Data looks perfect ... but the fitting was wrong.
Vn = Vdn + Z * sqrt( 2 e Idc ) ==> WRONG!!!
Dark noise and shot noise are not correlated. You need to take a quadratic sum!!!
Vn^2 = Vdn^2 + Z^2 *(2 e Idc)
And I was confused whether you need 2 in the sqrt, or not. Can you explain it?
Note that you are looking at the raw RF output of the PD and not using the demodulated output...
Also you should be able to fit Vdn. You should put your dark noise measurement at 10nA or 100nA and then make the fitting.
Here's another measurement of the noise of the REFL11 PD.
This time I made the fit constraining the Dark Noise. I realized that it didn't make much sense leaving it as a free coefficient: the dark noise is what it is.
Result: the transimpedance of REFL11at 11 MHz is about 4000 Ohm.
As well as the oplev construction for ITMs.
We anticipate the drift of the stack. So we need to revisit the alignment again.
Some tools and the level gauge were removed from the table.
Picture of the ETMX - reflection from the ITMX is hitting the mirror and Jamie's windmill.
0. The suspension tower had been placed on the table close to the door.
1. Brought the OSEMs from the clean room. Connected the satellite box to the ITMX suspension.
2. Went into the chamber. Leveled the table.
3. Released the mirror from the clamp. Put and adjust the OSEMs.
- Note that the side OSEM is located to the south side of the tower
so that we can still touch it after the placement of the TT suspension at the north side of the SOS tower.
4. Clamped the mirror. Moved the SOS tower according to the CAD layout.
5. Leveled the table again.
6. Released the mirror again and adjusted the OSEMs.
7. Turned on the end green laser pointer.
- The spot was slightly upside and left of the mirror. Adjusted it so that the spot is at the center.
8. Align ITMX in Pitch
- The spot was hitting the tube. Moved the pitch bias such that the beam get horizontal.
9. Align ITMX in Yaw
- Moved the SOS tower such that the approximate spot is on the ETMX. If I hit the right spot I could see the tube get grown green because of the huge scatter.
10. Adjusted the OSEMs again and check the alignment again. Repeated this process 2~3 times.
- Bias values at the end of the work: Pitch 0.7800 / Yaw 0.270
11. Close up the chamber
- Remove the level gauge. Some of the screws are still in the Al ship in the chamber.
- Close the light door.
Bob, Steve, and Koji
We opened North heavy door of the BS chamber in the afternoon.
In the evening, Koji worked on the PRM/SRM removal.
- Cleaned up the OPLEV mirrors to create some spaces near the door.
- Clamped PRM/SRM.
- Removed OSEMs. Made a record of the OSEMs. The record is on the wiki (http://lhocds.ligo-wa.caltech.edu:8000/40m/Upgrade_09/Suspensions)
- Found the SOSs are quite easy to remove from the table as they are shorter than the MOSs.
- Put a new Al sheet on a wagon. Put the SOSs on it. Wrapped them by the Al foils.
- Carried it to the clean room. They are on the right flow bench. Confirmed the wires are still fine.
- Closed up the chamber putting a light door.
Steve and Koji
We aligned the peeping mirrors to look at the surface of the ITMs.
They had been misligned as we move the positions of the ITMs, but now they are fine.
EDIT: I used an IFIT (inverse fast idiot transform) to change the x-axis of the plot from Hz to m. I think xlabel('Frequency [Hz]') is in my muscle memory now..
I have redone the beam fit, this time omitting the M2, which I believe was superfluous. I have made the requested changes to the plot, save for the error analysis, which I am still trying to work out (the function I used for the least squares fit does not work out standard error in fit parameters). I will figure out a way to do this and amend the plot to have error bars.
Zach and Koji
We measured uncalibrated angle-to-length coupling using tdssine and tdsdmd.
We made a simple shell script to measure the a2l coupling.
- Opened the IMC/OMC light door.
- Saw the large misalignment mostly in pitch. Aligned using MC2 and MC3.
- Locked the MC in the low power mode. (script/MC/mcloopson AND MC length gain 0.3->1.0)
- Further aligned MC2/3. We got the transmission of 0.16, reflection of 0.2
- Tried to detect angle-to-length coupling so that we get the diagnosis of the spot positions.
- Tried to use ezcademod. Failed. They seems excite the mirror but returned NaN.
- We used tdssine and tdsdmd instead. Succeeded.
- We made simple shell script to measure the a2l coupling. It is so far located users/koji/100421/MCspot
- We blocked the beam on the PSL table. We closed the chamber and left.
Good fit. I assumed sqrt(x) is a typo of sqrt(2).
Koji and Kevin measured the vertical beam profile of the Innolight 2W laser at one point.
This data was taken with the laser crystal temperature at 25.04°C and the injection current at 2.092A.
The distance from the razor blade to the flat black face on the front of the laser was 13.2cm.
The data was fit to the function y(x)=a*erf(sqrt(x)*(x-x0)/w)+b with the following results.
