Light propagation induces remarkable changes in the spectrum of focused diffracted beams. We show that spectral changes take place in the vicinity of phase singularities in the focal region of spatially coherent, polychromatic spherical waves of different Fresnel numbers. Instead of the Debye formulation, we use the Kirchhoff integral to evaluate the focal field accurately. We find that as a result of a decrease in the Fresnel number, some cylindrical spectral switches are geometrically transformed into conical spectral switches.
© 2004 Optical Society of America
Carlos J. Zapata-Rodríguez and Juan A. Monsoriu, "Spectral anomalies in focused waves of different Fresnel numbers," J. Opt. Soc. Am. A 21, 2418-2423 (2004)