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  4505   Fri Apr 8 20:43:46 2011 kiwamuSummaryIOORF combiner + resonant box : impedance and reflection coefficient

 The input impedance of the resonant box was measured when an RF combiner was attached to the box.

Indeed the combiner makes the impedance more 50 Ohm and reduces the reflection.


**** measurement conditions ****

* The output of box, where the EOM will be connected,  was open so that the box tries resonating with a parasitic capacitor instead of the real EOM.

* ZFSC-3-13, a 3-way combiner from mini circuit, was used.

* The S-port of the combiner was directly attached to the box with a short connector (~ 30 mm).

* Port 1 and 2 are terminated by 50 Ohm.

* The input impedance was measured on port 3 with AG4395A net work analyzer.

* Reflection coefficient 'Gamma' were calculated from the measured impedance 'Z' by using an equation Gamma = (50-Z)/(50+Z).


The resonances are found at 11, 29 and 73 MHz (55 MHz resonance was shifted to 73 MHz because of no EOM).

Note that the resonances are at frequencies where the notches appear in the reflection coefficient plot.

Don't be confused by a peak at 70 MHz in the impedance. This is an extra resonance due to a leakage inductance from the transformer in the circuit.

Quote: from #4504

An RF combiner should be included in the triple resonant box because it eases impedance mismatching and hence lowers undesired RF reflections.

  4504   Fri Apr 8 19:43:03 2011 kiwamuSummaryIOORF combiner eases impedance mismatching

An RF combiner should be included in the triple resonant box because it eases impedance mismatching and hence lowers undesired RF reflections.

Therefore we should use three cables to send the RF signals to the box and then combine them in the box.


(RF combiner)

 With proper terminations an RF combiner shows 50 Ohm input impedance.

But it still shows nearly 50 Ohm input impedance even if the source port is not properly terminated (i.e. non 50 Ohm termination).

This means any bad impedance mismatching on the source port can be somewhat brought close to 50 Ohm by a combiner.

  The amount of deviation from 50 Ohm in the input impedance depends on the circuit configuration of  the combiner as well as the termination impedance.

For example a resistive 3-way splitter shows 40 Ohm when the source port is shorten and the other ports are terminated with 50 Ohm.

Also it shows 62.5 Ohm when the source port is open and the other ports are terminated with 50 Ohm.

In this way an RF combiner eases  impedance mismatching on the source port.


(RF signal transfer at the 40m)

 According to the prototype test of the resonant box it will most likely have a non-50 Ohm input impedance at each modulation freqeucy.

If we install the resonant box apart from the combiner it will create RF reflections due to the mismatch (Case 1 in the diagram below)

The reflection creates standing waves which may excite higher harmonics and in the worst case it damages the RF sources.

 To reduce such a reflection one thing we can do is to install the combiner as a part of the resonant box (Case 2).

It will reduce the amount of the mismatching in the input impedance of the resonant circuit and results less reflections.

A rule we should remember is that a cable always needs to be impedance matched.



  4503   Fri Apr 8 01:05:45 2011 SureshUpdateRF SystemRF Source Harmonics


 The measured power levels of the RF source harmonics are given below:



We are considering inclusion of bandpass filters centered on 11 and 55 MHz  to suppress the harmonics and meet the requirements specified in Alberto's thesis (page 88).


Attachment 1: RF_Source_Harmonics_Sheet1.pdf
RF_Source_Harmonics_Sheet1.pdf RF_Source_Harmonics_Sheet1.pdf RF_Source_Harmonics_Sheet1.pdf RF_Source_Harmonics_Sheet1.pdf
  4502   Thu Apr 7 21:58:57 2011 AidanSummaryGreen LockingBeat note amplitude

Having convinced myself that the green Hartmut PD is giving an acceptable response at RF frequencies I decided to double-check the beatnote at IR (fiber transmission from the X-end beating with the PSL). This took a while because I had to realign the beam into the fiber at the X-end (I had a PD monitoring the output from the fiber on the PSL table and 40m of BNC cable giving me the signal from it at the X-end).

Eventually, I managed to get a beatnote on the PD. At first there was no signal at the temperature calculated using Koji and Suresh's calibration, but it turned out that the mode-overlap wasn't good enough on the PD. Now I can clearly see beats between a couple of modes, one of which is much stronger than the other. I think we should use a frequency discriminator on the output from the IR PD to servo the end laser and keep the strong beat note within <100MHz of DC.


  4501   Thu Apr 7 19:28:02 2011 KojiSummaryGreen Locking(In)sanity check of Green PD - some inconsistencies

Responsivity of SGD-444A


For instance, the PDA100A Si detector from Thorlabs has a responsivity of 0.35-0.4A/W at 1064nm.


Attachment 1: SGD-444A.png
  4500   Thu Apr 7 16:09:17 2011 AidanSummaryGreen Locking(In)sanity check of Green PD - some inconsistencies

I think I had underestimated the responsivity of the Silicon PD at 1064nm. The previous value was based on a rough search online for the responsivity of Silicon (I couldn't find the product number of the actual PD we are using). For instance, the PDA100A Si detector from Thorlabs has a responsivity of 0.35-0.4A/W at 1064nm. 

If we calculate the responsivity of the Hartmut PD from the measurements I made today (input power = 0.300mW, output voltage = 5.56mV, effective transimpedance = 80 Ohms), then the responsivity at 1064nm is 0.23 A/W which is not an unreasonable number given the response of the Thorlabs detector.


Measurement Value
Responsivity of Silicon PD at 1064nm 0.02 A/W (estimate)
Responsivity of 1611 New Focus PD at 1064nm ~0.8 A/W

There is one other troubling point: using the estimate of responsivity on the Harmut PD * incident power * transimpedance at DC = (0.02A/W) * (0.28mW) * (80 V/A) = 0.45 mV.

But the measured DC voltage is 6.5mV = inconsistent.


  4499   Thu Apr 7 13:14:23 2011 josephbUpdateCDSProposed plan for ITMX/ITMY control switch


The controls (fast and slow both) think ITMX is ITMY and ITMY is ITMX.


After some poking around today, I have convinced myself it is sufficient to simply swap all instances of ITMX for ITMY in the C1_SUS-AUX1_ITMX.db  file, and then rename it to C1_SUS-AUX1_ITMY.db (after having moved the original C1_SUS-AUX1_ITMY.db to a temporary holding file).

A similar process is then applied to the original C1_SUS-AUX1_ITMY.db file.  These files live in /cvs/cds/caltech/target/c1susaux.  This will fix all the slow controls.

To fix the fast controls, we'll modify the c1sus.mdl file located in /opt/rtcds/caltech/c1/core/advLigoRTS/src/epics/simLink/ so that the ITMX suspension name is changed to ITMY and vice versa.  We'll also need to clean up some of the labeling

At Kiwamu and Bryan's request, this will either be done tomorrow morning or on Monday.

