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

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.