I set up a test inverting amplifier circuit using the LT1677 opamp:
The input signal was a sine wave from the function generator with peak to peak amplitude of 20 mV and a frequency of 500 Hz and I received an output with an amplitude of about 670 mV and the same 500 Hz frequency, agreeing with the expected gain of -332k/10k = -33.2:
So now I know that the LT1677 works as expected with a negative supply voltage. My issue with Den's original circuit is that I was getting some clipping on the input to pin 2, which didn't seem to be due to any of the capacitors- I switched them all out. I set up a modified version of Den's circuit using a negative voltage input to see if I could fix this clipping issue:
I might reduce the input voltages to +5V and -5V- I couldn't get my inverting amp circuit to work with +12V and -12V. I'll start testing this new circuit next week and start setting up some amplifier boxes.
I could not get Den's circuit to work for some reason with microphone input, so I decided to try to use another circuit I found online. I made some modifications to this circuit and made a schematic:
Using this circuit, I have been able to amplify microphone input and adjust my passband. Currently, this circuit has a high-pass at about 7 Hz and a low-pass at about 23 kHz. I tested the microphone using Audacity, an audio testing program. I produced various sine waves at different frequencies using this program and confirmed that my passband was working as intended. I also used a function generator to ensure that the gain fell off at the cutoff frequencies. Finally, I measured the frequency response of my amplifier circuit:
A text file with the parameters of my frequency response and the raw data is attached as well.
These results are encouraging but I wanted to get some feedback on this new circuit before continuing. This circuit seems to do everything that Den's circuit did but in this case I have a better understanding of the functions of the circuit elements and it is slightly simpler.
# SR785 Measurement - Timestamp: Aug 03 2016 - 18:04:48
#---------- Measurement Setup ------------
# Start frequency (Hz) = 1.000000
# Stop frequency (Hz) = 102400.000000
# Number of frequency points = 800
# Excitation amplitude (mV) = 50.000000
# Settling cycles = 1
# Integration cycles = 5
#---------- Measurement Parameters ----------
# Measurement Group: "Swept Sine" "Swept Sine"
The Guralp cable has been pulled and put in the corner to the left of the water cooler:
Ben came by today before the cable had been pulled but he said he'll be back tomorrow.
I took the spectrum of an EM172 connected to my amplifier inside and outside a large box filled with foam layers:
I also made a diagram with my plan for the microphone amplifier boxes. This is a bottom view:
The dimensions I got from this box: http://www.digikey.com/product-detail/en/bud-industries/CU-4472/377-1476-ND/696705
This seemed like the size I was looking for and it has a mounting flange that could make suspending it easier. Let me know if you have any suggestions.
I'll be doing a Huddle test next week to get a better idea of the noise floor and well as starting construction of the circuits to go inside the boxes and the boxes themselves.
The Guralp cable has been reconnected and powered after having the connector changed out.
I set up 3 of my circuits in the interferometer near MC2 to do a huddle test. I have the signals from my microphones going into C1:PEM-MIC_1_IN1, C1:PEM-MIC_2_IN1, and C1:PEM-MIC_3_IN1. These are channels C17-C19. Here are some pictures of my setup:
I'll likely be collecting data from this for a couple of hours. Please don't touch it for now- it should be gone soon. There are some wires running along the floor near MC2 as well.
The summary pages have been updated with the new naming seismometer channel naming conventions. Here's a link to them working on my own page: https://ldas-jobs.ligo.caltech.edu/~praful.vasireddy/1154908817-1154909717/pem/seismic/
Let me know if the actual pages aren't working when they come back online or if there's something that needs to be changed.
The results of my first huddle test were not so good- one of the signals did not match the other two very well- so I changed the setup so that the mics would be better oriented to receive the same signal. Pictures of the new setup are attached.
I also noticed some problems with one of my microphones so I soldered a new mic to bnc and switched it out. Just judging from Dataviewer, the signals seem to be more similar now. I'll be taking data for another few hours to confirm.
