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Lasers with very stable properties (in frequency and amplitude) and high output power in continuous operation are required for the detection of gravitational waves. Suitable advanced laser technology is developed and permanently improved at AEI (Teilinstitut Hannover) in close collaboration with the LaserZentrum Hannover (LHZ). The monolithic Nd:YAG ring laser which is used at the GEO600 GW detector for example is subject to constant improvement.
AEI has also provided, delivered and installed the Enhanced LIGO 34W lasers both at the Hanford and Livingston observatory sites in 2008. The lasers have shown extremely stable and reliable operations since then. AEI will also provide the Advanced LIGO 200W pre-stabilized laser systems and will be carrying subsystem responsibility for these systems.
Both the preliminary design phase and the final design review are successfully completed now. A new pre-modecleaner design was developed to fulfill the new most stringent radio frequency power noise filtering requirement. First test results for the complete laser system indicate that all requirements are met, where the most stringent of these was the one on relative intensity noise RIN to be smaller than 2.10-9/?Hz at 10Hz. This corresponds to a shot noise limited sensitivity for 200 mA of photo current. We achieved this with a multi-photodiode detector, holding the current world record in this area.
Pointing into the future towards 3rd generation gravitational wave observatories and beyond, we also now hold another world record in power sensing in the frequency range 10MHz to 20MHz with a sensitivity of 7.10-10/?Hz, equivalent to a shot noise limited sensitivity for 700 mA of photocurrent. This was made possible by the development of a novel AC coupling measurement scheme that enables power measurements without destroying the carrier light. We have shown by theoretical analysis that optical AC coupling shows a fundamentally lower quantum shot noise limit than any conventional scheme.
Projects:
Frequency and amplitude stabilization, increase in output power, as well as efficient frequency doubling of diode lasers; development of lasers with pre-modecleaner design, AC coupling measurement scheme,non-linear Kerr-effect based sensors.
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