Both the analyzer cavity and reference cavity are able to be locked, and were simultaneously locked for a while yesterday . However, the temperature control loop is not working because the computer is not seeing the temperature data, so it didn't stay locked . But now we know it's possible !
The mirrors, beam splitter, and photodetectors are set up and aligned to measure the beat of the two signals and I am currently working on mode matching to get the beams the same size at the photodetector.
FSS_RCTRANSPD and ACAV_TRANSPD have been calibrated:
FSS_RCTRANSPD = 1.98 mW/V
ACAV_TRANSPD = 2.18 mW/V
To measure the noise of the PSL VCO driver, we used the same PLL set-up from previous noise measurements. The PLL consisted of the following: IFR/Marconi 2023A, the SR560, Mini-Circuits Frequency Mixer ZX05-1MHW-S+-0.5-600MHz, Mini-Circuits 15542 BLP-5+ Low Pass Filter 50 Ohm DC-5MHz, and the Stanford Research Systems Model SR560- Low Noise Pre-amplifier with a gain of 200 V/V. We connected another VCO to the RF port of the mixer. The Marconi had a carrier frequency of 80 MHz, an RF level of 13 dBm and FM dev set to 1 KHz Ext. DC.
We connected the VCO to a power supply by hooking up a 9-pin dsub breakout box into the VME interface. The VCO driver needs 24V from the power supply. From opening up the box, we found that there are three test points in the VME interface: TP1, TP2 and TP3. TP1 corresponds to -24V, TP2 corresponds to +24V and TP3 is ground. Additionally, we needed to figure out what pins to hook up the positive, negative and ground cables onto the breakout box. +24 V corresponds to pins 9 and 4, -24 V corresponds to pin 5 and ground corresponds to pins 8 and 3. There are also two switches that need to be connected to the ground in order for the driver to function properly. The test switch, which corresponds to pin 1 and the wide switch, which corresponds to pin 6 are both connected to pin 3(ground). We used the TENMA Laboratory DC Power Supply 72-2080 and it was set to 24 V and .5 A.
After locking the frequencies, we measured the transfer function and ASD with an FFT analyzer (Agilent 35670A Dynamic Signal Analyzer). The following data was obtained:
As per the request from LLO, the PSL VCO was sent to the site.
They had malfunctioning of the circuit and had no spare.
We have to figure out how we continue the work.
due to the crash temperature of ACAV is 48 Celsius and RCAV 36 Celsius.
all channels are working now
rebooted the PSL crate to see if it fixes the problem with some of the channels inaccessible from external computers
We don't have a full image of either acromag1 or ws3 in the PSL lab. This could be a problem if we have a drive failer.
I'd like to rebuild acromag1 at some stage using something newer than Ubuntu 12.01, but first we need backups.
In a tmux session on acromag1, I ran
sudo dd if=/dev/sda bs=64K | bzip2 > /mnt/external/acromag1Image.bz2
This should clone the whole drive into a compressed image but its going to take a while. To restore expect to run
bzcat /media/usb/acromag1Image.bz2 | dd of=/dev/sda
bzcat /media/usb/acromag1Image.bz2 | dd of=/dev/sda
Will check tomorrow to see if successful.
Clone of acromag1 was successful:
It hasn't reported any errors, not sure how to check the integrity.
I am backing up ws3 now.
Ran a backup of ws3, the computer used for medm interfaces in the lab, it completed successfully:
controls@ws3:/media/controls/CTNLABBAK$ sudo dd if=/dev/sda bs=64K | bzip2 > /media/controls/CTNLABBAK/ws3Image.bz2
3815602+1 records in
3815602+1 records out
250059350016 bytes (250 GB) copied, 38551.7 s, 6.5 MB/s
The external drive is in the hard drives draw in the blue cabinet.
The layout for the new PSL setup ( lenses, and their positions are to be calculated.)
A Lightwave 100mW NPRO laser will be the source. AOM will be in the ACav path.
Two cavities will be covered by a box of insulation/ heater.
1) From the laser to the PMC,
1/4 waveplate, to linearly polarize the elliptical polarized beam from NPRO
1/2 wave plates and PBS, to adj the power of the beam
lens, to focus the beam to the EOM
two lens, two mirrors, to mode match the beam to the PMC
a photodiode, a lens, two mirrors, (one for steering the beam, another one for attenuating the beam), for PDH locking
a photodiode and a ccd camera, for the beam behind the PMC
* there will be a Faraday Isolator somewhere here. I forgot to add it.