So the steps in order are:

1) cd /cvs/cds/caltech/target/c1susaux

2) mv C1_SUS-AUX1_ITMX.db C1_SUS-AUX1_ITMX.db.20110408

3) mv C1_SUS-AUX1_ITMY.db C1_SUS-AUX1_ITMY.db.20110408

4) sed 's/ITMX/ITMY/g' C1_SUS-AUX1_ITMX.db.20110408 > C1_SUS-AUX1_ITMY.db

5) sed 's/ITMY/ITMX/g' C1_SUS-AUX1_ITMY.db.20110408 > C1_SUS-AUX1_ITMX.db

6) models

7) matlab

8) Modify c1sus model to swap ITMX and ITMY names while preserving wiring from ADCs/DACs/BO to and from those blocks.

9) code; make c1sus; make install-c1sus

10) Disable all watchdogs

11) Restart the c1susaux computer and the c1sus computer


  4498   Thu Apr 7 13:12:23 2011 KojiHowToVIDEOVideo switching tip

Long time ago, I looked at the manual of the video switcher.
Here is the summary. This will be the basic of the more sophisticated switching program which may have GUI.

In principle, you can manually control the matrix via telnet. At the console machines, you can connect to the matrix using telnet


This opens TCP/IP port 23 of the specified machine. You will receive some messages.
Then type some command like:

  • 1*2!       (connect input#1 to output#2)
  • 1,           (save the current setting into preset1)
  • 1.           (restore the setting from preset1)


Basicaly that's all. There are many other features but I don't think we need them.

We can create a simple program with any of the language as any of the language has the capability of the TCP/IP connection.
e.g. C, Perl, Python. Tcl/Tk
Any of them are fine.

Now what we have to think about is how to implement the interface in the epics screen (or whatever).
It needs some investigation how the people is thinking as the ideal interface.
But, first of all, you should make the above three operations available as a simple UNIX command like:

videoswitch -i 1 2
videoswitch -i -store 1
videoswitch -i -recall 1
(There is no such command yet. These are showing what it should be!)

This can be done by a single day work and our life will be much better.

  4497   Thu Apr 7 11:51:13 2011 steveSummarySAFETYnew crane operator inaugurated


Mike Caton of Konecranes inspected and loadtested all 3  of the 40m cranes at max reach trolley positions with 1 ton.

 Konecrane representative gave crane operator training in the 40m. Koji has become a qualified, trained crane operator of the 40m lab.

Attachment 1: P1070535.JPG
  4496   Thu Apr 7 11:38:56 2011 steveUpdatePSLenclosure windows on the east side of the PSL

The PSL enclosure now have 4 windows on each side. The bottom rail guides on the east side will be replaced by  one  U-channel for smoother, more gentle sliding.

Door position indicator- interlock switches are not wired yet.

Attachment 1: P1070538.JPG
  4495   Wed Apr 6 22:13:24 2011 BryanConfigurationGreen LockingResonating green light!

Every so often things just work out. You do the calculations, you put the lenses on the bench, you manually adjust the pointing and fiddle with the lenses a bit, you get massive chunks of assistance from Kiwamu to get the alignment controls and monitors set up and after quite a bit of fiddling and tweaking the cavity mirror alignment you might get some nice TEM_00 -like shapes showing up on your Y-arm video monitors.

So. We have resonating green light in the Y-arm. The beam is horribly off-axis and the mode-matching, while close enough to give decent looking spots, has in no way been optimised yet. Things to do tomorrow - fix the off-cavity-axis problem and tweak up the mode-matching... then start looking at the locking...

  4494   Wed Apr 6 19:36:32 2011 AidanSummaryGreen Locking(In)sanity check of Green PD - some inconsistencies

I moved the Hartmut Green PD to the Jenne laser bench to try to determine if the response at RF was reasonable or somehow very much smaller than it should be. It was set up as shown in the attached diagram. The first pass at this was by comparing the ratio of the RF photocurrent of the green PD to the RF photocurrent of the New Focus 1611 InGaAs PD. That ratio (at a sufficiently low frequency) should be the same as the ratio the DC photocurrents of the two PDs.

Using the network analyzer I measured the ratio of the voltages of the two RF signals (and then scaled each of these by the respective transimpedances of the PDs: 700 Ohms for the 1611 and 240 Ohms for the Harmut PD). The resulting ratio is shown in the attached plot.

I measured the DC voltages from each PD and scaled those by the transimpedances to get the photocurrent (10 kOhm for the 1611 and 80 Ohm effective for the Harmut PD). The ratio of the DC photocurrents was 0.37. This is roughly 3x the ratio of the RF photocurrents at 500kHz (=0.14). This discrepancy is uncomfortably large.

 The full set of measurements is given in the table below:

Measurement Value
DC voltage from Hartmut PD 6.5mV (checked by turning laser on and off and measuring the difference)
DC voltage from 1611 InGaAs PD 2.20V
Transimpedance of Harmut PD at DC 80 Ohm (effective)
Transimpedance of Harmut PD at RF 240 Ohm
Transimpedance of 1611 InGaAs at DC 10 KOhm
Transimpedance of 1611 InGaAs at RF 700 Ohm
Incident Power on Hartmut PD (100% on PD area) 0.28mW (measured by Ophir power meter)
Incident Power on 1611 InGaAs (<100% on PD area) 0.64mW
Responsivity of Silicon PD at 1064nm 0.02 A/W (estimate)
Responsivity of 1611 New Focus PD at 1064nm ~0.8 A/W

There is one other troubling point: using the estimate of responsivity on the Harmut PD * incident power * transimpedance at DC = (0.02A/W) * (0.28mW) * (80 V/A) = 0.45 mV.

But the measured DC voltage is 6.5mV = inconsistent.

Attachment 1: PD_measurement.png
Attachment 2: plot_PD_RF_ratios.pdf
  4493   Wed Apr 6 18:55:49 2011 Jamie, LarisaConfigurationLSCmajor AP table cleanup

We ripped out all of the old AS, PLL, and REFL paths, green, orange, and cyan respectively on the old AP table layout photo:

  • AS (green): had already been re-purposed by putting a ThorLabs diode right after the first steering mirror.   Everything downstream of that has been removed.
  • PLL (orange): everything removed.
  • REFL (cyan): CCD was left in place, so everything upstream of that was not touched.  Everything else was removed, including all of the REFL detectors.
  • OMCT (purple): previously removed
  • OMCR (blue): left in place, but the diode and CCD are not connected (found that way).
  • MCT (magenta): previously removed.
  • IMRC (red): untouched

All optics and components were moved to the very south end of the SP table.

We also removed all spurious cables from the table top, and from underneath, as well as pulled out no-longer-needed power supplies.

  4492   Wed Apr 6 16:02:07 2011 Larisa ThorneUpdateElectronicsCable laying...continued

[Steve, Kiwamu, Larisa]


Having finished laying new cable last week, we moved on to connecting those on PSL table and AP table.

Cables connected:

--RCR, RCT, PMCR (all three are blue)

--OMCR (blue cable, ***now has a camera***), PMCT, IMCR, REFL, AS (white cable), OMCT (***now has camera***)


Unless otherwise noted, the cables are black on the AP table. Also on the AP table: cables were connected directly to the power source.

The wiki has been updated accordingly.


Steve noted that MC2T and POP cameras are not there.



