A pulsed excitation of the laser plasma in gas lasers creates an acoustic wave in the laser reservoir. It changes thermodynamic parameters of the laser plasma in the laser cavity like pressure, and temperature, as well, and consequently it changes the density of the laser plasma, or, in other words, the refractive index of the laser medium. Tuning laser frequency during the pulse developing is observed as a result. The measurements of the pressure, temperature, and refractive index changes in an RF pulsed excited CO2 slab-waveguide laser are purposes of the work. The pressure changes are measured with calibrated microphones situated close to the laser plasma. The temperature changes are calculated via measured refractive index characteristics, and simple formulas linking the refractive index with the gas density. The picture of the acoustic wave propagation in the laser cavity is presented. The obtained results give the picture of the laser plasma behavior during the pulsed excitation. It leads to a single frequency pulsed laser operation design.