Analysis of the optoacoustic signals generated with a tone-burst of nanosecond duration pulses

Biomedical optoacoustic (photoacoustic) imaging is generally performed with short laser pulses with durations in the order of a few nanoseconds. This enables maximizing the conversion efficiency of optical energy into acoustic (ultrasound) energy when light is absorbed in biological tissues. The generated ultrasound waves are generally very broadband, with typical frequency spectra ranging from tens of kHz to tens of MHz. Most ultrasound transducers used for the detection of optoacoustic signals have a finite detection bandwidth, in a way that they are not optimal for the acquisition of optoacoustic signals generated with a single pulse. In this work, we analyze a narrowband excitation approach based on a tone-burst consisting of multiple equally-delayed short pulses. We compare the power spectral density of the signals generated with a tone-burst with those generated with a single pulse having the same energy under safety exposure limits. We further analyze the performance of tone-burst excitation when non-linear effects take place. Specifically, we consider non-linearities associated to temperature increase and to optical absorption saturation.