  4491   Wed Apr 6 02:41:01 2011 kiwamuUpdateGreen Lockingnoise budget : some more noise

It turned out that the dark noise from the beat PD and the shot noise on the beat PD was overestimated.

So I corrected them in the plot of the last noise budget (#4482).

Additionally I added the end laser error signal in the plot. Here is the latest plot.


 The end laser error spectrum is big enough to cover most of the frequency range.
 (although it was taken at a different time from the other curves.)

Quote from #4482

According to the plot what we should do are :

  * More accurate PD noise measurement

  * More accurate shot noise estimation

  4490   Tue Apr 5 21:20:11 2011 KojiSummaryGreen LockingX-arm cavity locked with LB1005 servo box

Last Thursday, I tested Newport Servo Controller LB1005 with the X_arm green PDH servo.

The setup and the settings I could lock the arm is depicted in the attached figure.
To lock the cavity, follow the steps below

1) Toggle the switch to the "lower" position. This disengages the servo and reset the integrator.

2) Toggle the switch to the "middle" position. The zero freq is set to the "PI corner" freq. At the low freq the gain is limited
at the value of "LF Gain Limit". This gives us a single pole at the low freq.

3) Once the lock is acquired, toggle the switch to the "upper" position. This moves the pole freq to DC, resulting in the complete integration of the signal at the low frequency.

I measured the openloop transfer function (attachment 2). The amp is quite fast and exhibits almost no phase delay upto 100kHz.
The UGF was 10kHz with the phase mergin of ~45deg. I had to tune the input offset carefully to stay at the center of the resonance.

Attachment 1: servo.png
Attachment 2: OLTF.pdf
  4489   Tue Apr 5 19:54:39 2011 KojiSummaryGreen LockingHamamatsu S3399 test

Since last Friday I have been testing the broadband RF photodetector in order to figure out the capability of S3399 with the similar circuit as Matt's BBPD
We also like to figure out if it has sufficient performance for the 40m green locking.

The circuit diagram is shown in the first attachment. The RF amplifier is attached at the diode while the reverse bias voltage is applied at the other side of the diode. The amplifier's input impedance is used as the transimpedance resister. Note that the bandwidth of this configuration is limited by the RC filter that consists of the junction capacitance of the diode, the series resistance of the diode, and the transimpedance resister. This cut off freq is in general lower than that cut off obtained with the usual transimpedance amplifier which has the readout resister at the feedback path of the opamp.

The transfer function of the PD is measured using Jenne's laser. At the reverse bias voltage of 30V, the -3dB bandwidth of 178MHz was obtained. This is quite high bandwidth for the most of the applications at the 40m.

Because of the low transimpedance the low-noise level of the RF amplifier is very crucial. Recently we can obtain an ultra low noise RF amplifier like Teledyne Cougar AC688 which has the NF of 0.9dB with the bandwidth between 10MHz - 600MHz. Next step will be to obtain this kind of amplifier to test the noise performance.



Attachment 1: S3399_test_110405.png
Attachment 2: S3399_test_110405.pdf
  4488   Tue Apr 5 17:31:59 2011 steveSummaryGeneralnew laser pointers


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.


 Low power green-red laser pointers are in. High power green, red and blue pointers are confiscated.

Attachment 1: P1070530.JPG
  4487   Tue Apr 5 17:04:36 2011 steveSummarySAFETYcranes inspected and load tested

Mike Caton of Konecranes inspected and loadtested all 3  of the 40m cranes at max reach trolley positions with 1 ton.

Attachment 1: P1070522.JPG
Attachment 2: P1070532.JPG
  4486   Mon Apr 4 18:58:44 2011 BryanConfigurationGreen LockingA beam of purest green

We now have green light at the Y end. 

The set-up (with careful instructions from Kiwamu) - setting up with 100mW of IR into the oven.

Input IR power = 100mW measured.


Output green power = 0.11mW

(after using 2 IR mirrors to dump IR light before the power meter so losing a bit of green there light too)


And it's pretty circular-looking too. Think there might be a bit more efficiency to be gained near the edges of the crystal with internal reflections and suchlike things but that gives us an UGLY looking beam.  Note - the polarisation is wrong for the crystal orientation so used a lambda/2 plate to get best green  power out.


Efficiency is therefore 0.11/100 = 0.0011 (0.11%) at 100mW input power.


Temperature of the oven seems to be around 35.5degC for optimal conversion.

Took a picture. Ta-dah! Green light, and lots more where that came from! Well... about 3x more IR available anyway.





  4485   Mon Apr 4 14:20:32 2011 BryanConfigurationGreen LockingThe wonderful world of mode-matching

Last bit of oven matching for now.


I moved the lens before the oven position back along the beam path by about 1cm - waist should be just above position 9 in this case. Note - due to power-findings from previous time I'm maximising the power into the head to reduce the effect of offsets.


From position 9:

Position A1_13.5%_width A2_13.5%_width

(mm) (um mean) (um mean)

-1 121.1 123.6

0 112.5 113.8

1 106.4 106.1

2 102.9 103.4

3 103.6 103.6

4 106.6 107.4

5 111.8 112.5

6 118.2 120.1

7 126.3 128.8

8 134.4 137.1

9 143.8 146.5

10 152.8 156.1

11 163.8 167.1

12 175.1 176.4

13 186.5 187.0

14 197.1 198.4

15 210.3 208.9

16 223.5 218.7

17 237.3 231.0

18 250.2 243.9

19 262.8 255.4

20 274.7 269.0

21 290.4 282.3

22 304.3 295.5

23 316.7 303.1


Note - had to reduce power due to peak saturation at 15mm - don't think scale changed, but be aware just in case. And saturated again at 11. And again at 7. A little bit of power adjustment each time to make sure the Beamscan head wasn't saturating. Running the fit gives...




OK. The fit is reasonably good. Residuals around the area of interest (with one exception) are <+/- 2um and the waists are 47.5um (vertical) and 50.0um (horizontal) at a position of 9.09 on the bench. And the details of the fitting output are given below.



Vertical Fit


cf_ =


     General model:

       cf_(x) = w_o.*sqrt(1 + (((x-z_o)*1064e-9)./(pi*w_o.^2)).^2)+c

     Coefficients (with 95% confidence bounds):

       c =   5.137e-06  (4.578e-06, 5.696e-06)

       w_o =   4.752e-05  (4.711e-05, 4.793e-05)

       z_o =        1.04  (1.039, 1.04)



cfgood_ = 


           sse: 1.0699e-11

       rsquare: 0.9996

           dfe: 22

    adjrsquare: 0.9996

          rmse: 6.9738e-07



Horizontal Fit


cf_ =


     General model:

       cf_(x) = w_o.*sqrt(1 + (((x-z_o)*1064e-9)./(pi*w_o.^2)).^2)+c

     Coefficients (with 95% confidence bounds):

       c =    3.81e-06  (2.452e-06, 5.168e-06)

       w_o =   5.006e-05  (4.909e-05, 5.102e-05)

       z_o =        1.04  (1.04, 1.04)



cfgood_ = 


           sse: 4.6073e-11

       rsquare: 0.9983

           dfe: 22

    adjrsquare: 0.9981

          rmse: 1.4471e-06




  4484   Mon Apr 4 11:52:13 2011 JenneUpdatePEMSTS2s unpacked

I unpacked the STS2 seismometers that we borrowed from LLO.  They are sitting underneath the Xarm, in the middle of the mode cleaner, near the other seismometer stuff. 

