dV = 0.385V
Transimpedance = 1.5E4 V/A
therefore power= 0.385V / (1.5E4 * 0.65 V/W) = 40uW
Verified that the test-point for the current limit pot on the driver (Wavelength Electronics - LDTC 0520) was at 0.5V. Driver is set to INTERNAL set point at the moment. This is down about 10% below the current limited point.
Voltage across TP7 and TP9 = 0.970V = LD Current Mon
Voltage across TP2 and TP3 = 0.017V = LD P Mon
--- Hartmann sensor ---
-set the sampling rate on the CCD to 16HZ. With the current alignment and intensity this gives as maximum intensity of around 3850 out of 4095. Thus the pixels are not saturated.
- centroid_image located some of the spots - see attached image of spots where those located by the algorithm and circled. I need to play with the threshold level and spot_radius to get this to work properly.
8:10AM - I removed the base plate from the Hartmann sensor. I want to know what steady-state temperature the HWS achieves without the plate.
The photo below shows the current configuration.
11:22AM - (Digitizer - 52.2C, Sensor - 43.8C, Ambient - 21.8C)
I removed the cooling fins from the Hartmann sensor to see what steady-state temperature it reached without any passive cooling elements. I also dropped the set-point temperature for the lab to help keep for getting too hot.
After nearly 3 hours the temperature is:
(Digitizer: 54.3C, Sensor: 46.6C, Ambient: 19.6C)
I switched in just the base piece of the Hartmann sensor. The cooling fins are removed. I bolted the camera securely to the base plate and I bolted the plate securely to the table.
5:00PM - (Digitizer = 41.9C, Sensor = 33.8C, Ambient = 19.3C)
Back to Configuration 1 again - this time the fins were bolted very securely to the camera.
7:25 PM - [about 2 hours later] - Digitizer = 39.7C, Sensor = 31.4C, Ambient = 19.0C
Hour-long trend puts the lab temperature at 19.51C
I added some 0.004" thick indium sheet to the copper heat spreaders and and the heat sinks on the side of the HWS to try and improve the thermal contact. Once installed the steady state temperature of the sensor was the same as before. It's possible that the surface of the copper is even more uneven than 0.004".
The measurement from the on-board PD of the Superlum SLED seems to be falling. This effect started around 5PM last night which is right about the time we moved the position of the PD that the SLED is illuminating on the optical table (via optical fiber).
Curiously, the current set point and delivered current to the SLED are dropping as well.
Here's the data from the last 2 1/2 days of running the SLED. The decrease in photo-current measured by the on-board photo-detector is consistent with the decrease in the current set-point and the delivered current, but it is not clear why these should be changing.
Strictly speaking I should add some analysis that shows that delta_PD_voltage_measured = delta_I_set_measured * [delta_PD_voltage/delta_I_set (I_set)]_calculated ...
I've attached the Acceptance Test Report data from SUPERLUM for this SLED. I've also determined the expected percentage decrease in power/photo-current per mA drop in forward current.
The measured decrease in forward current over the last 2 1/2 days is around 1.4mA from around 111mA. The expected drop in power is thus (4.5% per mA)*(1.4mA) = 6.3%.
The drop in photo-current is around 37.5mA to 35mA = 2.5mA. The percentage drop is around 100*(2.5mA)/(36.3mA) = 6.9%.
Therefore, the drop in measured power is consistent with what we would expect given the decrease in forward current (which is consistent with the drop in the set point). Why the set-point is dropping is still a mystery.
I measured the AC and DC channel transfer functions of the eLIGO L1 TCSY ISS board for PD1 and PD2. The gain is quite high on the AC channels so I added +40dB of attenuation to the source from the SR785. As Frank pointed out, even though this isn't exactly +40dB at low frequencies, it still attenuates and that attenuation is common to both the input to the Channel 1 of the SR785 and the input to the ISS board.
The results are shown in the attached plot. I didn't bother including the phase, I'm just interested in the magnitude for calibration purposes.
The original data files from the SR785 are attached below:
The 200W Thermopile power head from Thorlabs arrive today. The scanned delivery note and calibration info are attached.
