Hiroo Fujii

Radio-frequency plasma jet generator of singlet delta oxygen with high yield

O2(a 1Δg) was generated in a flowing discharge of a radio-frequency (rf) hollow electrode. The radio frequency was 99.9 MHz and the rf power was 200 W. The discharge was done in the gas mixture O2:N2:NO=200:20:10 sccm and then it was chilled reactively by the mixture Ar:NO2=200:10 sccm. The O2(a 1Δg) relative yield of 32% was achieved at the pressure of 0.43 Torr. Usage of the mixtures O2:NO=200:100 sccm and Ar:NO2=100:100 sccm resulted in the O2(a 1Δg) yield of 25% at the pressure of 0.6–0.9 Torr. The effluent was mixed with molecular iodine in a far afterglow region and it was tested in an oxygen–iodine laser. The iodine flow rate was 0.3 mmol/min. A strong enhancement of atomic iodine spontaneous emission at the wavelength of 1315 nm was observed in the optical resonator.

RF plasma jet generator of singlet delta oxygen for oxygen-iodine laser

An RF plasma jet generator of singlet delta oxygen has been developed for use in an oxygen-iodine laser. The plasma jet was produced in an Al cylindrical nozzle, having the inner diameter of 3 mm and the length of 8 mm. The discharge was done in the gas mixture O2:N2:NO=200:20:10 sccm and then it was chilled reactively by the mixture Ar:NO2=200:10 sccm, which was injected into the plasma jet at the nozzle exit. The RF frequency was 99.9 MHz and the RF power was 200 W. The O2(?1AEg) relative yield of 32 % was achieved at the pressure of 0.43 Torr. The current device DSOG-3 was tested in a discharge oxygen-iodine laser (DOlL). The reaction scheme of DOlL is the same as in COIL, except of the generator of singlet delta oxygen. The pressure inside the laser was 0.6-0.9 Torr and the mixtures O2:NO=200: 100 sccm and Ar:NO=2100: 100 sccm were used. The iodine flow rate was 0.3 mmol/min. Both types axial and transverse subsonic flow lasers were examined. The latter had better performance. The CW output power was 3 nW at the laser wavelength of 13 15 nm, when the yield of O2(?1AEg) was 25%. The RF DOlL has been demonstrated experimentally.

Development of high‐power chemical oxygen‐iodine laser for industrial application

A scaling up of kW‐class chemical oxygen‐iodine laser (COIL) is achieved. The key issues for the system design of COIL for industrial application is discussed. The scaled up COIL system of 1‐kW output power is now under trial operations. In these operations, a maximum output power of 1100 W, and a continuous operation time of more than 2 h with a power of over 500 W is recorded.

Long-term stability in the operation of a chemical oxygen-iodine laser for industrial use

The influence of solution composition to the generation of the excited oxygen O2(1Δ) for a chemical oxygen‐iodine laser is studied. Moderate power operation of 100 W for a duration of more than 3 h was achieved. For the achievement of long‐term operation, new types of devices for water vapor trapping and new NaCl separation were developed.

FLOW AND OPTICAL FIELDS IN A SUPERSONIC FLOW CHEMICAL OXYGEN-IODINE LASER

The flow and optical fields of a supersonic, flow chemical oxygen-iodine lasers are simulated by solving the three-dimensional Navier-Stokes equations and the paraxial wave equation, and the laser power extraction characteristics are studied. The effects of the wall catalysis are also discussed by introducing the surface catalytic efficiency into the wall boundary condition. The numerical results show that the pair of contrarotating vortices behind the curved jet greatly enhance the mixing and the simultaneous chemical reaction. The effect of the residual flow non-uniformity on the output laser beam is small due to the low Mach number and the fairly good mixing. The wall catalysis reduces the laser performance in case a plenty of excited species diffuse toward the wall of nozzle blades.

