Abstract
Coherent backscattering, also referred to as weak localization, is an exciting multidisciplinary phenomenon that appears in disordered systems of multiple coherent-wave scattering. Providing proper scattering conditions in (2 + 1) dimensional randomized photonic systems, we optically implement, observe, and analyse transverse coherent backscattering. Ensembles of disordered wave-guide structures are prepared by random-intensity nondiffracting writing entities according to the beam’s intensity distribution. The structure size of the induced potentials naturally define an effective mobility edge, and thus, we identify a crucial impact of the plane probe waves’ spatial frequency on the strength and shape of the spectral coherent backscattering signal. We additionally observe transverse elastic scattering as a precursor of weak localization. To testify the coherent character as a fundamental condition for coherent backscattering, we propose a scheme to continuously reduce the spatial coherence of the probe beam which directly reduces the degree of localization and coherent backscattering. With our experiments, we propose a testing platform that allows comprehensive examination of coherent backscattering with a broad set of preparation parameters and under uncritical laboratory conditions. Our results are directly transferable to more complex systems of disordered wave potentials, not being restricted to photonic systems.
Highlights
Wave scattering in a random potential under coherent conditions is naturally accompanied by coherent backscattering (CBS) and fosters weak localization
A controllable randomness of the light potential is essential to detect CBS. In this contribution we describe the preparation of ensembles of two-dimensional random photonic potential landscapes to experimentally observe and analyse CBS
Besides Anderson localization[26], scattering conditions are offered that lead to CBS
Summary
Wave scattering in a random potential under coherent conditions is naturally accompanied by coherent backscattering (CBS) and fosters weak localization. Its appearance is outlined briefly by the occurrence of particular waves for which the average probability to propagate exactly anti-parallely to the direction of incidence[1] is significantly increased This effect bases upon wave interference present in various systems where proper scattering conditions and sufficient long propagation distances are provided. Between strong and weak localization—commonly referred to Anderson localization[22] and coherent backscattering—, it is most important to find model systems in which a transition between both regimes and comparison to ballistic propagation can be adapted at will It has been shown in several recent works[23,24,25,26] that proper conditions can be created in optically induced randomized potential ensembles in order to observe strong transverse localization[27]. To identify the impact of coherence on this effect, we introduce a method to reduce the probe beam’s spatial coherence that directly implicates a decline of the observed CBS signal
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