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ID Date Author Type Categorydown Subject
  389   Thu Feb 27 14:31:13 2020 KojiGeneralGeneralItem lending

Item lending as per Ian's request: Particle Counter from OMC Lab to QIL

 

Attachment 1: P_20200227_134755_vHDR_On.jpg
P_20200227_134755_vHDR_On.jpg
  390   Mon Aug 10 15:29:54 2020 KojiGeneralGeneralItem lending

The particle counter came back to the OMC lab on Aug 10, 2020

 

  392   Mon Aug 10 15:53:46 2020 KojiGeneralGeneralLab status check

Check-in to the OMC lab to see the status. Nothing seemed changed. No bug. The HEPA is running normal. The particle level was 0.

Went into the HEPA enclosure and put a cover on the OMC. Because of the gluing template, the lid could not be close completely (that's expected and fine).

The IPA vector cloth bag was not dry yet but seemed expired (some smell). There is no stock left -> 5 bags to be ordered.

  393   Mon Sep 28 16:03:13 2020 ranaGeneralGeneralOMC Beam Dump Production Cure Bake
are there any measurements of the BRDF of these things? I'm curious how much light is backscattered into the incoming beam and how much goes out into the world.

Maybe we can take some camera images of the cleaned ones or send 1-2 samples to Josh. No urgency, just curiosity.

I saw that ANU and also some labs in India use this kind of blue/green glass for beam dumps. I don't know much about it, but I am curious about its micro-roughness and how it compares to our usual black glass. For the BRDF, I think the roughnesss matters more for the blackness than the absorption.

  394   Mon Sep 28 16:13:08 2020 KojiGeneralGeneralOMC Beam Dump Production Cure Bake

According to the past backscatter test of the OMC (and the black glass beamdump: not V type but triangular type on a hexagonal-mount), the upper limit of the back reflection was 0.13ppm. https://nodus.ligo.caltech.edu:8081/OMC_Lab/209

I don't have a BRDF measurement. We can send a few black glass pieces to Josh.

  396   Fri Oct 9 01:01:01 2020 KojiGeneralGeneralTFT Monitor mounting

To spare some room on the optical table, I wanted to mount the two TFT monitor units on the HEPA enclosure frame.
I found some Bosch Rexroth parts (# 3842539840) in the lab, so the bracket was taken for the mount. This swivel head works very well. It's rigid and still the angle is adjustable.

https://www.boschrexroth.com/ics/cat/?cat=Assembly-Technology-Catalog&p=p834858

BTW, this TFT display (Triplett HDCM2) is also very nice. It has HDMI/VGA/Video/BNC inputs (wow perfect) and the LCD is Full-HD LED TFT.
https://www.triplett.com/products/cctv-security-camera-test-monitor-hd-1080p-led-display-hdcm2

https://www.newegg.com/p/0AF-0035-00016

https://www.bhphotovideo.com/c/product/1350407-REG/triplett_hdcm2_ultra_compact_7_hd_monitor.html

The only issue is that one unit (I have two) shows the image horizontally flipped. I believe that I used the unit with out this problem before, I'm asking the company how to fix this.

 

Attachment 1: 20201008214515_IMG_0152.jpg
20201008214515_IMG_0152.jpg
Attachment 2: 20201008214519_IMG_0153.jpg
20201008214519_IMG_0153.jpg
Attachment 3: 20201008214536_IMG_0154.jpg
20201008214536_IMG_0154.jpg
Attachment 4: 20201008220955_IMG_0155.jpg
20201008220955_IMG_0155.jpg
Attachment 5: 20201008221019_IMG_0156_2.jpg
20201008221019_IMG_0156_2.jpg
  397   Fri Oct 16 00:53:29 2020 KojiGeneralGeneralTFT Monitor mounting

The image flipping of the display unit was fixed. The vendor told me how to fix it.

- Open the chassis by the four screws at the side.
- Look at the pass-through PCB board between the mother and display boards.
- Disconnect the flat flex cables from the pass-through PCB (both sides) and reconnect them (i.e. reseat the cables)

That's it and it actually fixed the image flipping issue.

 

  398   Fri Oct 23 19:09:54 2020 KojiGeneralGeneralParticle counter transfered to Radhika

See this entry: https://nodus.ligo.caltech.edu:8081/40m/15642

  399   Fri Nov 6 18:38:00 2020 KojiGeneralGeneralPowermeter lent from OMC Lab to 2um ECDL

Thorlabs' powermeter controler + S401C head was lent from OMC Lab.

https://nodus.ligo.caltech.edu:8081/SUS_Lab/1856

  400   Mon Nov 9 22:06:18 2020 KojiMechanicsGeneral5th OMC Transport Fixture

I helped to complete the 5th OMC Transport Fixture. It was built at the 40m clean room and brought to the OMC lab. The fixture hardware (~screws) were also brought there.

Attachment 1: IMG_0211.jpg
IMG_0211.jpg
Attachment 2: IMG_0221.jpg
IMG_0221.jpg
  401   Fri Nov 20 18:51:23 2020 KojiGeneralGeneralInstrument loan

FEMTO DLPCA200 low noise preamp (brand new)

Keithley Source Meter 2450 (brand new) => Returned 11/23/2020

were brought to the OMC lab for temporary use.

https://nodus.ligo.caltech.edu:8081/QIL/2522

  407   Fri Feb 5 07:40:37 2021 StephenSupplyGeneralOMC Unit 4 Build Machined Parts

OMC Unit 4 Build Machined Parts are currently located in Stephen's office. See image of large blue box from office, below.

Loaned item D1100855-V1-00-OMC08Q004 to Don Griffith for work in semi-clean HDS assy.

This includes mass mounting brackets, cable brackets, balance masses, etc. For full inventory, refer to ICS load Bake-9527 (mixed polymers) and Bake-9495 (mixed metals).

Inventory includes all items except cables. Plasma sprayed components with slight chipping were deemed acceptable for Unit 4 use. Cable components (including flex circuit) are ready to advance to fabrication, with a bit more planning and ID of appropriate wiring.

Attachment 1: IMG_8117.JPG
IMG_8117.JPG
  408   Thu May 20 17:03:50 2021 KojiGeneralGeneralSRS LCR meter SRS720 borrowed from Downs

Item loan: SRS LCR meter SRS720 borrowed from Downs. The unit is at the 40m right now for testing with an excelitas PD. Once it is done, the setup will be moved to the OMC lab for testing the high QE PDs

Attachment 1: P_20210520_154841.jpg
P_20210520_154841.jpg
  409   Sun May 30 15:17:16 2021 KojiGeneralGeneralDCPD AF capacitance measirement

Attachment 1: System diagram. The reverse bias voltage is controlled by DS335. This can produce a voltage offset up to 10V. A G=+2 opamp circuit was inserted so that a bias of up to +15V can be produced. The capacitances of the photodiodes were measured with SR720 LCR meter with a probe. DS335 and SR720 were controlled from PC/Mac via serial connections.

