GW related research activities in Hannover UNI/AEI High power Laser development/ Laser stabilization Diffractive optics Alternative IFO layouts (multiple mirror cavities in the IFO arms) Thermal noise experiments LISA

Nd:YVO4 - Virgo Laser (20W) End Pumped Rods Nd:YAG - GEO600 Laser (14W) Nd:YVO4 - Virgo Laser (20W) Laser Zentrum Hannover

Injection Locked Oscillators - Hannover f 2f QR HR@1064 HT@808 YAG / Nd:YAG / YAG 3x 7x40x7 FI EOM NPRO 20 W Master BP High Power Slave modemaching optics YAG / Nd:YAG 3x2x6 output key elements: undoped bonded end-caps birefringence compensation pumplight homogenization

high power stage status Feb 2004 linear polarized with birefringence compensation Not injection locked yet

Grating development Two different options: Phase grating on substrate overcoated with a HR layer stack > Low eff. gratings Phase grating atop of a HR layer stack > Highly eff. gratings

Grating research summary Low efficiency grating can substitute transparent BS phase relations for gratings understood Losses of 1st test grating < 400ppm Will further investigate theoretically and experimentally new IFO topologies Investigate influence of grating on test mass Q produce gratings on silicon test masses and measure performance increase size of gratings Test low efficiency low angle coupler

Alternative IFO topologies Photodetektor Spiegel 11 Spiegel 21 Strahlteiler Spiegel 12 Spiegel 22 Spiegel 13 Spiegel 23 Spiegel 24 Spiegel 14 EOM 2 EOM 1 EOM 3

Thermally adaptive optics Correction of ROC of a GEO600 mirror Investigations of compensation of thermal lensing in the BS at high light powers Variation of the reflectivity of the signal recycling mirror Status

Avoiding astigmatism with a segmented heater 2 heatin elements for vertical ROC 2 heating elements control horizontal ROC Heater with separately controlled heating elements allows inhomogeneous bending of the mirror.

Controlling the SR bandwidth Bandwidth  Finesse of the SR cavity  Reflektivity of MSR Temp. controlled Signalrecycling-Etalon (r=150mm, d=75mm) Reflektivity is controlled by temperature

Test set-up suspended SR-Etalon in Vacuum set-up thermal environment identical to GEO600 Rediation shield: Galvanized copper, 0.4 µm Gold

Adjustable SR-gain (Garching prototype) Nach Re-Lock identische SR-Verstärkung

Squeezed Light Table top experiment for squeezed light generation and characterization @ GW frequencies Applications for GW detectors Application of Kerr media for GW detectors

LISA activities Laser frequency stabilization Optical layout for LISA pathfinder mission