Influence of surface cleanliness of optical element on its surface scattering characteristics

Aimed at the light scattering problem from the particles on optical surfaces of the systems in practical applications, and taken Al2O3 particles in air as an example, the variations of the bidirectional reflection distribution function (BRDF) with the scattering angle on the surfaces of optical components were simulated and analyzed based on Mie scattering theory, and then the total integral scattering (TIS) value of the surface was calculated quantitatively. On this basis, the effect of the BRDF and the TIS value were further analyzed under the conditions of different air cleanliness levels, the direction of the optical component surface, the exposure time. The results indicate that, the air cleanliness levels, the direction of the optical component surface and the exposure time have effect on scattering of the optical surface, in which the direction of optical components has significant impact on the scattering of the surfaces. When the particles buildup on horizontal upward facing surfaces (TIS=3.9310-3), the amount of scattering increases by an order of magnitude compared with that of the vertical ones (TIS=4.0710-4), and increases by two orders of magnitude compared with that of the downward ones (TIS=5.2210-5). Finally, based on the Cassegrain telescope, aimed at the tolerance of the particles on the primary mirror, the exposure time reaching the tolerance was carried out with different air cleanliness levels. The results can provide reference for particle control and reliability for effective detection of the weak signal in practice.