Techniques of diffractive optical elements (DOEs) based on computer-generated holograms are surveyed. This type of DOE is numerically designed and optimized by using an iterative diffraction algorithm or a nonlinear search algorithm. In this report, a beamshaper designed by employing the former type of algorithm is presented. The beamshaper is capable of transforming an incident Gaussian beam into a specific beamshape, which has a complicated pattern modeled on a printed circuit with a spatial resolution of tens of micron. The actual procedure for designing the beamshaper and the criteria used to determine the design parameters are reported. Furthermore, an evaluation of the designed and fabricated beamshaper and several ideas for improvingit are discussed.

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Recent developments of high-power and high-quality solid-state laser systems, in particular diode-pumped Nd: YAG lasers and fiber lasers, allow the development of various kinds of laser materials processing applicationsin production industries. Diffractive optical elements are employed as a key technology to achieve such applications. In this paper, the author describes the practical examples of a diffractive beam splitter, a diffractive beam homogenizer, a hybrid lens, and a long-focal-depth diffractive lens for a femtosecond laser.

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As a means to accomplish high throughput and damage-free processes, non-digitized (analog) diffractive beam splitters are effectual: they can afford fully suppress undesired diffraction beams by containing as much light energy as possible in a fan-out of beams meant for the process. The surface-relief structures of the splitters are designed using a Fourier-iterative algorithm and are formed on high-quality fused silica substrates using direct laser writing and reactive ion etching. For a 13-beam splitter, for example, a non-digitized element gives an efficiency of 97% with S/N=38, whereas a binary counterpart is as efficient as 78 % with S/N=5, where SIN is defined as the ratio between the minimum of the fan-out beam intensities and the maximum of higher-order diffraction intensities. We have tested these two types of elements in laser-machining applications and verified that the non-digitized element produces more satisfying results than the binary element.

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Because optical disc systems use a laser light source, the systems can easily utilize a diffractive optical element. Accordingly, high function objective lenses for optical disc systems have been developed as hybrid elements having diffractive and refractive surface. Achromatic hybrid objective lenses for MO drives, and objective lenses for DVD/CD compatible drives, are practical examples of such elements. Especially, almost all DVD/CD drives use hybrid objective lenses. In addition, hybrid objective lenses are being considered for use in new optical disc systems using a blue-laser.

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Diffractive Optical Element (DOE) has some different charactristics compared with conventional optical elementsuch as a lens. DOE has great potential power which can produce superior optical systems. We have developed dual-contact PF (Phase Fresnel) lens which has high diffraction efficiency in wide range of wavelengthand manufacturing robustness. We report the development of TC-E3PF (DSC 3×Tele-converter lens) as an application of dual-contact PF lens in this paper.

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Arbitrary distribution of refractive-index and birefringence can be realized artificially with the subwavelength structured surface. Various optical elements with subwavelength structure have been developed. The recent trends of studies on the subwavelength optical elements are toward the processing technologies for commercial production and the new applications. An optical lens with antireflection structured surface and a formbirefringence quarter-wave plate were fabricated with injection-molding or hot-embossing methods. A microretardar array was used as a key device of the polarization imaging camera system.

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We investigated a method for reducing work damage in micro-drilling using a Bessel beam of a nanosecondpulsed laser. While work damage (discoloration and concentric circular marks) was clearly visible on irradiated surfaces of SUS304 and copper, this kind of damage was barely visible on those of aluminum. Metals such as SUS304 and copper are easily damaged by pulsed laser irradiation as a result of discoloration due to surface oxidization. By contrast, metals that have transparent oxides are not readily damaged. By irradiating workpieces in a vacuum, oxidation can be avoided and penetration holes can be produced using a lower irradiation pulse energy density.

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