The Measurement Of High Reflectivity Based On Cavity Ring-down Method

The reflectivity of mirrors is one of important index which is used in high-power lasers. The reflectivity not only influence the laser's power but also take the main point on the system's efficiency of emission. With the development of thin film coating technology and chip polishing technique, the mirror whose reflectivity exceed 99.95% is already in common use, even the mirror of 99.9998% is emergence. At the same time, the traditional reflectivity measurement cannot reach the needs of the high reflectivity measurement. Thus, cavity ring-down method, which is based on the decay time of light transmission in the cavity, has gain the approval of universal is the most advanced method of measure the reflectivity or measure the ultra-low losses.This paper is aimed at measure the reflectivity of high reflectivity mirrors in DF high-power lasers. The main work is as follows:1. investigated in the development of technology of reflectivity measurement, compared each representative measurement methods, and summarized the history and currently development of cavity ring-down method;2. studied the theory of cavity ring-down method, discussed the influence of some main error factors to the measurement precision, simulated the results of cavity length maladjustment and cavity mirror tilt, gained the waveform of each maladjustment, to supply references to the undergoing of experiment; through the simulation , we found that: (1 )the detector with long response time influence the result reflectivity litter (2)small detector aperture response to the cavity maladjustment more and can use to adjust the cavity length;3. designed and established a set up of cavity ring-down method with pulse laser which is based on condition of our laboratory, measured the mirror's reflectivity of straight cavity and folded cavity at the wavelength of 1.06um, analyzed the results of experiment, the analysis show that the reflectivity of straight cavity and folded with measuring repetition is 10^-4, studied on the measuring accuracy, the analysis show that the error of reflectivity is 10^-3;4. analyzed the foreground of cavity ring-down method to DF wavelength, and put forward the plan.