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A point-diffraction interference microscope with a wire grid polarization pinhole and a high-speed liquid-crystal phase shifter was developed for observing a unicellular organism. Phase images of a moving Euglena could be observed at 8 fps.

Three-dimensional imaging using a complex transparency mask called a built-in lens mask is proposed in this paper. The mask is designed to have multiple focal planes at arbitrary depths for the seed patterns that form partial components of the three-dimensional structure. Three-dimensional imaging is demonstrated by the superposition of these seed patterns at various depths. Using computational lithography, the optical intensity profiles in space are demonstrated for several characters, and their three-dimensional imaging is confirmed. The separation characteristics of the optical images in the depth direction and the discretization of the complex transmittance of the built-in lens mask is discussed. Approach for novel 3-dimensional imaging by built-in lens mask lithography.Display Omitted 3-dimensional imaging through novel complex transparence mask named built-in lens mask is newly proposed.To realize 3-dimenstional imaging, superposition of the seed patterns in various depths is approached.Novel 3-dimensional imaging for characteristic structure is demonstrated by discretized optical complex transmitting mask by computational lithographic works.

We designed and fabricated a computer-generated hologram (CGH) as a beam shaping optical element for laser transformation hardening with a high-power diode laser (HPDL). Using three-dimensional thermal analysis based on the finite-element method, the intensity distribution of the shaped laser beam was optimized to obtain a uniform hardened depth with 4 mm width in a steel plate. Simple experiments of laser hardening were made to determine a material parameter for the numerical simulation. A binary CGH comprising small subholograms was designed in the spatially incoherent regime, because the HPDL comprised a stack of diode lasers. In addition the CGH was fabricated on a silica glass substrate by photolithography and reactive-ion etching. The observed intensity distribution of the shaped beam was well agreed with the designed intensity distribution.

The variation of stress field around an oscillating crack tip in a quenched thin glass plate is observed using instantaneous phase-stepping photoelasticity. The successive images around the propagating crack are recorded by a CCD camera that is equipped with a pixelated micro-retarder array. Then, the phase maps of the principal stress difference and the principal direction are easily obtained even though the photoelastic fringes cannot be visualized. The path of the crack growth as well as the stress intensity factors and the crack tip constraint are obtained from these phase distributions. Results show that the mode I stress intensity factor and the crack tip constraint vary remarkably with the crack growth. In addition, the results show that the mode-II stress intensity factor exists even though the crack propagates smoothly.

We describe a method for designing nonperiodic fine grating structures such as a small F-number diffractive cylindrical lens, to be fabricated by direct-writing electron-beam lithography. The design is based on a resist development simulator for estimating a proximity effect of electron dose and the finite difference time domain (FDTD) method for simulating an electromagnetic field. The surface profile and electron dose distribution are simultaneously optimized to obtain the high diffraction efficiency. For the design of a diffractive lens of 50 µm width and 25 µm focal length, the calculated diffraction efficiency is 49% for 650-nm-wavelength light, which is slightly lower than that of a diffractive lens profile optimized by electromagnetic analysis without restrictions on fabrication limits.

An instantaneous phase-stepping technique using a CCD camera equipped with a pixelated micro-retarder array is applied to the study of quasi-static crack growth in a quenched thin glass plate. The distributions of the principal direction as well as the principal stress diference around a growing crack tip are obtained by instantaneous phase-stepping photoelasticity. Then, not only the mixed-mode stress intensity factors but also the T-stress are evaluated from the distribution of the principal stress difference, and they are validated using the reconstructed phase maps. By applying the proposed method to the sucsessive images, the time-variations of the fracture mechanics parameters are evaluated quantitatively. Results show that the proposed instantaneous phase-stepping technique is effective for the study of the crack growth behavior in a thin glass plate

Digital image correlation technique is used for measuring vertical deflections of bridge girders during a bridge load testing. A bridge is loaded by a heavy cargo truck on the bridge road. Then, the deflection distribution is measured by digital image correlation. The applicability of digital image correlation to bridge deflection measurement is investigated by comparing the results obtained by digital image correlation with those obtained by displacement transducers. The effect of random pattern on an object surface is also investigated by measuring with and without random pattern. The results show that the deflection distributions of the bridge obtained by digital image correlation agree well with those obtained by the displacement transducers when the random pattern is attached on the bridge surface. In addition, it is found that the deflections can be measured even if the artificial random pattern is not applied to the surface of the bridge girder. It is emphasized that noncontact displacement measurement is possible by simple and easy procedure with digital image correlation for the structural evaluation of infrastructures.

