aLIGO LHO Logbook

H1 AOS

koji.arai@LIGO.ORG - posted 19:54, Tuesday 14 November 2017 (39436)

Repeated isolation measurement of the OFI in the optics lab

[Gerardo, Koji]

The isolation measurement of the OFI was repeated today to confirm the stability of the optical isolation performance. For the confirmation, we have used the usual photodiode technique, as well as the power meter. Also we made the dry run of the in-situ isolation test setup [LHO ALOG 39357]. All the measurements showed the consistent isolation better than 40dB. We are going to install the OFI optical table to HAM5 tomorrow.

Methods

PD measurement - Input beamed chopped at 342Hz. Used two large area Si PDs (PDA100). One is the reference, the other is the measurement. Take transfer functions between those as a measurement.
Power meter measurement - Set a Thorlabs S140C (integrating sphere PD) at the reflection port. Measure the reflected power with direct reflection, back reflection through OFI (isolation), the transmitted beam dumped with a glass beamdump (backscatter), the input beam dumped with the beamdump (dark offset).
In-situ measurement - Inject a 1mm (in rad) beam from the output port. Measure the input power and leakage power with the Thorlabs S140C.
Ophir power meter (PD stick type) was not able to sense the weak leakage from the OFI.
Thermometer: Fluke mini thermometer (missed to check the P/N: similar to Fluke 62 Mini)

Results

	LHO OFI 2017/11/13 After the adjustment [LHO ALOG 39418]	LHO OFI 2017/11/14 PD measurement	LHO OFI 2017/11/14 Power meter measurement	LHO OFI 2017/11/14 In-situ measurement
Temperature of the faraday rotator body	N/A	N/A	73degF = 22.8degC	76degF = 24.4degC
Transmission From the input port to the output port	0.967 +/- 0.002 (3.3% loss)	---	---	---
Back-scatter isolation S-pol From the input port to the squeezer port	1300 +/- 10 ppm	---	---	---
TFP AR reflection From the input port to the squeezer port	890 +/- 10 ppm	---	---	---
Isolation From the output port to the input port	52 +/- 13 ppm ( = 43 +/- 1 dB isolation)	48.4 +/- 0.7 ppm ( = 43.15 +/- 0.05 dB isolation)	42 +/- 2 ppm ( = 43.7 +/- 0.3 dB isolation)	34.5 +/- 0.4 ppm ( = 44.6 +/- 0.5 dB isolation)
Back-scattering From the input port to the input port	3.0 +/- 0.5 ppm	0.5 +/- 0.2 ppm	2 +/- 3 ppm	---
Squeezer transmission From the squeezer port to the input port	0.978 +/- 0.002 (2.2% loss)	---	---	---