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.