The pulse operation of a CO2 laser is commonly used in many applications. A feature of high power CO2 pulse lasers is the rotational line-hopping . The effect can create problems in some applications. It has been shown, that the line- hopping is responsible for the perturbations observed during the output pulse forming (see Fig. 1). It has been proved, that the subsequent of the laser signature is mapped on the laser output pulse profile. This effect has been used as a base for calculations of the laser tuning. In that way, observed and registered a line hopping sequence has been used as a measure of the refractive index changes. Additionally, the changes of the refractive index have been measured with the Mach-Zehnder interferometer. It allowed us to create a heuristic model of changes of both, temperature and pressure in the laser cavity in pulse regime of the laser plasma (Fig. 1). A simple arrangement for observing the pulse evolution of all oscillating spectral transitions contributing in the total shape of the output pulse has been designed. As shown, the jumps from line to line over the pulse duration form the sequence of lines, which is the subsequence of the static laser signature. Thus, the changes of the refractive index can be estimated by setting the static signature against the line hopping during the pulse operation of the laser. The elementary analysis of the detuning effect during the pulse operation based on a Gladstone-Dale formula linking a refractive index with the gas density has been presented. The experiment with the microphones placed in the laser cavity has been designed, to obtain a more precise picture of the behavior of the laser plasma in a pulse regime (Fig. 2). The registered acoustic signal has been associated with the changes of the plasma pressure. The experiment has been performed on the RF excited slab-waveguide laser with an unstable positive branch optical resonator. The experiment allowed observing the dynamic evolution of the pulse profile in time and spectrum, and the dynamic evolution of the laser plasma parameters (pressure, temperature) in time, as well. Moreover, it has been proved, that careful selection of the laser resonator length can inhibit the laser from line-hopping for cw and pulsed laser, as well . It can be helpful in designing a single frequency CO2 laser pulse operation, necessary in such a laser device like a lidar.
© 2003 Optical Society of AmericaPDF Article