A Unified Complex-Fresnel Model for Physically Based Long-Wave Infrared Imaging and Simulation.

Area of Science:

• Optics and Photonics
• Computational Physics
• Materials Science

Background:

• Accurate modeling of light-matter interactions at material interfaces is crucial for infrared (IR) imaging, rendering, and optical system simulations.
• The short-wave to long-wave infrared (SWIR-LWIR) spectrum presents challenges due to wavelength-dependent material properties (dispersion) and complex refractive indices.

Purpose of the Study:

• To develop a unified formulation of the Fresnel equations for physically consistent interface modeling across the IR spectrum.
• To address numerical instabilities and sign ambiguities in classical Fresnel equations, especially for absorbing materials and varying incidence angles.

Main Methods:

• Introduced a novel formulation of the Fresnel equations incorporating wavelength-dependent complex refractive index data.
• Reformulated classical expressions to eliminate sign ambiguities and improve numerical stability.
• Validated the model using spectral-rendering simulations and compared LWIR emission simulations with experimental measurements.

Main Results:

• The proposed model provides stable and physically consistent interface behavior for both dielectrics and conductors across incidence angles.
• Spectral-rendering simulations demonstrated realistic reflectance and transmittance for various IR optical properties.
• Simulated LWIR emission of a heated glass sphere showed good agreement with LWIR camera measurements.

Conclusions:

• The unified Fresnel equation formulation offers a practical and physically grounded tool for wavelength-parametric interface modeling in IR applications.
• The model supports advanced applications such as spectral rendering, synthetic data generation, and infrared system analysis.
• This work enhances the accuracy and stability of simulations for infrared optics and sensing systems.