Excited all optics
Sun Dec 7 16:07:32 PST 2008
I think I solved the problem (as you can probably see).
The cause was that this WYSIWYG interface for HTML is provided by an independent text editor called FCKeditor which is included in the elog. Although the elog installer has a bug and does not unzip properly the relative package. One has to do it by hand. (going to /elog/scripts/ and unzipping fckeditor.zip by hand in the same directory).
As a reference. The elog runs on background in nodus.
To kill the process:
1) pkill -3 elogd
2) rm -f /var/run/elogd.pid
To restart it:
elogd -p 8080 -c /export/elog/elog-2.7.5/elogd.cfg -D
So, near 2 of the trashcans in the control room and underneath a desk there are hundrends of ants. Is this normal?
I have been getting ready for the annual safety inspection in the past 2-3 days.
Comparing PSL-FSS-RMTEMP and PEM-MC1-TEMPS
So, to compare temp channels, I made a plot of PSL-FSS_RMTEMP and PEM-MC1_TEMPS(the test temp sensor channel after converting from cts to degC). This plot begins about 2 months ago t_initial=911805130. The temperature channels look kinda similar but MC1-TEMPS (the temp sensor clamped to MC1,3 chamber) is consistently higher in temperature than FSS_RMTEMP. See compare_temperature_channels.png.
MC1-TEMPS isn't exactly consistent with FSS-RMTEMP. I attached a few plots where I've zoomed in on a few hours or a few days. See compare_temperature_channels_zoom1.pdf & compare_temperature_channels_zoom2.pdf
Change the room temperature, see what happens to the chamber temperature
A while ago, somebody was fiddling around with the room temperature. See compare_temperature_channels_zoom4.pdf. This is a plot of PEM-MC1_TEMPS and PSL-FSS_RMTEMP at t0=911805130. You can see the chamber heating up and cooling down in happy-capacitory-fashion. Although, the PSL-FSS_RMTEMP and the PEM-MC1_TEMPS don't really line up so well. Maybe, the air in the location of the MC1,3 chamber is just warmer than the air in the PSL or maybe there's an offset in my calibration equation.
Calibration equation for PEM-MC1-TEMPS
For the calibration (cts to degC) I used the following equation based on the data-sheet for the LM34 and some measurements of the circuit:
How does the chamber temperature compare with the air temperature?
It looks like the chamber may be warmer than the air around it sometimes.
I wanted to check the temperature of the air and compare it with the temperature the sensor had been measuring. So, at t=918855087 gps, I took the temp sensor off of the mc1-mc3 chamber and let it hang freely, close to the chamber but not touching anything. See compare_temperature_chamber_air.png. MC1_TEMPS increases in temperature when I am handling the temp-sensor and then cools down to below the chamber temperature, close to FSS_RMTEMP, indicating the air temperature was less than the chamber temperature.
When, I reattached temp sensor to the chamber at t=919011131 gps, the the temperature of the chamber was again higher than the temperature of the air. See compare_temperature_air2chamber.pdf.
Also, as one might expect, when the temp-sensor is clamped to the chamber, the temperature varies less, & when it's detached from the chamber, the temperature varies more. See compare_temperature_air_1day.pdf & compare_temperature_chamber_1day.pdf.
New temp-sensor power supply vs old temp-sensor power supply
The new temp-sensor is less noisy and seems to work OK. It's not completely consistent with PSL-FSS_RMTEMP, but neither was the old temp-sensor. And even the air just outside the chamber isn't the same temperature as the chamber. So, the channels shouldn't line up perfectly anyways.
I unplugged the 'old' temp-sensor power supply for a few hours and plugged in the 'new' one, which doesn't have a box but has some capacitors and and 2 more voltage regulators. The MC1_TEMPS channel became less noisy. See noisetime.png & noisefreq.pdf. For that time, the minute trend shows that with the old temp-sensor power supply the temp sensor varies +/-30cts and with the new power supply, it is more like +/-5cts (and Volt/16,384cts * 1degF/10mV --> apprx +/-0.03degF). So, it's less noisy.
