pairs for a telescope for the mode cleaner (green) with accurate dimensions (see here for the drawing). Figures attached show lens pairs that seem acceptable and the parameters I used.
In the case of the first figure, the mode matching factors are 99.718% and 99.601% for vertical and horizontal axes, respectively.
In the case of the second figure, the mode matching factors are 100% and 99.727% for vertical and horizontal axes, respectively.
The lens with 75.6 mm focal length that we already have is one without any surface coating thus low transmissivity. So I think the first case is preferable.
Images attached to this comment
AkihiroTomura - 16:43, Wednesday 03 January 2018 (621)
Comment to Characteristics of SHG control loop with a new servo (Click here to view original report: 620)
Figures were missed in the entry. They are shown here.
Images attached to this comment
AkihiroTomura, MatteoLeonardi - 16:35, Wednesday 03 January 2018 (620)
Characteristics of SHG control loop with a new servo
Open-loop transfer function
On 12/21, we measured open-loop transfer function of SHG control, because a new servo was designed and installed by Matteo Leonardi. For the previous situation, please refer to an entry 585.Fig.1 shows open loop transfer function of the SHG control. We have three switches on the new servo, each of them is corresponding to a different integrator. Measurements were conducted for three combinations of these integrators. Noise level inserted were different depending on the conditions in order to keep the cavity being locked. PZT resonance point is located aroun 25 kHz. Unity gain frequency is shown on each graph by a black line (770 Hz, 1380 Hz, and 1610 Hz). You can see a high phase margin (approx. 90 degree) when the mid integrator ON.
We also measured power spectra of an error signal on the loop and DC signal from the photo detector which is monitoring transimitted light from the SHG (Fig.2). You can see a spike around 600 Hz. I am not sure what it means.
All spectra were taken by Agilent 36540A.
Output power stability
Fig.3 shows a long term (1000 second) stability of the SHG output. Stability of the SHG is much better than before. In this moment, we do not find a large fluctuation in the SHG output (532 nm) as we did so far.
Comments related to this report
Figures were missed in the entry. They are shown here.
Images attached to this comment
EleonoraCapocasa - 01:22, Friday 22 December 2017 (618)
Comment to abnormal behavior of local control, beam position, determination of PDH phase (Click here to view original report: 617)
A comment on the local controls large output: the voltage range at the output of the DAC is +/- 10 Volts. So If the correction signal is out of this range (as in the case of picture 1) the output is saturating and the control loop is likely not to be working properly (as can be seen from the large RMS in picture1).
More in general, looking at the error singnal, it seems to me that we are still affected by the "spikes issue". It could be useful to compare the open loop rms with the reference values in the absence of spikes.
YuhangZhao - 22:47, Thursday 21 December 2017 (617)
abnormal behavior of local control, beam position, determination of PDH phase
This week we installed steps for our optical bench, then we did some arrangement around the bench. It includes the rearrangement of equipments and cables.
We know for PDH control, the local oscillator phase and signal phase must match. But the cable length can affect this phase. So after changing cables, we need to set the phase of signal generator again.
Firstly, we need to close the loop for local control to make the light beam interferes well inside the cavity. However, I found the local control goes oscillation even with the previous value. The previous value means the value we used for locking yesterday. I should mention this abnormal case happened the day before yesterday.
After a very long time of adjusting, I found the the local can be fairly stable while the output of local is large(Fig 1). I adjusted it a little and make the output much smaller(but it is still around 40). Then I could find the beam through the end room camera.
Secondly, I took the photo of beam on the first iris(Fig 2,3) and the second iris(Fig 4).
Thirdly, I went to set the PDH phase. I set different value to see how the error signal looks like. I took three pictures(Fig 5,6,7) for this processes. We can deduce from them the worst case should between 80 and 90 degrees. So I set the phase as 175 degrees.
