[Eric, Alex]

For the RFPD frequency response project, we routed the fiber that will connect our REF DET (on the AS table) to our 1x16 optical splitter (in the OMC_North rack), as pictured. (The new fiber is the main one in the picture, which ends at the right edge near REF DET) Note that we secured the fiber to the table in two places to ensure the fiber would remain immobile and out of other optical paths already in place.

At 2:00 we plan to run fiber from our laser module (in rack 1Y1) to our 1x16 optical splitter (in the OMC_North rack) and measure the power output at one of the splitter's output ports. We plan to keep the output power limited to less than 0.5 mW per optical splitter output.

[Eric, Alex]

We decided that the POY Table would be a better home for our REF DET (Newport 1611 FC-AC) than the AS Table. We moved the PD to the POY Table (1st attachment) and routed a fiber from our 1x16 Optical Splitter in the OMC_North rack to the POY Table. REF DET's power supply is now located under the POY table (2nd attachment). We left the fiber described in the previous post on the AS Table.

Afterwards, we hooked a fiber up to our laser module to test it (3rd attachment). The laser was not being distributed, just going to one fiber with a power meter at its end. Everything turns out, but we realized we need to read the power supply's manual before continuing. 

I spent some time tracking down the AS beam which had vanished from the AP table. Eventually, by dramatically mis-aligning SRM, PRM and ITMY, returning BS to its Jan 1st PITCH and YAW values and tweaking the ITMX alignment [actual values to follow], I was able to get an AS beam out onto the AP table. I verified that it was the prompt reflection off ITMX by watching it move as I changed the YAW of that optic and watching it stay stationary as I changed the YAW of ITMY.

Jamie and I then steered the beam through a 2" PLCX-50.8-360.6 lens and placed the RF PD (AS55) at the focus. Additionally, we installed the AS camera to observe the leakage field through a Y1S steering mirror (as shown in the attached diagram).

Currently the PD has power but the RF and DC outputs are not connected to anything at the moment.

Atm 2 by Steve

AS port ITMX YAW  range where AS beam was visible = [-1.505, -1.225] - these extrema put the beam just outside of some aperture in the system -> set ITMX YAW to -1.365

ITMX PITCH range = [-0.7707, -0.9707] -> set to ITMX PITCH to -0.8707

I was going to lock MICH, but I don't see anything on dataviewer for either AS55Q or ASDC.  I went out onto the table, and there is beam on the diode, but no mV out on a voltmeter connected to the DC monitor point.  I shine a flashlight, and still I see 0.0mV.  So, something is up with AS55, but since the michelson is aligned right now, I'm not going to mess with the PD.  I won't lock MICH, I'll just move on.  Koji is taking a look at the diode, but if he doesn't get it figured out tonight, we can take a closer look after we pump down.

 Never mind.  I was using an LED flashlight, which doesn't emit light that the PD is sensitive to.  A regular flashlight gives plenty of signal on the DC out. 

Using an SR560 with 30Hz low pass and gain of 100, it was pretty easy to align the light on the PD. 

Koji calculates in his head that there is about 6 microwatts of light incident on the PD, which is not a lot of light. Our SNR may be kind of lame for locking right now.

 Adaptive filtering was applied to MC and X,Y arms at the same time. I used a very aggressive (8 order) butterworth filter at 6 Hz as an AI filter for MC not to inject noise to ARMS as was done before

Mu for MC was 0.2, downsample = 16, delay = 1. I was able to subtract 1 Hz. Stack subraction is not that good as for arms but this is because I used only one seismometer for MC that is under the BS. I might install accelerometers under MC2.

EDIT, JCD, 18Feb2013:  Den remembers using mu for the arms in the range of 0.01 to 0.1, although using 0.1 will give extra noise.  He said he usually starts with something small, then ramps it up to 0.04, and after it has converged brings it back down to 0.01.

 I actuate on ETMY for YARM and ETMX for XARM. For now I did adaptive filtering for both arms at the same time. I used the same parameters for xarm as for yarm.

