I've had the output from a fiber projected about 400mm onto the Hartmann sensor for around 5 days now. (The divergence angle from the fiber is around 86 mrad).
I played around with the temperature of the lab to induce some defocus changes in the Hartmann sensor. The system is mostly linear, but there are relatively frequent jumps in the defocus of the order of 1E-4 m^-1. This may be due to a number of things - the Hartmann plate may be moving, the fiber holder may be shifting back and forth, there may be some issue with the source wavelength shifting.
Sun 30th May 2011 - 11:40AM - the z-axis control on the NewFocus 9091 fiber coupling mount was not tightened. I tightened that to secure the control.
I ran through the procedure to calibrate the lever arm of the Hartmann sensor. The beam from a 632.8nm HeNe laser was expanded to approximately 12mm diameter and injected into a Michelson interferometer. The Hartmann sensor was placed at the output port of the Michelson.
The 50W Access Laser is now in the lab. We need to wire up the interlock to the laser, plumb the chiller lines to the power supply and to the laser head and also wire up all the electrical and electronics cables. Additionally, we will need to plumb the flow meter and attach a circuit to it that triggers the interlock if the flow falls too low.
I ran a test of the HWS with the QFLD-950-3S for 5 days. The test was terminated as we need to disconnect all the cabling and tidy up all the computers in the lab.
9:40PM PDT - I've just restarted the long term measurement of the Hartmann sensor noise with the QFLD-950-3S.
Around a year ago, Phil and I discussed the possibility of using an OPO to possibly generate our own laser beam at ~2 microns for TCS. This was to avoid all of the usual hassle of the 10 micron CO2 laser.
As it turns out, the 1.5-3 micron range doesn't have enough absorption in fused silica: the absorption depth would be basically the whole thickness of the optics and this is not so useful when trying to correct surface heating.
During my recent trip to JILA, Jan Hall mentioned to me that it should be possible to operate instead at ~5 microns, where laser technology may be solid state and where we can use Si:As detectors instead of the inefficient HgCdTe ones which we use now.
JWST, in partnerships with industry, have developed some Si:As detectors: http://www.jwst.nasa.gov/infrared.html
Some internet searching shows that there are now several laser technologies for the mid-IR or MWIR range. Some are <1 W, but some are in the ~10 W range.
Of course, its possible that we'll switch to Silicon substrates, in which case we need to re-evaluate the goals and/or existence of TCS.
- Had a meeting to talk about the basics of LIGO (esp. TCS) and discuss the project
- Created COMSOL model for the test mass with incident Gaussian beam.
- Added a ring heater to the previous file
- Set up SVN for the COMSOL repository
- Got access to and started working with SIS on Rigel1
- Fixed SVN issues
- Refined COMSOL model parameters and worked on a better way to implement the heating ring to get the astigmatic heating pattern.
-Discussed the actual project outline
-Installed Comsol on the system
-Learned the basics of Comsol with the help of tutorials available on 40m wiki
-Made few simple models in Comsol
-Studied LIGO GWADW slides for a better understanding of the project.
-Setup SVN to access remote repository.
- Created a COMSOL model with thermal deformations
- Added non-symmetrical heating to cause astigmatism
- Worked on a method to compute the optical path length changes in COMSOL
-Created a COMSOL model for variation of temperature in two mass system.
-Used the above model for cryogenic conditions.
-checked it analytically.
- Tried to fix COMSOL error using the (ts) module, ended up emailing support as the issue is new in 4.3
- Managed to get a symmetric geometric distortion by fixing the x and y movements of the mirror to be zero (need to look for a better way to do this as this may be unphysical)
- Worked on getting the COMSOL data into SIS, need to look through the SIS specs to find out how we should be doing this (current method isn't working well)
-Created a COMSOL model for cryogenically shielded test mass with compensation plate.
-Analyzed the behavior of the model in different size configurations.
- Fixed the (ts) model, got strange results that indicate that the antisymmetric heating mode is much more prominent than previously thought
- Managed to get COMSOL data through matlab and into SIS
-Continued with the same cryogenic model created and varied the length of outer shield and studied the temperature variation inside.
-Compared the temperature difference given by COMSOL with manually calculated one.
- Realized that the strange deformations that we were seeing only occur on the face nearest the ring heater, and not on the face we are worried about (the HR face)
- Read papers by Morrison et al. and Kogelnik to get a better understanding of the mathematics and operations of the optical cavity modeled in SIS
- Read some of the SIS manual to better understand the program and the physics that it was using (COMSOL licenses were full)
-Derived formula for manual calculation of temperature due to total influx.
-Compared the results by COMSOL and by the formula.
