Total internal reflection and evanescent fields
Total reflected flux does not mean zero field beyond the interface.
Key knowledge
For lossless isotropic media with n₁>n₂>0, light incident from medium1 at θ_i>arcsin(n₂/n₁) has no propagating refracted ray and unit reflected normal power at a single planar semi-infinite interface. The field in medium2 decays evanescently rather than vanishing. A nearby second high-index medium can couple that field and frustrate total reflection.
Values and equations
θ_c=arcsin(n₂/n₁); θ_i>θ_c for n₁>n₂
- θ_c,θ_i
- Critical and incident angles from the interface normal rad
- n₁,n₂
- Incident/transmitted medium refractive indices 1
Conditions and scope
- Stationary planar interface, classical monochromatic fields, isotropic transparent nonmagnetic media and incidence angle from the normal.
- Absorption, anisotropy, a finite second layer or other boundaries change the simple unit-reflection problem. The penetration depth can grow near the critical angle; “a few wavelengths” is not a uniform bound.
Sources · 2
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
- University Physics Volume 3, §1.4: total internal reflectionSamuel J. Ling, Jeff Sanny and William Moebs — OpenStax, Rice University, University Physics (2016)Textbook chapter
- Oscillations and Waves, Total Internal Reflection, equations7.102–7.121 and frustrated reflection discussionRichard Fitzpatrick — University of Texas at AustinCourse notes
Evidence and review
Read OpenStax§1.4 critical angle1.5 and Fitzpatrick actual Total Internal Reflection body equations7.102–7.121/7.125 plus frustrated-reflection paragraphs. Use only critical angle, exponential field and zero normal flux conclusions; exclude suspicious amplitude-label equations7.118/7.134 and the prose implication that a phase retarder polarizes unpolarized light.
2026-10-10 · /root/audit_life_earth_chemistry — independent Chemistry/Life/Earth editor. Independent AI editorial review of this entry's statements, equations, applicability conditions and source coverage. Source checks apply to these claims within their stated limits.
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