I used the Wiener filtering method described by Ignacio and Jessica (https://dcc.ligo.org/DocDB/0119/T1500195/002/SURF_Final.pdf and https://dcc.ligo.org/public/0119/T1500194/001/Final_Report.pdf) and got the following results:
The channel readout has a gain of 0.0005 and the ADC is 16-bit and operates are 20V. The channel also reads the data out in Pa. I therefore had to multiply the timeseries by 1/0.0005=2000 to get it in units of counts and then by (20 Volts)/(2^16 counts) to get back to the original signal in volts. The PSDs were generated after doing this calibration. I also squared, integrated, and square rooted the PSDs to get an RMS voltage for each microphone as a sanity check:
Mic 1: 0.00036 V
Mic 2: 0.00023 V
Mic 3: 0.00028 V
These values seem reasonable given that the timeseries look like this:
I didn't have a separate training set and data set, so I think that's why the graphs came out looking too good. The units on the graphs are also incorrect, I was interpreting PSD as ASD. I haven't been able to get my Wiener filtering code working well- I get unreasonable subtractions like the noise being larger than the unfiltered signal, so Eric showed me this frequency-dependent calculation described here: https://dcc.ligo.org/LIGO-P990002
This seems to be working well so far:
Here's all the plots on one figure:
Let me know if this looks believable.
Seems to good to be true. Maybe you're over fitting? Please put all the traces on one plot and let us know how you do the parameter setting. You should use half the data for training the filter and the second half for doing the subtraction.
For the past week, I've been trying to make a soldered amplifier circuit to use in a prototype box, However, I've been running into this same issue. The circuit, pictured below, works fine on a solderless breadboard.
When I amplify a sine wave, I get a clean looking result at the output on the solderless breadboard:
However, on my soldered circuit, if I turn up the negative voltage supply from the power supply past about -12.5V (the target is -15V), I get a strange signal that Gautam suggested looks like some kind of discharging.
At -12.3 V (soldered breadboard):
At -15.0 V (soldered breadboard):
The signal is much noisier. Zooming in on this second signal, this pattern appears:
This pattern is also showing up even when there is no input from the function generator and the circuit is just given a voltage supply of +/- 15V:
I have tried switching out both the positive and negative voltage regulators, the opamp, and remaking and resoldering the entire circuit but I'm still getting the same signal, which is absent from the solderless circuit. This output was produced with a function generator, so I have also ruled out the microphone as a source of this extra noise. The voltage dependence of this problem made me think it was the voltage regulator, but I've switched out the voltage regulator multiple times and it's still showing up. I'm not sure why this signal appears only as the negative voltage supply is increased- there is no problem with increasing the positive input voltage. Please let me know if you have any ideas as to what component or issue could be causing this.
The temperature is decreasing slowly but is still above 24 C.
The IFO room temp is up a bit and it is coming down. The out side temp is not really high.
I remade another soldered circuit, adding extra 100uF electrolytic bypass capacitors at the input and output of the voltage regulator and ensuring that every grounded component now has its own path to ground rather than going through other elements. This circuit now seems to be working just like the solderless circuit. Attached is the transfer function of the soldered circuit, which matches with the result from the solderless circuit.
Here are both on the same figure- they are about overlapping but are slightly different if you zoom in enough.
I have also attached a new version of the circuit schematic to reflect the changes and to make the physical layout more clear.
My next step for these last few days this summer will be designing a PCB using Altium. I've emailed Varun about how to use Altium on the iMac but he hasn't responded. If anyone else knows how to use the software, please let me know.
I added an EM172 to my soldered circuit and it seems to be working so far. I have taken a spectra using the EM172 in ambient noise in the control room as well as in white noise from Audacity. My computer's speakers are not very good so the white noise results aren't great but this was mainly to confirm that the microphone is actually working.
Do these look good for the ceramic capacitors? We're running low.