Finally, I found the transmitted signal decreases from 1V to 0.6V(Fig 8). And I found this is not caused by the SHG. Now the SHG locking is pretty pretty good! This is caused by the bad local control. The position of mirror drifts away fast. However, this maybe also caused by the large output of local control. Besides, I and Matteo measured the TF of BS pitch. Matteo said it is not a good control system according to this TF. So the local control definitely should be improved.
We know for PDH control, the local oscillator phase and signal phase must match. But the cable length can affect this phase. So after changing cables, we need to set the phase of signal generator again.
Firstly, we need to close the loop for local control to make the light beam interferes well inside the cavity. However, I found the local control goes oscillation even with the previous value. The previous value means the value we used for locking yesterday. I should mention this abnormal case happened the day before yesterday.
After a very long time of adjusting, I found the the local can be fairly stable while the output of local is large(Fig 1). I adjusted it a little and make the output much smaller(but it is still around 40). Then I could find the beam through the end room camera.
Secondly, I took the photo of beam on the first iris(Fig 2,3) and the second iris(Fig 4).
Thirdly, I went to set the PDH phase. I set different value to see how the error signal looks like. I took three pictures(Fig 5,6,7) for this processes. We can deduce from them the worst case should between 80 and 90 degrees. So I set the phase as 175 degrees.
Finally, I found the transmitted signal decreases from 1V to 0.6V(Fig 8). And I found this is not caused by the SHG. Now the SHG locking is pretty pretty good! This is caused by the bad local control. The position of mirror drifts away fast. However, this maybe also caused by the large output of local control. Besides, I and Matteo measured the TF of BS pitch. Matteo said it is not a good control system according to this TF. So the local control definitely should be improved.
Images attached to this report
Comments related to this report
A comment on the local controls large output: the voltage range at the output of the DAC is +/- 10 Volts. So If the correction signal is out of this range (as in the case of picture 1) the output is saturating and the control loop is likely not to be working properly (as can be seen from the large RMS in picture1).
More in general, looking at the error singnal, it seems to me that we are still affected by the "spikes issue". It could be useful to compare the open loop rms with the reference values in the absence of spikes.
MatteoLeonardi - 16:41, Thursday 21 December 2017 (616)
Comment to Mode cleaner telescope 1 (Click here to view original report: 613)
I upload the drawings of the MC (made by Uraguchi-san) as a reference for dimensions and specs.
Non-image files attached to this comment
ManuelMarchio - 04:10, Thursday 21 December 2017 (615)
Pump beam waist at different powers
see the attached document
Non-image files attached to this report
YuhangZhao - 22:14, Wednesday 20 December 2017 (614)
Locking of filter cavity again
After the installation of shield case and step around, we reconnect the cable. This cause the beam goes away. Now we can lock it again like figure 1.
While I check the first iris, I find the pattern on it is really similar with the pattern we get from infrared. So I think the problem should come from the bench. Refer to figure 2.
But the locking is not stable enough, I will check the phase of two signals sending to EOM. Refer to figure 3.
While I check the first iris, I find the pattern on it is really similar with the pattern we get from infrared. So I think the problem should come from the bench. Refer to figure 2.
But the locking is not stable enough, I will check the phase of two signals sending to EOM. Refer to figure 3.
Images attached to this report
AkihiroTomura - 18:47, Wednesday 20 December 2017 (613)
Mode cleaner telescope 1
I measured dimensions of the green beam after Mach-Zehnder to design a telescope for a mode cleaner. One of attached pictures shows a result. The x-axis of this graph starts from the output of EOM.
An eigenmode of the mode cleaner was calculated using values and a formula shown in a picture. A cavity length was roughly estimated from the number of holes on the optical table because I could not find it in e-logbook.
Based on these information, I searched for a optimal lens pair for telescope. One example is shown in a picture. In this case, mode matching factor for vertical and horizontal axis of the beam are 99.37 % and 99.56 %, respectively.
