Spectrum of shock waves produced by an optical discharge at a high laser-pulse repetition rate

The acceleration of a plasma jet by an optical pulsating discharge is studied. The optical discharge generated periodic shock waves or shock waves combined in periodic trains. For a pulse repetition rate f > 50 kHz, the line at frequency f dominated in the spectrum of periodic waves. The spectrum of trains following with the frequency F₀ << f contained an ultrasonic component and a low-frequency component. The trains produces a strong acoustic effect. The average power of the waves amounted to 160 W, and the conversion efficiency of laser radiation to shock waves was ~10% – 25%.