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Reports until 18:02, Monday 01 December 2025
H1 ISC
jenne.driggers@LIGO.ORG - posted 18:02, Monday 01 December 2025 (88298)
Locking success after Yend DAC swaps

[RyanS, Oli, Jenne, Jeff]

Locking went well, and we're currently at NomLowNoise (no squeezing though).  We're good to go for swapping the Xend DACs tomorrow.  

SRC1 during DRMI ASC seems to pull things away at the last little bit rather than converging, so we've been turning it off by hand.  If it's still being problematic when we next try to lock (tomorrow? or Wed?), then we should set it to False in the DRMI guardian. 

We also turned SRC1 off in full ASC during our first lock attempt, since it seemed to be wandering off.  But, we lost lock in MOVE_SPOTS, probably because we weren't by-hand making the SRM follow along (since the beam diverters were closed so we didn't really have anything to track with).  Second lock I left SRC1 on in full ASC, and things went fine and we got all the way to NLN.

The squeezer guardian is stuck in LOCK_OPO.  I tried once setting the SQZ_MANAGER to DOWN and again to FREQ_DEP_SQZ, but it's still not happy.  Since this is not what we were trying to test today (we were just seeing if the Yend DAC swaps worked), I'm just leaving the SQZ_MANAGER in DOWN.

We did, at Jeff's suggestion, have the VIOLIN_DAMPING guardian paused, since we didn't want to do bad things to violin modes if there was a big phase change with the new DAC.  However Daniel estimates that we should see about a 10 degree phase shift at 1kHz, and a much smaller shift at 500 Hz, so I've just unpaused that guardian and the modes seem to be damping fine. 

I am leaving the IFO locked, but requested ISC_LOCK to DOWN, so that if it does lose lock, it won't try to re-lock.  This, and the lack of squeezing, means that I am not setting the Observing bit.

H1 SUS
jenne.driggers@LIGO.ORG - posted 17:46, Monday 01 December 2025 (88297)
Maybe seeing fuzziness in ETMY oplevs

[Jenne, Oli]

I'm intermittently, while we're locking, seeing some fuzziness on the ETMY oplev (first 2 attachments, with 'fuzzy'). Oli did a brief check, and while they find a different behavior that is present 4 days ago and today (3rd and 4th attachments, with 'drop'), at least a quick glance isn't finding the fuzziness that I'm seeing. We haven't looked at enough past data to say whether this is new, but it doesn't seem to be hindering our ability to lock, so I think we're fine to go forward with ETMX tomorrow.

Images attached to this report
X1 DTS
joshua.freed@LIGO.ORG - posted 17:16, Monday 01 December 2025 (88293)
SPI Pathfinder, Phase noise measurements for Keysight 33600A waveform generator

J. Freed,

I took Phase noise measurements of the 2 channel Keysight 33600A waveform generator for its use in building SPI Pathfinder in the optics lab before install. Going only off of the phase noise graphs, it is sufficient as it shows comparable results to the SRS which had a phase noise considered to be good enough for SPI pathfinder.

Key.png Shows the phase noise results. C1, C2 are the phase noise results for Channel 1 and Channel 2 on the Keysight, respectively. (Set up shown below). Shown for comparison the SRS SG392, which was suggested as a possible frequency source for SPI. The last measurement shown is the direct measurement of phase noise between the 2 channels of the Keysight. This measurement reflects the intended use case of the Keysight for SPI. As we need 2 frequencies at slightly different frequencies locked to each other and SPI will be measuring the output phase difference. Note the 60Hz peak; most likely caused by unclean AC power. This is why we are not using an AC powered device in the final installation. 

Screenshot2025-12-01at50150 PM.png Shows the setup for C1, and C2. measurements. The SRS value was found with the same set up, just replacing the Keysight 33600A with a SRS. The C1-C2 is a direct measurement by plugging both channels into the BluePhase 1000. There is no 10MHz Ext back attachment in this measurment in order to best represent Keysight's theoretical performance in the optics lab.