Attachment 2: Overview

Attachment 3: How was the probe attached to the photodiode under the test

Attachment 4: The bias circuitry and the power supply

Attachment 5: G=+2 amp

Attachment 1: PD_cap_meas.pdf
PD_cap_meas.pdf
Attachment 2: 20210529013015_IMG_0577.jpeg
20210529013015_IMG_0577.jpeg
Attachment 3: 20210529013114_IMG_0580_2.jpeg
20210529013114_IMG_0580_2.jpeg
Attachment 4: 20210529013200_IMG_0584.jpeg
20210529013200_IMG_0584.jpeg
Attachment 5: 20210529013229_IMG_0586.jpeg
20210529013229_IMG_0586.jpeg
  410   Sun May 30 15:32:56 2021 KojiGeneralGeneralDCPD AF capacitance measirement

Measurement result:

The capacitance at no bias was 460~500pF. This goes down to below 300pF at 1.0~1.5V reverse bias. At maximum +15V, the capacitance goes down to 200~220pF.

On this opportunity, the capacitances of a couple of Excelitas C30665 photodiodes were measured. In Attachment 2, the result was compared with one of the results from the high QE PDs. In general the capacitance of C30665 is lower than the one from the high QE PDs.

Attachment 1: highQEPD_capacitance.pdf
highQEPD_capacitance.pdf
Attachment 2: C30665_capacitance.pdf
C30665_capacitance.pdf
  411   Wed Jul 7 14:21:50 2021 StephenSupplyGeneralOMC Unit 4 Build Machined Parts

More explicit insights into the inventory for the Unit 4 build. Image of inventory included below.

Machined Parts:

Cable Components:

  • Hughes Circuits made us Kapton flex circuits. These have not been processed in any way.
  • Rich had supplied a spool of Gore 4-conductor in-vacuum wire (see below image). I returned the sppol for Rich but it is living in Downs and available for use.
  • PEEK cable ties were damaged during bake, and will be replaced by SYS inventory.

Retrofit/Repair Capabilities:

  • Aluminum reinforcement brackets D1600316
  • Glass reinforcement brackets (Edmund Optics 45-072 and 45-071)

ref: E1900034 and other associated documents.

Attachment 1: IMG_9238.JPG
IMG_9238.JPG
Attachment 2: IMG_9236.JPG
IMG_9236.JPG
  4   Wed Jun 20 20:37:45 2012 ZachOpticsConfigurationTopology / parameter selection

EDIT (ZK): All the plots here were generated using my MATLAB cavity modeling tool, ArbCav. The utility description is below. The higher-order mode resonance plots are direct outputs of the function. The overlap plots were made by modifying the function to output a list of all HOM resonant frequencies, and then plotting the closest one as a function of cavity length. This was done for various values of highest mode order to consider, as described in the original entry.

Description:

This function calculates information about an arbitrary optical cavity. It can plot the cavity geometry, calculate the transmission/reflection spectrum, and generate the higher-order mode spectrum for the carrier and up to 2 sets of sidebands.

The code accepts any number of mirrors with any radius of curvature and transmission, and includes any astigmatic effects in its output.

As opposed to the previous version, which converted a limited number of cavity shapes into linear cavities before performing the calculation, this version explicitly propagates the gouy phase of the beam around each leg of the cavity, and is therefore truly able to handle an arbitrary geometry.

----------------Original Post----------------

I expressed concern that arbitrarily choosing some maximum HOM order above which not to consider makes us vulnerable to sitting directly on a slightly-higher-order mode. At first, I figured the best way around this is to apply an appropriate weighting function to the computed HOM frequency spacing. Since this will also have some arbitrariness to it, I have decided to do it in a more straightforward way. Namely, look at the spacing for different values of the maximum mode number, nmax, and then use this extra information to better select the length.

Assumptions:

  • The curved mirror RoC is the design value of 2.50±0.025 m
  • The ±9 MHz sidebands will have ~1% the power of the other fields at the dark port. Accordingly, as in Sam's note, their calculated spacing is artificially increased by 10 linewidths.
  • The opening angle of 4º is FIXED, and the total length is scaled accordingly

Below are the spacing plots for the bowtie (flat-flat-curved-curved) and non-bowtie (flat-curved-flat-curved) configurations. Points on each line should be read out as "there are are no modes of order N or lower within [Y value] linewidths of the carrier TEM00 transmission", where N is the nmax appropriate for that trace. Intuitively, as more orders are included, the maxima go down, because more orders are added to the calculation.

*All calculations are done using my cavity simulation function, ArbCav. The mode spacing is calculated for each particular geometry by explicitly propagating the gouy phase through each leg of the cavity, rather than by finding an equivalent linear cavity*

 ovlp_bowtie.pngovlp_non-bowtie.png

Since achievable HOM rejection is only one of the criteria that should be used to choose between the two topologies, the idea is to pick one length solution for EACH topology. Basically, one maximum should be chosen for each plot, based on how how high an order we care about.

Bowtie

For the bowtie, the nmax = 20 maximum at L = 1.145 m is attractive, because there are no n < 20 modes within 5 linewidths, and no n < 25 modes within ~4.5 linewidths. However, this means that there are also n < 10 modes within 5 linewidths, while they could be pushed (BLUE line) to ~8.5 linewidths at the expense of proximity to n > 15 modes.

Therefore, it's probably best to pick something between the red and green maxima: 1.145 m < L < 1.152 m.

By manually inspecting the HOM spectrum for nmax = 20, it seems that L = 1.150 m is the best choice. In the HOM zoom plot below and the one to follow, the legend is as follows

  • BLUE: Carrier
  • GREEN: +9 MHz
  • RED: -9 MHz
  • CYAN: +45 MHz
  • BLACK: -45 MHz

spect_zoom_bowtie.png

Non-bowtie

Following the same logic as above, the most obvious choice for the non-bowtie is somewhere between the red maximum at 1.241 m and the magenta maximum at 1.248 m. This still allows for reasonable suppression of the n < 10 modes without sacrificing the n < 15 mode suppression completely.

Upon inspection, I suggest L = 1.246 m

spect_zoom_non-bowtie.png

I reiterate that these calculations are taking into account modes of up to n ~ 20. If there is a reason we really only care about a lower order than this, then we can do better. Otherwise, this is a nice compromise between full low-order mode isolation and not sitting directly on slightly higher modes.

 

RoC dependence

One complication that arises is that all of these are highly dependent on the actual RoC of the mirrors. Unfortunately, even the quoted tolerance of ±1% makes a difference. Below is a rendering of the RED traces (nmax = 20) in the first two plots, but for R varying by ±2% (i.e., for R = 2.45 m, 2.50 m, 2.55 m).

ovlp_vs_R_bowtie.pngovlp_vs_R_non-bowtie.png

The case for the non-bowtie only superficially seems better; the important spacing is the large one between the three highest peaks centered around 1.24 m.

