Controllable dual-pulse laser directly for nonlinear photoacoustic microscopy

Nonlinear photoacoustic microscopy (PAM) usually requires dual-pulse excitation. Current approaches to realize dual-pulse laser train are indirect, mainly based on beam combinations. Here, we report a compact (∼5-cm-long cavity) laser source that directly outputs controllable nanosecond (∼34 ns) dual pulses, including the tunability of repetition rate (0-20 kHz), time delay (5-30 µs), and relative intensity ratio (20-500%), perfectly matching the requirements of nonlinear imaging in PAM. The single pulse energy is achieved up to ∼95 µJ. We showcase the nonlinear PA performance with this laser source in typical Grüneisen-relaxation-based applications with imaging contrast enhanced by 8 dB. The promising performance indicates that this dual-pulse laser can readily be applied to nonlinear PAMs, especially for portable applications.