Acoustics of the RF pulsed excited CO 2 laser discharge

Abstract

The paper presents studies on influence of the gas laser cavity shape on an acoustic wave created in the cavity. Results of investigations on an RF excited CO 2 slab-waveguide laser are shown. As is demonstrated, rapid changes of a laser plasma pressure appear in the laser gas mixture as a consequence of the pulsed RF discharge in the laser. The pressure variations create an acoustic wave propagated in the laser chamber, and involve changes of the refractive index of an excited plasma. As a result, the frequency of the optical wave emitted by the laser changes -a "line hoppings" effect appears. In the case of the slab-waveguide laser an acoustic wave propagates in a closed space -the laser reservoir, that is a special kind of an acoustic resonator. As known, a material from which cavity is made, a shape of the walls and their mutual position are significant for a wave propagation. In the experiment, the walls of the chamber are made of aluminum, so it is a very reflecting area. More, the walls are parallel that is an advantageous condition for creating standing waves. The aluminum wedges were used in the experiment to change the geometry of the reservoir. The influence of pulse duration time on the acoustic signal is investigated.