Hiroaki Ashizawa

Performance Characteristics of Narrow Linewidth Fiber Laser Pumped Mid-IR Difference Frequency Mixing Light Source for Methane Detection

A high-power, narrow-linewidth Yb fiber laser with a fiber Bragg grating (FBG) pumped difference frequency generation (DFG) in a periodically poled lithium niobate (PPLN) crystal was investigated in detail. A mid-IR power of approximately 2.3 microW at 3.3 micrometers with a slope efficiency of 0.85 mW/W2 was achieved. A Doppler-broadened absorption spectrum of CH4 at 3038.497 cm-1 (3.2911 micrometers) was obtained with a 0.1-m long-gas cell at a pressure of 133 Pa. The linewidth of the DFG source was evaluated to be less than 96 MHz from the observed spectral linewidth. Real-time monitoring of CH4 (approximately 1.78 ppm) in ambient air in a multipass cell which has an optical path length of 10 m was also demonstrated.

Trace NO/sub 2/ detection with Yb fiber laser pumped mid-IR difference frequency generation

A novel high power Yb fiber laser pumped cw narrow-linewidth tunable mid-IR coherent source based on a difference frequency generation (DFG) in a periodically poled LiNbO/sub 3/ (PPLN) crystal for trace gas detection was demonstrated.

Effects of a quartz beam-guide on high-precision laser-assisted etching of Al2O3 ceramics

Abstract Laser-assisted chemical etching of ceramic materials has been attracting continuous attention as a laser microfabrication technique with relatively low power levels. In this study, in order to improve the accuracy of etching depth and diameter, the application of a quartz beam-guide to the pulsed Nd:YAG laser-assisted etching process is proposed. By using this technique, possibilities of high-precision hole drilling with high aspect ratio and uniform surface etching in the radial direction of the beam using a beam-homogenizing effect of the beam-guide have been investigated for Al 2 O 3 ceramics immersed in H 3 PO 4 solution at room temperature. The results revealed that: (1) the distance between the beam-guide surface and the workpiece surface dominates the surface etching rate; (2) by using the beam-guide, the beam-homogenizing effect in the radial direction of the beam at the surface is confirmed; and (3) possibilities of uniform surface etching and high-precision hole drilling are demonstrated by applying the beam-homogenizing effects of the beam-guide.

Plasma characterization in laser cutting

Characterization of a blue plasma was conducted using a high- speed I.I. video camera, a color CCD video camera, and a spectrum multi-channel analyzer. A blight blue plasma, which contains Fe, N2 and N2+ was observed from a cutting point in laser cutting with either through- and non- through penetration when the cutting quality was not satisfactory. From the results, a use of the blue plasma signals can be effective for the in-process monitoring of a cut surface quality in laser cutting. Also, removal processes of molten material, can be divided into two types, (1) by the dynamic pressure of a coaxial gas jet, and (2) by the recoil force with an evaporation. An explosive evaporation of molten material from a point of laser irradiation was observed almost simultaneously with the plasma formation. At the cutting front, a small crater was seen at a point of the plasma formation. It was found that N2+ and N2 spectra are not emitted directly through a direct absorption of a laser beam by a gas jet, but presumably through the secondary collisions of N2 in a gas jet with electrons and/or Fe atoms emitted and accelerated from the material surface by a strong radiant energy of the laser beam.

NH/sub 3/ detection under water vapor influence by mid-IR source based on Yb fiber laser pumped difference frequency generation

NH/sub 3/ detection in water vapor contained gas mixture with mid-IR light source at 3 /spl mu/m based on difference frequency generation was demonstrated. High spectral resolution measurements of NH/sub 3/ avoiding interference of water are reported.

Yb fiber laser pumped mid-IR source based on difference frequency generation and its application to methane detection

Summary form only given. A cw narrow-linewidth tunable mid-IR coherent source has become a useful tool for trace gas detection since almost all gases exhibit fundamental rovibrational absorption lines with high absorption strength in the mid-IR. This particular source is obtained by a difference frequency generation technique which is that two near IR laser pump sources (/spl lambda//sub 1/, /spl lambda//sub 2/) are mixed to generate mid-IR (/spl lambda//sub 3/=(1//spl lambda//sub 1/-1//spl lambda//sub 2/)/sup -1/) in a quasi-phase-matched nonlinear optical crystal such as a periodically poled LiNbO/sub 3/ in single-pass geometry. Such a spectroscopic source can operate at room temperature with single spatial mode, single frequency and tunable in wide frequency region without mode hop. This paper reports an experimental study of a fiber laser (1063.8 nm) based mid-IR generation to detect methane.

Multiplicity and Lattice Relaxation of DX Center in AlGaAs:Si Studied by Electron Emission Spectra under Pressure

DX center in Al 0.3 Ga 0.7 As:Si consists of four components, of which each component has the same thermal activation energy (0.41±0.02 eV). The activation energy and emission-rate show no changes on pressure. One significant implication is that no lattice deformation occurs upon an electron emission