 

Images attached to this report
LHO General
ryan.short@LIGO.ORG - posted 17:08, Monday 01 December 2025 (88294)
Ops Day Shift Summary

TITLE: 12/02 Day Shift: 1530-0030 UTC (0730-1630 PST), all times posted in UTC
STATE of H1: Planned Engineering
INCOMING OPERATOR: None
SHIFT SUMMARY: Busy day upgrading DAC cards at EY. After suspensions were recovered, we wanted to relock the IFO to ensure the new DACs haven't introduced a problem, so I started an initial alignment. Unsurprisingly, ETMY and TMSY needed quite a bit of adjustment, but otherwise alignment went smoothly. Locking the IFO presented a couple of issues; after DRMI locked, I needed to turn of the SRC1_P loop as it appeared to be pulling alignment away. I turned this off again during ENGAGE_ASC_FOR_FULL_IFO as it appeared to be misbehaving for the second time. Eventually H1 lost lock during MOVE_SPOTS, but we're unsure as of yet what the cause was. H1 is attempting to lock again under the supervision of a few folks still here in the control room.
LOG:

Start Time System Name Location Lazer_Haz Task Time End
15:46 FAC Eric FCES N Checking air handler 16:19
16:12 FAC Nellie MY N Technical cleaning 17:01
16:16 FAC Kim MX N Technical cleaning 16:56
16:27 CDS Fil EY N AI chassis modifications 20:50
16:46 FAC Tyler, McD Miller FCES N Air handler fix 19:19
17:01 FAC Kim H2 N Technical cleaning 17:12
17:12 FAC Nellie Opt Lab N Technical cleaning 17:29
17:52 CDS Daniel CR N Beckhoff updates 19:19
17:52 SEI Jim Remote N Testing on HAM6 ISI 19:52
18:20 ISC Kar Meng Opt Lab Local OPO work 19:18
18:52 PEM Rene, Alicia CER N Moving magnetometer 19:02
20:21 CDS Dave EY N DAC card replacement susey 20:50
20:25 TCS RyanC MER N TCS chiller checks 20:32
20:36 AOS Betsy Opt Lab N Rearranging parts 21:28
20:44 JAC Jennie LVEA/Prep Lab N Grabbing parts then JAC table work 21:42
21:12 CAL Tony PCal Lab N Measurement setup 21:19
21:13 ISC Kar Meng Opt Lab N Looking for electronics 21:28
22:05 ISC Jennie LVEA/Prep Lab N JAC table work, maybe getting more parts 22:33
22:32 FAC Tyler Hi-bay N Loading scissor lift into hi-bay 23:30
00:47 PEM Rene, Alicia CER N Moving magnetometer 00:54
H1 CDS
david.barker@LIGO.ORG - posted 16:46, Monday 01 December 2025 - last comment - 16:56, Monday 01 December 2025(88292)
h1susey upgrade to LIGO-DACs

Richard, Jonathan, Fil, Marc, Daniel, EJ, Jeff, Oli, Ryan S, Dave:

h1susey was upgraded from Gen Std DACs (3x18bit, 2x20bit) to 2 LIGO-DACs.

Fil upgraded the three AI chassis to use the new SCSI interface board.

We removed the old Gen Std DACs and installed the two new LIGO-DACs.

The first LIGO-DAC drives the first standard AI, which in turn daisy-chain drives the second standard AI.

The second LIGO-DAC drives the special PI AI chassis.

After the hardware was changed the new h1iopsusey, h1susetmy, h1sustmsy and h1susetmypi models were rev-lock built and installed. A common model change for h1susetmy was accepted for its build.

EJ did a custom build for h1iopsusey due to rev-update issues found for watchdog source files. The user models were built with the production RCG-5.5.2

Following the model starts, the DAQ was restarted for new INI files due to removed DACs in h1iopsusey and h1susetmy.

Comments related to this report
jonathan.hanks@LIGO.ORG - 16:56, Monday 01 December 2025 (88295)

With the daqd restarts we made a few changes.

