Mounting Prism #16
Mounting Prism #20
Tonight, we locked the "fauxMC". We obtained a visibility of >99%.
Koji had aligned it roughly last night, but we wanted to have a couple steering mirrors in the path for this practice cavity (the periscope mirrors will serve this function in the real setup), so we marked the alignment with irises and installed two extra mirrors.
After obtaining flashes with the WinCam placed at the output coupler, we removed the WinCam and put a CCD camera at one of the curved mirror transmissions and used this to get a strong TEM00 flash. Then, we installed the REFL PD/CCD, swept the laser PZT and optimized the alignment by minimizing the REFL dips. Finally, we connected the RF electronics and locked the cavity with the LB box. We used whatever cables we had around to trim the RF phase, and then Koji made some nice SMA cables at the 40m.
One thing we noticed was that we don't have enough actuation range to keep the cavity locked for very long---even with the HV amp (100V). We are going to offload to the NPRO temperature using an SR560 or pomona box circuit. We may also make an enclosure for the cavity to protect it from the HEPA blasting.
Tomorrow, after we do the above things, we will practice measuring the transmission, length (FSR) and mode spectrum of the cavity before moving on to the real McCoy.
FM1 (input coupler): A8
FM2 (output coupler): A7
CM1 (curved mirror close to FM1): C6
CM2 (curved mirror close to FM2): C5
BS3 (BS for DCPDs): B5 B7
BS1 (input steering): E10
SM1 (steering mirror next to BS1): E12
BS2 (BS for QPD path): B3
SM2 (steering mirror next to BS2): E4
SM3 (steering mirror next to SM2): E16
- QPD mount aligned, QPD output checked
The spots are with 100um from the center of the diodes. [ELOG Entry (2nd photo)]
- TMS/FSR dependence on the PZT V
Shows significant dependence on the PZT voltages
It seems that the curvartures get longer when the voltages are applied to the PZTs.
The effect on these two PZTs are very similar. The dependence is something like
(TMS/FSR) ~ 0.219 - 1e-5 V
May cause resonance of the higher-order modes (like 13th order of the 45MHz sidebands) at a specific range of the PZTs.
We can't change anything any more, but the impact needs to be assessed
- DC response of the PZTs [ELOG Entry]
PZT voltages were swept. Observed multiple fringes during the sweep.
The data to be analyzed.
- AC response of the PZTs [ELOG Entry]
PZT1 and PZT2 well matched. The first resonance at 10kHz.
- Open loop TF of the servo
The UGF more than ~30kHz.
- Cleaning of the main optics with First Contact
Done. Visible scattering seen with an IR was reduced, but still exist.
All four cavity mirrors have about the same level of scattering.
Each scattering is a group of large or small bright spots.
It's actually a bit difficult to resolve the bright spots with the IR viewer.
- Raw transmission: i.e. Ratio between the sum of the DCPD paths and the incident power
May 8th (before the baking): 0.918
May 8th (First Contact applied): 0.940 (improved)
Jun 2nd (after the baking): 0.927 (worse)
Jun 2nd (First Cotact applied): 0.964 (improved)
- TMS/FSR/Finesse change before/after cleaning [ELOG Entry]
Just a small change from the parameters before the bake.
No quantitative difference.
BB EOM produces the AM sidebands together with the PM sidebands.
Ideally, the PM sidebands does not produce the signal at the transmission, the output is dominated by the AM component.
This is only true when there is no lock offset. In reality the curve is contaminated by the PM-AM conversion by the
static offset or dynamic deviation of the locking point. So I had to take the central part of the TF and check the
dependence of the fit region and the finesse.
Before the cleaning: Finesse 396.9
After the cleaning: Finesse 403.8
- Placement of the DCPD housings
- Through-put test with DCPDs
- Transmission dependence on the incident power
(although the max incident is limited to ~35mW)
- Application of the first contact for the surface protection
FM1 (input coupler): A9
FM2 (output coupler): A13
CM1 (curved mirror close to FM1): C9 (PZT ASSY #6 / M6 /PZT21/C9)
CM2 (curved mirror close to FM2): C4 (PZT ASSY #4 / M11/PZT25/C4)
BS3 (BS for DCPDs): B10
BS1 (input steering): E3
SM1 (steering mirror next to BS1): E5
BS2 (BS for QPD path): B9
SM2 (steering mirror next to BS2): E1
SM3 (steering mirror next to SM2): E2
In response to the failure of one of the PZTs on L1OMC (LLO:8366), we have been taking place an endurance test of
the four PZT sub-assemblies in prior to their being glued on the glass breadboard.
According to the technical note by Noliac, the common mode of PZT failure is degradation of the impedance
due to cyclic actuation (like 10^7 times) with over voltage. Therefore our procedure of the test to actuate the PZTs
at least 10^7 times with half voltage of the nominal operating voltage (i.e. nominal 200V) and check the degradation
of the impedance.
For the driving of the PZT, a thorlabs HV amp is used. A source signal of 3.5Vpp with an offset of 1.7V is produced
by DS345 function generator. This signal turns to a sinusoidal signal between 0 and 100V in conjunction with the gain
of 15 at the HV amp.
The maximum driving frequency is determined by the current supply limit of the HV amp (60mA). The capacitance
of each PZT is 0.47uF. If we decide to cycle the signal for 4 PZTs in parallel, the maximum frequency achievable
without inducing voltage drop is 100Hz. This yields the test period of 28hours in order to achive 10^7 cycles.
Initial impedance diagnosis
To check the initial state of the PZTs, a DC voltage of 100V was applied via 1kOhm output resistance.
(Note that this output resistance is used only for the impedance test.)
For each PZTs, both side of the resister showed 99.1V for all measurement by a digital multimeter.
Assuming the minimum resolution (0.1V) of the multimeter, the resistance of each PZT was more than 1MOhm before
the cycling test.
In order to detect any impedance drop of the PZTs, the driving signal is monitored on the oscilloscope via a 1:10 probe.
