Wavelength independent grating lens system

Abstract

Grating lenses can be made small and light, and can be mass-produced. However, wavelength variations in the light source cause aberrations and change the focal length of the grating lens. Therefore, it has been difficult to use grating lenses in high-precision optical systems that use light sources with wavelength variation. A new grating lens system with a high numerical aperture was proposed to suppress the aberration and keep the focal length constant over a wavelength range of a few tens of nanometers. Aberration calculations showed that the acceptable wavelength range was ±15 nm for a system with a numerical aperture of 0.50. The gratings were made using electron beam lithograpy, and their focusing ability was then evaluated.