Lock-in detection of photoacoustic feedback signal for focusing through scattering media using wave-front shaping.

Wave-front shaping techniques enable focusing and imaging through scattering media. Unfortunately, most approaches require invasive feedback inside or behind the sample, or use of spatial correlations (memory effect) limiting the application to specific types of samples. Recent approaches overcome these limitations by taking advantage of acoustic waves via the photoacoustic (PA) effect or via photon tagging. We present a fully analog signal processing lock-in scheme for PA detection to improve focusing through scattering media and to efficiently extract nonlinear photoacoustic signals towards wave-front optimization. Our implementation improves PA feedback performance in terms of SNR, speed, and resolution.