Under the extreme condition of the scattering length being much shorter than the wavelength, light transport in random media is strongly modified by mesoscopic interference, and can even be

We demonstrate a new concept for reconfigurable nanophotonic devices exploiting ultrafast nonlinear control of shaped wavefronts in a multimode nanomaterial consisting of semiconductor nanowires. Femtosecond pulsed laser excitation of the nanowire mat is shown to provide an efficient nonlinear mechanism to control both destructive and constructive interference in a shaped wavefront. Modulations of up to 63% are induced by optical pumping, due to a combination of multimode dephasing and induced transient absorption. We show that part of the nonlinear phase dynamics can be inverted to provide a dynamical revival of the wavefront into an optimized spot with up to 18% increase of the peak to background ratio caused by pulsed laser excitation. The concepts of multimode nonlinear switching demonstrated here are generally extendable to other photonic and plasmonic systems and enable new avenues for ultrafast and reconfigurable nanophotonic devices. Light: Science & Applications (2014) 3, e207; doi:10.1038/lsa.2014.88; published online 26 September 2014Keywords: nanophotonics; nanowires; nonlinear optics; reconfigurable; ultrafast; wavefront shaping INTRODUCTION Many of the available photonic technologies are based on perfectly regular, ordered structures such as waveguides, photonic crystals and metamaterials. There is, however, an increasing interest to exploit the additional degrees of freedom offered by aperiodic or disordered designs. [1][2][3][4] One way of controlling the flow of coherent energy transfer in such a medium with high efficiency is through optimization of the specific arrangement of the scatterers. 5,6 Exciting new techniques have emerged based on shaping of the light field itself to match a given scattering configuration, either through time reversal 7,8 or iterative schemes. 9,10 The method of wavefront shaping is based on the general concept that the transmission through any medium can be described by a matrix which connects all ingoing and outgoing degrees of freedom. In principle, knowledge of the transmission matrix, 11,12 along with an ability to completely control the incident light, 10 would allow the selection of any desired output, turning an opaque medium into a versatile optical element. Next to the interest for biomedical imaging, 13-15 wavefront shaping shows promise for reconfigurable optical elements [16][17][18][19][20] and control of random lasers. 21 While initial work concentrated on monochromatic continuous-wave radiation, focusing through opaque scattering media has also been achieved using ultrashort pulses 22,23 and polychromatic light. 24 Here, we demonstrate both destructive and constructive switching of a shaped wavefront on ultrafast time scales through nonlinear optical excitation of the scattering medium. With the rapid development of applications exploiting wavefront shaping, active control of such shaped fields is of great interest. The principle is illustrated in Figure 1a. Wavefront shaping amounts to aligning the phasors resulting from independent light paths in th...

We experimentally observe the spatial intensity statistics of light transmitted through threedimensional isotropic scattering media. The intensity distributions measured through layers consisting of zinc oxide nanoparticles differ significantly from the usual Rayleigh statistics associated with speckle, and instead are in agreement with the predictions of mesoscopic transport theory, taking into account the known material parameters of the samples. Consistent with the measured spatial intensity fluctuations, the total transmission fluctuates. The magnitude of the fluctuations in the total transmission is smaller than expected on the basis of quasi-one-dimensional (1D) transport theory, which indicates that quasi-1D theories cannot fully describe these open three-dimensional media.

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