Here is a list of tasks I think we should prioritize for the next two weeks. The idea is to get back to the previous state of being able to do single arm, PRMI-on-carrier and DRMI locking, before making further changes.

Once the new folding mirrors arrive, I'd like to modify the SRC length to allow locking in the signal-recycled config as opposed to RSE. Still need to do the detailed layout, but I think the in-vacuum layout will work. In that case, I'd like to also move the OMC and OMMT to the IY table, and also move the in-air AS photodiodes to the IY in-air optical table. This is why I've omitted the OMC alignment from this near-term list, but if we want to not move the OMC, then we probably should add alignment of the AS beam to the OMC to this list.

 Just felt an EQ. Impulse moved some vertical blinds by several mm.

Tue Aug 07 23:26:06 2012 

 All optics except MC2 and ETMX are crazy

I was helping Den get started in the cleanroom yesterday, and I noticed that the new active TTs, like the old passive ones, are set to be 4" from the table.  So, like the old ones, we need 1.5" risers to get the center of the mirror up to our in-vac 5.5" beam height.  I didn't see any risers in there when I was looking around. 

Steve says he still has the drawing that he gave to the shop for the old tip tilts, so he'll double check that the dimensions are the same, and then ask the shop to make 4 more.

[Lisa, Rana, Jenne]

Lisa asked to see a model of the PRMI sensing matrix with REFL165 included, in the hopes that it wouldn't be as degenerate as REFL33.

The conclusion, immediately after looking at this, is that I should make sure the REFL beam is nicely aligned onto the REFL165 PD (Koji did some tests, swapping out the REFL165 resonant PD with a broadband PD, and I don't remember if he aligned beam back onto the REFL165 PD).  Then, I need to measure the PRMI sensing matrix, including REFL165.  Hopefully, it is similar to the model, and we can use it as our 3f diode for locking.

There is no sensible REFL165 PD in the lab. I am supposed to prepare a new version of REFL165 using prototype BBPD.

I'm currently in the process of tracking down what legacy code is interfering with the new lsc model.

It turns out if you change the name of lsc file to something else (say scx as a quick test for example), it runs fine.  In fact, the lsc and scx GDS_TP screens work in that case (since they're looking at the same channels).  As one would expect, running them both at the same time causes problems.  Note to self, make sure the other one is killed first.  It does mean the lsc code gets loaded part way, but doesn't seem to communicate on EPICs or to the other models.  However, I don't know what existing code is interfering.  Currently going trhough the target directories and so forth.

Rob found puddles of water very close to the chiller during lunch time. We raised the unit and took the side cover off. All surfaces were dry and the water level in the tub normal.

Later on we discovered that one of the Vons distilled water bottle was leaking. Jenne and I checked for excess amount of condensing water droplets inside the MOPA box.

On the bare,not insulated tubing and valve are loaded with droplets of water. Relative humidity is 44% at 24 C and HEPA filter speed set to 80 V in the enclosure.

The Netgear Network Switch in the top shelf of Nodus' rack has a broken fan. It is the one interfaced to the Martian network.

The fan must have broken and it is has now started to produce a loud noise. It's like a truck was parked in the room with the engine running.

Also the other network switch, just below the Netgear, has one of its two fans broken. It is the one interfaced with the General Computer Side.

I tried to knock them to make the noise stop, but nothing happened.

We should consider trying to fix them. Although that would mean disconnecting all the computers.

Net switch mumbo-jumbo:

Although Rana is going to buy a replacement for the Netgear Switch for martian, I opened the lid of the Netgear as the fan already have stopped working.
Also the lid of the other network switch for GC (Black one) was opened as it has a broken fan and a noisy half-broken fan.

I have asked Steve to buy replacement fans. These would also be the replacement of the replacement.

During the work, it seemed that I accidentally toggled the power supply of linux1. It lead lengthy fsck of the storage.
This is why all of the machines which rely on linux1 got freezed. linux1 is back and the machines looked happy now.

If you find any machine disconnected from the network, please consult with me.

