Pulse slope may be more important than pulse length in photoacoustic wave generation: insights from an OR-PAM imaging experiment using a lab-made laser diode driver

From a series of optical-resolution photoacoustic microscopy imaging experiments performed using a lab-made laser diode driver, we found that although the pulse duration of the applied laser pulses was as long as 230 ns, it was still possible to acquire high-quality in vivo images with a sufficient signal-to-noise ratio, even when using a 25 MHz commercial high-frequency ultrasonic transducer. To interpret this interesting result, we performed additional experiments and consequently concluded that the slope of the rising or falling edge of an applied laser pulse may be a more critical factor than the overall pulse duration. In this paper, we present in vivo mouse ear imaging results acquired using both long and short pulses in a comparative manner as supporting evidence, along with the pulse profiles of the applied laser pulses.