2) From PMC to PBS
a lens to focus the beam to 35.5 Mhz EOM
1/2 wave plate, to adjust the power between two beams for ACav and RefCav
PBS, to split the beam into two paths
3) AOM path
1 PBS, for reflected beam from the AOM
a lens, an AOM, 1/4 waveplate, two irises, 1 curve mirror; to double pass the beam and shift the frequency
another iris and a mirror, to select only the 1st order beam and send it to ACav.
4) RefCav/ACav path
1/2 wave plate, to correct the polatization
two lens and a set of periscope, to mode match the beam to the cavity
a pbs with 1/4 wave plate, a lens, a mirror, a photodiode, to PDH lock the beam
5) Transmitted beam
1/4 waveplate, to linearly polarize the transmitted beam
a photodiode/ a ccd camera to monitor the transmitted beam with necessary mirrors
lenses, to focus the beam to the PD that measures the beat signal
a beam splitter, to mix two beams together
This is the schematic for PSL setup.
At this point, Pre Mode Cleaner (PMC) and Reference Cavity (RefCav) are locked. The rest will be locking Analyzer Cavity (ACav) and setting up for beat noise measurement.
ACav's beam path will have double pass AOM [Crystaltech 3080 194]. We'll use +1st order beam. When hook up the VCO, make sure that the power is on only when the VCO and the AOM are connected, otherwise the VCO dies.
Next is aligning the AOM. A good alignment will maximize the power of the +1st order beam. The beam should get close to the AOM's transducer as much as possible to minimize time delay.
The beam at the AOM will be focused to 75 um.
The mirror that reflects the beam back to the AOM is a 0.3m concave mirror, which will be placed 0.3 m away from the AOM. The reflected beam should completely overlap on itself. This will neutralize
the pointing instability when the modulating frequency shifts.
Then we can align ACav, this time I'll try not to remove the PMC when I scan the beam frequency (at~3-10Hz.) If the PMC cannot catch up with the laser, increase the gain of the PMC, sideband power.
ACav should be locked before Monday June 8.
removed the PTFE parts for mounting the copper shields from the baking oven.
Now baking the Nichrome wire wrapped onto one of the aluminum radiation shields from the cryo experiment.
I took some TF measurements, but I'm not sure if I used the right method to do this. All the resutls look essentially the same, so maybe I'm just measuring instrument noise and nothing else. Regardless, I' posting the results.
For both measurements, I sent the source signal, first directly to PZT or EOM and second with a 50 Ohm termination in parallel. In case of EOM, I also did another measurement with low power to see if I can uncover any saturation effects my high powered source might be causing.
The output of two photodiodes, Thorlabs PDA10CS at (110,44) at dumped end of a PBS before PMC and at (64,28) at dumbed end of INput PBS of Faraday Isolator after PMC was measured and I took DC level of the outputs averaged over 10 s right after taking TF measurement. This was divided by the measured TF to get units of 1/V i.e. from PZT/EOM to RIN.
The parameter configuration files for the measurements are in the data directory.
What might have gone wrong:
I suspect that maybe AG4395A is unable to drive the capacitive load of PZT and EOM after a certain frequency. I need to find a better way to actuate the PZT and EOM in a known fashion, possibly through the FSS box or some buffer driver.
In the case of EOM, I'm also uncertain if the amplitude of actuation would be enough to do anything whatsover. Maybe the transfer function needs to be taken with high voltage driver.
Any comments on my measurement techniques are welcome as I'm surely not doing this right.
Rana's question about PMC:
I concluded that PMC is causing the 433 kHz peak because the only time I do not see it in CTN/:2502 is behind PMC when FSS is OFF. I couldn't think of a way to check if PMC Servo is causing it on its own. Can I do that without closing the loop somehow?
Edited on Mon Dec 23 15:21:50 2019 .
Yesterday I spent awhile reading literature, then met with Rana and Tara. Rana wanted us to produce a sketch of the physical layout of our ECDL and generate some graphs comparing different parameters (diodes, gratings, cavity lengths) so we could determine exactly what parameters we'd need to order parts. Last night I made the plots in Mathematica (BAD). This morning I did the sketch of the mechanical layout of the ECDL. Will make a nicer sketch with the changes made today and post here this weekend.