Reduced chi squared = 14.07
x0 = (1.964 +- 0.002) mm
w = (0.216 +- 0.004) mm
a = (3.39 +- 0.03) V
b = (3.46 +- 0.03) V
1. The vertical axis should start from zero. The horizontal axis should be extended so that it includes the waist. See Zach's plot http://nodus.ligo.caltech.edu:8080/40m/2818
2. Even if you are measuring only the linear region, you can guess w0 and z0, in principle. w0 is determined by the divergence angle (pi w0/lambda) and z0 is determined by the linear profile and w0. Indeed your data have some fluctuation from the linear line. That could cause the fitting prescision to be worse.
3. Probably the biggest reason of the bad fitting would be that you are fitting with three parameters (w0, z0, zR) instead of two (w0, z0). Use the relation ship zR= pi w0^2/lambda.
Once you made a CDS model, please update the following wiki page. This will eventually help you.
LSC Plant Model. That is all.
I scanned the temperature of the crystal oven on Friday night in order that we can find the optimal temperature of the crystal for SHG.
The optimal temperature for this crystal was found to be 36.2 deg.
The crystal is on the PSL table. The incident beam on the crystal is 27.0mW with the Newport power-meter configured for 1064nm.
The outgoing beam had 26.5mW.
The outgoing beam was filtered by Y1-45S to eliminate 1064nm. According to Mott's measurements, Y1-45S has 0.5% transmission for 1064nm, while 90% transmission for 532nm. This means I still had ~100uW after the Y1-45S. This is somewhat consistent with the offset seen in the power-meter reading.
First, I scanned the temperature from 28deg to 40deg with 1deg interval.The temperature was scaned by changing the set point on the temperature controller TC-200.The measurements were done with the temperature were running. So, the crystal may have been thermally non-equilibrium.
Later, I cut the heater output so that the temperature could be falling down slowly for the finer scan. The measurement was done from 38deg to 34deg with interval of 0.1deg with the temperature running.
I clearly see the brightness of the green increase at around 36 deg. The data also shows the peak centered at 36.2deg. We also find two lobes at 30deg and 42deg. I am not sure how significant they are.
Give me the plot of the fit, otherwise I am not convinced.
I tried Koji's suggestions for improving the fit to the vertical beam profile; however, I could not improve the uncertainties in the fit parameters.
Kiwamu and Koji
The PRM/SRM were balanced with the standoffs. We glued them to the mirror.
This was the last gluing so far until we get new PRM/ETMs.
- Checked the SRM/PRM balancing after the gluing.
- The mirrors were removed from the suspensions for baking.
- Bob is going to bake them next week.
I liked to know quantitatively where the spot is on a mirror.
With an interferometer and A2L scripts, one can make the balance of the coil actuators
so that the angle actuation does not couple to the longitudinal motion.
i.e. node of the rotation is on the spot
Suppose you have actuator balancing (1+α) f and (1-α) f.
=> d = 0.016 x α [m]
Full Imbalance α = 1 -> d = 15 [mm]
10% Imbalance α = 0.1 -> d = 1.5 [mm]
1% Imbalance α = 0.01 -> d = 0.15 [mm]
Eq of Motion:
I ω2 θ = 2 R f
(correction) - I ω2 θ = D f cos(arctan(L/2/D))
(re-correction on Sep 26, 2017) - I ω2 θ = D f
m ω2 x = 2 α f ,
(correction) - m ω2 x = 2 α f ,
where R is the radius of the mirror, and D is the distance of the magnets. (kinda D=sqrt(2) R)
d, position of the node distant from the center, is given by
d = x/θ = α I / (m R) = 2 α β / D,
where β is the ratio of I and m. Putting R=37.5 [mm], L=25 [mm], β = 4.04 10-4 [m2], D~R Sqrt(2)
i.e. d = 0.015 α [m]
The spot positions on the MC mirrors were measured with coil balance gains.
The estimated spot positions from the center of the MC1 and MC3 are as followings:
MC1H = +0.29 mmMC1V = -0.43 mmMC3H = +1.16 mmMC3V = -0.68 mm
The cordinates are described in the figure
As far as the cavity mirrors are aligned to the incident beam, spots on the MC1 and MC3 tell us the geometry of the incident beam.
Note that spot position on the MC2 is determined by the alignment of the MC1 and MC3, so it does not a big issue now.
The calibration between the coil balance and the spot position are described in the previous entry.
MC Trans: 0.18
MC Refl: 0.12-0.13
MC Trans: 0.18
MC Refl: 0.12-0.13
(subtract 1, then multiply 10.8mm => spot position.)
Yes, of course. But so far I am trusting that the coils are inheretly balanced.
Probably you are talking about the dependence of the nodal position on the frequency...I need to check if 18Hz is sufficiently high or not for 0.1mm precision.
Also I am practicing myself to understand how I can adjust them by which screws as we probably have to do this adjustement many times.
(i.e. removal of the MZ, move of the table, PSL renewal and so on)
For the actuator calibration, we may be able to calibrate actuator responses by shaking them one by one while reading the OPLEV P/Y signals.
