Haruhiko Nagai

Development of a 2-kW XeCl laser with a surface corona preionization scheme and a spiker-sustainer circuit

A maximum average power of 2.1 kW is demonstrated in a XeCl laser with an efficiency of 3.0% at a repetition rate of about 800 Hz. The 2-kW laser has a discharge region of 4 cm in gap length, 2.5 cm in discharge width, and an effective discharge length of 3 m with a resonator length of 5.2 m. A reverse voltage mode spiker-sustainer circuit makes it possible to apply a steep voltage rise of nearly 1000 kV//spl mu/s across the main discharge electrodes and to supply excitation energy effectively into the discharge region. The control of the preionization timing before the initiation of the spiker circuit is found to be indispensable in maintaining a homogeneous volume discharge under high repetition-rate operation. These techniques enable the laser to realize a long pulse excitation under the high repetition-rate operation conditions. The excitation process is analyzed by computer-model simulation. The application of a cascaded stable resonator has improved the average power by 6% compared with that of a conventional stable resonator. >

Improvement of a 2 kW XeCI laser with a complex resonator

thyratron, a MOS Assisted Gate-triggered Thyristor (MAGT) was specially designed, where high-speed MOS structure is combined with a high power thyristor. An MAGT chip has excellent capacities such as the maximum anode voltage V, = 2.5 kV, the peak current density I, = 132 kA/cm* and the current rise time rate 142 kA/us/cm2. In a unit, 32 MAGTs were connected in series for high voltage operation. The semiconductor switch contains the MAGT unit and a low loss 1-stage MPC. The voltage and current rise time of the switch are equivalent those of a typical thyratron. The characteristics of XeCl laser oscillation were investigated, using thyratron power supply only. It was found that the discharge stability in HRR operation depends on the Xe contents dominantly. We determined the gas mixture ratio of Xe/ HCl/He = 0.53/0.09/177 kPa experimentally, referring to numerical calculation. For investigating the compatibility of the semiconductor switch to the thyratron, we equipped the laser chamber with the hybrid power supply consisted of the semiconductor switch and thyratrons. Figure 2 show the average laser power vs. repetition rate. The power of 0.51 kW is obtained at 5 kHz with 7 thyratrons. In the hybrid power supply, the power is increased to 0.56 kW with the MAGT unit working at 25kV-300A. The increasing ratio of the power is the same value as the length ratio of the discharge for the switch to thyratrons. It suggests that the laser gas is excited effectively by the switch. Moreover, we tried to excite the laser gas using the semiconductor power supply only. The discharge and optical resonator lengths were shorten according to the peak current capacity of the switch. The stable lasing with an average power of 11 W is obtained at 1 kHz. The laser power is the same value as that obtained with one thyratron. In conclusion, an average power of 0.56 kW was attained at 5 kHz with the hybrid power supply. Also the stable lasing with 11 W was confirmed at 1 kHz