I calculated a few values: the grating should be placed at an angle of 39.7 degrees in order for the first order diffraction go back into the cavity. I checked the tuning range, and concluded for a frequency change of 100 MHz - 4 GHz, we will see a change of output beam angle on the order of microradians. This means we will not need a mirror to make sure the output beam is directed correctly for frequency changes.
Tara and I met with Rana again. I got mocked excessively for using Mathematica, and will remake all the plots in Matlab this weekend. We decided on some parts to order, which are listed at the end of this entry. Other things to do:
Parts to order (bolded):
Today, I spent the day working on the first progress report for SURF, which Tara would like by Wednesday. I have everything complete except a nice figure of the planned experimental setup, which I will do tomorrow.
I also emailed Dmass about getting a current driver from the Cryo lab that we can modify and use.
I've also been corresponding with the companies that sell the laser diodes. It seems like neither can guarantee exactly 1064 nm wavelength, nor does either offer any way to preselect a diode. However, we should be able to tune the wavelength using temperature, since both diodes change at 0.3 nm/degree C. Tara is placing an order for several of the items today.
Today, the last of the parts we've decided on were ordered.
Dmass said they do not have any extra current drivers, nor does Eric Gustafson. Eric said that if we can find a commercial board, I can ask Alex Cole (one of his SURF students) to show me how to put the commercial board into a standard LIGO module. Not sure if we'll do this or not.
I spent the day finishing up my first progress report for SURF and uploaded it to the ECDL folder on the 40m SVN. Tara wants to look at this before I submit it next week.
I've also started reading about how to measure the frequency noise, so I can start planning for making measurements when the laser diode arrives.
Today I made some edits to my progress report for SURF, mainly with the graphs in Matlab. I tried to make them look better. The updated version is on the SVN.
I spent the rest of the day reading papers about how to measure frequency noise and some basics on the Peltier effect so I could understand how the TEC will work. I'm going to start figuring out the wiring and stuff so that we will be prepared when the parts arrive.
I made more edits to my SURF progress report. I need to remember to make good looking graphs in Matlab without being reminded by Tara. I just submitted the pdf of the final version. It is also on the SVN in the ECDL documents folder.
I spent more time trying to understand the difference between heterodyne and homodyne detection, and trying to figure out which method I would want to use for my ECDL measurements. My understanding is that homodyne detection involves superimposing the output beam with a modified version of itself, and measuring the beat frequency spectrum. Heterodyne detection involves superimposing the ECDL signal with a reference signal and measuring the beat frequency spectrum. I believe we will be using heterodyne detection because we have a very good reference laser at 1064 nm and this saves the trouble of having to modify the output beam. However, the literature has not been super descriptive for a beginner, and the exact mechanism of making this happen still confuses me. I will continue looking into this.
I also spent some time figuring out how we will wire the TEC and TEC controller. It seems fairly straightforward. See http://www.thorlabs.com/Thorcat/15900/TED200C-Manual.pdf, page 13. This explains how we will wire things. We will use an LED that can signal to us when the TEC element is on. I still need to figure out the thermistor we will use as a temperature sensor...
For future reference, the 2 parts that Tara ordered are:
Double checked the distance between the mirrors using the new periscope base Tara designed. Distance is 2.96in according to the 3D assembly, close enough to the 3" we want. CAD files are on the svn in the mechanical drawings folder.
Andrew and Craig
We took some quick TFs of the phase delay box (Model: DB64 - RG58A/U Coax Delay Box), it's literally just filled with a bunch of coax cables.)
We get at worst 7% loss at 30 MHz for 32 ns delay.
Edit (awade Sun Mar 26 20:15:26 2017) -- added actual model number for searchablity.
I'm currently working on measuring the phase noise of the Marconis at 80 MHz - I will be moving on to 160 MHz soon. I'm also working on learning how to make the computer do what I want it to, but I should be done with the measurements and post graphs later today. Then depending how long the measurements take today, I'll start measuring our Marconi and then move on to the VCO tomorrow and should be able to modify the VCO by Friday. One of the main things that's slowing me down is getting comfortable with processing the data on the computer.
Also, I've been having problems getting the Marconis to lock at any feedback gain below 2000. I've been using that to stay consistent and get a good lock between the two, because with lower gain there was always a sneaky little sine wave making it through the feedback loop and into the locked signal. I've accounted for this in the calibrations I've been making, with a UGF of around 1000 Hz.
