Fig. 1. (a) Photograph of the LD, (b) schematic diagram of the stabilization drive circuit of pulse LD, (c) measured pulse width of the LD where the trigger signal and pulse driving signal are delayed by 120 ns, and (d) exported energy stability test generated by each pulse of the excitation source.

Fig. 2. (a) The left is the photograph of system, and the right is the schematic diagram of the LD-OR-PAM system, (b) relationship of spot size and the distance between the reflective objective and spherical lens in the LD-OR-PAM system, and (c) the photoacoustic amplitude and energy density distribution of the sample absorption source along the z axis.

Fig. 3. (a) Reconstructed image of a USAF (4-1) and (b) assessed lateral resolution of the LD-OR-PAM system along the dotted line of (a).

Fig. 4. (a) Photoacoustic image of five carbon fibers and (b) photoacoustic image of crossed hair strands.

Fig. 5. (a) Photograph of subcutaneous microvascular networks in a mouse ear, (b) the acquired 2D photoacoustic image of the subcutaneous microvascular structure in vivo, and (c) the vessel diameter at the dotted line in (b) is estimated.

Fig. 6. (a) Photoacoustic image of another subcutaneous microvascular structure and (b) photoacoustic image of the same area as in (a) but at different depths.