I blocked the AP table's south west 10" ID port since it is obsolete with the new layout.
Reminder: items on the enclosure self can fall down in an earthquake. I moved oscilloscope and heavy calorimeter head from the edge of the cliff.
On Wednesday (21st) night, I checked the AP table as I wanted to try PRMI locking.
It was difficult to work with the table as there were so many unnecessary components on it.
Also the beams went through complicated paths as they have funny angles.
So I decided to clean up of IMC REFl WFS, IFO REFL, and IFO AS paths.
I found that the AS beam was highly astigmatic as the beam went through a (too-much-) tilted lens.
I made several blocked optical paths for REFL and AS for future extension of the detection system.
The current status of the table was uploaded below.
The optical spectrum analyzers and the aux NPRO were left untouched but they should be moved
somewhere (either on the table or outside) which does not disturb the other optical paths.
After the cleaning, I started locking PRMI. I could lock PRMI stably. But I could not figure out how
the intra-cavity mode looked like as I did not have the POP camera. The power recycling
gain was not quantitatively evaluated as I did not have POP and I wasn't sure how the beam was aligned at POX/POY.
We need to know:
- Quantitative evaluation of the beam shape in the PRC
- Quantitative evaluation of the power recycling gain
Some obvious things to be fixed
- The POX whitening filters seem not switching. This issue should be checked at the circuit module itself and at the BIO.
- The POX beam is not well focused on the PD. This was particularly clear when PRMI was locked with carrier.
- The POP beam is going nowhere. We need POP55 and POP CCD for diagnoses.
I haven't checked ITMY table.
Before we install the REFL 3f PDs I made a drawing of the current table layout, since there has been no update lately. Once I've incorporated the two extra PDs (now seen sitting bottom left), I will update the drawing and post in the wiki as well.
Please remember to cover the optical tables !
Access to the north side of the PSL table is blocked by the 8" beam guard. This opens the beam pathways between them.
MCRefl is absent, it is under investigation. I removed a bunch of hardware and note all spare optics along the edges.
The anti-symmetric port
spider webs fly in the wind
I've packaged an AP1053 in a Thorlabs box. The gain and the input noise level were measured. It has the gain of ~10 and the input noise of ~0.6nV/rtHz@50MHz~200MHz.
AP1053 was soldered on Thorlabs' PCB EEAPB1 (forgot to take a picture). The corresponding chassis is Thorlabs' EEA17. There is a 0.1uF high-K ceramic cap between DC and GND pins. The power is supplied via a DC feedthru capacitor (Newark / Power Line Filter / 90F2268 / 5500pF) found in the WB EE shop. The power cable has a connector to make the long side of the wires detachable. Because I did not want to leave the RF signal path just mechanically touched, the SMA connectors were soldered to the PCB. As the housing has no access hole, I had to make it at one of the sides.
The gain of the unit was measured using the setup shown in the upper figure of Attachment 2. When the unit was energized, it drew the current of about 0.1A. The measued gain was compensated by the pick off ratio of the coupler (20dB). The gain was measured with the input power of -20, -10, 0, 10, and 15dBm. The measurement result is shown in Attachment 3. The small signal gain was actually 10dB and showed slight degradation above 100MHz. At the input of 10dB some compression of the gain is already visible. It looks consistent with the specification of +26.0dBm output for 1dB compression above 50MHz and +24.0dBm output below 50MHz.
The noise level was characterized with the setup shown in the bottom figure of Attachment 3. The noise figure of the amplifier is supposed to be 1.5dB above 200MHz and 3.5dB below 200MHz. This is quite low and the output noise of AP1053 can not be measured directly by the analyzer. So, another LN amplifier (ZFL-500HLN) was stacked. The total gain of the system was measured in the same way as above. The measured noise level was ~0.7nV/rtHz between 50MHz and 200MHz. Considering the measurement noise level of the system, it is consistent with the input referred noise of 0.6nV/rtHz. I could not confirm the advertized noise figure of 1.5dB above 200MHz. The noise goes up below 50MHz. But still 2nV/rtHz at 3MHz. I'd say this is a very good performance.