The Phase Detector method was used to measure the phase noise of the 21.5 MHz Sine Wave generated by the RIGOL Waveform Function Generator. Noise measurements were taken using the SR785 across frequencies spanning 0.25 Hz to 102.4 kHz.
Great, it looks like you've got your setup working.
A few things about eloging, though. More information is almost always better. It would be good to add a bit more about your setup so that people know what you actually did and so you can repeat it if you come back in the future to look at your posts.
Maybe you can add another post with a schematic of your experiment labeled with part numbers, frequencies, power levels etc: everything somebody else would need if they were to do the build they same setup. Elog also has the ability to include latex markup which is handy for posting a few key equations. For example, there are a few Rigol function generators, I find it helpful in the elogs I make to explicitly include part numbers and also hyperlink those labels to the website/datasheet of those components. You want to actually explain what you did in some detail; some people use dot points, others write full sentences and paragraphs. The main thing is you include lots of context and useful information about what happened.
With the plot, it looks ok, but you want to increase the font sizes and include units on the y-axis. I'm not really sure what measurement you made was. It says its a transfer function but it should be in units that make sense like rad/sqrtHz or Hz/sqrtHz. Craig is good at making plots in python maybe have a chat to him about how to make nice plots.
I used the data for the phase noise of the marconis to calculate the individual phase noise of each marconi. The noise of the three are roughly the same. The noise increases with frequency and input range, with the maximum variation in our measurements about 1 order of magnitude. This shows the noise is fairly consistent, but does change with different frequencies used and different input ranges.
We also have some data for the phase noise of the VCO compared with Marconi 2 (with the feedback going to the Marconi). The VCO is currently much noisier than the Marconis, so hopefully we can reduce the noise by modifying the current VCO.
We used swept sine to find the gain of the feedback loop, with a UGF of roughly 2.8 KHz with a gain of 1. With a gain of 100, the UGF is roughly 280 kHz and a peak to peak voltage when unlocked of 438mV.
The gain (for calibration) with the poles and zeroes can be calculated as:
where 4/216 is the resolution of the ADC, pi/Vp-p gives the number of radians per volt, 1000 is the amplification of the signal into the ADC, 0.03 is the first zero (to compensate for the amplifier, which diminishes the signal below 0.03 Hz), and the UGF is the other zero. Multiplication by the zeros ensures the signal above the zeros will not be affected by the transfer function.
As a note - when the signals are calibrated in the DTT, the calibrated data can be saved by exporting the trace, not the signal itself, by exporting win0_pad0_trace1 or whichever trace it is saved under. This removes a need to calibrate the original data outside the DTT.
[ED by KA, catalogs should not be put on ELOG. This is public.]
Did we just miss this all along?
C30642 has a bandwidth of 20 MHz only. That means at 36 MHz and 37 MHz, the RF output would be -8.1 dB (0.3933) and -8.3 dB (0.3827) lesser than expected or maybe worse. However, this bandwidth is mentioned for load resistance of 50 Ohms, so I need to go into more details. But definitely will have to look into this.
Maybe we need to replace these with faster photodiodes. Do we have any of C30619 or C30641 in stock?
(NO - this is a incorrect interpretation of bandwidth in this case)
There is no problem. It is just a matter of noise requirement.
How much shotnoise intercept current do you require?
At the 40m, the 33MHz PD has the shotnoise intercept current of 0.52mA. https://wiki-40m.ligo.caltech.edu/Electronics/RFPD/REFL33
Is that enough? How much is yours?
You should be able to realize the similar value because the technology used for your resonant PD is the same as the 40m one, I suppose.
If you require super low noise like uA (=sub pA/rtHz current noise), then we will need a high gain and low junction capacitance.
Yeah, I realized I understood the mentioned bandwidth wrongly. It is mentioned for a direct 50 Ohm load while we load our photodiode with a different resonant circuit.
I haven't made actual measurements for the shot noise intercept current similar to the link, but I made a ltspice simulation of the circuit and I believe the shot noise intercept current is about 0.15 mA. Yes we are good with that. This topic should close here. False Alarm.
Hey, so I readjusted the resonant frequency of the photodiode so that resonance would be at ~35.5MHz frequency. Here is the photodiode circuit: . I chose L2 to be 100uH. Here is the optical transfer function:
Here is the Jenny Laser setup to measure the optical transfer function:
The power coming into the photodiode is 0.41mW. I recalculated the theoretical voltage that we are supposed to get from the quantum efficiency to be 12.1mV. I measured 7.09mV. I calculated the quantum efficiency from the equation QE= responsivity *hc/(lambda*e). From there, I multiplied power by QE to get the photocurrent. The voltage coming into the first detector would just be V=I*R, where R is 20 ohms. The next amplifier multiplies the voltage by about 1.9.
