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Medical applications of laser are measurement, laser surgery, in-situ monitoring, and processing of medical devices. In this paper, author briefly reviews the trends of medical applications, describes some new applications, and then discuss about the future trends and problems of medical applications. At present, the domestic market of laser equipment for medical applications is nearly 1/10 of that for industrial applications, which has registered significant growth continuously. Laser surgery as a minimum invasive surgery under arthroscope is expected to decrease the pain of patients. Precise processing such as cutting and welding is suitable for manufacturing medical devices. Pulsed laser deposition has been successfully applied to the thin film coating. The corneal refractive surgery by ArF excimer laser has been widely accepted for its highly safe operation. Laser ablation for retinal implant in the visual prosthesis is one of the promising applications of laser ablation in medicine. New applications with femtosecond laser are expected in the near future.

La0.7Ba0.3MnO3 (LBMO) thin films known to colossal magnetoresistance were deposited for uncooled infrared bolometers. The optimum oxygen pressure was examined in the process of the laser ablated LBMO films, and films were deposited on SrTiO3 (100), LaAlO3 (100) and MgO (100) substrates under the optimum oxygen pressure. The lattice mismatch between these substrates and LBMO films changed the surface structure of films. In X-ray diffraction and atomic force microscope, the LBMO film deposited on SrTiO3 (the LBMO/STO film) showed a high orientation for the substrate, and the grain growth of the LBMO/STO film was progressed. The temperature dependence of resistivity has a good agreement with that of LBMO bulk. In the near-room temperature, the LBMO/STO film showed a high TCR value, about 4%/K. Moreover, TCR values of the LBMO/STO film were over 2%/K from 300K to 335K. On the other hand, LBMO films deposited on LaAlO3 and MgO substrates, having large substrate-film lattice mismatches, showed a low TCR value, below 2%/K, in the near-room temperature.

It is known that local refractive index change occurs when femtosecond laser pulses with extremely high peak power are launched into glass. We focused 130-femtosecond laser pulses of 800 nm into the bulk of glass and examined the shape of the induced refractive index change. We found that the length of the spot of the refractive index change along the optical axis reached about 30 μm despite the diameter being about 2 μm. To estimate the distribution of induced refractive index change, we fabricated Bragg grating by scanning the focused spot and calculated the amount of the change by applying Kogelnik’s coupled mode theory to the measured diffraction efficiencies of the higher order diffracted beams.

It is favorable for the bolometer material used as an uncooled infrared detector device to have large TCR (temperature coefficient of resistance) near room temperature. La1-xCaxMnOz (LCMO) not only shows colossal magnetoresistance, but also has large TCR for the bolometer material. LCMO thin films deposited on LaA103 in several conditions by laser ablation method and were measured their resistivities to estimate TCR and analyzed their mechanism for the oxygen deficiency effect. As a result, we have got thin films which show large TCR by changing oxygen pressure in verger and anneal temperature. The oxygen deficiency effect clarifies to us that it is possible to apply LCMO thin films to bolometer materials.

The degradation of the spatial resolution in frequency-modulated continuous wave (FMCW) reflec-tometry due to the nonlinearity in the optical frequency sweep are discussed both experimentally and theoretically. The response lag in the optical frequency change of a laser diode behind the injection current change was experimentally measured, showing that there were several time constants in the optical frequency response. The interference signals in the FMCW reflectometry were theoretically calculated by taking account of the response lag. From these calculations, the beat frequency becomes low just after the turning point of the optical frequency sweep; this is due to the response lag in the optical frequency response. As a result, the spectrum of the interference signal is spread out toward the low frequency region and spatial resolution is degraded. Moreover, the spatial resolution is seriously degraded with increasing the diagnosing distance due to the nonlinearity in the optical frequency sweep. The calculated results agree well with the measured results.

As a method of high-bit-rate optical processing, the TM light injection-induced optical polarization bistability using Fabry-Perot type laser diodes has been experimentally demonstrated and theoretically analyzed. In these studies, although switching times less than 1 ns both for switch-up and switch-down have been reported, both of the TE and TM outputs exhibit longitudinal multimode spectra. In practical processing systems, a dynamically stable operation of the polarization switching is considered to be essential. It is the purpose of this paper to present an analytical study of the TM light injection-induced polarization bistability using a lambda /4-shifted distributed feedback (DFB) laser model and to describe the detailed picture of the mechanism. >

A simple method for measuring the linewidth enhancement factor alpha of a semiconductor laser by optical injection locking is described. Without knowledge of the absolute values of detuning and the optical injection level, the value of alpha is evaluated from only changes in optical power in the stable optical injection-locking state. The value of alpha of a 0.83-microm channeled substrate planar laser is evaluated to be 2.65 +/- 0.2. The measurement error of this method is also discussed.

