Kenichi Kurisu

Advanced laser optics for laser material processing

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-hat-shaped 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.

Characteristic of diffractive optical element for arbitrary pattern beam shaping

Laser materials processing has been used increasingly over the wide area of electronic industries, especially for drilling microvias in printed circuit boards, and poly-silicon annealing for thin film transistor of liquid crystal display. Intensity distribution of laser beam is usually a non-uniform gaussian profile. Therefore, the demand for uniform intensity distribution is rising rapidly in some applications of heat processing. To obtain higher uniformity, beam homogenizer of a diffractive optical element (DOE) has recently been developed and introduced to some promising applications. Through the improvement of optical design algorithms and micro-fabrication techniques of a phase pattern of DOE, it becomes possible to convert a non-uniform gaussian distribution not only into a simple distribution like a square and a line but also into a complicated distribution like a distribution of printed circuit pattern. In this study, we introduce a design and fabrication result of beam shaper of DOE that can convert a gaussian distribution into the distribution of a printed circuit pattern, and present the possibility and the point at issue of new laser material processing by using such optics.

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

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 s...

Developments in SiO2 multistep diffractive optical element for beam homogenizing

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.

Beam-splitting ZnSe diffractive optical element

ZnSe Diffractive Optical Element (DOE) is one of the advanced optics which utilizes the optical diffraction phenomena by fabricating a micron order pattern on polished mirror-like surface of ZnSe polycrystal substrate. Various applications for a carbon dioxide (CO 2 ) laser material processing such as beam-splitting, beam-shaping and beam-homogenizing are available. The micro pattern of ZnSe DOE is fabricated by the photolithography and reactive ion etching (RIE) technique. Its optical property is highly dependent on the depth precision of microfabricated pattern. In RIE by using BCl3 as the etchant gas we have achieved an etching technique to maintain the smooth surface of the ZnSe polycrystal with minimal etching rate dependency on the crystal orientation of each crystal grain. The surface roughness is 2nm Ra before etching and 5 nm Ra after about 4 microns depth etching. This good roughness brings better depth precision. With these etching technique beam-splitting ZnSe DOE with less than 10% intensity uniformity of splitted beams is successfully obtained and it can be put to use for practical CO 2 laser hole drilling.

Optical properties of ZnSe diffractive optical elements for spot array generation

The diffractive optical element (DOE) is a revolutionary technology for sophisticated optical systems. It has recently been launched within the optical industry, which is constantly seeking improvements over conventional optics. We have designed and fabricated three types of binary-phase DOE and a 4-level phase DOE for spot array generation. The surface relief of a ZnSe substrate was patterned and etched by using photolithography and reactive ion etching (RIE) technologies. The optical properties of anti-reflection coated samples were then examined by measuring the intensity distribution of the converging beams and the results compared with the calculated beam propagation.The diffractive optical element (DOE) is a revolutionary technology for sophisticated optical systems. It has recently been launched within the optical industry, which is constantly seeking improvements over conventional optics. We have designed and fabricated three types of binary-phase DOE and a 4-level phase DOE for spot array generation. The surface relief of a ZnSe substrate was patterned and etched by using photolithography and reactive ion etching (RIE) technologies. The optical properties of anti-reflection coated samples were then examined by measuring the intensity distribution of the converging beams and the results compared with the calculated beam propagation.

Characteristics of diffractive optical element for multispot beam homogenizing

Laser materials processing has been used increasingly over the wide area of electronic industries, especially for drilling microvias in printed circuit boards, and poly-silicon annealing for thin film transistor of liquid crystal display. To increase a processing speed, it has been developed a beam splitting element of a diffractive optical element (DOE). And the other hand, to obtain higher uniformity, because the intensity distribution of laser beam is usually a non-uniform gaussian profile, beam homogenizer of a DOE has recently been developed and introduced to some promising applications. Through the improvement of optical design algorithms, micro-fabrication techniques of a phase pattern of DOE and new method of optical system, it enables to combine its beam splitting function and homogenizing function. It can produce the simultaneous multi-spot homogenized beam. In this investigation, we introduce a concrete design and fabrication result of multi-spot beam homogenizing system for SHG-YAG laser that can convert a gaussian distribution into the plural number of uniformity intensity distribution, and present the possibility of new laser material processing by using such optics.

Microfabricated ZnSe diffractive optical elements for CO 2 laser

We have developed a new design of advanced optics for processing high-power laser material. We introduce the concept of DOE for high power CO2 lasers. The superior functionality of DOE means that it could become the new standard in optics for next generation devices. Here we describe the design of our DOE technology using scalar theory and micro fabrication using photolithography and RIE. We also present results of our ZnSe-DOE technology, mainly focusing on a novel spot-array generator.