比田井 洋史

本研究では，ガラス管を用いて，穴底部にレーザ光と水を同時に供給する穴あけ法を開発した．ガラス管の一端にレーザ光と水を供給すると，レーザ光はガラス管内を全反射し，ガラス管の反対側端面から水と同時に加工部に照射される．穴への管の挿入で，穴底部へ高エネルギの光の照射が可能になる．また，水を流すことで，デブリの排出も容易となる．実験装置の試作およびガラス管内をレーザ光を効率よく導波させるために導波解析を行った．本手法により，天然ゴムに穴径2.0mm，穴深さ30mmの穴加工を行った．また，曲がったガラス管を用いることで，曲がり穴加工を実現した．

本研究では，卓上精密旋盤を用いて形状精度の高い微細軸を作製する手法について検討した．旋削加工を行う際に生じる切削力のうち，背分力は軸の寸法や形状精度に影響を及ぼす．旋削条件のうち，工具のノーズ半径，アプローチ角および切込み量を適切に設定することで背分力を抑制する加工条件について検討した．その結果，背分力をゼロに抑制することが可能であることを示し，軸径50μm，長さ1mmの微細軸を旋削加工により作製することが可能であることを示した．また，切削抵抗に関する実用式と実験結果の比較を行い，その差異の要因について検討した．

We optically manipulated a metal particle in borosilicate glass. The glass in the neighborhood of the laser-heated metal particle softened; hence, the metal particle was able to migrate in the glass. In this letter, the driving force of the metal particle toward the light source in the glass provided by laser illumination was investigated. The variation in the surface tension of the glass at the interface between the glass and the metal particle induced by the temperature gradient was calculated via a numerical temperature calculation. It was found that the temperature at the laser-illuminated surface of a stainless-steel particle with a radius of 40 mu m was similar to 320 K higher than that on the nonilluminated side. The force applied to the metal particle from the surrounding glass was calculated to be similar to 100 mu N, which was approximately equal to the viscous resistance force. In addition, the experimental and numerically calculated speeds of the moving particle, which was measured while varying the laser power, are discussed. (c) 2013 Optical Society of America

In order to improve the laser micro-machinability of borosilicate glass, the glass surface was doped with metal (silver or copper) ions by electric field-assisted solid-state ion exchange. Doped ions drifted and diffused into the glass substrate under a DC electric field. The drift-diffusion behavior of metal ions in glass was numerically analyzed using standard explicit finite-difference method. The calculated penetration depths of both silver and copper showed good agreement with experimentally measured values. However, there was a difference between measured and calculated ionic fluxes, especially for the early-stage of ion exchange. This discrepancy was likely to be caused by an imperfect initial contact between metal foil and glass substrate. Therefore, the increase in electric current path with ion exchange time was necessary to be taken into consideration. The modified calculation enabled more accurate estimation of ionic penetration depths.

A laser forward transfer technique of gold nanoparticles (GNPs) deposited on glass substrates to silicon wafers and periodic patterning of transferred GNPs is demonstrated. Gold colloidal solution was prepared by citric acid reduction method. The GNPs were deposited by immersing glass substrates derivatized with (3-aminopropyl) trimethoxysilane (APTMS) in the gold colloidal solution for 0.5 h - 3 h. Dispersed or aggregated GNPs were deposited by using Gold colloidal solution with different concentrations. The glass substrate deposited with the GNPs was placed on a Si substrate. The GNPs deposited side was faced to the Si substrate. Then GNPs were illuminated with the second harmonic wave of Nd : YAG laser through the glass, as a result the gold nanoparticles were transferred to the Si substrate. The GNPs deposited on the silicon surface was sphere and dispersed, nevertheless, they were aggregated on the glass surface before transferring by the laser illumination. After the illumination of the Nd : YAG laser to the silicon surface with the GNPs, the periodic deposition of Au was observed. The periodic spacing of the Au were depended on the wavelength and incident angle of the laser beam.

