New design of beam expanding unit for excimer laser

The excimer laser beam is used widespread in the areas of photolithography, ophthalmic operations, cold working and others, because of its high power, high homogeneity and high stability. However, based on the rectangular cross-section distribution characteristic of the laser, it must be expanded in one dimension first to achieve square cross-section distribution for further use. The reported beam expanding units has the deficiencies of serious speckle effect of coherence and the strict tolerance of alignment, respectively. A kind of multi-components parallel reflective expander was proposed based on the shortages above. The structures of such beam expanding units were determined by calculating linear system of equations, and two kind of them were selected by analyzing the feasibilities of different structures due to the solves of equations. A synthesis comparison was executed at the aspects of tolerance analyzing, transmission efficiencies and uniformities of output beam. According to the results of simulations, the designed four components beam expanding unit is proven to be an optimal scheme because of the evident declines of the tolerance sensitivities and speckle effects. Meanwhile, the homogeneity of output beam is improved.

► The proposed laser beam expander reduced the serious speckle effect of coherence.
► This expander loosens the strict tolerance of alignment comparing prior ones.
► The structures of expander were determined by calculating linear-equation groups.
► Each sub-unit is considered as an element of one matrix to simplify calculations.
► The method can be generally used to design other excimer laser expanders.