EDIT: The script and template file have been moved to /opt/rtcds/caltech/c1/scripts/general/netgpibdata/

___________________________________________________________________________________________________________

The NEW and IMPROVED script for remotely getting data from Agilent 4395A network analyzer is located at /users/nichin

This script is quite different from the one in Elog 10108 and fetches us both magnitude and phase. There is an added feature of setting the IF Bandwidth.

The network analyzer is located at crocetta.martian (192.168.113.108)

How to run the script:

> python NWAG4395A_data_acq.py [filename.yml]

1. The script accepts sweep parameters and output options via a .yml file that is written following a template that can be found at /users/nichin/NWAG4395A_parameters.yml
2. The data obtained is stored as a .dat file and the corresponding details regarding the acquired data is in a .par parameter file
3. Separate .dat and .par files are created for phase and magnitude of voltage data.
4. You can choose to get a plot of the data obtained by specifying it in the .yml file. The plots are automatically stored as PDF.
5. Plots, data and parameter files are all stored in a new folder that is created with a timestamp in its name.
6. NOTE: Plotting options are only available in computers running numpy versions of 1.6.0 or above.(Currently only Ottavia and Chiara)

Test Run:

I connected a simple 2MHz Low pass filter between the modulation output and signal input of the NA and ran a scan from 100KHz to 20MHz. The script was run from Ottavia.

The expected plot was obtained and is attached here.

Current work:

Setting up the RF switch in rack 1Y1 to select between required PDs and scripts to tell it which channel to choose over the Ethernet.

netgpibdata.py -i 131.215.113.106 -d AG4395A -a 10 -f spectrum01

Just now we had another EPICS freeze. The network was still up; i.e. I could ssh to chiara and fb, who both seemed to be working fine.

I could ping c1lsc successfully, but ssh just hung. fb's dmesg had some daqd segfault messages, so I telnet'ed to daqd and shut it down. Soon after, EPICS came back, but this is not neccesarily because of the daqd restart...

[Eric Q, Gautam, Koji]

We went through the network connections to produce the mapping of the instruments.
Gautam summarized the notes into a spread sheet. See attachments.

We didn't find any irregular connections except for the connection of NETMGR port of c1ioo to Martian Network.
This cable was removed.

[johannes, gautam]

I forgot we had done this last year already, but we updated the control room network switch labels and double checked all the connections. Here is the status of the connections and labels as of today:

There are a few minor changes w.r.t. labeling and port numbers compared to the Dec 2015 entry. But it looks like there was no IP clash between Rossa and anything (which was one of the motivations behind embarking on this cleanup). We confirmed by detatching the cable at the PC end of Rossa, and noticed the break in the ping signals. Plugging the cable back in returned the pings. Because Rossa is currently un-bootable, I couldn't check the MAC address.

We also confirmed all of this by using the web browser interface for the switch (IP = 192.168.113.249).

Today I placed the PDA255 photodiode on the PSL table to catch the small amount of beam power reflected by the second polarizing beam splitter in my setup. I plugged the PD output to the oscilloscope to measure the voltage output and positioned the PD such that the voltage output was maximized. At best I was able to achieve a 300 mV DC output voltage from the PD, (which seems a bit low, as the PD is specified to go from 0 to 5 V and the specifications say that the response becomes nonlinear after 10 mW/cm^2 and my beam has an intensity of approximately 5 mw/cm^2. I would therefore expect to get more beam power but after over an hour of maneuvering, 300 mV was the highest voltage output I could get).

I am planning, tomorrow afternoon, to take a measurement of the amplitude response of the PZT driving the NPRO laser. I moved the 4395 spectrum/network analyzer to near the PSL table and connected the RF output to an RF splitter. I fed one output of that into the PZT and the other output into the R port on the network analyzer. I fed the PD output into the A port. I plan to measure A/R as a function of driving frequency, sweeping from 10 Hz to 30 mHz.