We have successfully demonstrated a method to produce glass nanoparticles by a continuous-wave (CW) CO<sub>2</sub> laser beam. Three types of glass composites were selected and generated glass nanoparticles exhibit lower melting temperature compared with bulk glass. To understand the mechanism of those particle size variations, we have simulated glass temperature and discussed on the strong relationship between glass transition temperatures and melting temperature of generated glass nanoparticles. Regarding melting temperature of glass particles, we investigated the cooling speed, fictive temperature of particles and the effect of the diffusion of water from increased surface area. Ejected particles collected were analyzed by scanning electron microscopy to determine particle sizes and evaluated the melting temperatures by differential thermal analysis. The measured mean particle diameters were 38, 141 and 222nm, and the differences of melting temperature between bulk and nanoparticles were 162, 46 and 3°C respectively.

It has been reported that heat accumulation enables the ablation threshold of the material lower and ablation rate higher in laser drilling. In this paper, the influence of the heat accumulation on high-aspect-ratio hole drilling with the fourth harmonic wave of Nd : YVO<sub>4</sub> laser was investigated. Repetition rate caused the much difference of the depth, for example, the depths of the holes were changed from 1200 μm to 3000 μm, by changing the repetition rate from 1 kHz to 10 kHz, when the laser energy was set at 100 μJ/pulse. The repetition rates which the deepest holes were obtained at were dependent on the pulse energies. Temperature rise with 10 kHz pulses was calculated to be 20 times higher than that with 1 kHz pulses, when the successive pulse illuminated. The reasons that the repetition rate caused the different of the depths, were the diameters at the entrance of the holes, the heat accumulation effect and shielding effect by ablated particles.

High-aspect-ratio microdrilling demonstrated by the forth harmonic of nanosecond Nd:YVO₄ laser. In this paper, we investigated the depths of the holes drilled in alumina, aluminum alloy, cemented carbide, high speed steel, silicon and stainless steel. Firstly, the depths of the holes drilled with the repetition rate of 1 kHz, 5 kHz, 10 kHz and 15 kHz, were measured. As a result, the deepest holes were drilled at the repetition rate of 10 kHz in all the materials. At the tip of the holes drilled in cemented carbide, high speed steel, silicon and stainless steel were blanched. The depths of the holes were 600 μm - 1400 μm. The range of the holes with the diameters less than 10 μm were measured, and aspect ratios were calculated. As a result aspect ratios of alumina, aluminum alloy, cemented carbide, high speed steel, silicon, and stainless steel were 104, 26, 17, 56, 64 and 55, respectively. No clear redepositon layer formed on the inner surface of silicon. Scanning electron microscope observation revealed that inner surface was not flat.

This paper aims at presenting a review of work at the Laser Thermal Laboratory on the microscopic laser modification of biological materials using ultrafast laser pulses. We have devised a new method for fabricating high aspect ratio patterns of varying height by using two-photon polymerization process in order to study contact guidance and directed growth of biological cells. Studies using NIH-3T3 and MDCK cells indicate that cell morphology on fiber scaffolds is influenced by the pattern of actin microfilament bundles. Cells experienced different strength of contact guidance depending on the ridge height. Cell morphology and motility was investigated on micronscale anisotropic cross patterns and parallel line patterns having different aspect ratios. A significant effect on cell alignment and directionality of migration was observed. Cell morphology and motility were influenced by the aspect ratio of the cross pattern, the grid size, and the ridge height. Cell contractility was examined microscopically in order to measure contractile forces generated by individual cells on self-standing fiber scaffolds.

We report on a permanent change in the physical properties inside silica glass by rapid heating and quenching using a continuous-wave laser beam. The absorption of the glass was enhanced by laser heating, and the heated spot moved as a result of thermal radiation and conduction. To trigger heating, an absorbent material was placed on the backside of a glass plate and irradiated through the glass. Laser illumination with a power of 11 W focused on the absorbent material induced a cylindrical modified zone along the laser beam with a length of up to 5.5 mm that was modified at a rate of similar to 130 mm/s. The characteristics of the modified silica glass were studied. The modified area consists of two layers, and the diameters of the inner and outer zones are similar to 40 and similar to 55 mu m, respectively. The inner zone was modified by laser heating. The fictive temperature is estimated to be similar to 1900 K. The etch rate and hardness of the modified glass increased owing to the increment of the fictive temperature. The outer zone was modified by tensile stress due to the densification of the inner zone. In the outer zone, the etch rate is increased and hardness is decreased.

