LIGO Document T0900096-v1

Tip-Tilt Mirror Specifications and Design

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T - Technical notes
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For the active beam steering, we need a vacuum-compatible mirror mount that has suitable range and bandwidth. Some vibration isolation is also desirable to reduce scattered-light path length noise. It is hard to know how much range is really needed, but probably at least a few milliradians. The bandwidth required for beam pointing stabilization is expected to be tens of hertz or less. On the other hand, we intend to generate alignment signals for the OMC via dither of the beam direction; this small-amplitude dither should be at as high a frequency as possible.

One option for the mount is a commercial PZT-based tip-tilt mirror, such as the type used in the iLIGO beam line readout system. However, these units have some disadvantages: their range is small (in order of a few milliradians); in our experience they are not very robust; they offer no vibration isolation. Given these downsides, we decided to develop our own mount instead. The design concept for these is something between the Newport Fast-Steering Mirror and the iLIGO small-optics suspension (SOS). The design, called a tip-tilt mount, has been developed and tested at ANU, and is being implemented on the eLIGO OMC beamline.

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