I also worked to improve the mode matching of the NPRO beam coming from the AP table to the reference cavity. I drove the temperature of the NPRO at 0.100 Hz with an amplitude of 0.300 V, which Koji told me corresponds to a 1GHz change in the laser frequency. The transmission from the cavity is being monitored by a camera connected to a TV monitor, and also by a PD connected to an oscilloscope. I then repositioned the second lens in my mode matching setup in an attempt to increase the transmission peaks from the zeroth order spacial mode and decrease the transmission peaks from higher order modes. I may have improved the mode matching slightly but I was unable to improve it significantly.

The ABSL beam had been blocked so that it wouldn't enter the interferometer. I moved the block so that the beam I've been using is unblocked by the beam going to the interferometer is still blocked.

I positioned a fast lens (f=28.7mm) a little over an inch in front of the PDA255 in order to decrease the spot size incident on the PD. I adjusted the rotation angle of the half wave plate to maximize the transmitted power through the PBS to the cavity and minimize the power reflected to my PD. I then adjusted the lens potion to fix the beam on the PD. The voltage output of the PD is now 150mW, but I have the ability to increase the incident power by rotating the wave plate slightly.

Now all I need is to set up the network analyzer again to record the amplitude response to modulating the PZT from 10 Hz to 30 MHz, reduce the input voltage into the analyzer using a DC block.

 I rolled the network analyzer over to the PSL table (on the south side). I'm borrowing the DC block from Kiwamu's green locking setup. I'm going to first measure the amplitude response of a low pass filter to made sure that the analyzer is outputting what I expect. Then I will measure the laser PZT amplitude response. I plan to finish the measurement and return the network analyzer to it's usual location tonight.

[Mike P / Koji / Tega / Anchal]

IMSS/LIGO IT notified us that "ILOM ports" of one of our hosts on the "114" network are open. We tried to shut down obvious machines but could not identify the host in question. So we decided to do a bit more systematic search of the host.

[@Network Rack]
- First of all, we disconnected the optical cables coming to the GC router while the ping is running on the AIRLIGO connected laptop (i.e. outside of the 40m network). This made the ping stopped. This means that the issue was definitely in the 40m.
- Secondly, we started to disconnect (and reconnect) the ethernet cables from the GC router one by one. We found that the ping response stops when the cable named "NODUS" was disconnected.

[@40m IFO lab]
- So we tracked the cable down in the 40m lab. After a while, we identified that the cable was really connected to nodus.

- Nodus was supposed to have one network connection to the martian network since the introduction of the bidirectional NAT router (rather than the old configuration with a single direction NAT router).

- In fact, the cable was connected to "non-networking" port of nodus. (Attachment 1). I guess the cable was connected like this long time, but somehow the ILOM (IPMI) port was activated along with the recent power cycling.

- The cable was disconnected at nodus too. (Attachment 2) And a tape was attached to the port so that we don't connect anything to the port anymore.

A few weeks ago we did some internet speed tests and found a dramatic difference between our general network and our internal Martian network in terms of access speed to the outside world.

As you can see, the speed from nodus is consistent with a Gigabit connection. But the speeds from any machine on the inside is ~100x slower. We need to take a look at our router / NAT setup to see if its an old hardware problem or just something in the software firewall. By comparison, my home internet download speed test is ~48 Mbit/s; ~6x faster than our CDS computers.

controls@megatron|~> speedtest
/usr/local/bin/speedtest:5: UserWarning: Module dap was already imported from None, but /usr/lib/python2.7/dist-packages is being added to sys.path
  from pkg_resources import load_entry_point
Retrieving speedtest.net configuration...
Testing from Caltech (131.215.115.189)...
Retrieving speedtest.net server list...
Selecting best server based on ping...
Hosted by Race Communications (Los Angeles, CA) [29.63 km]: 6.52 ms
Testing download speed................................................................................
Download: 6.35 Mbit/s
Testing upload speed................................................................................................
Upload: 5.10 Mbit/s
controls@megatron|~> exit
logout
Connection to megatron closed.
controls@nodus|~ > speedtest
Retrieving speedtest.net configuration...
Testing from Caltech (131.215.115.52)...
Retrieving speedtest.net server list...
Selecting best server based on ping...
Hosted by Phyber Communications (Los Angeles, CA) [29.63 km]: 2.196 ms
Testing download speed................................................................................
Download: 721.92 Mbit/s
Testing upload speed................................................................................................
Upload: 251.38 Mbit/s

I've added a new program called getdata (to scripts/general/getdata) that will conveniently pull arbitrary data from an NDS server, either DQ or online (ie. testpoints).

