Spectrophotometer for measuring spectral transmittance and reflectance of large aperture optical element

It is a difficult task to measure the optical uniformity of an optical coating with very large aperture. Here an automatic near-UV/VIS/NIR spectrophotometer has been developed for spectrum analysis of optical coatings on very large aperture optical elements. It can give two-dimensional scanning result of a sample with substrate surface size of 600mm*350mm and 70mm thickness. The testing beam can be s- or p-polarized, at an incident angle from 0 degrees to 70 degrees. The equipment is composed of optical system, mechanical structure, photo-translating module and computer control system. Because of the light deflection after passing through the very thick sample, an integrating sphere and a sphere moving structure was involved. The measuring beam is guided in a quartz fiber with a special interface that can improve coupling efficiency from the monochromator to fiber. The two-dimensional scanning work platform has the position accuracy about 0.05mm and a reproducibility of 0.01mm. The beam incident angle accuracy is controlled within 0.1 degrees. The measurement results show that in the near-UVNIS/NfR region, the overall photometric accuracy can get 0.1% and 0.2% for transmittance and reflectance, respectively. The wavelength scale is accurate to be within 0.4nm with a reproducibility of 0.05nm.