Mastering Asphere Metrology: Precision for Optics

Aspherical optics have revolutionized optical systems, promising enhanced performance and versatility. However, their complex geometry demands meticulous metrology techniques for precise manufacturing and quality assessment. In this article, we delve into the intricate world of asphere metrology, exploring advanced methods and their implications for optical engineering.

Unlike traditional spherical lenses, aspheres boast non-spherical curvature profiles, crucial for correcting aberrations and improving optical performance. These intricate optics defy simple geometric description and are characterized by polynomial equations.

Methods of Asphere Metrology

• Contact Profilometry: Utilizing a delicate probe, contact profilometry tracks surface variations, offering insights into roughness. While effective, its applicability is constrained by probe size.
• Optical Profilometry: Employing light sources instead of physical probes, optical profilometry enables nanometer-scale roughness detection. However, precise light orientation and reflective surfaces are prerequisites.
• Stitching Interferometry: Tailored for aspheres, stitching interferometry pieces together sectional measurements to construct a comprehensive surface map. Despite its effectiveness, it struggles with steep slopes and complex geometries.
• Computer-Generated Holography (CGH): CGH adapts interferometry for aspheres by creating custom holograms to match surface profiles. Ideal for high-slope aspheres, its practicality lies in large-scale production but faces challenges with inflection points.
• Chromatic Confocal Sensing: Harnessing chromatic aberration, this method utilizes light wavelength variations to probe surface profiles. While effective, it requires meticulous calibration and is suited for specific applications.
• Multiwavelength Interferometry: By integrating multiple wavelengths, this technique enhances measurement precision, albeit at a higher equipment cost.