Also unfortunately, this strong dependence is also true for the lowest-order modes. Below is the same two plots, but for the BLUE (nmax = 10) lines in the first plots.

 ovlp_vs_R_N10_bowtie.pngovlp_vs_R_N10_non-bowtie.png

Therefore, it is prudent not to pick a specific length until the precise RoC of the mirrors is measured.

 

Conclusion

Assuming the validity of looking at modes between 10 < n < 20, and that the curved mirror RoC is the design value of 2.50 m, the recommended lengths for each case are:

  • Bowtie: LRT = 1.150 m
  • Non-bowtie: LRT = 1.246 m

 HOWEVER, variation within the design tolerance of the mirror RoC will change these numbers appreciably, and so the RoC should be measured before a length is firmly chosen.

  5   Thu Jun 21 03:07:27 2012 ZachOpticsConfigurationParameter selection / mode definition

EDIT 2 (ZK): As with the previous post, all plots and calculations here are done with my MATLAB cavity modeling utility, ArbCav.

EDIT (ZK): Added input q parameters for OMMT 

found the nice result that the variation in the optimal length vs. variation in the mirror RoC is roughly linear within the ±1% RoC tolerance. So, we can choose two baseline mode definitions (one for each mirror topology) and then adjust as necessary following our RoC measurements.

Bowtie

For R = 2.5 m, the optimal length (see previous post) is LRT = 1.150 m, and the variation in this is dLRT/dR ~ +0.44 m/m.

Here is an illustration of the geometry:

geom_bowtie.png

The input q parameters, defined at the point over the edge of the OMC slab where the beam first crosses---(40mm, 150mm) on the OptoCad drawing---are, in meters:

  • qix = - 0.2276 + 0.6955 i
  • qiy = - 0.2276 + 0.6980 i

 

Non-bowtie

For R = 2.5 m, the optimal length is LRT = 1.246 m, and the variation in this is also dLRT/dR ~ +0.44 m/m.

Geometry:

geom_non-bowtie.png

q parameters, defined as above:

  • qix = - 0.0830 + 0.8245 i
  • qiy = - 0.0830 + 0.8268 i
  36   Thu Nov 8 19:47:55 2012 KojiElectronicsConfigurationSolder for PZTs

Rich saids:

I have ordered a small roll of solder for the OMC piezos. 
The alloy is: Sn96.5 Ag3.0 Cu0.5

  38   Thu Nov 8 20:12:10 2012 KojiOpticsConfigurationHow many glass components we need for a plate

Optical prisms 50pcs (A14+B12+C6+E18)
Curved Mirrors 25pcs (C13+D12)

  Qty

Prisms

Curved No BS OMC Wedge tested
Coating A: IO coupler   14 0  2 prisms 5/5
Coating B: BS 45deg   12 0  2 prisms  0/5
Coating C: HR   6 13 2 curved  
Coating D: Asym. output coupler   0 12 -  
Coating E: HR 45deg   18 0  4 prism (1 trans + 3 refl) 0/3
D1102209 Wire Mount Bracket 25      4  
D1102211 PD Mount Bracket 30      8  

 

  55   Fri Jan 18 13:25:17 2013 KojiOpticsConfigurationAutocollimator calibration

An autocollimator (AC) should show (0,0) if a retroreflector is placed in front of the AC.
However, the AC may have an offset. Also the retroreflector may not reflect the beam back with an exact parallelism.

To calibrate these two errors, the autocollimator is calibrated. The retroreflector was rotated by 0, 90, 180, 270 deg
while the reticle position are monitored. The images of the autocollimator were taken by my digital camera looking at the eyepiece of the AC.

Note that 1 div of the AC image corresponds to 1arcmin.

Basically the rotation of the retroreflector changed the vertical and horizontal positions of the reticle pattern by 0.6mdeg and 0.1mdeg
(2 and 0.4 arcsec). Therefore the parallelism of the retrorefrector is determined to be less than an arcsec. This is negligibly good for our purpose.

The offset changes by ~1div in a slanted direction if the knob of the AC, whose function is unknown, is touched.
So the knob should be locked, and the offset should be recorded before we start the actual work every time.

Attachment 1: autocollimator_calibration.pdf
autocollimator_calibration.pdf autocollimator_calibration.pdf autocollimator_calibration.pdf autocollimator_calibration.pdf
  63   Thu Feb 21 18:44:18 2013 KojiOpticsConfigurationPerpendicularity test

Perpendicularity test of the mounting prisms:

The perpendicularity of the prism pieces were measured with an autocollimator.

Two orthogonally jointed surfaces forms a part of a corner cube.
The deviation of the reflected image from retroreflection is the quantity measured by the device.

When the image is retroreflected, only one horizontal line is observed in the view.
If there is any deviation from the retroreflection, this horizontal line splits into two
as the upper and lower halves have the angled wavefront by 4x\theta. (see attached figure)

The actual reading of the autocollimator is half of the wavefront angle (as it assumes the optical lever).
Therefore the reading of the AC times 30 gives us the deviation from 90deg in the unit of arcsec.

SN / measured / spec

SN10: 12.0 arcsec (29 arcsec)

SN11: 6.6 arcsec (16 arcsec)

SN16: 5.7 arcsec (5 arcsec)

SN20: -17.7 arcsec (5 arcsec)

SN21: - 71.3 arcsec (15 arcsec)

 

Attachment 1: perpendicularity_test.pdf
perpendicularity_test.pdf perpendicularity_test.pdf
Attachment 2: P2203206.JPG
P2203206.JPG
  64   Wed Feb 27 18:18:48 2013 KojiOpticsConfigurationMore perpendicularity test

Mounting Prisms:
(criteria: 30arcsec = 145urad => 0.36mm spot shift)
SN  Meas.(div) ArcSec Spec.
10   0.3989    11.97   29    good
11   0.2202     6.60   16
    good
16   0.1907     5.72    5
    good
20  -0.591    -17.73    5
    good
21  -2.378    -71.34   15

21  -1.7      -51.     15
01  -0.5      -15.     52
02  -2.5      -75.     48
06  -1.0      -30.     15
    good
07   1.7       51.     59
12  -2.2      -66.     40
13  -0.3      - 9.     12
    good
14  -2.8      -84.     27
15  -2.5      -75.     50
17   0.7       21.     48
22   2.9       87.    
63

Mirror A:
A1  -0.5      -15.     NA    good
A3   0.5       15.     NA
    good
A4   0.9       27.     NA
    good
A5   0.4       12.     NA
    good
A6   0.1        3.
    NA    good
A7   0.0        0.
    NA    good
A8   0.0       
0.     NA    good
A9   0.0       
0.     NA    good
A10  1.0      
30.     NA    good
A11  0.3       
9.     NA    good
A12  0.1       
3.     NA    good
A13  0.0       
0.     NA    good
A14  0.6      
18.     NA    good

Mirror B:
B1  -0.9     
-27.     NA    good
B2  -0.6     
-18.     NA    good
B3  -0.9     
-27.     NA    good
B4   0.7      
21.     NA    good
B5  -1.1     
-33.     NA
B6  -0.6     
-18.     NA    good
B7  -1.8     
-54.     NA
B8  -1.1     
-33.     NA
B9   1.8      
54.     NA
B10  1.2       
36.     NA   
B11 -1.7     
-51.     NA
B12  1.1       
33.     NA

  65   Fri Mar 1 23:06:15 2013 KojiOpticsConfigurationMore perpendicularity test final

Perpendicularity of the "E" mirror was measured.