I kept the new temp-sensor power supply plugged in for about 8 hours, checking if new temp sensor power supply worked ok. Compared it with PSL-FSS_RMTEMP after applying an approximate calibration equation. See ver2_mc1_rmtemp_8hr_appxcal.png.
Just for kicks
Measuring time constant of temp sensor when detached from chamber. At 918858981, I heated up the temp sensor on of the mc1-mc3 chamber with my hand. Took hand off sensor at 918859253 and let it cool down to the room temperature. See temperature_sensor_tau.pdf.
CES Mezzanine is beeing rebuilt to accommodate our new neighbor: the 20ft high water slide...& .jacuzzi
All our ac power transformers are up there. Yesterday we labelled the power switch of 480VAC on the mezz
that we need to keep to run the 3 cranes in the lab.
While waiting for the installation of the 32-bit Matlab 2009a to finish, I tried updating our seisBLRMS.m code.
Although DMF is in SVN, we forgot to check it out and so the directory where we have been doing our mods is not a working copy and our changes have not been captured: Shame.
We will probably have to wipe out the existing SVN trunk of DMF and re-import the directory after checking with Yoichi for SVN compliance.
Also wrote a script: LSC/x2mc, which will transition from regular ETM based X Arm locking to the MC2 based locking. It ran once OK, but I get a segfault on the 'trianglewave' which was trying to run the 'ezcastep' perl script which was calling 'ezcastep.bin'.
I also restarted the seisBLRMS.m on a terminal on Mafalda in the new Matlab 2009a to see if it loses its NDS connection like it did with 2007a. I also reduced the 'delay' parameter to 4 minutes and the 'interval' to 1 minute. This should be so that the total delay is now 5 minutes between seismic noise and seismic trend.
I don't know who left the X arm locked, but I just ran the Align Full IFO script, so everything is good in case Yoichi/someone comes in to lock the IFO this weekend.
It's crucial that I get a stable transmitted power to have an accurate measurement of the PRC transmissivity and thus of its macroscopic length.
I measured the scatter from the eLIGO beam dumps as best I could. The experiment setup is shown in the attached diagram.
After familiarizing myself with the equipment in the morning I noticed three issues with the setup
1 - around the minimum scatter the back scatter from the beam dump is very susceptible to the incident angle (makes sense since the Si plate inside the beam dump at Brewster's angle when there is minimum scatter).
2 - The mirrored plug (Part 20 in D0900095) which is suppose to be used for alignment is not very effective. It moves around too much in its hole in the front face of the beam dump. Just by touching it I could make the reflected beam jump around by about 0.1 radians.
- I think to align these properly we'll have to partly assemble the dumps. If we leave off the front plate of the horn then we can measure the reflection off the Si. If we measure this with a power meter then alignment becomes a simple matter of rotating until this reflection is minimized.
3. - For this measurement the incident beam was a small (~ 1mm diameter) central beam with a small amount of spray of laser light beyond that central region. This spray was hitting the aluminium front face of the beam dump and was scattering back to the photodiode. This was clearly the limiting factor in the measurement. Most of this light was spread horizontally so I placed a couple of pieces of black glass on either side of the aperture, just blocking the edges a little. This reduce the background reading at the minimum scatter from 17.0uV to around 4.5uV with still a little bit of light hitting the top and bottom of beam dump face.
The incident power on the beam dump fluctuated a little but was in the range 20.5 to 22mW. The response of the PD is approximately 0.2 A/W and the transimpedance is 7.5E4 V/A.
The SR830 Sensitivity was set to 1x1 mV.
It was difficult to measure the actual angle of incidence. The dump pivoted about a point directly under the input aperture at the front. By measuring the displacement of a point on the back of the dump as I rotated it and knowing the distance between this point and the pivot point I was able to make a reasonably accurate measurement of a range of angles about the minimum.
