Application of a laser beam profile reshaper to enhance performance of holographic projection systems

Since many illumination applications, such as holographic projection systems, material processing, and laser fusion, require a laser beam to have a uniform energy profile, it is very important to provide a simple and energy efficient beam profile reshaping system. This study evaluates a refractive beam profile reshaping system and its application to a holographic projection system. This reshaper is a two-plano-aspherical lens system which can be designed to convert effectively an arbitrary radially symmetric beam profile into a desired beam profile. In this study, a Gaussian beam profile of a Helium Cadmium laser is converted into a uniform beam profile. The optical design of this reshaping system was based on two conditions: conservation of energy and constant optical path length, by which differential equations were written to solve the shapes of the two aspherical surfaces of the reshaper. The optical performance of this system was analyzed by the flux-flow equation and conventional optical analysis software (GENII-PLUS). Experimental results of testing this reshaper demonstrated that such a two-aspherical-lens system is an energy efficient and simple beam profile reshaping system. Therefore, the design theory has been established. Experimental results also have established that a reshaper designed to operate at one wavelength can effectively reshape a laser beam of a different wavelength, provided the lens spacing of the reshaper is adjusted to compensate for the change in index of the lens associated with the change in wavelength. Acceptable assembly tolerances were also investigated by tilting and decentering the two lenses, and the test results illustrated that such a two-lens reshaping system is a very stable system. This reshaper was then integrated into a holographic projection system which produces multiple coherent, uniform irradiance beams to generate various interference patterns. Based on the performance of the prototype of the laser beam reshaper and the holographic projector, a UV laser reshaping system was designed. It will be used in a UV holographic projector which will produce directional light filters, optical arrays, and other micro-elements.; The design and testing of the refractive beam reshaping system and its application to the holographic system demonstrated that such a two-lens reshaping system provides a simple and efficient solution to many uniform illumination applications.