- Plugged the output of the model with uniform heating into SIS using both modification of the radius of curvature, and direct importation of deflection data
- Generated a graph for asymmetric heating and did the same
- Aligned axes in model to better match with the axes in MATLAB and SIS so that the extrema in deflections lie along x and y (not yet implemented in the data below)
FP cavity modal analysis using cold optics parameters
ROC(ITM) = 1934, ROC(ETM) = 2245, Cavity lenggth = 3994.499999672, total Gouy = 2.7169491305278
Fval(ITM) = -4297.7777755379, OPL(ITM) = 0.13793083662307, Fval(ETM) = -4988.8888885557
waist size = 0.01203704073212, waist position from ITM = 1834.2198819617, Rayleigh range = 427.80682127602
Mode parameters of cavity fields
ETM AR (out base) : w = 0.0619634 R = 1548.276 z = 1519.925 z0 = 207.583 w0 = 0.008384783
- Verified that the SIS output does match satisfy the equations for Gaussian beam propagation
- Investigated how changing the amount of data points going into SIS changed the output, as well as how changes in the astigmatic heating effect the output
+ The results are very dependent on number of data points (similar order changes to changing the heating)
+ Holding the number of data points the same, more assymetric heating tends to lead to more power in the H(2,0) mode, and less in the H(0,2)
-Read about blue team design for maximum power budget.
-Read third generation talks to get a better understanding of the work.
- Did more modeling for different levels of heating and different mesh densities for the SIS input.
- Lots of orientation stuff
- Started on progress report.
- Attended a lot of meetings (Safety, LIGO Orientation)
- Finished draft of week 3 report (images attached)
-Attented LIGO orientation meeting and safety session.
-Prepared 3 week report
- Paper edits and more data generation for the paper (lower resolution grid data)
- Attended a talk on LIGO
-Updated 3 week progress report with new additions and deletions.
-Attended LIGO lecture which was very interesting and full of information.
- Discussed the further project with Dr. Brooks.
-Tried to derive formula for the test mass inside cryogenic shield(infinitely long shield from one side)
Plan for building the model
- Find the fields that would be incident on the beam splitter from each arm (This is done already)
- Propagate these through until they get to the OMC using the TELESCOPE function in SIS
- Combine the fields incident on the OMC in MATLAB and minimize the power to get the input field for the OMC (Most of this is done, just waiting to figure out what kind of format we need to use it as an SIS input)
- Model the OMC as an FP cavity in SIS
+ Need to think about how to align the cavity in a sensible way in SIS (need to find out more about how they actually do it)
- Pick off the fields from both ends of the OMC-FP cavity for analysis
- Add thermal effects to one of the arms and see how that changes the fields, specifically how the signal to noise ratio changes
- Finished the MatLab code that both combines two fields and simulates the adjustment of the beamsplitter to minimize the power out (with a small offset).
- Added the signal recycling telescope to the SIS code that generates the fields
To Do: Make the OMC cavity in SIS
-Discussed the project outline for next 6 weeks.
-made a write up for the tasks. (attached)
-Analyzed the variation of temperature of the test mass with input power for different lengths of the shield.
Made a COMSOL model that can include CO2 laser heating, self heating, and ring heating
Figured out how to run SIS out of a script and set up commands to run the two SIS stages of the model
These settings work to get a computer onto the TCS/ATF network.
Spelt out in a searchable fashion:
iface <portname> inet static
dns-nameservers 10.0.1.1 18.104.22.168 22.214.171.124
I've started a long-term measurement of the HWS fiber-launcher. I'm interested in seeing how stable the output is. The HWS is currently running in the following configuration:
The HWS is currently running at 57Hz. The HWS code is running on HWS (10.0.1.167). It is the same as the site code with some modifications to determine information about the Gaussian beam envelope. The following data is written to file on the HWS machine in files containing 10,000 cycles. Each cycle (or row) the following data is recorded:
These are saved to files on the HWS machine: ~/framearchive/C4/HWSlongterm/<GPSTIME>_CIT_HWS.txt
I noticed that the TCS lab temperature sensor batteries died. Apparently they died two days ago. I swapped in some new batteries this morning.
The data from the long-term measurement of the HWS is presented here. The beam envelope moves by, at most, about 0.3 pixels, or around 3.6 microns. The fiber-launcher is about 5" away from the HWS. Therefore, the motion corresponds to around 30 micro-radians (if it is a tilt). The beam displacement is around 4 microns.
The optical properties change very little over the full 38 days (about 2 micro-radians for tilt and around 2 micro-diopters for spherical power).
The glitches are from when the SLED drivers were turned off temporarily for other use (with the 2004nm laser).
I lent your fancy Newport TrueRMS Supermeter with the thermocouple plugs on the top to the SURF student Jordon. He has it in the cryo lab or the EE workshop with one of the PSL lab temperature probes.
