Improving photoacoustic-guided optical focusing in scattering media by spectrally filtered detection.

We study the potential of photoacoustic guidance for light focusing through scattering samples via wavefront-shaping and iterative optimization. We experimentally demonstrate that the focusing efficiency on an extended absorber can be improved by iterative optimization of the high frequency components of the broadband photoacoustic signal detected with a spherically focused transducer. We demonstrate more than 12-fold increase in the photoacoustic signal generated by a 30 μm wire using a narrow frequency band around 60 MHz. By monitoring the speckle pattern evolution during the optimization process with a CCD camera, we experimentally confirm that such optimization leads to a smaller optical focus than what would be obtained by optimizing lower frequencies of the photoacoustic feedback.