What I suggested was:
- For most cases, power decoupling capacitors for the regulators should be ~100nF "high-K ceramic capacitors" + 47uF~100uF "electrolytic capacitors".
- For opamps, 100nF high-K ceramic should be fine, but you should consult with datasheets.
- Usually, you don't need to use tantalum capacitors for this purpose unless specified.
- Don't use film capacitors for power decoupling.
79XXs are less stable compared to 78XXs, and tend to become unstable depending on the load capacitance.
One should consult with the datasheet of each chip in order to know the proper capacitors values.
But also, you may need to tweak the capacitor value when necessary. Above recipe works most of the case.
Gautam helped me drill holes in a metal box and I set up my circuit inside. Everything seems to be working so far. Tomorrow I'll be suspending the box near the PSL and setting up a data channel. Attached are some pictures of the box- sorry some of the angles turned out weird.
My box has been suspended in the PSL using surgical tubing, and it has been connected to C1:PEM-MIC_1 (C17) with a BNC. I made a braided power cable as well but it turned out to be slightly too short... Once this is fixed, everything should be ready and we can see if it's working correctly. I also set up a new tab on the summary pages for this channel:
This data is back from when I had my solderless breadboard running near MC2. I'll add this tab to the real pages once the box is working (which could be a while since I'm gone for a month). Let me know if you see any issues with either the tab or the box/cables.
I'll add a picture of the installation when I get back to campus and finish hooking up the power cable. I haven't added this channel to the actual pages yet because there's not any data right now- the box is still unpowered because my braided power cable wasn't long enough. I just changed the format of the spectrum to ASD and added spectrograms. Here's how the tab looks now: https://ldas-jobs.ligo.caltech.edu/~praful.vasireddy/1155014117-1155015017/pem/acoustic/
Let me know if there's anything else to change.
I made an Altium schematic for the microphone amplifier circuit for fabrication.
Q doesn't like elogging, but he sent me this nice detailed email, so I'm copying it into the log:
I’ve locked the power recycled Y arm numerous times today, to try and find a usable AO recipe for the full locking.
The MC had been unlocked for the last 4 hours and was crying out to me so I gave it some attention. Its happier now.
From the trend (AtM #1), I saw that the MC2 suspension has moved by ~10 microradians. Since the MC cavity divergence angle is lambda/(pi*w0) ~ 200 microradians, this isn't so much, but enough to cause it to lock on bad modes sometimes. Attackmint too shows that there's not much in monotonic drift over the last 40 nights.
I moved back MC2 to its old alignment with these commands:
ezcaservo -r C1:SUS-MC2_SUSPIT_INMON -s -1017 -g 0.0009 C1:SUS-MC2_PIT_COMM -t 300
ezcaservo -r C1:SUS-MC2_SUSYAW_INMON -s 490 -g 0.0009 C1:SUS-MC2_YAW_COMM -t 332
Then I went out to the table and aligned the beam into MC using the last two steering mirrors good enough so that the WFS coming on doesn't make the visibility any better. In this nominal state, I unlocked the MC and then aligned the reflected beam onto the center of the LSC PD as well as the WFS. The beam on the first WFS is a little small - next time someone wants to improve our Gouy phase telescope, we might try to make it bigger there. On the LSC PD, the beam was off-center by a few hundred microns.
At some point tonight we lost our CA connection to c1auxex (which is actually the computer at the X End and controls the ETMX, but has a Y sticker). We could telnet to it, but its puny RAM must have been overloaded with too many EPICS connections that bypassed the CArepeater. I went around and booted some machines and it seems to be back and allowing damping now. Along the way I keyed off the crate to c1auxex a couple of times.
When trying to close the rack door I saw that Charlie/Steve had illegally connected the power cable for the illuminator through the door so that it couldn't close, so I disconnected it so that they can run it properly and feel better about themselves.
Disclaimer: Steve had nothing to do with this connection. I rerouted the cable the correct way. 10-28-2013
** what does this coherence tell us about the noise in the arms ?
8 day minute trend of some of the IMC alignment signals.
