GaAs ultrafast photoconductive switches are reviewed from the point of view of their application to ultrafast photonic sampling of high-speed electron devices. The photoconductive switches are interdigitated metal-semiconductor-metal diodes fabricated on low-temperature grown GaAs which reveals femtosecond lifetime of photoexcited carriers. On the basis of ultrafast voltage transients of photoconductive switches, it is pointed out that the dispersion of signal transmission lines and the RC time constant due to electrode capacitance limit the ultrafast performance of the photoconductive switches. Monolithic integration technology is developed for the ultrafast photonic sampling. In this technology, photoconductive switches are connected with an electron device by high-speed waveguides. Fabrication of a nanometer-scale transistor integrated with photoconductive switches is described and ultrafast characteristics of the transistor is presented.

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In order to use the excimer laser ablation in the practical application of flexible printed circuit board production, a high-speed excimer laser micro-drilling apparatus has been developed. The apparatus has two significant technical points: (1) the increased energy efficiency of the optical system which is named Multiple Irradiation Optical System (MIOS), (2) the synchronous scanning system that enables large area processing. Newly developed MIOS with a spherical concave mirror is more stable than the MIOS with a flat mirror. The energy efficiency of the MIOS is high even for large mask openings.
The apparatus has been applied for drilling of via-holes of the size less than 20 microns. The processing time is about one minute for a polyimid film 100mm × 100mm wide and 25 microns thick.

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All-optical picosecond gate operation is demonstrated using the spin relaxation in a quantum well etalon. Electron spin-polarization photoexcited by circularly polarized light in GaAs quantum wells decays in picoseconds. With the use of the spin relaxation in a quantum well etalon, all-optical full switching is achieved with a decay time of as fast as 7 ps, by adopting a simple optical differential method, which uses only a quarter-wave plate and a polarizer in addition to the conventional all-optical setup. This switching exhibits a contrast between thehigh and the low reflection states of about 10: 7 for a pump pulse energy of 50 fJ/μm², which is more than 6 times as large as the switching contrast for conventional setup not using the spineffect.

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A conventional phase-Doppler method is useful for particle sizing, but is sensitive to the trajectory ambiguity or the Gaussian beam effect/defect which can cause sizing errors when a large particle is measured. This paper reports studies of the phase-diameter characteristics of the planar phase-Doppler method which was proposed to suppress the Gaussian beam defect. Numerical and experimental investigations have been performed to show the usefulness of the proposed method for measuring particles comparable with or larger than the measuring volume size without the Gaussian beam defect.

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A narrow linewidth excimer laser for photo-micro-lithography has been investigated . To satisfy the need for both high power and long lifetime of narrowing optics, we developed an original self-amplificaton resonator with two etalons and a prism.An out putpower of 8 watts with a spectralinewidth of 1.0pm can be obtained at a pulse repetition rate of 600pps by using the resonator we developed.An estimated intracavity laser power intensity through the etalonsis1/10and output power is twice that with a conventional narrowlinewidth resonator.

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Fabrication mechanisms of thin oxide films have been investigated by using the excimer laser induced metalorganic vapor deposition (Laser-MOCVD) method without heating substrates. TiO₂ and PbO films are successfully obtained on (100) Si substrates from their parent metalorganics, Ti (O-iC₃H₇) ₄ and (C₂H₅) ₃PbOCH₂C (CH₃) ₃, respectively. A ZrO₂ film is notf ormed from Zr (O-tC₄H₉) ₄. The laser wavelength and irradiation angle dependence measurements indicate that film formation proceeds via light absorption of the metalorganic species adsorbed on the substrates. The existence of one-photon process in the TiO₂ film formation is assured by laser fluence dependence measurements. The maximum growth rate, 0.05 Å per laser pulse, of TiO₂ film obtained in the experiments is compared with a rough estimation by a surface reaction model. The model can essentially explain the slow growth rate from the small absorption cross section of the metalorganics and the mild fluence of laser irradiation.

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An apparatus with a rotating mechanical chopper for thin film production has been developed. It is demonstrated that the energy of ablated particles is well selected by this method. Further, this method is applicable to Au thin film deposition and, is recognized to be useful to improve thin film quality because the number of droplets in the film are drastically decreased.

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