## page was renamed from Frequency Stabilization Servo
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).

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 . To lock:    

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

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 . The FSS has a [[PSL/Frequency Stabilization Servo/SLOW PID servo|/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''.    

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== List of FSS Related Electronics Schematics ==
 * MC Servo: [[attachment:D040180-C-1 MC_Servo.pdf]]
 * [[http://www.ligo.caltech.edu/docs/D/D040105-A/D040105-A.pdf|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)
 * Temperature Control Box (Rich Abbott then changes by Hugh Radkins and Paul Schwinberg) [[https://dcc.ligo.org/cgi-bin/private/DocDB/ShowDocument?.submit=Number&docid=D980400&version=|D980400]]
 * Variac on the HEPA (D. Busby's handiwork)
 * TTFSS interface board diagrams: [[attachment:D040423-A.pdf]] (Rev A, includes the DIN96 connector), [[attachment:D040423-C.pdf]] (Rev C), [[attachment:fssxcon.pdf]] (old xcon schematics)

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 . '''Test Results for The New TTFSS'''   

 * [[https://dcc.ligo.org/cgi-bin/private/DocDB/ShowDocument?docid=20783|Test Plan]](Cervantes, Schwinberg, Savage)   

 * Test Results,  [[https://dcc.ligo.org/cgi-bin/private/DocDB/ShowDocument?docid=22509|box#05]] , [[https://dcc.ligo.org/cgi-bin/private/DocDB/ShowDocument?docid=22273|box#06]],[[https://dcc.ligo.org/cgi-bin/private/DocDB/ShowDocument?docid=22356|box#07]](Chalermsongsak, Arai)   

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 See also [[PSL]].

{{attachment:C1PSL_FSS.png}}

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== 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).