If there is any significant impedance drop, the driver can't provide the driving current correctly. This can be found
by the deviation of the driving voltage from the reference trace on the oscilloscope (below).
Because of the loss angle of the PZT capacitance, heating of the PZTs is expected. In order to check the temperature rise,
an IR Viewer (FLIR) was used. We did not take care of careful calibration for the PZT emissibity as what we want was a
rough estimation of the temperature.
Before the driving (LEFT) and at the equilibrium (RIGHT)
The temperature change of the PZT was tracked for an hour (below). Fitting of the points indicated that the temperature rise is 2.3degC and the
time constant of 446 sec. This level of temperature rise is totally OK. (Note that the fitting function was T = 27.55 - 2.31 Exp[-t/446.])
20:27 25.2 degC, status OK
20:33 26.7 degC, status OK
20:41 26.9 degC, status OK
20:48 27.6 degC, status OK
20:54 27.4 degC, status OK
21:10 27.4 degC, status OK
21:37 status OK
70 minutes of driving (i.e. 4.2x10^5 cycles) => no sign of degradation
14:15, 24.5 degC, status OK
14:17, 26.0 degC, status OK
14:24, 27.0 degC, status OK
14:40, 26.8 degC, status OK
14:50, 26.8 degC, status OK
15:30, 26.8 degC, status OK
15:55 status OK
17:40 status OK
21:00 status OK (2.43Mcycles + 0.42Mcycles = 2.85Mcycles)
1d+12:00 status OK (7.83Mcycles + 0.42Mcycles = 8.25Mcycles)
1d+15:00 status OK (8.91Mcycles + 0.42Mcycles = 9.33Mcycles)
1d+18:40 status OK (10.23Mcycles + 0.42Mcycles = 10.65Mcycles)
After 10.65Mcycles no sign of degradationwas found.
The PZT tests were finished with the conclusion that the PZT won't be damaged with our expected usage.
This is another test of the PZTs to make sure small (~10V) reverse voltage does not break the PZTs.
At the site, we decided to use one of the PZT, which is still alive, for the HV and LV actuation.
The HV actuation is limited to 0 to 100V while the LV actuation is 10Vdc with 1Vpp fast dithering.
This means that a reverse voltage upto 10.5V will be applied to the PZT at the worst case.
From the technical note this level of reverse voltage does not induce polarization of the PZT.
The test is to ensure the PZT is not damaged or degraded by this small reverse voltage.
HV drive: Thorlabs HV amp (G=15) driven with DS345 function generator (3.5Vpp+1.7Vdc, 0.1Hz)
=> 0-100V @0.1Hz
=> The hot side of the potential is connected to the positive side of the PZT
LV drive: Phillips function generator (1Vpp+9.5Vdc@1kHz)
The driving frequency is limited by the current output of the function generator.
=> The hot side of the potential is connected to the negative side of the PZT
These drives shares the common ground.
Testing with spare PZTs
Started @19:23 (Aug 23)
Stopped @20:15+2d (Aug 25, duration 48h52m)
17600cycles for the 0.1Hz drive.
176Mcycles for the 1kHz drive.
Checked the impedances of PZT1 and PZT2.
Apply 100Vdc via a 1kOhm resister, 0V detected across the 1kOhm resister
This is equivalent to the resistance of 1MOhm.
Testing with the PZT subassemblies
Started shaking of the four PZT assemblies @20:20 (Aug 25)
No impedance change observed @11:10+1d
No impedance change observed @15:30+1d
Stopped shaking of the four PZT assemblies @XXXX (Aug 26)
Wiring for the test
New DCPD(T) = A1-23
DCPD(T) = DCPDB: extracted and accomodated in CAGE-G SLOT1
New DCPD(R) = A1-25
DCPD(R) = DCPDA: extracted and accomodated in CAGE-G SLOT2
Preparation of 3rd OMC for the use in H1
New DCPD(T) = B1-01
DCPD(T) = DCPDA: extracted and accomodated in CAGE-A SLOT1
New DCPD(R) = B1-16
DCPD(R) = DCPDB: extracted and accomodated in CAGE-A SLOT2
Working on the SN002 OMC fix. Checked the inventory. I think I am using C8 mirror as the new temporary CM1 and PZT24 as the new temporary CM2.
- DC output of the trans RF PD was connected to the BNC patch panel. => Now CH4 of the scope is monitoring this signal
- The RF sweep signal from the network analyzer is connected to the power combiner for the EOM drive via the SMA patch panel.
- The trans RF PD was aligned first to the leakage beam. It turned out that this signal is too weak. Then the PD was aligned to one of the main OMC transmission. For this purpose, the OMC DCPD (T) was removed from the OMC breadboard.
- It seems that there is a significant amount of RF AM from the EOM. I suspect it is associated with the residual S-pol and birefringence of the steering mirrors (45deg HR). But the HWP at the output of the Faraday is fixed on the Faraday body with a screw and cumbersome for fine adjustment. A PBS and an HWP are added right before the EOM. This made the fiber coupler slightly misaligned. I suppose this new setup still has S&P on the fiber too. Thus, readjustment of the fiber rotations at the input is necessary.
- Input power to the fiber should be determined before the EOM. Otherwise, touching the HWP before the EOM causes too much power change at the optics of the OMC side.
- Precise adjustment of the RFAM is still necessary.
- The OMC curved mirror should be held by the new fixture.
- Check the beam spots
- Measure cavity parameters. (transmission/FSR/HOM/etc)
==> Then the curved mirror and the PZT will be glued on the prism
Last week, I further worked on the RF system to install 20dB coupler on the agilent unit and setup the R channel. This allowed me to make the FSR/TMS measurement of the OMC.
And today several optical improvement has been done.
- The input/output fiber couplers were adjusted to have the maximum transmission through the PBS right before the OMC.
- The HWP on the output side of the faraday was adjusted to have ~40mW input to the OMC.
