Ultrasensitive broadband photoacoustic microscopy based on common-path interferometric surface plasmon resonance sensing

Ultrafast and sensitive response of surface plasmon polaritons to the ultrasonically-modulated changes in refractive index of the water allows photoacoustic impulses to be measured using surface plasmon resonance (SPR) sensors. However, the sensing modalities always suffer from either low sensitivity or instable signal output, possibly precluding imaging recovery. By exploiting that pressure transients can substantially produce phase shift in p-polarized optical reflection but have no impact on s-polarized component in SPR sensing, we develop a common-path interferometric SPR sensor for photoacoustic measurement, in which time-varying light interference between photoacoustically-perturbed p-polarized beam and its orthogonal s-polarized component of a single interrogation laser is monitored. Such configuration retains optimum photoacoustic measurement with concurrent very stable signal output, high sensitivity (noise-equivalent-pressure sensitivity of ∼95.6 Pa), and broad bandwidth (∼173 MHz). Volumetric microvascular imaging from mouse ear in vivo is obtained, suggesting that the novel sensing approach potentially advances biomedical photoacoustic applications.