  • This is the first restart with the daqd0 leg re-configured
    • Updated the restart scripts for the 0 leg to restart fw0 first and then the rest (tw0, nds0, gds0)
    • Updated the pause between starting fw0 and starting the other systems as the fw takes longer to start up.
  • Removed a old compatibility flag from the daqdrc on fw0 and fw1.
    • Removed the "USE_BROKEN_CONFIGURATION_NUMBER_HASH" line.  This is only needed for compatibility with older daqds and can be turned off if it is turned off on all daqd fw systems at the same time.  This deals with how the configuration hash is created, this hash value represents the channel list.  The hash is then sent to the run number server to get the configuration/run number to put in the frame.
  • Removed 8 channels from the GDS broadcaster list.
    • H1:FEC-98_DAC_OVERFLOW_ACC_2_[0,1,2,3]

    • H1:FEC-98_DAC_OVERFLOW_ACC_3_[1,2,3,4]

We did two restart passes as h1susetmypi needed an updated to deal with DAC changes.

H1 SUS (CDS)
oli.patane@LIGO.ORG - posted 16:39, Monday 01 December 2025 (88289)
Added/Updated DAC calibration filters in COILOUTF for TMSY and ETMY for new DACs

Jeff, Oli

Since the ETMY and TMSY electronics are now on 32CH, 28-bit DACs, we needed to add a calibration term that would account for the difference in bit count between the old and new DACs. The normal thing to do for these DAC upgrades is to add a gain in the COILOUTF filter banks that was gain(2^(NewBitCount-OGBitCount)). For example, during the conversion of ETMY L1/L2/L3 from their original 18-bit DACs to 20-bit DACs, the calibration was altered by the addition of a filter in their respective COILOUTF banks that was gain(4), since 2^(20-18) = 4.

This time, we needed the change in gain to be between the new bit count, 28, and the original bit count, 18, so gain(2^(28-18)) = gain(2^10)=gain(1024). These filters were added into the FM10 slot of ETMY_{M0,R0,L1,L2,L3}_COILOUTF and TMSY_M1_COILOUTF. In the case of ETMY L1/L2/L3, these gains overwrite the previous 20bitDAC filters since we don't need those anymore.

The other place where we needed to add these conversion filters was for ETMY PI, and even back in May 2025 Jeff had noticed that we had never added in any compensation for the 18-20-bit DAC upgrade (84522). To finally follow through on fixing that we added filter banks into the PI model (88285), which for ETMY PI are called H1:SUS-ETMY_PI_UPCONV_ESDOUTF_LF and H1:SUS-ETMY_PI_UPCONV_ESDOUTF_RT, and I added filters into FM10 for each that had that same gain(1024) in them. I also added these new filter banks to the PI medm screen (screenshot).

All these filters were loaded in, turned on, and accepted as on in safe sdf. We slowly turned everything back on, and it all looks to be working correctly.

Images attached to this report
LHO VE
david.barker@LIGO.ORG - posted 16:14, Monday 01 December 2025 (88290)
Mon CP1 Fill

Mon Dec 01 10:08:07 2025 INFO: Fill completed in 8min 3secs

 

Images attached to this report
H1 SUS
jeffrey.kissel@LIGO.ORG - posted 16:04, Monday 01 December 2025 (88288)
h1susey DAC Upgrade: SUS Recovery Complete
J. Kissel, O. Patane,

After 
- Adding/updating DAC calibration compensation gains
- Updating MEDM macros in order to confirm that DAC drive requests made it all the way out to the analog world on the right channels
- Pausing guardians to make sure they didn't take control when we didn't want them to yet,
- Making sure that all DAC requests were OFF
- Untripping watchdogs and turning ON the MASTER SWITCH
- Turning on small offsets to confirm those channel pathways were straight and linear,
- Turning damping loops, one DOF at a time to confirm function and that they had roughly the right ~few second ring-down time
- Turning on the alignment offsets to confirm that the whole suspensions move
- Restoring all nominal ability for ISC output requests by resuming the guardian and running it from SAFE to ALIGNED a time or two,
- Initiallizing new channels in SDF
- Accepting differences in SDF (almost entirely the turning ON of calibration gains for the stages that were 18-bit DACs)

We turned control over to the operations team with the words "all EY suspensions are confirmed functional and ready to use" at Dec 01 2025 ~15:45 PST (after having started at ~08:30 PST this morning; LHO:88274).
H1 SUS (ISC)
jenne.driggers@LIGO.ORG - posted 16:02, Monday 01 December 2025 (88287)
PI guardian's gain reduced in guardian by 4x, to account for SUS work today

[JeffK, Jenne]

Jeff pointed out that the PI damping gain (if no changes were made to guardian) would now be 4x higher than they were throughout O4, due to the work done today.  See alog 88285 for the actual work by Jeff and Oli.  To account for this, the SUS_PI guardian now has a 1/4 in the gain setting line.