Oh, but it gets even better: in order to trust the A2L script in this regard you have to know that the coil driver - coil - magnet gain is the same for each channel. Which you can't.
But we have these handy f2pRatio scripts that Vuk and Dan Busby worked on. They use the optical levers to balance the actuators at high frequency so that the A2L gives you a true spot readout.
But wait! We have 4 coils and the optical lever only gives us 2 signal readouts...
Deviations of the MC spot from the center of the mirrors were measured.
1) The vertical deviation looks easy being adjusted as they are mostly translation. They are ~0.5mm too high.
The distance from SM2 to MC is 1.8m. Thus what we have to do is
rotate SM2 Pitch in CW knob by 0.25mrad.
1 turn steers the beam in 10mrad. So 0.25mrad is 1/40 turn (9deg)
2) The horizontal deviation is more troublesome. The common component is easily being adjusted
but the differential component (i.e. axis rotation) involves large displacement of the beam
at the periscope sterring mirrors.
(MC3H - MC1H) / 0.2 m * 1.8 m = 8 mm
The beam must be moved in 8mm at the periscope. This is too big.
We need to move the in-vac steering mirror IM1. Move SM2Yaw in 7mrad. This moves the spot on IM1 by 5mm*Sqrt(2).
Then Move Im1 Yaw such that we see the resonance.
For the alignment adjustment, try to maximize the transmission by MC2 Yaw (cavity axis rotation) and SM2Y (beam axis translation)
Actual move will be:
- Move IM1Y CCW (assuming 100TPI 1.5 turn in total...half turn at once)
- Compensate the misalignment by SM2Y CW as far as possible.
- Take alignment with MC2Y and SM2Y as far as possible
This operation will move the end spot something like 15mm. This should be compensated by the alignment of MC1Y at some point.
Actually, I tried some tweaks of the input steering to get the beam being more centered on the MC mirrors on Saturday evening.
I made a mistake in the direction of the IM1Y tuning, and it made the horizontal spot position worse.
But, this also means that the opposite direction will certainly improve the horizontal beam angle.
Rotate IM1Y CCW!!!
The current setting is listed below
MC1H = +1.15 mm
MC1V = -0.13 mm
MC3H = +0.80 mm
MC3V = -0.20 mm
MC1H = +1.15 mm
MC1V = -0.13 mm
MC3H = +0.80 mm
MC3V = -0.20 mm
Lessons learned on the beam spot centering (so far)
The spot position on MC2 can be adjusted by the alignment of the mirror while maintaining the best overlapping between the beam and the cavity axes.
In general, there are two methods:
1) Use the cavity as a reference:
Move the MC mirrors such that the cavity eigenmode hits the centers of the mirrors.
-> Then adjust the incident beam to obtain the best overlapping to the cavity.
2) Use the beam as a reference:
Move the incident beam such that the aligned cavity has the spots at the centers of the mirrors.
-> Then adjust the incident beam to obtain the best spot position while the cavity mirrors keep tracking
the incident beam.
Found the method 1) is not practical.
This is because we can move the eigenmode of the cavity only by very tiny amount if we try to keep the cavity locked.
How much we can move by mirror alignment is smaller than the waist radius or the divergence angle.
For the MC, the waist radius is ~2mm, the divergence angle is 0.2mrad. This means the axis
translation of ~1mm is OK, but the axis rotation of ~4mrad is impractical.
Also it turned out that adjustinig steering mirror to the 10-m class cavity is quite difficult.
A single (minimum) touch of the steering mirror knob is 0.1mrad. This already change the beam position ~0.1mm.
This is not an enough resolution.
Method 2) is also not so easy: Steering mirrors have singular matrix
Indeed! (Remember the discussion for the IMMT)
What we need is the pure angle change of 4mrad at the waist which is ~2m distant from the steering mirror.
This means that the spot at the steering mirror must be moved by 8mm (= 4mrad x 2m). This is the result of the
nearly-singular matrix of the steering mirrors.
We try to avoid this problem by moving the in-vac mirror (IM1), which has somewhat independent move.
The refl beam path also has the big beam shift.
But once the vacuum manifold is evacuated we can adjust very little angle.
This can also be a good news: once the angle is set, we hardly can change it at the PSL side.
Koji and Zach
We improved the beam axis rotaion on the MC. We still have 3mrad to be corrected.
So far we lost the MC Trans spot on CCD as the beam is now hitting the flange of the window. We need to move the steering mirror.
To do next:
- MC2 spot is too much off. Adjust it.
- Rotate axis for 3mrad more.
- Adjust Vertical spot position as a final touch.
- Incident beam had 7mrad rotation.
- Tried to rotate in-vac steering mirror (IM1) in CCW
- After the long struggle the beam from PSL table started to hit north-east side of IM1 mount.
- Moved the IM1. All of the beam (input beam, MC Trans, MC Refl) got moved. Chaotic.
- Recovered TEM00 resonance. MC Trans CCD image missing. The beam axis rotation was 8.5mrad.
