High-repetition-frequency short pulses in a VHF discharge-excited slab-type carbon dioxide laser using an ultrasonic vibrator

We propose a novel method for producing high-repetition-frequency short pulses with a halved confocal configuration consisting of an unstable concave-convex resonator in a very high frequency (VHF) discharge-excited slab-type carbon dioxide laser. This method utilizes a fully reflective concave mirror with variable curvature which can be controlled by a piezoelectric device. In general, slab lasers are modulated directly by varying the pulse voltage. However, because plasma fluctuation occurs at the pulse transitions, the repetition frequency is less than 10 kHz and the minimum pulse width is 1 mus. On the other hand, in our method there is no disturbance of the plasma, because the power source is not modulated. There is also little mechanical constraint, because we use a piezoelectric device. As a result, pulse shortening with a high repetition rate is possible. The pulse shape is well reproduced by a three-level rate equation. The mechanism of the method involves changes in ejection efficiency with periodic variation of the radius of curvature of the mirror. Good agreement between observations and calculations was also obtained for the peak power and the pulse width. In this paper we compare measurements with calculations. The possibility of achieving high repetition rate oscillation and pulse shortening by this method is examined. The results confirm the possibility of achieving a repetition frequency between 1.4 kHz and 170 kHz. The shortest pulse width that can be achieved is 160 nanoseconds. (C) 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(3): 1-7, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10127.