DESIGNING AND VIBRATION ANALYSIS OF A TRANSPORTABLE REFERENCE OPTICAL CAVITY

Abstract

A Fabry–Pérot cavity is widely utilized in multiple areas of physics, for mode-locking, spectroscopy, signal transmission, interferometers etc. Its use as a short-term optical reference is particularly relevant. Reference optical resonators can achieve exceptional frequency stability, and generate narrow line-width output, which is essential for a plethora of applications. In order to do so, they are isolated from each and every source of noise, and operated in a controlled laboratory setup. Today, there is an increasing demand for reference optical cavities that are portable, and also functional in a non-laboratory environment, without any loss in their stability or performance. Such reference cavities, for out of the lab uses, are called transportable Fabry–Pérot cavities. The optical path length of the cavity is its absolute reference. The frequency instability of a Fabry–Pérot resonator is coupled to the relative length instability in the cavity. The length of the cavity, which is defined as the distance between the two reflecting surfaces, can vary due to temperature and pressure fluctuations, mechanical vibrations, acoustic noise, and even due to change of the gravitational acceleration, giving rise to permanent and dynamic deformations of the cavity. These external sources of noise are naturally more prevalent in non-laboratory conditions. Hence, developing a transportable Fabry–Pérot cavity that can maintain its stability in such conditions is extremely challenging. The precise and robust design of a transportable cavity is a result of smart ideas, rigorous simulations and quantitative analysis. This is done to investigate the stability of the cavity under the influence of all possible external perturbations. The goal of this thesis is to design a transportable reference optical cavity for practical applications. The focus is on compactness, and developing a novel robust mount for the cavity, which is the most critical component in deciding the resonator stability. In the process, we also present in detail the procedures involved in the designing of a transportable Fabry–Pérot cavity. The significance of this study extends to developing transportable ultra-stable laser systems for portable optical clocks.