[Camille, Thejas]
16 August 2023

We reconvened in the afternoon to begin realignment of the beam path through the mode-matching lenses. Before doing so, we placed two iris to mark our current beam path to the OMC. (one iris after the steering mirror, one iris right in front of the OMC (picture attached))
We made a few slights adjustments to the fiber coupler and the lenses: We used a level to adjust the height of the second lens so that it is at the same height as the first lens. We slightly adjusted the height of the fiber coupler mount so that the fiber height matches the height of the center of the lenses. We translated the fiber coupler slighly to adjust the centering while maintaining the same distance from the first lens.
After centering the path through the lenses, we repositioned the periscope mount and the steering mirror accordingly so that the beam path hits the centers of these mirrors.

Tomorrow, we will lock the cavity and repeat power measurements to determine if there is any improvement to the mode-matching.

[Camille, Thejas]
18 August 2023

We continued the work started on https://nodus.ligo.caltech.edu:8081/OMC_Lab/609. The beam is well-centered through the mode-matching lenses. We used the periscope to optimize cavity alignment while locked on the TEM00 mode.

We checked the steering on the REFL PD and the TRANS PD to make sure both are aligned.
The REFL PD signal was 3.0V (unlocked) and 46mV (locked). (This is the lowest REFL power we have had with this cavity.) A picture of the REFL CCD is attached.

We also checked the intensity of the HOMs on the mode spectrum (pictures attached). The TEM00 signal was ~7.2V while the observed HOMs had a signal of 23mV and 2 mV.

We proceeded to take 2 sets of power budget measurements (measurements and screenshot attached). After running the measurements in the power analysis script, we have and OMC throughput of ~99% and mode-matching efficiency of 98%. This seems to agree better with our mode-spectrum. (The excel spreadsheet with the analysis is attached as Attachment 5.)

This is WOW!

Excellent mode matching work.

The measurement is still consistent with the low loss even with the different mode-matching level.

99.5%? The IFO commissioners will cry.

Edit: Wait a sec. The incident * mode matching = 20.14mW. This is the cavity-coupled power.
And you have the transmission of 9.78*2=19.56mW.
The ratio of these is ~97% and not 99.5%. Did I miss something?

=> Ah, understood. You have the incident power measurement with a significantly different reference voltage from the one at the transmission measurement. (4.21V vs 4.11V)
This is because the laser output power depends on the laser PZT feedback.
The quick hack to reduce this is that check the laser PZT feedback voltage (on the Thorlabs driver) right before the unlock, and bring the "output offset" close to that value after unlocking.
This brings the laser frequency back to the one during lock. At the same time, the laser freq is now close to the cavity resonance. So reading the unlocked REFL voltage, you need a bit of care.

Thanks for clarifying that. We will repeat some power measurements and check the output offset voltage to the laser.

You should proceed to the next steps. You'll need to repeat the power measurements before the bonding. Next time, the measurement procedure will be improved.

Thanks Koji, we did observe this discrepency and thought that the code normalizes the power/voltage readings to the reference power value. We will then proceed towards FSR and TMS measurements today.

[Camille, Thejas]
22 August 2023

We used the network analyzer to measure the FSR of the cavity using the method described in section 3.2.1 of T1500060. We locked the OMC cavity and maximized transmission the TEM00 mode. (REFL PD signal was ~45-50mV and REFL CCD looked the same as in 610). We adjusted to input offset on the servo module (REFL PD signal ~95mV) and recorded the transfer function between the modulation signal (channel R) and the transmission PD signal (channel A). (See attached picture of transfer function and phase.) We fit the FSR data to the code to get a value of 264.658982 MHz.

We also recorded the TMS of the cavity (with 0V to the PZTs). We measured the horizontal and vertical mode spacing separately. After maximizing transmission of TEM00, we then used the fiber coupler to misalign in the vertical direction first (REFL PD signal ~100). Using the network analyzer, we observed the peak at ~58 MHz. We then misaligned the mirror that steers the transmited beam to the PD. We clipped the transmitted beam so as to maximize the peak at ~58 MHz. (See attached spectrum.)
We recoved vertical alignment and then repeated this process for the horizontal direction. (See attached spectrum.)

Analysis in the next elog entry. 