Even worse. Disappointed.
- We made a strategic plan after some deliberation.
- We returned to the initial alignment of Saturday only for yaw.
Not at once, such that we don't miss the resonance.
- Adjusted SM2Y and IM1Y to get reasonable resonance. Then adjusted MC2/3 to have TEM00 lock.
- Measured the spot positions. The axis rotation was 4.8mrad.
- Moved the spot on IM1 by 7mm by rotating SM2Y in CCW - ((A) in the figure)
- Compensated the misalignment by IM1Y CCW. ((B) in the figure)
Used a large sensor card with puch holes to see the spot distribution between the MC1 and MC3.
- Fine alignment by MC2/MC3. Lock to TEM00. The beam axis rotation was 3mrad.The beam axis translation was 3mm.
- This 3mm can be Compensated by IM1Y. But this can easily let the resonance lost.
Put the sensor card between MC1/MC3 and compensated the misalignment by MC3 and MC1.
Note: You match the returned spot from the MC2 to the incident beam by moving the spot deviation by MC3,
the spot returns to the good position on MC1. But the angle of the returned beam is totally bad.
This angle deviation can be adjusted by MC1.
Note2: This step should be done for max 2mm (2mrad) at once. As 2mrad deviation induces the spot move on the MC2 by an inch.
- After all, what we get is
MC1H = -0.15 mmMC1V = -0.33 mmMC3H = +0.97 mmMC3V = -0.33 mm
This corresponds to the axis rotation of 3mrad and the beam axis translation of 0.8mm (to north).
Ben, Steve, and Koji
Ben came to the 40m and hooked up a cable to the main interlock service.
We have tested the interlock and confirmed it's working.
[Now the laser is approved to be used by persons who signed in the SOP.]
The RC, PMC, and MZ were unlocked during the interlock maneuver.
Now they are relocked.
Zach and Koji,
MC1H = -0.12mm
MC1V = -0.13mm
MC2H = -0.15mm
MC2V = +0.14mm
MC3H = -0.14mm
MC3V = -0.11mm
MC1H = -0.12mm
MC2H = -0.15mm
MC2V = +0.14mm
MC3H = -0.14mm
MC3V = -0.11mm
The aperture right before the vacuum window has been adjusted to the beam position. This will ensure that any misalignment on the PSL table can have the correct angle to the mode cleaner as far as it does resonate to the cavity. (This is effectively true as the small angle change produces the large displacement on the PSL table.)
If we put an aperture at the reflection, it will be perfect.
Now we can remove the MZ setup and realign the beam to the mode cleaner!
- The beam axis rotation has been adjusted by the method that was used yesterday.
Differential: SM2Y and IM1Y
Common: SM2Y only
- We developped scripts to shift the MC2 spot without degrading the alignment.
These scripts must be upgraded to the slow servo by the SURF students.
- These are the record of the alignment and the actuator balances
C1:SUS-MC1_PIT_COMM = 2.4005
C1:SUS-MC1_YAW_COMM = -4.6246
C1:SUS-MC2_PIT_COMM = 3.4603
C1:SUS-MC2_YAW_COMM = -1.302
C1:SUS-MC3_PIT_COMM = -0.8094
C1:SUS-MC3_YAW_COMM = -6.7545
C1:SUS-MC1_ULPIT_GAIN = 0.989187
C1:SUS-MC1_ULYAW_GAIN = 0.987766
C1:SUS-MC2_ULPIT_GAIN = 0.985762
C1:SUS-MC2_ULYAW_GAIN = 1.01311
C1:SUS-MC3_ULPIT_GAIN = 0.986771
C1:SUS-MC3_ULYAW_GAIN = 0.990253
As per Steve's request I checked the MC incident power as a function of time.
The output is negative: the lower voltage, the higher power.
Before I put the attenuator the incident power was 1.1W. It appear as -5V.
Now the output is -0.1V. This corresponds to 22mW.
After the MZ-removal work:
- I found that the input steering (IM1) was right handed. This was different from the CAD layout. This was the main reason why the MC trans was kicked by the mount.
- Removed the mount from the post and converted it to a keft handed.
- Align IM1 so that we can get TEM00 lock. Align IM1 further.
- After the IM1 was optimized for the TEM00, move the periscope mirrors to have best alignment.
- Checked the beam spot positions. They looks quite good (MC2 is not the matter now).
C1:SUS-MC1_ULPIT_GAIN = 0.998053
C1:SUS-MC1_ULYAW_GAIN = 0.992942
C1:SUS-MC2_ULPIT_GAIN = 1.00856
C1:SUS-MC2_ULYAW_GAIN = 1.04443
C1:SUS-MC3_ULPIT_GAIN = 0.99868
C1:SUS-MC3_ULYAW_GAIN = 1.00041
This IPC stuff looks really a nice improvement of CDS.
Please just maintain the wiki updated so that we can keep the latest procedures and scripts to build the models.
