I updated our lockin simulink pieces to use the newer, more streamlined lockin piece that is currently in CDS_PARTS (with new documentation block!).  It means we are no longer passing clock signals through three levels of boxes.

In order to use the piece, you need to right click on it after copying from CDS_PARTS and go to Link Options->Disable Link.  This forces the .mdl to save all the relevant information about the block rather than just a pointer to the library.  I talked with Rolf and Alex today and we discussed setting up another model file, non-library format for putting generically useful user blocks into, rather than using the CDS_PARTS library .mdl.

The BS, ITMX, ITMY, PRM, SRM, ETMX, ETMY now have working lockins, with the input matrix to them having the 2nd input coming from LSC_IN, the 3rd from the oplev pitch, and the 4th from oplev yaw.

This necessitated a few name changes in the medm screens.  I also changed the lockin clock on/off switch to a direct amplitude entry, which turns green when a non-zero value is entered.

Currently, the Mode cleaner optic suspension screens have white lockins on them.  I started modifying a new set of screens just for them, and will modify the generate_master_screens.  Unfortunately, this requires modifying two sets of suspension screens going forward - the main interferometer optics and the MC optics.

The reason for using Alberto's laser is that some amount of work has already gone into characterising its phase noise.  Ref elog entry 2788

We use Alberto's laser for the Y end Green Locking.

Just for a record. We got 4 new laser pointers (2 greens, 1 blue, and 1 green and red combination). Don't lose them.

They reside in a bucket on the SP table, where IR viewers and sensor cards also reside.

 Prior to the works on the Y end setup I propose to perform the temperature scan business like Koji and Suresh did before (see this entry).

This business will allow us to easily find a beatnote at 532nm after the installation on the Y end.

 I guess the right persons for this work are Bryan and Suresh.

Bryan will have a safety guidance from Steve in this after noon. So after that they can start working on it.

/* - - - coarse plan - - - */

* remove Alberto's laser from the AS table

* setup Alberto's laser on the PSL table

* put some stuff such as lenses, mirrors and etc. (Use the IR beam picked off after the doubling crystal for the main laser source)

* mode matching

* measurement

Which laser are we going to use,  Alberto's laser or MOPA laser ?

[Joe, Alex]

Steve pointed out to me today he couldn't get trends for his PEM slow channels like C1:PEM-count_full. 

I experimented a bit and found for long time requests (over 20 days), it would produce minute trends up to the current time, but only if they started far enough back.  So the data was being written, but something was causing a problem for dataviewer/NDS to find it.

On further investigation it looks to be some incorrect time stamps at several points in the last few months are causing the problems.  Basically when Alex and I made mistakes in the GPS time stamp settings for the frame builder (daqd) code, the wrong time got written for hours to the raw minute trend data files.

So Alex is going to be running a script to go through the roughly 180 gigabytes of affected trend data to write new files with the correct time stamps.  Once it done, we'll move the files over.  We'll probably lose a few hours worth of recent trend data, depending on how quickly the scripts run, but after which minute trends should work as they are supposed to.

4. The blue Output Filters  section has been changed to agree with the new filter of matrices row, column labeling.  My fault for not testing it and realizing it was broken.  The change was made in /opt/rtcds/caltech/c1/medm/master/C1SUS_DEFAULTNAME.adl and then ,/generate_master_screens.py was run, updating all the screens.

5.  I have swapped the logic for the sensor filter banks (ULSEN, URSEN, etc).  It now sends a "1" to the Binary Output board controlling the OSEM analog whitening when the FM1 filter is ON.  This has been done for all the suspensions (BS, ITMX,ITMY, SRM, PRM, MC1, MC2,MC3, ITMX, ITMY).

I am also updating the first sensor filter banks for the BS, ITMX, ITMY, SRM, PRM,MC1,MC2,MC3, called "3:30", to match the Y and X ends.

8.  I can't find any documentation on how to get a momentary button press to toggle states.  I could stick a filter bank in and use the on/off feature of that part, but that feels like a silly hack.  I've decided for the moment to split the TM offset button into 2, one for ON, one for OFF.  I'll put in on the list of things to have added to the RCG code (either a method, or documentation if it already exists). 

