Digital Microscopes
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
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
Processed metal surface with coaxial illumination
IC with ring illumination
IC with coaxial illumination
