Investigation Of Phase Encoding And Fabrication Processing Of Beam Shaping Elements

The quality of laser beam is very important for many applications, such as beam shaping, diffuser, micro-lenses and MOEMS. Among the beam-shaping technologies, the binary optical element is one type of the important components for beam-shaping, due to its small size, high diffraction efficiency, and multiple-functions. There are many research activities involved in the fabrication of beam-shaping elements. Especially, binary optical elements used for beam shaping have been investigated on its design and fabrication processing.The Iterative Fourier Transform Algorithm (IFTA) has been used to design the phase structures of the binary optical elements with specific diffraction pattern and the technologies for fabricating the phase structures have been concerned in the paper. The aim of the current work is to find out a kind of optimal algorithm of phase encoding and develop a method of fabrication of binary optical elements with cost-effective and simple processing procedures.The design method of phase encoding of laser beam shaping elements with two phase levels has been investigated with modified Iterative Fourier Transform Algorithm. The beam shaping element with higher diffraction efficiency can be obtained by selecting the initialized phase of beam shaping element and adjusting amplitude freedom (AF) and phase freedom(PF). The influences of AF and PF values on the reconstructed image quality are discussed and analyzed. The design parameters will be helpful for getting the high diffraction efficiency of laser beam shaping elements.Projection optical objective is one of the key elements in the parallel laser direct writing system. We have used the optical design software ZEMAX to design the projection objective with double telecentric structure, whose reduction ratio is 10, and analyzed itsoptical performances. At the same time, we have also designed projection optical system byusing microscopic objective with reduction ratio of 23 for laser direct writing system with square spot. This laser direct writing system with square-shaped spot may be as an excellent tool for obtaining the high performance binary optical elements.In addition, we have also discussed the basic fabrication principle and procedures of binary optical elements of two phase levels. We have used three methods to shoot the phase structures of binary optical elements: Gaussian-spot photolithographic method, square-shaped spot photolithographic method and the projection photolithographic method with SLM on our laser direct writing system. The experimental results are given. The factors of yielding the experimental errors for the different photolithographic procedures have been analyzed in detail based on our Matlab software. The presented processing technologies will be useful for the diffraction optical elements with low cost, and high optical performance. Also, the beam-shaping elemer ts with high diffraction efficiency will be easily made with cost-effective, simple procedures, by using laser direct writing system with square-shaped spot.