Overdriven laser diode optoacoustic microscopy.

Laser diodes are small and inexpensive but don't afford the pulse energy and beam profile required for optoacoustic (photoacoustic) microscopy. Using two novel modulation concepts, i.e. overdriving continuous-wave laser diodes (CWLD) and frequency-wavelength multiplexing (FWM) based on illumination pulse-trains, we demonstrate concurrent multi-wavelength optoacoustic microscopy with signal-to-noise ratios of > 17 dB, < 2 µm resolution at repetition rates of 1 MHz. This unprecedented performance based on an adaptable trigger engine allowed us to contrast FWM to wavelength alternating acquisition using identical optical components. We showcase this concept's superiority over conventional optoacoustic microscopes by visualizing vascular oxygenation dynamics and circulating tumor cells in mice. This work positions laser diodes as a technology allowing affordable, tunable, and miniaturizable optoacoustic microscopy.