Mounting Prisms:
(criteria: 30arcsec = 145urad => 0.36mm spot shift)
SN  Meas.(div) ArcSec Spec.
10   0.3989    11.97   29    good
11   0.2202     6.60   16
    good
16   0.1907     5.72    5
    good
20  -0.591    -17.73    5
    good
21  -2.378    -71.34   15

21  -1.7      -51.     15
01  -0.5      -15.     52
02  -2.5      -75.     48
06  -1.0      -30.     15
    good
07   1.7       51.     59
12  -2.2      -66.     40
13  -0.3      - 9.     12
    good
14  -2.8      -84.     27
15  -2.5      -75.     50
17   0.7       21.     48
22   2.9       87.    
63

Mirror A:
A1  -0.5      -15.     NA    good
A3   0.5       15.     NA
    good
A4   0.9       27.     NA
    good
A5   0.4       12.     NA
    good
A6   0.1        3.
    NA    good
A7   0.0        0.
    NA    good
A8   0.0       
0.     NA    good
A9   0.0       
0.     NA    good
A10  1.0      
30.     NA    good
A11  0.3       
9.     NA    good
A12  0.1       
3.     NA    good
A13  0.0       
0.     NA    good
A14  0.6      
18.     NA    good

Mirror B:
B1  -0.9     
-27.     NA    good
B2  -0.6     
-18.     NA    good
B3  -0.9     
-27.     NA    good
B4   0.7      
21.     NA    good
B5  -1.1     
-33.     NA
B6  -0.6     
-18.     NA    good
B7  -1.8     
-54.     NA
B8  -1.1     
-33.     NA
B9   1.8      
54.     NA
B10  1.2       
36.     NA   
B11 -1.7     
-51.     NA
B12  1.1       
33.     NA

Mirror E:
E1  -0.8      -24.     NA    good
E2  -0.8      -24.    
NA    good
E3  -0.25     - 7.5   
NA    good
E4  -0.5      -15.     NA
    good
E5   0.8       24.     NA    good
E6  -1.0      -30.     NA
    good
E7  -0.2      - 6.     NA
    good
E8  -0.8      -24.     NA
    good
E9  -1.0      -30.     NA
    good
E10  0.0        0.     NA
    good
E11 -1.0      -30.     NA
    good
E12 -0.3      - 9.     NA
    good
E13 -0.8      -24.     NA
    good
E14 -1.0      -30.     NA    good
E15 -1.2      -36.     NA

E16 -0.7      -21.     NA
    good
E17 -0.8      -24.     NA
    good
E18 -1.0      -30.     NA
    good

  86   Thu Mar 28 03:37:07 2013 ZachOpticsConfigurationTest setup input optics progress

[Lisa, Zach]

Last night (Tuesday), I finished setting up and aligning most of the input optics for the OMC characterization setup. See the diagram below, but the setup consists of:

  • Faraday isolator/polarization definition
  • HWP+PBS for power splitting into two paths:
    • EOM path
      • Resonant EOM for PDH sideband generation
      • Broadband EOM for frequency scanning
    • AOM path
      • Double-passed ~200-MHz Isomet AOM for subcarrier generation. NOTE: in this case, I have chosen the m = -1 diffraction order due to the space constraints on the table.
  • Recombination of paths on a 50/50 beam splitter---half of the power is lost through the unused port into a black glass dump
  • Coupler for launching dual-field beam into a fiber (to OMC)

OMC_test_setup_IO.jpg 2013-03-27_05.48.20.jpg

Today, we placed some lenses into the setup, in two places:

  1. In the roundabout section of the AOM path that leads to the recombination, to re-match the AOM-path beam to that of the EOM path
  2. After the recombination beam splitter, to match the combined beam mode into the fiber

We (Koji, Lisa, and myself) had significant trouble getting more than ~0.1% coupling through the fiber, and after a while we decided to go to the 40m to get the red-light fiber illuminator to help with the alignment.

Using the illuminator, we realigned the input to the coupler and eventually got much better---but still bad---coupling of ~1.2% (0.12 mW out / 10 mW in). Due to the multi-mode nature of the illuminator beam, the output cannot be used to judge the collimation of the IR beam; it can only be used to verify the alignment of the beam.

With 0.12 mW emerging from the other end of the fiber, we could see the output quite clearly on a card (see photo below). This can tell us about the required input mode. From the looks of it, our beam is actually focused too strongly. We should probably replace the 75mm lens again with a slightly longer one.

Lisa and I concurred that it felt like we had converged to the optimum alignment and polarization, which would mean that the lack of coupling is all from mode mismatch. Since the input mode is well collimated, it seems unlikely that we could be off enough to only get ~1% coupling. One possibility is that the collimator is not well attached to the fiber itself. Since the Rayleigh range within it is very small, any looseness here can be critical.

2013-03-28_02.29.36.jpg

I think there are several people around here who have worked pretty extensively with fibers. So, I propose that we ask them to take a look at what we have done and see if we're doing something totally wrong. There is no reason to reinvent the wheel.

  87   Fri Mar 29 08:55:00 2013 ZachOpticsConfigurationBeam launched into fiber

Quote:

Lisa and I concurred that it felt like we had converged to the optimum alignment and polarization, which would mean that the lack of coupling is all from mode mismatch. Since the input mode is well collimated, it seems unlikely that we could be off enough to only get ~1% coupling. One possibility is that the collimator is not well attached to the fiber itself. Since the Rayleigh range within it is very small, any looseness here can be critical.

My hypothesis about the input-side collimator turned out to be correct.

I removed the fiber from the collimator and mount at the input side, and then injected the illuminator beam from this side. Since we already saw a nice (but dim) IR beam emerging from the output side the other night, it followed that that collimator was correctly attached. With the illuminator injected from the input side, I also saw a nice, collimated red beam emerging from the output. So, the input collimator was not properly attached during our previous attempts, leading to the abysmal coupling.

The problem is that the mount does not allow you to remove and reattach the fiber while the collimator is already attached, and the dimensions make it hard to fit your fingers in to tighten the fiber to the collimator once the collimator is in the mount. I disassembled the mount and found a way to attach/reattach the fiber that preserves the tight collimator contact. I will upload a how-to shortly.