Images attached to this report
Comments related to this report
I upload the drawings of the MC (made by Uraguchi-san) as a reference for dimensions and specs.
Non-image files attached to this comment
This is a correction of the entry 613.
In the entry 613, I made a miscalculation. This entry is a correct one.
I re-calculated optimal lens pairs for a telescope for the mode cleaner (green) with accurate dimensions (see here for the drawing). Figures attached show lens pairs that seem acceptable and the parameters I used.
In the case of the first figure, the mode matching factors are 99.718% and 99.601% for vertical and horizontal axes, respectively.
In the case of the second figure, the mode matching factors are 100% and 99.727% for vertical and horizontal axes, respectively.
The lens with 75.6 mm focal length that we already have is one without any surface coating thus low transmissivity. So I think the first case is preferable.
In the entry 613, I made a miscalculation. This entry is a correct one.
I re-calculated optimal lens pairs for a telescope for the mode cleaner (green) with accurate dimensions (see here for the drawing). Figures attached show lens pairs that seem acceptable and the parameters I used.
In the case of the first figure, the mode matching factors are 99.718% and 99.601% for vertical and horizontal axes, respectively.
In the case of the second figure, the mode matching factors are 100% and 99.727% for vertical and horizontal axes, respectively.
The lens with 75.6 mm focal length that we already have is one without any surface coating thus low transmissivity. So I think the first case is preferable.
Images attached to this comment
AkihiroTomura - 13:32, Wednesday 20 December 2017 (612)
Caution about AOM alignment
After the installation of the coverage on optical bench, we are now checking the situation.
Note that our AOM is very easily misaligned by touching the cable.
Temporarily, I put a post right next to the cable in order not to make it move a lot (see a figure attached).
Images attached to this report
MatteoLeonardi, YuhangZhao - 13:41, Tuesday 19 December 2017 (611)
Step around the optical bench
Yesterday the step was mounted by the company around the optical bench.
In order to allow their work all the cables from the bench were disconnected and the racks were moved away.
After the company work the cables are being reconnected (ongoing).
In order to allow their work all the cables from the bench were disconnected and the racks were moved away.
After the company work the cables are being reconnected (ongoing).
Images attached to this report
YuhangZhao,AkihiroTomura - 11:55, Friday 15 December 2017 (610)
irises realignment and checking infrared beam
During yesterday and the day before, we mainly did two things.
1. For leaving space for the shield case, we moved two irises close to PR. Due to one of them is used to fix the lens rail, so we need to adjust the lens again to get good mode matching. Adjusting that lens costed a period of time, and then we can lock the cavity as it before.
2. Then we improvised a tripod to hold the camera, which is used for the near iris in the vacuum tube. Then we adjusted its position. Note that the camera we used here if found on the optical bench in the central room.
3. While we can see the EM transmitted signal, we rise up both of two irises one by one. And we cannot see a clear infrared on the iris. At the same time, the transmitted signal was blocked partly.
By the way, I found the transmitted signal of EM is on the edge of EM chamber view port.
(You can see the infrared checking video by clicking the following link.)
https://drive.google.com/open?id=1CqVLnQrDSaECMgJzHP2Fivabp3ip_E8T
https://drive.google.com/open?id=18AbcXlJ9LMBlW7SOZ7-MdkWTKyISZRya
1. For leaving space for the shield case, we moved two irises close to PR. Due to one of them is used to fix the lens rail, so we need to adjust the lens again to get good mode matching. Adjusting that lens costed a period of time, and then we can lock the cavity as it before.
2. Then we improvised a tripod to hold the camera, which is used for the near iris in the vacuum tube. Then we adjusted its position. Note that the camera we used here if found on the optical bench in the central room.
3. While we can see the EM transmitted signal, we rise up both of two irises one by one. And we cannot see a clear infrared on the iris. At the same time, the transmitted signal was blocked partly.
By the way, I found the transmitted signal of EM is on the edge of EM chamber view port.
