We use the current PLL just now, but the renewal of the components are not immediate as it will take some time. Even so we need steady steps towards the better PLL. I appreciate your taking care of it.
Last night (Mar 17) I checked the PLL setup as Mott had some difficulty to get a clean lock of the PLL setting.
Now the beating signal is much cleaner and behave straight forward. I will add some numbers such as the PD DC output, RF levels, SR560 settings...
I also had noticed the progressive change of the aux NPRO alignment to the Farady.
I strongly agree about the need of a good and robust PLL.
By modifying the old PDH box (version 2008) eventually I was able to get a PLL robust enough for my purposes. At some point that wasn't good enough for me either.
I then decided to redisign it from scratch. I'm going to work on it. Also because of my other commitments, I'd need a few days/1 week for that. But I'd still like to take care of it. Is it more urgent than that?
Did you find what is the merit of their impedance matching technique?
In this LVC meeting I discussed about triple resonant EOMs with Volker who was a main person of development of triple resonant EOMs at University of Florida.
Actually his EOM had been already installed at the sites. But the technique to make a triple resonance is different from ours.
They applied three electrodes onto a crystal instead of one as our EOM, and put three different frequencies on each electrode.
For our EOM, we put three frequencies on one electrode. You can see the difference in the attached figure. The left figure represents our EOM and the right is Volker's.
Then the question is; which can achieve better modulation efficiency ?
Volker and I talked about it and maybe found an answer,
We believe our EOM can be potentially better because we use full length of the EO crystal.
This is based on the fact that the modulation depth is proportional to the length where a voltage is applied onto.
The people in University of Florida just used one of three separated parts of the crystal for each frequency.
I checked the setup further more.
Now I have significant fraction of beating (30%) and have huge amplitude (~9dBm).
The PLL can be much more stable now.
You don't need a lengthy code for this. It is obvious that the spot size at the distance L is minimum when L =
zR, where zR is the Rayleigh range. That's all.
Then compare the spot size and the aperture size whether it is enough or not.
It is not your case, but if the damage is the matter, just escape to the large zR side. If that is not possible
because of the aperture size, your EOM is not adequate for your purpose.
For your reference: Voltage noise of LM7815/LM7915 (with no load)
This is the first touch to the MC mirrors after the earthquake on 16th.
So far, I have aligned in Yaw such that the yaw peak is minimized.
This seal is good for daily use- operation only. The IFO has to be sealed with light metal doors every night so ants and other bugs can not find their way in.
Matt and Koji:
We closed the light doors of the chambers.
Kiwamu and Koji
Last night we have released PRM from the gluing fixture. All of the six magnets are successfully released from the fixture.
We put SRM on the fixuture and glued a side magnet which we had failed at the last gluing.
We let it cure in the Al house. This should be the last magnet gluing until ETMs are delivered.
ITMX (ITMU03): all of magnets/guiderod/standoffs glued, mirror baked; balance to be confirmed
ITMY (ITMU04): all of magnets/guiderod/standoffs glued, balance confirmed, mirror baked
SRM (SRMU03): magnets/guiderod/standoff glued; a side magnet gluing in process, balance to be confirmed, last stand off to be glued, mirror to be baked
PRM (SRMU04): magnets/guiderod/standoff glued; balance to be confirmed, last stand off to be glued, mirror to be baked
TT: magnets/guiderod/standoff glued; balance to be confirmed, last stand off to be glued, mirror to be baked
I measured the open loop gain of the FSS (as usual, I have multiplied the whole OLG by 10dB to account for the forward loop gain in the box). I used a source level of -20 dBm and made sure this was not saturating by changing the level.
Its clear that the BW is limited by the resonance at ~1.7 MHz. Does anyone know what that is?
EO resonance in the RC path?
Steve and Koji
WE started to build 5 TTs. 4 of them are used in the recycling cavities. One is the spare.
We built the structure and are building the cantilever springs.
PRM was released from the fixuture without any trouble. This was the last magnet gluing until ETMs are delivered.
The below is the up-to-date Jenne stat table.
The clean room is getting too narrow. I am thinking that we should install ITMs to the chamber so that we can accommodate SRM/PRM suspensions.
Why does the small spot size for the case (A) have small efficiency as the others? I thought the efficiency goes diverged to infinity as the radius of the cylinder gets smaller.
