Diffractive optical element (DOE) is used for off-axis illumination extensively in DUV lithographic system. A method for testing the optical performance of DOE using a visible laser is proposed to simplify the test process. In principle, the optical performance of DOE with a visible laser is analyzed with scalar diffraction theory and numerically simulated using MATLAB program. Compared with the DUV condition, the diffractive pattern distribution is enlarged proportionally with a zero-order spike under the visible laser condition. In experiments, the DOE is tested under He-Ne laser. Its far field diffractive pattern is compared and analyzed with the result tested under the working wavelength of 193.368nm. The shape, the opening angle, the azimuth angle and the pole balance coincide with the values tested in DUV condition. The usefulness of method is verified.
Transmission property of light through rain is discussed in this paper. Instead of the scattering methods usually used in
predicting rainfall attenuation, the principle of the blotting-out effect of raindrops on light transmission is introduced.
Based on this principle and an accurate raindrop size distribution, an initial model for predicting the attenuation due to
rain is first set up. However, when it rains heavily, this initial model is not accurate enough because the overlap effect
between the projected circles of raindrops is not considered. Therefore, by considering the blotting-out and overlap effect
of raindrops together with an accurate raindrop size distribution, a more accurate model for predicting the attenuation
due to rain is finally derived. Numerical simulations show that this model is in good agreement with experimental