Yend table - Current status
Today the 2m focal length lens along the oplev path (just after the laser) has been added. In Manasa's layout it allows to have a beam waist of 3.8mm on the OPLEV QPD, even if it seems to be smaller.
The laser is closer to the box wall than the layout shows (it's on the line n.1 instead of line n.9), so maybe it has to be moved in the position shown in the layout, as Steve suggests, to leave empty space just before the window.
Rana suggests a 2mm diameter beam on the QPD, so a new calculation has to be done to add a second lens.
The beam has been aligned until the doubler, but after the crystal it it has a small tilt, so a better alignment has to be done.
Moreover, the beam waist has to be measured after the Faraday for the green, in way to choose the focal length of the lenses necessary for the mode matching.
Then the three steering mirrors to send the beam into the arm have to be put.
A lens which has to be put on the Transmon path (already ordered) has to be added, and the beam alignment on the QPD-y and on the PDA520 has to be done.
Koji noticed that earlier this afternoon the Yarm ASS was working, but then after dinner it was no longer working. I saw that the ETMY trans camera beam was clipped. These things precipitated a visit to the Yend station.
I saw that the beam on the optic that steers the camera beam to the camera was very, very low, almost falling off the optic. The only mirror which steers to this optic is the harmonic separator which reflects the IR, and transmits the green. I turned the pitch knobs on the harmonic separator until the beam was roughly centered on all 3 optics between the separator and the camera (BS to QPD, BS to TRYDC and Y1 for camera). The yaw was fine, so I didn't touch it.
I then adjusted the steering mirror to the camera, and the BS pointing to the DC PD. I have not touched the BS pointing to the QPD. Once the beam was on the TRY PD, Koji ran the ASS script, and I recentered the beam on the DC PD. During this time, Koji had the Yarm triggering using -1 in the POYDC element of the matrix.
The harmonic separator is not mounted in a nice way (I'm assuming that Annalisa is in the middle of things, and she'll get back to it after the green work), so the TRY PD and camera will need to be aligned again, so I didn't do any ASS-recentering-ASS iteration tonight.
The Yarm ASS works nicely again, getting TRY to ~0.89 .
I'm planning to remove the ETMY optical table enclosure and move it over to CES Shop 8am Thursday morning.
We'll install spring loaded lathes, hooks and quick release pins.
The bridge will be reinforced with steel plate to support release pins on posts.
There will be an other cut out for cable feedtrough as it is shown on elog #8472
Let me know if this timing does not fit your work.
The new lenses arrived, and I put the right 250mm before the doubler. I'm still not so confident with the alignment, because I cannot get more than 11-12 uW out from the "green" Faraday, with more than 200uW going in.
I replaced the Y1 mirror with an HR1064-HT532. The alignment has to be done. Today the 50cm focal length lens arrived, and I'm going to put in tomorrow.
I still have problems in maximizing the power out from the doubler. I realized that the real green power I obtain is about 30 uW, and it is the power which really enters the Faraday.
Before I was measuring it just after the Harmonic separator, and there was some residual IR beam which increased the power on the power meter, that's why I obtained about 200 uW.
I also tried to slightly vary the position of the mode matching lens, but I was not able to get more than 30 uW on the power meter.
The 50 cm focal length lens has been added in the position shown on Manasa's layout, and the beam has been focused on the PD.
Today, I moved the router from on top of the PSL into the control room in order to perform dark field tests on the GC650 (which I also moved). The GC750 along with the lens that was on it and the mount it was on has been lent to Ricardo's lab for the time being. I successfully triggered the GC650 externally and I also characterized the average electronic noise. For exposure times less than 1 microsecond, the average noise contribution appears to be a constant 15 on a 12-bit scale.
I found two ThorLabs PDA55 Si photodetectors that says detect visible light from DC to 10MHz that I'm going to use from now on. I don't know how low of a frequency they will actually be good to.
Rather than make a new elog post every time I move something, I'm going to just keep updating this Google spreadsheet, which ought to republish every time I change it. It's already got everything I've done for the past week-ish. The spreadsheet can be accessed here, as a website, or here, as a pdf. I will still post something nightly so that you don't have to search for this post, but I wanted to be able to provide more-or-less real-time information on where things are without carpet-bombing the elog.