This paper demonstrates instantaneous phase-stepping and subsequent phase analysis methods for interferometry and two-dimensional photoelasticity. The camera that has a pixelated form-birefringent micro-retarder array acquires phase-stepped fringes in a single camera frame. Then, the distributions of Stokes parameters that represent the state of polarization are calculated from a single image. In the case of the polarization interferometer, the phase difference of the two orthogonally polarized light beam can be easily determined from the Stokes parameters. On the other hand, the phase distributions of the isochromatics and the isoclinics are obtained in the case of the photoelasticity. It is emphasized that this method is applicable to real-time inspection of optical elements as well as the study of the mechanics of time-dependent materials because multiple exposures are unnecessary for sufficient data acquisition in the completion of data analysis.

A new approach to simultaneous acquisition of phase-stepped photoelastic fringes using a CCD camera equipped with a pixelated micro-retarder array is described for the investigation of time-variant problems. This method is applied to the study of quasi-static crack growth in a quenched thin glass plate. The distributions of the principal direction as well as the principal stress difference around a growing crack tip are obtained by the proposed method. Then, not only the mixed-mode stress intensity factors but also the T-stress are evaluated from the distribution of the principal stress difference, and they are validated using the reconstructed phase maps. The results show that the proposed instantaneous phase-stepping technique is effective for the study of the crack growth behaviour in a thin glass plate.

The present paper describes a new phase-stepping algorithm for the analysis of isochromatics and isoclinics using retarders with arbitrary retardation. A retarder used in the proposed method is not necessarily a quarter-wave plate specified for the wavelength of the light used. Not only the isochromatic and isoclinic parameters but also the retardation of the input and output retarders are determined simultaneously by the proposed phase-stepping method. Thus, accurate analysis can be performed by the proposed method even if accurate quarter-wave plates are not used. In addition, any wavelength of visible light can be used in a single polariscope without requiring matching the wavelength of the quarter-wave plate. Thus, a multi-wavelength technique is easily combined with the proposed method for accuracy improvement, phase-unwrapping, or correction of ambiguity.

Two-dimensional displacement measurement using digital image correlation with lens distortion correction is described in this paper. A single cross-grating is used as a calibration reference. Using two-dimensional Fourier transform, the phases of the grating pattern are analyzed and lens distortion distribution is obtained from the unwrapped phase maps. After detecting lens distortion, the coefficients of lens distortion are determined using the least-squares method. Then, the displacement distributions without the lens distortion are obtained. The effectiveness of the method is demonstrated by applying the proposed method to the rigid body translation test and the uniaxial tension test. The results show that the proposed distortion correction method removes the effect of lens distortion from the measured displacements. By the proposed method, accurate measurements can be performed even if images are deformed by lens distortion.

An instantaneous phase-stepping and subsequent phase analysis method, using a CCD camera with a form-birefringent micro-retarder array, is proposed for interferometry. An optical setup of a polarization interferometry using a Twyman-Green interferometer with two polarizers is constructed to analyze the distribution of out-of-plane displacement. Light emerging from the interferometer is recorded using a CCD camera that has micro-retarder array on the CCD plane. This micro-retarder array has four different principal directions. That is, an image obtained by the CCD camera contains four types of data corresponding to four different optical axes of the retarder. The four images separated from the image recorded by the CCD camera are reconstructed using gray-level interpolation. Then, the distributions of the Stokes parameters that represent the state of polarization are calculated from the four images. The phase distribution of the interference fringe pattern produced by the Twyman-Green interferometer is then obtained from these Stokes parameters. This method is applicable to time-dependent phenomena because multiple exposures are unnecessary for sufficient data acquisition in the completion of phase analysis.

Optical switching in a guided-mode resonant grating (GMRG) with a Kerr medium was numerically simulated by the nonlinear finite differential time domain (FDTD) method. The asymmetric resonant grating was adopted to have two resonant reflection peaks for the pump light and the probe light. When the pump light had a wavelength which was slightly longer than the resonant wavelength, the light was suddenly enhanced at a certain intensity because of the nonlinear resonance phenomenon. This resonance is effective in reducing the pump intensity for optical switching. When we assumed the resonant grating of polydiacetylene toluene sulphonate (PTS) with a linear refractive index of 1.88, a third-order susceptibility of 8.5 × 10¹−0 esu and Q factors of resonant reflection which were ∼800, the pump light of 15 kW/mm² changed transmittance of the probe light from 0 to 80%. 2005 The Optical Society of Japan