File names:
test_22-08-2023_160812 --> FSR
test_22-08-2022_165728 --> TMS vertical
test_22-08-2022_170543 --> TMS horizontal
https://gla-my.sharepoint.com/personal/t_seetharamu_1_research_gla_ac_uk/_layouts/15/onedrive.aspx?id=%2Fpersonal%2Ft%5Fseetharamu%5F1%5Fresearch%5Fgla%5Fac%5Fuk%2FDocuments%2FA%2B%20OMC%20%231%2F22%5F08%5F2023&view=0

Attached are the analysis results from the measurements in 616.
FSR: 264.657354 +/- 0.003444 MHz

Pitch TMS: 58.45691858660249 MHz

Yaw TMS: 58.55821902092523 MHz

The attached plot shows the HOM spectrum with their sidebands. We see that there is overlap between TEM00 and one of the 9th-order modes which means this higher order mode will resonate with the TEM00 carrier.
We estimate that by increasing the FSR to ~266.7 MHz, we will avoid this as shown in the next attached plot (HOM_scan.pdf).
This will require us to decrease the cavity length by 16mm (4 mm each mirror). We plan begin adjusting the micrometers this afternoon.

[Camille, Thejas]

We checked the length-to-angle coupling of each PZT by monitoring the position of the transmitted beam on the CCD camera. The CCD camera was placed behind the steering mirror that guides the transmitted beam to the PD. We used a ThorLabs piezo controller to actuate the PZT.

We first tested PZT2. We increased the voltage to PZT2 in 50V increments from 0V to 150V. We did not observe any change in the position of the transmitted beam. We monitored the signal of the TRANS PD on the scope and did not see any change. (The signal was between 191-195V.) We monitored the REFL CCD and did see changes in the beamshape, which was expected (see pictures). The REFL PD signal also increased slightly with PZT actuation (see attachment).

We repeated this process for PZT1, which showed similar results (see attachment). We did not observe any movement in the position of the transmitted beam. Increasing PZT voltage shows increasing pitch misalignment in the REFL CCD and increasing REFL PD signal.

Examination into bonding template confimred the limitation of space available to change cavity length by at least 10 mm to improve the cavity HOM spectrum. Here's an anlysis of HOM spectrum for various possible ROCs and corresponding required cavity length change for optimum HOM spectrum. 

Assume: Astigmatism: Rx-Ry = 8mm

Current cavity length: 1.132 m

Ry = measured, Desired Cavity length: <1.12476 m

Ry = 2.5 m, Desired cav length: >1.13876 m

Ry = 2.55 m, “: No change 

Ry = 2.6 m, “:<1.12

So travel range of ~ (1.138 - 1.12) / 4 = 5 mm on each CM is required. WIth a safety factor for alignemnt say we require 30 mm/4 ~ 7 mm on each curved mirror.

I went in lab today and turned the HEPA filter (clsoe to the entrance) to high since we are not doing any measurements at the moment. 

New piezo actuated micrometers from thorlabs arrived last week. 

4 x MPIA10

1 x KPS201

1 x KIM101 

One of the micrometers' fucntioning was checked (SN..229). The micrometer was checked in jogging mode and velocity control mode using the software. 

Clean supplies & some cleaning tools are located at the right side of the entrance.
The file cabinet there was moved to the left side of the door, but will be removed eventually.

Ordered:

Office Depot
v AA battery Qty. 24
v 9V battery Qty. 4
v Floor cable cover (6ft)

Thorlabs
v HV PZT Driver
v Lenses

• BNC Patch Panel
  • 8x Amphenol Connex 112443 / Isolated BNC FEMALE TO FEMALE BULKHEAD ISOLATED ADAPTER - 50 ohm
    • http://www.newark.com/amphenol-rf/112443/bulkhead-adapter-bnc-jack-bnc/dp/99H4399
    • Hole Diameter: 13mm (0.512") D width 12.10mm (0.477")
  • 4x Amphenol RF 31-4803-75 (75Ohm)
    • http://www.newark.com/amphenol-rf/31-4803-75/bulkhead-adapter-bnc-jack-bnc/dp/50B8959
    • same as above
  • 2x Handle HAMMOND 98H1240
    • http://www.newark.com/hammond/1427b/equipment-handle/dp/98H1240
    • Hole Diameter: #4-40 (0.1120") Distance 1.25"
       
