Brewster's angle · reflection polarizes light

Shine unpolarized light on flat glass — is there an angle where the reflection vanishes for one polarization, and what does that reveal?

▶ Run the simulationSee the measured result

Units: dimensionless (refractive index n₂ of glass, air n₁ = 1)

How the lab tests it

Sweep the incidence angle θᵢ for unpolarized light hitting flat glass and split the reflected beam with the Fresnel equations into its s- and p-polarized parts; locate the angle where the p-reflectance R_p falls to zero, and read the refractive index n = tan θ_B off that null.

What it checks

Brewster's law — the p-reflectance hits EXACTLY zero at θ_B = arctan(n₂/n₁) ≈ 56.3° for glass, so the light reflected there is 100% s-polarized (the reflected and refracted rays come off perpendicular). Recovering n = tan θ_B from the R_p null is why polarized sunglasses kill glare and why laser cavities use Brewster windows. The polarization branch of the optics arc, after Snell, TIR, mirage and the rainbow.

Brewster's angle calculator

The angle at which the p-polarized reflection vanishes, and its inverse — read a refractive index straight off a measured polarization null.