A multilevel computer generated hologram (CGH) was fabricated for shaping a laser beam profile of a high-power CO2 laser. The surface relief has eight height levels with 0.94μm in step heights. A copper surface relief was formed on a flat copper substrate by electroplating with photo-resist masks. Standard deviation of the surface step height was less than 22% of the designed height. The CGH changes a CO2 laser beam of 14mm in diameter to a rectangular beam of 1mm×4mm and its diffraction efficiency was 69.2%. A 200W CO2 laser beam of 14mm in diameter did not damage the CGH surface.

This paper describes a proximity correction for fabricating a chirped diffraction grating by direct-writing electron-beam lithography. The electron dose distribution is optimized by calculation with an electron-scatter simulator and a resist development simulator. These simulators are based on the Monte Carlo method and a cell removal model, respectively. To avoid an excessive increase in calculation time, the calculation was performed with 100 nm×100 nm square cells at an accuracy larger than that desired. Also, the resist profile was estimated accurately by adopting the interpolation with the resultant cell profile. In the case of a chirped period grating of 5 mm in width, it took 24 h to calculate the optimum electron dose profile. Moreover to investigate the validity of this correction method a chirped period grating of 0.1 mm in width was fabricated with the calculated dose profile.

The traditional fractional fringe method has been applied to measure 1-dimensional size of a block gauge using multiple wavelengths. Recently, similar methods have been used in pattern interferometry and also in pattern projection profilometry. However, the technique does not seem to be based on a well-established principle. In this paper, the fractional fringe method is formulated on the basis of the least squares method and on its basis effects of errors in fractional fringes and wavelengths are analyzed and the effective selection of wavelengths is considered.

Various optical elements with subwavelength structured surfaces have been developed. The periods of the subwavelength structures are too short to generate diffracted light waves. But the structures are equivalent to refractive index materials with form birefringence. Many new optical elements are realized using the artificial refractive indices of these subwavelength structures. Some typical elements are described here in the passive element regime, and fabrication methods of the elements are explained.

It is known that a doubly periodic guided-mode resonant grating (GMRG) filter has a broad angular selectivity with a narrow spectral bandwidth. This means that the doubly periodic GMRG filter operates for small beam diameter and grating area. This report describes the wave localization in the doubly periodic GMRG filter. We investigated the spread area of light waves in the waveguide layer and the accumulation of field energy by numerical simulation using the finite differential time domain (FDTD) method. Simulation results showed that, in the case of a doubly periodic GMRG filter with a Q factor of 600, the field energy is spread over an area 5 um in width, which corresponds to the expected value from the angular tolerance. And the magnitude of the field energy in the waveguide layer was Q factor times greater than the incident energy. On the other hand, a singly periodic GMRG filter with the same Q factor spread the field energy over an area 72 urn in width. This filter does not work for a small size structure or a small diameter light beam.

A two-dimensional microstructure with low reflectance was fabricated on the surface of an SiO 2 plate by the precise regulation of its shape and surface morphology. A periodically dotted mask pattern of a positive resist was formed on SiO 2 by a two-beam interference method using a He-Cd laser with a wavelength of 325 nm. The substrate was rotated by 90° between the first and second irradiation steps. The microstructure of SiO 2 was etched using an electron cyclotron resonance plasma. The reflection loss was effectively minimized by overcoating an SiO 2 thin film on the microstructure followed by chemical etching in an HF solution. Steady fabrication of subwavelength structures (SWSs) having a reflectance less than 0.1% was possible by using these surface treatment methods.

Low-reflection microstructures were formed by the use of a two-beam interference patterning on a photosensitive ZrO2 gel film. Gel films coated on SiO2 glass were exposed to an interference fringe of 325 nm He–Cd laser beams. The substrate was rotated by 90° between the first and second irradiation steps. Island and lattice type periodic two-dimensional structures with a pitch of 1 µm were formed after the irradiation followed by leaching with ethanol. Reflectance of 0.1% for an optically polished SiO2 surface was attained at around a 1750 nm wavelength by the formation of an island-type microstructure. The transmission spectrum was successfully simulated by the rigorous coupled wave analysis. The heat treatment of the microstructure up to a temperature of 200°C was possible in an ambient atmosphere without a conspicuous increase in reflectance.

application/pdf, Article, Applied Physics Express (APEX). 2017, 10 (12), p.122501-1-122501-4

