title: Design considerations for low-light level low-Fresnel number optical systems.
abstract: Low-Fresnel number optical systems exhibit significant diffraction effects that cause a shift in the peaks of on-axis irradiance away from the geometric focal point. This is currently interpreted as a change of the focal length of an optical system, leading optical system designers to compensate for the effect by assuming the image plane is coincident with the peak of on-axis irradiance. While this may be an appropriate interpretation for certain applications, I show that despite the shift in peak irradiance away from the geometrical focal point, a change in a system's optical power will not increase the on-axis irradiance at that distance. This is important for low-light level applications where it is necessary to mitigate diffraction induced transmission losses. I also show that low-Fresnel number systems have increased tolerance on system power at the geometrical focal point and as a result are inherently achromatic.
authors.affiliation: Caltech Optical Observatories, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, USA. baranec@astro.caltech.edu
authors.forename: Christoph
authors.initials: C
authors.lastname: Baranec