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.
The attached plot shows the 30 day trend of the MC3 UL PD signal. The signal dropped to zero at some point but now it is close to the level it was a few weeks ago. There still could be a problem with the cable.
The rest of the MC1,2,3 PD signals looked ok.
I went push all the possible connectors for the MC3 shadow sensors including the SCSIs, flat cables and satellite box.
Also I put screws on them so that they won't become loose any more.
As a result UL_PDMON dropped from 0.6 V to 0.490 V and it becomes stable so far.
I didn't strain relief the cables but we must do it at some point before going into the full locking test.
The AA board shown in attachment 1 will be used in the seismometer hardware setup. A cartoon of this setup is shown in attachment 2.
BNC connectors are required for the seismometer breakout boxes. So the four-pin LEMO connectors present in the AA board were removed and panel mount BNC connectors were soldered to it. Red and blue colored wires were used to connect the BNC connectors to the board. Red wire connects the center of the BNC connector to a point on the board and that connection leads to the third leg (+IN) of the IC U### and the blue wire connects the shield of the BNC connector to the second leg (-IN) of the IC U###.
All the connections (including BNC to the AA board and in the AA board to all the filters) were tested using a multimeter by the beeping method and it was found that channel 10 (marked as C10) had a wrong connection from the point where the red wire (+ve) was connected to the third leg (+IN) of IC U91 and channel 32 (marked as C32) had opposite connections meaning the blue wire is connected to the third leg (+IN) of IC U311 and red wire is connected to the second leg (-IN) of IC U311.
I am starting work on the PSL table at the 40m. My goal is to lock the laser coming from the nearby table to the FP cavity and get a measurement of the response to a temperature step on the surrounding can.
I have to mode match the beam to the cavity. Specifically, I have to mode match to the beam coming from the PMC through the EOM to the polarizing beam splitter. Yesterday David and I measured the beam width at various distances (from a particular lens through which the beam traveled), and I fit that data using MATLAB to find the beam's waist size and location. However, I'm not convinced that the fit is any good, since we only took measurements at five spots and they had large error bars.
Here is the fit I obtained using fminsearch. The horizontal beam width measurements were smaller than the vertical width measurements, suggesting that the incoming beam was elliptical. I fit the data for each set of measurements separately and got two waist locations. The red trace is the fit for the horizontal width and the blue represents the vertical width of the beam. Averaging the two fitted waist locations and sizes gives
vert z_0= -1760 mm (waist location)
horiz z_0= -1540 mm (waist location)
vert w_0 = 0.286 mm (waist size)
horiz w_0 = 0.275 mm (waist size)
avg z_0= -1650 mm
avg w_0 = 0.281 mm
Here is the code I used:
I defined the function spotsize.m and then made a function gaussbeam.m that called it with input parameters and returned the least squares error. I then wrote another function twobeamfits.m that ran fminsearch to minimize the least squares error and made the above plot. I've pasted the code below.
function omega = spotsize(z_0, w_0, z)
function sse = gaussbeam(params,xvals,yvals)
%This f'n takes as its inputs
%three parameters (w_0, z_0, and lambda),
%a vector of x-values (distances),
%and an associated vector of y-values (spotsizes),
%It then generates a vector of fitted y-values by applying
%an exponential approach function (single pole), with the given parameters,
%to the x-values.
%It then returns the sum of the squares of the entries of the difference
%between the fitted y-vector and the actual y-vector
fityvals=spotsize(z_0, w_0, xvals);
error=(fityvals - yvals);% .*xvals;
% sse stands for sum of squares error
function [outputs] = twobeamfits(guesses, dists, vert, horiz)
%This f'n takes as its inputs
%two starting guess parameters (w_0 and z_0),
%a vector of distances (x-values),
%and two associated vectors of measured beam radii,
%the radius measured along the vertical axis
%and the radius measured along a horizontal axis (y-values).
%It then calls the gaussbeam f'n for each set of y-values and minimizes its output (sum of squares error)
%using the fminsearch f'n. It outputs the fit parameters it settles on.
