Precise measurement of transmittance and reflectance for large aperture optics

The uniformity measurement, transmittance and reflectance of the optics in other words, is one of the essential specifications for those large optics of high power laser facilities. Both high reproducibility for large-size and precision with wide dynamic range make such testing a real challenge to take. In this paper, a transmittance and reflectance measurement system with large aperture is demonstrated. With a laser source at 1053nm, three kinds of large aperture optics are tested by conventional direct detection. The results show that this system can realize high measuring precision (0.05% and 0.01% for transmittance and reflectance respectively) when tested parameter is small in value. In addition, the measurements precision with 532nm and 351nm laser sources are also tested compared, and the factors of measurement uncertainty with shorter wavelength are analyzed. To further promote accuracy and signal-noise ratio, coherent heterodyne detection and optical demodulation technique is proposed especially for high transmittance measurement. A demonstrative experiment of transmittance detection by balanced heterodyne and optical demodulation is performed, and a SD=0.052%, which is more than two order precision is achieved. It results that it is valid compared with conventional direct detection, and gives a promising method for higher precision during further practical applications.