ブラスト加工中に見られる発光現象に着目し，発光の加工状況のモニタリングへの適用の可能性を検討した．発光スペクトルの計測によると，発光は砥粒の破砕に由来するものと工作物の破壊に由来するものに分類できる．前者に関して，砥粒の破砕性との関係を検証し，砥粒破砕をモニタリングできる可能性があるとわかった．また後者の場合，その発光強度が工作物除去速度に比例することから，ブラスト加工中の発光は工作物除去速度のモニタリングに利用できることがわかった．

High-aspect-ratio microdrilling of borosilicate glass has been demonstrated by the forth harmonic of nanosecond Nd : YVO<sub>4</sub> laser. In this paper, we investigated about the influence of the beam profile on the hole profile. Beam profile was changed by using focal lens with the focal length of 10 mm, 20 mm, 30 mm, 50 mm and 100 mm. As a result the glass was drilled deeper than 2200 μm using the focusing lenses with the focal length of 20 mm, 30 mm and 50 mm. On the other hand, the depths of the holes were less than 800 μm using the focusing lenses with the focal length of 10 mm and 100 mm. The profiles of the holes drilled with the focusing lens with the focal length of 20 mm, 30 mm and 50 mm were almost same. The diameters of the holes were smaller than 15 μm in the range deeper than 500 μm, therefore the aspect ratio was higher than 110. Drilled depths and profiles were measured with changing focus positions. No clear were difference were observed when the defocus distances were less than ∼70 % of Rayleigh range. Transmitted laser energy passing through the holes were measured by using the glass plates with different thickness and compared with calculated energy supposing the laser beam propagates as Gaussian beam and no reflection on the inner surface of the drilled hole. As a result the energy of the transmitted light was almost same as that of the calculated energy when the plate was thinner than 1 mm. On contrast, when the plate thickness was 2 mm, the transmitted light was larger than that of the calculated energy. This result conducts the laser beam was reflected and the reflected laser was dominant when the hole was deeper than 1mm.

We demonstrate metal particle implantation technique into glass plate by continuous-wave (CW) laser beam illumination. Platinum film with the thickness of 1 μm was deposited on one side of Pyrex glass surface. The platinum film was radiated with a focused Ar ion laser beam from the other side of the glass. The laser power was set at 4.2 W. As a result, the platinum film was melted and a platinum particle with the diameter of 5 μm was implanted into the glass within 0.1 s after the laser illumination. The glass around the platinum particle heated by the laser illumination was softened, which enables the platinum particle migration in the glass. Interestingly, the particle moved more than 3 mm toward the light source with the speed of ∼ 0.2 mm/s. Energy dispersive X-ray spectroscopy (EDS) clarify that the particle was platinum, and silicon and oxygen, which were components of glass, were not detected. Trajectory of the platinum particle migration was modified and was able to be observed by an optical microscope. No platinum was detected in the trajectory of the platinum particle. The diameter of the modified zone was ∼ 10 μm.

We studied on the modification inside glass formed in the trajectory of a platinum particle implanted by laser illumination. A 1-μm-thick platinum film was deposited on the surface of Pyrex glass. The platinum film was irradiated by a focused Ar ion laser beam with a laser power of 4.2 W from the other side through the glass. As a result, platinum film was melted and a platinum particle with the diameter of 5 μm was implanted into the glass. The glass around the platinum particle heated by the laser illumination was softened, which enables the platinum particle migration in the glass. The threshold fluence for the platinum particle implantation was 0.1 MW/cm<sup>2</sup>. The speed of the platinum particle migration increased in the range from 0.1 mm/s to 10 mm/s with increasing laser fluence. Platinum was not detected and no clear composition change was detected in the trajectory of the platinum particle migration by energy dispersive X-ray spectroscopy. Etching of the modified zone formed cone shaped structures. The modified zone was bended and curved by changing the direction of the laser beam.