The measured scatter (in V measured directly by the PD and as a fraction of the incident power) is shown in the attached plots.
I think I can do a better job cleaning up the incident beam - so these numbers only represent an upper limit on the scatter.
attachment 1: beam dump assembly
attachment 2: experimental layout
attachment 3: scatter measurement
attachment 4: BRDF - (scatter divided by the solid angle = 1.1 m steradians)
attachment 5: (slightly blurred )photo of dump - overhead view
I've spent most of the last week doing background reading; fourier transforms, shm, e&m, and other physics that I didn't cover at school. I also read a few chapters in Saulson, especially the chapter on noise and shot noise. To get a better grip on what I'm going to be doing I read through the polarization chapter in Hobbs' "Optics" text, mostly on wave plates since that's a large part of this readout. Since then I've been working up to calculating the shot noise, starting with the electric field throughout the new interferometer readout.
I have created the attached EOM circuit with resonances at 11 MHz, 29.5 MHz, and 55 MHz (the magnitude and phase of the voltage across the EOM are shown in the attached plot). The gain is roughly the same for each resonant peak. Although I have managed to get the impedances at all of the resonant frequencies to equal each other, I am having more trouble getting the impedances to be 50 Ohms (they are currently all around 0.66 Ohms).
For the current circuit, initial calculations show that we will need around 4.7 - 14.2 A of current to drive the EOM at the desired voltage (8 - 24 V); this is much higher than the current rating of most of the available transformers (250 mA), but the necessary current will change as the impedance of the circuit is corrected, so this is probably not a cause for concern. For example, the necessary driving voltages for the current circuit are (2.8 - 8.5 V); if we assume that the 50-Ohm impedance will be purely resistive, then we get a current range of 56 - 170 mA.
I spent the last week working a lot with the differences between a basic Michelson readout and the new one as a displacement sensor. The new one (w/ wave plates) ends with two differently polarized beams and should have better sensitivity; I've also been going through noise/sensitivity calculations for each, although that hit a road block when I had to start the 1st SURF progress report, which has taken up most of my time since Saturday.
Since last week, I have come up with a new circuit, which is shown in the attached figure. The magnitude (solid) and phase (dashed) of the voltage across the EOM (red), the ratio between the voltage across the EOM and the voltage across the primary nodes of the transformer (blue), and the impedance through the primary port of the transformer (red) are also shown in an attached figure. As can be seen on the plot, resonance occurs at 11 MHz, 29.5 MHz, and 55 MHz, as specified. Also, at these resonant frequencies, the impedance is about 50 Ohms (34 dB). The gain between the voltage across the EOM and the voltage across the primary nodes of the transformer (or output of the crystal oscillator) is about 12 dB; we'd like a higher gain than this, but this gain is primarily governed by the ratio between the secondary and primary inductances in the transformer, and we are using the largest available ratio (on the Coilcraft website) that has the necessary bandwidth. Because of this, we will likely have to add another component between the crystal oscillator and the EOM circuit, to get the voltage to the desired 8.5 Vp across the EOM (for an optical modulation depth of 0.1 rad).
The current and power through the primary port of the tranformer are 43-85 mA and 25-92 mW, respectively. Since the transformer ratings are 250 mA and 1/4 W for current and power; these values should be safe to use with the intended transformer. Also, the highest power dissipated by a resistor in the circuit (not including the 50 Ohm resistor that is part of the crystal oscillator setup) is around 74 mW.
This week, I've been working on adapting the last week's circuit to make it buildable. Mostly this has involved picking components that are already in the lab, adding tunable components when necessary, and planning roughly how the components should be laid out on a board. I then built the circuit and put it in a box with BNC connectors for easy connection during testing. A picture of the built circuit is attached.
