The Pre Mode Cleaner is triangular ring cavity mounted on a mostly monolithic fused silica spacer.

Its purpose is mainly to passively filter out laser noise above ~1 MHz. This is needed because none of our active servos do anything good at such high frequencies.

A secondary purpose is that it also spatially filters the light which comes out of the MOPA.

In reality, the PMC is mostly superfluous at the 40m. The raw laser noise falls off like 1/f^2 above the ~600 kHz relaxation oscillation of the NPRO and none of our demodulation frequencies are below 30 MHz. We would need to detect ~300 mA of photocurrent in order to be able to detect the NPRO's RFAM.

List of FSS Related Electronics Schematics

• PMC 35.5 MHz Frequency Reference Card (R. Abbott)
• PMC Servo (by Karwoski, based on the R. Abbott original - modified by Rana/Jenne based on the Hartmut mods)
• PMC RFPD (old LSC kind by Dale Ouimette)

attachment:premodecleaner.jpg

See Also

• [http://www.ligo.caltech.edu/docs/T/T010145-00.pdf PSL Commissioning Report]