• SMA Patch Panel
  • 8x Isolated SMA-SMA adapter
    • https://www.pasternack.com/sma-female-sma-female-straight-adapter-pe9067-p.aspx
    • Hole Diameter: 0.312" D width 0.295"

== Office Depot ==
Really Useful Box 9L x 6 (delivered)
Really Useful Box 17L x 5 (ordered 4/4)
P-TOUCH tape (6mm, 9mm, 12mmx2, 18mm) (ordered 4/4)

== Digikey ==
9V AC Adapter (- inside, 1.3A) for P-TOUCH (ordered 4/4)
12V AC Adapter (+ inside, 1A) for Cameras (ordered 4/4)

== VWR ==
Mask KIMBERLY CLARK "KIMTECH Pure M3" ISO CLASS 3 (ordered 4/4)

Here is a summary of the events of the last week, as they relate to EP30-2.

1) I lost the EP30-2 syringes that had been ordered for the OMC, along with the rest of the kit.

• Corrective action: Found in the 40m Bake Lab garbing area.
• Preventative action: log material moves and locations in the OMC elog
• Preventative action: log EP30-2 moves and locations in PCS via location update [LINK]
• Preventative action: keep EP30-2 kit on home shelf in Modal Lab unless kit is in use

2) The EP30-2 syringes ordered for the OMC Unit 4 build from January had already expired, without me noticing.

• Corrective action: Requested LHO ship recently-purchased EP30-2 overnight
• Preventative action: log expiration dates in OMC elog
• Preventative action: begin purchasing program supported by logistics, where 1 syringe is maintained on hand and replaced as it expires

3) LHO shipped expired epoxy on Thursday. Package not opened until Monday.

• Corrective action: Requested LHO ship current EP30-2 overnight, this time with much greater scrutiny (including confirming label indicates not expired)
• Preventative action: Packages should be opened, inspected, and received in ICS or Techmart on day of receipt whenever possible.

4) Current, unopened syringe of EP30-2 has been received from LHO. Expiration date is 22 Jan 2020. Syringe storage has been improved. Kit has been docked at its home in Downs 303 (Modal Lab) (see attached photo, taken before receipt of new epoxy).

Current Status: Epoxy is ready for PZT + CM subassembly bonding on Monday afternoon 23 September.

The following items are presently staged at the 40m Bake Lab (see photo indicating current location) (noting items broght by Koji as well):

1. Bonding fixtures, now modified with larger washers to constrain springs, and with modification from OMC elog 358.
2. Curved Mirrors and Tombstones as selected by Shruti in OMC elog 374.
3. PZTs as debonded from first iteration subassemblies (SN 12 and SN 13)
4. Epoxy-cure-testing toaster oven
5. Other items I can't think of but will populate later  =D

The following item is in its home in Downs 303 (Modal Lab)

1. EP30-2 epoxy (expiration 2020 Jan 22) with full kit (tracked in PCS via location update [LINK])

The following is the current status of the epoxies used in assembly of the OMC (excerpt from C1900052)

Re-purchasing efforts are underway and/or complete

• DONE
  • Masterbond EP30-2 currently located in Downs 303, Modal Lab (see image)
    • ( WILL EXPIRE JANUARY 2020 )
    • ( tracked using THIS PCS LINK https://services.ligo-la.caltech.edu/Inventory/history.php?recid=1582&invtype=cit_noncap )
  • Electronic Materials Inc Optocast 3553-LV procured via PCard, will arrive today 22 October
    • plan to track using PCS is WIP
• WIP
  • Epoxy Pax EP-1730-1 quoted and requisitioned, PO is WIP

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.

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

Machined Parts:

• New fabrication = Contents of Storage-11112 are consistent with upgrade ECR.
• Old leftovers = Storage-9482 and Storage-9483 .

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.

Clean Supply Ordered

• TexWipe TX8410 AlphaSat Vectra Alpha 10 50 sheets x 12 pk  (VWR TWTX8410)
• Mask KIMTECH PURE® M3 Pleat-Style Face Masks 50 masks x 10 pk (VWR 15628-213)
• Stainless Pan x3 (VWR 10193-562)
• Ansell Accutech Latex Gloves 6.5 25*8pk (Fisher 19162026)
• Ansell Accutech Latex Gloves 7.0 25*8pk (Fisher 19162027)