With a 30mm PPKTP crystal the conversion efficiency from 1064nm to 532nm is expected to 3.7 %/W.
Therefore we will have a green beam of more than 2mW by putting 700mW NPRO.
Last a couple of weeks I performed a numerical simulation for calculating the conversion efficiency of PPKTP crystal which we will have.
Here I try to mention about just the result. The detail will be followed later as another entry.
The attached figure is a result of the calculation.
The horizontal axis is the waist of an input Gaussian beam, and the vertical axis is the conversion efficiency.
You can see three curves in the figure, this is because I want to double check my calculation by comparing analytical solutions.
The curve named (A) is one of the simplest solution, which assumes that the incident beam is a cylindrical plane wave.
The other curve (B) is also analytic solution, but it assumes different condition; the power profile of incident beam is a Gaussian beam but propagates as a plane wave.
The last curve (C) is the result of my numerical simulation. In this calculation a focused Gaussian beam is injected into the crystal.
The numerical result seems to be reasonable because the shape and the number doesn't much differ from those analytical solutions.
The shape of the TF looks nice but the calibration must be wrong.
Suppose 1/f slope with 10^-4 rad/V at 100kHz. i.e. m_pm = 10/f rad/V
This means m_fm = 10 Hz/V. This is 10^6 times smaller than that of LWE NPRO.
(Edit: Corrected some numbers but it is not significant)
Kiwamu and I measure the PZT response of the Innolight this evening from 24 kHz to 2MHz.
We locked the PLL at ~50 MHz offset using the Lightwave NPRO and and swept the Innolight with the network analyzer (using the script I made; it has one peculiar property, but it does work correctly).
We will post the plot of the Lightwave PZT response tomorrow morning.
Innolight: 100rad/V @ 100kHz => 1e7/f rad/V => 10MHz/V
LWE: 500rad/V @ 100kHz => 5e7/f rad/V => 50MHz/V
They sound little bit too big, aren't they?
- We removed old ITMX/Y from the chambers. Now they are temporarily placed on the flow table at the end. Steve is looking for nice storages for the 5inch optics.
- We wiped new ITMX/Y by isopropanol as they were dusty.
- We put them into the corresponding towers. Checked the balancing and magnet arrangements with the OSEMs. They were totally fine.
- We clamped the mirrors by the EQ stops. Wrapped the towers by Al foils.
Tomorrow we will put them into the chambers.
Innolight 10 rad/V @ 100kHz => 1e6/f rad/V => 1MHz/V
LWE 30 rad/V @ 100kHz => 3e6/f rad/V => 3MHz/V
BTW, don't let me calculate the actuator response everytime.
The elog (=report) should be somewhat composed by the following sections
Motivation - Method - Result (raw results) - Discussion (of the results)
We realized that we had measured the wrong calibration value; we were using the free-running error signal with the marconi far from the beat frequency, which was very small. When we put the Marconi right at the beat, the signal increased by a factor of ~12 (turning our original calibration of 10 mV/rad into 120 mV/rad). The re-calibrated plots are attached.
Steve and Koji (Friday, Apr 02)
Intsallation of ITMs are going on. Two new ITMs were placed on the optical table in the vacuum chambers. ITM for the south arm was put at the right place in accordance to the CAD drawing. ITM for the east arm is still at a temporaly place.
Tower placement (10:30-11:30)
- Put the tower on the table at a temporary place such that we can easily work on the OSEMs.
ITM (South arm) (14:00-16:30)
- Put the tower on the table at a temporary place such that we can easily work on the OSEMs.
- Leveled the table approximately.
- Released the EQ stops
- Removed anchors for the OSEM cables as it was too short. The wire distribution will be changed later.
- Put the OSEMs. Adjust the insertion to the middle of the OSEM ranges.
- Clamped the EQ stops again
- Placed the tower to the right place according to the CAD drawing.
- Released the EQ stops again.
- Check the OSEM values. The LL sensor showed small value (~0.5). Needs to be adjusted.
ITM (South) damping adjustment
- Found the signs for the facing magnets are reversed.
- Otherwise it damps very well.
Albeto and Koji
We took the tip replacement from the blue tower.
I am looking at http://www.cooperhandtools.com/brands/weller/ for ordering the tips.
The burnt one seems to be "0054460699: RT6 Round Sloped Tip Cartridge for WMRP Pencil" We will buy one.
