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Research group | Sub-Hz Lasers and High-Performance Cavities

Optical resonator made of mono-crystalline silicon. Photo: PTB Braunschweig
Model of the cryostat for the optical resonator. Image: PTB Braunschweig

The research project deals with the development of ultra-stable laser systems for applications in ultra-high resolution spectroscopy as well as metrology. For instance, the short-term stability of an optical clock is nowadays limited by the frequency instability of the laser probing the optical atomic transition, the “pendulum” of the atomic clock. To attain superior frequency stability the frequency of the laser is typically stabilized to a narrow resonance line of an optical cavity. The frequency instability of the laser is then determined by the stability of the reso- nator length itself. Changes in the cavity length might arise from seismic or acoustic noise as well as temperature fluctuations.

Currently the frequency stability of the best lasers is limited by thermal length fluctuations caused by the Brownian motion of the molecules in the resonator material. This so-called thermal noise can be suppressed by using crystalline structures of high mechanical quality instead of amorphous glass as a cavity material. To this end the research project is currently investigating mono-crystalline silicon as resonator material. At a temperature of -150 °Celsius the material should be insensitive against thermal length fluctuations. Therefore a vibration-free cooling mechanism is currently being developed. Additionally, the research project is investigating novel highly-reflective materials to reduce the thermal noise arising from the mirror coatings of the optical resonator.

Further Information is available on the project page at the PTB …