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.
© 2009 Optical Society of America
Diffraction and Gratings
Original Manuscript: September 3, 2009
Manuscript Accepted: October 7, 2009
Published: November 4, 2009
Christoph Baranec, "Design considerations for low-light level low-Fresnel number optical systems," Appl. Opt. 48, 6259-6263 (2009)