EDIT:  TM offset still doesn't work.  Will worry about it next week.

9.  Fixed a connection in SPY/SPX models where  the side senor path that was missing a constant to a modulo block.

I did some work on the ETMY real and Sim.

1. Set SUS coil gains to have the same quadropole arrangement as the magnets do (-1, 1, 1, -1) so that POS = POS instead of pringle.
2. Set the Sim Magnet polarities to match this. These are the ETMY_CI filter banks.
3. Found that the Xycom cable from the ETMY slow controls was unplugged at the Xycom side. This was preventing enabling the ETMY coil driver and so there was no real damping of the suspension going on. I plugged it in and checked that the mirror could now be moved.
4. The C1SUS_ETMY master screen's BLUE output filter area is now mis-labeled. If you trust the screen you would set it up to drive the suspension incorrectly. This MUST be fixed along with all of the other misleading features of the screen.
5. ETMY SUSSIDE filter bank had a 2048 Hz sample rate and was making the damping not work correctly. Fixed to 16384 Hz.
6. 12 Hz, 4th order Cheby low pass added and turned on for the local damping filtering. This is not optimum, but its just there to give us some filtering without introducing some instability via phase lag around 3 Hz.
7. ETMY OL beam re-aligned on ISCT-EX.
8. TM Offset buttons not working on the main overview screen.

It seems like there is still a problem with the input whitening filters. I believe the Xycom logic is set such that the analog whitening of the OSEM signals is turned ON only when the FM1 is turned OFF. Joe has got to fix this (and elog it) so that we can damp the suspension correctly. For now, the damping of the ETMY and the SETMY require different servo gains and signs, probably because of this.

 John has changed the NDS2 code and restarted it on Mafalda. The issue is that it goes off the rails everytime the DAQD is restarted on FB because of filename convention war between GDS and CDS.

Until this is resolved, please make sure to restart the NDS2 process on Mafalda everytime you restart DAQD by doing this:

pkill -KILL nds2

/users/jzweizig/nds2-mafalda/start_nds2

The FM1 filter module change for XXSEN was propagated to the ETMX suspension.  This was a change from a 30,100:3 with a DC gain of 1 to a 3:30 which just compensates the hardware filter.

The good gains for the Sim damping were found to be:  100 for ETMX_SUSPOS, 0.1 ETMX_SUSPIT, and 0.1 ETMX_SUSYAW, ETMX_SUSSIDE is -70.  Gains much higher tended to saturate the simulated coils (i.e. hitting 10V limit) and then had to have the histories cleared for the RESPONSE matrix.

These seem to work to damp the real ETMX as well.

New Focus Servo Controller has just arrived. We have 25 days to evaluate this product.

It will have to be shipped back to the vendor on April 4, 2011 the latest in order to get full refund.

While fixing up some medm screens and getting spectra of the simulated plant, I realized that the naming convention for the Matrices of Filter banks was backwards when compared to that of the normal matrices (and the rest of the world).  The naming was incorrectly column, row.

This has several ramifications:

1) I had to change the suspensions screens for the TO_COIL  output filters.

2) I had to change the filters for the suspension with regards to the TO_COIL output filters so they go in the correct filter banks.

3) Burt restores to times previous March 11th around noon, will put your TO_COIL output filters in a funny state that will need to be fixed.

4) The simplant RESPONSE filters had to be moved to the correct filter banks.

5) If you have some model I'm not aware of that uses the FiltMuxMatrix piece, it is going to correctly build now, but you're going to have to move filters you may have created with foton.

Ridiculous and hacky. Digital stabilization removed as well as the old "leave a pile of equipment on a stool" strategy.

We used a a BNC cable to send a pickoff of the beam before the recombination to the end via an SR560.

[Kiwamu, Larisa] 

We want to increase gain in the lower frequencies, so a circuit must be designed (a passive low pass filter). 

First, measurements were taken at the X arm for impedance and capacitance, which were 104.5kOhms and 84.7pF respectively. Kiwamu decided to make the circuit resemble a voltage divider for ease of calculation, such that Vout/Vin would be a ratio of some values of the equivalent circuit reactance values. After a few algebra mistakes, this Vout/Vin value was simplified in terms of the R, C measured and the R', C' that would be needed to complete the circuit. 

