LIGO Document P1400149-v1

[Thesis] Design, Implementation and Characterization of the Advanced LIGO 200 W Laser System

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Observations of the universe will be conducted with the Advanced LIGO grav- itational wave detectors starting early 2015. These detectors reach an unprece- dented sensitivity aiming for the first direct detection of gravitational waves.
Advanced LIGO employs a new high power laser system. The development and implementation of the high power laser together with a filter cavity called Pre-Modecleaner, the power- and frequency stabilization systems is described in this thesis.
Three Advanced LIGO laser systems were characterized over the course of three years at output power levels of 17 W and 180 W. The laser systems operate reliably and at their design performance level. For spatial and temporal filtering of the high power laser beam a bow tie shaped Pre-Modecleaner was designed, tested and extensively characterized.
Furthermore, the implementation of the in vacuum sensor for the power sta- bilization is discussed. The performance of the power stabilization is simulated and the simulations are compared to the measured results. A quantum noise limited performance over a wide frequency band from 30 Hz to 500 Hz was achieved at a relative power noise level of 3.5 10−8/√Hz.
The existing frequency stabilization scheme from a prior LIGO configuration was adapted for Advanced LIGO and the effects impressed by the high power oscillator, which amplifies the output power up to 200 W, are evaluated. The high bandwidth feedback control loop which employs a rigid cavity as fre- quency reference is characterized and a frequency noise measurement is ob- tained with the Advanced LIGO Input-Modecleaner, a suspended in vacuum resonator with a round trip length of 32 m.
A high power test in order to study thermal effects in the Input-Modecleaner is conducted with input power levels up to 120 W.
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