Ultrafast Dephasing of Light in Strongly Scattering GaP Nanowires

Abstract

We demonstrate ultrafast dephasing in the random transport of light through a layer consisting of strongly scattering GaP nanowires. Dephasing results in a nonlinear intensity modulation of individual pseudomodes which is 100 times larger than that of bulk GaP. Different contributions to the nonlinear response are separated using total transmission, white-light frequency correlation, and statistical pseudomode analysis. A dephasing time of 1.2±0.2 ps is found. Quantitative agreement is obtained with numerical model calculations which include photoinduced absorption and deformation of individual scatterers. Nonlinear dephasing of photonic eigenmodes opens up avenues for ultrafast control of random lasers, nanophotonic switches, and photon localization. PACS numbers: 42.25Bs, 78.67Uh The appearance of an interference pattern after transport of coherent light through a multiple scattering medium is the result of coherent summation of thousands of light paths with random phases. In recent years, new methods have been developed to exploit the coherent aspects of diffuse light transport for imaging [1,2]. Classical waves, like light or sound, provide unique opportunities to study mesoscopic wave transport, such as localization, in the absence of many-body interactions usually found for electrons [3,4]. Coherent light scattering has recently lead to exciting new directions of research, such as coupling of localized states with quantum emitters [5], transverse localization, and combined effects of localization and nonlinearity [6].Although the lack of many-body interactions makes phase coherence generally more robust for optical waves than for electrons, several dephasing processes can influence the transport of light, such as magnetic fields, scattering from moving particles, and polarization effects [7][8][9]. The time required for electrons or photons to loose their coherence due to inelastic collisions is known in the theory of electronic conductance as the phase breaking time [10]. While for electrons phase breaking (decoherence) processes have only been measured indirectly through changes in the conductivity with temperature, dephasing can be observed directly for optical waves by the changes in speckle pattern [11], which is used in diffusing wave spectroscopy [12].In this Letter, we demonstrate a new regime of reversible dephasing in a random medium on ultrafast time scales. The ultrafast dephasing takes place a million times faster than other dephasing mechanisms such as Brownian movement, opening up new applications in ultrafast control of random lasers, quantum emitters, and localization phenomena. The material under study consists of a layer of semiconductor nanowires, which are important for novel applications in optoelectronics and photovoltaics [13][14][15]. We have recently demonstrated that these semiconductor nanowires form one of the most efficient light trapping layers available to date [16]. Here, we combine these favorable scattering properties with the intrinsic nonlinearity of the semiconducto...

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