(You can see the infrared checking video by clicking the following link.)
https://drive.google.com/open?id=1CqVLnQrDSaECMgJzHP2Fivabp3ip_E8T
https://drive.google.com/open?id=18AbcXlJ9LMBlW7SOZ7-MdkWTKyISZRya
YuhangZhao - 14:04, Sunday 03 December 2017 (609)
About the second iris's camera, SHG and infrared beam
Today I tried to find infrared beam again. But I found two things.
Firstly, I checked the camera for the second iris. I brought two cameras and one cable around the second iris back. We have a PR's camera, so I used it to check. The method is to replace one thing at a time. In this way, we can diagnose the replaced component. I found the cable is fine but two cameras are broken.
Broken camera 1: SONY NO.92980
Broken camera 2:SONY NO.161274
Secondly, I found the drifting of SHG is really serious.(with the driven voltage set around 50V). Within only 30 min or less, the power decreased from 50mW to 30mW and final 10mW. The measurement point is ahead of filter cavity's EOM.
Finally, I took a picture of the beam which is sent to our filter cavity. You can see from the attached photo. The beam is a combination of a large bright beam point and a small weak point. I cannot make it a rough circle by just adjusting the turing mirror or local control offset.
Firstly, I checked the camera for the second iris. I brought two cameras and one cable around the second iris back. We have a PR's camera, so I used it to check. The method is to replace one thing at a time. In this way, we can diagnose the replaced component. I found the cable is fine but two cameras are broken.
Broken camera 1: SONY NO.92980
Broken camera 2:SONY NO.161274
Secondly, I found the drifting of SHG is really serious.(with the driven voltage set around 50V). Within only 30 min or less, the power decreased from 50mW to 30mW and final 10mW. The measurement point is ahead of filter cavity's EOM.
Finally, I took a picture of the beam which is sent to our filter cavity. You can see from the attached photo. The beam is a combination of a large bright beam point and a small weak point. I cannot make it a rough circle by just adjusting the turing mirror or local control offset.
Images attached to this report
YuhangZhao - 01:31, Saturday 02 December 2017 (608)
Finding the infrared beam
I'm trying to find the infrared beam during these two days. I was trying to find it in-between two half of the halos.
Firstly, about the losing of the camera of the second target(or irises or aperture). I checked the link and cable. I also changed the driver for this camera. All of them didn't bring back our camera. But I found there was a gap on the case of camera.(As you can see in the figure one.) Maybe this is one reason, so I will check its capability further more.(Since we can see the scattered light or halo, I think there is no need to use the second irises. But brining it back will be a good thing for the future.)
Secondly, about the cable in the end room. I almost stumble because of the cable around the end room's bench. The reason is one of the cables is really short, which makes it suspended away the ground. And this happened on Thursday. On Friday, I cannot find the transmitted signal from the end mirror. I checked many things and finally realized where the problem would be. If you read previous part carefully, you can see the problem comes from the short cable. It causes the misalignment of the QPD. So I think we should do something to avoid this happens again.
Thirdly, I can find something really similar with yuefan's previous infrared beam gazing. You can find the video I took from the link in the bracket. But I tried to change the local control offset for each mirror, finding it's really different from the behavior of green beam. For example, the changing of this possible infrared beam does't follow the changing of the local control offset very well. Sometimes it looks really like the halo after changing the local control offset. I need to confirm this strictly, but the signal here is really weak! I feel the confirmation is really difficult.
(https://drive.google.com/file/d/12OmtNB93hNnNigcgu_0SNxJNy5pxSIPq/view?usp=sharing)
Fourthly, Tomura-san found we can use the sensor card to sense the infrared beam in the end room. I used it to check the light from EM chamber output port to the camera. I found almost one third of the beam is lost because the alignment on the end room bench. So I changed the alignment a little bit. The change includes one lens, one 45 degree mirror(Actually I don't know what this mirror for) and the camera. Now we can see the whole two half of halos by changing the angle and height of camera. You can see the video by clicking the attached link as following.