Then, the OMC curved mirror is now held by the new in-situ gluing fixture instead of the conventional fixture attached upside down.
The OMC was ocked again and the input alignment was adjutsed. The fixture is blocking the QPD path, so it's not possible to confirm the proper alignment of the cavity (w.r.t. the QPD paths).
The precise positions of the spots could not be confirmed as the battery of the IR viewer was empty. Quick check of the spots by the card tells that the spot on the CM2 (PD side) is slightly too close to FM2 (output coupler). I wonder if this could be solved by rotating the curved mirror.
Otherwise everything look good. Let's try to glue the curved mirror tomorrow.
Note: Spot on CM2 is too close to the edge of the hole on the mounting prism. The meausrementof CM1 is telling that the curverture center is located 2.7mm upper side of the center of the mirror if the HR side arrow is up (and it is the case). If we move the arrow to the QPD path side (90deg CW viewed from the face side), this corresponds to ~1.1mrad CCW tilt in Yaw (viewed from the top of the prism). According to the matrix calculation (T1500060) this will induce ~1.5mm shift of the beam. This should be tried before gluing.
- Replaced the PZT with the one used from the beginning. This must be PZT #21. After the replacement, the spot positions look very good. I even went up. So I decided this is the configuration to proceed to the gluing. The CM1 mirror has the HR arrow at the top.
- The input beam was realigned w.r.t. the OMC.
- Tried to use the IR viewer with the new rechargable battery brought from the 40m. But the view still didn't work. The possibility is a) the viewer is broken b) the battery is empty.
- Tried to use the stainless clean regulartor for the UHP N2. The outlet has a short tube with a different diameter. The O.D. of the old tube is 6.3mm, while the new one is 9.5mm. If I insert the thinner tube in the new tube, it approximately fits. But I don't believe this is the way...
D1200105 SN006 was selected as the breadboard for OMC(004).
The reason is the best parallelism among the unused ones.
The attached is the excerpt from T1500060 with the #006 highlighted.
We are going to use A5 and A14 for FM1 and FM2. (The role of these two can be swapped)
The reason for the selection is the better perpendicularity among the available prisms.
A11 has the best perpendicularity among them. However, the T didn't match with the others. The pair of A5 and A14 has a good matching with small compromise of the perpend.
The attachment is the excerpt from T1500060.
We are going to use B6 for the DCPD BS (BS2), and B1 for the QPD BS (BS3). Their role can not be swapped.
B6 has the best loss among the available ones, while the perpendicularity is not so critical due to the short arm.
B1 has the OK perpendicularity, while the loss is also moderately good.
The attachment is the excerpt from T1500060 with some highlighting.
We are going to use E6, E9, E11, and E14 for BS1, SM1, SM2, and SM3. They (and E18) are all very similar.
The attachment is the excerpt from T1500060 with some highlighting
[Koji,Philip, Liyuan, Joe]
We moved the curved mirrors to these positions:
inner = 0.807mm
outer = 0.983 mm
inner = 0.92 mm
outer = 0.85 mm
To do this so that realignment was easier, we moved the screws in steps of 5um. We alternated which mirror we adjusted so that we could monitor with a wincam how well aligned the beam into the cavity was. We only moved the cavity mirrors a small amount so we could still see higher order mode flashes transmitted through the cavity (e.g.TM03 modes). We would then improve the input alignment, and then move the cavity mirrors some more. Once the mirrors were adjusted according to http://nodus.ligo.caltech.edu:8080/OMC_Lab/190422_195450/misalignment4.pdf the spot positions looked near the middle of the curved mirrors (using a beam card). We began beam walking but we ran out of range of the bottom periscope screws in the yaw dof. We tried using the third screw to move the mirrror in both yaw and pitch, hopefully this will let move the mirror such that we can use the just the yaw screw. This screw also ran out of range, so we decided that the cavity needed a small adjustment.
The curved mirrors were moved slightly (>5um) and then we tried to get alignment. By using the fibre coupler translation stage, we move the beam side ways slightly, and then tried to get the periscope mirrors back to a position where the screws could move the mirrors. Once we had an ok alignment, we checked the beam. It looked like it was pretty close to the centre of the curved mirrors, which is where we wanted it to be.
We then tried locking the cavity, although the error signal was quite small. The adjusted the input offset and gain of the servo (there is apparently some problem to do with the input and output offsets). Once the cavity was locked we could make the final adjustments to aligning. We still ran out of range on the periscope. We decided to move the breadboard with the fibre coupler and mode matching lenses on it. Because we knew that the cavity was aligned such that the beam hits the centres of the curved mirrors, we could regain flashes quite quickly. We saw the error signal go down, but eventually this decrease was just to do with the beam clipping on the periscope mirrors. We moved the spot back to where we ok aligned, and slid the periscope so we were not clipping the mirror. This worked very well, and then optimised the alignment.
We then tried to improve the mode matching.
We took photos of the spot positions (quite near the center) and made the detuned locking measurement. The fitting of the data (attachment 1) wsa 1.1318m (what error should we put here?).
I think the order we did things in was:
We want to perform a damage test of OMC DCPDs with high power beam. The OMC DCPD is the 3mm InGaAs photodiodes with high quantum efficiency, delivered by Laser Components.
The sites want to know the allowed input power during the OMC scan for beam mode analysis. The nominal bias voltage of the PDs is +12V. Therefore, 30mA of photocurrent with the transimpedance of 400 Ohm is already enough to saturate the circuit. This means that the test is intended to check the damage of the photodiode mainly by the optical power.
The test procedure is as follows:
1. Illuminate the diode with certain optical power.
2. Measure the dark current and dark noise of the PD with no light on it.
3. Check the condition of the PD surface with a digital camera.
4. Repeat 1~3 with larger optical power.
The beam from an NPRO laser is delivered to the photodiode. The maximum power available is 300~400mW. The beam shape was regulated to have the beam radius of ~500um.
- When the PD is exposed to the high power beam, the circuit setup A) is used. This setup is intended to mimic the bias and transimpedance configuration used in the DCPD amp at the site.
