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Q: Fachverband Quantenoptik und Photonik

Q 30: Poster Präzisionsmessungen und Metrologie

Q 30.7: Poster

Dienstag, 11. März 2008, 16:30–19:00, Poster C2

Thermal noise limit of the Fabry-Perot cavities used for laser stabilisation at sub-Hz level — •Janis Alnis, Nikolay Kolachevsky, Arthur Matveev, Thomas Udem, and Theodor Hansch — Max Planck Institute of Quantum Optics, 85748 Garching, Germany

Precision optical spectroscopy experiments require lasers with extremely narrow spectral line widths that can be achieved by stabilising the laser to a high-finesse Fabry-Perot (FP) cavity. We have developed two independent external-cavity diode laser systems at 972 nm with 0.5 Hz spectral line width that is limited by the thermal noise properties of the FP cavity spacer and mirrors [1]. The thermal noise limit is reached thanks to a mid-plane mounting of the cavities making them insensitive to ambient vibrations. The line drift is always smaller than 0.5 Hz/s as the cavities are made from Ultra-Low-Expansion (ULE) glass possessing a zero expansion temperature. Our new design with Peltier coolers in vacuum allows us to keep any ULE FP cavity at this particularly advantageous temperature.

With this narrow laser source after amplification and frequency quadrupling to 243 nm we excite the 1S-2S two-photon transition in atomic hydrogen [2]. The diode laser has an unusually long (20 cm) resonator that significantly reduces the high-frequency noise typical to diode lasers and allows efficient doubling of the narrow optical carrier.

References

1. J. Alnis et al., in preparation for Appl. Phys. B.

2. N. Kolachevsky et al., Phys. Rev. A 73, 021801(R) (2006).