(https://drive.google.com/file/d/1MsWtaURQJLrXH1PSE4-g_qudrmI73w9c/view?usp=sharing)
Fifthly, Tomura-san suggested there is possibility that something is blocking on the infrared. Because you can see a black line in the spot of reference infrared beam. But I check the layout of our experiment, it's not the beam sending to cavity. However, the reference which is sending to cavity has also something like defect. The defect is the combination of a small spot and a larger spot. It's really like the scenario we can see from the infrared transmitted signal of EM, where there is a bright halo and a darker halo.(You can see this combination from the second video)
Sixthly, I checked the bright halo by changing the local control offset. As you can see from the attached second and third photo, there is angle changing of halo. And the halo is flashing. I suspect this halo can be the what we want to find. I will try to figure it out soon.
In the end, I can ride the bicycle very well now! I need to go to end room and go back many times to find the signal, which drives me to ride bicycle many times. This is really an useful skill and a good way to calm down or feel balance. &( ^___^ )&
Firstly, about the losing of the camera of the second target(or irises or aperture). I checked the link and cable. I also changed the driver for this camera. All of them didn't bring back our camera. But I found there was a gap on the case of camera.(As you can see in the figure one.) Maybe this is one reason, so I will check its capability further more.(Since we can see the scattered light or halo, I think there is no need to use the second irises. But brining it back will be a good thing for the future.)
Secondly, about the cable in the end room. I almost stumble because of the cable around the end room's bench. The reason is one of the cables is really short, which makes it suspended away the ground. And this happened on Thursday. On Friday, I cannot find the transmitted signal from the end mirror. I checked many things and finally realized where the problem would be. If you read previous part carefully, you can see the problem comes from the short cable. It causes the misalignment of the QPD. So I think we should do something to avoid this happens again.
Thirdly, I can find something really similar with yuefan's previous infrared beam gazing. You can find the video I took from the link in the bracket. But I tried to change the local control offset for each mirror, finding it's really different from the behavior of green beam. For example, the changing of this possible infrared beam does't follow the changing of the local control offset very well. Sometimes it looks really like the halo after changing the local control offset. I need to confirm this strictly, but the signal here is really weak! I feel the confirmation is really difficult.
(https://drive.google.com/file/d/12OmtNB93hNnNigcgu_0SNxJNy5pxSIPq/view?usp=sharing)
Fourthly, Tomura-san found we can use the sensor card to sense the infrared beam in the end room. I used it to check the light from EM chamber output port to the camera. I found almost one third of the beam is lost because the alignment on the end room bench. So I changed the alignment a little bit. The change includes one lens, one 45 degree mirror(Actually I don't know what this mirror for) and the camera. Now we can see the whole two half of halos by changing the angle and height of camera. You can see the video by clicking the attached link as following.
(https://drive.google.com/file/d/1MsWtaURQJLrXH1PSE4-g_qudrmI73w9c/view?usp=sharing)
Fifthly, Tomura-san suggested there is possibility that something is blocking on the infrared. Because you can see a black line in the spot of reference infrared beam. But I check the layout of our experiment, it's not the beam sending to cavity. However, the reference which is sending to cavity has also something like defect. The defect is the combination of a small spot and a larger spot. It's really like the scenario we can see from the infrared transmitted signal of EM, where there is a bright halo and a darker halo.(You can see this combination from the second video)
Sixthly, I checked the bright halo by changing the local control offset. As you can see from the attached second and third photo, there is angle changing of halo. And the halo is flashing. I suspect this halo can be the what we want to find. I will try to figure it out soon.
In the end, I can ride the bicycle very well now! I need to go to end room and go back many times to find the signal, which drives me to ride bicycle many times. This is really an useful skill and a good way to calm down or feel balance. &( ^___^ )&
Images attached to this report