- When the dark noise is measured, the circuit setup B) is used. This setup is low noise enough to measure the dark noise (and current) of the PD.
- The test procedure is going to be tested with an Excelitas 3mm InGaAs PD (C30665), and then tested with the high QE PD.
C30665 (3mm) camera test. The camera was Canon PowerShot G7X MkII. Exposure 1/15s, F 5.6, ISO 125, MF (~the closest), no zoom.
This image was taken before the beam illumination. Will tune the green lighting to have some gradient on the surface so that we can see any deformation of the surface.
(In short, attachment 1 shows the two chosen sets of components and the configuration according which they must be bonded to minimize the total vertical angular deviation.)
The specfic components and configuration were chosen as follows, closely following Section 2.3.3 of T1500060:
Mounting prisms: 1,2,12,14,15 (Even though there is mention of M17 in the attachments, it can not be used because it was chipped earlier.)
Curved mirrors: 10,13
For a given choice of prism, PZT and mirror, the PZT can be placed either at 0deg or 180deg, and the mirror can rotated. This allows us to choose an optimal mirror rotation and PZT orientation which minimises the vertical deviation.
Total vertical angle
was measured by Koji as described in elog 369.
, are the wedge angle and orientation respectively and were measured earlier and shown in elog 373 .
, The measurement of the location of the curvature bottom (d, ) of the mirrors is shown in elog 372 . The optimal is to be found.
These steps were followed:
These are the ones that were chosen:
The method of attaching them is depicted in Attachment 1.
The Windows laptop for WincamD/Beam'R2 (DELL Vostro3300) was not functional.
- Windows 7 got stuck in the starting up process (Google "startup repair loop")
- The battery can't charge and the adapter connection is flaky
I decided to newly install Win10.
I made a new bootable Win10 DVD from the ISO downloaded from IMSS. The ISO file was converted to CDR using Disk Utility on Mac.
This deleted the past disk partitions. The installation process has no trouble and Win10 ran successfully. The machine is slow but still acceptable for our purpose.
Dataray Version 7.1H25Bk was downloaded from the vendor website https://dataray.com/blogs/software/downloads and installed successfully.
The devices ran as expected by connecting the heads and selecting the proper device in the software.
Then, the Win10 fell into "Hibernation Loop" and "Shutdown loop" (after disabling hibernation in the safe mode).
This is probably the combination of extremely slow windows update (feature update i.e. beta OS update) and the occasional shutdown due to the flakiness of the AC connection
Win10 was reinstalled and automatic Win update was disabled via windows policy manager or something like that. Still, it tries to download and update some of the updates (what's happening there!?
Here are my strong recommendations on how to use this laptop
Here is the proposed RoC measurement setup. Koji tells me that this is referred to as "Anderson's method".
We would like to use a linear cavity to measure the RoC of the curved mirrors independently (before forming the ring cavity), since the degeneracy of HOMs will make the fitting easier.
If we decided that the symmetric sidebands are too unwieldy, or that we have issues from sidebands on sidebands, we can accomplish the same style measurement using an AOM-shifted pickoff of the pre-PDH EOM beam. The advantage of the former method is that we don't have to use any polarization tricks.
Nic Smith sent me a bunch of elog lists where the results of the mode scan can be found.
There have been many mode scan analyses done at LLO:
We didn't do as much of this at LHO. At some point we were trying to figure out how the arm cavity mode was different from the carrier mode:
Here's a long mode scan that was done, and the data is attached to the elog, but none of the amplitudes are analyzed.
Here is a more detailed version of the setup, so that we can gather the parts we will need.
Significant improvement has been achieved in the RoC measurement.
By these changes, dramatic increase of the signal to noise ratio was seen.
Now both of the peaks corresponds to the 1st-order higher-order modes are clearly seen.
The peak at around 26MHz are produced by the beat between the carrier TEM00 and the upper-sideband TEM01 (or 10).
The other peak at around 57MHz are produced by the lower-sideband TEM01 (or 10).
From the peak fitting we can extract the following numbers:
Note that the cavity itself has not been touched during the measurement.
Only the laser frequency and the incident beam alignment were adjusted.
The results are calculated by the combination of MATLAB and Mathemaica. The fit results are listed in the PDF files.
In deed the fitting quality was not satisfactory if the single Lorentzian peak was assumed.
There for two peaks closely lining up with different height. This explained slight asymmetry of the side tails
This suggests that there is slight astigmatism on the mirrors (why not.)
The key points of the results:
- FSR and the cavity length: 83.28~83.31MHz / L=1.799~1.800 [m] (surprisingly good orecision of my optics placement!)
- Cavity g-factor: Considering the flatness of the flat mirror from the phase map, the measured g-factors were converted to the curvature of the curved mirror.
RoC = 2.583~4 [m] and 2.564~7 [m]. (Note: This fluctuation can not be explained by the statistical error.)
The mode split is an order of 10kHz. This number also agrees with the measurement taken yesterday.
If the curved mirror had the nominal curvature of 2.5m, the flat mirror should have the curvature of ~20m. This is very unlikely.
- Approximate cavity line width: FWHM = 70~80kHz. This corresponds to the finesse of ~500. The design value is ~780.
This means that the locking offset is not enough to explain the RoC discrepancy between the design and the measurement.
Wedge angle test
Result: Wedge angle of Prism A1: 0.497 deg +/- 0.004 deg
o Attach a rail on the optical table. This is the reference of the beam.
o A CCD camera (Wincam D) is used for reading out spot positions along the rail.
o Align a beam path along the rail using the CCD.
o Measure the residual slope of the beam path. (Measurement A)
o Insert an optic under the test. Direct the first surface retroreflectively. (This means the first surface should be the HR side.)
o Measure the slope of the transmitted beam. (Measurement B)
o Deflection angle is derived from the difference between these two measurements.
o An Al plate of 10" width was clamped on the table. Four other clamps are located along the rail to make the CCD positions reproducible.
o A prism (Coating A, SN: A1) is mounted on a prism mount. The first surface is aligned so that the reflected beam matches with the incident beam
with precision of +/-1mm at 1660mm away from the prism surface. ==> precision of +/- 0.6mrad
o In fact, the deflection angle of the transmission is not very sensitive to the alignment of the prism.