That step ~2 days ago in the WFS2 yaw control signal shows that I didn't do such a good job on yaw.
Nic is going to come over some time and give us a new Gouy telescope that let's us have bigger beams on the WFS. At LLO, Hartmut demonstrated recently how bigger beams can reduce offsets somehow...mechanism TBD.
Also, we must angle the WFS and figure out how to dump the reflections at the same time that we rework the table for the telescope.
Steve, can you please put 2 mounted razor dumps near the WFS for this purpose??
Tuesday: Razor dumps are waiting for you.
Steve, can you please put 2 mounted razor dumps near the WFS for this purpose??
I couldn't find any dumps near the WFS. Koji looked. I looked twice. Maybe they are spooky and absorbing all of the light?
The MC alignment was bad and the WFS were making it drift. Koji aligned the beam into the PMC. I then restored the MC suspensions to where they were 8 days ago (back when the transmission and reflection were good). With the WFS OFF, this gave us a MC trans ~ 16000. With WFS ON it goes to 17500 which is about as good as its been over the last 80 days.
I centered the beam on the WFS with the MC unlocked and also centered the beam on the whole WFS path (it was near clipping between WFS 1 & 2). Also for some reason that beamsplitter which steers the beam onto WFS1 is a R=33% (!? why is this not a R=50% ??).
Steve, please swap this out to a BS1-1064-50-1025-45S if we have one sitting around. If not, we want to add this to the CVI purchase list, but not buy until we get a bigger list together.
I also centered this newly aligned beam into the IMC onto the PSL QPDs. We should now use these as a pointing reference for the beam into the IMC.
While doing this I noticed that the beam was almost clipping on the Uniblitz shutter used to block the PSL beam. That shutter is mounted too short and was also not centered horizontally. I removed it for now so that Steve can find a more adjustable mount for it and put it back into play. The beam going into the IMC is BIG, so you have to very careful when centering the shutter. Might be that we cannot leave it at 45 deg and still get a big enough aperture.
Note #3 for Steve: please also replace the mount for last steering mirror into the IMC with a Polanski or a Superman, that black Ultima is no good. Also the dogs must be steel - no aluminum dogs for our sensitive places.
Since the pointing has gone bad again, I went to the PSL to investigate. Found some bad things and removed them:
1) There was a stopped down iris AGAIN in the main beam path, after the newly installed mirror mount. I opened it. Stop closing irises in the beam path.
2) The beam dump for the IOO QPD reflection was just some black aluminum. That is not a real dump. I removed it. We need two razor blade dumps for this.
3) There was an ND filter wheel (???) after one of the PMC steering mirrors. This is not good noise / optics practice. I removed it and dumped the beam in a real dump. No elog about this ?!#?
The attached trend shows the last 20 days. The big step ~2 weeks ago is when Steve replaced the steering mirror mount with the steel one. I don't understand the drift that comes after that.
Today I also spent ~1 hour repairing the Aldabella laptop. Whoever moved it from the PSL area to the SP table seems to have corrupted the disk by improper shutdown. Please stop shutting the lid and disconnecting it from the AC power unless you want to be fixing it. Its now running in some recovery mode. Lets leave it where it is next to the PSL and MC1.
I steered the MC suspensions back to where they were on the trends before the PSL mirror mount swap and then aligned the PSL beam into it by touching the last 2 steel mounts. Once the alignment was good without WFS, I centered the beams on the IOO QPDs. If it behaves good overnight, I will center the unlocked beams on the MC WFS.
Please stay off the PSL for a couple days if you can so that we can watch the drift. This means no opening the doors, turning on the lights, or heavy work around there.
Since I saw that the trend was good, I aligned the MC refl path to the existing IMC alignment:
The reflected spots from the PD are not hitting the dump correctly. WE need to machine a shorter post to lower the dump by ~1 cm to catch the beams.
Nice camera work Steve! I will use these for publicity photos.
