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An exotic resonator called the off-axis confocal unstable resonator is analyzed for large-bore low-gain high-saturation-intensity high-power lasers such as chemical pumped oxygen–iodine energy transfer laser (COIL), for which suitable resonators with high beam quality have not existed until now. The result of the calculations clearly showed that the off-axis confocal unstable resonator could produce multi-kW output with excellent beam quality for COIL.

The inorganic material cutting capability of a chemical oxygen-iodine laser (COIL) was estimated as a basic study for field applications such as nuclear power plant decommission, disaster relief, and civil engineering. First, laser-matter interaction characteristics were measured by a commercial 2 kW CO2 laser and a 300 W small-scale COIL, then the cutting performance at an arbitrary output power was estimated using a simplified thermal balance model describing the beam-material interaction. The validity of the model is verified using the CO2 laser. It was estimated that a 100 mm concrete slab can be cut by a 10 kW COIL at a cutting speed of 250 mm/min.

High-efficiency operation of supersonic chemical oxygen-iodine laser (COIL) with an advanced jet-type singlet oxygen generator using nitrogen as buffer gas was demonstrated. Laser output was remarkably increased when buffer gas was cooled with liquid nitrogen. The effects of buffer gas temperature on the characteristics of the oxygen-iodine laser medium was discussed. A net chemical efficiency of 23.4% was obtained at 405 W when the chlorine molar flow rate was 19 mmol/s.

This is a report on a method of sheet plasma production using a TP-D plasma source, which includes a detailed description of the machine. A sheet plasma is a magnetized plasma whose thickness is approximately equal to the mean ion cyclotron diameter. By this method it is possible to produce a steady-state sheet plasma characterized by its large density, high degree of ionization, and high spatial uniformity. The major conditions required for ensuring the proper operation for the machine are (1) to keep the working gas pressure high so far as circumstances permit, (2) to confine the discharge to extending only over the path between the cathode and the rim of the anode slit, (3) to prevent ions attracted to the cathode from concentrating in a limited area of the cathode, and (4) to accumplish coincidence of the central axis of the discharge path through the anode and floating-electrode system and the axis of the magnetic field. In an argon sheet plasma produced by this method, we obtained an electron temperature of about 10 eV and an electron density of the order of 10 12 cm −3 for discharge currents in the range of 5 to 20 A. It has been confirmed that the sheet plasma can be regarded as a very thin boundary-like plasma, in which the plasma space potential is far lower around the midplane of the plasma than on the boundary and a sharp potential well is formed.

The coil system designed to free from the magnetic force and to confine the high β plasma is proposed. We carry out the calculation of the magnetic field for the proposed coil by using the Biot-Savart law. It is noted that no or very weak magnetic fields are appeared in the central region of the proposed coil, while the strong magnetic field localizes at the outside of this region, being satisfied the requirement of confining the high β plasma.The simplified model is considered in order to reduce the cpu time for the computation. From the results of the computation, it is shown that the proposed coil is able to be replaced by the simplified model.

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.

Rapid NO/sub 2/ detection by mid-infrared coherent light source based on difference frequency generation that used a fiber laser as pumping source was demonstrated. High resolution spectroscopic measurements of NO/sub 2/ are reported.

Some resonators were two-dimensionally analyzed zed using a partially coherent input field. The calculation based on the Fresnel-Kirchhoff integral formula showed the applicability of new type resonators to high-power and high-quality laser.

Miki Pulley has pursued the development of a prototype COIL module for field and industrial applications since its transfer from Tokai University in 2000. The test module has already been constructed in our laboratory. The current status of the development is presented. The achieved chemical efficiency was 17.5% at the chlorine flow rate of 13.2 mol/min. The corresponding laser power was 3.5 kW.

In recent years, a laser resonators with the high brightness output beam has been the most preferable for many applications such as remote sensing, optical instrumentation, material processing, and so on. One of the key issues to achieve high brightness operation is in design considerations of the laser resonator geometry matched to a specific laser medium including gain distribution, medium uniformity. In the paper, we report the theoretical analysis and the experimental investigations of a transversely excited atmospheric pressure (TEA) CO/sub 2/ laser and a chemically pumped oxygen-iodine laser (COIL) with newly proposed unstable resonators comparing them with the conventional unstable resonator laser.

The isotope separation experiment in a sheet plasma has been studied by using ion cyclotron resonance heating. The sheet plasma flowed into two parallel plate electrodes to which an rf electric field with a frequency equal to an ion cyclotron for the desired isotopic species was applied. The observed resonance frequency is 180 kHz, however, the ion cyclotron frequency of Ar ion is 65 kHz. This discrepancy may be explained in terms of plasma space potential in the sheet plasma. The ion saturation current in a Langmuir probe gives a maximum value of 6.7 V/cm and 2.3 kG.

The effect of space potential well in sheet plasma on the resonance condition in isotope separation by means of ion cyclotron resonance method is elucidated numerically by computer simulation. It is found that the resonance frequency and minimum rf peak electric field increase monotonously with the increase of peak space potential well of sheet plasma.