With this fix, I was able to align the input beam and get decent coupling:

EOM path: ~70%

AOM path: ~50%

  94   Thu Apr 4 00:35:42 2013 ZachOpticsConfigurationMMT installed on breadboard, periscope built

[Koji, Zach]

We installed the MMT that matches the fiber output to the OMC on a 6"x12" breadboard. We did this so that we can switch from the "fauxMC" (OMC mirrors arranged with standard mounts for practice locking) to the real OMC without having to rebuild the MMT.

The solution that Koji found was:

z = 0: front face of the fiber output coupler mount

z = 4.8 cm: f = 35mm lens

z = 21.6 cm: f = 125mm lens

This should place the waist at z ~ 0.8 m. Koji has the exact solution, so I will let him post that.

The lenses are on ±0.5" single-axis OptoSigma stages borrowed from the TCS lab. Unfortunately, the spacing between the two lenses is very close to a half-integer number of inches, so I had to fix one of them using dog clamps instead of the screw holes to preserve the full range.

Koji also built the periscope (which raises the beam height by +1.5") using a vertical breadboard and some secret Japanese mounts. Part of it can be seen in the upper left corner of the photo below---sorry for not getting a shot of it by itself.

2013-04-03_23.43.00.jpg

  97   Thu Apr 4 23:44:52 2013 KojiOpticsConfigurationBeam launched into fiber

We had to move our flipper mirror to share the beam between Peter's setup and ours as our flipper is at the place where the ISS PD array base is supposed to be!
There was no place to insert the flipper in the setup. We (Peter and Koji) decided to move the laser back for ~2".

This entirely changed the alignment of the setup. The fiber coupler was my reference of the alignment.
Once the beam is aligned, I check the coupling to the fiber. It was 50%.

I tweaked the lens and eventually the coupling is improved to 83%. (24.7mW incident, 20.4mW obtained.)

Then, I started to check the AOM path. I noticed that the 1st (or -1st) order beam is very weak.
The deflection efficiency is ~0.1%. Something is wrong.
I checked the driver. The driver's coupler output (1:10) show the amplitude ~1V. (good)
I check the main output by reducing the offset. When the coupler output is 100mV, the main output was 1V. (good)
So is the AOM itself broken???

  99   Fri Apr 5 18:18:36 2013 ZachOpticsConfigurationAOM probably broken

Quote:

Then, I started to check the AOM path. I noticed that the 1st (or -1st) order beam is very weak.
The deflection efficiency is ~0.1%. Something is wrong.
I checked the driver. The driver's coupler output (1:10) show the amplitude ~1V. (good)
I check the main output by reducing the offset. When the coupler output is 100mV, the main output was 1V. (good)
So is the AOM itself broken???

As Koji noticed that the AOM efficiency was very low, I figured I would try looking at it with a fresh set of eyes. The end result is that I have to agree that the AOM appears to be broken.

First, I measured the input impedance of the AOM using the AG4395A with the impedance test kit (after calibrating). The plot is below. The spec sheet says the center frequency is 200 MHz, at which Zin should be ~50 ohms. It crosses 50 ohms somewhere near 235 MHz, which may be reasonable given that the LC circuit can be tuned by hand. However, it does surprise me that the impedance varies so much over the specified RF range of ±50 MHz. Maybe this is an indication that something is bad.

Isomet_1250C_zin_4_5_13.png

I removed the cover of the modulator (which I think Koji did, as well) and all the connections looked as I imagine they should---i.e., there was nothing obviously broken, physically.

I then tried my hand at realigning the AOM from scratch by removing and replacing it. I was not able to get better than 0.15%, which is roughly what Koji got.

So, perhaps our best course of action is to decide what we expect the Zin spectrum to look like, and whether that agrees with the above measurement.

  103   Mon Apr 8 20:56:52 2013 KojiOpticsConfigurationPZT & Curverd Mirror arrangement

Assembly #1:

Mounting Prism #16
PZT #26
Mirror C6

Assembly #2:

Mounting Prism #20
PZT #23
Mirror C5

Attachment 1: PZT_assembly.pdf
PZT_assembly.pdf PZT_assembly.pdf
  105   Mon Apr 8 23:42:33 2013 KojiOpticsConfigurationFake OMC roughly aligned

Mode matching:

 

Attachment 1: beam_profile.pdf
beam_profile.pdf
Attachment 2: mode_matching.pdf
mode_matching.pdf
  107   Wed Apr 10 00:40:30 2013 ZachOpticsConfigurationfauxMC locked

[Koji, Zach]

Tonight, we locked the "fauxMC". We obtained a visibility of >99%.

Koji had aligned it roughly last night, but we wanted to have a couple steering mirrors in the path for this practice cavity (the periscope mirrors will serve this function in the real setup), so we marked the alignment with irises and installed two extra mirrors.

After obtaining flashes with the WinCam placed at the output coupler, we removed the WinCam and put a CCD camera at one of the curved mirror transmissions and used this to get a strong TEM00 flash. Then, we installed the REFL PD/CCD, swept the laser PZT and optimized the alignment by minimizing the REFL dips. Finally, we connected the RF electronics and locked the cavity with the LB box. We used whatever cables we had around to trim the RF phase, and then Koji made some nice SMA cables at the 40m.

One thing we noticed was that we don't have enough actuation range to keep the cavity locked for very long---even with the HV amp (100V). We are going to offload to the NPRO temperature using an SR560 or pomona box circuit. We may also make an enclosure for the cavity to protect it from the HEPA blasting.

Tomorrow, after we do the above things, we will practice measuring the transmission, length (FSR) and mode spectrum of the cavity before moving on to the real McCoy.

fauxMC_labeled.jpg

  113   Tue Apr 16 09:43:58 2013 KojiOpticsConfigurationMirror list for L1OMC

L1 OMC

Cavity Mirrors

FM1 (input coupler): A8
FM2 (output coupler): A7
CM1 (curved mirror close to FM1): C6
CM2 (curved mirror close to FM2): C5

DCPD path

BS3 (BS for DCPDs): B5 B7

QPD path

BS1 (input steering): E10
SM1 (steering mirror next to BS1): E12
BS2 (BS for QPD path): B3
SM2 (steering mirror next to BS2): E4
SM3 (steering mirror next to SM2): E16

OMC_breadboard_mirror_config.png

  135   Mon Jun 3 18:58:08 2013 KojiOpticsConfigurationOMC final tests

- QPD mount aligned, QPD output checked
  The spots are with 100um from the center of the diodes. [ELOG Entry (2nd photo)]

- TMS/FSR dependence on the PZT V
  Shows significant dependence on the PZT voltages
 
It seems that the curvartures get longer when the voltages are applied to the PZTs.
  The effect on these two PZTs are very similar. The dependence is something like
  (TMS/FSR) ~ 0.219 - 1e-5 V
  May cause resonance of the higher-order modes (like 13th order of the 45MHz sidebands) at a specific range of the PZTs.
  We can't change anything any more, but the impact needs to be assessed


- DC response of the PZTs [ELOG Entry]
  PZT voltages were swept. Observed multiple fringes during the sweep.
  The data to be analyzed.