Start times and durations may be specified.  If past data is requested, you must of course be requesting DQ channels.  If no start time is specified, data will be pulled "online", in which case you can specify testpoints.

If an output directory is specified, the retrieved data will be stored in that directory in files named after the channels.  If an output directory is not specified, no output will be

Help usage:

controls@pianosa:~ 0$ /opt/rtcds/caltech/c1/scripts/general/getdata --help
usage: getdata [-h] [-s START] [-d DURATION] [-o OUTDIR] channel [channel ...]

Pull online or DQ data from an NDS server. Use NDSSERVER environment variable
to specify host:port.

positional arguments:
  channel               Acquisition channel. Multiple channels may be
                        specified acquired at once.

optional arguments:
  -h, --help            show this help message and exit
  -s START, --start START
                        GPS start time. If omitted, online data will be
                        fetched. When specified must also specify duration.
  -d DURATION, --duration DURATION
                        Length of data to acquire.
  -o OUTDIR, --outdir OUTDIR
                        Output directory. Data from each channel stored as
                        '.txt'. Any existing data files will be
                        automatically overwritten.
controls@pianosa:~ 0$ 

For reasons unknown, the seismic spectra posted above Rosalba has been wrong since ~January when it was first posted.  The noise that we were claiming was waaaay lower than is really possible.

Rana and I checked the calibrations, and the numbers in DTT for the Ranger and the Guralp are correct (it's unknown what was being used at the time of the bad plot) - Cal for the Guralp is 3.8e-9 m/s, and for the Ranger is 1.77e-9 m/s.

Something is funny with the accelerometer calibration.  Hopefully Kevin's investigation will sort it out.  Their calibration used to be 1.2e-7 m/s^2 , but it was changed to be 7e-7 m/s^2 to match the noise level of the accelerometers with the seismometers at ~10Hz. We need to go through the calibration carefully and figure out why this is!

Posted above Rosalba for easy reference, and attached below, is the new seismic spectra.  The black trace is when the Ranger's mass is locked down, and the teal circle markers indicate the Guralp Spec-Sheet Noise Floor.

** Rana says> the y-axis in Jenne's plot is (m/s)/sqrt(Hz). The Guralp has a velocity readout bandwidth of 0.03-40 Hz, so we would have to modify the calibration to make it right in those frequencies. I believe the Ranger cal has the correct poles in it. The huge rise at low frequencies is because of the 1/f noise of the SR560.

[Jenne Koji]

The PD signals are transmitted to the suspension now.

The trigger thresholds were set to -1. This means the triggers are always on.

A new type of plot is now available for use in the summary pages, based on EricQ's 2D histogram plots (elog 11210). I have added an example of this to the SandBox tab (https://nodus.ligo.caltech.edu:30889/detcharsummary/day/20151119/sandbox/). The usage is straighforwad: the name to be used in config files is histogram2d; the first channel corresponds to the x-axis and the second one to the y-axis; the options accepted are the same as numpy.histogram2d and pyploy.pcolormesh (besides plot limits, titles, etc.). The default colormap is inferno_r and the shading is flat.

Todd informed me that the ADC Timing adaptor boards we had ordered arrived today. I had to solder on the components and connectors as per the schematic, though the main labor was in soldering the high density connectors. I then proceeded to shut down all models on c1lsc (and then the FE itself). Then classic problem of all vertex machines crashing when unloading models on c1lsc happened (actually Koji noticed that this was happening even on c1ioo). Anyways this was nothing new so I decided to push ahead. 