ETMX oplev had 6 mm diameter beam on the qpd. I relayed the beam path with 2 lenses to get back 3 mm beam on the qpd
BRC 037 -100 Bi _concave lens and PCX 25 200 VIS do the job. Unfortunately the concave lens has the AR 1064.
The uncoated bi-concave lens was replaced by AR coated one: KBC 037 -100 AR.14 resulting 35% count increase on qpd
I have uploaded ARBCAV v3.0 to the SVN. The major change in this release, as I mentioned, is the input/output handling. The input and output are now contained in a single 'model' structure. To define the cavity, you fill in the substructure 'model.in' (e.g., model.in.T = [0.01 10e-6 0.01]; etc.) and call the function as:
model = arbcav(model);
Note: the old syntax is maintained as legacy for back-compatibility, and the function automatically creates a ".in" substructure in the output, so that the user can still use the single-line calling, which can be convenient. Then, any individual parameter can be changed by changing the appropriate field, and the function can be rerun using the new, simpler syntax from then on.
The function then somewhat intelligently decides what to compute based on what information you give it. Using a simple option string as a second argument, you can choose what you want plotted (or not) when you call. Alternatively, you can program the desired functionality into a sub-substructure 'model.in.funct'.
The outputs are created as substructures of the output object. Here is an example:
>> th = 0.5*acos(266/271) *180 /pi;
OMC.in.theta = [-th -th th th];
OMC.in.L = [0.266 0.284 0.275 0.271];
OMC.in.RoC = [1e10 2 1e10 2];
OMC.in.lambda = 1064e-9;
OMC.in.T = 1e-6 * [8368 25 8297 33];
OMC.in.f_mod = 24.5e6;
in: [1x1 struct]
>> OMC = arbcav(OMC,'noplot')
Warning: No loss given--assuming lossless mirrors
> In arbcav at 274
in: [1x1 struct]
df: [1000x1 double]
coefs: [1000x4 double]
HOM: [1x1 struct]
f: [1x1 struct]
pwr: [1x1 struct]
carr: [15x15 double]
SBp: [15x15 double]
SBm: [15x15 double]
Some other notes:
I have added lots of information to the help header, so check there for more details. As always, your feedback is greatly appreciated.
This is interesting. I suppose you are acting on the ETMY.
Can you construct the compensation filter with actuation on the MC length?
Also can you see how the X arm is stabilized?
This may stabilize or even unstabilize the MC length, but we don't care as the MC locking is easy.
If we can help to reduce the arm motion with the MCL feedforward trained with an arm sometime before,
this means the lock acquisition will become easier. And this may still be compatible with the ALS.
Why did you notched out the 16Hz peak? It is the dominant component for the RMS and we want to eliminate it.
I actuate on ETMY for YARM and ETMX for XARM. For now I did adaptive filtering for both arms at the same time. I used the same parameters for xarm as for yarm.
I've notched 16 Hz resonance because it has high Q and I need to think more how to subtract it using FIR filter or apply IIR.
I'll try MC stabilazation method.
Adaptive filtering was applied to MC and X,Y arms at the same time. I used a very aggressive (8 order) butterworth filter at 6 Hz as an AI filter for MC not to inject noise to ARMS as was done before
Mu for MC was 0.2, downsample = 16, delay = 1. I was able to subtract 1 Hz. Stack subraction is not that good as for arms but this is because I used only one seismometer for MC that is under the BS. I might install accelerometers under MC2.
EDIT, JCD, 18Feb2013: Den remembers using mu for the arms in the range of 0.01 to 0.1, although using 0.1 will give extra noise. He said he usually starts with something small, then ramps it up to 0.04, and after it has converged brings it back down to 0.01.
