Optical and acoustic observation of photodisruption in two liquid perfluorocarbons induced by nanosecond laser

Abstract

Photodisruption can be used to generate microbubble or microbubbles in vivo, thus has potential as an important tool in theranostics. However, high laser intensity and extremely short pulse length in femtosecond, and thus the high cost limit its wide applications. In the study, photodisruption induced by nanosecond laser pulse in two liquid perfluorocarbons (PFCs), perfluoropentane (PFP) and perfluorohexane (PFH), were realized and detected in optical and acoustic way to reveal the effective parameters for photodisruption. A confocal microscopic system was performed to record the bubble dynamics by high speed photography, and simultaneously the acoustic signal emitted during photodisruption. A 532 nm laser, with pulse duration of 3 ns and average power of 50 µJ, was focused to the cellulose tube where the laser, acoustic detection and microscopic imaging were aligned and PFCs were injected. Passive acoustic detection (PCD) was realized by a 1 mm needle hydrophone connected via a receiver amplifier to a high speed digitizer. The spectrum analysis and time-frequency analysis were used to show the acoustic characteristics of photodisruption in liquid PFCs. Then, the laser energy thresholds of photodisruption and the influences of ambient temperature on photodisruption were revealed. The bubble behavior mainly followed three patterns in PFP but two patterns in PFH. The difference among patterns was closely related with the ambient temperature. In acoustic detection, significant signals were recorded by PCD once photodisruption occurred in either PFP or PFH. The PCD signals of PFP and PFH showed difference in time-domain. However, their frequency spectrums were mainly distributed between 0–2 MHz and seemed without significant difference. The time-frequency analysis verified their difference in time-domain. The physical process of photodisruption was closely associated with both laser parameters and liquid properties. It was indicated that the thresholds for PFP and PFH were 43.33 µJ and 45 µJ, respectively. But the increasing ambient temperature was helpful to photodisruption in both PFP and PFH.