Fig. 1. Typical structures of piezoelectric ultrasonic transducers and different kinds of laser-generated ultrasound transducers. (a) Typical structure of piezoelectric ultrasonic transducer^[96]; (b) laser-generated ultrasound transducer based on fiber with scale bar of 50 μm^[80]; (c) structural diagram of omnidirectional laser-generated ultrasound transducer^[110]; (d) omni-directional laser-generated ultrasound transducers used to generate omni-directional ultrasound^[110]

Fig. 2. Frequency domain distributions of laser with different pulse widths

Fig. 3. Influence of thickness of laser-generated ultrasound transducer on laser-generated ultrasound pulse^[59]. (a) Schematics of laser acting on laser-generated ultrasound transducers with different thicknesses; (b) schematics of determining laser-generated ultrasound pulses of laser-generated ultrasound transducers with different thickness by convolution integral

Fig. 4. Time domain and frequency domain information under different laser pulse widths and material thicknesses. (a) Schematic of laser-generated ultrasound system^[115]; (b) frequency domain distribution of 10 μm diameter black microsphere under excitation with different laser pulse durations^[115]; (c) time domain distribution of laser-generated ultrasound^[115]; (d) reconstructed image of 10 μm diameter microsphere obtained by laser-generated ultrasound method^[115]; (e) sound pressures and spectra of samples with different deposition time (10, 30, 120 s) obtained under low laser energy input^[89]

Fig. 5. Distribution of sound field of laser-generated ultrasound transducer. (a) Simulated sound field distribution generated by planar ultrasound^[72]; (b) experimental sound field distribution generated by planar ultrasound^[119]; (c) simulated sound field distribution generated by focusing ultrasound^［54］; (d) schematic of focusing ultrasonic transducer generation^[75]; (e) sound field distribution of omnidirectional ultrasound^[124]

Fig. 6. Transcranial stimulation in vitro by OFUS^[75]. (a) Schematic of transcranial stimulation in vitro; (b) representative images of neurons before and after transcranial stimulation with scale bar of 50 μm; (c) averaged calcium response trace of transcranial OFUS stimulation; (d) statistics of threshold pressure of direct and transcranial stimulation in single cycle

Fig. 7. Imaging by ultra-wide bandwidth AO-IVUS^[54]. (a) Imaging diagram of vessel wall by AO-IVUS; (b) power spectrum of AO-IVUS catheter ultrasound response; (c) 2D cross-sectional image acquired by AO-IVUS; (d) 3D ultrasound data of arterial wall by rotation-pullback scan with AO-IVUS

Fig. 8. Micro-scale fragmentation of solid materials by LGFU^[109]. (a) Model of kidney stone with scale bar of 4 mm; (b) single micro-hole on polymer film produced by single LGFU pulse with scale bar of 20 μm; (c)(d) high-speed microscopic images of fragmentation process on polymer-coated glass substrate

Fig. 9. Targeted cell removal by LGFU with scale bar of 520 mm^[95]. (a) Cultured ovarian cancer cells (SKOV3) before ultrasound exposure; (b) selective removal of single cell after LGFU exposure; (c) cellular interconnection is severed when LGFU spot is moved to black dot region

Fig. 10. Locating and removal of tumor using FOG and AR system^[124]. (a) Principle diagram; (b) photograph of compact integrated system on cart; (c) visualization of FOG tip in breast of human sample

Fig. 11. Fiber optoacoustic guide for tumor localization with sub-millimeter accuracy^[111]. (a) Photographs of fiber optoacoustic guide, zinc oxide nanoparticles, and epoxy; (b) signal-to-noise ratio of generated optoacoustic signal from FOG tip at different angles; (c) representative optoacoustic signal waveform recorded at 8 cm away from FOG tip in forward direction; (d) frequency spectrum of representative optoacoustic signal waveform after normalization of detector response; (e) signal-to-noise ratio of generated optoacoustic signal after passing chicken breast tissues with different thicknesses

Fig. 12. Shadowgraph images at air-water interface with scale bar of 100 μm^[164]. (a) Water micro-jets; (b) bubbles