I was going to lock MICH, but I don't see anything on dataviewer for either AS55Q or ASDC. I went out onto the table, and there is beam on the diode, but no mV out on a voltmeter connected to the DC monitor point. I shine a flashlight, and still I see 0.0mV. So, something is up with AS55, but since the michelson is aligned right now, I'm not going to mess with the PD. I won't lock MICH, I'll just move on. Koji is taking a look at the diode, but if he doesn't get it figured out tonight, we can take a closer look after we pump down.
Never mind. I was using an LED flashlight, which doesn't emit light that the PD is sensitive to. A regular flashlight gives plenty of signal on the DC out.
Using an SR560 with 30Hz low pass and gain of 100, it was pretty easy to align the light on the PD.
Koji calculates in his head that there is about 6 microwatts of light incident on the PD, which is not a lot of light. Our SNR may be kind of lame for locking right now.
I spent some time tracking down the AS beam which had vanished from the AP table. Eventually, by dramatically mis-aligning SRM, PRM and ITMY, returning BS to its Jan 1st PITCH and YAW values and tweaking the ITMX alignment [actual values to follow], I was able to get an AS beam out onto the AP table. I verified that it was the prompt reflection off ITMX by watching it move as I changed the YAW of that optic and watching it stay stationary as I changed the YAW of ITMY.
Jamie and I then steered the beam through a 2" PLCX-50.8-360.6 lens and placed the RF PD (AS55) at the focus. Additionally, we installed the AS camera to observe the leakage field through a Y1S steering mirror (as shown in the attached diagram).
Currently the PD has power but the RF and DC outputs are not connected to anything at the moment.
Atm 2 by Steve
AS port ITMX YAW range where AS beam was visible = [-1.505, -1.225] - these extrema put the beam just outside of some aperture in the system -> set ITMX YAW to -1.365
ITMX PITCH range = [-0.7707, -0.9707] -> set to ITMX PITCH to -0.8707
We added our reference photodetector (Newport 1611, REF DET) to the southern edge of the AS table, as pictured. The detector's power supply is located under the southwest corner of the table, as pictured. We have connected the detector to its power supply, and will connect the detector's fiber input and RF output tomorrow.
For the RFPD frequency response project, we routed the fiber that will connect our REF DET (on the AS table) to our 1x16 optical splitter (in the OMC_North rack), as pictured. (The new fiber is the main one in the picture, which ends at the right edge near REF DET) Note that we secured the fiber to the table in two places to ensure the fiber would remain immobile and out of other optical paths already in place.
At 2:00 we plan to run fiber from our laser module (in rack 1Y1) to our 1x16 optical splitter (in the OMC_North rack) and measure the power output at one of the splitter's output ports. We plan to keep the output power limited to less than 0.5 mW per optical splitter output.
We decided that the POY Table would be a better home for our REF DET (Newport 1611 FC-AC) than the AS Table. We moved the PD to the POY Table (1st attachment) and routed a fiber from our 1x16 Optical Splitter in the OMC_North rack to the POY Table. REF DET's power supply is now located under the POY table (2nd attachment). We left the fiber described in the previous post on the AS Table.
Afterwards, we hooked a fiber up to our laser module to test it (3rd attachment). The laser was not being distributed, just going to one fiber with a power meter at its end. Everything turns out, but we realized we need to read the power supply's manual before continuing.
For the photodetector frequency response project, I finished the construction of our baluns chassis and mounted it in rack 1Y1 (1st picture).
After consulting with Jenne, I mounted the fiber launcher for REFL165 on the AS table such that it would not cause an obstruction. I aligned the launcher using a multimeter to monitor the DC output of REFL165, but looking at the data I got, it seems I need to do a better alignment/focusing job to get rid of a bunch of noise.