I had to get a cable from Downs that connects the actual GS ADC card to this adaptor board. I powered off the expansion chassis, installed the adaptor board, connected it to the ADC card and restarted the expansion chassis and also the FE. I also reconnected the SCSI cable from the AA board to the adaptor card. It was a bit of a struggle to get all the models back up and running again, but everything eventually came back(after a few rounds of hard rebooting). I then edited the c1x04 and c1lsc simulink models to reflect the new path for the X arm ALS error signals. Seems to work alright.

At some point in the afternoon, I noticed a burning smell concentrated near the PSL table. Koji traced the smell down to the c1lsc expansion chassis. We immediately powered the chassis off. But Steve later informed me that he had already noticed an odd burning smell in the morning, before I had done any work at the LSC rack. Looking at the newly installed adaptor card, there wasn't any visual evidence of burning. So I decided to push ahead and try and reboot all models. Everything came back up normally eventually, see Attachment #1. Particle count in the lab seems a little higher than usual (actually, according to my midnight measurement, they are ~factor of 10 lower than Steve's 8am measurements), but Steve didn't seem to think we should read too much into this. Let's monitor the situation over the coming days, Steve should comment on the large variance seen in the particle counter output which seems to span 2 orders of magnitude depending on the time of the day the measurement is made... Also note that there is a BIO card in the C1LSC expansion chassis that is powered by a lab power supply unit. It draws 0 current, even though the label on it says otherwise. I a not sure if the observed current draw is in line with expectations.

The spare (unstuffed) adaptor cards we ordered, along with the necessary hardware to stuff them, are in the Digital FE hardware cabinet along the east arm.

Steve:  particle count in the 40m is following outside count, wind direction, weather condition .....etc. The lab particle count is NOT logged ! This is bad practice.

 [Manasa, Masayuki]

We made a new flowchart of ALS autolocker. We added the additional step to find the beat note frequency. We have to find a way to read the PSL temperature. By reading the PSL temperature we can decide the sweep range for the end green laser temperature with the curve which measured in previous measurement (in this entry)

We have three thresholds of error signal. One is the threshold for checking the arms are stabilized or not. It should be some hundreds count. Another threshold is to check that the suspensions are not kicked. This should be some thousands counts (in flow chart, it is 2K counts). The other is to check the optimal servo gain. If the servo gain is too high, the UGF is also too high and we will not have enough gain margin. The error signal start to oscillate at the UGF. We will check this oscillation and find the optimal gain. In flow chart this threshold is 1K counts.

The expected error signals derived from the estimated free running error signals of the ALS.

1) Previously estimated free-running noise (blue)
2) Previous in-loop ALS error signal (red)
3) Estimated error signal with the new servo (green)
4) Out-of-loop noise of the ALS with the arm controlled with the IR PDH (black)

Now the error signal (green) is expected to be very white.
The suppressed noise between 3 to 20Hz are below the sensing noise level.
There seems a little excess at 24.5Hz and 28Hz. If it is limiting the RMS, we need to take care of them.

Here are the MATLAB scripts and LISO codes for all of these servo analyses

The new ALS/LSC servo was implemented for the X arm.

I'll upload more data later but here I make quick remarks:

- We need to give the gain of 12 to have correct UGF with the ALS.

- With this servo, the Xarm PDH lock oscillates with the gain of 0.02. We need to lower the gain to 0.015.
  Also FM trigger should be changed not to trigger unused FMs (FM7/8)

New ALS servo performance

Attachment 1:

Comparison between the old (orange) and new (red). The new error signal (red) is suppressed like a white noise as expected.

Comparison between the out-of-loop evaluation (black) and the in-loop signal (red). Below 50Hz the out-of-loop is limited by the sensor-noise like something.
This out-of-loop stability was measured with the ALS stayed at the top of the resonance and calibrated the POX11 error signal.

Attachment 2:

New ALS servo with the LSC PDH signal. When the PDH signal is used for the control, FM4 is additionally used.
In this condition, the error signal was measured and calibrated into frequncy noise (Hz/sqrtHz).