Now we need to get one of the video cameras hooked into the MUX so that we can see the flashing and do some image subtraction.
The trend shows a big jolt to the MC1/3 pointing this morning at 8:30.
If not, we will have to put a 'no janitor' sign on all of the 40m doors permanently to prevent mops misaligning our interferometer.
Demod boards should be at 90 deg, not 82.7 or 12 or yellow or ****. We should re-inject the RF and then set the D Phase in the filter module to make the signals orthogonal. 165 is a challenging one to get right, but its worth it since the signals are close to degenerate already.
[Radhika, Paco, Anchal]
I placed a lens in the B-beam path to focus the beam spot onto the RFPD [Attachment 1]. To align the beam spot onto the RFPD, Anchal misaligned both ETMs and ITMY so that the AS and LO beams would not interfere, and the PD output would remain at some DC level (not fringing). The RFPD response was then maximized by scanning over pitch and yaw of the final mirror in the beam path (attached to the RFPD).
Later Anchal noticed that there was no RFPD output (C1:LSC-BH55_I_ERR, C1:LSC-BH55_Q_ERR). I took out the RFPD and opened it up, and the RF OUT SMA to PCB connection wire was broken [Attachment 2]. I re-soldered the wire and closed up the box [Attachment 3]. After placing the RFPD back, we noticed spikes in C1:LSC-BH55_I_ERR and C1:LSC-BH55_Q_ERR channels on ndscope. We suspect there is still a loose connection, so I will revisit the RFPD circuit on Monday.
I measured the transmitted power @1064nm on one of the LaserOptik mirrors labled SN6
Here is the data
The mirror is not a good reflector at 0 deg.
More data on the transmission. Measured the tranmission as a funtion of incidence angle at 1064nm
From the trend, it seems that the Reference Cavity's temperature servo is working fine with the new copper foil. I was unable to find the insulating foam anywhere, but that's OK. We'll just get Frank to make us a new insulation with his special yellow stuff.
The copper foil that Steve got is just the right thickness for making it easy to form around the vacuum can, but we just have to have the patience to wrap ~5-10 more layers on there. We also have to get a new heater jacket; this one barely fits around the outside of the copper wrap. The one we have now seems to have a good heating wire pattern, but I don't know where we can buy these.
I also turned the HEPA's Variac back down to the nominal value of 20. Please remember to turn it back up to 100 before working on the PSL.
This is the trend so far with the copper foil wrapping. According to Megan's calculation, we need ~1 mm of foil and the thickness of each layer is 0.002" (1/20th of a mm), so we need ~20 layers. We have ~5 layers so far.
As you can see the out-of-loop temperature sensor (RCTEMP) is much better than before. We need another week to tell how well the frequency is doing -
the recent spate of power cycles / reboots of the PSL have interrupted the trend smoothness so far.
I wrapped another ~3 layers onto there. It occurs to me now that we could just get some 2mm thick copper plates made to fit over the stainless steel can.
They don't have to completely cover it, just mostly. I also took the copper circles that Steve had made and marked them with the correct beam height
and put them on Steve's desk. We need a 1" dia. hole cut into these on Monday.
To compensate for the cooling during my work, I've set the heater for max heating for 1 hour and then to engage the temperature servo.
I also noticed the HEPA VARIAC on the PSL was set to 100. Please set it back to 20 after completing your PSL work so that it doesn't disturb the RC temperature..
[Koji, Rana, Nic, Steve]
We went to the 25-pin D cable which connects to the TT1 quadropus and succeeded eventually in swapping pins 12/24 into the 13/25 positions.
A heavy duty plastic box is the likeliest candidate for the optical table toolbox. It measures 5 9/16 in. x 11 5/8 in. x 4 5/8 in. and fits all the tools comfortably. ( http://www.mcmaster.com/#plastic-bin-boxes/=m4yh4m , under Heavy Duty Plastic Bin Boxes)
The list of tools has been updated to include a pen and a wire cutter as well as everything previously stated.
