The demand for uniform intensity distribution is rising rapidly in the field of thermal processing. In this study we propose beam homogenizers with aspheric lenses or diffractive optical elements (DOE) that can convert a non-uniform Gaussian distribution into a top-hatshaped uniform intensity distribution. The circular beam homogenizer consists of two aspheric lenses. And we propose several types of beam homogenizer, namely, rectangular and linear using DOE technology. Especially, we present a spot array generation homogenizer that can anneal several points simultaneously. This paper suggests possibilities of advance laser optics for new types of laser material processing.

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Diffractive Optical Element (DOE) is an advanced optics which utilizes the optical diffraction phenomena by a microstructure on its surface and can realize various applications such as homogenizing, shaping and splitting in laser material processing. The optical property of DOE is influenced by the accuracy of its microstructure formed by photolithography and the dry etching technique. The development of the reproducible dry etching technique of fused silica to obtain high depth precision in a microstructure by inductively coupled plasma reactive ion etching (ICP-RIE) is described. In ICP-RIE depth is controlled by the time determined by the etching rate of the previous batch. To stabilize the etching rate which is determined by ion energy, the ICP power is reduced to decrease the range of ion energy distribution and the thickness of grease for cooling the substrate is controlled between each batch. Depth precision of less than 10nm has been obtained. Good depth uniformity of less than 30nm P-V at the 1183nm target depth in the 50mm diameter area is also obtained using gas flow simulation. With these improvements a beam-homogenizer DOE with a 16-step microstructure for 532nm YAG-SHG is produced. Intensity is changed by this DOE from the Gaussian beam to the flat top beam whose optical intensity uniformity is less than 10% in the 1.0 0.5 mm region.

A multilevel phase fan-out diffractive optical element (DOE) has been developed and introduced into various kinds of laser materials processing such as drilling, cutting, welding, and soldering. The larger the number of arrayed spots the DOE generates on the surface of the workpiece, the more sensitive the intensity uniformity of the spots becomes to fabrication errors, which are deviations between designed and fabricated surface microstructures. Errors in etch depth have, in particular, a significant effect on the intensity uniformity. A new design method has been developed for increasing the tolerance to the etch depth error, and applied to the design of a 16-level phase 7×7 fan-out element. The result indicates a uniformity less sensitive to etch depth error. The effect of a linewidth error due to the side etch introduced during a plasma etching process is also evaluated by computing high-resolution graphics data representing the phase of the DOE with the line width errors. Mask alignment errors, the slant of sidewalls, and other fabrication errors are discussed further. The diffraction efficiency and intensity uniformity are measured for fabricated DOE prototypes, and a comparison made between the calculated and measured properties shows good agreement.

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