By comparing the POX (with the new servo) and POY (with the old servo) signals, one can see that the new servo has better supression below 30Hz with almost no cost at ~100Hz.

I've installed a new 2pin lemo cable going from the CM servo out to in2 of the MC servo board, and removed the temporary BNC. I used some electrical tape to give the cable some thickness where the lemo head screws on to try to strain relieve the solder joints; hopefully this cable is more robust than the last. 

I put an excitation into the CM board, and saw it come out of MC_F, so I think we're set. 

As promised, I have made a final AP table drawing, including the MC camera relocation changes by Kiwamu. I have posted it in the wiki on the tables list, and on the AP table page I've attached the inkscape .svg I used to make it, if someone needs to do small modifications.

Attached is a pdf version of it.

Big changes:

1) REFL beam has been split into 4, to go in equal powers and equal beam size to the now 4 REFL RFPDs, 11, 33, 55 and 165. A lens had to be added for REFL165 because it's a 1mm PD instead of 2mm like the other 3.

2) MC camera has moved.

3) I've cleaned up most of the random components on the table, put them away, and tidied up the cabling.

I wanted to try out the ASS tonight, but I wanted some kinds of screens thrown together so I would know what I was doing.  Turns out screens take longer than I thought.  Am I surprised? Not really. 

They're probably at the ~85% mark now, but I should be able to try out the ASS tomorrow I think.

The free running PSL+AUX beat frequency noise spectrum has been measured via PLL. AUX laser PZT PM and AM responses were measured too. 

Rough notes about these measurements:

Laser -> QWP -> HWP -> PBS -> 10% BS -> Beat
3.4Vpp out of PD, (40% contrast)
20dB Coupler, output to analyzer, coupled output to Mixer (-a few dBm, didn't check specifically)
Mixer: ZP-3+, BLP-5.1 at output
LO: OCXO @ 36MHz 13dBm->5dB Att-> +8dBm LO at Mixer

Got ~65mVpp out of Mixer

Mixer out -> SR560, LP 3Hz, G=500 -> Pomona Summing node -> Laser PZT
~30kHz UGF ~30 deg phase

Spectra, OLG via SR785 taken with free running PSL, anthropomorphic temperature servo. Data sheet calibration used for PZT. SR560 output noise dominates over analyzer, mixer, PD. Spectrum looks ok, I think.

PM measured with AG4395. High impedance probe used for laser PZT, otherwise couldn't lock. PM calibrated via mixer voltage span for fringe-to-fringe. 

PSL beam blocked, AUX power increased to read 8.0V, AM measured with AG4395.

AM/PM doesn't look to dissimilar to old measurements on wiki. ~230kHz looks like a fine modulation freq. 

Still to be done to AUX laser:
- joint PSL/AUX temperature sweeps
- Output power vs. diode current
- Beam profile

I've performed the temperature sweep of PSL vs Innolight 1W AUX laser.

• I followed the procedure in this elog - started by turning of FSS and FSS Slow servos, closed the PSL shutter, noted down the value of PSL temperature
• As noted in elog 3759, there are multiple temperatures at which a beat can be found. I recorded all that I could find. The IR beat frequency was < 20MHz at the temperatures recorded (and had an amplitude of a few dBm, but I used a 20dB coupler to look at the signal on the HP spectrum analyzer
• The PMC unlocked each time I changed the PSL temperature, but the PMC autolocker worked for me every time
• We should use curve 3 in attachment 1, it is the most reliable set of temperatures at which a beat can be found
• PSL diode current was 2.100A, AUX laser diode current was 2.001A
• Attachment 2 is the data

It remains to measure the output power vs diode current, and the beam profile. I will do the latter on the SP table where there is a little more space. Because we have 1W from this NPRO, the knife-edge method requires a power meter that has a large dynamic range and is sensitive enough to profile the beam accurately. After consulting the datasheets of the power meters we have available (Scientech, Ophir and Coherent) together with Koji, I have concluded that the Coherent calorimeter will be suitable. Its datasheet claims it can accurately measure incident powers of up to 100uW, although I think the threshold is more like 5-10mW, but this should still be plenty to get sufficient resolution for a Gaussian intensity profile with peak intensity of 1W. We also checked that the maximum likely power density we are likely to have during the waist measurement process (1W in a beam of diameter 160um) is within the 6kW/cm^2 quoted on the datasheet.