One problem that I know of is that the spot size of the laser hitting the photodiode isn't the smallest it could be. The spot size hitting the diode could be smaller if I moved the photodiode back. However, I ran into problems trying to do this. After I positioned the photodiode to the point where the spot size was smallest, the beam ended up clipping off the lens whenever I tried to readjust the reflector. It took me forever to adjust the Jenny laser so that the beam was collimated and the laser hit decent parts of the 50/50 beam splitter and reflector. So I think in the near future, I will try to raise the lens by some amount so it doesn't clip.
I took the transfer function of the photodiode () from the test input to rf out and found that the resonance and notch where at the same frequency and that the biggest difference is in the gain. Thus, I conclude that it is safe to use the test input to assist someone in readjusting the notch and resonance.
We also want to adjust the dc output gain so that a photocurrent of 5mA will produce 10V at DC output. Before the buffer amplifier, the 5mA produces a voltage of 0.1V. So we would like the last amplifier to amplify this voltage by 100. Since it is a non-inverting amplifier, we would like that R16/R11=99. However, I can't think of a combination of resistors in our possession that will produce this. I therefore chose R11=10ohms and R16=1kohms.The board has been modified accordingly.
This is sort of OK, but check out the 40m elog for the right way to characterize RFPDs. You really need more resolution to resolve the notch and the y-axis should be in units of Ohms.
Also, the test input is a fine rough guide, but its not accurate to get the high frequency characteristics right or the 2f notch with any accuracy.
Redesigned D1400384-v2 is ready and uploaded on dcc. PCB Layout, circuit schematic, Gerber files, LISO analysis, front panel and full BOM are attached.
The circuit is kept the same except for replacing LT1128 with OPA827 in the transimpedance amplifier stages and adding few OMIT and ZERO resistances to have more options for using the circuit. Following are the notes (also present as ReadMe.txt in the .zip file in dcc):
1) To not have whitening option, do not populate IC5, U8, U9 and their peripheral resistors and capacitors and put a 0 Ohm resistor (Jumper) at R20 and R26
2) To have fixed transimpedance, do not populate IC8 and its peripheral resistors and capacitors and populate R7 and R22 with the desired transimpedance.
3) In case of switchable transimpedance, R11=R15=100 and R14=R28=10k are the two options in present design. These can also be changed according to choice. Mark the front panel accordingly with the choices.
4) For low transimpedances, it is better to replace U5 and U7 with LT1128 instead.
Currently, I am working on modifying a photodiode so that will be used to lock the laser to the reference cavity. We want to modify it so that it resonates at 35.5MHz and so that it is optimized for a low powered laser (~100microWatts). Here is the schematic for the photodiode circuit.
Using LISO, I modeled the RF part of the circuit using the values they suggested in the table to make it resonant at 35.5MHz. Here is the file that I used to plot the RF part
And here is the obtained transfer function.
Frank is unsatisfied with the resonance at 35.5 MHz.
We then try to optimize the circuit for a smaller laser power. We want to adjust the resistors connected to U1 to change the gain at that stage. I plotted on LISO the transfer function of that single op amp for various amplifications to see if 35.5MHz would fall in the nonlinear region of the op amp if we increased the gain.
I found that we can't really increase the gain much without it becoming nonlinear. Frank said it wasn't worth trying.
I plan to adjust the DC path for low power on Monday.
So the plan is to test the functionality of the PD at it's current state, which is to resonate at 54MHz. Once we determine that the PD is working properly, we will adjust it to resonate at 35.5MHz, and see how else we can optimize it from there.
Today, we just did a smoke test of the PD and everything seems ok so far.
P.S. I soldered for the first time today. I made my first cable today, and it only took my an entire afternoon! :p
Today I learned how to solder an inductor onto a board.
We measured the transfer function of the photodiode board from the test input to the RF output. I changed parts on the board to have resonance at 35.5 MHz and a notch at 71 MHz. We changed L2 to 330nH and and L8 to 330nH. Frank also changed parts on the board, but I'm not exactly sure what he did.
Here is the schematic of the board along with the recommended values for a 35.5MHz resonant frequency.