%It then plots the input data, the fitted curves, and the residuals
fitvert=spotsize(vertparams(1), vertparams(2), dists);
spoterror=[.1, .1, .1, .1, .1]; %uncertainties, all in mm
fithoriz=spotsize(horizparams(1), horizparams(2), dists);
errorbar(dists, vert, spoterror, 'x')
errorbar(dists, horiz, spoterror, 'r*');
plot(points,spotsize(vertparams(1), vertparams(2), points));
plot(points,spotsize(horizparams(1), horizparams(2), points),'r');
xlabel('Distance z (mm)')
title('Gaussian Beam Fits')
ylabel('Spotsize w (mm)')
legend('Vertical Spotsize','Horizontal Spotsize','Vertical Fit',...
legend('Vertical Fit Residuals','Horizontal Fit Residuals',...
Later on I may repeat some measurements and try to gain more certainty in my fit. In the mean time I will use this beam profile for mode matching.
I added an U channel based bottom shelf at the south end today.
I'm working on similar shelf at ETMY. Precondition: NPRO in bypass mode, heater for doubling in bypass........since power outage? Optical level servo turned off.......
U-channel based shelf in place. Oplev servo is back on at 11:15am The table may moved. The oplev return is missing the quad by a few milimeter.
This week, the other SURF students and I got acquainted with the caltech campus, LIGO 40m lab and the expectations of the SURF program. We went to a lot of safety meetings and lectures that established a framework for the jobs we will be doing over the course of the summer. I went on several tours of the 40m interferometer (one each with Jenne, Jamie and Steve) to get an overview of the layout and specifics of the setup. I read parts of R. Ward and A. Parameswaran's theses and Saulson's book in order to prepare myself and gain a broader understanding of the purpose of LIGO.
I also began working in Python this week, primarily graphing PSDs of data from the C1:SUS-ETMY_SENSOR_LR, C1:SUS-ETMY_SENSOR_LL, C1:SUS-ETMY_SENSOR_UR, and C1:SUS-ETMY_SENSOR_UL channels. I will eventually be using Python to generate the plots for the summary pages, so this is good practice. The code that I have been working on can be found in /users/elizabeth.davison/script5.py. Additionally, I have been going through the G1 summary pages and attempting to understand the plots available on them and the code that is available.
My plans for the upcoming week begin with modifying my code and potentially calibrating the channel data so that it is in units of length instead of counts. I will also access the code from the G1 pages and go over it in depth, hopefully gaining insight into the structure of the website.
I tried to make ringdown measurements at the IMC using the DC falling edge as the trigger. Input to the MC was switched off by changing the polarity of the MC servo. But it does not seem to give the needed data as there seem to be several DC falling edges as soon as the polarity is switched. We should think about a better trigger or try to setup data recording from the oscilloscope seamlessly.
Also an ethernet cable has been connected to the router from the oscilloscope at the MC trans, but has not been set up to record data yet.
The ringdown measurements are in progress. But it seems that the MC mirrors are getting kicked everytime the cavity is unlocked by either changing the frequency at the MC servo or by shutting down the input to the MC. This means what we've been observing is not the ringdown of the IMC alone. Attached are MC sus sensor data and the observed ringdown on the oscilloscope. I think we need to find a way to unlock the cavity without the mirrors getting kicked....in which case we should think about including an AOM or using a fast shutter before the IMC.
P.S. The origin of the ripples at the end of the ringdown still are of unknown origin. As of now, I don't think it is because of the mirrors moving but something else that should figured out.
It is HIGHLY unlikely that the IMC mirrors are having any effect on the ringdown. The ringdowns take ~20 usec to happen. The mirrors are 0.25 kg and you can calculate that its very hard to get enough force to move them any appreciable distance in that time.
The huge kick observed in the MC sus sensors seem to last for ~10usec; almost matching the observed ringdown decay time. We should find a way to record the ringdown and the MC sus sensor data simultaneously to know when the mirrors are exactly moving during the measurement process. It could also be that the moving mirrors were responsible for the ripples observed later during the ringdown as well.
* How fast do the WFS respond to the frequency switching (time taken by WFS to turn off)? I think this information will help in narrowing down the many possible explanations to a few.
We have done some work at ETMX today. We installed the baffle and placed two mirrors on the table.
The baffle position/orientation still needs to be checked more thoroughly to make sure that the beam will pass through the center of the baffle hole.
One of the two mirrors will stay on the table as pickoff. The other is only temporarily installed for alignment purposes. Later today we will shoot a laser into the chamber that will reflect off one of these mirrors towards the center of ITMX, then go back to the pickoff mirror next to ETMX and hopefully make it through the viewport.
To place the pickoff mirror, we had to move the "cable rack" next to ETMX a few inches towards the back of the table.