We developed an orange fiber laser as the source for photocoagulation in ophthalmic applications. While the beam quality (M2=1.2) is excellent in comparison with the existing solid state laser (M2=7~8), there is the unfortunate necessity of an additional optical system to make the focusing beam uniform after transmission into the 50μm core diameter multimode fiber used in the existing photocoagulator. The purpose of this paper is to obtain a high luminance spot while maintaining the uniformity of the beam. We used 4.7μm Mode field diameter, single mode fiber (SMF) to focus the laser beam emitted from the developed 580nm orange fiber laser source. A coupling efficiency of 70% was obtained at the input power of 500 mW. Moreover, the beam quality of M2=1.27 was achieved after fiber coupling. No additional optical system was necessary to make the beam uniform owing to the SMF characteristics. As a result, the beam diameter at the irradiation point became 12.2μm, and the power density was calculated to be about 25 times higher than that of the existing photocoagulator. Significantly high luminance beams were obtained in the method described above. If the laser spot can be focused near the diffraction limit using adaptive optics in the future, it can be used in new operative procedures such as microsurgery in the macular region. When this method is used in photocoagulation, improvement in the quality of vision of patients is expected due to minimizing any damage to the retina. The effects of high luminance laser irradiation on pseudobiological tissue will be examined in a future paper.

Recent progress in quasi-phase-matched crystal quartz will be reported. Fine period twinning by mechanical stress application achieved a 12 um twin structure. Milliwatt-level second harmonic generation was demonstrated at 266 nm by 2nd-order QPM.

We demonstrate that one can seize and translate voids formed by IR femtosecond laser pulses inside silica glass and can also cause two voids to merge into one. We also present clear evidence of a void and its surrounding region by showing scanning electron microscope images of cleaved voids, which we produced by cleaving through the glass along a plane that included a thin laser-ablated line on the surface of the glass and the voids formed inside.

Large-scale integration of compact photonic devices may be the key technology for the future information age. If optical-waveguide structures with small radius of curvatures are integrated inside a small glass tip along with active devices, a paradigm of microphotonics inside glass may become possible. We will review the fabrication techniques for the waveguides and photonic-band structures inside glass with the ultrashort laser pulses and present our recent results of fabrication experiments. The experimental studies include fabrication of birefringent waveguides, formation of small vacancies called voids, and drilling of a narrow but long hole from the rear side of a glass. We will show the birefringence properties of waveguides that are induced by the lienarly-polarized ultrashort laser pulses of approximately 100 fs duration. Birefringence of the waveguides depends on the polarization states of the fabrication beam. The experimental studies on the stabilities of a void during the fabrication process are also presented. We will show that the voids move during the fabrication process although the beam and sample are fixed. It will be shown that the void moves from pulse to pulse toward the upstream direction along the optical axis. We can currently drill a long hole of more than 200 microns with a diameter of several microns. We also present the results of numerical analysis of optical propagation through photonic structures that are based on the array of voids.

La0.7Ba0.3MnO3-(delta ) (LBMO) has been noticed as a potential candidate for an uncooled IR bolometer material, which has a large temperature dependent electrical resistance, as a potential candidate for an uncooled IR bolometer material. The LBMO thin films were deposited on SrTiO3 substrates by a laser ablation method. The films were characterized by an x-ray diffractometer. In the observation by an atomic force microscope, the size of the crystal grains and the number of grain boundaries on the films were extremely sensitive on the ambient oxygen pressure during the deposition. The grain size found to have an effect on both the magnitude of the resistivity and the temperature dependence of resistivity. The films deposited under the oxygen pressures of 53.3-80.0Pa, having the temperature dependence of resistivity like a bulk, and it showed a large temperature coefficient of resistance over 3 percent K near room temperature.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Many researchers have investigated the interaction of femtosecond laser pulses with a wide variety of materials. The structural modifications both on the surface and inside the bulk of transparent materials have been demonstrated. When femtosecond laser pulses are focused into glasses with a high numerical-aperture objective, voids are formed. We demonstrate that one can seize and move voids formed by femtosecond laser pulses inside silica glass and also merge two voids into one. We also present clear evidence that a void is a cavity by showing a scanning-electron-microscope image of cleft voids: we clove through the glass along a plane that includes the laser-ablated thin line on the surface and the voids formed inside. The optical seizing and merging of voids are important basic techniques for fabricate micro-optical dynamic devices, such as the rewritable 3-D optical storage.

