Coaxial Illumination

Optical Illumination Technique - Coaxial Lighting

Viewing highly-reflective objects with flat surfaces, such as ICs and cross-sectioned samples, is typically difficult to accomplish using ring illumination. When light hits the surface, most of it will reflect away from the lens and result in a dark image. Instead, coaxial (brightfield) illumination is used to view these targets and produce a bright image. Generally, this type of lighting makes use of a half-mirror to match the optical axes of the illumination and lens.

Schematic of light reflected from a specular surface

Light from an angle reflects away from the lens

Light from an angle reflects away from the lens
A : Lens　B : Illumination　C : Reflected light

Vertically illuminated light reflects to the lens

A : Illumination　B : Lens & CCD　C : Specular reflection light
D : Half mirror (A half mirror reflects half of the light and transmits the rest)　E : Mirrored surface

Schematic of coaxial illumination

Coaxial illumination image samples

Processed metal surface with ring illumination