Dual-wavelength, nanosecond, miniature Raman laser enables efficient photoacoustic differentiation of water and lipid

Functional photoacoustic microscopy (PAM) requires laser sources with multiple wavelengths targeting abundant substances, where lipid and water are important components of living organisms. Here, we propose to use a single compact dual-wavelength passively Q-switched solid-state laser as the excitation source to directly achieve PA differentiation of water and lipid simultaneously. The main contribution of our work is to use the excitation difference under 1064- and 1176-nm lasers for mapping water and lipid in PAM, respectively. Meanwhile, the miniature structure (cavity size: ∼10 × 10 × 5.5 mm3) of the laser source is not only promising for portable applications but also benefits the PA-desired nanosecond (<2 ns) laser pulse establishment. Our technique is confirmed by efficient PA imaging of water and lipid in biological tissues at high spatial resolution and improved sensitivity. This laser provides a novel and low-cost imaging source for PAM to track changes in water and lipid distribution.