I reattached the Hartmann Sensor to the LENOVO machine that is running Ubuntu and turned it on (it's been disconnected for a couple of months). The /opt/EDTpdv/serial_cmd was able to communicate successfully with the camera.
Steve and I measured the current drawn by the Dalsa 1M60 by connecting it to the BK Precision 1735 lab power supply that display current and voltage supplied. We tried the camera at a variety of different voltages. The results are presented below:
Voltage Current(t<5s) Current(5s<t<10s) Current(t>10s)
12.7V 0.6A 0.8A 1.11A
15.0V 0.55A 0.69A 0.91A
18.0V 0.41A 0.57A 0.75A
20.0V 0.42A 0.52A 0.67A
Additionally, we tried running the other camera with the lab power supply. I varied the exposure mode and exposure time and checked the current drawn. The supplied voltage was 18.0V.
Exposure Mode 4: current = 0.67A
Exposure Mode 2: 58Hz, exposure time = 16 ms, current = 0.70A
Exposure Mode 2: 58Hz, exposure time = 16 ms, current = 0.70A
Exposure Mode 2: 58Hz, exposure time = 100 us, current = 0.72A
Exposure Mode 2: 58Hz, exposure time = 100 us, current = 0.72A
Exposure Mode 2: 1Hz, exposure time = 998 ms, current = 0.68A
Exposure Mode 2: 1Hz, exposure time = 16 us, gm 0, current = 0.69A
Exposure Mode 2: 1Hz, exposure time = 16 us, gm 2, current = 0.69A
This measurement was made with the Thorlabs DCC1545M-GL camera with an RG850 3mm long-pass filter over the CCD.
The beam radius (w) is 191 pixels, where the beam intensity = exp[-2 (x/w)^2 ]
The pixel size is 5.2um. Hence the beam size is 993.2um, which is basically near enough to 1mm radius.
9:40PM PDT - I've just restarted the long term measurement of the Hartmann sensor noise with the QFLD-950-3S.
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.
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.
I've started building the NFS server for the QIL cymac. It's sitting on the workbench in the TCS lab next to the rack. Please don't move it or any of the parts behind it.
Despite some considerable time spent, I was not able to get the Omega SCR controllers working. The first unit definitely arrived damaged. None of its LED indicator lights ever functioned, despite those on the second controller working fine under the same setup. I tried swapping in the second controller, but it has no voltage output and a red LED is illuminated which, according to the manual, means "malfunction on trigger board" or "open SCR." Either way, the remedy is to "consult factory."
Since we have get moving with data collection, I installed a simple variable transformer (borrowed from the 40m) which steps up/down the AC voltage from 0-120 V with the turn of a knob. I soldered the leads of one of the heaters to a standard power cable which plugs directly into the transformer. I have tested it and confirmed it to work.
I took images of the heat pattern projected on a piece of paper produced by the semi-circle reflector. I used 108V to drive current throught he heater. I tested the reflector without any coating and then with the dull and shiny sides of Al foil. I wasn't able to test the focal-point cut reflector because I had to glue a screw to it with epoxy which cures overnight. I will do these measurements tomorrow. Figure 2 shows the setup I used to get the data. The shiny side of Al foil is better at IR, so we will use that for the wavefront measurements.
We got 11 new semi-circle cut reflectors of radius ~3.6 cm. I glued a screw to the back of one reflector using the same epoxy as for the previous reflectors. Due to the bigger ROC of the reflector, a tight focus is achievable at greater distances (~15 cm).
I reduced the height of the Hartmann sensor box. This is what it looks like now:
See attached delivery note ...
30mm T-junctions, grounding straps and T-slot covers have arrived
I labelled and strung 8 of the 16 custom 40' BNC cables from L-Com between the HWS table and the BNC feed-through on the rack. Each cable is labelled HWS TABLE CHxx where 01<= xx <= 08. I'm going to leave the other 8 until we have room in the BNC feedthrough on the rack.
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.
Caltech Facilities has determined that the walls in the SE corner of the TCS Lab in West Bridge were water damaged during last weekend’s rain. They are going to remove the plaster from the walls and dehumidify the area for a week or so. All tables in the room are going to be covered with plastic for this process. In the short term I’ve shutdown all the equipment in the lab (including FB4). The 2-micron cavity-testing fabrication has been moved next door to the QIL.