- AC response of the PZTs [ELOG Entry]
  PZT1 and PZT2 well matched. The first resonance at 10kHz.

- Open loop TF of the servo
  The UGF more than ~30kHz.

- Cleaning of the main optics with First Contact
  Done. Visible scattering seen with an IR was reduced, but still exist.
  All four cavity mirrors have about the same level of scattering.
  Each scattering is a group of large or small bright spots.
  It's actually a bit difficult to resolve the bright spots with the IR viewer.

- Raw transmission: i.e. Ratio between the sum of the DCPD paths and the incident power
  May 8th (before the baking):      0.918
  May 8th (First Contact applied): 0.940 (improved)
  Jun 2nd (after the baking):         0.927 (worse)
  Jun 2nd (First Cotact applied):   0.964 (improved)

 

Date 2013/6/2 2013/6/2 2013/6/2
Condition  Before the cleaning  After the FC cleaning  After drag wiping
Input Power [mW]  39.8  38.4  38.4
REFLPD dark offset [V]  -0.0080  -0.0080  -0.0080
REFLPD locked [V]  0.048  0.0437  0.046
REFLPD unlocked [V]  6.41  6.39 6.37
       
 Transmitted Power to DCPD1 (T) [mW]  18.8  18.8  18.8
 Transmitted Power to DCPD2 (R) [mW]  18.1  18.2  18.2
 FM2 transmission [mW]  -  -  -
 CM1 transmission [mW]  0.200  0.193  0.198
 CM2 transmission [mW]  0.204  0.204  0.205
 Input BS transmission [mW]  0.260  0.228  0.245
       
 Cavity Finesse 396.9  403.79  403.79
       
 Junk Light Power (Pjunk) [mW]  0.303  0.302  0.317
 Coupled beam power (Pcouple) [mW]  39.50  38.10  38.08
 Mode Matching (Pcouple/Pin) [mW]  0.992  0.992  0.992
 Cavity reflectivity in power  0.00112  0.000211  0.000206
 Loss per mirror [ppm]  111  35.9  34.8
 Cavity transmission for TEM00 carrier
 0.934  0.971  0.972

 

- TMS/FSR/Finesse change before/after cleaning [ELOG Entry]
  Just a small change from the parameters before the bake.
  No quantitative difference.

  Method:
  BB EOM produces the AM sidebands together with the PM sidebands.
  Ideally, the PM sidebands does not produce the signal at the transmission, the output is dominated by the AM component.
  This is only true when there is no lock offset. In reality the curve is contaminated by the PM-AM conversion by the
  static offset or dynamic deviation of the locking point. So I had to take the central part of the TF and check the
  dependence of the fit region and the finesse.

  Before the cleaning: Finesse 396.9
  After the cleaning: Finesse 403.8


To Do

- Placement of the DCPD housings
- Through-put test with DCPDs
- Transmission dependence on the incident power
  (although the max incident is limited to ~35mW)

- Application of the first contact for the surface protection

  151   Fri Aug 16 15:31:17 2013 KojiOpticsConfigurationMirror list for OMC(002)

OMC(002)

Cavity Mirrors

FM1 (input coupler): A9
FM2 (output coupler): A13
CM1 (curved mirror close to FM1): C9 (PZT ASSY #6 /  M6 /PZT21/C9)
CM2 (curved mirror close to FM2): C4 (PZT ASSY #4 / M11/PZT25/C4)

DCPD path

BS3 (BS for DCPDs): B10

QPD path

BS1 (input steering): E3
SM1 (steering mirror next to BS1): E5
BS2 (BS for QPD path): B9
SM2 (steering mirror next to BS2): E1
SM3 (steering mirror next to SM2): E2

OMC_breadboard_mirror_config.png

 

 

  156   Thu Aug 22 15:40:15 2013 KojiElectronicsConfigurationPZT endurance test

[Koji, Jeff]

Background

In response to the failure of one of the PZTs on L1OMC (LLO:8366), we have been taking place an endurance test of
the four PZT sub-assemblies in prior to their being glued on the glass breadboard.

According to the technical note by Noliac, the common mode of PZT failure is degradation of the impedance
due to cyclic actuation (like 10^7 times) with over voltage. Therefore our procedure of the test to actuate the PZTs
at least 10^7 times with half voltage of the nominal operating voltage (i.e. nominal 200V) and check the degradation
of the impedance.

Driving signal

For the driving of the PZT, a thorlabs HV amp is used. A source signal of 3.5Vpp with an offset of 1.7V is produced
by DS345 function generator. This signal turns to a sinusoidal signal between 0 and 100V in conjunction with the gain
of 15 at the HV amp.

The maximum driving frequency is determined by the current supply limit of the HV amp (60mA). The capacitance
of each PZT is 0.47uF. If we decide to cycle the signal for 4 PZTs in parallel, the maximum frequency achievable
without inducing voltage drop is 100Hz. This yields the test period of 28hours in order to achive 10^7 cycles.

P8214340.jpg

Initial impedance diagnosis

To check the initial state of the PZTs, a DC voltage of 100V was applied via 1kOhm output resistance.
(Note that this output resistance is used only for the impedance test.)
For each PZTs, both side of the resister showed 99.1V for all measurement by a digital multimeter.
Assuming the minimum resolution (0.1V) of the multimeter, the resistance of each PZT was more than 1MOhm before
the cycling test.

Failure detection

In order to detect any impedance drop of the PZTs, the driving signal is monitored on the oscilloscope via a 1:10 probe.
If there is any significant impedance drop, the driver can't provide the driving current correctly. This can be found
by the deviation of the driving voltage from the reference trace on the oscilloscope (below).

P8214337.jpg

Temperature rise

Because of the loss angle of the PZT capacitance, heating of the PZTs is expected. In order to check the temperature rise,
an IR Viewer (FLIR) was used. We did not take care of careful calibration for the PZT emissibity as what we want was a
rough estimation of the temperature.

Before the driving (LEFT) and at the equilibrium (RIGHT)
IR_0457.jpg
IR_0461.jpg

The temperature change of the PZT was tracked for an hour (below). Fitting of the points indicated that the temperature rise is 2.3degC and the
time constant of 446 sec. This level of temperature rise is totally OK. (Note that the fitting function was T = 27.55 - 2.31 Exp[-t/446.])

 

Results

DAY1:

Start driving
20:27 25.2 degC, status OK
20:33 26.7 degC, status OK
20:41 26.9 degC, status OK
20:48 27.6 degC, status OK
20:54 27.4 degC, status OK
21:10 27.4 degC, status OK
21:37 status OK
Stop driving

70 minutes of driving (i.e. 4.2x10^5 cycles) => no sign of degradation

DAY2:

Start driving
14:15, 24.5 degC, status OK
14:17, 26.0 degC, status OK
14:24, 27.0 degC, status OK
14:40, 26.8 degC, status OK
14:50, 26.8 degC, status OK
15:30, 26.8 degC, status OK
15:55 status OK
17:40 status OK
21:00 status OK (2.43Mcycles + 0.42Mcycles = 2.85Mcycles)
1d+12:00 status OK (7.83Mcycles + 0.42Mcycles = 8.25Mcycles)
1d+15:00 status OK (8.91Mcycles + 0.42Mcycles = 9.33Mcycles)
1d+18:40 status OK (10.23Mcycles + 0.42Mcycles = 10.65Mcycles)
Stop Driving

After 10.65Mcycles no sign of degradationwas found.

