Stefan Hild 1Ilias WG1 meeting, June 2005 Title Beam clipping Problems in GEO 600 ?? Max-Planck-Institut für Gravitationsphysik (Albert-Einstein-Institut) Stefan Hild Ilias WG1 meeting, June 2005

Stefan Hild 2Ilias WG1 meeting, June 2005 Introduction After installation of new Power Recycling mirror less light power was observed than expected: Hypothesis: Mode matching into PR cavity is not too bad (?) Hypothesis: beam is clipping somewhere inside the cavity Expected (simulations)  4.5 kW Measured  1.5 kW

Stefan Hild 3Ilias WG1 meeting, June 2005 Simple model cavity Intracavity power [W] reflected power [W] Losses in cavity overcoupled undercoupled Simple model: 2 mirror cavity, 1.7 W incident, T 1 = 900ppm, T 2 represents losses Looking for intracavity losses of the order of 500 ppm reality expected

Stefan Hild 4Ilias WG1 meeting, June 2005 Power Recycling reaction mass CCD Clearly much light on the reaktion mass, but at least beam seems to be centered (in respect to the reaction mass) Main beam

Stefan Hild 5Ilias WG1 meeting, June 2005 Potential clipping spots in TCC MPR dark port east arm north arm

Stefan Hild 6Ilias WG1 meeting, June 2005 Power Recycled Michelson Used HeNe-Laser from endstadions to project the free aperture onto MPR reaction mass. Result: no clipping inside the power recycling cavity

Stefan Hild 7Ilias WG1 meeting, June 2005 Signal Recycling cavity We definitely see clipping between beamsplitter and MSR (see blue line) HeNe from far end locked DRMI Side note: there is also clipping on MSR reaction mass.

Stefan Hild 8Ilias WG1 meeting, June 2005 Smoking gun: BDBSs1 CCD Suspect the beam to clip the beam dump (blue arrows)

Stefan Hild 9Ilias WG1 meeting, June 2005 E n d

Stefan Hild 10Ilias WG1 meeting, June 2005 Misalignment of MSR

Stefan Hild 11Ilias WG1 meeting, June 2005 Dark port image

Stefan Hild 12Ilias WG1 meeting, June 2005 Strange beam MFE