Development of a High Finesse Cavity for Portable Clock Applicationsa

Portable optical atomic clocks based on dipole-forbidden narrow linewidth optical transitions have shown significant promise for next-generation applications in positioning, navigation, and timing (PNT) domain. Such optical clocks are poised to revolutionize PNT applications in communication, deep space missions, VLBI (very long baseline interferometry), and geodetic measurements due to their exceptional frequency stability. Achieving this stability involves the use of narrow linewidth lasers, stabilized to ultra-stable high finesse optical cavities using the Pound-Drever-Hall (PDH) technique of laser frequency stabilization. Stability in frequency is directly determined by the stability in optical length of the high finesse cavity. However, the stability in optical length of these cavities is limited by fundamental thermal noise and external noise sources such as vibrations, temperature fluctuations, acoustic noise, etc. Finite Element Analysis (FEA) plays a pivotal role in optimizing cavity design by exploring various configurations, materials, and mounting strategies to minimize these instabilities. This article examines the influence of the fundamental thermal noise floor on stability, considering factors such as cavity length and mirror curvature. It also presents and discusses methodologies using FEA to identify the optimal mounting positions to minimize the acceleration sensitivity and deformation due to self-weight.