  157   Fri Aug 23 19:24:32 2013 KojiElectronicsConfigurationPZT endurance test (II)

The PZT tests were finished with the conclusion that the PZT won't be damaged with our expected usage.


This is another test of the PZTs to make sure small (~10V) reverse voltage does not break the PZTs.

Background

At the site, we decided to use one of the PZT, which is still alive, for the HV and LV actuation.
The HV actuation is limited to 0 to 100V while the LV actuation is 10Vdc with 1Vpp fast dithering.
This means that a reverse voltage upto 10.5V will be applied to the PZT at the worst case.

From the technical note this level of reverse voltage does not induce polarization of the PZT.
The test is to ensure the PZT is not damaged or degraded by this small reverse voltage.

Method

HV drive: Thorlabs HV amp (G=15) driven with DS345 function generator (3.5Vpp+1.7Vdc, 0.1Hz)
=> 0-100V @0.1Hz
=> The hot side of the potential is connected to the positive side of the PZT

LV drive: Phillips function generator (1Vpp+9.5Vdc@1kHz)
The driving frequency is limited by the current output of the function generator.
=> The hot side of the potential is connected to the negative side of the PZT

These drives shares the common ground.

Tests

Testing with spare PZTs 

Started @19:23 (Aug 23)
Stopped @20:15+2d (Aug 25, duration 48h52m)
17600cycles for the 0.1Hz drive.
176Mcycles for the 1kHz drive.

Checked the impedances of PZT1 and PZT2.

Apply 100Vdc via a 1kOhm resister, 0V detected across the 1kOhm resister
This is equivalent to the resistance of 1MOhm.

 

Testing with the PZT subassemblies

Started shaking of the four PZT assemblies @20:20 (Aug 25)
No impedance change observed @11:10+1d
No impedance change observed @15:30+1d
Stopped shaking of the four PZT assemblies @XXXX (Aug 26)

 

Wiring for the test

PZT_shaking.png

 

 

  261   Fri Jun 10 17:12:57 2016 KojiGeneralConfigurationL1 OMC DCPD replacement

New DCPD(T) = A1-23
DCPD(T) = DCPDB: extracted and accomodated in CAGE-G SLOT1

New DCPD(R) = A1-25
DCPD(R) = DCPDA: extracted and accomodated in CAGE-G SLOT2

  263   Fri Aug 12 14:58:17 2016 KojiGeneralConfigurationH1 OMC DCPD replacement

Preparation of 3rd OMC for the use in H1

New DCPD(T) = B1-01
DCPD(T) = DCPDA: extracted and accomodated in CAGE-A SLOT1

New DCPD(R) = B1-16
DCPD(R) = DCPDB: extracted and accomodated in CAGE-A SLOT2

  277   Tue May 16 19:05:18 2017 KojiOpticsConfigurationOMC SN002 fix - temporary optics

Working on the SN002 OMC fix. Checked the inventory. I think I am using C8 mirror as the new temporary CM1 and PZT24 as the new temporary CM2.

  278   Fri May 26 21:53:20 2017 KojiGeneralConfigurationTrans RF PD setup

Recent work

- DC output of the trans RF PD was connected to the BNC patch panel. => Now CH4 of the scope is monitoring this signal

- The RF sweep signal from the network analyzer is connected to the power combiner for the EOM drive via the SMA patch panel.

- The trans RF PD was aligned first to the leakage beam. It turned out that this signal is too weak. Then the PD was aligned to one of the main OMC transmission. For this purpose, the OMC DCPD (T) was removed from the OMC breadboard.

- It seems that there is a significant amount of RF AM from the EOM. I suspect it is associated with the residual S-pol and birefringence of the steering mirrors (45deg HR). But the HWP at the output of the Faraday is fixed on the Faraday body with a screw and cumbersome for fine adjustment. A PBS and an HWP are added right before the EOM. This made the fiber coupler slightly misaligned. I suppose this new setup still has S&P on the fiber too. Thus, readjustment of the fiber rotations at the input is necessary.

Next step

- Input power to the fiber should be determined before the EOM. Otherwise, touching the HWP before the EOM causes too much power change at the optics of the OMC side.

- Precise adjustment of the RFAM is still necessary.

- The OMC curved mirror should be held by the new fixture.

- Check the beam spots

- Measure cavity parameters. (transmission/FSR/HOM/etc)

==> Then the curved mirror and the PZT will be glued on the prism

  279   Tue Jun 6 00:49:48 2017 KojiGeneralConfigurationTrans RF PD setup

Last week, I further worked on the RF system to install 20dB coupler on the agilent unit and setup the R channel. This allowed me to make the FSR/TMS measurement of the OMC.

And today several optical improvement has been done.

- The input/output fiber couplers were adjusted to have the maximum transmission through the PBS right before the OMC.
- The HWP on the output side of the faraday was adjusted to have ~40mW input to the OMC.

Then, the OMC curved mirror is now held by the new in-situ gluing fixture instead of the conventional fixture attached upside down.
The OMC was ocked again and the input alignment was adjutsed. The fixture is blocking the QPD path, so it's not possible to confirm the proper alignment of the cavity (w.r.t. the QPD paths).

The precise positions of the spots could not be confirmed as the battery of the IR viewer was empty. Quick check of the spots by the card tells that the spot on the CM2 (PD side) is slightly too close to FM2 (output coupler). I wonder if this could be solved by rotating the curved mirror.

Otherwise everything look good. Let's try to glue the curved mirror tomorrow.

Note: Spot on CM2 is too close to the edge of the hole on the mounting prism. The meausrementof CM1 is telling that the curverture center is located 2.7mm upper side of the center of the mirror if the HR side arrow is up (and it is the case). If we move the arrow to the QPD path side (90deg CW viewed from the face side), this corresponds to ~1.1mrad CCW tilt in Yaw (viewed from the top of the prism). According to the matrix calculation (T1500060) this will induce ~1.5mm shift of the beam. This should be tried before gluing.

  280   Tue Jun 6 22:00:36 2017 KojiGeneralConfigurationTrans RF PD setup

- Replaced the PZT with the one used from the beginning. This must be PZT #21. After the replacement, the spot positions look very good. I even went up. So I decided this is the configuration to proceed to the gluing. The CM1 mirror has the HR arrow at the top.

- The input beam was realigned w.r.t. the OMC.

- Tried to use the IR viewer with the new rechargable battery brought from the 40m. But the view still didn't work. The possibility is a) the viewer is broken b) the battery is empty.

