Homogenization Of The High Power Semiconductor Laser Beams Using Fresnel Diffractive Micro-lens Array

High power semiconductor lasers are widely used in industrial process, medical,military, scientific research and other fields due to their high efficiency, small size,low cost, low weight, long life, high reliability. And more, they are used as a lightingor pumping source. But these applications has strict requirement on the beam quality,such as: uniform energy distribution, high energy efficiency, a variety of spot size andshape. However, the intensity distribution of the semiconductor laser beams areserious imbalance between the fast axis direction and the slow axis direction, so itneeds to be homogenized, then the intensity of focal spot will be well-distributed andthe energy efficiency will be increased.The theory and application of micro-lens array have been very mature on thebeam shaping. And the micro-lens array has many advantages with a compactstructure, good stability, high transmission, convenient to install and test, and it can beconcentric used. However, there are also some disadvantages, for low filling ratio,difficult to control the surface type, which due to the limitation of technology level.While the Fresnel micro lens is a typical diffraction optical element, with a highfilling ratio, small size, high diffraction efficiency, good dispersion correctioncapability, design freedom, along with all the features of the refractive micro-lens. Sothis paper presents an approach that using Fresnel micro-lens array to homogenize thehigh power semiconductor laser beams by integrating the advantages of both.This paper has introduced the present situation and methods of beam shaping bymicro-lens array, then introduced the theory of design Fresnel diffraction micro-lensbased on the scalar diffraction theory. After that, a system that homogenization of highpower semiconductor laser beams by using Fresnel micro-lens array has beendesigned. Then the numerical simulation has been carried out to analyze the influenceof various factors on the focal spot uniformity. Finally the feasibility of the system hasbeen demonstrated by experiments. For the focal spot, the non-homogeneity of is12.34%and the energy efficiency is96.6%in the fast axis; the non-homogeneity is5.42%and the energy efficiency is95.74%in the slow axis. The problem that the highfill factor and accuracy of the refractive lens are difficult to realize have been resolvedsuccessfully by the systems.