Large-area, uniform light field generated using a galvo scanning system for bi-directional reflectance distribution function measurement

Abstract

The wavelength range of a femtosecond laser system can be extended to cover 190 nm ~ 4000 nm via optical parametric oscillation and various harmonic generation processes starting from a Ti:Sapphire mode-locked femtosecond pulsed laser. The laser beams can be well adjusted to be coupled to a galvo scanning system to generate a large-area, uniform light field which is highly suitable for the bi-directional reflectance distribution function (BRDF) measurement of the surface of a large-size objective. The scanning route was carefully designed with a few sub-cycles to provide the same illumination time over different spots on the measurement surface. The irradiance of the light field @ 532 nm was measured using a silicon photodiode with an integration time in the range of 0.1 s ~ 10 s and the non-uniformity was measured to be < 4% over a 60 mm × 60 mm area. The integration time of the radiance sensor for the BRDF measurement sensor was adjusted in the range of 0.1 s ~ 10 s, as well, and the BRDF of a 60 mm × 60 mm surface can be achieved with a standard uncertainty of 5%.