Focusing light by wavefront shaping through disorder and nonlinearity

Abstract

Wavefront shaping is a powerful technique that can be used to focus light through scattering media, which can be important for imaging through scattering samples such as tissue. The method is based on the assumption that the field at the output of the medium is a linear superposition of the modes traveling through different paths in the medium. However, when the scattering medium also exhibits nonlinearity, as may occur in multiphoton microscopy, this assumption is violated and the applicability of wavefront shaping becomes unclear. Here we show, using a simple model system with a scattering layer followed by a nonlinear layer, that with adaptive optimization of the wavefront light can still be controlled and focused through a scattering medium in the presence of nonlinearity. Notably, we find that moderate positive nonlinearity can serve to significantly increase the focused fraction of power, whereas negative nonlinearity reduces it. arXiv:1607.08105v2 [physics.optics]

Wave condensation with weak disorder versus beam self-cleaning in multimode fibers

“…Such a partially coherent few-mode interaction regime can be mastered by a fine tuning of the transverse profile of the laser excitation [67,90]. In the recent experiments [90] beam cleaning of many low-order modes has been reported owing to an ingenious feedback-induced adaptive profiling of the transverse wavefront phase of the coherent beam excitation (also see [91]). More precisely, owing to a feedback loop, the transverse wavefront phase of the injected beam is adjusted by an iterative procedure so as to force the beam to convergence toward a pre-established target mode at the fiber output.…”

Light scattering control in transmission and reflection with neural networks

“…While some methods that optimize a single mode can be very fast (for example 33.8 ms in [11]), this still results in a comparable correction time for a full field of view (of about 5 minutes for 96 × 96 pixels in this example). for example in nonlinear situations [77].…”

A comparative study of optimization algorithms for wavefront shaping

“…Wavefront shaping has been used in di®erent high-resolution imaging modalities such as optical coherence tomography (OCT),°uorescence microscopy, two-photon microscopy (TPM), and photoacoustic microscopy (PAM) to improve their resolution or penetration depth. 1,2 Wavefront shaping using computer-controlled spatial light modulators (SLMs) has been widely used in these modalities 1,[3][4][5][6][7][8][9][10][11] and hence, choosing an appropriate optimization algorithm for a particular modality or application is of prime importance.…”