In addition, Steve has recommended that boxes should be secured to the walls or surfaces near the optical tables as opposed to the optical tables themselves, as to keep the tables from wobbling when tools are being exchanged.
A diagram of tentative box placements will go out soon.
No, the small boxes must be attached to the optical tables. They won't be heavy enough to change the table tilt.
Also, all tools must be color coded according to the optical table using the 3M Vinyl table color code:
I worked on the script SPAG4395A.py tonight with Masayuki's help. This sets up the parameters on the Agilent 4395A and then acquires the spectrum data. It had a couple of bugs before: no matter what channel you requested, you always got channel R. It also would disobey any requests to reduce the attenuation and left the Auto Atten ON. The version now in the SVN allows you to choose the channel and the attenuation.
It then makes this plot using matplotlib. The attached image is from the REFL165 pickoff at a time tonight when the arm powers were ~5-10. I have converted the spectrum from RF electrical Watts into Volts (V = 50*sqrt(W)). To go from the analyzer input to the demod board input we should scale this spectrum by a factor of ~15 (to account for the 20 dB from the coupler and the 3 dB of the splitter and a little more for losses). On the oscilloscope we see Vpp ~5 mV, so that's ~75 mVpp at the output of the BBPD which we're using for REFL165. Perhaps we can handle another factor of ~2-3 ? I'm not sure what we have in terms of linearity measurements on this thing.
EDIT: Evan is right, its V = sqrt(50*W), not V = 50*sqrt(W). ignore y-axis above
The controller would be in the c1sus model, and connects to the c1sup plant model. So the controller doesn't go in the plant model.
Both the controller and the plant can be modeled using a single filter module in each separate model as you've drawn, but they go in separate models.
Summary: This afternoon we managed to get the temperature control of the reference cavity working again.
We bypassed the MINCO PID by connecting the temperature box error signal directly into EPICS.
We couldn't configure the PID so that it worked with the modified temperature box so we decided to just avoid using it.
Now the temperature control is done by a software servo by using the channel C1:PSL-FSS_MINCOMEAS as error signal and driving C1:PSL-FSS_TIDALSET (which we have clip-doodle wired directly to the heater input).
We 'successfully' used ezcaservo to stabilize the temperature:
ezcaservo -r C1:PSL-FSS_MINCOMEAS -s 26.6 -g -0.00003 C1:PSL-FSS_TIDALSET
We also recalibrated the channels:
with Peter King on the phone by using ezcawrite (EGUF and EGUL) but we didn't change the database yet. So please do not reboot the PSL computer until we update the database.
More details will follow.
I installed ligoDV in the /ligo/apps/ligoDV/
Now, by pointing the tool at the local NDS2 server (megatron:31200) you can access the recent local data (raw, trends, etc.)
by running /ligo/apps/ligoDV/ligodv from the command line.
We locked the PRMI, this time really on the sidebands, using the two REFL55 signals.
Here are the parameters: triggering on POP22_I in at 140, out at 20. No normalization. MICH gain -0.15, PRCL gain 0.1
It seems that the lock is not very stable. It seems likely to come from some large angular motion of one of the mirrors. We'll need to calibrate the optical lever signals to understand which one is moving too much.
Before we installed the video switch box, we also took some photos of it. We uploaded them onto the 40m Picasa.
The first photo is the an entire view of the switch box. The following four photos are the details of the switch matrix.
The slideshow below is a dump of the last several months of photos from the Olympus. The originals have been deleted.
This past week I have completed the following tasks:
1. Built a trigger and power box for the camera GC 750M (06058) and took some test images to see whether the trigger box really works. Result: It is doing fine!
