Electromagnetic point of view on the absorption of light by subwavelength thin films
Bibliographic record
Abstract
Light absorption by matter is a fundamental process at the heart of modern physics. With the advent of nanofabrication and two-dimensional materials, optical studies are increasingly performed on thin films whose thickness is smaller than the wavelength of light. Although these films can be composed of very diverse materials, their transmission, reflection, and absorption share the same electromagnetic framework when described classically by Maxwell’s equations, a dielectric tensor, and appropriate boundary conditions. Understanding absorption in thin films is therefore essential, as it manifests in all optical measurements made in this geometry. In this work, we clarify the physical origin of absorption in thin films and provide a unified description that bridges concepts traditionally treated separately across different scientific communities. Absorption in bulk materials is governed by resonances in the dielectric function, and the absorbed power scales with its imaginary part. This remains true for thin films when the electric field lies parallel to the interfaces. However, when the field is oriented perpendicular to the interfaces, absorption arises from an electric-field enhancement induced by the reduction of the real part of the dielectric function and the electromagnetic boundary conditions. Based on this mechanism, we derive simple expressions that accurately predict the spectral positions of the corresponding absorption peaks. We illustrate these concepts for both isotropic and uniaxially anisotropic materials— both relevant to many contemporary systems such as h-BN and transition-metal dichalcogenides. Our analysis offers an intuitive interpretation of effects that are often obscured in textbook formalisms and are named differently across fields (e.g., the Berreman effect, depolarization shift). We aim to provide a unified and simple physical understanding of absorption phenomena in thin films.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.002 |
| Scholarly communication | 0.001 | 0.002 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.003 |
| Insufficient payload (model declined to judge) | 0.004 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".