I drew up one way we could set up the three available bake ovens in the TCS lab on the single oil pump.
If this looks feasible to others, we can move the ovens into the TCS lab. Duo and I will be occupied at KNI during Tuesday and Monday morning, so the usual lab cleanup time may not be the best. Perhaps Monday afternooon we can at least get the ovens out of the hallway and get one of them set up for baking.
My preference is to have tubes back towards the wall where possible. We might be able to drill a large diameter hole in the table top to accommodate them.
We have to get confirmation that the exhaust can be extracted - otherwise this whole thing is moot.
I have borrowed TCS's label maker in CTN for few days. If you need it, you can take it from the top of blue cabinets.
In anticipation of the point absorber SURF project, I cleaned up the server rack and installed a new workstation today.
The workstation replaces the old one, whose hard drive had failed, with a more powerful machine. The hostname (tcs-ws), IP address (10.0.1.168), user name (controls), and standard password (written in the secret place) are all the same as before.
I moved the control consol from its old spot in the back corner of the lab to the bench beside the rack. This is a more convenient location because the Hartmann sensor realtime GUIs can now be easily seen from the optical tables. I mounted the HWS machine in the rack as well and reconnected the video multiplexer to all the machines.
I tested the Hartmann sensor Python software and confirmed it to be working. It required a minor bug fix to the realtime gradient field GUI code. It seems that since this script was last run, the input data file type has switched from pickled numpy to HDF5.
Aidan and I continued the lab clean-up today. There's still more to do, but we did fully clear the large optical table which formerly housed the 50 W CO2 laser. I moved the optical enclosure over from the small table to serve as the area for the point absorber experiment. Inside it I mounted the Hartmann sensor and a 532 nm Thorlabs LED source. The LED still needs collimating/focusing optics to be installed.
The VGA signal outputted by the multiplexer is too weak to drive two monitors. This has required video cables to be manually switched back and forth between the monitor mounted above the laser table and the desktop console.
Today I solved this problem by installing an amplifying (active) VGA splitter on the video output of the multiplexer. One output of the amplifier goes to the desktop monitor and the other to the laser table. We can now monitor the HWS realtime GUIs directly above the optical setup, with no cable swapping.
Today, I set up a system consisting of the 520 nm laser, a 2'' mirror and two lenses of focal lengths f1 = 40 cm and f2 = 20 cm. The goal was to collimate the beam coming from the laser, so it goes parallel through the test optic at a radius of ~2.5 cm and then focus it to a radius of ~ 1.2 cm to fit the CCD dimensions of the HWS. The mirror was placed about 1 cm close to the laser and the first lens is setup at a distance~f1=40cm from the mirror. The test optic is placed between the two lenses and the second lens is placed about 10 cm from the CCD. The distance between the two lenses isn't important and could change in the future. The lenses and mirrors are all labeled.
I measured the approximate angle of divergence (0.06 rad) of the laser by taking the beam diameter at different positions along the propagation axis. This allowed for the ABCD matrix calculations to be finalized and the focal lengths of the lenses be chosen accordingly.
In order to have more space in the box, I removed everything that was not necessary to the side.
The previous 2-lens setup focused the beam to a tight spot, however due to the divergence angle of the laser beam, a significant amount of power was not being captured by the fiirst lens at a distance of 40 cm from the source. The divergence angle seems to be bigger than 0.06 by a factor of 2, so a f = 20 cm lens was used to collimate the beam and a f = 30 cm lens was used to focus it. A mirror was used to reflect the beam, so we obtain steering control. Additionally, the focusing lens was placed on a small 1-axis stage in order to control the distance of the lens from the CCD, providing control over the focused beam size.
Note: The 30 cm lens was cleaned with methanol, however it still has some residue on the surface. The beam imaged to the Harrtmann Sensor looks good, however the lens will be cleaned by using a different solvent or replaced by a different 30 cm lens. The 3 lenses at the edge of the box will stay inside in order to prevent contamination, however they will not be used in the design.
