We present a general procedure to analyze the axial-irradiance distribution generated by an unlimited diffractive lens under coherent, Gaussian illumination. The resulting on-axis diffraction pattern, which is evaluated in terms of the power complex spectrum of the Fresnel-zone transmittance, explicitly depends on the truncation parameter that we define, which evaluates the effective number of zones illuminated by the Gaussian beam. Depending on the value of this parameter, different kinds of axial behavior are observed. In particular, for moderate values a multiple-focal-shift phenomenon appears, and a simple formula for its evaluation is presented. Additionally, for low values of the truncation parameter, a focal-merge effect is observed in multifocal zone plates.
© 1999 Optical Society of America
(220.2560) Optical design and fabrication : Propagating methods
Carlos J. Zapata-Rodríguez, Manuel Martínez-Corral, Pedro Andrés, and Amparo Pons, "Axial behavior of diffractive lenses under Gaussian illumination: complex-argument spectral analysis," J. Opt. Soc. Am. A 16, 2532-2538 (1999)