Refection

-Antireflection

Reflection-interaction of electromagnetic in materials with light

Reflection can be estimated using Fresnel equations.

Angle of incidence (θᵢ), Refractive indices n₁, n₂, Polarization (s or p)

Snell’s law: n₁ sin(θᵢ) = n₂ sin(θₜ)

s-Polarized Light: Electric field ⟂ to the plane of incidence

Reflection coefficient: rₛ = (n₁ cos θᵢ - n₂ cos θₜ) / (n₁ cos θᵢ + n₂ cos θₜ)

Transmission coefficient: tₛ = 2n₁ cos θᵢ / (n₁ cos θᵢ + n₂ cos θₜ)

p-Polarized Light: Electric field ∥ to the plane of incidence

Reflection coefficient: rₚ = (n₂ cos θᵢ - n₁ cos θₜ) / (n₂ cos θᵢ + n₁ cos θₜ)

Transmission coefficient: tₚ = 2n₁ cos θᵢ / (n₂ cos θᵢ + n₁ cos θₜ)

R= ½(rₛ²+rₚ²)

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Polymer has low reflection-Metal has high reflection

Structural reflection – interference/scattering (Mie scattering), which is obtained by geometries

Ex) textiles, paints, powder

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Refractive index

(Geometric mean)

=sqrt(n1,n2)

n2

n1

Thickness?

1. Thin film intereference-destructive interference

2. Geometrical methods

Surface reflection (not full reflection inside)

In terms of Energy

Interference: wavelength selective destructive-constructive

Roughness size – high visible transparency

Red

Blue

IR reflection of textiles

PET

Cotton