The baffle has been moved away from ETMX towards the edge of the table (in fact, it is a little beyond the edge). It is also rotated so that its long edge is horizontal. In this way it was possible to center the baffle hole with respect to the optical axis, but also make it possible that the camera looks over the baffle.
We have tried to get an alignment beam from view port -> ETMX pick-off ->ITMX-> back to EX. This work was pretty much unsuccessful though. We could see the green laser scattering around ITMX, but there was no good way to know when the beam hit ITMX. So tomorrow we will find a better way to check where the beam is hitting at ITMX and finish the alignment of the scattering pick-off mirror.
The alignment of the pick-off mirror near ETMX is done. Everything turned out to be easy once we realized that there is no sense getting the alignment laser (going through viewport to pick-off to ITMX) back to ETMX. It is only necessary to hit ITMX somehow, since this makes sure that there is one scattered beam that will make it from ITMX to pick-off through viewport.
After the auxiliary optic (that we never used in the end) was removed again, we levelled the optical table.
So in the current setup, we can have small-angle scattering measurements on ITMX and large-angle scattering measurements on ETMX.
We have installed the pick-off mirror at the ETMY table for the small-angle scattering measurement on ITMY. As we had already done for the X arm pick-off, the pick-off mirror at ETMY was aligned shooting a green laser normally through the viewport on the pick-off and steering it onto ITMY.
A baffle was also installed at a distance of about 30cm from ETMY near the edge of the table.
With a curvature radius of about 57m for the ETMs, flat ITMs at the beam waist, and using 39m for the arm lengths, one finds that the beam radius at the ETMs is about 5.3mm. The clipping power loss of a 5.3mm beam through a 20mm radius baffle hole would be less than a ppm of a ppm if the beam was perfectly centered. If the baffle hole had 15mm radius, the clipping loss would be 0.01ppm. If the baffle hole had 10mm radius, the loss would be 810ppm. The loss values are calculated using the formula of the "Gaussian beam" Wikipedia article, "Power through an aperture" section. So I did not check if that one is ok.
IMC transmission photodiode has been aligned.
Which PD? The 'regular' DC one, or the newer one? Why did it need realigning? What mirrors did you touch to do the alignment?
Did you do anything else in the last 3 days? I want to see ALL the gory details, because it can help people doing future measurements, or help us debug if something is wrong with the interferometer later.
MORE WORDS! Thanks.
No, not the "regular DC one", the "newer one" along with the controls of the corresponding mirror only i touched.
It needed to be realigned cause last week when we fitted a longer cable there, which may reach the network analyzer, it got misaligned since it got touched.
No other component in that box except that PD and the corresponding mirror controls I touched.
For my last 2 days work, I feel my last elog is reliable.
Today other than doing this, I checked for the higher order modes of the cavity, misaligning one of the MC mirror though the software only. I didn't mention it in my elog cause although I saw the presence of the higher order modes I didn't record it, so I can not upload any picture in support of such a statement.
Summary: Recorded the presence of higher order modes in IMC
What I did: Misaligned the flat mirror MC1 by small amount in both pitch and yaw (it was needed to be done cause at the beginning of the experiment no higher order modes were present) and scanned the cavity for frequency-range 32MHz to 45MHz.
I found the presence of higher order modes around 36.7MHz (1st order) and 40.6MHz (2nd order) along with two other strong modes near 35MHz and 42.5MHz.
Here I am attaching the schematic diagram of the experimental set-up for IMC cavitymode scanning. A 30- 45MHz scanning signal generated by Agilent 4395A network analyzer enters EOM, which in turn modulates the laser beam entering IMC. The cavity response can be verified from reflected/transmitted beam.
I worked with the reflected beam last days. But I got no clue about the percentage of reflected light reaching the photodiode and also the photodiode response. I would like to measure the power reaching photodiode and also would like to perform the test with transmitted beam - on wednesday if possible.
Today I checked the optical lay-out in MC REFL board of the MC REFL path on the AS table (I will put the updated diagram in a few hours), and took a record of the reflected power of unlocked MC and power entering MC REFL PD. The power coming out of MC cavity when unlocked is 1.25W and power entering REFL PD 112mW (Jenne measured these powers for me).
I also got a description of the MC demodulation board from Jenne.
(Edits by Jenne)
Also, when I walked through the control room later, the WFS were driving the MC crazy. I turned off / disabled the WFS from the WFS screen. In my infinite spare time, I need to put in the real-time triggering, so that the WFS turn off as soon as the cavity unlocks.