We've set up a preliminary test bed for the phase camera. It simply uses a HeNe that is split into two beams. One is frequency shifted by an AOM by -40 MHz - df, where df is some acoustic frequency. The second beam is transmitted through a 40MHz EOM to get sidebands. The two beams are recombined and are, currently, incident on a photodetector, but this can be replaced by the phasecamera.

We turned everything on with df = 1kHz and confirmed that a 1kHz signal is visible on the output from the photodetector (PD). The signal looks to be about 1:300 of the DC level from the PD.

1. In terms of the AOM:

How much beam power is incident on the AOM? How much is the deflection efficiency?
i.e. How much is the power lost by the crystal, deflected in the 1st order, and remaining in the oth order?

I am curious because I assume the AOM (which vender?) is designed for 1064nm and the setup uses 632nm.

2. In terms of the EOM:

How much sidebands do you expect to have?

I assume the EOM is designed for 1064nm, the only difference is the coating at the end. Is this right? 

3. Beating

How much beating strength do you expect?

Is your beating level as expected?

How much is the contrast between the PM sideband and the frequency shifted carrier?
This must include the consideration on the presence of the carrier and the other sidebands.

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.

We made an attempt at cleaning up the phase camera setup electronics.

We have moved a portion of the electronics onto the SP table (specifically the mixer, splitters, amplifiers, and associated power).  We put away a large number of cables which were unneeded, both BNC and power cables. The Innolight Mephisto power supply and one signal generator are still behind 1Y2 on top of a non-functioning VME crate.  The second VME crate was put along the south arm where two other VME crates already were.  We placed a fair number of BNC cables and power cords back on their cable racks or approriate storage space, so the rats nests of cables has been reduced.

We moved one power strip from plugging in beyind 1Y1, to the far side of the SP table (closer to the 1Y3 rack), and also found and plugged in another power strip (also on the far side of the SP table) and placed this underneath the SP table to be able to power the signal generator and Innolight Mephisto laser (its not plugged in currently, but we'd like to do so next week).

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.

Attached are some calculation that I did previously for the phasecamera setup. This shows the nature of the beat signal that we are measuring.

I am also trying to characterize the noise source of the camera also. Following images shows the mean dark noise (with no light on the camera) and the standard deviation for 100 snaps at an exposure time of 500 µs.

My target now is to measure the response gain of each pixel and how they vary over intensity. I already have a simplified setup on the table and will work on it today. Details will follow at the end of the day.

Aidan and I made some attempt to measure the power of the sidebands so that we can calculate our expected signal strength.

Our setup looks like the following:

As light from the laser is split into two at BS1, the transmitted beam has higher power as our BS1 is only coated for 1064nm. We get two reflected beams from BS1, one reflected of the front surface and the other from the back surface. We took the stronger back reflected beam to the EOM driven at 40 MHz (also at 25 MHz at  a later time). The AOM produced a reference beam with 40 .000 005 MHz offset which we recombined with the sidebands obtained from the EOM. The beat produced is sent off to PDA 10CF connected to 4395A spectrum analyzer.

The plots for 40MHz sidebands and 25 MHz sidebands looks like this:

From the above spectra, at 40 MHz sideband regime:

Power of the carrier @ 40 MHz = -39.72 dBm

Power of the sideband @ 80 MHz = -60.39 dBm

At 25 MHz sideband regime,

Power of the carrier @ 40 MHz = -40.22 dBm

Power of the upper sideband @ 65 MHz = -61.72 dBm

Power of the lower sideband @ 15 MHz = -60.99 dBm

Power Measurement:

We made some necessary power measurement using a PD connected to a voltmeter after the EOM and the AOM when the EOM is driven at 40 MHz:

___________________________________________________________

Dark :  0.025 V

AOM on: 4.10 V    (EOM blocked)

EOM : 2.425 V      (AOM blocked)

___________________________________________________________

 From the earlier calculation (ref: Elog entry July 28) the power that we expect to see at the PD is,

P= A_c ^2 + A_r^2 + A_(-sb)^2+ A_sb ^2 +2* A_r* A_sb * cos ( w_(r,sb) t ) ,                         where A_c= carrier;   A_r= reference beam;     A_sb=Upper sideband;    A_(-sb)= Lower sideband,     w_(r,sb) = w_r - w_sb

P = A_c ^2 + A_r^2 + A_(-sb)^2+ A_sb ^2 +2* A_r* A_sb  , letting cos (w_(r,sb) go to 1) is order to approximate the maximum signal

So the signal that we expect to see relative to the DC ( i.e    A_c ^2 + A_r^2 + A_(-sb)^2+ A_sb ^2,    the first four terms of the power equation) is,

Sig = 2* A_r* A_sb    / { A_c ^2 + A_r^2 + A_(-sb)^2+ A_sb ^2 },

Since the modulation index is small, the power in the sideband is very small compared to carrier and the reference beam. So we can ignore the sideband power for the signal expression.

So,

Sig = 2* A_r* A_sb  /  ( A_c ^2 + A_r^2 )

So if we want to maximize this signal w.r.t the reference then,

d (sig)/ d(A_r) = 2 { ( A_c ^2  - A_r^2) *A_sb } / {( A_c^2 + A_r^2)} ^2

Thus, the signal is maximized when,

A_r^2 = A_c^2

We adjusted the AOM to be driven at + 7.7 dBM so that the new power at the AOM matched the EOM power, which is 2.397 in the voltmeter.