Since we set up the 2-lens system focusing the laser beam to the CCD, the next step was to mount the spherical reflector (31 mm wide) and the heater (~3 mm diameter). I used a small 3-axis stage to mount the heater, providing 3 degrees of freedom that would allow to manipulate the height of the heater, its position with respect to the reflector (left-right and in-out). The reflector was mounted in such a way that we can control its rotation angle, height and horizontal displacement. The current design is not quite sophisticated as it is just a first test, however I will look into different tools in the lab to see if I can use less mounts to get the same degrees of freedom.
The new heaters are supposed to be heated using AC. We used a DC power supply and ran ~30V through the wire, however only about ~50 mA of current was running through it. Jon will look into the specs of the new heaters to see if the power supply was the problem.
Yesterday, we were able to take some data using the 120 V DC power supply. The reflectors cut at the focal point and radius were both tested; the semi-circle cut proved to give a better focus, likely because roughly half the heat is lost using the focal-point reflectors. For upcoming tests, the semicircle reflectors will be used. We varied the surface shine by using the dull and reflective side of Al foil, as well as using the machined Al itself. The best result was given by using the more reflective side of Al foil.
Figure 1 shows the steady-state surface deformation profile detected by the HWS. The heaters don't have a uniform distribution along the wire, so more heat is radiated in the center of it, thus more of it is being focused to the center of the test optic. The data needs to be analyzed to determine the radius of the focus. Our rough estimate is about ~1.5 - 2 cm. We cannot collect any more data until we get a new power supply (AC 120 V).
Today, I came up with a new design for mounting the reflectors. I used a big 3-axis stage and a small 4-axis stage. This provides 5 degrees of freedom: 3 translational and 2 rotational, which is what we need for fine-tuning the focus and directing it at different angles incident to the test optic. The only problem with this design is that the 3-axis stage is too tall for the box, so the lid won't close.There is a smaller one available, but I have to figure out a way to increase its height, since the screw size is different from the ones on the pedestals available.
Additionally, Chub used metal-to-metal epoxy to glue a screw to the back of a reflector. I will wait until tomorrow to test it, because it is a slow acting epoxy. If it works, I have the necessary tools to do the same with the other reflectors. With the current deisgn the reflector wil be screwed in to where the round screw is in the stage. If it heats up a lot and affects the material of the stages, a small optical post (top of stage) will be used to make up for the absorbed heat.
Facilities came in on Friday and teed off a new duct to provide exhaust for the proposed new vacuum bake area in the TCS Lab. Photos are attached.
We installed a plastic sheet between the work area and the rest of the lab (the rest of the lab was overpressurized relative to the work area). Also, they use a vacuum when doing any drilling.
I cleaned up the HWS table in preparation for replacement with the 4x10 table. We still need to move the cabinet and get the enclosure out of the way.
The carpentry shop removed wet plaster sections from the wall following the flood (process was gentle scraping of wet plaster flakes, supervised by me). The wet section of wall needs a few days to dry and then they will plaster and paint it.
Does this work?
I've been looking to see what the time constant of the ring heater is. The attached plot shows the voltage measured by the photodiode in response to the heater turning on and off with a period of 30 minutes.
The time constant looks to be on the order of 600s.
I just replaced the brass Hartmann plate with the Invar one. The camera was off during the process but has been turned on again. The camera is now warming up again. I've manually set the temperature in the EPICS channels by looking at the on-board temperature via the serial communications.
I also made sure the front plate was secured tightly.
Here's a plot of the 15-day output of the SLED.
Currently there is an 980nm FC/APC fiber-optic patch-cord attached to the SLED. It occurred to me this morning that even though the patch cord is angle-cleaved, there may be some back-reflection than desired because the SLED output is 830nm (or thereabouts) while the patch cord is rated for 980nm.
I'm going to turn off the SLED until I get an 830nm patch-cord and try it then.
Correction: I removed the fiber-optic connector and put the plastic cap back on the SLED output. The mode over-lap (in terms of area) from the reflection off the cap with the output from the fiber is about 1 part in 1000. So even with 100% reflection, there is less than the 0.3% danger level coupled back into the fiber. The SLED is on again.