Pulsed CO 2 laser oscillator excited by microwaves

Abstract

ABSTRACT The optimum excitation conditions for pulsed C02 laser oscillation excited by microwaves are investigated to achieveoscillation with a short pulse width at a high repetition rate. The excitation conditions are optimized as follows;1) by evaluating the decay time of excited N2 molecule population density to optimize the gas mixture, and2) by evaluating the discharge stability and the laser output waveform to optimize the magnetron drive conditions.We have developed a new coaxial fast gas flow pulsed C02 laser oscillator excited by microwaves, which producespulses output with a rise time of less than 5usec rise-time and a l/e-fall time of 3O sec at a maximum repetition rate of 5kHz.It is also possible to modulate the output power and the pulse waveform at high speed. The oscillator is currently beingtested for application to a laser drilling system for printed wired boards.Keywords: C02 laser, pulse laser, microwave, drilling. 1. INTRODUCTION Recently, besides cutting sheet metals, the applications of C02 lasers such as drilling, marking, scribing and weldingon various electronic devices are rapidly increasing. The C02 laser oscillator used for processing electronic devices is re-quired to possess a higher pulse repetition rate and a shorter pulse waveform width, as well as various modulated output wave-forms, compared with a conventional C02 laser. Many energy input techniques have been developed to realize these char-acteristics. Since a magnetron can respond quickly to its driving current, the discharge by microwaves can be easily pulsatedat high speed. Therefore, the excitation by microwaves is expected to be a suitable approach for pulsed C02 laser oscilla-tion.This paper presents the results of our investigation for the optimization of the pulsed oscillator for applications to proc-ess electronic devices. The schematic structure of the microwave-excited coaxial fast gas flow C02 laser oscillator1' 2)