We picked up AS WFS comissioning for daytime work as suggested by gautam. In the end we want to comission this for the PRFPMI, but also for PRMI, and MICH for completeness. MICH is the simplest so we are starting here.
We started by restoromg the MICH configuration and aligning the AS DC QPD (on the AS table) by zeroing the C1:ASC-AS_DC_YAW_OUT and C1:ASC-AS_DC_PIT_OUT. Since the AS WFS gets the AS beam in transmission through a beamsplitter, we had to correct such a beamsplitters's aligment to recenter the AS beam onto the AS110 PD (for this we looked at the signal on a scope).
We then checked the rotation (R) C1:ASC-AS_RF55_SEGX_PHASE_R and delay (D) angles C1:ASC-AS_RF55_SEGX_PHASE_D (where X = 1, 2, 3, 4 for segment) to rotate all the signal into the I quadrature. We found that this optimized the PIT content on C1:ASC-AS_RF55_I_PIT_OUT and YAW content on C1:ASC-AS_RF55_I_YAW_OUTMON which is what we want anyways.
Finally, we set up some simple integrators for these WFS on the C1ASC-DHARD_PIT and C1ASC-DHARD_YAW filter banks with a pole at 0 Hz, a zero at 0.8 Hz, and a gain of -60 dB (similar to MC WFS). Nevertheless, when we closed the loop by actuating on the BS ASC PIT and ASC YAW inputs, it seemed like the ASC model outputs are not connected to the BS SUS model ASC inputs, so we might need to edit accordingly and restart the model.
[koji, ian, tega, paco]
With the remote/local assistance of Tega/Ian last friday I made changes on the c1sus model by connecting the C1:ASC model outputs (found within a block in c1ioo) to the BS and PRM suspension inputs (pitch and yaw). Then, Koji reviewed these changes today and made me notice that no changes are actually needed since the blocks were already in place, connected in the right ports, but the model probably just wasn't rebuilt...
So, today we ran "rtcds make", "rtcds install" on the c1ioo and c1sus models (in that order) but the whole system crashed. We spent a great deal of time restarting the machines and their processes but we struggled quite a lot with setting up the right dates to match the GPS times. What seemed to work in the end was to follow the format of the date in the fb1 machine and try to match the timing to the sub-second level. This is especially tricky when performed by a human action so the whole task is tedious. We anyways completed the reboot for almost all the models except the c1oaf (which tends to make things crashy) since we won't need it right away for the tasks ahead. One potential annoying issue we found was in manually rebooting c1iscey because one of its network ports is loose (the ethernet cable won't click in place) and it appears to use this link to boot (!!) so for a while this machine just wasn't coming back up.
Finally, as we restored the suspension controls and reopened the shutters, we noticed a great deal of misalignment to the point no reflected beam was coming back to the RFPD table. So we spent some time verifying the PRM alignment and TT1 and TT2 (tip tilts) and it turned out to be mostly the latter pair that were responsible for it. We used the green beams to help optimize the XARM and YARM transmissions and were able to relock the arms. We ran ASS on them, and then aligned the PRM OpLevs which also seemed off. This was done by giving a pitch offset to the input PRM oplev beam path and then correcting for it downstream (before the qpd). We also adjusted the BS OpLev in the end.
Summary; the ASC BS and PRM outputs are now built into the SUS models. Let the AS WFS loops be closed soon!
Addenda by KA
- Upon the RTS restarting,
sudo date --set='xxxxxx'
rtcds start c1x01
telnet fb1 8083
- Today we once succeeded to restart the vertex machines. However, the RFM signal transmission did fail. So the end two machines were power cycled as well as c1rfm, but this made all the machines in RED again. Hell...
- We checked the PRM oplev. The spot was around the center but was clipped. This made us so confused. Our conclusion was that the oplev was like that before the RTS reboot.
I touched steering mirrors for AS and REFL at AP table.
AS beam and REFL beam now hits cameras at center and their respective PDs.