So I finished writing a script which takes an .ipc file (the one which defines channel names and numbers for use with the RCG code generator), parses it, checks for duplicate channel names and ipcNums, and then parses and .mdl file looking for channel names, and outputs a new .ipc file with all the new channels added (without modifying existing channels).
The script is written in python, and for the moment can be found in /home/controls/advLigoRTS/src/epics/simLink/parse_mdl.py
I still need to add all the nice command line interface stuff, but the basic core works. And already found an error in my previous .ipc file, where I used the channel number 21 twice, apparently.
Right now its hard coded to read in C1.ipc and spy.mdl, and outputs to H1.ipc, but I should have that fixed tonight.
Hey, what a quick work!
1) The radius of the beam was measured by the razor blade.
2) The diameter of the beam (13.5% full-width) at each point was measured by Beam Scan. The one at z=~7cm was consistent with 1)
3) The data 2) was fitted by a function w = sqrt(w0^2+lambda^2*(x-x0)^2/(pi*w0)^2). This is defined for the radius, isn't it?
So the fitting must be recalculated with correct radius.
Make sure that you always use radius and write with a explicit word "radius" in the record.
Kiwamu and Kevin measured the beam profile of the green laser by the south arm ETM.
The following measurements were made with 1.984A injection current and 39.65°C laser crystal temperature.
Two vertical scans (one up and one down) were taken with a razor blocking light entering a photodiode with the razor 7.2cm from the center of the lens. This data was fit to
b + a*erf(sqrt(2)*(x-x0)/w) with the following results:
scan down: w = (0.908 ± 0.030)mm chi^2 = 3.8
scan up: w = (0.853 ± 0.025)mm chi^2 = 2.9
giving a weighted value of w = (0.876 ± 0.019)mm at this distance.
The beam widths for the profile fits were measured with the beam scanner. The widths are measured as the full width at 13.5% of the maximum. Each measurement was averaged over 100 samples. The distance is measured from the back of the lens mount to the front face of the beam scanner.
This data was fit to w = sqrt(w0^2+lambda^2*(x-x0)^2/(pi*w0)^2) with lambda = 532nm with the following results:
For the vertical beam profile:
reduced chi^2 = 3.29
x0 = (-87 ± 1)mm
w0 = (16.30 ± 0.14)µm
For the horizontal beam profile:
reduced chi^2 = 2.01
x0 = (-82 ± 1)mm
w0 = (16.12 ± 0.10)µm
Strange. I thought the new result became twice of the first result. i.e. w0=32um or so.
Can you explain why the waist raidus is estimated to be three times of the last one?
Can you explain why the measured radius @~70mm is not 0.8mm, which you told us last time,
but is 0.6mm?
The measurements have been done at the outside of the Rayleigh range.
This means that the waist size is derived from the divergence angle
theta = lambda / (pi w0)
At the beginning you used diameter instead of radius. This means you used twice larger theta to determine w0.
So if that mistake is corrected, the result for w0 should be just twice of the previous wrong fit.
reduced chi^2 = 3.25
x0 = (-86 ± 1)mm
w0 = (46.01 ± 0.38)µm
reduced chi^2 = 2.05
x0 = (-81 ± 1)mm
w0 = (45.50 ± 0.28)µm
I could not understand this operation. Can you explain this a bit more?
It sounds different from the standard procedure to adjust the Faraday:
1) Get Max transmittion by rotating PBS_in and PBS_out.
2) Flip the Faraday 180 deg i.e. put the beam from the output port.
3) Rotate PBS_in to have the best isolation.
* To get a good isolation with the Faraday we at first rotated the polarization of the incident beam so to have a minimum transmission. And then we rotated the output polarizer until the transmission reaches a minimum. Eventually we got the transmission of less than 1mW, so now the Faraday should be working regardless of the polarization angle of the incident beam. As we predicted, the output polaerizer seems to be rotated 45 deg from that of the input.
The old small MMT was removed and wrapped by Al foils.
The steering mirror IM2-IM4 were displaced and aligned.
The Faraday isolator block is moved and aligned.
The MC is realigned and resonatng TEM-00.
Now the MC has slightly miscentered beam on the mirrors owing to change of the stack leveling.
OSEMs are also in a strange state. We should check this later.
??? I still don't understand. What principle are you rely on?
I could not understand why you rotated the HWP to the "minimum" transmission
and then minimized the transmission by rotating the output PBS. What is optimized by this action?
Probably there is some hidden assumption which I still don't understand.
Something like: Better transmission gives best isolation, PBS has some leakage transmission
of the S-pol light, and so on.
Tell me what is the principle otherwise I don't accept that this adjustment is "to get a good isolation with the Faraday".
P.S. you could flip the faraday without removing it from the V-shaped mount. This does not roll the Faraday.
The procedure you wrote down as a standard is right. I explain reasons why we didn't do such way.
For our situation, we can rotate the polarization angle of the incident beam by using a HWP in front of the Faraday.
This means we don't have to pay attention about the PBS_in because the rotation of either PBS_in or the HWP causes the same effect (i.e. variable transmission ). This is why we didn't carefully check the PBS_in, but did carefully with the HWP.