The effect of the misalignment on the measurement is negligible.
o Refractive index of Corning 7980 at 1064nm is 1.4496
Z (inch / mm), X (horiz [um] +/-4.7um), Y (vert [um] +/-4.7um)
0” / 0, -481.3, -165.1
1.375" / 34.925, -474.3, -162.8
3" / 76.2, -451.0, -186.0
4.375" / 111.125, -432.5, -181.4
6" / 152.4, -432.5, -181.4
7.375" / 187.325, -330.2, -204.6
9" / 228.6, -376.7, -209.3
With Prism / SN of the optic: A1
Z (inch / mm), X (horiz [um] +/-4.7um), Y (vert [um] +/-4.7um)
0” / 0, -658.3, -156.8
1.375" / 34.925, -744.0, -158.1
3" / 76.2, -930.0, -187.4
4.375" / 111.125, -962.6, -181.4
6" / 152.4, -1190.4, -218.6
7.375" / 187.325, -1250.9, -232.5
9" / 228.6, -1418.3, -232.5
Wedge angle of Prism A1: 0.497 deg +/- 0.004 deg
[Click for a sharper image]
Horiz Wedge 0.497 +/- 0.004 deg
Vert Wedge 0.024 +/- 0.004 deg
Horiz Wedge 0.549 +/- 0.004 deg
Vert Wedge 0.051 +/- 0.004 deg
Horiz Wedge 0.463 +/- 0.004 deg
Vert Wedge 0.009 +/- 0.004 deg
Horiz Wedge 0.471 +/- 0.004 deg
Vert Wedge 0.019 +/- 0.004 deg
Horiz Wedge 0.458 +/- 0.004 deg
Vert Wedge 0.006 +/- 0.004 deg
Now it's enough for the first OMC (or even second one too).
Today's measurements all distributed in theta>0.5deg. Is this some systematic effect???
I should check some of the compeled mirrors again to see the reproducibility...
A1 Horiz Wedge 0.497039 +/- 0.00420005 deg / Vert Wedge 0.02405210 +/- 0.00420061 deg
A2 Horiz Wedge 0.548849 +/- 0.00419993 deg / Vert Wedge 0.05087730 +/- 0.00420061 deg
A3 Horiz Wedge 0.463261 +/- 0.00420013 deg / Vert Wedge 0.00874441 +/- 0.00420061 deg
A4 Horiz Wedge 0.471536 +/- 0.00420011 deg / Vert Wedge 0.01900840 +/- 0.00420061 deg
A5 Horiz Wedge 0.458305 +/- 0.00420014 deg / Vert Wedge 0.00628961 +/- 0.00420062 deg
B1 Horiz Wedge 0.568260 +/- 0.00419988 deg / Vert Wedge -0.00442885 +/- 0.00420062 deg
B2 Horiz Wedge 0.556195 +/- 0.00419991 deg / Vert Wedge -0.00136749 +/- 0.00420062 deg
B3 Horiz Wedge 0.571045 +/- 0.00419987 deg / Vert Wedge 0.00897185 +/- 0.00420061 deg
B4 Horiz Wedge 0.563724 +/- 0.00419989 deg / Vert Wedge -0.01139000 +/- 0.00420061 deg
B5 Horiz Wedge 0.574745 +/- 0.00419986 deg / Vert Wedge 0.01718030 +/- 0.00420061 deg
E1 Horiz Wedge 0.600147 +/- 0.00419980 deg / Vert Wedge 0.00317778 +/- 0.00420062 deg
E2 Horiz Wedge 0.582597 +/- 0.00419984 deg / Vert Wedge -0.00537131 +/- 0.00420062 deg
E3 Horiz Wedge 0.592933 +/- 0.00419982 deg / Vert Wedge -0.01082830 +/- 0.00420061 deg
To check the systematic effect, A1 and B1 were tested with different alignment setup.
A1 Horiz Wedge 0.547056 +/- 0.00419994 deg / Vert Wedge 0.0517442 +/- 0.00420061 deg
A1 Horiz Wedge 0.546993 +/- 0.00419994 deg / Vert Wedge 0.0469938 +/- 0.00420061 deg
A1 Horiz Wedge 0.509079 +/- 0.00420003 deg / Vert Wedge 0.0240255 +/- 0.00420061 deg
B1 Horiz Wedge 0.547139 +/- 0.00419994 deg / Vert Wedge 0.0191204 +/- 0.00420061 deg
Mirror T test
The mirror was misaligned to have ~2deg incident (mistakenly...) angle.
C1: Ptrans = 7.58uW, Pinc = 135.0mW => 56.1ppm
C1 (take2): Ptrans = 7.30uW, Pinc = 134.4mW => 54.3ppm
C2: Ptrans = 6.91uW, Pinc = 137.3mW => 50.3ppm
C3: Ptrans = 6.27uW, Pinc = 139.7mW => 44.9ppm
C4: Ptrans = 7.62uW, Pinc = 139.3mW => 54.7ppm
C5: Ptrans = 6.20uW, Pinc = 137.5mW => 45.1ppm
A1: Ptrans = 1.094mW, Pinc = 133.6mW => 8189ppm
In order to resume testing the curvatures of the mirrors, the same mirror as the previous one was tested.
The result looks consistent with the previous measurement.
It seems that there has been some locking offset. Actually, the split peaks in the TF@83MHz indicates
the existence of the offset. Next time, it should be adjusted at the beginning.