We studied on the implantations of various metals into glass with a continuous-wave (CW) laser beam. Platinum, nickel, SUS304, tantalum, tin, silver and copper were examined to implant into borosilicate glass. Platinum, tantalum, tin and silver were deposited with a thickness of 1 μm and nickel, SUS304 and copper foils with a thickness of 10 μm were placed on the backside of the glass. A CW laser beam oscillating at a wavelength of 514 nm was used to illuminate the film through the glass. The laser beam was focused on the films by a convex lens. As a result, platinum, nickel and SUS304 were implanted in the same manner. However, tantalum, tin, silver and copper were not implanted. The thermal conductivities and melting points of the implanted metals were below 100 W/m·K and ranged from 1500 to 2200 K, respectively. We supposed that the temperature at the laser spot governed the difference. Hence, numerical calculations were performed to estimate the temperature. As a result, the temperature of platinum, nickel, SUS304, tantalum and tin exceeded their melting points within 0.01 s after the laser illumination, whereas those of silver and copper did not exceed their melting points even after 1s. The diameter of the particles was controlled by changing the film thickness. The diameters of the particles were ∼3 μm and ∼50 μm when the thicknesses of the deposited films were 0.1 μm and 5 μm, respectively.

High-aspect-ratio microdrilling of borosilicate glass has been demonstrated by the forth harmonic of nanosecond Nd : YVO<sub>4</sub> laser. Borosilicate glass plate with a thickness of 2 mm was drilled through. Firstly, the profile of the drilled hole was measured. As a result, diameters were φ8.2 ± 3.1 μm andφ6.3 ± 1.0 μm at the depth from 480 μm to 2040 μm and from 1360 μm to 2040 μm, resulting in an aspect ratio of higher than 190 and 100, respectively. Drilling process was observed by ceasing laser illumination every 500 pulses. Depth of the drilled hole increased ∼200 μm by very 500 pulses. Re-deposition layer with a thickness of a few micrometer was observed in the range from the top surface to a depth of 1600 μm. Inner surface of the drilled hole was observed by scanning electron microscope (SEM). Melted surface was observed at around the surface (in the range ∼100 μm from the surface) area. Debris with diameters of less than 500 nm was observed in the range of 100 μm - 600 μm from the surface. At around 650 μm, debris with diameters of 500 nm - 1 μm were recognized. In the area deeper than 700 μm, no clear debris was observed and flat surface was obtained. Cracks were observed in the same area where the re-deposition occurred.

太陽電池用シリコンのマルチワイヤソーにかわる新しいスライス方法として，ワイヤ放電加工が研究されている．しかし，放電加工時にウェハ表面に変質層が形成されるため，これを除去することが課題となっている．そこで本研究では，セラミックス等の硬脆材料の加工に適用されているブラスト加工を用いて変質層の除去を試みた．その結果，変質層をブラスト加工で除去できることを明らかにするとともに，従来のマルチワイヤソーでスライスされたウェハと同程度の表面性状をもつウェハを作製することができた．

Drilling of crystalline silicon with a laser beam emerged from an as-cut glass optical fiber in wet etchant has been investigated in this report. This method enables deeper drilling than conventional laser drilling methods such as focusing a beam with a lens, because the beam can be delivered to the bottom of the hole by inserting the fiber in the hole. KOH based solution was used for the etchant and H_2O_2 was added to it in order to prevent the etching of the non-irradiated area. A CW Ar laser and a frequency doubled pulsed Nd:YLF laser were compared. Through-hole drilling of the wafer (0.5mm thickness) was investigated using different types of laser source. The average powers of the lasers were 10W. With the Ar ion laser 40 min. irradiation was needed to perforate the wafer and the hole was cone-shaped. On the other hand, with the Nd:YLF laser, through holes were drilled in less than 1 min. of irradiation and the hole had a smoother and sharper wall than with the Ar laser. No damage was observed on the optical fiber. Through holes were also drilled on 3mm-thick wafers.

CWレーザ背面照射法によってガラス内部に形成された変質部は,中心付近とその周辺部に分かれた同心円2層構造をしている.中心付近と周辺部の物性変化を調べたところ,エッチングレート及び硬度の変化について相関が見られた.変質部のラマン分光分析の結果,これらの物性変化にはガラスの構造変化に伴う密度変化が影響していることがわかった.

We describe filamentary crack-free modification in silica glass, pyrex glass and soda-lime glass by a CW Laser Backside Irradiation (CW-LBI) method. In this method, an absorbent, which is attached on one side of a glass plate, is irradiated from the opposite side through the glass with CW laser beam. Arion laser is used and metal foil is chosen as absorbent. An intense flash moving from the absorbent toward the opposite direction of the incident laser beam at the speed of approximately 20cm/s is observed and then modification appears in the flashed zone. With increasing irradiated laser power, the length of modification increases but the diameter is almost constant. Our experiments indicate the start of this modification may be due to thermal absorption from the heated absorbent by laser irradiation.

