Chaos: A new mechanism for enhancing the optical generation rate in optically thin solar cells

Chaotic cavity design of a UV-C disinfection chamber for uniform radiation distribution

UV-C radiation has been used extensively for disinfection wherein the dosage of radiation varies with the microorganism concerned. The efficacy of disinfection largely relies on the radiation reaching uniformly across the chamber without simultaneously leaving out dark regions within the chamber. The regular geometries of the chambers, such as with circular or rectangular cross sections, invariably lead to hot spots accompanied by regions that remain dark, thereby severely limiting the germicidal effects of the UV-C radiation. We propose and demonstrate the use of a chaotic Bunimovich stadium design chamber that ensures uniform UV-C exposure without any accompanying "dark spots." The design incorporates the shape parameters of a chaotic Bunimovich stadium, wherein ray-tracing simulations confirm the space-filling nature of the photon trajectories, typical of chaotic dynamics. This leads to uniform radiation distribution across the whole volume. Experimental results are presented for a biosafety cabinet that can be used for UV-C disinfection wherein the UV-C light intensity distribution is more evenly distributed than the conventional regular (cuboidal) geometry. Adaptation of this simple design consideration is paramount for air disinfection, wherein dark regions in conventional air ducts can severely compromise the efficacy of the disinfection.

Wave chaos enhanced light trapping in optically thin solar cells

Enhancing the energy output of solar cells increases their competitiveness as a source of energy. Producing thinner solar cells is attractive, but a thin absorbing layer demands excellent light management in order to keep transmission- and reflection-related losses of incident photons at a minimum. We maximize absorption by trapping light rays to make the mean average path length in the absorber as long as possible. In chaotic scattering systems, there are ray trajectories with very long lifetimes. In this paper, we investigate the scattering dynamics of waves in a model system using principles from the field of quantum chaotic scattering. We quantitatively find that the transition from regular to chaotic scattering dynamics correlates with the enhancement of the absorption cross section and propose the use of an autocorrelation function to assess the average path length of rays as a possible way to verify the light-trapping efficiency experimentally.

The effect of deformation of absorbing scatterers on Mie-type signatures in infrared microspectroscopy

Mie-type scattering features such as ripples (i.e., sharp shape-resonance peaks) and wiggles (i.e., broad oscillations), are frequently-observed scattering phenomena in infrared microspectroscopy of cells and tissues. They appear in general when the wavelength of electromagnetic radiation is of the same order as the size of the scatterer. By use of approximations to the Mie solutions for spheres, iterative algorithms have been developed to retrieve pure absorbance spectra. However, the question remains to what extent the Mie solutions, and approximations thereof, describe the extinction efficiency in practical situations where the shapes of scatterers deviate considerably from spheres. The aim of the current study is to investigate how deviations from a spherical scatterer can change the extinction properties of the scatterer in the context of chaos in wave systems. For this purpose, we investigate a chaotic scatterer and compare it with an elliptically shaped scatterer, which exhibits only regular scattering. We find that chaotic scattering has an accelerating effect on the disappearance of Mie ripples. We further show that the presence of absorption and the high numerical aperture of infrared microscopes does not explain the absence of ripples in most measurements of biological samples.