Details for remembering later:

In June 2020, we upgraded from 18-bit to 20-bit DACs, and as Jeff notes in alog 88285, we didn't have a place to nicely account for the effective gain change digitally in the PI damping path.  Effectively, we should have put in a filter with gain of 4x to account for the number of bits changed.  Since we didn't, we have been actuating PIs (assuming same digital gains) 4x less during O4 than we had been in O3.  Not a huge deal, since we had PI dampers and PI damping settings that were effective. 

With today's work, Jeff and Oli have put in a digital place to correctly account for the gain change with the new 28-bit DACs.  To keep the 'accounting' neat and tidy, they've put in the whole correction gain from 18-bit to 28-bit (not just 20-bit to 28-bit).  This means that they've put in the forgotten-during-O4 gain of 4x, so if things were left alone in the SUS_PI guardian, we'd be sending 4x actuation strength to the ETMs.  In O4, the 4 PI modes we've been damping have only gone to the ETMs.  Since we don't have automatic gain adjustment in the PI damping guardian, I've divided the gain setting line by 4 in SUS_PI, so that we'll end up with the same actuation strength now as we did have in O4. 

H1 SUS (CDS, ISC, SUS)
jeffrey.kissel@LIGO.ORG - posted 15:02, Monday 01 December 2025 - last comment - 16:42, Monday 01 December 2025(88285)
h1susey DAC Upgrade: Added ESDOUTF_LF and _RT filter banks susetmpi models' library part; h1susetmypi model now has it
J. Kissel, O. Patane
ECRs: E2400409 and E2500296
IIET: 35739 and 35706, respectively
WP: 12901
DWG: D1002741

Oli was working their way through adjusting the SUS "OUTF" FM10 blocks that are traditionally used to adjust the calibration of the DACs being used, and we re-realized that we've never had a place in the PI model to adjust the DAC gain thru the upgrades from 18- to 20-, and now 28-bit DACs -- see the original discovery back in May 2025 (LHO:84522, which quotes that ETMY's PI DAC had been misalibrated by a factor of 4x since Jun 2020).

In that May 2025 aLOG, I "mildly advocated" for an implementation of ESDOUTF banks like there is in every other SUS drive chain. 
Today, I implemented that change, since (a) the gain difference between a 18-bit and 28-bit DAC is now a factor of 2^10 = 1024x -- much more noticeable, and (b) it's a total no brainer change that's easy to do while we're already restarting this model for the DAC upgrade proper.

The update to the library, 
    /opt/rtcds/userapps/release/sus/common/models
        PI_MASTER_V2.mdl          r26600 --> r34033
is within the ETM_UPCONV_V2 block, which I show in the attached BEFORE vs AFTER.

We have compiled, installed, and restarted h1susetmypi front-end model so that it has this minor change.
Oli will aLOG the installation of the gains.
Images attached to this report
Comments related to this report
oli.patane@LIGO.ORG - 16:42, Monday 01 December 2025 (88291)

Gain install alog: 88289

H1 SUS (CDS, ISC)
jeffrey.kissel@LIGO.ORG - posted 14:22, Monday 01 December 2025 (88283)
SVN up'd ESD_LINEARIZATION_WITH_CHARGE Library Part; Inconsequential Change
J. Kissel, D. Barker

As an inadvertent result of us using the new "rev lock" RCG feature during the build of front-end model h1susetmy, we discovered that there was a newer revision of the sub-sub library part used within the QUAD_MASTER library part -- 
    /opt/rtcds/userapps/release/sus/common/models/
        ESD_LINEARIZATION_WITH_CHARGE_MASTER.mdl : r16336 --> r30316
where the latter text shows the userapps svn repo version that the h1susetmy model was last compiled with, and what it will be compiled with if we use latest rev of the model (r34028, see LHO:88282).

The ESD_LINEARIZATION_WITH_CHARGE_MASTER.mdl is *actually* a library, i.e. it contains a library of library parts that can be used for linearization.
One is the ESD_LIN_CHARGE_MASTER, and the other is ESD_LINE_CHARGE_GENERIC_MASTER.