Even when we changed L2 to 330nH instead of the recommended 81nH, resonance is at around 40MHz. However, the response still looks good and we do indeed see a notch and a resonance. Frank suspects that there is something wrong with the capacitance of the photodiode (might be broken)
Today I spent the whole day wondering why I obtained a bad optical transfer function from the photodiode. It turned out that the power supply to the reference diode in the Jenny laser setup was unplugged. Seriously, a certain person told me that the power supply to the reference was already setup, and another certain person told me that the power supply looked like it was on when I asked for help. I was also getting a readout from the DC output. I still don't understand why I got a DC readout if the power supply was turned off!
Frank also replaced the photodiode in the circuit (perhaps unnecessarily).
The transfer function seems to look good. The notch frequency is at 71.5MHz, which is where we want it to be. I need to modify the board so that the resonance is at 35.5MHz. Currently it is around 11MHz.
I also need to double check my calculations for the quantum efficiency with Frank. We both suspect that the dc voltage out is too low given the responsivity and the measured input power of 0.39mW
Tomorrow, I plan on finishing modifying the photodiode board to be resonant at 35.5MHz and to optimize the dc output for a low powered laser. I also plan on modifying the summing box.
We need to figure out GPIB for the HP8560E so we can directly get data off of there. In the meantime here is a picture of our transmission beatnote and the messy spectrum around it.
The Caltech plumbing shop called to say they will have all the parts they need to start work Friday morning. There is a bit of masonary work to be done to the down pipe hole. So there will be some dust.
I have ordered materials from McMaster for wrapping the experiment up again. I got extra so we will have a cling-wrap-kit® for the WB labs ready to go in the future. I didn't get a tracking recipt, but the order went through around COB on the 26th. Should be here today or tomorrow.
I called facilities. They say with their new purchase approval process, and lead time on parts, that they expect the repair jobs on piping would start early next week.
There will be a bit of manual alterations to the through hole coming down into the ceiling so we need to do some dust mitigation. I will order some more cling wrap and salvage some of the plastic sheeting from the last episode.
The lab is all wrapped up and ready to go. I'm trying to get in contact with plumbing to see if we can move the job forward to Thursday.
Edit awade Wed Feb 28 14:58:12 2018: Got throught o Raymond at ext 1252, the job is locked in for Friday morning and can't be moved forward. Hopefully we can get to cleaning the lab by Friday afternoon and reboot for the weekend.
In line with what we already started we decided:
1. Build the North and South optical paths by July 17th (12:59pm) (Antonio North path for now, Andi South path)
2. Week of July 18th beat noise measurements with what we have;
A summary with a slight different timing (written before the meeting) is in the following PDF (sorry for the weird layout)
I listed some issues for FSS experiment that we should discuss within this week and other small details.
1) heater/insulation for the cavities, If we don't want to actively control the temperature, insulation inside the chamber might not be necessary.
2) the appropriate AOM type, and
3) Local oscillator for beat measurement
As Koji suggested, I list out the plans which will be implemented in the setup and why do we want it. Comments and suggestions are very welcome.
The target is to measure the coating thermal noise from the beat signal to get
keeping both cavities in the same chamber will reduce the drift of the beat frequency. The design for the stack will be done and submitted to the machine shop before this Friday by Frank.
Since both cavities do not have the exact same length, we need to be able to heat the cavity individually to obtain the required beat frequency (~10kHz). The heater will operate at DC level with no feedback control, so the noise from heater should be small. The stack, heater, and shield should be ready in 2 weeks. Once we have them we will just clean them without baking, since we are not worrying about residual gas.
The periscope still has high Q resonance, we might need to think about damping it.
We want RFPDs for lower power (1mW or less). Raphael is still working on it.
The current RFPD is 120 MHz, so the area of the PD is very small. The beam has to be collimated down to ~100 um (the diameter of 1811 is 0.3 mm). The small spot size might cause extra scattering noise in the detection. So if we can reduce the beat frequency to ~ 10kHz, the beat RFPD can be a bit larger and scattering light may be lower.
The RF summing box is for adding 35.5 MHz signal and high voltage feedback from the servo to the broadband EOM. It's not completely fixed yet (the ideal goal is to have resonant frequency at 35.5 MHz with 50 ohms impedance). Once we fix this, we can check if the loop performance is getting better or not.