I've notched 16 Hz resonance because it has high Q and I need to think more how to subtract it using FIR filter or apply IIR.

I'll try MC stabilazation method.

I have uploaded ARBCAV v3.0 to the SVN. The major change in this release, as I mentioned, is the input/output handling. The input and output are now contained in a single 'model' structure. To define the cavity, you fill in the substructure 'model.in' (e.g., model.in.T = [0.01 10e-6 0.01]; etc.) and call the function as:

model = arbcav(model);

Note: the old syntax is maintained as legacy for back-compatibility, and the function automatically creates a ".in" substructure in the output, so that the user can still use the single-line calling, which can be convenient. Then, any individual parameter can be changed by changing the appropriate field, and the function can be rerun using the new, simpler syntax from then on.

The function then somewhat intelligently decides what to compute based on what information you give it. Using a simple option string as a second argument, you can choose what you want plotted (or not) when you call. Alternatively, you can program the desired functionality into a sub-substructure 'model.in.funct'.

The outputs are created as substructures of the output object. Here is an example:

>> th = 0.5*acos(266/271) *180 /pi;

OMC.in.theta = [-th -th th th];

OMC.in.L = [0.266 0.284 0.275 0.271];

OMC.in.RoC = [1e10 2 1e10 2];

OMC.in.lambda = 1064e-9;

OMC.in.T = 1e-6 * [8368 25 8297 33];

OMC.in.f_mod = 24.5e6;

>> OMC

OMC = 

    in: [1x1 struct]

>> OMC = arbcav(OMC,'noplot')

Warning: No loss given--assuming lossless mirrors 

> In arbcav at 274 

OMC = 

         in: [1x1 struct]

        FSR: 2.7353e+08

        Lrt: 1.0960

    finesse: 374.1568

    buildup: 119.6956

         df: [1000x1 double]

      coefs: [1000x4 double]

        HOM: [1x1 struct]

>> OMC.HOM

ans = 

      f: [1x1 struct]

    pwr: [1x1 struct]

>> OMC.HOM.pwr

ans = 

    carr: [15x15 double]

     SBp: [15x15 double]

     SBm: [15x15 double]

Some other notes:

• The annoying Mdo.m has been internalized; it is no longer needed.
• For the next release, I am working on including:
  • Finite mirror thickness/intracavity refractive elements - If, for god knows what reason, you decide to put a mirror substrate within a cavity 
  • Mode overlap - Calculating the overlap of an input beam to the cavity
  • Mode matching - Calculating a mode matching telescope into the cavity for some defined input beam
  • Anything else?

I have added lots of information to the help header, so check there for more details. As always, your feedback is greatly appreciated.

 The uncoated bi-concave lens was replaced by AR coated one: KBC 037 -100 AR.14 resulting 35% count increase on qpd

I've packaged an AP1053 in a Thorlabs box. The gain and the input noise level were measured. It has the gain of ~10 and the input noise of ~0.6nV/rtHz@50MHz~200MHz.

Details

AP1053 was soldered on Thorlabs' PCB EEAPB1 (forgot to take a picture). The corresponding chassis is Thorlabs' EEA17. There is a 0.1uF high-K ceramic cap between DC and GND pins. The power is supplied via a DC feedthru capacitor (Newark / Power Line Filter / 90F2268 / 5500pF) found in the WB EE shop. The power cable has a connector to make the long side of the wires detachable. Because I did not want to leave the RF signal path just mechanically touched, the SMA connectors were soldered to the PCB. As the housing has no access hole, I had to make it at one of the sides.

The gain of the unit was measured using the setup shown in the upper figure of Attachment 2. When the unit was energized, it drew the current of about 0.1A. The measued gain was compensated by the pick off ratio of the coupler (20dB). The gain was measured with the input power of -20, -10, 0, 10, and 15dBm. The measurement  result is shown in Attachment 3. The small signal gain was actually 10dB and showed slight degradation above 100MHz. At the input of 10dB some compression of the gain is already visible. It looks consistent with the specification of +26.0dBm output for 1dB compression above 50MHz and +24.0dBm output below 50MHz.

