PSL Overview
The purpose of the PSL is to deliver very stable laser light to the interferometer.
This means that it takes the already stable light from the NPRO and further stabilizes it using an Intensity Stabilization Servo (ISS) and a Frequency Stabilization Servo (FSS).
Above the bandwidth of these servos, the Pre Mode Cleaner (PMC) passively filters the fluctuations of the light.
At the end of the PSL table, the beam goes up through a periscope and into the vacuum system, and then goes into the suspended Mode_Cleaner.