Stefan Hild 1 Ilias WG1 meeting, June 2005

Title

Beam clipping Problemsin GEO 600 ??

Max-Planck-Institut für Gravitationsphysik(Albert-Einstein-Institut)

Stefan Hild Ilias WG1 meeting, June 2005

Stefan Hild 2 Ilias 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 kWMeasured 1.5 kW

Stefan Hild 3 Ilias WG1 meeting, June 2005

Simple model cavityIn

trac

avity

pow

er [

W]

refle

cted

pow

er [

W]

Losses in cavity

overcoupled undercoupled

Simple model: 2 mirror cavity, 1.7 W incident, T1 = 900ppm, T2 represents losses

Looking for intracavity losses of the order of 500 ppm

reality

expected

Stefan Hild 4 Ilias WG1 meeting, June 2005

Power Recycling reaction mass

CCD

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 5 Ilias WG1 meeting, June 2005

Potential clipping spots in TCC

MPR

dark port

east arm

north arm

Stefan Hild 6 Ilias 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 7 Ilias 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 8 Ilias WG1 meeting, June 2005

Smoking gun: BDBSs1

CC

D

Suspect the beam to clip the beam dump (blue arrows)

Stefan Hild 9 Ilias WG1 meeting, June 2005

E n d

Stefan Hild 10 Ilias WG1 meeting, June 2005

Misalignment of MSR

Stefan Hild 11 Ilias WG1 meeting, June 2005

Dark port image

Stefan Hild 12 Ilias WG1 meeting, June 2005

Strange beam pattern @ MFE