2. Went over the setup that is already sitting on the table. Ref: Aidan's elog entry
3. Attended seminars and talks given by Alan, Jahms, Koji and Rana.
4. Attended the mandatory laser safety training by Peter.
Expected task for this week (could be more):
1. Work out analytical expressions of the power of the carrier and sidebands going to the camera in the setup. (As suggested by Rana and Joe)
2. Work on producing beat signal to the camera using the He-Ne laser setup.
3. Move,if possible, to the Nd:YAG setup.
4. Go over the codes and paper by the past SURFers on the phase camera experiment.
This week I have completed following tasks:
1. Worked out the analytical expressions for the amount of power of the DC and oscillatory part going into the camera.
2. Realigned the He-Ne PhaseCam setup as we had to replace the first steering mirror after the laser with a silvered mirror ( one without a dielectric coating for 1064 nm).
3. Gone through the code written by a previous surfer (Zach Cummings).
4. Read the paper 'Real-time phase-front detector for heterodyne interferometers'- F. Cervantes et. el. where they talk about constructing a phase detector for LISA pathfinder mission. One interesting fact I found was that, they used InGaAs chip for their CCD Cam which has a amazing QE of 80% @ 1064 nm. Unfortunately, the one we are using (Micro MT9V022 CMOS) has only ~5% QE for 1064 nm and 50% for 633 nm. One top of it MT9V022 has a built-in infra-red filter infront of it to make it more insenstive to 1064. In such limitations, we may have to find a work-around for this issue. Any idea?
5. Read about the EOM and AOM and their vibrating (!) way to add on and alter the incident light on them. (Source: Intro to Optical Electronics-Yariv)
One task that we couldn't accomplish even though I planned on doing is:
1. Move,if possible, to the Nd:YAG setup.
Task for this week:
1. Produce breathtaking calibration of the camera at He-Ne setup.
2. Read 'Fringe Analysis'-Y.Surrel and 'Phase Lock Technique'-Gardner.
3. Modify the phasecam code.
4. Produce an alternate triggerbox using diodes instead of Op-Amp as op-amp is suspected to fail at some point driving the camera due to impedance mismatch.
5. Answer Koji's question at Aidan's ELOG .
I have completed the following tasks:
1. Find a simplified calibration of the exposure time for the current He-Ne setup. Basically, I triggered the camera to take 20 snapshots with a 20 Hz driving signal at different exposure time beginning from 100 us (microsecond) upto 4000 us with an increment of 200 us.
Result: The current power allows the camera to have an exposure time of ~500 us before the DC level begans to saturate.
2. Aidan and I did some alignment and connected the AOM and corrected the driving frequency of its PZT to 40 Mhz(which apparently was disconnected which in turn gets the credit of NO beat signal for me until Tuesday 07/06/2010 5:30 PST) .
Result: I got the beat signal of 1 Hz and 5 Hz. Image follows (the colormap shows the power in arbitrary units).
3. Finished writing my Progress Report 1 .
Here are some more details about the current phasecam setup. We are using a He-Ne laser setup
A crude snap shot of the setup....
We sent light through SM2 (Steering Mirror 2) to BS1(Beam-Splitter 1) where the laser light is split into two parts, one going to the AOM and the other to the EOM. The EOM adds 40 MHz sidebands to the incoming carrier light after SM3, and the AOM shifts the frequency of the incident light on it to 40.000 005 MHz. The purpose for doing this juggling is to intentionally create a beat signal off the reference beam from the AOM with the sidebands added at the EOM. Note that, we are driving the AOM at 7dBm and the EOM at 13 dBm with 0 (nil) modulation. The two lights are combined at the BS2 and sent off through SM5 to the camera. The CMOS of the camera contains silicon based Micro MT9V022 chip which has a quantum efficiency of 50% at 633 nm. Thus we expected a fairly good response to this He-Ne setup from the camera.
