Effect of laser pulse shaping on photoacoustic dosimetry in retinal models.

Photoacoustic sensing can be a powerful technique to obtain real-time feedback of laser energy dose in treatments of biological tissue. However, when laser therapy uses pulses with microsecond duration, they are not optimal for photoacoustic pressure wave generation. This study examines a programmable fiber laser technique using pulse modulation in order to optimize the photoacoustic feedback signal to noise ratio (SNR) in a context where longer laser pulses are employed, such as in selective retinal therapy. We have demonstrated with a homogeneous tissue phantom that this method can yield a greater than seven-fold improvement in SNR over non-modulated square pulses of the same duration and pulse energy. This technique was further investigated for assessment of treatment outcomes in leporine retinal explants by photoacoustic mapping around the cavitation-induced frequency band.