Reduction of two-photon holographic speckle using shift-averaging.

Holographic speckle is a major impediment for the emerging applications of multiphoton holographic projection in biomedical imaging, photo-stimulation and micromachining. Time averaging of multiple shifted versions of a single hologram ("shift-averaging") is a computationally-efficient method that was recently shown to deterministically eliminate holographic speckle in single-photon applications. Here, we extend these results and show, computationally and experimentally, that in two-photon holographic excitation shift-averaging also reduces holographic speckle better than "random" averaging of multiple calculated holograms.