Since the measured C was very small and the measure R was fairly high, the simplified form allowed us to pick values of R' and C' that would make the critical frequency occur at 0.1Hz: set the R' resistance to 1MOhm and C' capacitance to 10uF, which would yield a gain ~1.

With these values a circuit we can start actually making the circuit.

Aidan: Joe and I have added a channel that takes the DC output from the vertex beatnote PD and sends it, via RFM, to a DAC at the ETMX end. Immediately before the output is a filter C1GCX_AMP_CTRL. The output of the DAC is connected to the CURRENT LASER DIODE modulation input on the back of the Innolight driver. This will modulate the current by 0.1A/V input.

We should be able to modulate the green laser on the end now and stabilize the intensity of the amplitude on the beatnote PD at the vertex. (In this configuration, the ampltiude noise of the PSL laser will be injected onto the end laser - we may want to revisit that).

Joe's comments on model change:

I added a RFM connection at the output of the C1:GCV-XARM_BEAT_DC filter in the c1gcv model.  The RFM connection is called: C1:GCV-SCX_ETMX_AMP_CTRL.

This RFM connection goes to the c1scx model and into Kiwamu's GCX box, which uses top_names.  There's a filter inside called AMP_CTRL, so the full filter name is C1:GCX-AMP_CTRL.  The output then goes to the 7th DAC output.

Photos:

1. NPRO CURRENT CTRL plugged into DAC channel 7
2. You can actually see it's channel 7 in this image
3. The other end plugged into the back of the Innolight driver
4. Schematic of the setup
5. Updated C1ALS_OVERVIEW MEDM screen (I don't know why the field in the background turned orange - maybe it's coming into a long dry summer?)

The reason that I chose this PD is that, apparently, the green light coming from the cavity is clipped when it is picked off for its DC PD.

There are 3 standard techniques to reduce this effect:

1) Stabilize the end laser by sensing the green light coming into the PSL before recombination and feeding back with SR560 (this is the only one that you should try at first).

2) Moving to the center of the MFD fringe via ETM steps.

3) Auto-alignment of the beam to the arm.

We can modify the freq divider circuit to make it a comparator.

The next steps we should do are :

We are limited by the intensity noise of the X arm transmitted green light.

Since the intensity noise from the PSL wasn't big enough to explain the differential noise (#4392), so this time I measured the noise contribution from the X arm transmitted light.

(coupling measurement)

  I performed the same intensity noise coupling measurement, but this time between the DC signal of the beatnote RFPD and the beatnote signal.

 While measuring it, I excited the intensity of the PSL laser by using the same AOM like I did yesterday. This AM cause the observable intensity noise on the beatnote RFPD.

With the excited AM, we can pretend to have an excited AM on the green transmitted light from the X arm, of course assuming the intensity noise coupling from the PSL is less.

To simulate digitization noise, the easiest way I found was to use the MathFunction block, found in the CDS_PARTS model, under simLinkParts. 

The MathFunction block supports square of input value, square root of input value, reciprocal of input value, and modulo of two input values.

The last is useful because it casts the input values as integers before taking the modulo.By placing this block after the saturation block (set to +/- 32768), adding 32768.5, choosing the 2nd input to be larger than 2 * 32768 (100,000 in this case), and then subtracting 32768, we wind up with a rounding function. 

The above method has been applied to the c1spy model in the CI and SO out sub-blocks.

I measured the transfer function, shot noise, and dark spectrum of AS55.

From the shot noise measurement, the RF transimpedance is (556.3 +- 0.8) Ohms and the dark current is (2.39 +- 0.01) mA. The dark noise agrees with the approximate value calculated from the circuit components.

There are no anomalous oscillations when there is no light on the photodiode. I am working on fitting the transfer function in LISO but the other plots are on the wiki at http://blue.ligo-wa.caltech.edu:8000/40m/Electronics/AS55

Today was a banner day for Simulated Plants.