Curved mirror SN: C1
RoC: 2.5785 +/- 0.000042 [m]
=> 2.5830, 2.5638 => sqrt(RoC1*RoC2) = 2.5734 m
=> 2.5844, 2.5666 => sqrt(RoC1*RoC2) = 2.5755 m
C1: RoC: 2.57845 +/− 4.2e−05m
C2: RoC: 2.54363 +/− 4.9e−05m
C3: RoC: 2.57130 +/− 6.3e−05m
C4: RoC: 2.58176 +/− 6.8e−05m
C5: RoC 2.57369 +/− 9.1e−05m
==> 2.576 +/- 0.005 [m] (C2 excluded)
The thicknesses of the prism mirrors (A1-A5) were measured with micrometer thickness gauge.
Since the thickness of the thinner side (side1) depends on the depth used for the measurement,
it is not accurate. Unit in mm.
A1: Side1: 9.916, Side2: 10.066 => derived wedge angle: 0.43deg
A2: Side1: 9.883, Side2: 10.065 => 0.52
A3: Side1: 9.932, Side2: 10.062 => 0.38
A4: Side1: 9.919, Side2: 10.060 => 0.40
A5: Side1: 9.917, Side2: 10.058 => 0.40
Total (excluding C2, C7, C8): 2.575 +/- 0.005 [m]
C6: RoC: 2.57321 +/− 4.2e-05m
C7: RoC: 2.56244 +/− 4.0e−05m ==> Polaris mount
C8: RoC: 2.56291 +/− 4.7e-05m ==> Ultima mount
C9: RoC: 2.57051 +/− 6.7e-05m
C2: RoC: 2.54363 +/− 4.9e−05m ==> Josh Smith @Fullerton for scattering measurement
Measured the thickness of a curved mirror:
Took three points separated by 120 degree.
S/N: C2, (0.2478, 0.2477, 0.2477) in inch => (6.294, 6.292, 6.292) in mm
Conclusion: Good. First contact did not damage the coating surface, and reduced the loss
- Construct a cavity with A1 and C2
- Measure the transmission and FWHM (of TEM10 mode)
- Apply First Contact on both mirrors
- Measure the values again
2.66 +/- 0.01 V -> 2.83 +/- 0.01 V
==> 6.3% +/- 0.5 % increase
FWHM of TEM10:
Before: (66.1067, 65.4257, 66.1746) +/- (0.40178, 0.38366, 0.47213) [kHz]
After: (60.846, 63.4461, 63.7906) +/- (0.43905, 0.56538, 0.51756) [kHz]
==> 5.1% +/- 2.7% decrease
Question: What is the best way to measure the finesse of the cavity?
Yesterday I measured the thickness of the PZTs in order to get an idea how much the PZTs are wedged.
For each PZT, the thickness at six points along the ring was measured with a micrometer gauge.
The orientation of the PZT was recognized by the wire direction and a black marking to indicate the polarity.
A least square fitting of these six points determines the most likely PZT plane.
Note that the measured numbers are assumed to be the thickness at the inner rim of the ring
as the micrometer can only measure the maximum thickness of a region and the inner rim has the largest effect on the wedge angle.
The inner diameter of the ring is 9mm.
The measurements show all PZTs have thickness variation of 3um maximum.
The estimated wedge angles are distributed from 8 to 26 arcsec. The directions of the wedges seem to be random
(i.e. not associated with the wires)
As wedging of 30 arcsec causes at most ~0.3mm spot shift of the cavity (easy to remember),
the wedging of the PZTs is not critical by itself. Also, this number can be reduced by choosing the PZT orientations
based on the estimated wedge directions --- as long as we can believe the measurements.
Next step is to locate the minima of each curved mirror. Do you have any idea how to measure them?
- Autocollimator (AC) borrowed from Mike Smith (Nippon Kogaku model 305, phi=2.76", 67.8mm)
- Retroreflector (corner cube)
- Two V grooves borrowed from the 40m
- Autocollimator calibration
o Install the AC on a optical table
o Locate the corner cube in front of the AC.
o Adjust the focus of the AC so that the reflected reticle pattern can be seen.
o If the retroreflection and the AC are perfect, the reference reticle pattern will match with the reflected reticle pattern.
o Measure the deviation of the reflected reticle from the center.
o Rotate the retroreflector by 90 deg. Measure the deviation again.
o Repeat the process until total four coordinates are obtained.
o Analysis of the data separates two types of the error:
The average of these four coordinates gives the systematic error of the AC itself.
The vector from the center of the circle corresponds to the error of the retroreflector.
- Wedge angle measurement
To be continued
The wedge angle of the prism "A1" was measured with the autocollimator (AC).
The range of the AC is 40 arcmin. This means that the mirror tilt of 40arcmin can be measured with this AC.
This is just barely enough to detect the front side reflection and the back side reflection.
The measured wedge angle of the A1 prism was 0.478 deg.
Ideally a null measurement should be done with a rotation stage.
[Jeff, Yuta, Koji]
Gluing test with UV-cure epoxy Optocast 3553-LV-UTF-HM
- This glue was bought in the end of October (~3.5 months ago).
- The glue was taken out from the freezer at 1:20pm.
- Al sheet was laid on the optical table. We made a boat with Al foil and pour the glue in it (@1:57pm)
- We brought two kinds of Cu wires from the 40m. The thicker one has the diameter of 1.62mm.
The thinner one has the diameter of 0.62mm. We decided to use thinner one being cut into 50mm in length.
- The OMC glass prisms have the footprint of 10mmx20mm = 200mm^2. We tested several combinations
of the substrates. Pairs of mirrors with 1/2" mm in dia. (127mm) and a pair of mirrors with 20mm in dia. (314mm).
- Firstly, a pair of 1/2" mirrors made of SF2 glass was used. A small dub on a thinner Cu wire was deposited on a mirror.
We illuminated the glue for ~10sec. When the surfaces of the pair was matched, the glue did not spread on the entire
surface. The glue was entirely spread once the pressure is applied by a finger. Glue was cured at 2:15pm. 12.873mm
thickness after the gluing.