High resolution FMCW reflectometry by the maximum entropy method is described. The spatial resolution is improved by a factor of 4 as compared with that by the Fourier analysis

The morphologies of stearic acid and cytochrome c (cyt.c)-adsorbed stearic acid monolayers were investigated by Brewster angle microscopy (BAM) with various molecular areas of stearic acid. With an area of more than 0.38 nm2/molecule, many blight island domains and some bright circles were observed in the BAM image of the stearic acid monolayer. The blight site part became to occupy all the surface with compression, and then became more closely packed with an area of 0.22 nm2/molecule. On the other hand, a different BAM image was obtained for the cyt.c-adsorbed stearic acid monolayer, as follows: (i) a striped pattern was only observed in the presence of cyt.c; (ii) the number of bright circles in the presence of cyt.c was less than that in its absence. Furthermore, when a uniform BAM image was observed for the stearic acid monolayer with cyt.c, the intensity of the absorbance at 409 nm of cyt.c was the highest. By calculating the amount of cyt.c adsorbed on a stearic acid monolayer from the absorbance value, it was shown that cyt.c was most closely packed when an uniform BAM image was observed. These results suggest that the use of BAM and visible absorption spectroscopy together is useful for studying the morphology of a monolayer.

Since perovskite manganese oxide Bi–La–Sr–Mn–O (BLSMO) has a large temperature coefficient of resistance (TCR: defined as 1/R dR/dT) of above 3%/K, it has been considered to be a suitable candidate for use as an uncooled IR bolometer material. We fabricated a single pixel device of the BLSMO microbolometer and evaluated it. The BLSMO film was deposited by RF magnetron sputtering at ambient temperature in an oxygen atmosphere. The film showed the TCR of 3.1%/K at room temperature. The size of the single pixel device is 38×38 µm2. To achieve high infrared absorption, the detector contains an infrared absorbing membrane with a high fill factor of 90%. In a vacuum, the detector showed a thermal conductance of 1.3×10-7 W/K and a responsivity of 4.8×105 V/W. According to these numerical values, a noise equivalent temperature difference (NETD) of the BLSMO microbolometer was estimated as being about 0.1 K with f/1.0 optics.

La0.7Sr0.3MnO3-δ (LSMO) films have a large temperature coefficient of resistance (TCR: defined as 1/R dR/dT) at near room temperature. Bi0.34La0.33Sr0.33MnO3-δ (BLSMO) film in which La in LSMO is substituted by Bi, was deposited at low temperature, 400°C, by a laser ablation method. The BLSMO film on the SiO2/Si (100) substrate is polycrystalline without any preferred orientations. The low-temperature deposition and the Bi substitution eliminate the Curie temperature of the BLSMO film, and raise its TCR. The film has a large TCR, more than 2%/K, in the wide temperature range of 10–150°C.

In this study, we are exploring the use of perovskite manganese oxide for bolometric applications. To obtain a large temperature coefficient of resistance (TCR: defined as 1/R d R/d T) at near-room temperature, we formed (Bi, La)1-x Sr x MnO3 (BLSMO) bulk samples. The substituted Bi in samples function to reduce the crystallization temperature and to eliminate the ferromagnetic phase. In this report, we discuss the issues related to the influence of the substituted Bi on features such as the surface morphologies, crystallinities and electrical transport properties. For the samples, the temperature dependence of resistivity indicates thermally activated behavior like that of a semiconductor, and a higher activation energy implies a larger TCR value. The maximum TCR value of the samples was 3.6%/K at room temperature.

Oxygen 1s photoelectron spectra have been measured for La1-x Ca x MnO z (LCMO) thin films. The results on the second peak shift and the separation of the peaks are discussed. The second peak shift indicates the oxygen increase causing magnetic transition. The separation of the peaks shows that the oxygen stoichiometry in the crystal is improved. This tendency confirms that the amount of activated oxygen increases with annealing temperature. It is considered that the oxygen 1s photoelectron spectra and the oxygen deficiency effect in resistivity measurements are significantly related.

We describe experimental results of loss measurement in optical waveguide devices by coherent frequency-modulated continuous-wave reflectometry composed of a frequency-swept semiconductor laser and a two-beam interferometer. The backscattered light in a potassium-ion-exchanged single-mode optical waveguide is successfully detected, and the loss along the optical waveguide is evaluated to be 1.0 dB/cm.

Characteristics are described of a novel probe sensitive to the amplitude and phase of the radio-frequency magnetic field which is composed of a laser diode linked with a small loop antenna, an optical fiber, and a phase-sensitive detection instrument. The probe is highly sensitive and is radio-frequency interference free. The minimum detectable radio-frequency magnetic field is 10 μA/cm (38 nW/cm2in power density).

For measuring spectral linewidth of semiconductor lasers, a reflection-type delayed self-homodyne method using a solitary monomode fibre is described. The special features are an extremely simple optical configuration and its excellent long term stability.