  4483   Fri Apr 1 23:49:24 2011 kiwamuSummaryGreen Lockingtwo states in green beat-note

According to the measurement done by Aidan and me, there are two beat-note state.

One gave us a small beat signal and the other gave us a bigger signal by approximately 20 dB.


 A possible reason for this phenomenon is that the end laser is operating at a special temperature that somehow drives the laser with two different modes at the same time.

So that it permits the laser sometimes locked with one of the two modes and sometimes with the other mode.

For the first step we will change the temperature such that the laser can run with a single stable mode.

Then for investigating it we will put a scanning cavity on the X end table to see if it really exhibits a two modes or not.

Quote from #4472

The attached table shows the amplitude of the green beat note when the end laser was in various states. We can increase the beat note amplitude dramatically by switching to a different states.

  4482   Fri Apr 1 23:05:58 2011 kiwamuUpdateGreen Lockingnoise budget

I made a coarse noise budget in order to decide our next actions for the X arm green locking.

So be careful, this is not an accurate noise budget !

 Some data are just coming from rough estimations and some data are not well calibrated.


 Assuming all the noise are not so terribly off from the true values, the noise at high frequency is limited by the dark noise of the PD or it already reaches to the IR inloop signal.

The noise at low frequency is dominated by the intensity noise from the transmitted green light although we thought it has been eliminated by the comparator.

In any case I will gradually make this noise budget more accurate  by collecting some data and calibrating them.


According to the plot what we should do are :

  * More accurate PD noise measurement

  * More accurate shot noise estimation

  * Searching for a cause of the small beat signal (see here) because a bigger beat signal lowers the PD noise.

  * Investigation of the Intensity noise

  4481   Fri Apr 1 18:54:41 2011 BryanConfigurationGreen LockingY end doubling oven

The doubling oven is now ready to go for the Y arm. The PPKTP crystal is mounted in the oven:


Note - the crystal isn't as badly misaligned as it looks in this photo. It's just an odd perspective shot. I then closed it up and checked to make sure the IR beam on the Y bench passes through the crystal. It does. Just need to tweak the waist size/position a bit and then we can actually double some frequencies!


  4480   Thu Mar 31 20:46:11 2011 AidanSummaryGreen LockingGreen beat note PD DC response

I measured the DC response of the Green PD

Power into PD at DC (green laser pointer) = 285 uW
Voltage out of PD = 552mV/(100x SR560gain) = 5.52mV
Photocurrent = 5.52mV/(241 Ohms)*3 = 68.7uA
Responsivity = 68.7/285 = 0.24 A/W

Therefore, since the responsivity is in the correct range for a Silicon PD at 532nm, the DC output is giving us sensible response to an input signal.

But, there is a 2.12MHz, 328mV oscillation on the DC output irrespective of the incident power.

  4479   Thu Mar 31 20:37:10 2011 AidanSummaryGreen LockingRF amplitude source

 I gutted one of the $2 red laser pointers to build a laser source whose amplitude we could modulate at RF frequencies. Basically, I cut off the bulk of the housing from the pointer and soldered a BNC connection into the two terminals that the 2x 1.5V batteries were connected to. When I applied 3V across this BNC connector the diode still worked. So far so good.

Next I added a bias tee to the input. I put 3V across the DC input of the bias tee and added a -3dBm signal into the RF port of the tee. The laser beam was incident on a PDA100A (bandwidth of 1.7MHz) and, sure enough, Kiwamu and I could see a flat response in the amplitude at a given drive frequency out to around 1.7MHz.

We should check the response on a faster PD to see how fast the laser diode is, but we should be able to use this now to check the RF response of the green beat note PD. 


1. Add some capacitors across the DC input of the bias tee.

2. Do something about the switch on the laser diode.

3. Attach some labels to the laser that specify what is the required DC voltage and the maximum acceptable RF modulation amplitude.

Attachment 1: P1000543.jpg
Attachment 2: P1000544.jpg
Attachment 3: P1000545.jpg
  4478   Thu Mar 31 19:58:11 2011 kiwamuUpdateCDSc1iscex crashed

After I did several things to add new DAQ channels on c1iscex it suddenly became out of network. Maybe crashed.

Then c1iscex didn't respond to a ping and all the epics values associated with c1iscex became not accessible.

I physically shut it down by pushing the reset button. Then it came back and is now running fine.


(how I broke it)

Since activateDAQ.py has screwed up the 'ini' files including C1SCX.ini, I was not able to add a channel to C1SCX.ini by the usual daqconfig GUI.

So I started editing it in a manual way with an editor and changed some sentences to that shown below


Then I rebooted fb to reflect the new DAQ channels.

After that I looked at the C1_FE_STATUS.adl screen and found some indicator lights were red.

So I pushed "Diag reset" button and "DAQ Reload" button on the C1SCX_GDS_TP.adl screen and then c1iscex died.

After the reboot the new DAQ channels looked acquired happily.

This is my second time to crash a front end machine (see this entry)

  4477   Thu Mar 31 15:23:14 2011 BryanConfigurationGreen LockingThe wonderful world of mode-matching


3. Zoomed-in plot for the SHG crystal show no astigmatism. However, the zoomed out plot shows some astigmatism.

How consistent are they? ==> Interested in seeing the fit including the zoomed out measurements.

Right. Fitting to the data. Zoomed out plots first. I used the general equation f(x) = w_o.*sqrt(1 + (((x-z_o)*1064e-9)./(pi*w_o.^2)).^2)+c for each fit which is basically just the Gaussian beam width parameter calculation but with an extra offset parameter 'c'

Vertical fit for zoomed out data:

Coefficients (with 95% confidence bounds):

       c =   7.542e-06  (5.161e-06, 9.923e-06)

       w_o =   3.831e-05  (3.797e-05, 3.866e-05)

       z_o =       1.045  (1.045, 1.046)


Goodness of fit:

  SSE: 1.236e-09

  R-square: 0.9994

Horizontal fit for zoomed out data:

Coefficients (with 95% confidence bounds):

       c =   1.083e-05  (9.701e-06, 1.195e-05)

       w_o =   4.523e-05  (4.5e-05, 4.546e-05)

       z_o =       1.046  (1.046, 1.046)


Goodness of fit:

  SSE: 2.884e-10

  R-square: 0.9998

  Adjusted R-square: 0.9998

  RMSE: 2.956e-06





OK. Looking at the plots and residuals for this, the deviation of the fit around the waist position, and in fact all over, looks to be of the order 10um. A bit large but is it real? Both w_o values are a bit lower than the 50um we'd like, but… let's check using only the zoomed in data -  hopefully more consistent since it was all taken with the same power setting.