I fit the data from the beam profile that Jenne measured on 5/21/2010. The distances are measured from halfway between MC1 and MC3 to the beam scanner. The fits give the following where w0 is the waist size and z0 is the distance from the waist to halfway between MC1 and MC3.
For the horizontal profile:
reduced chi^2 = 0.88
z0 = (1 ± 29) mm
z0 = (1
w0 = (1.51 ± 0.01) mm
w0 = (1.51
For the vertical profile:
reduced chi^2 = 0.94
z0 = (673 ± 28) mm
z0 = (
w0 = (1.59 ± 0.01) mm
w0 = (1.59
I calculated the radius of curvature of MC2 using these values of w0:
horizontal: (16.89 ± 0.06) m
vertical: (17.66 ± 0.07) m
For this calculation, I used the value of (13.546 ± .0005) m for the length of the mode cleaner measured on 6/10/2009. The specification for the radius of curvature of MC2 is (18.4 ± 0.1) m.
In the following plots, the blue curve is the fit to the vertical beam radius, the purple curve is the fit to the horizontal beam radius, * denotes a data point from the vertical data, and + denotes a data point from the horizontal data.
the lead spheres that were placed below the granite slab have been flattened by hammering to have lesser degree of wobbling of the slab.
the height of each piece, and the flatness of their surfaces was checked by placing another slab over them and checking by the spirit level.
Wednesday after the meeting - Started report, learnt mode cleaner locking from Kiwamu and Rana, saw how to move optics on the tables with Rana and kiwamu.
Thursday - Made the report
Tuesday - report.
Today - am trying locking the MC with kiwamu's help to see the WFS signals and also to start characterizing the QPD.
Kiwamu and I found that the first lens in the PMC mode matching telescope was mislabeled. It is supposed to be PLCX-25.4-77.3-C and was labeled as such but in fact it was PLCX-25.4-103.0-C. This is why the PMC mode matching was bad. We swapped the lens for the correct one and got the PMC visibility of 82%. The attached plot shows the beam scans before and after the PMC. The data were taken with the wrong lens. The ABCD model shown in the plot uses the lens that was there at the time - PLCX-25.4-103.0-C. The model for the PMC is just the waist of 0.371 mm at the nominal location. The snap shot of the ABCD file is attached. The calculation includes the KTP for FI and LiNb for EOM with 4 cm length. The distances are as measured on the table.
The attached plot shows the beam scans of the beam leaking from the back mirror of the PMC to the BS cube that first turns the S-pol beam 90 deg to the AOM and then transmits the AOM double passed and polarization rotated P-pol beam to the reference cavity. The beam from the PMC is mode matched to the AOM using a single lens f=229 mm. The ABCD file is attached. The data were taken with VCO control voltage at 5 V. We then reduced the voltage to 4 V to reduce the astigmatism. Tara has the data for the beam scan in this configuration in his notebook.
The beam from AOM is mode matched to the reference cavity using a single lens f=286.5 mm. The ABCD file is attached.
I measured the RF power output of the VCO Driver box as a function of slider value. I measured using the Gigatronics Handheld power meter and connected to the AOM side of the cable after the white Pasternak DC block.
* at low power levels, I believe the waveform is too crappy to get an accurate reading - that's probably why it looks non-monotonic.
* the meter has a sticker label on it saying 'max +20 dBm'. I went above +20 dBm, but I wonder if maybe the thing isn't linear up there...
- NPRO injection current 1.0 A
- PMC losses ~32%
- FSS AOM diffraction efficiency ~52%
The attached plots show the PMC cavity line width measurement with 1 mW and 160 mW into the PMC. The two curves on each plot are the PMC transmitted power and the ramp of the fast input of the NPRO. The two measurements are consistent within errors - a few %. The PMC line width 3.5 ms (FWHM) x 4 V / 20 ms (slope of the ramp) x 1.1 MHz / V (NPRO fast actuator calibration from Innolight spec sheet) = 0.77 MHz.
