Side-pumped Geometry Research Articles

Distribution of hydrogen isotopes retained in the divertor tiles used in JT-60U

Distribution of deuterium and hydrogen retained in graphite tiles placed in the divertor region of JT-60U with the dual side pumping geometry was investigated by thermal desorption spectroscopy. The retention of hydrogen isotopes was nearly proportional to the thickness of the carbon redeposited layers, though their concentration changes with the poloidal location and orientation of the surface tiles. The least concentration of (H + D)/C (∼0.02) was found in the redeposited layers on the inner divertor tile. Rather high hydrogen concentration was found in the redeposited layers on plasma shadowed area. In particular, the redeposited layers on the bottom side of the outer dome wing tile shadowed from plasma and facing to the pumping slot showed the highest concentration of 0.13 in (H + D)/C. In JT-60U, however, the carbon deposition in the shadowed area is very small, resulting in a smaller total retention in the divertor area compared to other large tokamaks.

高輝度高出力ファイバーレーザー

The recent progress of high-power fiber lasers is remarkable. Advantages of a fiber laser in characteristics such as ultra-low loss, high-damage threshold, and waveguide structure enable the outstanding high-power operation with excellent beam quality. In this paper, with the overview of the progressive advances of fiber lasers, our work on high-power fiber lasers is reported. The power limitation of double-clad fiber laser is discussed, which clarifies the importance of scaling the launching capability of pump power. A concept of a fiber-disk laser with a side-pumping geometry was developed and more than 1 kW output power was demonstrated, which is the highest power from a single fiber laser. For further power and brightness scaling, coherent beam combining of many fiber lasers is also investigated. N fiber lasers simply coupled by fused fiber couplers generate power-summed output from one of N fiber ports with high addition efficiencies of more than 85% for N≤8 due to selective excitation of constructive interference modes.

Optical pumping in ferromagnet-semiconductor heterostructures: Magneto-optics and spin transport

Epitaxial ferromagnetic metal - semiconductor heterostructures are investigated using polarization-dependent electroabsorption measurements on GaAs p-type and n-type Schottky diodes with embedded In1-xGaxAs quantum wells. We have conducted studies as a function of photon energy, bias voltage, magnetic field, and excitation geometry. For optical pumping with circularly polarized light at energies above the band edge of GaAs, photocurrents with spin polarizations on the order of 1 % flow from the semiconductor to the ferromagnet under reverse bias. For optical pumping at normal incidence, this polarization may be enhanced significantly by resonant excitation at the quantum well ground-state. Measurements in a side-pumping geometry, in which the ferromagnet can be saturated in very low magnetic fields, show hysteresis that is also consistent with spin-dependent transport. Magneto-optical effects that influence these measurements are discussed.

Simple analytical method to calculate the radial energy deposition profile in an isotropic diode-pumped solid-state laser rod

We provide an approximate but simple analytical solution to the radial distribution of deposited energy in a diode-array-pumped laser rod, subject to some assumptions that are naturally fulfilled for most applications of practical interest. The solution is useful to survey quickly irradiance distributions for a wide variety of pumping geometries and to find the radially most uniform energy deposition. We find that the radial deposition profile, as well as the pump light absorption efficiency, is largely controlled by just two dimensionless parameters: the number of absorption depths and the ratio of the width of the unabsorbed pump beam at the rod center divided by the rod radius. A side-by-side comparison with a numerical model is given. Results describing the best achievable trade-off between absorption efficiency and pumping uniformity are presented in the form of a recipe that can be followed without studying our research in detail. Finally, the model equations are applied to a practical side-pumped geometry.

Discretely tunable multiwavelength diode-pumped Nd:YALO laser

Operation of a moderate-to-high repetition-rate Q-switched quadrupled diode-pumped Nd:YALO laser discretely tunable between 266 and 275 nm is reported. Intracavity frequency doubling of the fundamental yielded 5.4 and 4.4 mJ at 532 and 550 nm, respectively, at a 600-Hz repetition rate. The laser radiation was frequency quadrupled to the UV external to the cavity with an output of 0.28 and 0.24 mJ at 266 and 275 nm, respectively. Astigmatic focal lengths that are due to thermal lensing effects of the Nd:YALO rod in the side-pumping geometry are presented.

One joule output from a diode-array-pumped Nd:YAG laser with side-pumped rod geometry

Output of 1.25 J per pulse (1.064 mu m) with an absolute optical efficiency of 28% and corresponding electrical efficiency of 10% was demonstrated in a diode-array-pumped Nd:YAG laser using a side-pumped rod geometry in a master-oscillator/power-amplifier configuration. In Q-switched operation, an output of 0.75 J in a 17-ns pulse was obtained. The fundamental laser output was frequency doubled in KTP with 60% conversion efficiency to obtain 0.45 J in a 16-ns pulse at 532 nm. The output beam had high spatial quality with pointing stability better than 40 mu rad and a shot-to-shot pulse energy fluctuation >

High-peak-power operation of a diode-pumped Q-switched Nd:YAG laser

We have obtained peak output powers of 587 kW from a diode-laser-pumped Q-switched Nd:YAG laser. Pulse energies of 4.4 mJ with pulse durations of 7.5 nsec were measured. Efficient operation of the Nd:YAG laser in low-order spatial modes was made possible by using a side-pumped geometry that provides high gain.

Efficient laser diode side pumped neodymium glass slab laser

The authors report efficient pulse operation of an Nd:glass slab laser-side-pumped by laser diode arrays. 7.5 mJ output and a slope efficiency of 29% were obtained with 35 nJ pump energy at 0.8 mu m in 200 mu s pulses. The wide absorption band at 0.8 and low laser loss in this phosphate glass allow for efficient pump light absorption and straightforward scalability to high power. The authors demonstrate 22% optical efficiency in a long pulse, multimode diode pumped laser oscillator based on a phosphate laser glass, LHG-8, highly doped with Nd/sub 2/O/sub 3/. The strong and wide absorption bands in such phosphate glasses allow efficient pumping while somewhat relaxing the expensive wavelength selection requirements for laser arrays compared with crystal line host materials. With such materials, smaller slab thickness or rod diameters that are feasible with Nd:YAG can be used in the side-pumping geometry.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>