Joe and Jamie have been working to get it all happening and this afternoon we started stuffing filters into the plant to make it act like the:

We put in the following features so far:

1. Anti-Imaging filters (these are hacked to be approximate since the real ones are 7570 Hz LP filters and the SimAI only can have filters up to 8192 Hz).
2. Dewhitening filters (copied from the SimDW in the SUS-ETMY screens)
3. Coil Driver transimpedance (1 / 200 Ohms)
4. Magnet-coil force constant (0.016 N/A)
5. Conversion from Coil to DOF Basis
6. All DOFs of the mechanical model are represented as simple harmonic oscillators with Q~100 and f ~ measured free swinging peaks.
7. Signals/Noise can be injected either as force noise on the test mass or as displacement noise at the suspension point.
8. Conversion from DOF to Shadow Sensor basis.
9. Optical Levers (with whitening)
10. Shadow Sensors have 2V/mm readout gain and whitening filters before being digitized by the SimADC.

We have also changed the switching logic for the SUS and SimETMs for the shadow sensor whitening. It used to be that either the hardware OR the software whitening was on. Now we have made it like all of the other whitening/antiwhitening in LIGO and the whitening/antiwhitening come on together. Joe and Jamie are going to propagate this to the other SUS. The hardware filter is a 30,100:3 (poles:zeros) whitening filter. The digital filter used to also be 30,100:3 with a DC gain = 1. I've changed the FM1 filter in the XXSEN filter banks into a 3:30 for the ETMY so that it now comes on and just compensates the hardware filter. This change should be propagated to all other SUS and the MEDM screens updated to show the new situation.

After this change, we decided to calibrate the {UL,UR,LL,LR,SD}SEN channels into units of microns. To do this we have made an FM6 filter called 'cts2um' that accounts for the OSEM gain and the ADC conversion factors. These channels are now in units of microns without applying any calibration in the DTT or Dataviewer. The plot below shows the OSEM shadow sensor time series with all damping loops ON and a very rough version of seismic noise being injected in all 6 DOFs (note that the y-axis is microns and the x-axis is seconds).

Next, Jamie is adding the angular calibrations (so that SUSPIT and SUSYAW are in rads) and Chris is making vectift quality seismic noise injectors.

We also need to add coating thermal noise, suspension thermal noise, substrate thermal noise, ADC/DAC noise and a lot of MEDM screen indicators of what state we're in. I myself can't tell from the OSEM time series if its real or Sim.

For some reason the c1ioo machine suddenly died just 30 miteus before.

It died after we added a DAQ channel for c1gcv and rebooted the frame builder.

It didn't respond to a ping command. Therefore I rebooted the machine by clicking the physical reset button.

Now it seems fine.

Here is a new plot for the differential noise measurement. I plot a noise contribution from the intensity noise (brown curve).

If we believe this data, the differential noise is NOT dominated by the intensity noise of the PSL.

(intensity noise coupling measurement)

 Here is a plot for the transfer functions (TFs) from the intensity noise DCPD to the beat signal.

   In principle these TFs tell us how much intensity noise are contributed into the differential noise.

When I measured the spectra shown above, the frequency offset of the beatnote was at about 8 MHz from the zero cross point.

Keeping the same lock, I measured the transfer function (red curve) by using the swept sine technique on DTT. The setup for this measurement is depicted on the last entry (#4389).

Then I made the spectra above by multiplying the intensity spectrum by this TF.

  Later I measured another transfer function when the beatnote was at about 2 MHz from the zero cross point.

According to this measurement, our MFD gets insensitive to the intensity noise as the beat offset goes close to the zero cross point. This is consistent with what we expected.

We have one single O-ring on the 40m vacuum envelope. It is on the OOC west side, facing the AP table. This O-ring has to be protected from the force of this

door. There should be 3 shims  ~120 degrees apart to carry the full load, so it is not the O-ring that is getting squashed.

This morning I found only one of these shims in place.

[Koji, Steve, Suresh, Kiwamu]

The following video cables have been newly laid down :

  - MC1F/MC3F (65 ft.)

  - PMCR (100 ft.)

  - PSL spare (100 ft.)

  - PSL1  (100 ft.)

  - PSL2  (100 ft.)

Here is a diagram for our intensity noise coupling measurement.