Three-dimensional lithography processes are required to fabricate the complex structures of advanced MEMS devices. The built-in lens mask has a complex transmittance amplitude and emulates the optical wave planes of arbitrarily shaped images that are to be focused on a focal plane. In our previous work, the authors proposed a novel three-dimensional imaging method using a multifocusing built-in lens mask in a computational simulation study. In this work, the authors study the three-dimensional photolithography process experimentally using this built-in lens mask. A pyramidal frame pattern is used to expose a negative thick resist layer (SU-8), and three-dimensional structures are successfully obtained using a single mask and a single-shot photolithography process. The experimental results agree fairly well with those from the computational simulations.

Novel photo-lithography is newly proposed named built-in lens mask lithography. The method emulates optical propagation plane in exposure system using binary transmittance and phase mask instead of projection lens. The performance of the built-in lens mask lithography is studied by numerical simulation and experimental study using conventional proximity exposure system. The result shows resolution enhancement in deep focus plane.

An X-ray shearing interferometer with a line source is presented. The line source broadens X-ray beams and enables us to obtain a phase image with an X-ray image sensor without mechanical scanning. It can reduce the measuring time compared with image acquisition by mechanical scanning. Small phase difference is measured with the phase shift method using acrylic wedges. Although the output beam is overlapped with the non-interfering beams, we can obtain interference fringes with reasonable contrast. With this system we can obtain a projected phase image of an acrylic plate with cellophane tape.

A system of interferometric computed tomography (CT) for measuring temporal variation of refractive index distribution in a transparent medium such as a flow field has been developed. The system adopts shearing interferometers with double-period diffraction gratings to obtain path-length differences between sheared rays. In order to obtain projection images simultaneously six shearing interferometers are placed in six different directions. The image data for the six interferometers are stored in image memories at the rate of 30 frames per second. Refractive index distribution in the sectional plane of the flow field is calculated with the data using the algorithm of CT modified for shearing interferometers. In experiments temporal variations of refractive index distributions due to a flame and gas flow from a nozzle are measured. These experiments verified that the shearing interferometers are suitable for interferometric computed tomography because they are simple in arrangement and insensitive to disturbances such as mechanical vibration. Potential of the shearing technique and comparison between the CT with the shearing type of interferometer and that with another type of wavefront sensor are discussed.

The force-feedback method is a promising technique to measure accurate force curves in atomic force spectroscopy. In this article, we describe criteria of the stability for the force-feedback system containing a proportional amplifier with first-order lag. We derive the criteria from an equation of the cantilever movement with higher-order vibration modes under force interaction. The criteria predict that a proportional amplifier with a certain gain and a “very high” cutoff frequency is required to stabilize the feedback system when the critical force gradient exceeds the cantilever stiffness. To measure a force curve, including the steep part (−17 N/m) with a soft (0.2 N/m) and poor-damping (2×10−7 kg/s) cantilever, the amplifier for the force-feedback controller must have a frequency response wider than 16 MHz and gain larger than 16.8. Moreover, the feedback controller with only an integrator, which is popular in scanning tunneling microscopy and atomic force microscopy, does not contribute to reducing...

Cost effective micro lithography tool is demanded for fine micro devices. However, resolution of a conventional proximity exposure system is not sufficient below several micron feature size for deep focus depth. On the other hand, a reduction projection system is sufficient to resolve it but the cost of the tool is too much high compared to proximity exposure systems. To enhance the resolution of photolithography, there has been proposed a number of novel methods beside shorting of wave length. Some of them are utilized in current advanced lithography systems, for example, the immersion lithography1 enhances effective NA and the phase shift mask2 improves optical transmittance function. However, those advanced technology is mainly focused on improvement for advanced projection exposure systems for ultra-fine lithography. On the other hand, coherence holography pattering is recently proposed and expected for 3-dimentional pattering3-5. Also, Talbot lithography6-8 is studied for periodical micro and nano pattering. Those novels pattering are based on wave propagation due to optical diffraction without using expensive optical lens systems. In this paper we newly propose novel optical lithography using built-in lens mask to enhance resolution and focus depth in conventional proximity exposure system for micro lithographic application without lens systems. The performance is confirmed by simulation and experimental works.

A point-diffraction interference microscope with a wire-grid polarization pinhole was developed for quantitative phase-imaging. The phase image was obtained, and a focused image was calculated from the defocused phase image with the digital holography technique.

