Abstract
We report optical measurements of the spectral width of open transmission channels in a three-dimensional diffusive medium. The light transmission through a sample is enhanced by efficiently coupling to open transmission channels using repeated digital optical phase conjugation. The spectral properties are investigated by enhancing the transmission, fixing the incident wavefront and scanning the wavelength of the laser. We measure the transmitted field to extract the field correlation function and the enhancement of the total transmission. We find that optimizing the total transmission leads to a significant increase in the frequency width of the field correlation function. Additionally we find that the enhanced transmission persists over an even larger frequency bandwidth. This result shows open channels in the diffusive regime are spectrally much wider than previous measurements in the localized regime suggest.
Highlights
Many well-known effects in wave transport result from interference and cannot be described by diffusion theory
Open channels were observed in optics by wavefront shaping to selectively couple light into them [16,17,18], and by transmission matrix measurements in microwave and acoustical waveguides [19, 20]
A recent microwave experiment in quasi-1D geometry shows that in the Anderson localized regime, where transport is dominated by a single quasimode [31], the open transmission channels are spectrally narrower than the average channel width, inhibiting applications [23]
Summary
Many well-known effects in wave transport result from interference and cannot be described by diffusion theory. A striking interference phenomenon is the existence of highly transmitting channels in multiple scattering systems, which allow unity transmittance through arbitrarily thick non-absorbing diffusive layers. These highly transmitting channels, usually called “open channels”, were initially predicted for electrons [6,7,8,9,10], while later the theory was generalized to other waves [3, 11, 12]. A recent microwave experiment in quasi-1D geometry shows that in the Anderson localized regime, where transport is dominated by a single quasimode [31], the open transmission channels are spectrally narrower than the average channel width, inhibiting applications [23]. We find that in our 3D diffusive samples the transmission enhancement is spectrally broader than the well known C1 speckle correlation function [34] that represents the channel average
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