So the power at both the AOM and the EOM are:

P_AOM = ( V_AOM - V_dark) / (PD responsitivity * Transimpedance gain)

               = ( 2.397 - 0.025 ) / ( 0.45  * 1.5 x 10 ^5 )

               = 3.51 x 10 ^ - 5  W

P_EOM = (V_EOM - V _dark) / (PD responsitivity * Transimpedance gain)

               = ( 2. 425 - .0.025) / ( 0.45 * 1.5 x 10 ^5 )

               = 3.55 x 10^ - 5  W

From the spectra of the 40 MHz sideband above, the ratio of the carrier and the sideband amplitude is:  A_c / A_sb = 10.8 .

P_EOM = A_c ^2 + 2 A_sb ^2

Therefore, A_sb = sqrt ( P_EOM / 118.64) = 5.47 x 10^ - 4   V/m

Thus,     A_c = 5.908 x 10^ -3   V/m

and    A_r = sqrt ( P_AOM) = 5.92 x 10 -3    V/m.

This measurement can be used to calculate the signal to contrast ratio (SCR) that we expect to see:

SCR = 2 A_r * A_sb  / ( A_c^2  + A_r^2 )  = 0.09

Our next step is to measure the actual signal to constrast ratio as seen by the camera. Details of that will be posted soon.

I made some measurement of the SCR (signal to contrast ratio) from the signal from the EOM and the AOM.

The recipe for that was:

1. Trigger the camera at 20 Hz (from function generator).

2. Take a series of 20 images.

3. Do FFT to take out the DC component.

4. Extract the beat signal out of the FFT'd data.

5. Block the EOM.

6. Take another set of images of the AOM beam.

7. Take more(!) images, but this time of the background (blocking both EOM and AOM).

So the SCR is calculated by the ratio of the FFT'd DC and the 5 Hz signal. Using the CCD, I obtained the SCR to be 0.075 ± 0.01. Previously, we expected our SCR to be 0.09 as in the previous e-log entry.

The plot for that is:

 After measuring the SCR, I also measured the amplitude of the sideband and made an amplitude profile of the 40 MHz sideband.

The amplitude measurement is done as follows:

We know that the our 5 Hz signal consists of,

Sig = A_r * A_sb    where A_r = amplitude of the reference beam, A_sb= amplitude of the sideband

So, A_sb = Sig / A_r .

But,  A_r = sqrt ( P_AOM - Background),

Thus  A_sb = Sig / sqrt( P_AOM - Background) .

So the amplitude profile is done by taking the 5 Hz beat signal and dividing by the square root of the AOM beam minus the background light.

The plots looks like this:

The solo sideband profile looks like this:

Next we plan to trigger the camera with a 1 KHz signal and take snaps at n* T/4 (where n=0,1,2,3) of the period of the beat signal. So the plan is to trigger the camera at the point where the red dots appear in following cartoon.

Some more details of this setup will be posted later.

This sounds very relieving although this could be a lower bound of the number.
Why didn't you use the output on the PD which just give us the direct observation of your so-called SCR.

Ed: I meant time series of the PD output

 The SCR was at first measured using the output of the PD. That was exactly from where we got our 0.09 (previous elog entry). The second measurement was from the CCD.

Alan and Alberto conducted a tour of 40 high-school students.
It may be the same tour that Rana found a spare PMC during the tour explanation as far as I remember...

 The control room desk tops heights on the east side were lowered by 127 mm

I've created a 40m Google account. Please post all the 40m related photos to this site. If you don't already have it, download Picasa to make this easier.

40m Installation Photos">

the password is in the usual password place.

1/4" exposure, standard room lights                                                                              3" exposure, slowly moving LED bar light from ~60 cm distance

Note:
Because of the light behind, the focus was attracted by the far objects...
Evenso the magnet ball looks better in the right picture.

The technique is as follows:
Use longer exposure time, move the LED bar illumination through the area like painting the light everywhere.
It is supposed to provide a picture with more uniform light and the diminished shadow.

(KA)

Before we installed the video switch box, we also took some photos of it. We uploaded them onto the 40m Picasa.

Video Matrix

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.

 I updated the photo of ETMY end table on the wiki.

http://lhocds.ligo-wa.caltech.edu:8000/40m/Optical_Tables

Some pictures of "magnet inspection" from Picasa.

The coating of some magnets are chipped...

Were these magnets chipped before the Ni plating?

RA: Yes, it looks like this is the case. We also smashed some of the magnets against a metal surface and saw that a black grime was left. We should hold the magnets with a clean teflon clamp to measure the Gauss. Then we have to wipe the magnets before installing. I share Jenne's concern about the press-fit damaging the plating and so we need to consider using using glue or the ole magnetic attachment method. We should not rely on the structural integrity of the magnets at all.

 One day I'll get to be part of the krew

Prof Alan Weistein guided the 24 student through the 40m. His performance was rated as  an enthusiastic 9.5

 I uploaded some pictures taken in the last and this week. They are on the Picasa web albums.

 in vac work [Nov. 18 2010]

 in vac work [Nov 23 2010]

 CDS work [Nov 24 2010]

The 40m lab was visited by  ~ 30 LSC members  the end of last week.

Suresh is captivating his audience with gravity waves on last Friday, March 25

.....Happy.... Birthday.... to.... Joseph... and... Jamie...Happy....Birthday..... to.... You............sing with us........Happy Birthday.....to you