The below is a plot for the intensity noise on the DCPD. (I forgot to take a spectra of the PD dark noise)

For some reason, the RIN spectrum becomes sometimes noisier and sometimes quieter. Note that after 10 pm it's been in the quiet state for most of the time.

An interesting thing is that the structure below 3 Hz looks like excited by motion of the MC when it's in the louder state.

The screens for the simplified c1spx model have been updated.  I re-introduced the suspension point information into the sensor output matrix so we can take into account the fact that as the entire supporting structure moves, the osems moves relative to the optic.

Master screens for the noise filters (i.e. 60 Hz, suspension point motion, and optic noise) have been created.

I have currently set the matrix values of the c1spx model to handle just longitudinal motion.  I.e. Coils drive only in the POS degree of freedom and sensor read outs are also only in the POS degree of freedom.  I've turned off all the noise inputs.

I added a simple double pole at 1 Hz in the C1:SUP_ETMX_PL_F2P_0_0 filter bank.

Ansell AccuTech 91-300 clean room gloves  ONLY in the 40m lab.

Cleaning and preparation must be carried out in these gloves also.

Noise below 10 Hz became larger again compared with the data before (see here #4352)

Note that the Y-axis is in MHz.

[Joe/Kiwamu]

 We found there are some filter names that we can not properly build for some reason.

The following names are not properly going to be built :

 - REFL_DC

 - AUX

If we use the names shown above for filters, it doesn't compile any filter modules.

We took a quick look around the src files including feCodegen.pl, but didn't find any obvious bugs.

[Jenne, Chris, Kiwamu]

 A photo diode and an AOM driver have been newly setup on the PSL table to measure the intensity noise coupling to the beat note signal.

We tried taking a transfer function from the PD to the beat, but the SNR wasn't sufficient on the PD. So we didn't get reasonable data.

(what we did)

  - put a DCPD after the doubling crystal on the PSL table. The PD is sitting after the Y1 mirror, which has been used for picking off the undesired IR beam.

  - installed the AOM driver (the AOM itself had been already in place)

  - injected some signals onto the AOM to see if we can see an intensity fluctuation on the PD as well as the beat signal

(intensity noise)

  In order to have better SNR for the intensity measurement, we put an AC coupled SR560 with the gain of 100 just before the ADCs.

When a single frequency signal was applied from a Stanford Research's function generator to the AOM, we could clearly see a peak at the doubled frequency of the injected signal.

Also a peak at the same frequency was found on the beat note signal as well.

But when random noise was injected from the same function generator, the random noise looked below the ADC noise.

Jenne adjusted the output voltage from the PD to about 1 V to avoid a saturation in the analog path, but later we realized that the ADC counts was marely ~ 20 counts.

So we will check the ADC tomorrow. Hopefully we will get a good SNR.

[Joe, Jamie]

We modified the c1scx model to have a switch to go between simulated and real plants.  The channel is currently C1:SCX-SIM_SWITCH. 

When this channel is zero, the simulated plant channels are going to the ADCs and zeros  are going out to the real DACs.  When this channel is one, the real ADCs are coming in, and real data is going out to the DACs.

Jamie will be adding a big green/red light to the suspension screens which indicate the state of the simulated plant.  We will also eventually add this to the overall status screen.

A control screen for the simulated plant is located at /opt/rtcds/caltech/c1/medm/c1spx/master/C1SUP_ETMX.adl.  These are currently a work in progress.

Here I explain how I estimate the contribution from the differential noise shown in the plot on my last entry (#4376) .

(background)

 According to the measurement done about a week ago, there is a broadband noise in the green beatnote path when both Green and IR are locked to the X arm.

The noise can be found on the first plot on this entry (#4352) drawn in purple. We call it differential noise.

However, remember, the thing we care is the noise appearing in the IR PDH port when the ALS standard configuration is applied (i.e. taking the beatnote and feeding it back to ETMX).

So we have to somehow convert the noise to that in terms of the ALS configuration.

In the ALS configuration, since the loop topology is slightly different from that when the differential noise was measured, we have to apply a transfer function to properly estimate the contribution.

(How to estimate)

 It's not so difficult to calculate the contribution from the differential noise under some reasonable assumptions.