Normally we should take a maximum transmission according to a instruction paper from OFR, but we figured out it was difficult to find a maximum point. In fact looking at the change of the power with such big incident (~1W) was too hard to track, it only can change 4th significant digit ( corresponds to 1mW accuracy for high power incident ) in the monitor of the Ophir power meter. So we decided to go to a minimum point instead a maximum point, and around a minmum point we could resolve the power with accuracy of less than 1mW.
After obtaining the minimum by rotating the HWP, we adjusted the angle of PBS_out to have a minimum transmission.
And then we was going to flip the Faraday 180 deg for fine tuning, but we didn't. We found that once we remove the Faraday from the mount, the role angle of the Faraday is going to be screwed up because the mount can not control the role angle of the Faraday. This is why we didn't flip it.
Thanks Zach.This was a great job.
It was not mentioned but: was the Faraday clamped down on the table?
Fixing at the next time is absolutely OK.
Ah... no, I didn't. That explains why there were loose dogclamps on the table. I wrapped them in foil and put them on the clean cart. Can this wait until the next time we open the tank (i.e. to measure the beam profile), or should I go over there and clamp it down today?
Don't make a short cut. The beam size at a single place does not tell you anything.
Measure the mode of of the beam at multiple points. Calculate the mode matching ratio.
Align the mirrors precisely. Try to see the DC fringe. Predict the size of the DC fringe.
Test the demodulation system with a function generator. Find the 200kHz signal using the spectrum analyzer to find the signal and the optimal alignment.
Put the DC signal and the AC signal to the oscilloscope as X&Y.
Let me remind you how to lock and align the IMC
1. Open the doors for the IMC/OMC chambers. Open the manual shutter of the PSL just in front of the optical window
2. Run scripts/MC/mcloopson
3. Set the MC length path gain 0.3 / Set the MC total gain "+20"
4. If you want to avoid excitation of the mirrors by air turbulence, put a big plastic film and put three posters on the top and both the sides on the floor to block the wind go into the chamber.
To shut down
1. Run scripts/MC/mcloopsoff
2. Close the manual shutter, Remove the wind blockers, and the light door of the chambers
To align the MC
1. Tweak MC2 and MC3 to get maximum transmittion and/or minimum reflection.
OK. Don't worry. This is just an initial confusion which we also had for the suspensions a while ago.
The faraday must be clamped. It shakes the table terribly but it is fine. The leveling may change a bit but should be small enough. Otherwise, just tweak the weights. In fact, the faraday has enough large apertures and we hope we don't need to move it again, as far as the MC incident beam is not moved. But if necessary, we don't move the mirrors but move the faraday itself.
Usually the alignment of the MC is taken by MC2/MC3 such that we don't move the refl. But if you think what have moved is the MC1/MC3 (i.e. activity in the IMC chamber), take the alignment of the MC1/MC3.
It is just a matter of time to get TEM00. If you get TEM11, it is already close. If you align for TEM11, it is enough aligned to lock TEM10 or TEM01. Once you got better mode, align for it again. Eventually you will get TEM00.
The leveling may change by moving the optics and the weight again. But once the leveling is recovered by arranging the weights somewhere else,
the pointing must be fine again. If necessary, You can remove two optics for squeezing injection (strange motorized rotating mirror and a mount sticking out from the table to south.)
Yes, we need to move the PZT mirror. For the connection, only Steve can give us the right way to do it. If it is too much hussle, just move only the mirror and ignore the wiring for now.
I will update how the mirrors should be migrated from the table to the table.
Here is the upadted list http://lhocds.ligo-wa.caltech.edu:8000/40m/Upgrade_09/Optics
I will update how the mirrors should be migrated from the table to the table.
Good! What was the key?
The MC2 spot looks very high, but don't believe the TV image. Believe the result of script/A2L/A2L_MC2. What you are looking at is the comparison of the spot at the front surface and the OSEMs behind the mirror.
We opened up the MC chambers again, and successfully got the MC locked today! Hooray! This meant that we could start doing other stuff....
First, we clamped the Faraday. I used the dog clamps that Zach left wrapped in foil on the clean cart. I checked with a card, and we were still getting the 00 mode through, and I couldn't see any clipping. 2 thumbs up to that.
Then we removed the weight that was on the OMC table, in the way of where MMT2 needs to go. We checked the alignment of the MC, and it still locks on TEM00, but the spot looks pretty high on MC2 (looking at the TV view). We're going to have to relevel the table when we've got the MMT2 optic in the correct place.
We were going to start moving the PZT steering mirror from the BS table to the IOO table, place MMT2 on the OMC table, and put in a flat mirror on the BS table to get the beam out to the BS oplev table, but Steve kicked us out of the chambers because the particle count got crazy high. It was ~25,000 which is way too high to be working in the chambers (according to Steve). So we closed up for the day, and we'll carry on tomorrow.
Photos of the weight before we removed it from the OMC table, and a few pictures of the PZT connectors are on Picasa.