The noise level was characterized with the setup shown in the bottom figure of Attachment 3. The noise figure of the amplifier is supposed to be 1.5dB above 200MHz and 3.5dB below 200MHz. This is quite low and the output noise of AP1053 can not be measured directly by the analyzer. So, another LN amplifier (ZFL-500HLN) was stacked. The total gain of the system was measured in the same way as above. The measured noise level was ~0.7nV/rtHz between 50MHz and 200MHz. Considering the measurement noise level of the system, it is consistent with the input referred noise of 0.6nV/rtHz. I could not confirm the advertized noise figure of 1.5dB above 200MHz. The noise goes up below 50MHz. But still 2nV/rtHz at 3MHz. I'd say this is a very good performance.

                   Sad situation

    The anti-symmetric port

spider webs fly in the wind

MCRefl is absent, it is under investigation. I removed a bunch of hardware and note all spare optics along the edges.

Access to the north side of the PSL table is blocked by the    8" beam guard. This opens the beam pathways between them.

Please remember to cover the optical tables !

Before we install the REFL 3f PDs I made a drawing of the current table layout, since there has been no update lately. Once I've incorporated the two extra PDs (now seen sitting bottom left), I will update the drawing and post in the wiki as well.

On Wednesday (21st) night, I checked the AP table as I wanted to try PRMI locking. 
It was difficult to work with the table as there were so many unnecessary components on it.
Also the beams went through complicated paths as they have funny angles. 

So I decided to clean up of IMC REFl WFS, IFO REFL, and IFO AS paths.
I found that the AS beam was highly astigmatic as the beam went through a (too-much-) tilted lens.
I made several blocked optical paths for REFL and AS for future extension of the detection system.

The current status of the table was uploaded below.

The optical spectrum analyzers and the aux NPRO were left untouched but they should be moved
somewhere (either on the table or outside) which does not disturb the other optical paths.
 

After the cleaning, I started locking PRMI. I could lock PRMI stably. But I could not figure out how
the intra-cavity mode looked like as I did not have the POP camera. The power recycling
gain was not quantitatively evaluated as I did not have POP and I wasn't sure how the beam was aligned at POX/POY.

We need to know:

- Quantitative evaluation of the beam shape in the PRC

- Quantitative evaluation of the power recycling gain

Some obvious things to be fixed

- The POX whitening filters seem not switching. This issue should be checked at the circuit module itself and at the BIO.

- The POX beam is not well focused on the PD. This was particularly clear when PRMI was locked with carrier.

- The POP beam is going nowhere. We need POP55 and POP CCD for diagnoses.

I haven't checked ITMY table.

I blocked the  AP table's south west 10" ID port since it is obsolete with the new layout.

Reminder: items on the enclosure self can fall down in an earthquake. I moved oscilloscope and heavy calorimeter head from the edge of the cliff.

The most up to date pictures of the AP table and ETMX table that Steve took have been uploaded to the relevant page on the wiki. It seems like the wiki doesn't display previews of jpg images - by using png, I was able to get the thumbnail of the attachment to show up. It would be nice to add beam paths to these two images. The older versions of these photos were moved to the archive section on the same page.

I measured the power in various beams on the AP table to check and see if any beam is having too much power. 

I am uploading two pics one is in the "high power state" and the other is the "low power state".   High power in the MC REFL PD occurs when the MC is unlocked.  In addition the WFS also will see this  hike in power. We wish to make sure that in either state the power levels do not exceed the max power that the PDs can tolerate.

Low Power state: MC locked, PRM not aligned.                                                   High Power state: MC unlocked,  PRM aligned.

New stage can hold the correct polarization.

DRAWING CORRECTION:  Post block height was lowered to be 1.88" from 2.0"

The new stage missed the right height by ~2 mm.

Even if I completely bottom out the (New Focus 9071) 4-axis stage, its not short enough. So I removed the AOM from the beam and re-aligned into the PMC.

Steve, please get the aluminum piece remachined to go down by 2.5 mm so we can have some height adjustment room.