We're 100.0% confident that the h1susetmy, which uses QUAD_MASTER, uses the ESD_LIN_CHARGE_MASTER block, that's poorly commissioned and has its settings configured to not use it.
We're 98.5% that r16336 --> r30316 update to the library is the creation and commissioning of the other ESD_LINE_CHARGE_GENERIC_MASTER block, given Dec 2024 LLO aLOGs like LHO:74555 and 74771. The 1.5% lack of confidence is only that it's challenging to follow LLO's QUAD front-end model's references to libraries.

Anyways -- this is just to say explicitly that we're going forward with using this r30316 version of the library, but it won't change any function or form of the h1susetmy model.
Images attached to this report
H1 SUS (CDS, ISC, SUS)
jeffrey.kissel@LIGO.ORG - posted 13:55, Monday 01 December 2025 - last comment - 14:12, Monday 01 December 2025(88280)
h1susey DAC Upgrade: SUS ETM / TMS Simulink Model Prep for 28-bit 32CH DACs
D. Barker, J. Kissel, O. Patane
ECRs: E2400409 and E2500296
IIET: 35739 and 35706, respectively
WP: 12901
DWG: D1002741

Following the solidifying of the wiring plan / IO chassis layout (see LHO:88276), Dave did the lion's share of updating the front-end USER models in prep to the 28-bit 32CH upgrade. I merely reviewed it to make sure we understood all the moving pieces and that the connections to the analog world made sense, and am documenting it here.

Recall -- although the wiring diagram -v11 had shown all 20-bit DACs, in order to best reflect the 2022 ideal as of 
    - TST stage :: ECR E1800306 / IIET: 11689,
    - PUM stage :: ECR E1900216 / IIET: 13232
    - Everything else :: ECR E2100485 / IIET:20828, 
but H1 had not yet achieved that ideal, as we instead put our money toward developing and waiting for the 28-bit 32CH DACs. As such, in the "BEFORE" shots, you'll see the reality of the mix of 18-bit and 20-bit DACs. In short, the QUAD TOP (M0 and R0) and TMTS TOP (M1) had not yet been upgrade to 20-bit DACs. So those stages now "skip a version" and go straight to 28-bit 32CH DACs (D2200368).

Attached are screen-shots of the DAC section of the user models BEFORE vs. AFTER:
    - h1susetmy BEFORE vs. AFTER
    - h1sustmsy BEFORE vs. AFTER
    - h1susetmypi BEFORE vs. AFTER

I also include a view of the 28-bit 32CH DAC card usage from each model that uses it; a view which better shows the consumption of channels by function across USER models.
    - DAC0 AFTER
    - DAC1 AFTER

This view helps identify some index / naming convention issues with DAC1 (see DAC1 usage screenshot). This DAC controls *only* the TST stage ESD, but spans the h1susetmy and h1susetmypi USER models. In both the susetmy and susetmypi models, the card_num parameter is set to 1 (one). HOWEVER, because the h1susetmy model uses both of the new two DACs (card_num=0 and card_num=1), the card_num=1's block name is DAC_1. In h1susetmypi which only uses the second card (card_num=1 ), it's block name is DAC_0. 
It's confusing when you look at it like this, and the RCG (current) forces it to be this way because of IO chassis which have mixed DAC card types (unlike ADCs, which the RCG will happily accept cherry pick ). The solution will be as it has been -- update the MEDM macro files that support the user interface, such that we get the UI showing the signal flow through the USER model output and IOP model output without folks having to think about it.

 
Images attached to this report
Comments related to this report
jeffrey.kissel@LIGO.ORG - 14:12, Monday 01 December 2025 (88282)
Here's the svn rev numbers for the versions I screenshot above
    /opt/rtcds/userapps/release/sus/h1/models/
        h1susetmy.mdl       r34028
        h1susetmypi.mdl     r34029
        h1sustmsy.mdl       r34030
H1 OpsInfo
jennifer.wright@LIGO.ORG - posted 13:54, Monday 01 December 2025 (88281)
Moved pump cart and bench near HAM 6

I need access to the two ISC/SQZ cheats of drawers that sit past HAM6 to get spare optomechanics to populate the in-air optics table for JAC.

