aLIGO LHO Logbook

H1 SQZ (SQZ)

sheila.dwyer@LIGO.ORG - posted 10:37, Wednesday 15 July 2026 - last comment - 14:40, Tuesday 28 July 2026(91043)

lens distances in HAM7

Rahul, Sheila

We measured distances in HAM7 on the VIP. For optic names see D2000021 (A:L2 and A:L3 are actually one lens, we will call it A:L2)

A:M3 to A:DC2: = 61mm
D:DC2 to A:L2 = 35+-2mm
A:DC2 to SFI1 wedge= 215mm
A:L2 to SFI1 wedge:
SFI1 wedge to A:P1 = 257mm
SFI1 wedge to B:M1= 389mm
B:M1 to B:M2= 221mm
BM1 to B:L1= 87+-3 mm
B:L1 to B:M2: skip
B:M2 to B:P1 = 57mm (+-1mm)
B:P1 to SFI2 wedge: 277+-2mm
SF2 wedge to B:M3: 57mm
B:M3 to B:L2= 96 +-2mm
B:M3 to B:BS1 = 207mm
B:BS1 to B:M4:97+-2mm
A:P1 to A:L1: 66+-2mm
A:P1 to A:M2= 87mm
A:M2 to A:M1: 41mm
A:M1 to A:DC1 = 67mm
A:DC1 to edge of OPO box:63mm

Comments related to this report

sheila.dwyer@LIGO.ORG - 14:40, Tuesday 28 July 2026 (91289)

Link

Drawing showing where OPO M1 is relative to the edge of the box: D1500296 (71.949 mm-24.104 mm)/cos (12 degrees) = 48.9mm

Summarizing these measurements above in terms of the distances needed in the finesse file:

length_OPOM1_to_L1: 220e-3 #48.9+63+67+41+(87-66) #was 0.2404

L1_F: 222e-3 # [m] PlanoConvex 100mm RoC

length_L1_AFI1: 0.066 #was 0.0675 # (AFI1 must mean A:P1, not A:F1 as I first assumed)

length_AFI1_L2: 0.437 #257+(215-35) #was 0.428

L2_F: 222e-3 # [m] PlanoConvex 100mm RoC

length_L2_M3: 0.068 #(35+61 mm)

BL1_F: 764e-3 # [m] 350mm RoC

BL2_F: 1112e-3 # [m] 500mm RoC

length_AFI1_BL1: 0.219 # (I am thinking that AFI1 is actaully A:P1, (389-257)+87

length_BL1_BL2: .621 # (221-87)+57+277+57+96 was 0.6625

length_BL2_M4: 0.208 #207-96+97 was 0.131

The main change needed in the finesse file is for the location of L2, which is because this lens was designed to be 2 lenses.

I'm also dividing the alpha value in the finesse file for ZM1-6 by 2. I think that these are supposed to be AOI, but as Camilla and Eric have realized they must be angles between incoming and outgoing beams instead.

These changes are committed to the ligo-commissoning modeling lho_O4 yml file here