RF plasma jet generator of singlet delta oxygen and RF discharge pre-dissociation of iodine for oxygen-iodine laser at lowered temperature

A new RF plasma jet generator (DSOG-5) of singlet oxygen has been developed for use in an oxygen-iodine laser. The plasma jet was produced in Al nozzles, which were fed by the radio-frequency (100 MHz) power of up to 200 W. The usual mode of operation was an energy transfer from Ar plasma jet to a neutral O2 gas stream. The yield of singlet delta oxygen was up to 24%. Iodine molecules were dissociated by 200 MHz RF discharge with the power of 60 W prior to injection into the mixing zone of laser. The pre-dissociation enhancement was up to 22% of iodine spontaneous emission intensity. Both the DSOG-5 and the RF iodine pre-dissociation were tested in laser experiments in a transverse flow Discharge Oxygen-Iodine Laser (DOIL). The effluent of DSOG-5 was cooled by liquid nitrogen to temperatures in the range 120-300 K. There was a temperature dependent loss of singlet delta oxygen on the walls. The singlet delta oxygen yield and the atomic iodine luminescence at the wavelength of 1315 nm were measured. The highest luminescence was achieved at pressures of ~1 Torr with the yield of 10-20%. Laser oscillations have not been achieved.

Hybrid oxygen-iodine laser with a discharge singlet oxygen generator

The trial for world first oscillation of oxygen iodine laser using high frequency discharge was conducted. Maximum excited oxygen efficiency was recorded up to 21% by the microwave (MW) discharge and 32% by the radio frequency (RF) discharge. The highest efficiency of 32% singlet oxygen was achieved by producing plasma jet through the hollow cathode of RF discharge. Laser oscillation test was carried out connecting with RF discharge singlet oxygen generator (DSOG) to a resonator which was arranged longitudinal to the gas flow. Spontaneous emission of its wavelength 1.315 micrometer from iodine electronic transition was detected by the spectra-analyzer from laser output mirror. The laser oscillation was confirmed by detecting an amplification of the emission when laser mirrors were aligned.

Improved rf plasma jet generation of singlet delta oxygen

Rf oxygen plasma jets were studied experimentally as an alternative source of molecular singlet delta oxygen for an oxygen-iodine laser. The relative yield of singlet delta oxygen was measured under a wide variety of experimental conditions. The rf frequency range was 27.2 - 99.9 MHz and the rf power was up to 200 W. The oxygen output pressure was 0.05 - 0.40 torr and the oxygen flow rate was 195 - 1000 sccm. High purity oxygen or its mixtures with Ar, N2, NO and Hg at the pumping velocity of 250 m3/h were used. The plasma jet was produced in nozzles, having the inner diameter of 1 - 6 mm and the length of 1 - 16 mm. The nozzle materials Al, Ti, Ta and W gave significantly better results than Pt and Ni. The dependence of singlet delta oxygen production on the radiofrequency was increasing monotonously. Other dependencies were not monotonous and exhibited an optimum. The cw mode of operation gave usually better results than a pulsed mode. The most effective admixture was N2, which gave the highest enhancement. This resulted in the relative yield of singlet delta oxygen exceeding 15%.

Development of chemical oxygen-iodine laser for industrial application

Since the first oscillation of a ruby laser obtained in 1960, an enormus amount of efforts have been concentrated on laser researches. Fundametal researches were almost finished in 1960s, then aims of investigations were turned to find out new applications.

COIL activities in Japan (Industrial COIL development)

Chemical oxygen iodine laser (COIL) is the only laser expected to be applied for thick plate cutting, for instance, by high laser power over 5 kW transferred to the processing fields by the optical silica fiber. As a result of the first stage of industrial COIL development, a 1 kW subsonic COIL was delivered as a commercial processing device first in the world in 1992. The supersonic COIL development was carried out at the second stage and the output power of over 5 kW was obtained in 1995. Using this high power beam, superiority of the COIL as an industrial laser was studied by processing metals.