1. We should be careful not to shine the glue pot by the UV illuminator.
2. The gluing surface should be drag wiped to remove dusts on the surface.
- Secondly, we moved onto 20mm mirror pair taken from the remnant of the previous gluing test by the eLIGO people.
This time about 1.5 times more glue was applied.
- The third trial is to insert small piece of alminum foil to form a wedge. The thickness of the foil is 0.041mm.
The glue was applied to the pair of SF2 mirror (1/2" in dia.). A small dub (~1mm in dia) of the glue was applied.
The glue filled the wedge without any bubble although the glue tried to slide out the foil piece from the wedge.
So the handling was a bit difficult. After the gluing we measured the thickness of the wedge by a micrometer gauge.
The skinny side was 12.837mm, and the thicker side was 12.885mm. This is to be compared with the total thickness
12.823mm before the gluing. The wedge angle is 3.8mrad (0.22deg). The glue dub was applied at 2:43, and the UV
illumination was applied at 2:46.
- At the end we glued a pair of fused silica mirrors. The total thickness before the gluing was 12.658 mm.
The glue was applied at 2:59pm. The thickness after the gluing is 12.663 mm.
This indicates the glue thickess is 5um.
EDIT (ZK): Koji points out that (1 - Ti) should really be the non-resonant reflectivity of the aligned cavity, which is much closer to 1. However, it should *actually* be the non-resonant reflectivity of the entire OMC assembly, including the steering mirror (see bottom of post). The steering mirror has T ~ 0.3%, so the true results are somewhere between my numbers and those with (1 - Ti) -> 1. In practice, though, these effects are swamped by the other errors.
More information about the power-dependent visibility measurement:
As a blanket statement, this measurement was done by exact analogy to those made by Sam and Sheon during S6 (c.f. LHO iLog 11/7/2011 and technical note T1100562), since it was supposed to be a verification that this effect still remains. There are absolutely better ways to do (i.e., ways that should give lower measurement error), and these should be investigated for our characterization. Obviously, I volunteer.
All measurements were made by reading the output voltages produced by photodetectors at the REFL and TRANS ports. The REFL PD is a BBPD (DC output), and the TRANS is a PDA255. Both these PDs were calibrated using a Thorlabs power meter (Controller: PM100D; Head: S12XC series photodiode-based---not sure if X = 0,2... Si or Ge) at the lowest and highest power settings, and these results agreed to the few-percent level. This can be a major source of error.
The power was adjusted using the HWP/PBS combination towards the beginning of the experiment. For reference, an early layout of the test setup can be seen in LLO:5978 (though, as mentioned above, the REFL and TRANS PDs have been replaced since then---see LLO:5994). This may or may not be a "clean" way to change the power, but the analysis should take the effect of junk light into account.
Below is an explanation of the three traces in the plot. First:
Now, the traces
The error bars in the measurement were dominated, roughly equally, by 1) systematic error from calibration of the PDs with the power meter, and 2) error from noise in the REFL_L measurement (since the absolute AC noise level in TRANS and REFL_L is the same, and TRANS >> REFL_L, the SNR of the latter is worse).
(1) can be helped by making ALL measurements with a single device. I recommend using something precise and portable like the power meter to make measurements at all the necessary ports. For REFL_L/UL, we can place a beam splitter before the REFL PD, and---after calibrating for the T of this splitter very well using the same power meter---both states can be measured at this port.
(2) can probably be helped by taking longer averaging, though at some point we run into the stability of the power setting itself. Something like 30-60s should be enough to remove the effects of the REFL_L noise, which is concentrated in the few-Hz region in the LLO setup.
One more thing I forgot was the finite transmission of the steering mirror at the OMC input (the transmission of this mirror goes to the QPDs). This will add a fixed error of 0.3%, and I will take it into account in the future.
I found that, in fact, I had lowered the modulation depth since when I measured it to be 0.45 rads --> Psb = 0.1.
Here is the sweep measurement:
This is Psb = 0.06 --> gamma = 0.35 rads.
This changes the "raw transmission" and "coupling", but not the inferred visibility:
I also measured the cavity AMTF at three powers today: 0.5 mW, 10 mW, and 45 mW input.
They look about the same. If anything, the cavity pole seems slightly lower with the higher power, which is counterintuitive. The expected shift is very small (~10%), since the decay rate is still totally dominated by the mirror transmissions even for the supposed high-loss state (Sam and Sheon estimated the roundtrip loss at high power to be ~1400 ppm, while the combined coupling mirrors' T is 1.6%). I have not been able to fit the cavity poles consistently to within this kind of error.
o Purpose of the measurement
- Test Si QPDs (C30845EH) for ISC QPDs Qty 30 (i.e. 120 elements)
- Test InGaAs PDs (C30665GH) for OMC Qty 10 (i.e. 10 elements)
o Measurement Kit
- Inherited from Frank.
- Has relays in it.
- D0 and D1 switches the measurement instrument connected to an element
- D2 and D3 switches the element of the QPDs
- Digital switch summary
d0 d1 0 0 - ln preamp
d0 d1 1 0 - dark c
d0 d1 0 1 - omc preamp
d0 d1 1 1 - impedance
d2 d3 0 0 - A x x x
d2 d3 1 0 - C x o x
d2 d3 0 1 - B o x o
d2 d3 1 1 - D o o o
- The universal board in the box is currently configured for C30845.
Pin1 - Elem A. Pin3 - B, Pin7 - C, Pin9 - D, Pin 12 - Case&Bias
o Labview interface
- Controls NI-USB-6009 USB DAQ interface and Agilent 82357B USB-GPIB interface
o Dark current measurement
- Borrowed Peter's source meter KEITHLEY 2635A
- For C30845GH the maxmum reverse bias is set to -20V. This drops the voltage of the each element to the bias voltage.
o Spectrum measurement
- The elements are connected to FEMTO LN current amp DLPCA-200.
