Fig. 1. Pulse-pumped PQS-SSL. (a) Illumination requirements and types of light sources for PAM. Comparison of AQS- and PQS-SSL. (b) Comparison of the lasing process between CW/QCW-pumped and pulse-pumped PQS-SSL. (c) Control of the output laser under the modulation of pump duration time (T) and pump power (P) in pulse-pumped PQS-SSL. (d) Configuration of pulse-pumped PQS-SSL-based PAM imaging system. f, modulation frequency; L, lens; M, mirror. (e) Photo of the pulse-pumped PQS-SSL in hand.

Fig. 2. Frequency lock in pulse-pumped PQS-SSL. Lasing performance (a) under the modulation of pump power while keeping a constant pump duration, (b) under the modulation of pump duration while keeping a constant pump power, and (c) under the modulation of both the pump power and duration while keeping a constant pump energy. (d)–(f) PRR control of the output laser, including (d) pump beam modulation, (e) pump train, and (f) laser pulse train.

Fig. 3. Laser characteristics. (a) Output laser pulse train at the PRR of 20 kHz. (b) Histogram of 1000 laser pulses. (c) Frequency spectra of pulse and CW-pumped PQS-SSLs. (d) Power stability of pulse and CW pumped PQS-SSLs over 2 h. (e) Output power, PW, and PE at different PRRs. (f) Laser pulse profile at PRR of 20 kHz. (g) Beam quality factor (M2) and beam profile (Visualization 1).

Fig. 4. Multi-pulse pump. (a) Multi-pulse pump accumulation process. (b) Multi-pulse pump for PRR tunability. (c), (d) Comparison of pump power requirements (c) and output power (d) for single-pulse and multi-pulse pump at the same PRR (Visualization 2).

Fig. 5. Pulse-pumped PQS-SSL for PAM. (a) Diagram of the PAM system with pulse-pumped PQS-SSL. RM, reflecting mirror; L, lens; Obj., objective; UT, ultrasound transducer; RFA, radio-frequency amplifier; LPF, low-pass filter; OSC, oscilloscope; PC, personal computer. (b) Lateral and (c) axial resolution of the PAM system. (d) Excited PA signal over 10 ms under the 20-kHz laser excitation. (e) Statistical distribution of intensities for 1000 PA signals. (f) PA image of zebrafish. Scale bar: 400 μm. (g) PA images of USAF1951 at different laser PRRs (10, 15, and 20 kHz). Scale bar: 40 μm. (h) PA image of carbon fiber. Scale bar: 40 μm.

Fig. 6. Functional PAM and Raman-shifted wavelength for lipid. (a) Optical absorption spectra of typical components in tissues, including DNA [21]; RNA, glucose [2]; HbR, HbO2, water [22]; lipid [23]. (b) Output laser spectrum after Raman frequency shift with YVO4. (c) Photo of beef slice. (d) PA image of beef slice.