Dynamic and spectral properties of transmission eigenchannels in random media

TL;DR

This paper investigates how transmission eigenchannels in random media behave dynamically and spectrally, revealing their mode composition and how they can be controlled for efficient wave propagation in complex systems.

Contribution

It provides new insights into the temporal and spectral properties of transmission eigenchannels and demonstrates experimental control over mode excitation in random media.

Findings

Lower-transmission eigenchannels respond more quickly to pulses.

Eigenchannels are correlated over a broad frequency range.

Modal analysis explains the dynamic and spectral behavior of eigenchannels.

Abstract

The eigenvalues of the transmission matrix provide the basis for a full description of the statistics of steady-state transmission and conductance. At the same time, the ability to excite the sample with the waveform of specific transmission eigenchannels allows for control over transmission. However, the nature of pulsed transmission of transmission eigenchannels and their spectral correlation, which would permit control of propagation in the time domain, has not been discussed. Here we report the dramatic variation of the dynamic properties of transmission with incident waveform. Computer simulations show that lower-transmission eigenchannels respond more promptly to an incident pulse and are correlated over a wide frequency range. We explain these results together with the puzzlingly large dynamic range of transmission eigenvalues in terms of the way quasi-normal modes of the medium combine to form specific transmission eigenchannels. Key factors are the closeness of the illuminating waves to resonance with the modes comprising an eigenchannel, their spectral range, and the interference between the modes. We demonstrate in microwave experiments that the modal characteristics of eigenchannels provide the optimum way efficiently excite specific modes of the medium.