In recent years, photoacoustics has attracted intensive research for bothanatomical and functional biomedical imaging. However, the physical interactionbetween photoacoustic generated endogenous waves and an exogenous ultrasoundwave is a largely unexplored area. Here, we report the initial results aboutthe interaction of photoacoustic and external ultrasound waves leading to amicro-Doppler photoacoustic (mDPA) effect, which is experimentally observed andconsistently modelled. It is based on a simultaneous excitation on the targetwith a pulsed laser and continuous wave (CW) ultrasound. The thermoelasticallyinduced expansion will modulate the CW ultrasound and leads to transientDoppler frequency shift. The reported mDPA effect can be described as frequencymodulation of the intense CW ultrasound carrier through photoacousticvibrations. This technique may open the possibility to sensitively detect thephotoacoustic vibration in deep optically and acoustically scattering medium,avoiding acoustic distortion that exists in state-of-the-art pulsedphotoacoustic imaging systems.
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