For initial testing, the transformer was removed from the design; since this changed the response of the circuit, I added two resistors to correct the response. A figure showing a schematic of the built circuit is attached. The expected responce of the circuit is also shown; the magnitude (solid) and phase (dashed) of the voltage across the EOM are shown in green, and the impedance of the circuit is shown in blue. While this response has sharp peaks and 50 Ohms (34 dB) of impedance at resonances, the gain is low compared to the circuit with the transformer. This means that, as is, this circuit cannot be used to drive the EOM; it is simply for testing purposes.
The last week I've spent mostly working on calculating shot noise and other sensitivities in three michelson sensor setups, the standard michelson, the "long range" michelson (with wave plates), and the proposed EUCLID setup. The goal is to show that there is some inherent advantage to the latter two setups as displacement sensors. This involved looking into polarization and optics a lot more, so I've been spending a lot of time on that also. For example, the displacement sensitivity/shot noise on the standard michelson is around 6:805*10^-17 m/rHz at L_=1*10^-7m, as shown in the graph.
Before heading back to the 40m to check on the computer situation, I thought I'd check the web screenshots page that Kakeru worked on, and it looks like none of the screens have been updated since June 1st. I don't know what the story is on that one, or how to fix it, but it'd be handy if it were fixed.
This week I've been working on testing the first version of the prototype circuit. Initially, I tested the circuit that I built last week, which had resistors in the place of the transformer. The magnitude and phase of the transfer function, as measured by the Agilent 4395A, are shown in the attached plot (first plot, MeasuredTransferFunction_R.jpg). The transfer function doesn't look like the simulated transfer function (second plot, BuiltCkt_ExpectedResponse.png), but I think I see the three peaks at least (although they're at the wrong frequencies). I spent some time trying to recreate the actual transfer function using LTSpice, and I think it's reasonable that the unexpected response could be created by extra inductance, resistance, capacitance and interaction between components.
When the transformer arrived yesterday, I replaced the resistors in the circuit with the transformer, and I have measured the following response (last plot, MeasuredTransferFunction.jpg). The gain is much lower than for the circuit with the resistors; however, I am still trying to track down loose connections, since the measured transfer function seems very sensitive to jiggled wires and connections.
Meanwhile, the parts for a flying-component prototype circuit have been ordered, and when they arrive, I'll build that to see if it works a little better.
I've spent most of the last week working on finishing up the UCSD calculations, comparing it to the EUCLID design, and thinking about getting started with a prototype and modelling in MATLAB. Attached is something on EUCLID/UCSD sensors.
Using FET probes, I was able to measure a transfer function that looks a little more like what I expected. There are only two peaks, but I think this can be explained by a short between the two capacitors (and two tunable capacitors) in the LC pairs, as shown (in red) in the circuit diagram attached. The measured transfer function (black), along with the simulated transfer functions with (red) and without (blue) the short are shown in the attached plot. The measured transfer function doesn't look exactly like the simulated transfer function with the short, but I think the difference can be explained by stray impedances.
Apparently I broke this when I added op540m to the webstatus page. It's fixed now.
I have built a version of the circuit with flying components; the completed circuit is shown in the attached picture. I built the circuit in segments and measured the transfer function after each segment to see whether it matched the LTSpice simulation after each step. The segments are shown in the circuit diagram.
After building the first segment, the measured transfer function looked pretty much the same as the simulated transfer function; it appears shifted in the attached plot, but this is because I didn't do a careful job of tuning at this point, and I'm relatively sure that I could have tuned it to match the simulation. After adding the second segment of the circuit, the measured and simulated transfer functions were similar in shape, but I was unable to increase the frequency of the peaks (through tuning) any more than what is shown in the plot (I could move the peaks so that their frequency was lower, but they are shown as high as they will go). When I added the final segment to complete the circuit, the measured and simulated transfer functions no longer had the same shape; two of the peaks were very close together and I was barely able to differentiate one from the other.
In order to understand what was happening, I tried making modifications to the LTSpice model to recreate the transfer function that was measured. I was able to create a transfer function that closely resembles the measured transfer function in both the circuit as of the 2nd segment and the completed circuit by adding extra inductance and capacitance as shown in red in the circuit diagram. The transfer functions simulated with these parasitic components are shown in red in both plots. While I was able to recreate the response of the circuit, the inductance and capacitance needed to do this were much larger than I would expect to occur naturally within the circuit (2.2uH, 12 pF). I'm not sure what's going on with this.