Vertical data fit using only the zoomed in data:


Coefficients (with 95% confidence bounds):

       c =   1.023e-05  (9.487e-06, 1.098e-05)

       w_o =   4.313e-05  (4.252e-05, 4.374e-05)

       z_o =       1.046  (1.046, 1.046)


Goodness of fit:

  SSE: 9.583e-11

  R-square: 0.997


Horizontal data fit using only the zoomed in data:


Coefficients (with 95% confidence bounds):

       c =   1.031e-05  (9.418e-06, 1.121e-05)

       w_o =    4.41e-05  (4.332e-05, 4.489e-05)

       z_o =       1.046  (1.046, 1.046)


Goodness of fit:

  SSE: 1.434e-10

  R-square: 0.9951





The waists are both fairly similar this time 43.13um and 44.1um and the offsets are similar too  - residuals are only spread by about 4um this time.


I'm inclined to trust the zoomed in measurement more due to the fact that all the data was obtained under the same conditions, but either way, the fitted waist is a bit smaller than the 50um we'd like to see. Think it's worthwhile moving the 62.9mm lens back along the bench by about 3/4 -> 1cm to increase the waist size.






  4476   Thu Mar 31 14:10:00 2011 BryanConfigurationGreen LockingThe wonderful world of mode-matching


 I went through the entries.

1. Give us a photo of the day. i.e. Faraday, tilted lens, etc...

2. After all, where did you put the faraday in the plot of the entry 4466?

3. Zoomed-in plot for the SHG crystal show no astigmatism. However, the zoomed out plot shows some astigmatism.
How consistent are they? ==> Interested in seeing the fit including the zoomed out measurements.

 OK. Taking these completely out of order in the easiest first...

2. The FI is between positions 27.75 and 32 on the bench - i.e. this is where the input and output apertures are. (corresponds to between 0.58 and 0.46 on the scale of those two plotsand just before both the vertical and horizontal waists) At these points the beam radius is around 400um and below, and the aperture of the Faraday is 4.8mm (diameter).

1. Photos...

Laser set up - note the odd angles of the mirrors. This is where we're losing a goodly chunk of the light. If need be we could set it up with an extra mirror and send the light round a square to provide alignment control AND reduce optical power loss...



Faraday and angled lens - note that the lens angle is close to 45 degrees. In principle this could be replaced with an appropriate cylindrical lens, but as long as there's enough light passing through to the oven I think we're OK.


3. Fitting... coming soon once I work out what it's actually telling me. Though I hasten to point out that the latter points were taken with a different laser power setting and might well be larger than the actual beam width which would lead to astigmatic behaviour.

  4475   Thu Mar 31 11:30:51 2011 steveConfigurationGeneralstrain relieved rf cables

I strain relieved RF cables labeled 33 MHZ LO and 166 MHZ to EOM at 1X2  This is a temporary setup for the 11 MHZ

The coax N  bulkheads connectors are mounted on the plastic front panel now.

Attachment 1: P1070491.JPG
  4474   Thu Mar 31 08:31:44 2011 SureshUpdateVIDEOCable laying...continued

The video work has crossed a milestone.    

Kiwamu and Steve have shifted the three quads from the control room to the Video MUX rack (1Y1) and have wired them to the MUX.

The monitors in the control room have been repositioned and renumbered.  They are now connected directly to the MUX. 

Please see the new cable list for the input and output channels on the MUX.

As of today, all cables according the new plan are in place.  Their status   indicated on the wiki page above is not verified .  Please ignore that column for now, we will be updating that soon.

I shifted the MC1F/MC3F camera and the MC2F cameras onto the new cables.  Also connected the monitors at the BS chamber and end of the X arm to their respective cables.  I have removed the RG58B BNC (black) cables running from MC2 to BS and from ETMXF to the top of the Flow Bench. 

Some of the old video cables are still in place but are not used.   We might consider removing them to clear up the clutter. 

Some of the video cables in use are orange and if the lab's  cable color code is to be enforced these will have to be replaced with blue ones..

Some of the cables in use running from the MUX to the monitor in the control room are the white 50 Ohm variety.  There are also black RG59 Cables running the same way ( we have surplus cables in that path)  and we have to use those instead of the white ones. 

There are a number of tasks remaining:

a)  The inputs from the various existing cameras have to be verified. 

b) There are quite a few cameras which are yet to be installed.

c) The Outputs may not not be connected to their monitors.  That the monitors may still be connected to an old cable which is not connected to the MUX.  The new cable should be lying around close by.  So if you see a blank monitor please connect it to its new cable. 

d) The status column on the wiki page has to be updated.

e) Some of the currently in place may need to be replaced and some need to be removed.  We need to discuss our priorities and come up with a plan for that.

After checking everything we can certify that the video cabling system is complete.

I would like Joon Ho to take care of this verification+documenting process and declaring that the job is complete. 


Steve attached these two pictures.

Attachment 1: P1070489.JPG
Attachment 2: P1070494.JPG
  4473   Thu Mar 31 02:59:49 2011 KojiConfigurationGreen LockingThe wonderful world of mode-matching

 I went through the entries.

1. Give us a photo of the day. i.e. Faraday, tilted lens, etc...

2. After all, where did you put the faraday in the plot of the entry 4466?

3. Zoomed-in plot for the SHG crystal show no astigmatism. However, the zoomed out plot shows some astigmatism.
How consistent are they? ==> Interested in seeing the fit including the zoomed out measurements.

  4472   Wed Mar 30 21:46:10 2011 Aidan, KiwamuUpdateGreen LockingStates of the Green beat note

The attached table shows the amplitude of the green beat note when the end laser was in various states. We can increase the beat note amplitude dramatically by switching to a different states.

State 1
C1:GCX-GRN_REFL_DC:             638 counts
C1:GCV-XARM_BEAT_DC: (PSL blocked)    950 avg counts (zero = -794 counts)
amplitude of beat note:            -23dBm (after PD + amps) (f ~ 30 MHz)?
C1:GCX-SLOW_SERVO2_OUT:            318 counts

State 2
C1:GCX-GRN_REFL_DC:             180 counts
C1:GCV-XARM_BEAT_DC: (PSL blocked)    1270 avg counts (zero = -794 counts)
C1:GCV-XARM_BEAT_DC: (PSL unblocked)    1700 avg counts (zero = -794 counts)
amplitude of beat note:            -7dBm (after PD + amps) f = 60MHz
amplitude of beat note:            0dBm (after PD + amps) f = 30MHz
C1:GCX-SLOW_SERVO2_OUT:            290 counts

State 3
C1:GCX-GRN_REFL_DC:             220 counts
C1:GCV-XARM_BEAT_DC: (PSL blocked)    1120 avg counts (zero = -794 counts)
C1:GCV-XARM_BEAT_DC: (PSL unblocked)    1520 avg counts (zero = -794 counts)
amplitude of beat note:            0dBm (after PD + amps) f = 15MHz
C1:GCX-SLOW_SERVO2_OUT:            305 counts

PSL temp = ??
C1:PSL-FSS_SLOWM = -3.524

  4471   Wed Mar 30 21:43:31 2011 Aidan, KiwamuSummaryGreen LockingCalculation of the green contrast on the RF PD

Skip to final thought ...

