Chapter 7 - Focusing through high numerical aperture objective

Abstract

High numerical aperture (NA) optical objective lenses are widely used in high spatial-resolution optical imaging and fabrication techniques. In optical microscopy, these high NA objectives produce tightly focused optical fields as probes to interrogate the sample properties within the focal volume and generate the contrast for imaging. In optical micro- and nanofabrication, they are used to concentrate the optical energy to produce changes of materials properties within the intended dimensions. Hence, controlling the optical field characteristics within the focal volume plays a critical role in determining the function and performance of these optical systems. Consequently, it is very important to understand the physics of optical focusing through high NA objective lens. In this chapter, a brief review of the diffraction theory that can handle high NA focusing of both scalar and vectorial optical illuminations is presented. Various focus engineering techniques that can be used to create optical focal fields with many exotic intensity distributions and internal field characteristics is briefly discussed. Aberrations and mitigation methodology is also mentioned toward to the end of this chapter.