Coded Photoacoustic Doppler excitation with near-optimal utilization of the time and frequency domains

We propose and experimentally demonstrate a new photoacoustic (PA) excitation and analysis method which achieves an almost complete utilization of the available time and frequency windows. The method, which enables spectral and spatial characterization of flow, is based on interleaving tens of tone-burst sequences at equally spaced frequencies. Depending on the application, the interleaved signals can be generated by a single optical source or by multiple sources, possibly at different wavelengths. Upon reception, the responses corresponding to the different tone-burst sequences are spectrally de-multiplexed. As demonstrated in the current work, this method can be used to improve the SNR of PA systems based on optical sources with limited peak power. Alternatively, if the interleaved excitation signals are at different wavelengths, the PA responses can be used for multispectral characterization of the medium.