Using a trigger circuit, we triggered the camera at 20 Hz by sending a 20Hz sinusoidal signal to it. The trigger circuit converts this to a positive square waves. Then I roughly figured out the optimum exposure time for the camera before the DC levels saturates it by writing a code for taking a series of 25 images at different exposure time. I found that 500µs seems to be a reasonable exposure time. So, using this data, I took 20 consecutive images and sent them through a short Fourier Transform segment using Matlab to see the beat signal. Note that the DC component from these processing of the images have some fringe pattern which is due to the ND 2.5 filter that we were using to reduce the light power incident on the camera. The FT method also gave us the presence of the beat signal at the corresponding bin of the FT (for example: for 5Hz beat signal, I got the DC at bin 1 of the FT and 5Hz component at bin 6 as expected). Then I changed the AOM driving frequency to 40.000 001 MHz in order to see a 1 Hz beat signal. The results for both is in my previous post.
Razib and I were attempting to get the output of a photodiode (PD55A in this case) recorded, so that we could independently measure the slow (~1-10 Hz) fluctuations of the light incident on the camera. This would then allow us to subtract those fluctuations out, letting us get at the camera noise in the case with signal present (as opposed to just a dark noise measurement when we look at the noise with no signal present).
Originally I was thinking of using one empty patch panel BNCs used for PEM channels down by the 1Y7 rack and go through a 110B, although Alberto pointed out he had recently removed some monitoring equipment, which watched the amplitude modulation at various frequencies of the RF distribution (i.e. 33 MHz, etc). This equipment output a DC voltage proportional to the amplitude of the RF signals. The associated channel names were C1:IOO-RFAMPD_33MHZ, C1:IOO-RFAMPD_33MHZ_CAL, C1:IOO-RFAMPD_133MHZ, etc. These are slow channels, so I presume they enter in via the slow computers, probably via pentek (I didn't check that, although in hindsight I probably should have taken the time to find exactly where they enter the system). The connections them selves were a set of BNCs on the south side, half way up the 1Y2 rack.
We simply chose one, the 33 MHz channel in this case, and connected. At around this time, the MC did become unlocked, although it looked like it was due to the MC2 watchdog tripping. The initial theory was we had bumped the Mode Cleaner while looking around for some BNC cables, although from what Rana had to do last night, it probably was the connection. We were able to restore the watchdog and confirm that the optic started to settle down again. Unfortunately, I had to leave about 5 minutes later, and didn't do as thorough an investigation as was warranted.
Before I left, I disconnected the PD55, so the 33 MHz channel wasn't physically connected to anything!!! Only one end of the wire was connected to the rack while the other was free...
So it wasn't the PD connection that is responsible for MC tripping at the later time...
This week I was mainly interested in investigating the noise source at the phase camera. So having this issue in mind, my activities are the following:
1. I worked on producing multiple beat signal (1Hz and 5Hz). Elog entry.
2. I altered the setup so that instead of triggering the camera from the signal generator, we are now triggering it from the beat signal from the reference beam and sideband.
3. I made the nice little aluminium table for all the amplifiers, mixer and splitters to sit at one place instead of floating around.
4. I talked with Aidan and Joe and verified my calculation and extended it to further investigation of the noise source in the setup.
Plan for the upcoming week:
1. Measure and calibrate the camera w.r.t the power incident on it.
2. Investigate the noise source.
This past week I have worked on the following:
1. Setting up the infrastructure to do noise analysis: We added a temporary channel on the DAQ to connect to the PD 55 which we are using to take the power measurement. Before that, I connected the PD55 to an oscilloscope and recorded the power.
The power at PD55 as measured using the oscilloscope = 600 µV.
Then I tried to calibrate the channel by sending up a signal from the function generator and measuring up the offset.. However, the channels seems noisy enough, especially due to electronics noise as suggested by the measurements and FFT calculation.
2. I worked on trying to sync the data acquisition of the PD and the CAM. After sometime spent on fiddling with the software method such as taking images at stamped time and then lining them up with the daq timestamps, I found a hardware method as suggested by Aidan. It was putting up a shutter (Uniblitz shutter and driver VMMD1) in the setup. I synced the shutter with the camera for which I had to tear apart the previously made trigger box and add a sync output from the camera (took a while as I also had to make a new cable).
3. I worked (still working) on making a differential amplifier to blow up the signal from the PD.