An Optical Fiber Ultrasonic Emitter Based on the Thermal Cavitation Effect

In this study, we have developed an optical fiber ultrasound emitter based on the thermal cavitation effect. A tube filled with a highly absorptive liquid is sealed at the end of an optical fiber pigtail. A continuous-wave laser is transmitted through the fiber, heating the highly absorptive copper salt solution near the fiber end face to its spinodal limit. Using a single-mode fiber, we achieved ultrasound pulses with an amplitude of 330 kPa and a repetition rate of 4 kHz in the frequency range of 5–17 MHz, and a bandwidth of 12 MHz was obtained by using a low laser heating power of 52 mW at a wavelength of 974 nm. This optical fiber ultrasound emitter features a simple fabrication process, low cost, and low optical power consumption. Its flexible design allows for easy integration into medical devices with small dimensions and makes it suitable for non-destructive testing in confined spaces.