There is a lot of stuff against this wall so I had to move a pump cart and table to get access to them. Checked with operator + Travis before doing this.

Let me know if I need to shuffle anything around.

Images attached to this report
H1 TCS
ryan.crouch@LIGO.ORG - posted 12:35, Monday 01 December 2025 (88279)
TCS Chiller Water Level Top-Off - Biweekly

Closes FAMIS27829, last checked in alog88104.

For TCSX I added 100mL to bring it from 30.3 to 30.4.

For TCSY I added 80mL to bring it from 10.3 to 10.4.

The dixie cup was empty.

H1 CDS
david.barker@LIGO.ORG - posted 08:52, Monday 01 December 2025 - last comment - 15:52, Monday 01 December 2025(88274)
h1susey down for LIGO-DAC upgrade

WP12901 LIGO-DAC upgrade

Daniel, Fil, Marc, Jonathan, Richard, EJ, Ryan S, TJ, Jeff, Oli, Dave:

h1susey was fenced and power down at 08:25 in preparation for its upgrade to LIGO-DACs. SWWD was bypassed on

Fil is at EY upgrading the AI chassis to accept the new SCSI links from the DACs.

Comments related to this report
filiberto.clara@LIGO.ORG - 14:31, Monday 01 December 2025 (88284)

The following AI Chassis were updated:

AI Chassis D1000305 S1108084 (SUSEY-C1, slot U32)
AI Chassis D1000305 S1108070 (SUSEY-C1, slot U31)
AI Chassis D1500177 S1500300 (SUSEY-C1, slot U26)

The rear panel and DAC AI Interface Board D1000551 were removed. A new D2400308 LIGO DAC Anti Image Chassis Rear Panel and LIGO DAC AI Interface D2500097 were installed.

jeffrey.kissel@LIGO.ORG - 15:52, Monday 01 December 2025 (88286)
"Yes, and..." to Fil's inventory and comments about what's changed within them --

AI Chassis D1000305 S1108084 (SUSEY-C1, slot U32) has now been transformed into a D2500353 AI chassis assembly
AI Chassis D1000305 S1108070 (SUSEY-C1, slot U31) has now been transformed into a D2500353 AI chassis assembly
AI Chassis D1500177 S1500300 (SUSEY-C1, slot U26) has now been transformed into a D2500400 AI chassis assembly
H1 ISC
jennifer.wright@LIGO.ORG - posted 10:58, Monday 27 October 2025 - last comment - 17:27, Monday 01 December 2025(87766)
Change of reflected power from OMC during DARM offset step

I made plots of anti-symmetric power P_AS vs. power at reflected port of OMC P_OMC_REFL during the DARM offset step measurement on September 4th, (see LHO alog #86785 and 87629).

I had to use the Beckhoff reported power for this (H1:OMC-REFL_A_DC_POWER) as the front-end channel is calibrated wrongly (see LHO alog #87648).

I also plotted the P_OMC_REFL vs.  P_DCPD, ie. reflected vs. transmitted power for the OMC.

The plots for our two measurements taken at different times during IFO thermalisation are below, both were taken when OM2 was hot.

Non-image files attached to this report
Comments related to this report
jennifer.wright@LIGO.ORG - 15:25, Wednesday 26 November 2025 (88259)

I reran these plots as the axis limits of the P_REFL vs. P_DCPD plot were wrong and were cutting off end point, plus removed line that explained what the y-intercept was for each plot as different dependent on whether we plot P_REFL vs P_AS or P_REFL vs. P_DCPD.

I also switched the P_REFL channel being used in my code to H1:OMC-REFL_A_DC_POWER from H1:OMC-REFL_A_DC_POWERMON as this latter channel has a factor of 100 relative to the former that I don't really undestand. The DC_POWER channel seems to give a realistic reading for the OMC reflected power that is much less than the power into HAM6.

First link contains two plots when we were half-way thermalised:

First plot is power at the OMC reflected PD vs. power at the antisymmetric port (calibrated into the power into HAM6) for the case where we were 1Hr 25 mins into lock.