We proposed a new unstable resonator, in which forward-mode and backward-mode coupled each other, for low gain large bore laser media such as COIL. The calculations showed that the new unstable resonator can be useful for COIL, which does not oscillate with the usual unstable resonators. The parameters of the resonator for the best performance are also gotten for COIL and carbon-dioxide laser medium.

The isotope separation experiment in a sheet plasma has been studied by using the principle of ion cyclotron resonance heating. Although the effective application of ion cyclotron resonance electric field to a magnetized sheet plasma was considered as a most powerful method from the view point of the selective separation of ion species. Our recent experimental results have shown that a high potential difference between the center and the boundary of the sheet plasma deteriorated markedly the separation efficiency.

A sheet plasma has been generated by use of a TPD (Test Plasma produced by Direct current) type plasma source that all shapes of cathode, slits of anode and floating electrodes, vacuum chambers and magnetic coils are modified rectangularly. Such a machine called a TU–1 or a TU–2 machine, has structural feature that can be produced a steady-state, high density and fully ionized sheet plasma in a low pressure vacuum region along by uniform magnetic field. There are two conditions to produce a sheet plasma with good uniformity of a spatial density distribution in the direction of the plasma width: first it is extremely important to make the centers of the electrode slits coincide precisely with the central axis of the magnetic coils and to keep the mid–plane of the electrode slits parallel to that of the magnetic coils and secondly it is necessary to maintain the discharge uniform near the cathode. In this article, we describe special characteristics of the TU–2 machine and a relation between discharge current and uniformity of electron density distribution.

We proposed a new type of unstable resonator. Generally it is difficult for the unstable resonator to put out laser beam in a low gain laser medium (ex. Chemical Oxygen Iodine Laser: COIL). We considered the new type of unstable resonator, which stimulated more times of transitions in cavity. Output power of unstable resonator was simulated and compared with the confocal one.

Anew type of the laser resonator has been studied for low gain and large aperture lasers. Numerical analyses clearly show the usefulness of the resonator. Experimental results are shown comparing to the analyses.

A high speed photography technique was demonstrated in order to explore transient laser beam cutting phenomena. Dynamic cutting kerf production during a CO2 laser irradiation on soft steel and stainless steel sheets are imaged using a fix velocity cine moving picture camera. Such observation suggested that a detail analysis of the relations between laser induced plume contour and fusion zone should be required for the improved processing quality.

The Chemical Oxygen lodine Laser (COIL) has unique characteristics and it is expected to be used in the energy field. Usually, Lasing threshold of COIL is decreased by the supersonic expansion. To obtain the high stagnation pressure at the plenum, helium is added as a buffer gas. However, using large amount of expensive helium is out of the question for industrial applications. We achieved a high efficiency operation of COIL using nitrogen as buffer gas. Obtained overall efficiency was 23.5% and it is the highest among the supersonic COILS using nitrogen gas a buffer gas.

A new type of laser resonator, the forward-mode and backward-mode coupled unstable resonator, was two-dimensionally analyzed using a partially coherent input field. Under the optimum output power condition, the oscillating mode was annular even at the far field. The experiments with transverse electric atmospheric (TEA) CO2 laser qualitatively showed the same results as those calculated.

A new type of unstable resonator is proposed, in which the inward mode is coupled with the outward mode through the reflection from a flat mirror located at the outlet of the confocal unstable resonator, and the output is taken from the aperture at the center of the concave mirror. The calculation based on the Fresnel-Kirchhoff integral showed the applicability of the new resonator to high-power and high-quality laser.

A strongly magnetized slab plasma with a thickness as thin as the mean ion Larmor diameter, or a sheet plasma, has been successfully produced using a TP-D type plasma source with rectangular magnetic coils and discharge electrodes. The technique of sheet plasma production is described in detail. Applications of sheet plasmas to various fields of science and technology are listed.

A small plasma generator has been developed using the same principle of plasma production as the Nagoya University TP-D machine in order to make an electron emitter with long lifetime for the ion source used in ion implantation and deposition techniques. The highly ionized and high density plasma flowing from the generator can be used instead of the tungsten filament of the Freeman type ion source. This paper reports the noteworthy ability of a flowing plasma to ionize a gas fed into the main discharge chamber whose ionization potential is lower than that of gas in the plasma generator. Also, the possibility of practical use as an ion source having a long lifetime is reported.

A simple hollow cathode ion source has been developed and investigated for increasing ion source lifetime and beam current capability. The experimental results of a LaB6 cathode show that a plasma density of up to 1012/cm3 can be generated with a discharge current of 4.0 A and a pressure of 6.7 Pa, resulting in extracted ion beams that are extremely quiet and stable. The ions of non-volatile elements of cathode materials can be easily obtained by virtue of the sputtering effect of a SUS cathode. The lifetime of our ion sources can be shown to be more than 150 hours.

The concept of a novel method for separation of isotopes, the sheet plasma method, is described. A unique feature of this method is to perform isotope separation in a special kind of magnetized plasma: a sheet plasma: ions of a desired isotopic species in this plasma are selectively energized by ion cyclotron resonance heating. Owing to the unique characteristics of sheet plasmas — (i) the guiding centers of all gyrating ions he in the vicinity of the midplane of a plasma and (ii) the plasma thickness is as thin as twice the mean ion Larmor radius — extremely efficient separation of isotopes is possible.