1. Give us the designed arm length. What is the criteria?
2. The arm lengths got shorter as the ITMs had to shift to the end. To make them longer is difficult. Try possible shorter length.
Very nice as usual. Can you add the curve to show the ideal mode of the MC on the profile plot?
I fit the data from the beam profile that Jenne measured on 5/21/2010. The distances are measured from halfway between MC1 and MC3 to the beam scanner. The fits give the following where w0 is the waist size and z0 is the distance from the waist to halfway between MC1 and MC3.
For the horizontal profile:
reduced chi^2 = 0.88
z0 = (1 ± 29) mm
z0 = (1
w0 = (1.51 ± 0.01) mm
w0 = (1.51
For the vertical profile:
reduced chi^2 = 0.94
z0 = (673 ± 28) mm
z0 = (
w0 = (1.59 ± 0.01) mm
w0 = (1.59
I calculated the radius of curvature of MC2 using these values of w0:
horizontal: (16.89 ± 0.06) m
vertical: (17.66 ± 0.07) m
For this calculation, I used the value of (13.546 ± .0005) m for the length of the mode cleaner measured on 6/10/2009. The specification for the radius of curvature of MC2 is (18.4 ± 0.1) m.
That's true. But I thought that you measured the mode after those optics and the effect of them is already included.
Rana pointed out that the anticipated mode calculation should be modified to include the index of refraction of the crystals in the Faraday, and the polarizers in the Faraday. This may affect where we should put MMT1, and so this should be completed before round 2 measurements are taken, so that we can move MMT1.
Congratulation! Probably you are right, but I could not get this is a real lock or something else.
1) How much was the fringe amplitude (DC) of the reflected beam? (Vref_max=XXX [V] and Vref_min=YYY [V])
Does this agree with the expectation?
2) Do you have the time series? (V_ref and V_error)
I guess I succeeded in locking of the cavity with the green beam
Strictly speaking, the laser frequency of the end NPRO is locked to the 40 meter arm cavity.
Pictures, some more quantitative numbers and some plots are going to be posted later.
After the alignment of the cavity I could see DC fringes in its reflection. Also I could see the cavity flashing on the monitor of ETMY_CCD.
I drove the pzt of the NPRO with f=200kHz, and then the spectrum analyzer showed 200kHz beat note in the reflection signal. This means it's ready to PDH technique.
And then I made a servo loop with two SR560s, one for a filter and the other for a sum amp.
After playing with the value of the gain and the sign of the feedback signal, the laser successfully got lock.
To make sure it is really locked, I measured the open loop transfer function of the PDH servo while it stayed locked. The result is shown in the attached figure.
The measured data almost agrees with the expected curve below 1kHz, so I conclude it is really locked.
However the plot looks very noisy because I could not inject a big excitation signal into the loop. If I put a big excitation, the servo was unlocked.
The current servo is obviously too naive and it only has f-1 shape, so the filter should be replaced by a dedicated PDH box as we planed.
Hm... You touched the optics between the MC and the Faraday... This will lead us to the painful work.
I am afraid that the beam is already walking off from the center of MC1/MC3 after the work on the PSL table.
This may result in the shift of the spot on those MC mirrors. So I recommend that:
- Lock the cavity
- Check the A2L for MC1/3
- Adjust it by the periscope
- If it is fine, adjust the optics after the MC (steering, Faraday, etc)
Off-centering of the MC2 spot is no problem. We can move it easily using Zach's scripts.
Tell me when the work is planed on Sunday as I might be able to join the work if it is in the evening.
[Alberto, Kiwamu, Kevin, Rana]
Today we tried to measured the beam shape after the MC MMT1 that Jenne installed on the BS table.
The beam scan showed a clipped spot. We tracked it down to the Farady and the MCT pickoff mirror.
The beam was getting clipped at the exit of the Faraday. But it was also clipping the edge of the MCT pick-off mirror. I moved the mirror.
Also the beam looked off-center on MC2.
We're coming back on Sunday to keep working on this.
Now things are bad.
Remember that you only can introduce the axis translations from the PSL table.
It is quite difficult to adjust the axis rotation.
The calibration factor from A2L results to the beam position is dx = (A2L_result - 1) *10.8mm
If I believer the result below, the spot positions on the mirrors are
MC1 Pitch -1.1mm
MC1 Yaw -0.20mm
MC3 Pitch -1.5mm
MC3 Yaw +0.35mm
This means that the beam is 1.3mm too high and 0.28mm too much in north
This corresponds to tilting SM2 by
0.33mrad in pitch (23deg in CW)
0.10mrad in yaw (7deg in CW).
C1:SUS-MC1_ULPIT_GAIN = 0.900445
C1:SUS-MC1_ULYAW_GAIN = 0.981212
C1:SUS-MC3_ULPIT_GAIN = 0.86398
C1:SUS-MC3_ULYAW_GAIN = 1.03221
C1:SUS-MC1_ULPIT_GAIN = 0.900445
C1:SUS-MC1_ULYAW_GAIN = 0.981212
C1:SUS-MC3_ULPIT_GAIN = 0.86398
C1:SUS-MC3_ULYAW_GAIN = 1.03221
I checked the effect of the arm length to the reflectance of the f2(=5*f1) sidebands.
