Study of cavitation noise without subharmonics

The evolution of the cavitation noise (CN) spectra in the field of a focusing emitter with an increase in the intensity of ultrasound (US) was studied. Spectra without subharmonics $f_0/2$ were recorded for the first time, where $f_0$ is the frequency of the ultrasound generating cavitation. Such a spectrum is observed in partially degassed water at a high duty cycle of ultrasonic pulses. The threshold for the appearance of sonoluminescence (SL) coincides with the threshold for the appearance of the frequency $f_0/2$ in the CR spectrum. In a pulsed field at an ultrasonic intensity much higher than the cavitation threshold, the SL intensity increases with an increase in the duty cycle of the pulses, while the intensity of the $f_0/2$ line in the CS spectrum decreases.