The replaced one is "0054460299: RT2 Fine Point Cartridge for WMRP Pencil" We will buy two.
I like to try this: "0054460999: RT9 Chisel Tip Cartridge for WMRP Pencil" We will buy one.
This morning the pencil soldering iron of our Weller WD2000M Soldering Station suddenly stopped working and got cold after I turned the station on. The unit's display is showing a message that says "TIP". i checked out the manual, but it doesn't say anything about that. I don't know what it means. Perhaps burned tip?
Before asking Steve to buy a new one, I emailed Weller about the problem.
Some tools and the level gauge were removed from the table.
BAD news: I could clearly see scatter of the green beam path because of the dusts in the arm tube. Also many dusts are seen on the ITM surface.
Picture of the ETM - reflection from the ITM is hitting the mirror and the suspension structures.
1. Shoot the ITM center with the green beam.
- Two persons with walkie-talkies required for this work.
- Turn on the end green pointer. We could see the long trace of the beam sliced by the beam tube wall.
- Look at the tube peeping mirror for the CCD.
- Adjust yaw such that the beam trace on the tube wall is parallel to the arm.
- Adjust pitch such that the beam trace on the tube gets longer. This means that spot gets closer to the ITM.
- Continue pitch adjustment until some scatter appears on the ITM tower.
- Once the spot appears on the tower, you can easily adjust it on the mirror
2. Adjust pitch/yaw bias such that the reflection hits the ETM.
- Initially the ITM alignment is totally bad. ==> You clealy see the spot on the wall somewhere close to the ITM.
- Adjust pitch/yaw bias such that the spot goes farther as far as possible.
- Once you hit the suspension tower, the scatter is obviously seen from the peeping mirror.
- You can match the incident beam and the scattering of the reflection. You also can see the reflection from the ETM towards the ITM as the spot size gets huge (1/2 tube diameter).
- We found that the bias is ~-2 for pitch and ~-6 for yaw.
3. Go into the chamber. Check the table leveling.
- Open the light door.
- I found that the table is not leveled. Probably it drifted after the move of the weight (i.e. MOS removal).
- Removed one of the round-shaped weight. Moved the other weights such that the table was leveled.
4. Remove the bias for yaw and rotate suspension tower such that the reflection hit the center of the ETM.
- Removed the yaw bias. This makes the reflected spot totally off from the ETM.
- Rotate suspension tower so that the beam can approximately hit the ETM.
- Look at the peeping mirror, the beam is aligned to the ETM.
5. Adjust OSEMs
- Push/pull the OSEMs such that we have the OSEM outputs at the half of the full scale.
6. Adjust alignment by the bias again.
- Moving OSEMs changes the alignment. The pitch/yaw biases were adjusted to have the beam hitting on the ETM.
- Bias values at the end of the work: Pitch -0.8159 / Yaw -1.2600
7. Close up the chamber
- Remove the tools and the level gauge.
- Close the light door.
What??? I don't see any gray trace of Rs in the plot. What are you talking about?
Anyway, if you are true, the circuit is bad as the noise should only be dominated by the thermal noise of the resonant circuit.
Something must be wrong.
1. Physical Unit is wrong for the second term of "Vn = Vdn + Sqrt(2 e Idc)"
2. Why does the fit go below the dark noise?
3. "Dark noise 4 +/- NaN nV/rtHz" I can not accept this fitting.
Also apparently the data points are not enough.
From the measurements of the 11 MHz RFPD at 11Mhz I estimated a transimpedance of about 750 Ohms. (See attached plot.)
The fit shown in the plot is: Vn = Vdn + sqrt(2*e*Idc) ; Vn=noise; Vdn=darknoise; e=electron charge; Idc=dc photocurrent
The estimate from the fit is 3-4 times off from my analsys of the circuit and from any LISO simulation. Likely at RF the contributions of the parassitic components of each element make a big difference. I'm going to improve the LISO model to account for that.
The problem of the factor of 2 in the data turned out to be not a real one. Assuming that the dark noise at resonance is just Johnson's noise from the resonant circuit transimpedance underestimates the dark noise by 100%.
One dell is in the clean room for the suspension work.
I can't find the DELL laptop anywhere in the lab. Does anyone know where it is?
Also one of the two netbooks is missing.
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.
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.
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.
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.
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