Once the RF summing box is fixed, we can measure the TF again. The measured bandwidth of the new TTFSS is about 200kHz, but we expect ~500kHz. We want to make sure that it works as designed and have enough gain. The current gain that we measured might be too low to suppress NPRO noise below thermal noise.
For test, we will use the previous FSS for RCAV (from iLIGO). The gain for this servo just has to be large enough to suppress VCO noise. If we need a better servo, we can switch to the UPDH 2.0.
I have to minimize the RFAM from EOM, but it will be a common mode effect. I have to think about what noise level it will show up in the beat detection if the two cavities are not exactly identical.
Time line(week start with)
Aug 1 : submit design for seismic stack/thermal insulation (M1,M2), optimize the setup for RCAV loop (O1, O4), order periscope (M3)
Aug 8 : Fix RF summing box ( E3), determine TTFSS loop performance (E4) (2011/08/09), if we are lucky, we can test the modified 35.5 MHz RFPD as well (E1)
Aug 15 : Start install ACAV optics (O2), finish lay out for beat (O3)
Aug 22 : Have seismic stack ready and put two cavity in the same chamber. work on ACAV servo (E5) ( Do and pass candidacy exam)
Aug 29: install beat setup (O5), Try to get beat signal & configuration, try new beat RFPD (E2).
Sep 5: If we are lucky, we should see beat signal by the end of this week
Sep 12: done with poster. for Sep LVC meeting.
The plan of action has been moved to a new wiki page for better documentation.
We have come to the conclusion that to properly tune PID, we need to accurately model a physical system that represents the cavity thermodynamics and use it to tune PID coefficients. For this, we need good temperature sensors on the cavity (not present right now) and better heat actuation with known control. Awade also mentioned that we have new gold plated heat shields ready to be installed. So we have decided to replace the heat shield and install new temperature sensors as well. Following is the plan of action for the same:
Hopefully, by the end of this work, we get better stability on beatnote frequency locking to get good spectrum reading at higher resolution from Marconi.
Overview schematics of thermal controls' elements and of control loops. These are the basic elements and some numbers.
2010-12-19 (Sunday UTC, Saturday/Sunday PT)
I am only going to point out a few differences or similarities to the previous day. The next plots that I intend to post are long-term (weekly, or monthly) plots. If people want to look at daily plots, then they can ask me. I have them on my PC.
The hour-lines plot seems to tell us that there is more going on than the day before, but remember that it is plotted with a different normalization. It is much quieter in fact. Still, as on the previous day, the real action can only be seen in the horizontals. It is almost exclusively underground luxury to observe horizontals that are as weak as the vertical.
Quiet-time and total-time spectra are more similar than on the previous day. What I find noteworthy is that the H/V ratios haven't changed much.
Weekend histograms are even more stationary (not surprisingly).
There is again this peculiar near-10Hz feature that goes away during night (although it stays in the horizontal...).
I was a little suprised to see particle trajectories to be very similar to the ones on the previous day. I always thought of surface seismicity of something that must vary strongly in terms of seismic sources.
quickplot.py makes quick plots of data from desired channels. See: https://github.com/shufay/LIGO-plots.
On ws1 cd to ~/Git/LIGO-plots. In Ipython: %run quickplot.py <channel 1> <channel 2> ... <(optional) gpsLength> < (optional) gpsStop>
%run quickplot.py <channel 1> <channel 2> ... <(optional) gpsLength> < (optional) gpsStop>
To see usage: %run quickplot.py usage
%run quickplot.py usage
<channel 1> <channel 2> ... Channels that you want to make plots of
<channel 1> <channel 2> ...
<gpsLength> Length of time to fetch data. Default is 3600s.
<gpsStop> GPS time to fetch data until. Default is now. So the default parameters would fetch data from (now-3600, now).
Pointing into both cavities has been recovered.
I could not get the PMC on the south path to lock, so I have just taken it out for now. Then I resteered through the BB EOM and resonant EOM and into the south cavity.
The north path did not require much resteering. North seems to lock OK, although I have not checked the health of the PDH loop. On south we need to install an HV supply before locking.
I temporarily removed the QWP immediately before the periscope. Then I added a HWP directly in front of the vacuum chamber window.
While sweeping the laser across the south TEM00 resonances, I monitored the peak voltage of each resonance.
For this particular HWP mount, rotating the mount to 23(1) degrees produces s polarization, in the sense that placing this HWP between two PBSs causes the second PBS to reflect 100% of the beam.