Akira Ohzu

Characteristics of high-power excimer laser master oscillator power amplifier system for dye laser pumping

Abstract A master oscillator power amplifier (MOPA) system using two XeCl lasers is constructed for pumping dye laser. The average power of 370 W, and the pulse energy of 740 mJ with the beam divergence of 0.5 mrad are obtained at the pulse repetition rate of 500 Hz. The energy extraction efficiency of the amplifier is nearly 90%. The amplification characteristics are analyzed by a rate equation with non-saturable loss, which results in the gain to loss ratio of around 100 for the amplifier.

Temporal Change of Thermal Lens Effects on Highly Pumped Ytterbium Glass by Wavefront Measurement

The temporal change of thermal lens effects has been measured for the development of high efficient laser system. Ytterbium phosphate glass was used due to its high saturation fluence property. A free running flashlamp pumped Ti:sapphire laser was developed for the high energy pump source. Pumping intensity on the glass surface exceeded 800 kW/cm2 which is enough high for laser diode simulator. Shack-Hartmann wavefront sensor system was applied to measure the thermal lens effects on a highly pumped ytterbium glass oscillator. The temporal change of wavefront was successfully measured at high repetition rate of 100 Hz. The measured wavefront were expanded to Zernike coefficients. Cooling process for the focus coefficient agreed well with the prediction of unsteady one dimensional heat conduction.

Influence of Cs and Ag metal vapor on output characteristics of a HyBrID copper vapor laser

Effects of Cs and Ag metal vapor additives on the lasing performance of a HyBrID copper vapor laser have been experimentally investigated. By adding Cs to the discharge plasma of the laser, the optimum HBr gas flow rate is changed to be smaller than that without the additives. And the average output power increases by about 20%. With the addition of Ag, the output power increases by 30%. And the output power characteristics at high-pulse repetition frequency from 16 to 20 kHz are improved. Based on a relaxation of the laser lower level of Cu atoms in the metastable state and a reduction in the remanent free electron density in the interpulse period, the mechanisms for the remarkable improvement are discussed.

Soft x-ray output from a pinch plasma using laser-induced Au plasma

An experimental investigation of the characteristics of soft x-ray output emitted from a pinch plasma using a laser-induced Au plasma has been performed. The Au plasma is produced by focusing a laser pulse with a focal spot diameter of 100 μm on the tip of an Au pin anode electrode. A pulsed pinch discharge driven by a Marx generator utilizes the plasma as a discharge medium. Soft x-ray output with a pulse duration of ∼120 ns, an energy of ∼1 μJ mm−2, and an effective photon energy of ∼1 keV, has been obtained with the discharge. It is shown that the output characteristics depend strongly on the Marx charging voltage, laser pulse energy, and delay time of the discharge from the laser irradiation.

Characteristics of hard x-ray emission from laser-induced vacuum spark discharges

An experimental study of the characteristics of hard x-ray emission in laser-induced vacuum spark discharges has been carried out. The spark discharge is performed in a gap (10 mm) of pin electrodes using a Marx generator and a laser pulse to produce Au plasma on the tip of an anode. When spark discharge with charge voltage of 150 kV occurred simultaneously with the incidence of a laser pulse, an x-ray pulse made of a short (∼20 ns) x-ray spike pulse and a long (∼400 ns) pulse was emitted with high intensity (∼10 mR per shot). The two pulses appeared at the beginning and at the latter part of discharge. The effective photon energy was around 150 and 80 keV, respectively. The results show that the x-ray intensity strongly depends on the timing of the onset of the discharge with respect to the laser irradiation, the laser intensity, and the charge voltage. The mechanisms responsible for the x-ray emission are discussed in terms of the results observed.

Comparative study of gas composition in a low temperature operated copper vapor laser

Abstract The effect of gas composition on a HyBrID copper vapor laser has been experimentally investigated by changing a gas mixture combination of hydrogen halide gas HBr and HI with a buffer gas comprising He, Ne, and Ar under the same operating conditions. It is observed that the output power characteristics is strongly influenced by the gas combination. A maximum output power of 80 W is obtained with gas combinations of both HBr and HI gas with Ne buffer gas. On using He buffer gas, the maximum output power decreases to 40% of that with HBr and Ne, and to 25% of that with HI and Ne. Laser action is not observed at all with Ar buffer gas. At a high pulse repetition frequency of more than 17 kHz, it is found that the gas combination of HI with Ne can produce a higher output power than that with HBr. The mechanism responsible for the difference in characteristics is discussed.

High-energy flash-lamp-pumped Ti-sapphire laser for Yb:glass CPA

A high energy flashlamp pumped Ti:sapphire laser has been developed for the pumping source of Yb:glass chirped pulse amplification. The free running oscillator generates 12 Joule/pulse at 793 nm at 1 Hz repetition. The output energy of 6 Joule/pulse at 920 nm has been obtained.

Remote Particle Counter Using Backscattered Light Imaging

An optical particle counter using a short laser pulse and a charge coupled devices (CCD) camera with a fast gate shutter is proposed for the remote and real-time monitoring of large particles suspended in air. The counter can be used to visualize the laser-induced backscattered light from the particles in a limited region around two hundreds of meters apart from the observation station. The number of the particles and a histogram of the backscattered light were derived through image data processing. The process used to determine the concentration and size distribution of the particles is described.

Effect of gas convection induced by cross-field discharge in a copper vapor laser

Abstract Magnetic field has been applied to a copper vapor laser with an intention of improving the laser characteristics by inner gas convection. The convection induced by the J×B cross-field discharge (the Lorentz force) is used for partially replacing or mixing the laser medium in a highly heated discharged region with relatively cold gas surrounding the region. It is observed that the output power increases with the increase of the magnetic field. A 23% increase in the output power is obtained with a magnetic field of 150 gauss. The cross-field discharge causes an increase in the peak discharge voltage and a reduction in the initial part of discharge current (Phantom current). Based on the results observed, the possible mechanisms for increasing the power are discussed.

Time-Resolved Laser-Induced Fluorescence of Asbestos in Visible Region

Nanosecond time-resolved laser-induced fluorescence spectroscopy was performed on five types of asbestos (chrysotile, crocidolite, amosite, tremolite, and anthophyllite) using an ultraviolet laser pulse of 266 nm. Most of the fluorescence spectra had a broad wavelength band of 350–700 nm and a maximum at approximately 450 nm in the visible region. The spectra also varied in shape over time. Although all the spectra were similar in shape, a significant difference in the relative ratio of fluorescence intensity between the two different wavelength regions was identified. The lifetime and total fluorescence intensity were also investigated and differences were observed for the different types of asbestos. The observed fluorescence decay curves of the different types of asbestos were almost biexponential in form. The total fluorescence intensity for anthophyllite was the largest among the five types of asbestos. Several methods potentially useful for identifying asbestos from other materials on the basis of their fluorescence characteristics are discussed.