Also, the turning mirror mount just after the EOM and before the AOM is a U-100 and we want it to be a Suprema for stability - let's not forget to swap that after Steve gets the mount fixed.

Edit/manasa/ Data has not been fit correctly in here. A proper fit will follow this elog.

Proper fits and numbers are here :elog

Earlier last week I had tried to measure the AOM ringdown and concluded I could not make one.

I was proved wrong and I was able to make a measurement. I am still not sure why I was not able to make the measurement earlier with the very same settings and configuration.

What I did:

I gave the AOM a 0-1V modulation input using the signal generator (50 ohm feedthrough bnc was used to impedance match the AOM driver's modulation input). For the measurement here I used a 1Hz square wave. I used a 300MHz oscilloscope to look at the falling edge of the ringdown PD output installed.

I recorded a few ringdown samples. To get a quick number, I fit one such sample to find the AOM switching time as 1.48us (Plot attached). 

i reconnected the AOM driver to the AOM in the main beam path (it was hijacked for the AOM in the AUX laser path for Anjali's MZ experiment). I also temporarily hooked up the AOM to a CDS channel to facilitate some swept-sine measurements. This was later disconnected. The swept sine will need some hardware to convert the bipolar drive signal from the CDS system to the unipolar input that the AOM driver wants (DTT swept sine wont let me set an offset for the excitation, although awggui can do this).

Good job Johannes and Subham.

 {Jan, Manasa}

We tried towards calibrating the RF driver of the AOM. We decided to use the normal power supply for both the driver control voltage and the ALC voltage.  But we could not figure out the type of the ALC port to find a compatible mating connector...it did not match with SMA, SMB or SMP. Finally I wrote to the company and got to know it is a filtered feed through. Now that we know how to control the ALC voltage, we will try looking at the signal for varying ALC voltage and see how that goes. 

But when we tried to see the 2W RF signal through the RF scope, with ALC open, we found that the RF signal was distorted and did not measure 80MHz.  It was lame that we did not get a snapshot 

P.S. The AOM has been left disconnected from the RF driver. 

 {Jan, Manasa}

We started again to calibrate the RF driver. We connected the ALC to the power supply and observed the output RF power on the scope. The RF power did change with ALC voltage, but the RF signal still seems not to be operating at 80MHz 

There is some kind of additional disturbance to the waveform at 80MHz (the frequency of just the waveform with tall peaks or small peaks alone). We made sure we get a snapshot this time!! I am not sure if it will be safe to feed this RF signal to the AOM as such

 AOM driver has been removed from the PSL table for testing. However the AOM is still inside; so there should be no problems with the alignment. 

Mannasa and Unni and I looked at the RF driver for the AOM. It was fine.

With the ALC input left unconnected, with the power supply set to +28V, it was drawing 0.56 A.

By adjusting the modulation input we were able to get 1.1 Vrms into the scope (terminated at 50 Ohms) after going through 2 10dB attenuators. 11 Vrms into 50 Ohms is 33.8 dBm ~ 2W.

The RF power trimpot on the front of the driver is now adjusted so that -0.31 to 0.69 V takes the driver output from off to 2W output at 80 MHz.

The previous distorted signal that Jan and Manasa saw was at a level of ~100 mVrms, which is ~0.5 mW of power. At this tiny drive level, the internal amplifier is not linear and is mostly putting out a signal at ~160 MHz.

We checked by putting a square wave into the modulation input that the RF power from the driver would indeed shut off with a time scale of ~20 ns. Manasa will add a picture to this entry. We are ready now to calibrate the transmitted power of the AOM v. the modulation input voltage and then to measure the step time of the AOM.

Remember: do NOT believe the spec sheet of whatever PD you are using. All commercial PDs are slower than they advertise. In order to measure a <1 us step time you must use a PD with a >50 MHz 'bandwidth'.

    {Jan, Manasa}

We installed the AOM driver back on the PSL table this morning. To calibrate the AOM RF output we connected a 1V dc to the modulation input of the driver and we are convinced with the setup.

