[en] This study investigates alteration of regional cerebral blood flow (rCBF) and identification of epileptic foci in interictal frontal lobe epilepsy (FLE) using statistical parametric mapping (SPM). Noninvasive rCBF measurements using ^99mTc-ECD SPECT were performed on 23 patients with frontal lobe epilepsy and 49 age-matched normal subjects. The FLE patients were divided into three groups, 3 patients with dorsolateral and frontocentral seizures, 2 patients with supplementary motor seizures, and 18 patients with frontobasal-cingulate seizures by Mihara's classification determined by clinical and EEG findings. The SPM analysis revealed rCBF abnormality in frontal lobes in 12 patients when compared rCBF data for each patient with those for normal subjects in accordance with Mihara's classification in 8. On the contrary, rCBF abnormality in frontal lobes was detected in 4 patients by visual inspection in accordance with the classification in only one. The rCBF significantly decreased in orbito-frontal regions, frontopolar regions, and anterior cingulate gyrus in the group with frontobasal-cingulate seizures as compared with age-matched normal subjects with confounding covariates of plasma concentrations of antiepileptic drugs. These results suggest that SPM analysis of brain perfusion SPECT gives us useful information about frontal lobe epilepsy even in the interictal phase. (author)

[en] As a tunable laser source for the study of real time LIDAR (LIght Detection And Ranging) technique to detect some trace impurities and radioactive material in atmosphere, a dye laser using liquid fluid as a laser media has been employed. However, the dye laser which has a complex structure is difficult to handle. Therefore, it is considered that the dye laser may not be used as a practical light source for real time LIDAR. A tunable solid stat laser composed of an optical parametric oscillator (OPO) which has a wide wavelength range from violet to infrared with a single nonlinear crystal is one of the promising tunable light sources, however, there is no OPO with high repetition rate and large pulse energy for real time LIDAR. Therefore, high repetition rate lasing characteristics of OPO are studied. In this experiment, β-Barium Borate (BBO) crystal which has wide wavelength range is utilized as a gain medium of OPO and pumped by the second harmonic of Nd: YAG laser with the pulse repetition rate of 0.5 kHz. The threshold pumping peak powers for Type-I and -II BBO-OPO are around 16 MW/cm² and 20 MW/cm², respectively. Maximum average output power of around 5.4 W corresponding to the pulse energy of 11 mJ is obtained for Type-I OPO with the power conversion efficiency of around 45%. At the average pumping power of 14W, the average output power of OPO still increases and undesirable thermal effects are not observed. (author)

[en] An external loop phase conjugate mirror with a 45 deg. -cut rhodium-doped BaTiO₃ is constructed and characterized. The external loop is composed of an image-relay telescope, a 90 deg. -image rotator and a phase modulator. An Nd:YAG laser with the phase conjugate mirror produces a pulse energy of 330 mJ at 100 Hz with a beam quality of 1.2xDL

[en] We built a laser diode pumped solid state green laser (LDPSSGL) rated at high repetition rate. Two laser heads are placed in one cavity with a rotator in between to design to avoid thermal lensing and thermal birefringence effect. Although average green laser power higher than 10 W was obtained at 1 kHz repetition rate with pulse width of 20-30 nsec, the beam quality was so much deteriorated that energy efficiency was as low as 2 %. Learning from this experience that high power oscillator causes a lot of thermal distortion not only in the laser rod but also in the Q-switch device, we proceeded to built a oscillator/amplifier system. A low power oscillator has a slab type crystal in the cavity. As a result spatial distribution of laser power was extremely improved. As we expect that the high repetition rate solid state laser should be CW operated Q-switch type laser from the view point of lifetime of diode lasers, a conventional arc lamp pumped CW Q-switch green YAG laser of which the repetition rate is changeable from 1 kHz to 5 kHz and the pulse width is 250-570 nsec was also tested to obtain pumping characteristics of a dye laser as a function of power, pulse width etc., and dye laser pulse width of 100-130 nsec were obtained. (author)