Let us assume that the MC servo and the end PDH servo have a higher UGF than the ALS, and assume their gains are sufficiently big.

Then those assumptions allow us to simplify the control loop to like the diagram below:

 Since we saw the differential noise from the beatnote path, I inject the noise after the frequency comparison in this model.

Eventually the noise is going to propagate to the f_IR_PDH port by multiplying by G/(1+G), where G is the open loop transfer function of the ALS.

The plot below shows the open loop transfer function which I used and the resultant G/(1+G).
 

In the curve of G/(1+G), you can see there is a broad bump with the gain of more than 1,  approximately from 20 Hz to 60 Hz.

Because of this bump, the resultant contribution from the differential noise at this region is now prominent as shown in the plot on the last entry (#4376).

with script

 
Fast work indeed! It would be nice if we could have the following details filled in as well
a) A short title and caption for the table, saying what we are measuring
b) the units in which this physical quantity is being measured.

It is good to keep in mind that people from other parts of the group, who are not directly involved in this work, may also read this elog.

I made a noise budget for the ALS noise measurement that I did a week ago (see #4352).

I am going to post some details about this plot later because I am now too sleepy.

Its been well noted in the past that sweeping the PMC at high power leads to a distortion of the transmitted power curve. The explanation for this was coating absorption and thermo-elastic deformation of the front face of the mirrors.

Today, I did several sweeps of the PMC. I turned off its servo and tuned its PZT so that it was nearly resonating. Then I drove the NPRO via the HV driver (gain=15) with 0-150 V (its 1.1 MHz/V) to measure the PMC transmitted light. I adjusted the NPRO pump diode current from 2A on down to see if the curves have a power dependent width.

In the picasa web slideshow:

There are 3 significant differences between this measurement and the one by John linked above: its a new PMC (Rick says its the cleanest one around), the sweep is faster - since I'm using a scope instead of the ADC I feel free to drive the thing by ~70 MHz in one cycle. In principle, we could go faster, but I don't want to get into the region where we excite the PZT resonance. Doing ~100 MHz in ~30 ms should be OK. I think it may be that going this fast avoids some of the thermal distortion problems that John and others have seen in the past. On the next iteration, we should increase the modulation index for the 35.5 MHz sidebands so as to get a higher precision calibration of the sweep's range.

By eye I find that the FWHM from image #4 is 11 ms long. That corresponds to 300 mV on the input to the HV box and 15 V on the PZT and ~16.5 MHz of frequency shift. I think we expect a number more like 4-5 MHz; measurement suspicious.

Finished calculations for harmonic distortion at each of the 10 outputs of the RF distribution box. The diagram can be found on Suresh's post  http://nodus.ligo.caltech.edu:8080/40m/4342

THD calculation consisted of gather data on the dBm at harmonics of the fundamental frequency. These dBm values were converted into units of power and plugged into the appropriate THD equation pulled from Wikipedia: 

On the table, the number 1-6 correspond to the harmonic number of the input frequency used. For example, the first five PD's listed used an 11MHz source, while the second set of five PD's listed used a 55MHz source. Values listed under certain harmonics are dBm measurements at the corresponding frequency. The P-subscript values are essentially the dBm measurements converted to units of power (Watts) for ease of calculation in the equation above. THD is then calculated using these power units; I have converted the ratios to percentages.

It should be noted that as with all THD calculations, the more data points collected, the more precise the THD % will be.

By the way, the outputs on the physical RF distribution box for REFL165 and AS165 are actually labeled as REFL166 and AS166. 

 I somehow screwed up the PDH box at the X end station. 

Right now it's not working, so I am going to check and fix it today.

 In the last evening I found that one of the gain stages on the PDH box wasn't fully functional.

So I started investigating it and I though it was going to finish soon, but actually it wasn't so easy.

  The PDH box has several gain stages. So an input signal goes through a buffer, a filter, a boost and an output buffer stages sequentially.

The boost stage is supposed to have gain of 10, but I found it didn't have such gain.

In fact the gain was something like -30dB which is pretty small. Plus this boost stage was imposing an wired bump on the transfer function around 50 kHz.

