Koichiro Shinohara

Frequency response for partially coherent imagery ROS

Application of the partially coherent imagery method to the laser raster output scanning (ROS) system with acousto-optic modulator (AOM), appears to lead to a nonlinear modulation transfer function (MTF). When using AOM for laser ROS, it is necessary to consider not only conventional parameters but also two more conditions, the illumination geometry of AOM, and the dynamic image of the sound wave in the AOM. The illumination geometry of the ROS is similar to that of a microscopy system. The calculation of partially coherent image is useful for such systems. The most important factor of that calculation is relative numerical aperture (RNA), the ratio between illuminative NA and objective NA. Replacing the laser beam diameter with the illuminative NA, leads to the MTF curve for the static optical system. This system shows a nonlinear response, due to a nonlinearity between light amplitude and intensity. The response for the dynamic image of the sound wave at the AOM, enables to calculate the MTF of the dynamic optical system which has constant velocity error. Combining these and other MTF responses, the total system MTF curves are investigated. The nonlinearity manifests itself by the peak value which is enhanced in comparison to the continuous lighting level. As a total, the response of this system is higher than the response of a conventional ROS system in practical spatial frequency domain.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.