- Tried to use the stainless clean regulartor for the UHP N2. The outlet has a short tube with a different diameter. The O.D. of the old tube is 6.3mm, while the new one is 9.5mm. If I insert the thinner tube in the new tube, it approximately fits. But I don't believe this is the way...

  328   Thu Apr 11 12:15:31 2019 KojiMechanicsConfigurationPZT sub assy mirror orientations
Attachment 1: PZT_subassy.png
PZT_subassy.png
Attachment 2: PZT_subassy.pdf
PZT_subassy.pdf PZT_subassy.pdf PZT_subassy.pdf PZT_subassy.pdf
  338   Tue Apr 16 16:35:09 2019 KojiOpticsConfigurationOMC(004): Glass breadboard selection

D1200105 SN006 was selected as the breadboard for OMC(004).
The reason is the best parallelism among the 
unused ones.

The attached is the excerpt from T1500060 with the #006 highlighted.

Attachment 1: BB_selection.pdf
BB_selection.pdf
  339   Tue Apr 16 16:40:26 2019 KojiGeneralConfigurationOMC(004): A Mirror selection

We are going to use A5 and A14 for FM1 and FM2. (The role of these two can be swapped)

The reason for the selection is the better perpendicularity among the available prisms.

A11 has the best perpendicularity among them. However, the T didn't match with the others. The pair of A5 and A14 has a good matching with small compromise of the perpend.

The attachment is the excerpt from T1500060.

Attachment 1: A_Mirror_selection.pdf
A_Mirror_selection.pdf
  340   Tue Apr 16 16:52:36 2019 KojiOpticsConfigurationOMC(004): B Mirror selection

We are going to use B6 for the DCPD BS (BS2), and B1 for the QPD BS (BS3). Their role can not be swapped.

B6 has the best loss among the available ones, while the perpendicularity is not so critical due to the short arm.

B1 has the OK perpendicularity, while the loss is also moderately good.

The attachment is the excerpt from T1500060 with some highlighting.

Attachment 1: B_Mirror_selection.pdf
B_Mirror_selection.pdf
  341   Tue Apr 16 17:24:56 2019 KojiOpticsConfigurationOMC(004): E Mirror selection

We are going to use E6, E9, E11, and E14 for BS1, SM1, SM2, and SM3. They (and E18) are all very similar.

The attachment is the excerpt from T1500060 with some highlighting

Attachment 1: E_Mirror_selection.pdf
E_Mirror_selection.pdf
  353   Tue Apr 23 10:21:12 2019 JoeOpticsConfigurationMoving the spots to the centre of the curved mirrors

[Koji,Philip, Liyuan, Joe]

CM1:

We moved the curved mirrors to these positions:

inner = 0.807mm

outer = 0.983 mm

CM2:

inner = 0.92 mm

outer = 0.85 mm

To do this so that realignment was easier, we moved the screws in steps of 5um. We alternated which mirror we adjusted so that we could monitor with a wincam how well aligned the beam into the cavity was. We only moved the cavity mirrors a small amount so we could still see higher order mode flashes transmitted through the cavity (e.g.TM03 modes). We would then improve the input alignment, and then move the cavity mirrors some more. Once the mirrors were adjusted according to http://nodus.ligo.caltech.edu:8080/OMC_Lab/190422_195450/misalignment4.pdf the spot positions looked near the middle of the curved mirrors (using a beam card). We began beam walking but we ran  out of range of the bottom periscope screws in the yaw dof. We tried using the third screw to move the mirrror in both yaw and pitch, hopefully this will let move the mirror such that we can use the just the yaw screw. This screw also ran out of range, so we decided that the cavity needed a small adjustment.

The curved mirrors were moved slightly (>5um) and then we tried to get alignment. By using the fibre coupler translation stage, we move the beam side ways slightly, and then tried to get the periscope mirrors back to a position where the screws could move the mirrors. Once we had an ok alignment, we checked the beam. It looked like it was pretty close to the centre of the curved mirrors, which is where we wanted it to be.

We then tried locking the cavity, although the error signal was quite small. The adjusted the input offset and gain of the servo (there is apparently some problem to do with the input and output offsets). Once the cavity was locked we could make the final adjustments to aligning. We still ran out of range on the periscope. We decided to move the breadboard with the fibre coupler and mode matching lenses on it. Because we knew that the cavity was aligned such that the beam hits the centres of the curved mirrors, we could regain flashes quite quickly. We saw the error signal go down, but eventually this decrease was just to do with the beam clipping on the periscope mirrors. We moved the spot back to where we ok aligned, and slid the periscope so we were not clipping the mirror. This worked very well, and then optimised the alignment.

We then tried to improve the mode matching. 

We took photos of the spot positions (quite near the center) and made the detuned locking measurement. The fitting of the data (attachment 1) wsa 1.1318m (what error should we put here?).

I think the order we did things in was:

  • turning anti clockwise on the fibre coupler and misalign the diode, we measured the modespacing.
  • returned the alignment for the photodiode, and realign fibre couple.
  • miss align the photodiode horizontally, and then used fibre coupler to maximise the peak higher order mode peak height. We then used the PD again to make the peak height bigger.
  •  
Attachment 1: FSR_detuned_locking.pdf
FSR_detuned_locking.pdf
Attachment 2: CM1_IMG_7702.JPG
CM1_IMG_7702.JPG
Attachment 3: CM2_IMG_7704.JPG
CM2_IMG_7704.JPG
  363   Mon May 20 19:53:17 2019 KojiOpticsConfigurationDCPD high power test

We want to perform a damage test of OMC DCPDs with high power beam. The OMC DCPD is the 3mm InGaAs photodiodes with high quantum efficiency, delivered by Laser Components.
The sites want to know the allowed input power during the OMC scan for beam mode analysis. The nominal bias voltage of the PDs is +12V. Therefore, 30mA of photocurrent with the transimpedance of 400 Ohm is already enough to saturate the circuit. This means that the test is intended to check the damage of the photodiode mainly by the optical power.

The test procedure is as follows:

1. Illuminate the diode with certain optical power.
2. Measure the dark current and dark noise of the PD with no light on it.
3. Check the condition of the PD surface with a digital camera.
4. Repeat 1~3 with larger optical power.

The beam from an NPRO laser is delivered to the photodiode. The maximum power available is 300~400mW. The beam shape was regulated to have the beam radius of ~500um.

- When the PD is exposed to the high power beam, the circuit setup A) is used. This setup is intended to mimic the bias and transimpedance configuration used in the DCPD amp at the site.

- When the dark noise is measured, the circuit setup B) is used. This setup is low noise enough to measure the dark noise (and current) of the PD.

- The test procedure is going to be tested with an Excelitas 3mm InGaAs PD (C30665), and then tested with the high QE PD.

Attachment 1: BIAS.pdf
BIAS.pdf
Attachment 2: P_20190520_204822.jpg
P_20190520_204822.jpg
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