Spectrally Sharp Near-Field Thermal Emission: Revealing Some Disagreements between a Casimir-Polder Sensor and Predictions from Far-Field Emittance

TL;DR

This paper uses a Casimir-Polder sensor to investigate near-field thermal emission from sapphire, revealing discrepancies with far-field predictions, especially regarding spectral sharpness and frequency shifts at elevated temperatures.

Contribution

It introduces a novel sensor-based method to probe near-field thermal emission and highlights disagreements with existing far-field models, emphasizing the importance of dispersion and dissipation effects.

Findings

Sensor detects sharper, red-shifted polariton emission compared to far-field predictions.

Near-field emission shows temperature-dependent spectral evolution.

Discrepancies suggest the need to refine theoretical models of near-field thermal radiation.

Abstract

Near-field thermal emission largely exceed blackbody radiation, owing to spectrally sharp emission in surface polaritons. We turn Casimir-Polder interaction between Cs(7P1/2) and a sapphire interface, into a sensor sharply filtering, at 24.687 THz, the near-field sapphire emission at ~ 24.5 THz. Temperature evolution of sapphire mode is demonstrated. The Cs sensor, sensitive to both dispersion and dissipation, suggests the polariton to be red-shifted and sharper, as compared, up to 1100 K, to predictions from far-field sapphire emission, affected by birefringence and multiple resonances.