©LZH ZA GEO 600 Laser System as in the optics lab of Callinstraße 38 at LIGO-G D

©LZH ZA New Features of GEO 600 Slave Laser Resonator spacer and base plate made of Invar (FeNi36 / ) –low thermal expansion   8x10 -7 / K (average 20-50°C) (thermal change of optical path length in air at const. pressure   - 9x10 -7 / K) Diode laser power monitor

©LZH ZA GEO 600 Slave Laser

©LZH ZA GEO 600 Slave Laser

©LZH ZA GEO 600 Slave Laser

©LZH ZA “Long Term” Stability Maximum power after two mirrors and an adjustable attenuator consisting of a polarizer a half wave plate and a 2nd polarizer. Laser left untouched, attenuator varied for different purposes 2 % / 1.5 % pump power drop observed over full 21 day period

©LZH ZA “Long Term” stability II (20 h preliminary) All other acquired data stable to measurement resolution –room temperature: 1 K –pump power: 0.2 % –output power : 1%

©LZH ZA Slave Intensity Noise Suppression

©LZH ZA Slave Intensity Noise Suppression Transfer of Pump Current Modulation to Amplitude Modulation

©LZH ZA Slave Intensity Noise Suppression Full Open Loop Transferfunction of AM Servo (preliminary setup)

©LZH ZA Slave Intensity Noise Suppression First Results (of preliminary setup)

©LZH ZA Power Scaling of End Pumped Nd:YAG

©LZH ZA Power Scaling of End Pumped Nd:YVO 4 Advantages of Nd:YVO 4 1) amplifies 1064 nm emission of Nd:YAG (? at what temperature difference ?) birerefingence n a = 1.96 / n c = 2.17  no depolarization emission  || = 25x cm -2   = 7x cm -2  polarized emission large product of  ||  sp (  sp  90  s)  loss insensitive high gain lasers 8 nm broad 808 nm  low requirements on pump diodes Disadvantage of Nd:YVO 4 1) low pump intensity damage threshold 58 W / mm 0.5 % doping 29 W / mm 1.0 % doping increased by 50 % by undoped endcaps 1) Data from Y.-F. Chen, IEEE J. Q. E. 35(2), 234 (1999) / Tsunekane et. al. Elt. Lett. 32(1), 41 (1996) / VLOC, Casix, Castech web pages

©LZH ZA Problems of the slave Atmospheric pressure changes –  p  dl/(l dp)  2.8x10 -7 / hPa –50 hPa and 0.5 m  7  m Mirrors on single long range piezos tilt –  10  rad /  m Long range piezos have large low frequency resonances

©LZH ZA Possible Solutions Sophisticated piezo mount pre tension / damping / thick mirrors multiple piezos Thermal length actuator 30 mm Al/FeNi36  0.5  m / K pessimistic assumption:  f  10 6 Hz / Hz 1/2, f x-over  0.01 Hz  piezo:  l RMS  10 nm Hermetically airproof resonator constant density of air  nearly constant optical path length expansion dependent on spacer material only  Suprainvar / Zerodur / ULE