Here is the output of the calculation using Malik Rakhmanov code:
modematching = 8.4121e-01
transmission1 = 2.4341e-03
transmission2 = 2.4341e-03
transmission3 = 5.1280e-05
averageLosses = 6.1963e-04
visibility = 7.7439e-01
fw = 0.77e6; % width of resonance (FWHM) in Hz
Plas = 0.164; % power into the PMC in W
% the following number refer to the in-lock cavity state
Pref = 0.037; % reflected power in W
Ptr = 0.0712; % transmitted power in W
Pleak = 0.0015; % power leaking from back of PMC in W
We installed the ISS AOM in the PSL. The AOM was placed right after the EOM. The beam diameter is ~600 um at the AOM. The AOM aperture is 3 mm.
We monitored the beam size by scanning the leakage beam through the turning mirror after the AOM. The beam diameter changed from 525 um to 515 um at a fixed point. We decided that the AOM thermal lensing is not large enough to require a new scan of the mode going into the PMC and we can proceed with PMC mode matching using the scan that was taken without the AOM (to be posted).
We made a model for the dither angular stabilization system c1ass.mdl. The attached file shows the diagram.
The idea is to dither a combination of 6 optics (ETMs, ITMs, PZTs) at different frequencies and demodulate three PDs (TRX, TRY, REFL11I). Then form the DOFs from demodulted signals, filter, and send each DOF to a combination of optics.
This is enough to get started with arm cavities alignment (we may need to add the BS for the Y arm). More optics and PD can be added as they become available and/or needed.
The DAC for the fast PZT are not connected and have to be commissioned.
I have been editing and reloading the c1ioo model last two days. I have restarted the frame builder several times. After one of the restarts on Sunday evening the fb started having problems which initially showed up as dtt reporting synchronization error. This morning Kiwamu and I tried to restart the fb again and it stopped working all together. We called Joe and he fixed the fb problem by fixing the time stamps (Joe will add details to describe the fix when he sees this elog).
The following changes were made to c1ioo model:
- The angular dither lockins were added for each optics to do the beam spot centering on MC mirrors. The MCL signal is demodulated digitally at 3 pitch and 3 yaw frequencies. (The MCL signal was reconnected to the first input of the ADC interface board).
- The outputs of the lockins go through the sensing matrix, DOF filters, and control matrix to the MC1,2,3 SUS-MC1(2,3)_ASCPIT(YAW) filter inputs where they sum with dither signals (CLOCK output of the oscillators).
- The MCL_TEST_FILT was removed
The arm cavity dither alignment (c1ass) status:
- The demodulated signals were minimized by moving the ETMX/ITMX optic biases and simultaneously keeping the arm buildup (TRX) high by using the BS and PZT2. The minimization of the TRX demodulated signals has not been successful for some reason.
- The next step is to close the servo loops REFL11I demodulated signals -> TMs and TRX demodulated signals -> combination of BS and PZTs.
The MC dither alignment (c1ioo) status:
- The demodulated signals were obtained and sensing matrix (MCs -> lockin outputs) was measured for pitch dof.
- The inversion of the matrix is in progress.
- The additional c1ass and c1ioo medm screens and up and down scripts are being made.
I put the PMC last mode matching lens (one between the steering mirrors) on a translation stage to facilitate the PMC mode matching.
Currently 4% of incident power is reflected by the PMC. But the reflected beam does not look "very professional" on the camera to Rana - meaning there is too much TEM20 (bulls eye) mode in the reflected beam.
I locked the PMC on bulls eye mode and measured the ratio of the TEM20/TEM00 in transmission to be 1.3%. Thus the PMC mode matching is ~99% and the incident beam HOM content is ~3%.
While working on the PMC I found that the source of PMC "blinking" is not the frequency control signal from MC to the laser (the MC servo was turned off) but possibly some oscillation which could be affected even by a small change of the pump current 2.10 A to 2.08 A. I showed this behaviour to Kiwamu and we decided to leave the the current at 2.08 A for now where things look stable and investigate later.