Goro Watanabe

1.4-MHz repetition rate electro-optic Q-switched Nd:YVO4 laser

An electro-optic (EO) deflector was used for Q-switching of a laser cavity with a Nd-doped yttrium vanadate (Nd:YVO(4)), enabling a short pulse width and a high peak power to be achieved at a high repetition rate of over 1 MHz. The EO deflector has a low optical loss during Q-switching without polarizers and can be used to form a short laser cavity. A repetition rate of 1.4 MHz with a pulse width of 39 ns was achieved. An output power of 2.7 W was obtained at a pump power of 6.5 W.

Modeling of crossflow jet-type singlet oxygen generator

A quasi-two-dimensional model has been developed to predict the performance of a crossflow jet singlet oxygen generator. The model takes into account HO2− depletion, gas temperature variation due to the pooling deactivation of O2(Δ1), and the stretch effect of gas/liquid interaction area due to the jet-induced pressure loss. The modeling results compare favorably with the test data measured over a wide range of geometries and operation conditions. The overall agreements between measured and calculated values in terms of root-mean-square errors for utilization, yield, and gas temperature are 0.030, 0.035, and 16.23K, respectively.

Analysis of cross-flow jet-type singlet oxygen generator

A cross-flow jet-type singlet oxygen generator has been developed, tested and analyzed in order to characterize the dependence of output performance on major input parameters. A thermal-balance model, which can predict O/sub 2/(/sup 1//spl Delta/) yield, gas temperature, and gas residence time, is proposed, and the resultant theoretical results are compared to the experimental data. Combined with computational fluid dynamics-based gas residence-time analysis, the model provides good agreement with the measured value of the O/sub 2/(/sup 1//spl Delta/) yield and the gas temperature. The surface chemistry model was applied to the measured Cl/sub 2/ utilization data, and was found to be inconsistent in the regime of high Cl/sub 2/ loading on the basic hydrogen peroxide jet, indicating that depletion of HO/sub 2//sup -/ is taking place.

Technical progress in industrial COIL

Chemical oxygen-iodine laser (COIL) has a great potential for applications such as decommissioning and dismantlement (D&D) of nuclear reactor, rock destruction and removal and extraction of a natural resource (Methane hydrate) because of the unique characteristics such as power scalability, high optical beam quality and optical fiber beam. Five-kilowatt Chemical oxygen-iodine laser (COIL) test facility has been developed. The chemical efficiency of 27% has been demonstrated with a moderate beam quality for optical fiber coupling. Our research program contains conventional/ejector-COIL scheme, Jet-SOG/Mist-SOG optimization, fiber delivery and long-term operation.

Comparison Study of Subsonic and Transonic Mixing in a Multi-Kw Grid-Nozzle Supersonic Chemical Oxygen Iodine Laser

The present study compares the laser medium properties for subsonic and transonic iodine injection schemes of a multi-kW grid-nozzle supersonic chemical oxygen iodine laser (COIL). Two supersonic nozzles of similar geometry having subsonic or transonic iodine injectors were investigated in the present study. Small signal gain (SSG) and internal cavity temperature (ICT) were experimentally measured as a function of the iodine flow rate and coordinate in the direction of the gas flow. Dissociated fraction of iodine F and the number N of O2(1Δ) molecules consumed for the dissociation of one iodine molecule were estimated by an analytical method, utilizing SSG and ICT as input parameters. Both gain and temperature were measured by diode laser spectroscopy. Pressure broadening of the spectroscopic line of iodine atom was taken into account when calculating the gas temperature in the cavity.

Tunable pulse width and multi-megawatt peak-power pulses from a nonlinearly compressed monolithic fiber MOPA system

We report on tunable pulse width and high peak power pulse generation from a nonlinearly compressed monolithic fiber MOPA system. The master seed source employs a Mach-Zehnder intensity modulator (MZIM). This seed source has operational flexibility with respect to pulse width, 90 ps to 2 ns and repetition rate, 200 kHz to 2 MHz. The seed pulses are amplified by a monolithic three-stage amplifier system based on polarization maintain Yb-doped fibers. The maximum output power was 32 W at the shortest pulse condition, the pulse width of 90 ps and the repetition rate of 750 kHz. A spectral width after amplification was broadened to 0.73 nm at RMS width. Both of ASE and SRS are not observed in the spectrum. After amplification, we also demonstrated pulse compression with a small piece of chirped volume Bragg-grating (CVBG) which has the dispersion rate of 81 ps/nm. As a result of pulse compression, the shortest pulse width was reduced from 90 ps to 3.5 ps, which brought an increase of the peak power up to 3.2 MW. The compressed pulses are clean with little structure in their wings. We can expand the operation range of the monolithic fiber MOPA system in pulse width, 3.5 ps to 2 ns.

Performance measurements of a cross flow jet SOG for chemical oxygen iodine laser

No abstract available.

A new project for developing a prototype COIL module at Miki Pulley

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 13.2mol/min. The corresponding laser power was 3.5kW.

Ejector Chemical Oxygen–Iodine Laser with Supersonic Nozzle Bank Based on a Trip-Jet Mixing System

Nozzle banks for an ejector chemical oxygen–iodine laser consisting of two-dimensional slit nozzles with a trip-jet mixing system were tested in the cold- and hot-flow operation regimes. Horizontal Pitot scan experiments demonstrated that the mixing ability of the trips is excellent. The Mach number of the mixed flow was approximately 3. Gain measurements were conducted, and the results of these measurements revealed that the maximum gain was approximately 0.54 m-1. The gain cut off length exceeded 200 mm. Lasing experiments were also conducted, and the power was approximately 3 kW at a chemical efficiency of approximately 18%.

Optimization of jet-type singlet-oxygen generator for ejector-COIL

This report describes the experimental and theoretical analysis of a cross-flow jet-type singlet oxygen generator (cross-flow J-SOG) in order to identify the optimal conditions needed to satisfy the ejector-COIL requirement. The optimal conditions had been analyzed under various generator geometries (reaction region length, jet diameter, and chlorine inlet height), gas/BHP flow rates, and gas pressures. The performance was achieved Cl2 utilization of 90% and O2(1Δ) yield of 70% at the plenum pressure of 20 Torr.