Borrowed thorlabs power meter on 21 Sep 2017. It is on the south table of the ATF lab.
I replaced the dead 24" monitor on the work bench, which is connected to the video multiplexer. Mike Pedraza was kind enough to bring us us a new one and take away the old one.
Today I made the first characterization measurements of the mocked-up adaptive wavefront control system planned for the signal recycling mirrors.
Inside the light-tight enclosure on the center table, I've assembled and aligned a 10.2 micron CO2 projector which provides a heating beam of up to 150 mW incident on an SRM-like test optic. A co-aligned 633 nm probe beam and Hartmann wavefront sensor are used to measure the resulting thermal lens. I've written and installed new software on the machine hws (10.0.1.167) for viewing the wavefront distortion in real time, as shown in the below screenshot. This viewer is launched from the terminal via the command $stream_gradient_CIT
There is also a second utility program for displaying the raw Hartmann sensor CCD image in real time, which is useful for aligning the probe beam. It is launched by the terminal command $stream_intensity_CIT
Lens Formation Time Scale
First, I made a time-resolved measurement of the thermal lens formation on the test optic at maximum heating beam power (150 mW). The lens appears to reach steady-state after 30 s of heating. When the heating beam is turned off, the lens decays on a very similar time scale.
Lens Strength v. Incident Heating Power
Second, I measured the thermal lens strength as a function of incident heating beam power, which I measured via a power meter placed directly in front of the test optic. Below is the approximate maximum optical path difference induced at several heating beam powers.
The above optical path differences are approximate and were read-off from the live display. I recorded Hartmann sensor frame data during all of these measurements and will be analyzing it further.
I measured the reflectivity of a possible HWS replacement mirror at 532nm. Thorlabs BB2-EO3
Incident power = 1.28mW
Reflected power = 0.73mW
R = 56% at 45 degrees AOI.
I installed the Maku Gigabit CCD camera driver software on the hws-ws machine. The camera viewer can be opened from the terminal (from any directory) with the command
and there is also a shortcut icon on the desktop. The camera is ocurrently on the subnet at 10.0.1.157 and is configured to get its IP via DHCP. We can assign it a static IP if we'd like to keep it on the network permanently.
I left the camera mounted on the CO2 laser table. It's connected and ready to use.
There were known to be huge (65%) heating beam power losses on the SRM AWC table, somewhere between the CO2 laser and the test optic. Today I profiled the setup with a power meter, looking for the dominant source of losses. It turned out to be a 10" focusing lens which had the incorrect coating for 10.2 microns. I swapped this lens with a known ZnSe 10" FL lens (Laser Research Optics LX-15A0-Z-ET6.0) and confirmed the power transmittance to be >99%, as spec'd. There is now ~310 mW maximum reaching the test optic, meaning that the table losses are now only 10%.
Using a single-axis micrometer stage I also made an occlusion measurement of the heating beam radius just in front of the test optic. I moved the 10" focusing lens back three inches away from the test optic to slightly enlarge the beam size. In this position, I measure a beam radius of 3.5+/-0.25 mm at 1.5" in front of the test optic (the closest I can place the power meter). The test optic is approximately 20" from the 10" FL lens, so the beam has gone through its waist and is again expanding approaching the test optic. I believe that at the test optic, the beam is very close to 4 mm.
There is an SDK for the camera with compiled examples. For a really quick image grab from the command line, use the following:
This will produce a BMP image. We should probably recompile the C code to produce a 16-bit TIFF image.
Aidan found a C demo code for acquiring a single image from the Mako CCD camera and saving it to disk (SynchronousGrab -- aliased on tcs-ws as makoGrab). I wrapped that inside my realtime HWS beam profiler code to create a realtime beam profiler for the Mako camera. The interface is identical to that for the HWS.
The Mako camera is running on the tcs-ws machine (10.0.1.168) and is launched from the console via the command
It is currently configured to write a raw image to the local frame archive every 5 seconds (it prints the write location in the console), which can be disabled by setting the "-d" flag.
I fixed a bug in how the raw Mako CCD camera images are being read into memory. The bmp files turn out to have a block memory layout that broke my in-place reader.
I've added a softIoc to TCS-WS to capture the beam size from the MAKO camera. The IOC is run using ...
controls@tcs-ws:~$ softIoc -S EPICS_IOC/iocBoot/iocfirst/st.cmd &
The st.cmd contains the following text:
controls@tcs-ws:~$ more EPICS_IOC/iocBoot/iocfirst/st.cmd
The db file is:
controls@tcs-ws:~$ more EPICS_IOC/db/beamSize.db
These are also being written to frames on FB4.
See attached photo for how data is written to frames ...
For archive purposes, attached is a write-up of all the HWS measurements I've made to date for the SRM CO2 projector mock-up.