What I did:
1. Aligned Y arm and X arm.
2. Locked FPMI and aligned BS + X arm by minimizing ASDC (DC output of the AS55 PD, C1:LSC-ASDC_OUT reached ~ -1.43).
3. Put -2V offset to the OMC stage 2 in yaw to avoid AS clipping. The offset is currently given by SRS DS345 on AUX_OMC_NORTH rack.
4. Misaligned ETMs, locked MI in the bright fringe. Maximized ASDC (C1:LSC-ASDC_OUT reached ~ 1.22) by aligning 2 mirrors right after the vacuum chamber. This also centered beam spot on the AS camera.
5. Locked MI in the dark fringe. Maximized REFLDC (DC output of the REFL55 PD, C1:LSC-REFLDC_OUT reached ~ 2.5) by aligning 2 mirrors after the vacuum chamber. Beam spot on the REFL camera was centered, too.
[ericq, lydia, gautam]
IMC realignment, Arm dither alignment
We aligned MICH (first locked Yarm, but didn't optimize since we don't have TRY, then locked Xarm, then aligned MICH), but there was no beam on AS55. We went out to check, and the beam was almost not hitting the small steering mirror between AS55. We adjusted the BS splitting the beam between camera and PD, and got the beam back on AS55. We could then lock MICH.
We also futzed with the REFL55 phase to get PRCL stuff in I, and MICH stuff in Q. The procedure was to align PRMI, then kick PRM in pos, and adjust the phase so we got signal mostly in I after the kick. We started at the original value of 60deg, but are leaving it at -20deg.
We conducted a beam scan on the AP table of the AS beam. We used a lens to focus the beam onto a power meter, and slowly moved a razor blade across the beam using a micrometer, vertically and horizontally both in front of and behind the beam. We also had to block the beam next to the AS beam in order to do this, but is unblocked now. Mike will begin curve fitting the data to try and see if there is a different spot size given by the x-axis vs. the y-axis, and if the lens has any effect.
[ericq, mikej, some input from zach]
After realigning the MC, the measurement was repeated this afternoon. This time, however, we isolated the beam from ITMY by misaligning ITMX. The beam looked somewhat elliptical to me, and Mike should have fits up tonight. Afterwards, ITMX was returned to the position I found it in, and the PMC shutter and access connector were closed. (Sorry about last night!)
14.112 hundredths of an inch in the vertical direction
10.883 hundredths of an inch in the horizontal direction
Plots and error bars to come soon.
Results of the Razor Blade Beam Scan
The horizontal blade test measured the beam intensity as a razor blade passed in between it and a power meter from the left side of the beam (negative x values) until blocking it. The resulting function, found through least-squares regression of the error function, calculates a beam height of 3.6 mm +/- 16 mm. However, the function has a chi-squared value of 3.2, so that value may not be accurate.
The vertical blade test measured beam intensity as a razor moved from below the beam (negative x values) until blocking it. This function, found the same way as above, calculates a beam width of 2.8mm +/- 9.6 mm, and has chi-squared value of 0.77.
Both data sets have a y-error of 0.5 micro-Watts, and an x-error of 0.127 mm. The Python code used to analyze the data and plot the results is attached.
# Python code for finding Gaussian-beam #
# spot size w(z) from intensity #
# vs. blocked portion of beam #
# Coded by Mike Jenson #
import numpy as np
from scipy.special import erf
Manasa and I are trying to get the AS beam onto the AS camera with a focusing lens. Currently, the mirror immediately preceding the camera has been removed and the camera and lens are sitting directly behind the BS.
In the afternoon, we took the heavy door off the OMC chamber as well, such that we could trace the AS beam all the way out to the AP table.
In summary, we determined the following today:
Attachment #5 is extracted from the 40m CAD drawing which was last updated in 2012. It shows the beam path for the output beam from the BS all the way to the table (you may need to zoom in to see some labels. The drawing may not be accurate for the OMC chamber but it does show all the relevant optics approximately in their current positions.