Kiwamu and I have set about measuring the contrast of the signal on the RF PD. We can only do this when the end green laser is locked to the cavity. This is because the green transmission through the cavity, when unlocked, is too low. Unfortunately, once we lock the green beam to the cavity, we can't keep the beatnote on the RF PD stable to within a few hundred Hz of DC (remember that the cavity is swinging around by a couple of FSRs). So we also lock the PSL to cavity.

At this point we're stuck because we can't get both of these beams resonant within the cavity AND have the frequency difference between them be less 1kHz - when the lasers are locked to the cavity, their frequencies are separated by an integer number of FSRs + a fixed frequency offset, f_offset, that is set by the phase difference on reflection from the coating between the two wavelengths (532nm and 1064nm). We can never get the frequency difference between the lasers to be less than this offset frequency AND still have them both locked to the cavity.


So our contrast measuring method will have to use the RF signal.


So this is our method. We know the incident power from each beam on the RF PD (see Kiwamu's elog entry here), but to recap,

P_green_PSL = 72 uW (as measured today)

P_green_XARM = 560 uW (as measured by Kiwamu last week).

The trans-impedance of the RF PD is 240 Ohms. We'll assume a responsitivity of 0.25 A/W. So, if the XARM transmission and PSL green beams are perfectly matched then the maximum value of the RF beat note should be:

RF_amplitude_max = 2* SQRT(P_green_PSL*P_green_XARM) * responsivity * transimpedance = 240*0.25*2*(72E-6*560E-6)^(1/2) (volts)

= 24 mV = -19.5 dBm (or 27.5dBm after the +47 dB from the two  ZFL-1000LN+ amplifiers - with +15V in - that protrude from the top of the PD)

The maximum RF strength of the beat-note that we measure is around -75 dBm (at the RF output of the PD). This means the contrast is down nearly 600x from optimal. Or it means something is broken.

Final thought: at the end of this procedure we found that the RF beat note amplitude would jump to a different and much higher amplitude state. This renders a lot of the above useless until we discover the cause.

  4470   Wed Mar 30 21:21:15 2011 BryanConfigurationGreen LockingThe wonderful world of mode-matching

Step 4: Matching into the oven



Now that the astigmatism is substantially reduced, we can work out a lens solution to obtain a 50um waist *anywhere* on the bench as long as there's enough room to work with the beam afterwards. The waist after the Faraday and lens is at position 22.5 on the bench. A 50 mm lens placed 18 cm after this position (position 14.92 on the bench) should give a waist of 50 um at  24.57 cm after the waist (position 12.83 on the bench). This doesn't give much room to measure the beam waist in though - the Beamscan head has a fairly large finite size… wonder if there's a slightly less strong lens I could use…

OK. With a 66 mm lens at 23 cm (position 13.45 on the bench) after the waist we get a 50 um waist at 31.37 cm after the waist (position 10.15 on the bench). 




Closest lens I found was 62.9mm which will put the 50um point a bit further towards the wall, but on the X-arm the oven is at position 8.75 ish. So anything around there is fine.


Using this lens and after a bit of manual fiddling and checking with the Beamscan, I figured we needed a close in, fine-grained measurement so set the Beamscan head up on a micrometer stage Took a whoie bunch of data around position 9 on the bench:



Position A1_13.5%_width A2_13.5%_width

(mm) (um mean) (um mean)

-15 226.8 221.9

-14 210.9 208.3

-13 195.5 196.7

-12 181.0 183.2

-11 166.0 168.4

-10 154.0 153.1

-9 139.5 141.0

-8 127.5 130.0

-7 118.0 121.7

-6 110.2 111.6

-5 105.0 104.8

-4 103.1 103.0

-3 105.2 104.7

-2 110.9 110.8

-1 116.8 117.0

0 125.6 125.6

0 125.6 125.1

1 134.8 135.3

2 145.1 145.6

3 155.7 157.2

4 168.0 168.1

5 180.5 180.6

6 197.7 198.6

7 211.4 209.7

8 224.0 222.7

9 238.5 233.7

10 250.9 245.8

11 261.5 256.4

12 274.0 270.4

13 291.3 283.6

14 304.2 296.5

15 317.9 309.5




And at this point the maximum power available at the oven-waist is 298mW. With 663mW available from the laser with a desired power setting of 700mW on the supply. Should make sure we understand where the power is being lost. The beam coming through the FI looks clean and unclipped, but there is some stray light around.


Position A1_13.5%_width A2_13.5%_width

(bench) (um mean) (um mean)

7 868.5   739.9

6 1324 1130

5 1765 1492

4 2214 1862


The plot looks pretty good, but again, there looks to be an offset on the 'fitted' curve. Taking a couple of additional points further on to make sure it all works out as the beam propagates. I took a few extra points at the suggestion of Kiwamu and Koji - see the zoomed out plot.  The zoomed in plot has by-eye fit lines - again, because to get the right shape to fit the points there appears to be an offset. Where is that coming from? My suspicion is that the Beamscan doesn't take account of the any background zero offsets when calculating the 13.5% and we've been using low power when doing these measurements - very small focussed beams and didn't want to risk damage to the profiler head.


Decided to take a few measurements to test this theory. Trying different power settings and seeing if it gives different offset and/or a changed width size


7 984.9 824.0 very low power

7 931.9 730.3 low power

7 821.6 730.6 higher power

7 816.4 729.5 as high as I'm comfortable going


Trying this near the waist…


8.75 130.09 132.04 low power

8.75 106.58 105.46 higher power

8.75 102.44 103.20 as high as it can go without making it's saturated


So it looks like offset *is* significant and the Beamscan measurements are more accurate with more power to make the offsets less significant. Additionally, if this is the case then we can do a fit to the previous data (which was all taken with the same power setting) and simply allow the offset to be a free parameter without affecting the accuracy of the waist calculation. This fit and data coming to an e-log near you soon.


Of course, it looks from the plots above (well... the code that produces the plots above) that the waist is actually a little bit small (around 46um) so some adjustment of the last lens back along the beam by about half a cm or so might be required.

  4469   Wed Mar 30 20:50:43 2011 BryanConfigurationGreen LockingThe wonderful world of mode-matching

Step 3b: Non-circular? We can fix that...

A quick Beamscan sweep of the beam after the Faraday:

Position A1_13.5%_width A2_13.5%_width

(bench) (um mean) (um mean)

25.8 503.9 478.8

25 477.5 489.0

24 447.1 512.4

21 441.6 604.5

20 476.3 645.4

19 545.4 704.1

18 620.3 762.8




OK. It looks not too bad - doesn't look too different from what we had. Note that the x axis is in local table units - I found this useful for working out where things were relative to other things (like lenses and the FI) - but it means the beam propagates from right to left in the plot. in other words, the horizontal waist occurs first and is larger than the vertical waist. Also - they're not fitted curves - they're by-eye, best guesses and there's no solution for the vertical that doesn't involve offsets... discussion in a later part of the thread.


