The FSS stabilizes the fluctuations in the laser frequency by comparing it to a quiet Reference Cavity. The light is picked off just before it goes into the Pre Mode Cleaner, sent through a EOM and the frequency shifting AOM and then into the RC.

The FSS actuates on the NPRO Piezo (called the FAST path) and on a phase correcting Pockels cell (which is faster than the FAST path).

To lock:

Run the FSSAutolock script from the C1PSL_FSS screen (under the yellow ! button).

The FSS has a /SLOW PID servo which offloads the FAST (PZT) path by feeding back to the NPRO's SLOW input. The FAST has a rough calibration of 5 MHz/V while the SLOW is more like 5000 MHz/V. It has a ~0.1 Hz pole and so that's why its called SLOW.

List of FSS Related Electronics Schematics

• TT FSS Box (by Schwinberg, Myers, and Savage, based on the Rich Abbott original)
• TT ISS Box (by Flavio Nocera w/ lots of prodding from Rana)

• [http://www.ligo.caltech.edu/docs/D/D980401-B1.pdf VCO Driver Box] (R. Abbott)

• FSS RFPD (old LSC kind by Dale Ouimette)
• Variac on the HEPA (D. Busby's handiwork)

See also PSL.

attachment:C1PSL_FSS.png

References

• [http://www.ligo.caltech.edu/docs/P/P960008-10.pdf P960008-10]: Improved Multistage Wide Band Laser Frequency Stabilization, by Seiji Kawamura, Alex Abramovici, Mike Zucker (1996).