EQ will put up photos from the ITMY and BS/PRM chambers.
Plan for Monday: Reconfirm all the findings from today immediately after running the dither alignment so that we can be sure that the ITMs are well-aligned. Then start at OM1 and steer the beam out of the chambers, centering the beam as best as possible given other constraints on all the optics sequentially. All shutters are closed for the weekend, though I left the SOS iris in the chamber...
Here is the link to the Picasa album with a bunch of photos from the OMC chamber prior to us making any changes inside it - there are also some photos in there of the AS beam path inside the OMC chamber...
I surveyed the lab today to see what we may need to buy for the AS laser setup.
NPRO 200 mW + Driver
Faraday Isolator from cabinet
ISOMET Model 1201E: This is a free space AOM I found in the modulator cabinet. It needs to be driven at 40MHz (to be confirmed) with ~6W of electrical power. For a 500 micron beam it can allegedly achieve rise times of '93' [units not specified, could this be nanoseconds?]. I did not find a dedicated driver for it, however there was a 5W minicircuits amplifier ZHL-5W-1 in the RF cabinet and a switch ZSDR-230, which has a typical switch time of 2 microseconds, however I'm not sure how this translates to rise/fall times of the deflected power. It seems we have everything to set this up, so we'll by the end of the week if we can use a combination of these things or if we need to buy additional driver electronics.
New Focus model 4004 broadband phase modulator which is labeled as dusty, and in fact quite dirty when looking through. We should attempt to clean this thing and maybe we can use it here or at the ends.
Probably all the optics we need for the PSL table setup.
Beat PD: How about one of these: EOT ET-3000A? I didn't find a broadband PD for the beat with the PSL
Fiber Stuff: coupler & polarization maintaining fiber 20m & collimator. There are a couple options here, which we can discuss in the meeting.
Faraday Isolator: If we want to inject P-polarization. If S is okay we can use a polarizing plate beamsplitter instead.
Possibly some large lenses for mode-matching to IFO (TBD)
We finally managed to steer the AS beam from ITMY chamber, through BS and IMC chambers, to the in-air AP table.
We moved the AS5 mirror north to its nominal position and we also moved the ASL lens on BS chamber back to its nominal position. Attached photos are taken after today's alignment work.
[Tega, Yehonathan, Koji, Yuta]
We tried to align AS path this afternoon.
IMC is not aligned now after the work today
Green mirrors/perisocope in IMC chamber were removed since some of them was clipping the AS beam, and this changed the balance of the IMC stack and thus MC1 and MC3 alignment.
Summary of changes:
- Rotated AS2 in roll by 90 deg to have more aperture for the transmission (photo)
- IR beams are now centered on AS1, AS2, AS3 and AS4 (photo, photo)
- Moved ASL towards -X direction for about 1/4 inch
- Installed GRY_SM2 at the nominal position (re-used GR_SM3 from IMC chamber)
- Removed green optics GR_SM4, GR_SM3, GR_PERI2L (GR_PERI2L is now stored at Xend)
- Removed IFI camera mirrors FIV1, FIV2 (they are now stored at Xend) (photo, photo)
- GR_SM4 mount is now reused as GRY_SM1 (Y2-2037-0 is now mounted instead of previously mounted Y2-LW1-2050-UV-45P/AR), and GRY_SM1 is installed at the nominal position (photo)
- Moved weights to balance the stack
OMC chamber (we don't have OMC in this chamber...)
- We swapped AS5 and AS6 so that the nobs comes in -X direction to have more spacing between AS beam and IMC REFL beam (photo)
- Moved weights to balance the stack
What we did:
1. Misaligned ITMX and use ITMY reflected beam to align AS path
2. Centered the IR beam on AS1 using SR2
3. Centered the IR beam on AS2 and ASL using AS1. AS2 was rotated in roll by 90 deg to have more aperture for the transmisson.