I checked the voltages on some components around the boost stage and confirmed there were no strange voltage.

Then I suspected that the op-amp : LF356 had been broken for some reason. So I replaced it by LT1792 to see if it fixes the issue.

Indeed it did make it functional. However after few minutes of the replacement, it went back to the same bad condition.

I have no idea about what was going on at that time. Anyway it needs more careful investigations.

  I temporarily put a jumper cable on the board to skip this stage, but now the PDH lock is not healthy at all.

Here is a partial list of stuff which is being packed at LLO to be shipped to CIT.  The electronics ckt boards are yet to be added to this list.  Will do that tomorrow.

The previous measurement for the shot noise of POY had the dark noise at ~100 nV/rtHz. I redid the measurement and got 26 nV/rtHz for the dark noise. I think that when I made the previous measurement, the spectrum analyzer had automatically added some attenuation to the input that I failed to remove. This added attenuation raised the noise floor of the measurement making the dark noise of POY appear larger than it is.

The updated measurement can be found on the wiki at http://lhocds.ligo-wa.caltech.edu:8000/40m/Electronics/POY.

Kiwamu and I noticed that there is a ghost beam on the green beam going into the ETM. What we see is some interference fringes on the edge of the transmission of the green beam through the dichroic beam splitter (DCBS). If we look at the reflection from the dichroic beam splitter these are much more pronounced.

The spacing of the fringes (about 2 per 10mm) indicates an angle between the fields of around 0.1 mrad.

We were able to cause significant motion of the fringes by pushing on the knobs of the steering mirrors that steer the beam into the DCBS. A rough calculation of the derivative of optical path difference between the ghost and the primary beam as a function of input angle gives about 15 microns per mrad. What filtering the effect the arm cavity will have on the ghost beam is not immediately clear, but the numbers shouldn't be too difficult to determine.

As previously noted, there are multiple beams coming back from the ETM surface onto the PDH PD on the end table. They are spread out in a vertical pattern. All the spots swing together (as the ETM moves?).

I moved the PDH Green PD on the end table so that it was further away from the Faraday and I added an iris in between the Faraday and the PD. Now only the principle reflection from the ETM is incident on the PD. See attached photos. In order to sneak past the neighbouring optics, I had to steer the beam down a bit, so the PD is now lower than it previously was.

Just FYI: the angle between the returning beams is about 5 or 6 mrad at the PD. Before the beams get to the PD they go through a telescope that de-magnifies the beam by about 5 or 6 times. This implies that the angle between adjacent returning beams from the ETM is around 1 mrad at the ETM.

This does make the position of the spot on the PD more susceptible to the alignment of the ETM - we should use a short focal length lens and image the ETM plane onto the PD.

First image - overview of table

Second image - the three returning beams immediately before the IRIS

Third image - a close up of the IRIS and PDH PD. 

I moved old POX shutter from ITMY optical table to the south end. MEDM POX mechanical shutter screen is now closing the green beam  injection into the Y arm.

I kluged in a 40m long bnc cable that Alberto left on the floor for control. It is labelled POX-sht  This is a temporary set up.

[Koji / Rana]

- Since the MC servo had UGF up to ~20kHz and huge servo bump at 50kHz, we needed more phase between 20kHz to 100kHz.

- Today a phase compensation filter in a Pomona box has been inserted between the MC servo box and the FSS box.
  This is a passive filter with zero@14kHz and pole@140kHz. We obtain ~60deg at around 50kHz.

- After the insertion, the lock of the MC was achieved immediately. The overall gain as well as the PZT fast gain was tweaked
  such that the PC feedback is reduced down to 1~2.

- The OLTF has been measured.
  The insertion of the filter change increased the UGF to 130kHz even with "40:4kHz" and double super boost turned on.
  The phase margin is 54deg. Quite healthy.

- Rana modified the existed Auto Locker script.
  It is now continuously running on op340m!
  We made a couple of testsif it correctly relock the MC and it did. VERY COOL.

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NEXT STEPS
- Measure the PMC cavity pole
- Measure the circuit TF and try to shave off the phase lag.
- Measure the PZT resonance of the NPRO and put notch in the PZT path
- Increase the UGF / measure the openloop TF