The last week I've started setting up the HeNe laser on the PSL table and doing some basic measurements (Beam waist, etc) with the beam scan, shown on the graph. Today I moved a few steering mirrors that steve showed me from at table on the NW corner to the PSL table. The goal setup is shown below, based on the UCSD setup. Also, I found something that confused me in the EUCLID setup, a pair of quarter wave plates in the arm of their interferometer, so I've been working out how they organized that to get the results that they did. I also finished calculating the shot noise levels in the basic and UCSD models, and those are also shown below (at 633nm, 4mw) where the two phase-shifted elements (green/red) are the UCSD outputs, in quadrature (the legend is difficult to read).
After speaking with Rana and realizing that it would be better to use smaller inductances in the flying-component circuit (and after a lot of tinkering with the original), I rebuilt the circuit, removing all of the resistors (to simplify it) and making the necessary inductance and capacitance changes. A picture of the circuit is attached, as is a circuit diagram.
A plot of the measured and simulated transfer functions is also attached; the general shape matches between the two, and the resonant frequencies are roughly correct (they should be 11, 29.5, and 55 MHz). The gain at the 55 MHz peak is lower than the other two peaks (I'd like them all to be roughly the same). I currently have no idea what the impedance is doing, but I'm certain it is not 50 Ohms at the resonant peaks, because there are no resistors in the circuit to correct the impedance. Next, I'll have to add the resistors and see what happens.
0. Probably, you are working on the SP table, not on the PSL table.
1. The profile measurement looks very nice.
2. You can simplify the optical layout if you consider the following issues
A. The matching lenses just after the laser:
You can make a collimated beam only with a single lens, instead of two.
Just put a lens of f0 with distance of f0 from the waist. (Just like Geometrical Optics to make a parallel-going beam.)
Or even you don't need any lens. In this case, whole optical setup should be smaller so that your beam
can be accomodated by the aperture of your optics. But that's adequately possible.
B. The steering mirrors after the laser:
If you have a well elevated beam from the table (3~4 inches), you can omit two steering mirrors.
If you have a laser beam whose tilte can not be corrected by the laser mount, you can add a mirror to fix it.
C. The steering mirrors in the arms:
You don't need the steering mirrors in the arms as all d.o.f. of the Michelson alignment can be adjusted
by the beamsplitter and the mirror at the reflected arm. Also The arm can be much shorter (5~6 inches?)
D. The lenses and the mirrors after the PBS:
You can put one of the lenses before the PBS, instead of two after the lens.
You can omit the mirror at the reflection side of the PBS as the PBS mount should have alignment adjustment.
The simpler, the faster and the easier to work with!
This is a quite nice measurement. Much better than the previous one.
1) For further steps, I think now you need to connect the real EOM at the end in order to incorporate
the capacitance and the loss (=resistance) of the EOM. Then you have to measure the input impedance
of the circuit. You can measure the impedance of the device at Wilson house.
(I can come with you in order to consult with Rich, if you like)
Before that you may be able to do a preparatory measurement which can be less precise than the Wilson one,
but still useful. You can measure the transfer function of the voltage across the input of this circuit,
and can convert it to the impedance. The calibration will be needed by connecting a 50Ohm resister
on the network analyzer.
2) I wonder why the model transfer function (TF) has slow phase changes at the resonance.
Is there any implicit resistances took into account in the model?
If the circuit model is formed only by reactive devices (Cs and Ls), the whole circuit has no place to dissipate (= no loss).
This means that the impedance goes infinity and zero, at the resonance and the anti-resonance, respectively.
This leads a sharp flip of the phase at these resonances and anti-resonances.
The real circuit has small losses everywhere. So, the slow phase change is reasonable.