Conclusion: If we choose L_arm = 38.4 [m], it looks sufficiently being away from the resonance
We may want to incorporate small change of the recycling cavity lengths so that we can compensate the phase deviation from -180deg.
f1 of 11.065399MHz is assumed. The carrier is assumed to be locked at the resonance.
Attachment 1: (Left) Amplitude reflectance of the arm cavity at f2 a a function of L_arm. (Right) Phase
Horizontal axis: Arm length in meter, Vertical Magnitude and Phase of the reflectance
At L=37.93 [m], f2 sidebands become resonant to the arm cavity. Otherwise, the beam will not be resonant.
Attachment 2: close-up at around 5 f1 frequency.
The phase deviation from the true anti resonance is ~0.7deg. This can be compensated by both PRC and SRC lengths.
The alarm had kept crying. I reduced the LOW to be 0.90 and the LOLO to be 0.85 both in psl.db and with ezcawrite.
We changed the HIGH/LOW values of the PMC_TRANS.
The edited file was updated on the svn.
Since the PMC_TRANSPD was replaced behind the pzt mirror (see the entry), its nominal value were reduced to something like ~1V from the previous value of ~2V.
In the medm screen C1PSL_PMC.adl the PMC_TRAN always indicated red because the value were low compared with the previous one.
We went to /cvs/cds/caltech/target/c1psl, then edited psl.db
- Here are the new parameters we set up in the file.
- - - -
These values are based on ~4days trend of the PMC_TRAN.
Then we manually updated those numbers by using ezcawrite in order not to reboot C1PSL.
So now it nicely indicates green in the medm screen.
Just note that MMT1 has RoC of -5m (negative!). This means that it is a lens with f=-2.5 m,
This is what I already told to Kevin and Rana:
A direct output beam is one of the most difficult measurements for the mode profiling.
I worried about the thermal lensing.
Since most of the laser power goes through the substrate (BK7) of the W2 window, it may induce thermal deformation on the mirror surface.
An UV fused silica window may save the effect as the thermal expansion coefficient is 0.55e-6/K while BK7 has 7.5e-6.
In addition to the thermal deformation issue, the pick-off setup disables us to measure the beam widths near the laser aperture.
I rather prefer to persist on the razor blade then use the pick off between the blade and the PD.
I also confess that the description above came only from my knowledge, and not from any scientific confirmation including any calculation.
If we can confirm the evidence (or no evidence) of the lensing, it is a great addition to my experience.
[Rana, Kiwamu, Kevin]
The Innolight 2W beam profile was measured with the beam scan. A W2-IF-1025-C-1064-45P window was used to reflect a small amount of the main beam. A 5101 VIS mirror was used to direct just the beam reflected from the front surface of the W2 down the table (the beam reflected from the back surface of the W2 hit the optic mount for the mirror). A razor blade beam dump was used to stop the main transmitted beam from the W2. The distance from the laser was measured from the front black face of the laser to the front face of the beam scan (this distance is not the beam path length but was the easiest and most accurate distance to measure). The vertical and horizontal beam widths were measured at 13.5% of the maximum intensity (each measurement was averaged over 100 samples). These widths were divided by 2 to get the vertical and horizontal radii.
The mirror was tilted so that the beam was close to parallel to the table. (The center of the beam fell by approximately 2.1 mm over the 474 mm that the measurement was made in).
The measurement was taken with an injection current of 2.004 A and a laser crystal temperature of 25.04°C.
This data was fit to w = sqrt(w0^2+lambda^2*(x-x0)^2/(pi*w0)^2) with lambda = 1064nm with the following results
reduced chi^2 = 4.0
x0 = (-138 ± 3) mm
w0 = (113.0 ± 0.7) µm
reduced chi^2 = 14.9
x0 = (-125 ± 4) mm
w0 = (124.0 ± 1.0) µm
In the following plots, the blue curve is the fit to the vertical beam radius, the purple curve is the fit to the horizontal beam radius, * denotes a data point from the vertical data, and + denotes a data point from the horizontal data.
Last night we stopped the air conditioning. It made HDTEMP increase.
Later we restored them and the temperature slowly recovered. I don't know why the recovery was so slow.
Is the cooling line clogged? The chiller temp is 21C See 1 and 20 days plots
I could not dare to share my google doc with this site...
BTW, latex launched this new thing for writing pdfs. doesnot require any installations. check http://docs.latexlab.org
A thermal feedback was installed to the end PDH locking and it works well. There are no saturations
As I said the feedback signal was sometimes saturated at the sum-amp because the drive signal going to the laser PZT was large at low frequency (below 1Hz).
So I made a passive low pass filter which filters the signal controlling the temperature of the laser crystal, and put it before the temperature drive input.
Now the amount of the feedback signal got reduced when it is locked, and there are no saturations. It's very good.