- Bias voltage is set to +10V. This lifts up the outside of the amplifier input to +10V.
o Impedance measurement
- Agilent 4395A at PSL lab with impedance measurement kit
- For C30845GH the maxmum reverse bias is set to -15V. This drops the voltage of the each element to the bias voltage.
- Calibration: open - unplug the diode from the socket, short - use a piece of resister lead, 50Ohm - a thin metal resister 51Ohm
- Freq range: 30-50MHz where the response of the cables in the setup is mostly flat.
- Labview VI is configured to read the equivalent circuit parameters in the configuration "D" (series LCR).
- Labview fails to read the series resistance. This was solved by first read the equiv circuit param and then read it with Sim F-CHRST.
F-CHRST does nothing on the parameters so the second request successfully acquires the first ones.
- For the dark noise measurement, the lid of the die-cast case should also contact to the box for better shielding. This made the 60Hz lines almost completely removed, although unknown 1kHz harmonics remains.
- The precise impedance of the setup can not be obtained from the measurement box; the cable in between is too long. The diode impedance should be measured with the impedance measurement kit.
- With the impedance measurement kit, the bias voltage of +5V should be used, in stead of -5V.
- diode characteristics measured at 10-100MHz
- Typical impedance characteristics of the diodes
Excelitas (Perkin-Elmer) C30665GH Rs=9Ohm, Cd=220pF, L=0~1nH (Vr=5V)
Excelitas (Perkin-Elmer) C30642G Rs=12Ohm, Cd=100pF, L=~5nH (Vr=5V) longer thin wire in a can?
Excelitas (Perkin-Elmer) C30641GH Rs=8Ohm, Cd=26pF, L=12nH (Vr=5V) leg inductance? (leg ~30mm)
- PD serial
C30665GH, Ls ~ 1nH
1 - 0782 from PK, Rs=8.3Ohm, Cd=219.9pF
2 - 1139 from PK, Rs=9.9Ohm, Cd=214.3pF
3 - 0793 from PK, Rs=8.5Ohm, Cd=212.8pF
4 - 0732 from PK, Rs=7.4Ohm, Cd=214.1pF
5 - 0791 from PK, Rs=8.4Ohm, Cd=209.9pF
6 - 0792 from PK, Rs=8.0Ohm, Cd=219.0pF
7 - 0787 from PK, Rs=9.0Ohm, Cd=197.1pF
8 - 0790 from PK, Rs=8.4Ohm, Cd=213.1pF
9 - 0781 from PK, Rs=8.2Ohm, Cd=216.9pF
10 - 0784 from PK, Rs=8.2Ohm, Cd=220.0pF
11 - 1213 from the 40m, Rs=10.0Ohm, Cd=212.9pF
12 - 1208 from the 40m, Rs=9.9Ohm, Cd=216.8pF
13 - 1209 from the 40m, Rs=10.0Ohm, Cd=217.5pF
C30642G, Ls ~ 12nH
20 - 2484 from the 40m EG&G, Rs=12.0Ohm, Cd=99.1pF
21 - 2487 from the 40m EG&G, Rs=14.2Ohm, Cd=109.1pF
22 - 2475 from the 40m EG&G glass crack, Rs=13.5Ohm, Cd=91.6pF
23 - 6367 from the 40m ?, Rs=9.99Ohm, Cd=134.7pF
24 - 1559 from the 40m Perkin-Elmer GH, Rs=8.37Ohm, Cd=94.5pF
25 - 1564 from the 40m Perkin-Elmer GH, Rs=7.73Ohm, Cd=94.5pF
26 - 1565 from the 40m Perkin-Elmer GH, Rs=8.22Ohm, Cd=95.6pF
27 - 1566 from the 40m Perkin-Elmer GH, Rs=8.25Ohm, Cd=94.9pF
28 - 1568 from the 40m Perkin-Elmer GH, Rs=7.83Ohm, Cd=94.9pF
29 - 1575 from the 40m Perkin-Elmer GH, Rs=8.32Ohm, Cd=100.5pF
C30641GH, Perkin Elmer, Ls ~ 12nH
30 - 8983 from the 40m Perkin-Elmer, Rs=8.19Ohm, Cd=25.8pF
31 - 8984 from the 40m Perkin-Elmer, Rs=8.39Ohm, Cd=25.7pF
32 - 8985 from the 40m Perkin-Elmer, Rs=8.60Ohm, Cd=25.2pF
33 - 8996 from the 40m Perkin-Elmer, Rs=8.02Ohm, Cd=25.7pF
34 - 8997 from the 40m Perkin-Elmer, Rs=8.35Ohm, Cd=25.8pF
35 - 8998 from the 40m Perkin-Elmer, Rs=7.89Ohm, Cd=25.5pF
36 - 9000 from the 40m Perkin-Elmer, Rs=8.17Ohm, Cd=25.7pF
1mm Au wire with dia. 10um -> 1nH, 0.3 Ohm
20mm BeCu wire with dia. 460um -> 18nH, 0.01 Ohm
For various reasons, I had to switch NPROs (from the LightWave 126 to the Innolight Prometheus).
I installed the laser, realigned the polarization and modulation optics, and then began launching the beam into the fiber, though I have not coupled any light yet.
A diagram is below. Since I do not yet have the AOM, I have shown that future path with a dotted line. Since we will not need to make AMTFs and have a subcarrier at the same time, I have chosen to overload the function of the PBS using the HWP after the AEOM. We will operate in one of two modes:
One thing that concerns me slightly: the Prometheus is a dual-output (1064nm/532nm) laser, with separate ports for each. I have blocked and locked out the green path physically, but there is some residual green light visible in the IR output. Since we are planning to do the OMC transmission testing with a Si-based Thorlabs power meter---which is more sensitive to green than IR---I am somewhat worried about the ensuing systematics. I *think* we can minimize the effect by detuning the doubling crystal temperature, but this remains to be verified.
EDIT (ZK): Valera says there should be a dichroic beam splitter in the lab that I can borrow. This should be enough to selectively suppress the green.