Anyway! The wonderful thing about this plot is that the horizontal and vertical widths cross and the horizontal focussing at this crossing point is shallower than the vertical. This means that we can put a lens in at the crossing point and rotate it such that the lens is stronger in the horizontal plane. The lens can be rotated until the effective horizontal focal length is right to fix the astigmatism.



I used a 200mm lens I had handy - a rough check sweeping the Beamscan quickly indicated should be about right though. Adjusting the angle until the beam size at a distant point is approx circular - I then move the profiler and adjust again. Repeat as required. Now… taking some data. with just that lens in:


Position A1_13.5%_width A2_13.5%_width

(bench) (um mean) (um mean)

24 371.7 366.1

21 360.3 342.7

20 447.8 427.8

19 552.4 519.0

18 656.4 599.2

17 780.1 709.9

16 885.9 831.1




Well now. That looks quite OK. Fit's a bit rubbish on vertical but looks like a slight offset on the measurement again.

The angle of the lens looks awful, but if it's stupid and it works then it isn't stupid. If necessary, the lens can be tweaked a bit more, but there's always more tweaking possible further down the line and most of the astigmatic behaviour has been removed. It's now just a case of finding a lens that works to give us a 50 um beam at the oven position...



  4468   Wed Mar 30 20:31:30 2011 BryanConfigurationGreen LockingThe wonderful world of mode-matching

Step 3: Inserting FI and un-eliptical-ification of the beam

The FI set up on it's mount and the beam passes through it - centrally through the apertures on each side. Need to make sure it doesn't clip and also make sure we get 93% through (datasheet specs say this is what we should achieve). We will not achieve this, but anything close should be acceptable.

Setting up for minimum power through the FI is HWP @125deg.

Max is therefore @ 80deg


Power before FI = 544 mW

Power after FI =     496 mW (after optimising input polarisation)

Power dumped at input crystal = 8.6mW

Power dumped at input crystal from internal reflections etc = 3.5mW

Power dumped at output crystal on 1st pass = approx 8mW


OK. that gives us a 90.625% transmission and a 20.1mW absorption/unexplained loss.


Well - OK. The important part about isolators isn't their transmission, it's about how well they isolate. Let's see how much power gets ejected on returning through the isolator…


Using a beam splitter to pick off light going into and returning from the FI. A 50/50 BS1-1064-50-1025-45P. And using a mirror near the waist after the FI to send the beam back through. There are better ways to test the isolation performance of FI's but this will suffice for now - really only want to know if there's any reasonable isolation at all or if all of the beam is passing backwards through the device.


Power before BS = 536 mW (hmmn - it's gone down a bit)

Power through BS = (can't access ejected on first pass)

Power through FI = 164 mW (BS at odd angle to minimise refractive effect so less power gets through)

Power lost through mirror = 8.3mW (mirror is at normal incidence so a bit transmissive)


Using earlier 90.6% measurement as reference, power into FI = 170.83 mW

So BS transmission = 170.83/536 = 0.3187

BS reflectivity therefore = 1 - 0.3187 = 0.6813


Power back into FI = Thru FI - Thru mirror = 155.7 mW


Power reflected at BS after returning through FI = 2.2mW

Baseline power at BS reflection from assorted internal reflections in FI (blocked return beam) = 1.9mW

Note - these reflections don't appear to be back along the input beam, but they *are* detectable on the power meter.


Actual power returning into FI that gets reflected by BS = 0.3 mW

(note that this is in the fluctuating noise level of measurement so treat as an upper limit)


Accounting for BS reflectivity at this angle, this gives a return power = 0.3/0.6813 = 0.4403 mW


Reduction ratio (extinction ratio) of FI =  0.4403/155.7 = 0.00282


Again - note that this upper limit measurement is as rough and ready as it gets. It's easy to optimise this sort of thing later, preferable on a nice open bench with plenty of space and a well-calibrated photodiode. It's just to give an idea that the isolator is actually isolating at all and not spewing light back into the NPRO.


Next up… checking the mode-matching again now that the FI is in place. The beam profile was scanned after the FI and the vertical and horizontal waists are different...

  4467   Wed Mar 30 20:14:17 2011 BryanConfigurationGreen LockingThe wonderful world of mode-matching


I fired up some old waistplotter routines, and set the input conditions as the measured waist after the lens and used that to work out what the input waist is at the laser. It may not be entirely accurate, but it /will/ be self consistent later on.


Vertical waist      = 105.00 um at 6.282 cm after laser output (approx)

Horizontal waist = 144.63 um at 5.842 cm after laser output (approx)


Definitely astigmatic.


  4466   Wed Mar 30 20:08:34 2011 BryanConfigurationGreen LockingThe wonderful world of mode-matching

Step 2: Getting the beam through the Faraday isolator (FI).

Started out with an f=100mm lens at position 32,T on the bench which gave a decent looking waist of order 100 um in the right sort of position for the FI, but after checking the FI specs, it's limited to 500W/cm^2. In other words, if we have full power from the laser passing into it we'd need a beam width of more than 211 um. Solution? Use an f=150mm lens instead and don't put the FI at the waist. I normally don't put a FI at a waist anyway, for assorted reasons - scattering, thermal lensing, non-linear magnetic fields, the sharp changing of the field components in an area where you want as constant a beam as possible.  Checked with others to make sure they don't do things differently around these parts… Koji says it doesn't matter as long as it passes cleanly through the aperture. So… next step is inserting the Faraday.

The beam profiles in vertical and horizontal around the FI position with the f=150mm lens in place are attached. Note that the FI will be going in at around 0.56m.





  4465   Wed Mar 30 19:54:19 2011 BryanConfigurationGreen LockingThe wonderful world of mode-matching

RIght! Overview out of the way - now comes the trivial first bit


Step 1: Beam out of the laser - this will be tricky, but we'll see what we can actually measure in this set-up. Can't get the Beamscan head any closer to the laser and using a lambda/2 plate + polariser to control power until the Faraday isolator is in place. Using 1 inch separation holes as reference points for now - need better resolution later, but this is fine for now and gives an idea of where things need to go on the bench. The beam is aligned to the 3rd row up (T) for all measurements, the Beamscan spits out diameters (measuring only the 13.5% values) so convert as required to beam radius and the beam is checked to ensure a reasonable Gaussian profile throughout.


Position A1_13.5%_width A2_13.5%_width

(bench) (um mean) (um mean)

32 2166.1 1612.5

31 2283.4 1708.3

30 2416.1 1803.2

29 2547.5 1891.4

27 2860.1 2070.3

26 2930.2 2154.4

25 3074.4 2254.0

24 3207.0 2339.4


OK. As expected, this measurement is in the linear region of the beampath - i.e. not close to the  waist position and beyond the Rayleigh length) so it pretty much looks like two straight lines. There's no easy way to get into the path closer to the laser, so reckon we'll just need to infer back from the waist after we get a lens in there. Attached the plot, but about all you really need to get from this is that the beam out of the laser is very astigmatic and that the vertical axis expands faster than the horizontal.

Not terribly exciting, but have to start somewhere.






