Axial irradiance distribution arising from the diffraction of a uniform, converging, spherical wave at a circular aperture is studied on the basis of scalar boundary-diffraction wave theory. The combined effects of Fresnel number and angular aperture on the focal shift are evaluated, and the validity of the results is checked against the Kirchhoff boundary conditions.
© 2003 Optical Society of America
Yajun Li, "Focal shift in small-Fresnel-number focusing systems of different relative aperture," J. Opt. Soc. Am. A 20, 234-239 (2003)