Nondestructive spectral reflectance measurement of antireflection coatings on optical lenses using a modified confocal reflectance probe

Antireflection coatings on optical lenses minimize light reflection, improve transmission, and reduce glare. All coated lenses undergo spectral reflectance inspections for adherence to design specifications. Measuring spectral reflectance from a lens’s top surface using standard spectrophotometry requires painting the bottom surface matte black to suppress backside reflections, which damages the lens and takes time. This study presents a nondestructive technique for measuring the spectral reflectance without rear-surface modification using modified chromatic confocal microscopy. The method was validated by measuring spectral reflectance of a bare fused silica glass plate, matching theoretical Fresnel reflection with a mean absolute error (MAE) of 0.02% over 400–800 nm. Spectral reflectance measurements from antireflection-coated spectacle lenses matched spectrophotometer results with MAE < 0.10%. The confocal method enables rapid spectral reflectance measurements of optical components without surface modification, preventing damage.