Interferometric measurements often require an extraordinary high power stability of the light source. The crucial part of power stabilization experiments is the sensing of the power fluctuations. AEI physicists were able to achieve the world-wide best power stability of a laser which is equivalent to the shot noise of 200 mA of photocurrent [Kwee et al. Opt. Lett. (2009)].
In an novel power noise measurement scheme called optical AC coupling they were able to measure power fluctuations equivalent to the shot noise of a photocurrent of 32 A [Kwee et al. Opt. Lett. (2011)]. Experiments in this area continue to transfer the high sensing accuracy to a high power stability.
A small table-top experiment is used to test and optimize the length and alignment control of two cavities used in a particle-physics experiment called ALPS in collaboration with DESY Hamburg. The main challenge of this experiment is, to stabilize an optical resonator to an imaginary gaussian beam without using any light with the same properties as this fictive beam.