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Torquato Group Designs Transparent Dense Solids

Research Highlights- - By Wendy Plump

Expanding on a series of papers over the last few years that deepen our understanding of emerging stealthy hyperuniform systems, Salvatore Torquato publishes a predictive theory for the inverse design of the wave characteristics of disordered layered media.

The approach involves engineering the spectral densities of these unusual disordered, two-phase composites. At its core, the research is a demonstration that these systems have “perfect” transparency intervals – in other words, a solid that is fully transparent to light for a range of frequencies, an idea that runs counter to the conventional wisdom that disordered composites cannot be made transparent.

Written with first author Jaeuk Kim, a postdoc in the Princeton Materials Institute (PMI) under his mentorship, Torquato’s research, Effective electromagnetic wave properties of disordered stealthy hyperuniform layered media beyond the quasistatic regime, appears in the journal Optica this week as a featured selection.

The research marks the first study of the electromagnetic properties of one-dimensional disordered stealthy hyperuniform layered media.

Illustration of a transparent layered composite medium consisting
of two different materials (red and blue). The light incident on the left side
of the composite comes out the other end unaltered, that is, without any absorption or reflection.

Graphic courtesy of the Torquato Group

“How can you make a solid material so that it is fully transparent to light? One way of doing so is to make alternating layers of materials with variable refractive indices,” said Torquato, the Lewis Bernard Professor of Natural Sciences, Professor of Chemistry and PMI. “Until recently, it was thought that these different layers had to be spaced in an ordered manner because `disordered’ arrangements would preclude transparency.

“We show that an emerging class of exotic disordered stealthy hyperuniform composites have potentially extraordinary optical properties, including novel transparency and absorption regimes. This work provides a new path for the inverse design of the wave characteristics of disordered layered media with unprecedented behaviors and technological applications.” 

Discussing his new theory, Torquato bats aside the statement that there is already a common example of a transparent solid: glass. This research, he said, covers an entirely different phenomenon. For example, the wavelength of light is huge compared to the atomic scale and that, in considering glass, the mechanism for transparency has to do the fact that visible light is not absorbed.

“What’s really bizarre about what we’ve done is that nobody thought you could make it transparent if you have any kind of disordered layering,” said Torquato.

 “We’re basically saying, look, we have a theory that enables us to manipulate these kinds of exotic disordered arrangements. I can give you, by a kind of tuning of a knob, absorption for this frequency range or transparency for another frequency range. That’s what I mean by inverse design. We can tune the amount of disorder I want to put in, and make it span the spectrum from exotic disorder to perfect order. “ 

The full paper can be accessed here.

This research is supported by funding from the Army Research Office (W911NF-425 22-2-0103).