Study Of Vibration Sensitivity Of Optical Cavities Used For Stable And Narrow-linewidth Laser System

Stable and narrow-linewidth lasers are essential in the development of optical clocks that will serve as future optical frequency standards. Furthermore, they have important applications in many other fields such as high-precision laser spectroscopy and fundamental physics tests. To achieve superior stability, a free-running laser is usually servo-locked to the resonance of an optical cavity. Therefore, the remaining instability of the locked laser is a combination of the instability of the length of the frequency reference itself and the defects of the servo-locking system. It is shown that environmental vibrations and temperature fluctuations are the dominant factures which degrade the stability of the optical length of the cavity and limit the laser linewidth into Hertz or sub-Hertz level.In this paper, a detailed numerical analysis of optical cavities is performed for state-of-the-art laser stabilization. Elastic deformation due to vibrations of the cavities with different shapes and mounting methods is quantitatively analyzed using finite element analysis. We show that with modified cavity geometry and suitable mounting schemes it is feasible to minimize the susceptibility of the optical length to vibrational perturbations.For linear cavities, simulation results of the optical length to vibrations are obtained by removing material form the underside of a cylindrical cavity and a rectangular one for the purpose of deformation compensation. A sensitivity of vertical vibrations of 25 kHz/ms^-2 is achieved. By vertically supporting a tapered cavity at its midplane, we find that the deformation is still asymmetrical to the supporting surface even when the structure is symmetrical to it. After delicately adjusting the weight distribution to compensate the vertical deformation, the vibrational sensitivity is reduced to zero. Ring cavities which have the characteristic of avoiding optical feedback effects are proposed to serve as the frequency references in the PDH laser stabilization system for the first time. A series of research and analysis of vibration sensitivity of a ring cavity is given. By adjusting the position of supporting beams, we show that the optical path can remain unchanged at a certain supporting position for each beam width, which means that ring cavities can also obtain low vibration sensitivities as linear cavities. The results discussed here offer experimental parameters that can be adjusted to achieve vibration immune conditions and provide theoretical support for the experiments.By comparing the test result of the stable and narrow-linewidth laser system with a modified tapered cavity as its frequency reference to the theoretical result, validity of this research is then verified.