A microforce sensor with a force feedback method for scanning force microscopy is presented. The force sensor is constructed by using an optical fiber and a microcantilever. The facet of the optical fiber is coated with a gold thin film 15 A thick. This gold film acts not only as a partially reflected mirror but also as an electrode of the electrostatic actuator. The interaction force between a probe tip and a sample is balanced by the electrostatic force. The deflection of the cantilever is measured by an interferometer consisting of the facet of the optical fiber and the cantilever surface. We have made the force sensor and measured some force curves of a mica surface with a SiN probe tip. The force curves obtained by this sensor are quite different from the curves by a conventional measurement without a feedback system. The force resolution of the system is 10−10 N with a bandwidth of dc∼1 kHz.

A measurement system for refractive index distribution using optical computed-tomography has been developed. A shearing interferometer with a double-frequency diffractive grating was used to obtain the optical path differential. The double-frequency grating generates fine parallel fringes which are modulated by the optical path differential. The interference fringes were analyzed by the Fourier transform method. For the calculation of the index distribution, we applied an algorithm for beam deflection tomography to our system. This reconstruction algorithm is a modified filtered back-projection method, which determines the index distribution directly from the optical path differential with no integral operation.

Scanning force microscopes (SFMs) are sometimes used to obtain a force curve, which shows the force variation as a function of tip–sample distance. In the force curve measurement, if the spring constant of the force detecting lever is small, the measured force curve has discontinuity and is different from the true force curve. In this paper, we present a new type of force balancing force sensor built in SFM. This force sensor employs an optical lever for detecting the rotation of the lever and two electrostatic force actuators with transparent electrodes. This sensor has two operating modes; with and without feedback. In the feedback mode, the force detecting lever is balanced with the electrostatic force. This system has the effect of enlarging the effective spring constant of the whole sensor. In the nonfeedback mode, this sensor acts as an ordinary force sensor. By using this sensor in both modes we will show the effectiveness of the force feedback in force curve measurements.

In the recent researches of subwavelength relief gratings, the effective refractive indices are used for calculating the coefficients of reflection and transmission of light waves. The effective refractive indices are given by the effective medium theory for light waves propagating in a bulky stratified medium. This paper describes the ability and limitation of the theory applied to estimate the performance of such subwavelength gratings. The limitation is revealed by numerical calculations using a rigorous electromagnetic grating theory and the effective medium theory. As a result, an understanding of the wave behavior in the subwavelength grating has been acquired, which explains the limitation of the effective medium theory.

An atomic force microscope has been constructed which enables us to observe sample surfaces through a metallurgical optical microscope. The cantilever deflection is detected by a polarization common‐path interferometer with optical heterodyne technique. The optical system of the interferometer is incorporated in the commercial optical microscope. The common‐path interferometer is rather insensitive to the effects of environmental disturbance such as thermal drift and mechanical vibration. The sample surface and the cantilever are observed by a microscopic objective of ×20. We can adjust the interferometer easily by observing both the cantilever and laser beams. The detection system has a total rms noise of 0.35 A in a frequency bandwidth of 0.5–200 Hz on a free Si3N4 cantilever of 0.1 N/m spring constant.

A triangular-hole array with a subwavelength-period was designed and fabricated for vertical light coupling from an optical fiber into a SOI slab-waveguide. The fabricated triangular-hole array had a coupling efficiency of 33%.

Double Focus interferometers are attractive for reducing the influence of ambient conditions due to their common-path configuration. This paper describes the influence of sample setting errors in these interferometers. They have been divided into two types, i.e. the normal illumination type and the oblique illumination type. For each type, an equation of the measurement error due to sample setting error has been derived with Gaussian optics. The measurement error of the normal illumination type becomes a parabolic function of the position on the sample surface. The derived error equations have been verified by ray tracing and by experiment. The error of the oblique type is smaller than that of the normal type.

To measure the retardation distribution of the optic retinal nerve fiber layer (RNFL) from a single image, we have developed a new polarization analysis system that is able to detect the Stokes vector using a fundus camera. The polarization analysis system is constructed with a CCD area image sensor, a linear polarizing plate, a microphase plate array, and a circularly polarized light illumination unit. In this system, the Stokes vector expressing the whole state of polarization is detected, and the influence of the background scattering in the retina and of the retardation caused by the cornea are numerically eliminated. The measurement method is based on the hypothesis that the retardation process of the eye optics can be quantified by a numerical equation that consists of a retardation matrix of all the polarization components. We show the method and the measurement results for normal eyes. Our results indicate that the present method may provide a useful means for the evaluation of retardation distribution of the RNFL.

