Millimeter Wave Localization: Slow Light and Enhanced Absorption

TL;DR

This paper uses millimeter wave techniques to study localization, slow light, and absorption in random dielectric media, providing experimental evidence and an algorithm for parameter retrieval.

Contribution

It introduces an experimental approach to observe localization and slow light in random media and presents an algorithm to extract internal parameters from external measurements.

Findings

Observation of transmission resonances indicating localization

Experimental evidence of disorder-induced slow light and superluminal velocities

Algorithm successfully retrieves absorption and localization length from measurements

Abstract

We exploit millimeter wave technology to measure the reflection and transmission response of random dielectric media. Our samples are easily constructed from random stacks of identical, sub-wavelength quartz and Teflon wafers. The measurement allows us to observe the characteristic transmission resonances associated with localization. We show that these resonances give rise to enhanced attenuation even though the attenuation of homogeneous quartz and Teflon is quite low. We provide experimental evidence of disorder-induced slow light and superluminal group velocities, which, in contrast to photonic crystals, are not associated with any periodicity in the system. Furthermore, we observe localization even though the sample is only about four times the localization length, interpreting our data in terms of an effective cavity model. An algorithm for the retrieval of the internal parameters of random samples (localization length and average absorption rate) from the external measurements of the reflection and transmission coefficients is presented and applied to a particular random sample. The retrieved value of the absorption is in agreement with the directly measured value within the accuracy of the experiment.