Objective Ultrastable laser has excellent characteristics such as extremely low frequency noises and extremely high coherence, and it is widely used in cold atomic light clocks, geodesy, gravitational wave detection, and optical frequency transmission. When the laser frequency is locked on the Fabry -Pérot (FP) cavity using Pound -Driver -Hall (PDH) frequency stabilization technology, the frequency stability of the laser depends entirely on the cavity length stability of the cavity. The temperature fluctuation of the FP cavity is one of the main factors that affect the cavity length. How to quickly analyze its temperature characteristics has been the research focus of ultrastable lasers. The cavity length change of the FP cavity is mainly affected by the temperature fluctuation of the external environment. To suppress this effect, researchers both in China and abroad usually place the cavity in a vacuum chamber with multilayer thermal shields to obtain a larger thermal time constant and a lower temperature sensitivity. Therefore, to quickly and accurately analyze the influence of the thermal shield parameters in the vacuum chamber on the temperature of the FP cavity, global researchers have carried out corresponding research based on various thermal analysis methods, such as the transfer function method, finite element analysis method, and direct differential method. At present, most of the thermal analysis methods of the FP cavity system only focus on the law of the temperature of the cavity changing with time, and the research results of the temperature sensitivity of the FP cavity required by the actual working conditions cannot meet the urgent needs of the actual working conditions. Therefore, this paper proposes a thermal analysis method of the FP cavity after comprehensively considering heat conduction and radiation and establishes the relationship between temperature sensitivity and corresponding physical parameters of the system, which can guide the design of the FP cavity system in practical engineering.Methods In this paper, a typical FP cavity vacuum system is taken as the research object. Through theoretical analysis,
