Control of Bubble Formation at the Optical Fiber Tip by Analyzing Ultrasound Acoustic Waves

The problems of controlling the processes of generation of acoustic waves and microbubbles at the optical fiber tip of moderate-power surgical lasers with wavelengths of 1.9 µm and 0.97 µm using active and passive acoustic methods are considered. It is shown that microbubbles of various sizes can be detected with an ultrasound method, in which the interaction area is recorded simultaneously at two frequencies. By measuring noise with a receiving transducer of an ultrasonic locator, we determine the frequency range of the acoustic signals occurring when large diameter bubbles, including gas-vapor bubbles, collapse. Model experiments are conducted to detect noise and bubbles in water and in a water-saturated 1.5% agarose phantom at various laser powers with an optical fiber tip having a strongly absorbing coating.