An ultraviolet two-spherical-wave interferometer was developed in order to make a subwavelength structured surface on a curved surface. The change in fringe period on the curved surface was significantly suppressed compared with the two-plane-wave interferometer. The optical setup method for suppressing the change in fringe period is described. The effect of the two-spherical-wave interferometer was investigated by numerical simulations. In an experimental demonstration for a concave spherical surface with 11.1 mm radius of curvature and 10 mm diameter, the change in period of the photoresist pattern was reduced to 12 nm for the target period of 250 nm.

A micro optical prism and micro lenses with metal-and-dielectric multilayered subwavelength structure (MDMS) are discussed. The MDMS prism has a highly dispersive optical property. Light waves do not spread out in the small prism because of the restriction of propagation direction of light. Optical properties of a curved MDMS prism were investigated by theoretical analysis and numerical simulations. The curved MDMS prism with a structure period of 0.4 microm and an apex angle of 90 degrees had angular dispersion of 0.11 degrees /nm for light of 1.5 microm wavelength. A convexo-plane MDMS lens and a gradient-index MDMS lens were also investigated, and the optical behavior for the curved prism with the convexo-plane lens was demonstrated by a numerical simulation.

The thickness measurement of the optic nerve fiber layer is one of the most important evaluations for carrying out glaucoma diagnosis. Because the optic nerve fiber layer has birefringence, the thickness can be measured by illuminating eye optics with circular polarized light and analyzing the elliptical rate of the detected polarized light reflected from the optic nerve fiber layer. In this method, the scattering light from the background and the retardation caused by the cornea disturbs the precise measurement. The latter problem can be avoided by using a Babinet-Soleil compensator. If the Stokes vector expressing the whole state of polarization can be detected, we can eliminate numerically the influence of the background scattering and of the retardation caused by the cornea. Because the retardation process of the eye optics can be represented by a numerical equation using the retardation matrix of each component and also the nonpolarized background scattering light, it can be calculated by using the Stokes vector. The instruments that are currently on the market do not detect the Stokes vectors of the components of the eye. Also, at this time, they are not able to measure retardation distribution in one shot. We applied a polarization analysis system that can detect the Stokes vector onto the fundus camera. The polarization analysis system is constructed with a CCD area image sensor, a linear polarizing plate, a micro phase plate array, and a circularly polarized light illumination unit. With this simply constructed system, we can calculate the retardation caused only by the optic nerve fiber layer and it can predict the thickness of the optic nerve fiber layer. We report the method and the results graphically showing the retardation of the optic nerve fiber layer without the retardation of the cornea.

A computer generated hologram (CGH) has been developed for laser transformation hardening with a fiber-coupled high-power diode laser (HPDL). The laser beam shaped with the CGH is purposely non-uniform in order to obtain uniform depth of the hardened profile. The optimum intensity distribution of laser beam has been determined with the numerical simulation of dynamic thermal analysis based on the finite element method. A binary phase CGH of silica glass was designed and fabricated to realize the optimized intensity distribution of laser beam. When a steel plate surface was hardened by the 330W laser beam with the fabricated CGH, the cross-sectional hardened profile had a uniform depth, compared with experimental results for a defocused Gaussian beam and a flat-top shaped beam.A computer generated hologram (CGH) has been developed for laser transformation hardening with a fiber-coupled high-power diode laser (HPDL). The laser beam shaped with the CGH is purposely non-uniform in order to obtain uniform depth of the hardened profile. The optimum intensity distribution of laser beam has been determined with the numerical simulation of dynamic thermal analysis based on the finite element method. A binary phase CGH of silica glass was designed and fabricated to realize the optimized intensity distribution of laser beam. When a steel plate surface was hardened by the 330W laser beam with the fabricated CGH, the cross-sectional hardened profile had a uniform depth, compared with experimental results for a defocused Gaussian beam and a flat-top shaped beam.

A method of laser processing with a space-variant polarized laser beam is discussed for drilling a square hole. Fourfold rotationally symmetrically polarized beams were proposed. The square-hole was formed by using the difference in the absorption of polarized light for oblique incidence. The feasibility of square hole drilling with the polarized beams was investigated by numerical simulations of laser processing. The calculated holes had square openings with sharp corners. Moreover, one of the square openings was about the same size as a circular hole drilled with a circularly polarized focused beam.