Quantum Thermal Interference - Characterization of Thermal Light Interference in Multi-Slit Systems

Overview

Controlling the spatial distribution of thermal radiation is important for passive thermal management in microelectronics, suppression of thermal noise in quantum and cryogenic systems, and the design of efficient infrared emitters and sensors. Because these systems use thermal, partially coherent sources rather than lasers, it is necessary to understand how interference and photon transport behave under realistic conditions. This project investigates whether first-order interference can be observed using thermal light and how asymmetric slit geometry can engineer the spatial distribution of thermal photons. A double-slit setup using an incandescent tungsten filament as a broadband thermal source was constructed. The filament voltage was varied to control temperature, changing spectral radiance and peak wavelength according to Planck’s radiation law and Wien’s displacement law. Despite short temporal coherence, observable interference fringes formed due to sufficient spatial coherence at micron-scale slit separations. Fringe spacing depended on wavelength and slit separation, while fringe visibility decreased with increasing spectral bandwidth. The observed pattern was both a pinhole image and an interference pattern. The recognizable curved structure of the filament shows that the aperture formed a pinhole image, since light traveling in straight lines projected the filament shape onto the screen. However, the bright and dark regions showed diffraction and interference caused by wave behavior at the aperture. Symmetric and asymmetric slit geometries produced similar fringe spacing but different diffraction envelopes, demonstrating that geometric asymmetry can imprint structure onto incoherent thermal radiation, enable passive control of thermal photon flow, and promote constructive interference.

Competition history

• CSEF 2026 Physics & Astronomy (Junior Division) · Entry J-17-08

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