The Ni-Fe alloy consumable that applies to the welding of 9% nickel steel for LNG storage tanks is highly susceptible to solidification cracks. To evaluate susceptibilities such as the brittleness temperature range (BTR), a Trans-Varestraint test is generally conducted. However, it is difficult to evaluate the minimum strain value for the BTR and the real temperature at both ends of a solidification crack in a conventional Trans-Varestraint test because these values are measured indirectly. In this study, we propose determining the temperature range by conducting in-situ observations during a Trans-Varestraint test using a highspeed camera and two-color pyrometry so that the temperature range can be measured directly from the temperatures at both ends of the crack. Furthermore, we measured the augmented strain from the time elapsed since the initiation of bending. This method allowed us to successfully measure the augmented strain and the temperature range in the Trans-Varestraint test and to determine the BTR more accurately.

We report the gain measurement of a laser diode pumped Tm:YAG laser by using a cavity loss method. The maximum gain and the saturation parameter of a single-longitudinal-mode Tm:YAG laser were determined to be O.04cm1 and 13kW/cm2, respectively, were obtained in a single-longitudinal-mode.

We have developed a compact kW-class CO laser excited by transverse-RFdischarge.The discharge and output characteristics of the RF-excited CO laser were investigated experimentally.Six gas conditions (pressure, temperature, flow speed, CO-, N2-and 02-concentration) are chosen as the experimental parameters.The optimum values of them to maximize the output power are 50 Torr, 200 K, 17 m/s, 5 %, 12 % and 0.4 % respectively.The maximum output power obtained is 1.3 kW with the electrical conversion efficiency of 27 % and the slope efficiency of 39 %.

Spiking laser oscillation, which is often observed in solid-state lasers, in a flashlamp-pumped Cr,Tm:YAG laser was smoothed by insertion of a Ge crystalline plate in the laser cavity as a nonlinear optical limiting element. Although the laser efficiency was reduced more with the use of this Ge plate than with SHG crystals, Ge is expected to be used for low-cost and field-use systems because of its robustness.

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