arXiv subjects

Kartika N. Nimje

Publications and source records attributed to Kartika N. Nimje.

3 recordsLinked to original sources

arXiv2026

Analytical Theory of Photon Tunneling and Near-Field Heat Transfer Between Dissimilar Materials

Near-field radiative heat transfer can exceed the blackbody limit through evanescent-mode coupling across nanoscale gaps. This enhancement underpins applications including thermophotovoltaic energy conversion, electroluminescent cooling, thermal rectification, and photon absorption in plasmon-assisted photodetection. These systems most often involve photon- or heat-exchange between dissimilar interfaces, particularly between a semiconductor and a metal. Despite the prevalence of this asymmetric configuration, no closed-form description of its near-field interaction exists. Here, we derive a closed-form analytical description of photon tunneling that clarifies the roles of material properties, namely the plasma frequency, optical loss, and semiconductor absorption, in the thermal exchange. We show that the dominant in-plane wave vector of the radiative heat transfer is an approximate average of the corresponding values for two symmetric reference systems: a plasmonic-plasmonic cavity and a semiconductor-semiconductor cavity. These results establish a compact analytical framework for near-field heat transfer between dissimilar materials.

physics.optics↗

arXiv2025

The critical role of substrates in mitigating the power-efficiency trade-off in near-field thermophotovoltaics

Near-field thermophotovoltaic systems can achieve ultra-high power densities, however, this often comes at the cost of reduced efficiency. We show that this power-efficiency trade-off can be mitigated through substrate engineering. We exploit gradient-based optimization and show that thin lossless metallic films with plasma frequencies resonantly matched to the plasmonic emitter can yield high power and spectral efficiency by spectrally enhancing and confining radiative heat transfer to a narrow spectral range just above the photovoltaic bandgap. Compared to noble metals and air-bridged structures, designs deriving from such optimization yield more than an order-of-magnitude increase in radiative power density while maintaining high efficiency. Our results highlight the critical role of the substrate and the potential of substrate optimization for overcoming fundamental limitations of near-field thermophotovoltaic systems.

physics.optics↗

arXiv2023

Hot-carrier thermophotovoltaic systems

A thermophotovoltaic (TPV) energy converter harnesses thermal photons emitted by a hot body and converts them to electricity. When the radiative heat exchange between the emitter and PV cell is spectrally monochromatic, the TPV system can approach the Carnot thermodynamic efficiency limit. Nonetheless, this occurs at the expense of vanishing extracted electrical power density. Conversely, a spectrally broadband radiative heat exchange between the emitter and the cell yields maximal TPV power density at the expense of low efficiency. By leveraging hot-carriers as a means to mitigate thermalization losses within the cell, we demonstrate that one can alleviate this trade-off between power density and efficiency. Via detailed balance analysis, we show analytically that one can reach near-Carnot conversion efficiencies close to the maximum power point, which is unattainable with conventional TPV systems. We derive analytical relations between intrinsic device parameters and performance metrics, which serve as design rules for hot-carrier-based TPV systems.

physics.app-ph↗