We describe modification of various glasses by a CW Laser Backside Irradiation (CW-LBI) method. In this method, an absorbent which was attached on one side of a glass sheet, was irradiated from the other side through the glass with CW laser beam. Ar ion laser was used and copper foil was chosen as an absorbent. Silica, Pyrex and soda-lime glasses were tested as sample glasses. When the absorbent was irradiated, heated spot appeared in the glass adjacent to the absorbent and it ran to the other side of the glass in the path of laser beam. Then cylindrical modified zone that was transparent and crack-free was produced. Diameter of the modified Column was 30 similar to 100 mu m and the cylinder Could grow Lip to 30 mm. The growth rate was approximately 200 mm/s. The dimension of modified zone depended on irradiation conditions, such as laser fluence or beam profiles. The threshold fluences for modification of the glasses were 1-2.5 x 10(5) W/cm(2). Then the characteristics of modified zone were examined by etching in 5 wt. % HIF solution. As a result, it turned out that modified zone consisted of two layers and etching rate of the inner part was lower than that of the outer part. The Raman spectroscopy revealed that the density of the inner part increased by the modification.

Reaction between cubic boron nitride(cBN) and metal has been studied in this paper. Cubic BN grains immersed in metal powders : iron, chromium, nickel, manganese and molybdenum were heated up to 1100℃ in argon or vacuum. Hollows observed on the heated cBN grains reveals that cBN should react with metal. The shapes etched depend on the metal, the crystallographic polarity of the cBN surface and the oxygen remaining in the chamber. Nickel powder made particularly large and clear hollows. Moreover, the reaction was applied to microprocessing of cBN. A polycrystalline cBN on which nickel thin films had been deposited was heated up to 1100℃ in vacuum. Removing the films exposed discolored marks. Raman spectroscopy revealed that the discolored areas contain Ni_3B. The areas were easily turned to be shallow holes by lapping.

Water is decomposed by ArF excimer laser irradiation and decomposed products contain radicals and so on. We propose a new blind hole cleaning technique by those decomposed products. This technique can clean the surface without direct laser irradiation. Therefore we applied to blind hole cleaning. Specifically, water was filled into the blind hole then the laser was irradiated to the water. Firstly, decomposed products were investigated by (1) spectroscopy (2) redox titration (3) etching various metals. Secondly blind hole cleaning was examined. As a result, (1) H and O_2^+ peaks were observed in the emission spectrum. (2) Discolor was recognized by inletting KI and KMnO_4 to the water just after laser irradiation. (3) Decomposed products were affected to zinc, nickel and copper plates by placing parallel to the laser beam. As a result, zinc was etched and mass was decreased. Mass decrease was not recognized in the case nickel and copper. These results revealed that water was decomposed by the laser irradiation, and decomposed products were oxidative. Tapping oil on SUS304 steel was cleaned 5mm around focus point by the laser irradiation. Tapping oil on the sidewall of the blind hole was removed.

Water droplets forms spherical surface due to the surface tension, and changing the size of droplets can vary the radius. In this paper, the availability of a droplet as a lens was investigated by applying for laser processing. Silica glass was used as a workpiece. Defocused ArF excimer laser beam was irradiated to the glass with / without droplets respectively. As a result, the laser beam could be focused by the droplets and caused cracks inside of the glass not at the surface. Changing the size of the droplets and the wettability of the glass enables to control focal length. Aspheric droplets formed by varying the wettability of the glass surface spatially, can control the laser beam intensity distribution. Many small droplets on the glass surface condensed by cooling enables to reduce the threshold of the laser fluence to process and enhance the processing speed.

