Hand-held laser for miniature photoacoustic microscopy: triggerable, millimeter scale, cost-effective, and functional

Miniaturization of photoacoustic microscopy (PAM) to portable and wearable levels requires special design of scanning, detection, acquisition, and excitation units. Now the first three can be minimized to gram and millimeter levels, but the excitation sources usually remain bulky and also face different challenges, including low pulse energy, wide pulse width, limited wavelength, or high cost. Here, we propose a high-performance laser source specially designed for a miniature PAM system, that is, the pulse-pumped passively Q -switched solid-state laser (PQS-SSL). Its kilohertz repetition rate, nanosecond pulse width, microjoule pulse energy, and UV to NIR spectra are exactly within the requirements of functional PAM imaging, together with the merits of millimeter scale and low cost, originating from the all-crystal-based configuration. The pulsed pump technique empowers the laser with frequency lock and trigger-in ability for system synchronization, overcoming the conventional free-running drawbacks, and the senior multi-pulse pump is also feasible to further compress the laser size and cost. We showcase its PAM performance on the USAF1951, carbon fiber, zebrafish, and lipid (wavelength extension to ∼1.2 μm ). The novel, to our knowledge, pulse-pumped PQS-SSL is not only promising for general PAM, but also paves the way to develop miniature PAM systems, such as hand-held or brain-wearable modalities.