I made an Altium schematic for the microphone amplifier circuit for fabrication.

mic_schematicv2.pdf

Two new BBPDs have been installed on the PSL table.

The first one was installed by Koji a few days ago, and I stalled the second one today.

They will serve as beat-note detectors for the green locking.

Next step : I have to lay down a long SMA cable which goes from the BBPD to the IOO rack.

Yuta and I bought some new BS mounts so that we could use the 4th port of the beamsplitters which are combining the PSL green and the arm transmitted beam, just before the Beat PD for each arm.  I just placed the Yarm one, and have aligned the light onto both the Beat PD and the Trans DC PD. 

I'll do the Xarm after lunch.

The new laptop for the Beam Profiler is ready for usage.

From the last meeting, we came to the idea of having 2 laptops that are designated for the beam profiler specifically. We now one laptop over at WestBridge, and one here at 40m. This makes it easier to travel with just the Beam Profiler heads, rather than carrying the Profiler heads + laptop. This machine has been named Stella by ChatGPT. Feel free to use it! (Only runs Windows 10)

Here is a photo of the board inside the broadband photodiode (one of them) that I took from the Gyro experiment:

This PD is Serial Number S1200271.

We need to have a look at the schematic, figure out what's in here now, and then modify this to be useful (appropriate resonances / notches, as well as amplification) for POP 22/110.

General Remarks on the BBPD

- To form the LC network: Use fixed SMD inductors from Coilcraft. SMD tunable capacitors are found in the shelf right next to Steve's desk.
  If the tuning is too coarse, combine an appropriate fixed ceramic SMC C and the tunable C (in parallel, of course)

- L1/C1a/C1b pads are specifically designed for an additional notch

- Another notch at the diode stage can be formed between the middle PD pin (just left of the marking "C3b") to the large GND pad (between C1a/C1b to C3a).
  You have to scratch off the green resin with a small flat screw driver (or anything similar)

- A notch at the amplifier stage can be formed between the output of MAR-6SM ("+" marking)  and one of the GND pads (left side of the "U1" marking)

- The original design of the PD is broadband. So additional notches on the diode stage provides notches and resonances.
  Check if the resonances do not hit the signal frequencies.

- One would think the PD can have resonant feature to reduce the coupling of the undesired signals.
  In some sense it is possible but it will be different from the usual resonant tank circuit in the following two points.

  * Just adding a parallel L between the cathode and ground does not work. As this DC current should be directed to the DC path,
    L&C combo should be added. In fact this actually give a notch-resonance pair. This C should be big enough so that you can ignore it
    at the target resonant frequency. Supply complimentary small C if necessary to keep low impedance of the Cs at the target frequency.
    (i.e. Check SRF - self-resonant frequency of the big C)

  * Since the input impedance of MAR-6SM is 50Ohm, the top of the resonant curve will be cut at 50Ohm. So the resultant shape looks
    like a bandpass rather than a resonance.

- So in total, simulation of the circuit is very important to shape the transimpedance. And, consider the circuit can not be formed as simulated
  because of many practical imperfections like stray Ls and Cs.

 I looked at the BBPD design so that we could make a POP22/110. It looks like it will be easy (I hope).

 The first attachment shows the schematic with the RF notch modified to handle 55 MHz. As long as the capacitor in this notch can be kept to below 20 pF, it doesn't degrade the noise so much,

The second attachment shows the TF and input referred noise. We ought to be able to get 20 pA/rHz at the input to the first RF amplifier.

The LISO files are in the svn under liso/examples/aLIGO_BBPD/,

Later, if we have to notch more than just 55 MHz, we can add a notch between the 2 RF amplifiers as Koji has done for the REFL165.