Chemical vapor deposition (CVD) is one of the most popular film deposition methods on solid substrates. We propose a new powder synthesis method utilizing CVD process, that uses a liquid instead of a solid as a substrate. The gas close to the liquid surface and or dissolved in the liquid was decomposed by laser irradiation and particles were synthesized. Water was used as a liquid, because of its large solubility. Diamond like carbon particles were synthesized by ArF excimer laser irradiation to the methane dissolved in water. Grain size of the particle synthesized from the gas close to the liquid surface was 50-200nm, and that from the gas dissolved in the water was 200-700nm. Grain size could be varied with laser power. Energy dispense spectroscopy (EDS) clarified that the powder mostly consisted of carbon, and oxygen and nitrogen could not detected. High resolution transmission electron microscope (HR-TEM) and electron diffraction revealed that the powder was composed of diamond like carbon (DLC) and multiwall carbon nanotube was grown on the DLC

In this paper, spherical surface molding of polymer using a liquid mold system is described. A liquid droplet has spherical surfaces at the liquid-liquid interface due to interfacial tension. The curvature of the spherical surface is determined by the degree of interfacial tension applied at each interface. Interfacial tension between some liquids was measured, and the shape of a photopolymer droplet between the liquids was calculated. Ultraviolet light was irradiated onto a photopolymer droplet located at the liquid-liquid interface, using a superhigh-pressure mercury lamp. Photopolymer droplets solidified and lens-shaped objects were produced. Cross sections of these objects were observed, and the curvatures of the spherical sufaces were found to correlate with the interfacial tension. A spherical solid was formed at a water/salt solution interface. The possibility of forming various spherical surfaces by exploiting liquid-liquid interfaces was revealed.

In this paper, hydrothermal reaction assisted laser process was suggested. Silicon nitride (Si_3N_4) and cubic boron nitride (cBN) were selected as ceramics. Argon ion laser was irradiated to them in water, steam, air, vacuum, argon, and oxygen. Threshold laser power that Si_3N_4 could be processed in water and steam was lower than that in other atmosphere. Removed depth of laser processed single crystal cBN was twice in water and six times in steam as deep as that in air. Hydrothermal reaction was certified by detection of hydrothermal products, such as ammonium and silica ion from Si_3N_4,ammonium and boric ion from cBN. Binder-less sintered cBN was also enhanced by processed in steam.

In this paper, a new, simple, high-speed method of selective, metal deposition on glass substrates is proposed. Metal powders, placed on a glass substrate were irradiated by an argon ion laser beam. Soda glass, Pyrex glass and silica glass were used, and aluminum and copper powders were chosen. Both metal powders could be deposited on all the glasses. Furthermore, silicon wafer, which placed on Pyrex glass substrate, could be bonded to glass by the similar method.

In this paper, a new method of selective deposition on glass substrates is proposed. Metal powders placed on a glass substrate are irradiated by a laser bam through the glass from the other side and consequently the powders are sintered on the glass substrates. Soda glass, Pyrex glass and silica glass were used as substrates from the viewpoint of their thermal properties, and stainless steel (SUS316L) powders with grain size of 7 μm and 60 μm were chosen. An Ar ion laser beam was used because glass is highly transparent. Fine metal powder was deposited on every glass substrate, and the size of the deposited metal powder was controllable from 120 μm to 840 μm in diameter, and from 45 μm to 330 μm in height by varying the laser power and irradiation time. In the experiment, changing the glass substrate revealed that the adherence of the metal powder was the strongest on the soda glass of all the glasses. Also varying atmosphere and powder size clarified that the metal powder adhered to glass better in air than in vacuum and with fine powder than coarse powder.

Solids and gases have widely studied in laser processing but there have not been so many reports about liquids applied to laser processing. Characteristics of liquids are as follows : liquid has high thermal conductivity, can suspend small particles and colloid, and dissolves gases. These characteristics suggest the possibility of using liquid as a substrate for film synthesis, surface-treating particles suspended in liquid and synthesizing small particles by excited gas dissolved in liquid by laser irradiation, respectively. This study focused on gases dissolved in liquid, so water was chosen as a liquid because of its large solubility, stability and high thermal conductivity. An ArF excimer laser was used because its wavelength is close to absorption edge of water. Firstly, the influence of the dissolved gas was studied and it is found that there is possibility of synthesizing substance in/on the water dissolving methane by laser irradiation. Secondly, synthesizing substance was tried. As a result, carbon films were obtained on the water by laser irradiation to the water from above. According to elementary analysis, solubility, Fourier transform infrared spectrometer, Raman spectrum and scanning electronic microscope, the films contain hydrogen and consist of small particles 30nm in diameter.