Ultra-stable laser based on cryogenic silicon Fabry-Perot cavity

This thesis consists in developing a frequency stabilized laser on a Fabry-Perot cavity at very low temperature. Indeed, the optical cavity is designed in silicon material and cooled down to a temperature around 18,1 K. Working at this temperature where the thermal expansion coefficient of silicon is low, and the reduction of the mechanical constraints acting on the cavity, give the possibility of reaching stabilized laser performances below 1×10⁻¹⁶ on short times, to answer the needs of optical clocks. The system consists of a 1,5 µm fiber laser whose frequency is controlled by the resonance mode frequency of the optical cavity. The cavity is 14 cm long and a dielectric coating has been deposited on the mirror substrate. A low vibration pulsed tube cryogenerator is used to cool down the cavity to the desired temperature. In this work, the researchers have also implemented an active system to suppress the residual amplitude modulation, which is one of the main limitations of the ultra-stable laser performances. Finally, the theoretical limit evaluated in terms of fractional frequency stability is given as 3×10⁻¹⁷ at 1 s, corresponding to the cavity thermal noise.

Ultra-stable laser, optical Fabry-Perot cavity, frequency locking, cryogenic temperature

Full document (FR) : TEL-03851524