4. Centered the IR beam on AS3 using AS2 nobs, centered the IR beam on AS4 by rotating AS3 in yaw.
5. "AS beam" (it turned out that what we are looking was actually not the AS beam!! Some stray light) was in +X direction by 1 inch or so at AS5. Moving AS5 to center the beam would clip IMC REFL beam. So we swapped AS5 and AS6 so that the nobs comes in -X direction to have more spacing between AS beam and IMC REFL beam.
6. Balanced OMC chamber stack again using IMC REFL beam as a referece (bring the IMC REFL beam to the reference red circle on the monitor).
7. Tweaked the alignment of TT1 and TT2 to have Yarm flashing to ~0.9 in TRY.
8. Moved AS5 towards +X by an inch or so to center the "AS beam."
9. Moved ASL towards -X direction for about 1/4 inch and re-centered the beam by AS1 to see if the "AS beam" gets far from IMC REFL at OMC chamber, but the "AS beam" didn't move much.
10. By blocking the beam from ITMY, we found that "AS beam" was not the actual one.
11. Opened IMC chamber and found that AS beam is blocked by the past optics.
12. Removed old green optics and IFI camera mirrors. GR_SM4 mount and GR_SM3 were reused as mentioned above.
13. Tried to balance IMC chamber stack to recover IMC alignment. We used IMC REFL beam as a reference, but it was hard to completely bring the IMC REFL beam to the reference red circle on the monitor. It is now off by a beam diameter or so. No IMC flashing now.
Theoretically, balancing IMC chamber stack would recover all the IFO alignment, but maybe tough. It is maybe easier to align MC1 and MC3 to have IMC locked. Assuming input pointing to IMC is not drifted too much, we should be able to recover Yarm flashing by tweaking TT1 alignment only. However, MC3 SD OSEM is at the edge of the range. We might have to balance the stack more or tweak SD OSEM position.
Status of the AS-port auxiliary laser injection
Using Gautam's Finesse file and the cad files for the 40m optical setup I propagated the arm mode out of the AS port. For the location of the 3.04 mm waist I used the average distance to the ITMs, which is 11.321 m from the beam spot on the 2 inch mirror on the AS table close to the viewport. The 2inch lens focuses the IFO mode to a 82.6 μm waist at a distance of 81 cm, which is what we have to match the aux laser fiber output to.
I profiled the fiber output and obtained a waist of 289.4 μm at a distance of 93.3 cm from the front edge of the base of the fiber mount. Next step is to figure out the lens placement and how to merge the beam paths. We could use a simple mirror if we don't need AS110 and AS55, we could use a polarizing BS and work with s polarization, or we find a Faraday Isolator.
While doing a beam scan with the razor blade method I noticed that the aux laser has significant intensity noise. This is seen on the New Focus 1611 that is used for the beat signal between PSL and aux laser, as well as on the fiber output PD. There is a strong oscillation around 210 kHz. The oscillation frequency decreases when the output power is turned down, the noise eater has no effect. Koji suggested it could be light scattering back into the laser because I couldn't find a usable Faraday Isolator back when I installed the aux laser in the PSL enclosure. I'll have to investigate this a little further, look at the spectrum, etc. This intensity noise will appear as amplitude noise of the beat note, which worries me a little.
For the arm cavity ringdowns, I guess we don't need AS55/AS110 (although I think the camera will still be useful for alignment). But for something like RC Gouy phase characterization, I'd imagine we need the AS detectors to lock various cavities. So I think we should go for a solution that doesn't disturb the AS PD beams.
It's hard to tell from the plot in the manual (pg 52) what exactly the relaxation oscillation frequency is, but I think it's closer to 600 kHz (is this characteristic of NdYAG NPROs)?? Is the high RIN on the light straight out of the NPRO?