  4464   Wed Mar 30 19:43:33 2011 BryanConfigurationGreen LockingThe wonderful world of mode-matching

Right. I've got a whole load of info and data and assorted musings I've been saving up and cogitating upon before dumping it into these hallowed e-pages. there's so much I'll probably turn it into a threaded entry rather than put everything in one massive page.

An overview of what's coming:

I started out using http://lhocds.ligo-wa.caltech.edu:8000/40m/Advanced_Techniques/Green_Locking?action=AttachFile&do=get&target=modematch_END.png as a reference for roughly what we want to achieve... and from http://nodus.ligo.caltech.edu:8080/40m/100730_093643/efficiency_waist_edit.png we need a waist of about 50um at the green oven. Everything else up to this point is pretty much negotiable and the only defining things that matter are getting the right waist at the doubling oven with enough available power and (after that point) having enough space on the bench to separate off the green beam and match it into the Y arm.



Step 1: Measure the properties of the beam out of the laser. Really just need this for reference later because we'll be using more easily measurable points on the bench.

Step 2:
Insert a lens a few cm from the laser to produce a waist of about of a few 100um around the Faraday. Note that there's really quite a lot of freedom here as to where the FI has to be - on the X arm it's around columns 29/30 on the bench, but as long as we get something that works we can get it closer to the laser if we need to.

Step 3:
After inserting the FI need to measure the beam after it (there *will* be some distortion and the beam is non-circular to begin with)

Step 3b:
If beam is non-circular, make it circular.

Step 4:
Insert a lens to produce a 50um waist at the doubling oven position. This is around holes 7/8 on the X arm but again, we're free to change the position of the oven if we find a better solution. The optical set-up is a little bit tight near that side of the bench on the X end so we might want to try aiming for something a bit closer to the middle of the bench? Depends how the lenses work out, but if it fits on the X end it will fit on the Y end.

Oh... almost forgot. While I've been doing most of the grunt-work and heavy lifting - thanks go out to Suresh, Kiwamu, Koji, Steve and everyone else who's helped out with discussion of results and assorted assists to numerous to mention.


  4463   Wed Mar 30 18:50:57 2011 KojiConfigurationComputer Scripts / ProgramsAdded a sitemap alias

I thought that "m40m" was the traditional alias for the sitemap...


m40m ${medm_base} ${medm_newtail} &
sitemap medm -x /cvs/cds/rtcds/caltech/c1/medm/sitemap.adl

rossa:~>set|grep medm
medm_base       medm
medm_newtail    -x /opt/rtcds/caltech/c1/medm/sitemap.adl

medm_tail       -x /cvs/cds/caltech/medm/sitemap.adl


I added an alias to the sitemap MEDM screen in /cvs/cds/caltech/target/cshrc.40m

Now you can enjoy launching sitemap from a terminal.

alias sitemap 'medm -x /cvs/cds/rtcds/caltech/c1/medm/sitemap.adl'



  4462   Wed Mar 30 17:01:08 2011 Larisa ThorneUpdateVIDEOCable laying...continued

[Steve, Suresh, Kiwamu, Larisa]


Only the PRM/BS cable was laid today.

In one of the previous updates on cable laying, it was noted that the MC2 cable needed an additional 10' and the MC2T needed an additional 15' to reach their destinations.  We cut and put BNC ends on 10' and 15' cables and connected them to the original cables in order to make them long enough.


This concludes the laying of new cables. Suresh is currently working on the QUADs...

  4461   Wed Mar 30 16:57:13 2011 kiwamuUpdateGeneralturned off c1aux

[Steve / Kiwamu]

 As a part of the video cable session, we reconnected some power cords on 1Y1 rack.

During the work we momentarily turned off c1aux, which handles DMF, Illumintators, mechanical shutters and the old video epics.

I think it automatically reverted the things, but we may need to check them.

  4460   Wed Mar 30 16:32:29 2011 AidanConfigurationComputer Scripts / ProgramsAdded a sitemap alias

I added an alias to the sitemap MEDM screen in /cvs/cds/caltech/target/cshrc.40m

Now you can enjoy launching sitemap from a terminal.

alias sitemap 'medm -x /cvs/cds/rtcds/caltech/c1/medm/sitemap.adl'

  4459   Wed Mar 30 02:55:02 2011 SureshConfigurationElectronicsRF System : Status and Plans

I have prepared several diagrams outlining the current state of the RF System.

These are uploaded into the svn40m here  and will be kept uptodate as we complete various parts of the task.  These plans have taken into account

the new priorities of the LSC (set out by Koji here )

We (Koji, Kiwamu and I) took stock of the RF cables which we have inherited from the earlier RF system and have made new plans for them.

I took stock of the filters purchased for the modifying the demod boards.  We have pretty much everything we need so I will start modifying the boards right away.   The following table summarises the modifications


PD freq # of PDs

LP Filter (U5)

  Demod board

Qty available Inline HP filter Qty available
11 MHz 5 SCLF-10.75 7 - -
22 MHz 1 SCLF-21.4 3 - -
33 MHz 2 SCLF-36 3 SHP-25 1
55 MHz 3 SCLF-65 4 SHP-50 2
110 MHz 1 SCLF-135 3 SHP-100 1
165MHz 3 SCLF-190 1 SHP-150 1

We seem to have a spare SHP-175.  I was wondering where that is supposed to go. 

This is the status and tentative schedule for completing the various tasks.  I have put the dates based on priority and state of the hardware.


The RF Cable layout plans are drawn on top of a Lab Layout.  The various subsystems are drawn (not to scale) on separate layers.  The graffle files are located here  .  I thought they might come in handy for others as well.



  4458   Tue Mar 29 22:29:16 2011 kiwamuUpdateGeneralsome tasks tomorrow

 *  Temporary strain relief for the heliax cables on 1X2 (Steve)

 *  RF diagrams and check lists (Suresh)

      => In the lunch meeting we will discuss the details about what we will do for the RF installation.

 *  Electronics design and plan for Green locking (Aidan / Kiwamu)

      => In the lunch meeting we will discuss the details.

 *  LSC model (Koji)

 *  Video cable session (team)

 * LPF for the laser temperature control (Larisa)

  4457   Tue Mar 29 15:50:21 2011 KojiUpdateElectronicsLow pass filter for X arm laser temperature control

For bode plot:

USE LOG-LOG plot for the amplitude

USE LOG-LINEAR plot for the phase


Search "Bode Plot" on web

  4456   Tue Mar 29 15:01:58 2011 Larisa ThorneUpdateElectronicsLow pass filter for X arm laser temperature control

 This is the continuation of http://nodus.ligo.caltech.edu:8080/40m/4402


The first picture is of the actual component, where the resistor is 1M and capacitor is 10uF. 

But before the component can be put into place, its transfer function had to be checked to make sure it was doing what we calculated it would do. The results of these are in the graphs generated: frequency vs. gain, and frequency vs. phase.




According to these graphs, we are not achieving the targeted cutoff frequency: need to recalculate and compensate for the extra 100k resistance being encountered.

Attachment 1: DSC_2889.JPG
Attachment 2: LPFgraph.pdf
LPFgraph.pdf LPFgraph.pdf LPFgraph.pdf LPFgraph.pdf
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