[en] For the in-situ measurement of various substances in the atmosphere by using DIAL (Differential Absorption LIDAR), a high repetition rate tunable laser is required to obtain data within a few seconds. As the pump source of the tunable laser, the performance of high repetition rate and high average power is indispensable. For the generation of high quality laser radiation, a laser oscillator with 1 kHz pulse repetition rate is made and seeded with very narrow linewidth single-longitudinal mode laser radiation from the outside of the oscillator cavity and its characteristics are studied. As the results, after the thermal equilibrium of the oscillator laser crystal, a single-longitudinal and near TEM₀₀ transverse mode are realized at the pulse repetition rate between 0.5 kHz and 1 kHz. Single frequency operation is preserved by controlling the cavity length. The average output power of 3W (3 mJ per pulse) is obtained. It is confirmed that this oscillator has enough performance as a oscillator of MOPA (Master Oscillator Power Amplifier) system. (author)

[en] The characteristics of a LD pumped zigzag slab YAG laser double-pass amplification is studied. The amplified laser power of 43W in IR is obtained, and the energy extraction efficiency from Nd:YAG crystals 40%. The electrical efficiency is 3.7%. The green power is 19W by using a KTP crystal, with the conversion efficiency of 46%. In this condition, electrical energy efficiency is 1.4%. We also study the quality of the laser beam, and shows that the M² of the laser beam is around 1.5 at high average power condition. (author)

[en] For the pumping of wavelength tunable laser, a high repetition rate, high average power solid state laser pumped by a high duty laser diode (LD) array has been developed. The solid state laser using Nd:YAG zigzag slab crystals consists of an oscillator and an amplifier. Using this Nd:YAG MOPA system, the maximum fundamental average power of 33 W is obtained. The wavefront distortion of amplified laser beam is within 0.3 wavelength. M² measured is about 1.5 which means the laser beam is near diffraction limited. By using nonlinear crystals, fundamental laser radiation is converted to second, third and fourth harmonics. The average power is 15.5 W at 532 nm, 1.2 W at 355 nm and 2.3 W at 266 nm. The beam quality of the second harmonic is good. With the measurement of the laser parameters, it is confirmed that the high repetition rate, high power and high quality second harmonic can be produced by the LD pumped Nd:YAG laser MOPA system. (author)

[en] Laser diode pumped all solid state high repetition rate, high average power Nd:YAG laser MOPA system is developed as a pumping source of tunable laser for atomic vapor laser isotope separation. The Nd:YAG laser consisting of an oscillator and three amplifiers is operated at the pulse repetition frequency of 1 kHz. The average output power of about 95 W at 1064 nm and 50 W at second harmonic by a KTP crystal is obtained. The pulse duration of the fundamental is 50 ns, and that of second harmonic is around 40 ns with the cavity length of 100 cm, which is suitable to pump tunable laser. The electrical efficiency is 1.6% which is greater than that of copper vapor laser. (author)

[en] An optical parametric oscillator with a periodically poled KTiOPO₄ (KTP) as a gain medium pumped by a pulsed Nd:YAG green laser with a maximum pulse repetition frequency of 100 Hz is demonstrated. Output energy of 5.8 mJ at the pulse repetition frequency of 100 Hz with the conversion efficiency of about 40% is obtained by a double-pass pumping scheme. Threshold pumping energy is 1.6 mJ with a peak power as low as 18 MW/cm². At a pulse repetition frequency between 10 Hz and 100 Hz, the conversion efficiency is almost constant and undesirable thermal effects are not observed. (author)

[en] An experimental study focused on the radial scaling of HyBrID (Hydrogen Bromide In Discharge) copper vapor lasers has been carried out by using laser tubes (length 1.2 m) of inner diameter 40, 60 and 80 mm. The detailed parametric dependence on laser output power with each of the bore tubes is compared under the same operating conditions. 90 W of output power was obtained with both a 40 and 60 mm bore tube. By increasing the tube temperature, similar high output power can be produced with a 80 mm bore tube. Enlarging the tube bore results in a reduction of extractable average output power. It has been found that the output characteristics strongly depend on the tube temperature. Control of the tube temperature is crucially important for efficiently producing high output power. A discussion is presented in which the lasing performance under the differing tube conditions is compared. (author)