We could use a simple mirror if we don't need AS110 and AS55, we could use a polarizing BS and work with s polarization, or we find a Faraday Isolator.
There is a strong oscillation around 210 kHz. The oscillation frequency decreases when the output power is turned down, the noise eater has no effect.
Instead of trying to couple the fiber output into the interferometer, I'm doing the reverse and maximize the amount of interferometer light going into the fiber. I set up the mode-matching solution shown in attachment #1 and started tweaking the lens positions. Attachment #2 shows the setup on the AS table. After the initial placement I kept moving the lenses in the green arrow directions and got more and more light into the fiber.
When I stopped this work yesterday I measured 86% of the AS port light coming out the other fiber end, and I have not yet reached a turning point with moving the lenses, so it's possible I can tickle out a little more than that.
It occured to me though that I may have been a little hasty with the placement of the mirror that in attachment #2 redirects the beam which would ordinarily go to AS55. For my arm ringdown measurements this doesn't matter, I could actually place it even before the 50/50 beamsplitter that sends light onto AS110 and double the amount of light going into the IFO. What signals are needed for the Guoy phase measurement? Is AS 110 sufficient, or do we need AS55?
I think we need AS55 for locking the configuration Jon suggested - AS55 I and Q were used to lock the SRMI previously, and so I'd like to start from those settings but perhaps there is a way to do this with AS110 I and Q as well.
What signals are needed for the Guoy phase measurement? Is AS 110 sufficient, or do we need AS55?
I was planning to set up the additions to the AS table that are outlined in Attachment #1. Unfortunately the beam is too large for the 2mm clear aperture Faraday rotators that we have available at that position. I checked the 40m and QIL and found 5 Faraday isolators/rotators for 1064 nm total, but none have large enough aperture for the current setup. Some options for buying a larger aperture isolator are:
I wanted to leave the rest of the setup undisturbed at first, but I think a much easier solution would be to move the 2" focusing lens up by about 12", which moves the beam focus away from AS55 to where the Faraday will be placed, but we can re-focus it with another lens. I may have to change the mode-matching for the aux laser fiber slightly to accomodate this change, but if there are no other concerns I would like to start this work tomorrow (Wednesday).
Here is a set of mode scans of the AS port, using the OMC as a mode scanner. The plot overlays various configurations of the IFO.
To remove PZT nonlinearity, each scan was individually flattened in fsr-space by polynomial (3rd order) fitting to some known peak locations (the carrier and RF sidebands).
[Jenne, Jamie, Manasa, Ayaka]
Flipped mount of OM2, moved OM2 behind POY pickoff so we're out of the way of POY. Adjusted and recovered rest of AS path.
We found that IPANG was not on its photodiode, but determined that it was centered on all of the in-vac mirrors, and that it was just a little bit of steering on the ETMY end out-of-vac table that needed to be done.
Got green flashes in Yarm, moved down periscope to the north by ~1 inch in order to get y green out to PSL table. This also involved moving the steering mirror on the IOO table immediately after the down periscope to match. We measured the MC spot positions before and after touching the periscope, and there was no significant change.
Aligned X green to X arm (centered on ITMX, ETMX, although no flashes since we didn't move ETMX's biases around), then made sure it was centered on all of its steering mirrors, and came out of the vacuum.
Manasa took photos of all test mass chambers and the BS chamber, so we can keep up-to-date CAD drawings.
Oplevs and IPPOS/IPANG are being centered as I type. Manasa and Ayaka are moving the lens in front of IPANG such that we have a slightly larger beam on the QPD.
In the morning, Jamie is going to put apertures back on 2 of the suspended mirrors for one last check that moving things on the IOO table didn't do anything bad, but since the AS and REFL beams on those cameras didn't move significantly, we think things are fine.
Heavy doors go on in the morning, and access connector at ~1pm, if not before lunch. Then Steve will start pumping early Monday morning! Hooray!
PS, for reference,