Optoacoustic system based on 808-nm high energy short pulse diode laser stacks

In the last few decades, high power diode lasers (HPDL) have been introduced as alternative laser sources for optoacoustic imaging (OAI), due to their high repetition rates (a few kHz) for fast OA image acquisition, lower cost and size if compared to solid state lasers. Nevertheless, their drawbacks consist in a low energy per pulse (mu J) and a relatively highly divergent beam that needs collimation optics. At this purpose, the employment of diode laser stacks significantly increases the energy per pulse up to several mJ. The diode laser stacks imply a big challenge if compared to single emitters for several reasons. Firstly, they need very demanding electronic requirements, as forward voltages and currents of several tens of volts and hundreds of amperes, respectively. Secondly, their highly divergent beam profile requires precise collimation by means of fast axis and slow axis collimation. In this work, we show an 808-nm diode laser stack driven with 17 V and similar to 200 A by a low-cost current driver for emitting pulses of 1 mJ at 1 kHz. Particular emphasis will be attributed to the design of the high current pulses driver and the optics employed to collimate and after focus the beam in a spot. The light spot will be applied to an ink inclusion hosted in turbid phantom. We demonstrate that our system is able to generate appreciable OA signals in turbid phantoms. This aspect represents a novelty in OAI systems because it is demonstrated that HPDL sources can efficiently replace solid-state lasers.