Design and performance of multilevel phase fan-out diffractive optical elements for laser materials processing

Abstract

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.

Thermal fatigue on pistons induced by shaped high power laser. Part II: Design of spatial intensity distribution via numerical simulation

“…The spatial shaping of laser beam is the process of redistributing the irradiance of laser. Diffractive optical elements (DOEs) can modulate freely the irradiance and phase profile of laser beam using their surface relief microstructures [5]. A very common beam shaping requirement is a laser profile that is uniform over some cross-section [3,6], which is the case of the present study.…”

Study on the temperature field loaded by a shaped laser beam on the top surface of a cylinder head for thermal fatigue test

“…The temperature field on the top surface of cylinder head in work conditions is measured by thermocouples and it is assumed to be the target temperature distribution. The shaped laser beam is produced with the aid of diffractive optics element (DOE) which can modulate freely the irradiance and phase profile of laser beam using their surface relief microstructures [10]. Before a DOE can be manufactured, the temperature field loaded by the shaped laser beam can be calculated based on finite element model (FEM) [11]- [13].…”