Before we direct the rf signal to the AOM, in order to check its diffraction efficiency, we would like to setup an rf PD at the AOM output. We think we have place for a filter and PD after the AOM (replacing a beam dump) and would like to confirm the position before we actually install them. The layout is the picture below showing sweet spots for the new pd to sit. If you think it may disturb the system in any way, let us know!

The rf PD and filter have been installed at the earlier proposed spot on the PSL table.  

{Jan, Manasa}

We set start to check the performance of the AOM on the PSL table. The AOM driver spits out ~1.5W rf at 80MHz for 1V DC at its modulation input. In order to align the AOM, we reduced the input power to the AOM to ~10% using the QWP between the PBS and the laser. We touched the steering mirror before the AOM...but did not succeed in getting any appreciable first order deflection. We then released the AOM mount and moved it a few microns in and out until we obtained a significant change in power along the zero-order beam from 400mV to 100mV when the rf power was changed from 0 to ~1.5W (by changing modulation input from 0 to 1V).  The AOM was clamped at this alignment and the QWP was rotated to give maximum input power. 

During the course of aligning the AOM, the PMC unlocked and was restored after the alignment. 

All went well without having to make any emergency calls to anyone

We will now have to think about switching the AOM on and off for ringdown measurements. This could be done by either using a high-power rf switch or by switching the modulation DC input between 0 and 1V; whichever will be more comfortable to take many many ringdown measurements.

After the AOM work the beam wasn't well aligned to the PMC. The PMC REFL CCD shows large misalignment in yaw.

 {Jan, Manasa, Den}

We wanted to align the PMC and followed Koji's procedure detailed to us by mail. We touched the 2 steering mirrors in front of the PMC for alignment.

- Stand in front of the PMC.
- Find an oscillosocpe on the shelf in the PSL enclosure.
- This has two signals connected. One is the PMC refl dc.
  The other is the PMC trans dc.
- Minimize the refl. Maximize the trans.
- You have the CRT monitor on the MC chamber.
- Project the image of the PMC refl CCD.
  This should show some what symmetric image like an LG mode.
- Use the dataviewer to see how C1:PSL-PMC_PMCTRANSPD is recovered.

We were able to obtain 0.7 at PMC trans; but the PMC was never really stable dropped from 0.7 to 0 abruptly from time to time.

Jenne and Jamie also find that the PMC is behaving very weird 

Summary: Problem unresolved 

 Can someone detail what "weird" means? Is it singing old songs from Guns & Roses?

 It isn't singing Jan..it's dancing between 0.7 to 0 and we are not able to figure out whose the DJ ; there seems to be something else that is controlling the PMC as there is no coordination between what we do (tweaking the mirrors) and what we observe (the PD signals).

Do more investigation to understand what is causing the power reduction.

Is the alignment inadequate? Check the in-lock ccd image.

Is the incident power reduced? (by what?) Use dataviewer.

Is the AOM doing something? Is it active? Then how much power is it eating?

BY THE WAY, how the deflected beam is dumped?
If you don't have anything for blocking the 1st order beam, you have to expect Steve coming to you.

The PMC has been aligned and is all happy happy 

I have installed an  iris to dump the higher order beams deflected by the AOM. After installing the iris, I found that the PMC trans dropped to 0.58V and the PMC misaligned in pitch. So I've touched the 2 steering mirrors before the PMC. Now it is satisfactorily locked with PMC trans at 0.84.

I have also checked the alignment with AOM switched on. PMC trans drops to 0.15 with AOM on and comes back to 0.84 when AOM is switched off without losing lock .

Subham and I have placed the AOM back into the setup right in front of the PMC.

