Abstract
Modulated differential wavefront sensing (MDWS) is an alignment control scheme in the regime of beams with strong higher order transversal modes (HOMs). It is based on the differential wavefront sensing (DWS) technique. MDWS represents a significant upgrade over conventional techniques used in the presence of high HOM content as it allows for higher control bandwidths while eliminating the need of auxiliary alignment modulations, that otherwise cause loss of applied squeezing. The output port of gravitational wave (GW) interferometers (IFO) is one such place where a lot of HOMs are present. These are filtered out by a cavity called the output mode cleaner (OMC), whose alignment gets challenging due to the presence of HOMs. In this paper, we present the first demonstration of the MDWS scheme for aligning the fundamental mode from the IFO to the OMC at the gravitational wave detector-GEO 600.
Highlights
GEO 600 is a Dual Recycled Michelson Interferometer (DRMI) [1], which operates with a small dark fringe offset (DFO), which allows a certain amount of carrier light to leave the interferometer (IFO) at the output port (Figure 1)
We demonstrated the proof of principle test for Modulated differential wavefront sensing (MDWS) and obtained control bandwidth of up to
To ensure that the actuation stays well decoupled a gain hierarchy is maintained such that BDO1 loops mainly compensate for the misalignment while BDO3 acts on residual misalignment
Summary
GEO 600 is a Dual Recycled Michelson Interferometer (DRMI) [1], which operates with a small dark fringe offset (DFO), which allows a certain amount of carrier light to leave the interferometer (IFO) at the output port (Figure 1). The process of dithering introduces additional jitter of the beam incident on the OMC, which has been shown to cause a 0.2 dB loss in squeezing at the 5.5 dB level [3,9] To get around these limitations, we have tested a new scheme called Modulated Differential Wavefront Sensing (MDWS), which allows for a higher control bandwidth and eliminates the need for dithering. It was first proposed and a preliminary demonstration was shown in [10]
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