Kazuyoku Tei

Critical Power of Stimulated Brillouin Scattering in Multimode Optical Fibers.

A set of coupled-wave equations for stimulated Brillouin scattering (SBS) in multimode optical fibers excited by single-mode laser light is derived. The analytical solution of the critical pump power is also derived. The solution explains the experimental results well.

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.

Efficient UV generation of a Yb-fiber MOPA producing high peak power for pulse durations of from 100 ps to 2 ns

We demonstrate an average ultraviolet (UV) power generation of 20 W by harmonically converting the output of an all-fiber master oscillator power amplifier (MOPA) system. The third-harmonic generation (THG) UV output provides a conversion efficiency of 40% from the amplified fundamental output. The seed source, which consists of a 1064-nm-wavelength continuous-wave laser diode and two cascaded intensity modulators, produces chirp-free pulses with tunable durations from 100 ps to 2 ns at arbitrary repetition rates and a high dynamic extinction ratio. The fiber MOPA system generates a maximum average power of 50 W and a maximum peak power of 83 kW.

Simple Real Time Trace Nitrogen Dioxide Detector Based on Continuous-Wave Cavity Ringdown Spectroscopy Using Passively Locked External Cavity Diode Laser

We report on a compact trace nitrogen dioxide (NO2) detector based on cavity ringdown spectroscopy (CRDS), using a passively locked external cavity diode laser (PLEC-DL) in the visible wavelength region. Tailoring the spatial mode matching conditions of an antireflection (AR)-coated diode laser with a high finesse external cavity for effective optical feedback into the DL allows for stable resonant enhancement in the external cavity without any electric feedback apparatus. The external cavity having a finesse in excess of 1.4×105 acts as a ringdown cavity with an effective optical volume (i.e., detection volume) of less than 1 cm3. We successfully demonstrated a noise equivalent absorption loss of 1.4×10-8 cm-1, corresponding to a detection limit of 40 ppb NO2 concentration with a very compact configuration. For differential absorption CRDS, we realized a dual wavelength-locked PLEC-DL in an external cavity simultaneously. Measurements of various NO2 concentrations in N2 based on differential absorption CRDS were performed.

Extraction of Methane from Methane Hydrate Using Lasers

A new laser tool for the extraction of methane from methane hydrates is proposed, and its superiority over other methods is discussed. The type of laser suitable for the extraction is also discussed, and the chemically pumped oxygen-iodine energy transfer laser (COIL) is found to be the most suitable candidate.

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.

Development of a prototype COIL for decommissioning and dismantlement

A study of chemical oxygen-iodine laser (COIL) for the use of decommissioning and dismantlement of nuclear facilities is conducted. A scaled-down model was developed as a prototype. Laser duct and optical cavity were designed so that it can be operated in both supersonic mode and high-pressure subsonic mode for the comparative study. A 1.34kW output with chemical efficiency of 24.6% was obtained in the supersonic mode. In the high-pressure subsonic mode, output power was 1 .12kW with chemical efficiency of 20.6%. A subsonic operation at 12Torr was demonstrated for the first time. A preliminary experiment of thick steel cutting was demonstrated by the developed system. The obtained data was in good agreement with published data.

High-pressure pulsed COIL assisted with an instantaneous production of atomic iodine

A new strategy for pulse oscillation of chemical oxygenNiodine laser based on a combination of a porous pipe SOG with an instantaneous atomic iodine generation, has been developed to seek the potential of COIL as an amplifier of the nuclear fusion driver. This new scheme allows one to produce a large aperture high pressure laser medium, which is favorable to the laser amplifier, while maintaining a minimum degradation of stored energy by water vapor. The experimental apparatus consists of the porous pipe SOG, an iodine donor (CH3I) injector, a flash lamp for the iodine dissociation, and an optical resonator. Operational characteristics of the apparatus including dependence of output energy on an iodine concentration was studied. As the result, the maximum output energy of 800mJ was obtained. It was also found that the CH3I was dissociated through unidentified chemical reaction associated with the O2(1AE).

Diffusion Bonded KTiOPO4 Crystal for the Second Harmonic Generation of High Average Power Zigzag Slab Nd:YAG Laser

For the second harmonic generation (SHG) of a high-repetition rate and high pulse energy zigzag slab Nd:YAG laser, the direct bonding of two KTiPO4 (KTP) crystals is carried out and their characteristics are studied using the zigzag slab laser that produces 2.1 J energy pulses with a beam having a rectangular cross section at a pulse repetition rate of 100 Hz. Although an angle mismatch of four minutes between two tuning curves is observed for the bonded crystals, the energy conversion efficiency is the same as that of a single KTP crystal. The second harmonic produced is 1 J.