Steps undertaken:

1. The HEPA filters were turned off for some reason. They were turned back on, running at 100% while the enclosure was open.
2. Before the installation, after initial realignment, the PMC TRANSPD read out 748 mV.
3. The laser injection current was dialed down to 0.8 A (just above the threshold, judging by PMC cameras.
4. AOM was attached to the new mount while staying connected to its driver. Put in place, a clamp prevents the cable from moving anywhere near the main beam.
5. Aligned AOM to beam, centering the beam (by eye) on front and back apertures.
6. We then applied an offset to the AOM driver input, eventually increasing it to 0.5 V. A secondary beam became clearly visible below the primary beam.
7. In order to place the razor blade dump (stemming from a box, labeled "cleaned for atm use") before the PMC, where the beam separation was about 3 mm, to make sure we can hit the edged area, we had to place the dump at an angle, facing up.
8. Keeping the 0.5V offset on the driver input, with the lights off, we increased the laser diode current in steps of ~200 mA to its original value of 2.1A, while checking for any IR light scattered from the beam dump. Not a trace.
9. At original current setting, we realigned the beam into the PMC, and obtained 743 mV on the TRANSPD in the locked state.
10. Closed off PSL table, dialed HEPAs down to 50%

We spent an hour today to put the AOM back in the beam before the PMC and verified that the diffraction is working.

1. The fuse holder was missing from the rack. We inserted a 5A fuse. We expect that the quiesscent draw is < 0.5 A. The power is from the +24V Sorensen supply.
2. The alignment was tricky, but we optimized it as well as we could in translation and the RZ direction. Its a fixed mount still.
3. We noticed that according to the datasheet, the polarization is wrong! It wants S-Pol light and we're giving it P-Pol. How come no one noticed this? We expect that the efficiency is reduced because of this. We (Steve) need to brainstorm what kind of mount we can use there to mount it at 90 deg to the plane of the table.
4. The lens after the AOM has f = +400 mm. The distance from the AOM to the lens is ~800-900 mm so its not so terrible. However, if someone were to put the AOM halfway between the turning mirrors there, the beam diffraction would be canceled.
5. The AOM input impedance seems to be 50 Ohm as advertised. The previous Koji entry claim of 25 Ohm is mysterious. We checked the Ohmage by sending a signal into the AM input of the AOM using the DS345 which as a 50 Ohm output. 1 Vpp from the DS345 made 1 Vpp on the input of the AM input as measured by Oscope connected by T with high impedance setting.
6. With 0.5 V offset and a 1 Vpp signal, we get ~20-25% modulation of the power.
7. We have left it running with a 4444.4 Hz modulation and a small amplitude. This is to see if we can use this to measure the cavity poles of the MC and the arms.
8. We noticed some hash on the Teed input monitor. It was backstreaming of the RF drive. Whoever uses this thing in an ISS feedback ought to make sure to put an RF choke between the servo and this AOM driver.

We also removed a 50/50 pickoff mirror which was used to take one of the NPRO -> EOM polarizer reject beams and send it across the table into a floppy dump. Its now hitting a closer floppy dump. Let's stop using these crappy anodized aluminum flappers anywhere, Steve.

We also noticed that the PMC REFL path uses a W1 from CVI to send the PMC reflection to the REFL RFPD. The dim beam from the AR coated surface is being used rather than the bright beam from the uncoated surface. Ooops. Steve, can you please order another W1 for 1064 from CVI, but get it with a 2-3 deg wedge angle? This one has a wedge which is too small.

{Yehonathan, Rana}

In order to setup a ringdown measurement with perfect extinction we need to align the first order beam from the AOM to the PMC instead of the zeroth order.

We connected a signal generator to the AOM driver and applied some offset voltage. We spot the first order mode and align it to the PMC. The achieved transmitted power is roughly as it was before this procedure.

Along the way few changes has been made in the PSL table:

1. Some dangling BNCs were removed.

2. Laser on the south east side of the PSL table was turned off.

3. DC power supplies were removed (Attachment 1 & 2). The rubber legs on the first one are sticky and leave black residue.

4. The beam block that orginally blocked the AOM high order modes was raised to block the zeroth order mode (Attachment 3).

5. The unterminated BNC T junction (Attachment 4 - before picture). from the PMC mixer to the PMC servo was removed.

However, we are currently unable to lock the PMC on high gain. When the gain is too high the PZT voltage goes straight to max and the lock is lost.

Just realized that the diffracted beam is frequency shifted by 80MHz. It would shift the PZT position in the PMC lock acquisition, wouldn't it?