Second plot is power at the OMC reflected PD vs. power transmitted to the DCPDs for the case where we were 1Hr 25 mins into lock.

 

The second link contains two plots also when we were thermalised:

First plot is power at the OMC reflected PD vs. power at the antisymmetric port (calibrated into the power into HAM6) for the case where we were 3 hrs 59 mins into lock.

Second plot is power at the OMC reflected PD vs. power transmitted to the DCPDs for the case where we were 2 hrs 59 mins into lock.

Non-image files attached to this comment
jennifer.wright@LIGO.ORG - 17:13, Wednesday 26 November 2025 (88262)

We can write down an equation for P_REFL from the OMC in terms of P_DCPD, using our linear fit.

P_REFL = ( c*P_DCPD + d ) mW

We know the nominal setting for P_DCPD is 40mA, and we can take the responsivity of the DCPDs at 100 % efficiency to be 

responsivity = e * lambda / (c * h)

From the squeezer budget (E2400269) we can get a number for the Q.E. of the PD that also includes OMC losses for the transmitted beam, transmissivity = 0.937

Therefore the power at the DCPDs at nominal DARM offset is 40mA/(responsivity*transmissivity) = 49.7 mW.

The reflectivity of the OMC breadboard is 2.75e-4 as calculated from parameters given in T1500060-v3.

The formula for the power measured at the reflected port of the OMC can also be expressed as:

P_REFL = R_cav [ P_00_arm + P_00_cd] + P_HOM_arm + P_sb + P_HOM_cd

where P_00_arm is the power in the fundamental carrier mode which changes with DARM offset, P_00_cd is the contrast defect light that is in the fundamental carrier mode, P_HOM_arm is light at higher order mode frequencies which also change with DARM offset, P_sb is power in the sidebands, P_HOM_cd is contrast defect light at higher order mode frequencies.

Whereas the formula for the power transmitted by the OMC can be described as:

P_DCPD = T_cav [ P_00_arm + P_00_cd]

As we assume that all HOM and sidebands are reflected by the OMC.

The mode-matching, MM, of the OMC to the differential arm mode is defined as:

P_00_arm / ( P_HOM_arm + P_00_arm )

This can be calculated using:

P_00_arm = (P_DCPD - d)/T_cav

P_HOM_arm = P_REFL - d - (R_cav*P_00_arm)

If we do this calculation for the half-way thermalised measurement we get 

MM = 0.9975

For the fully thermalised case we get:

MM = 0.9978

The code to calculate this is in: Calculate_refl_power.py located at /ligo/home/jennifer.wright/git/2025/DARM_OFFSET/

 

jennifer.wright@LIGO.ORG - 17:27, Monday 01 December 2025 (88296)

Correction to above calculation where I made a mistake in how to calculate P_00_arm:

The mode-matching, MM, of the OMC to the differential arm mode is defined as:

P_00_arm / ( P_HOM_arm + P_00_arm )

The power from higher order modes of the carrier from the differential arm motion can be calculated using:

P_HOM_arm = P_REFL - d - (R_cav*P_00_arm)

In order to calculate P_00_arm we need to use the measurement of contrast defect which can be obtained from our Sep 4th DARM offset measurements by running

python /ligo/gicommon/labutils/darm_offset_step/plot_darm_optical_gain_vs_dcpd_sum.py

on the offset step data we took on Sep 4th (see LHO alog #86744). This code plots the P_AS vs. P_DCPD graphs I mentioned in that alog, but also works our how the optical gain changes from the PCAL line height changes in DARM as the offset is changed. The plot of P_DCPD vs. optical gain has a minimum where the optical gain is zero and the power level here is considered the contrast defect (P_00_cd * T_cav) in our notation.

The contrast defect for the 255 Hz line is 1.202 mW for the partially thermalised interferometer and 1.268 mW for the fully thermalised interferometer.

Then we can obtain the power in the carrier from differential arm motion as:

P_00_arm = (P_DCPD - contrast defect)/T_cav

If we do this calculation for the half-way thermalised measurement we get 

MM = 0.9978

For the fully thermalised case we get:

MM = 0.9981

The code to calculate this: Calculate_refl_power.py located at /ligo/home/jennifer.wright/git/2025/DARM_OFFSET/ has been updated.

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