Chapter 5 - Nonlinear Focused Beams by Axisymmetric Gratings

Abstract

Previously, we presented the diffraction of waves on axisymmetric uniform gratings can conform a Bessel beam. Here, the spacing between slits is designed in order to provide focusing as in Fresnel Zone Plates. The device presents a very narrow focal spot, that is between the sub-diffraction and the sub-wavelength limits. As common from other Fresnel-like lenses, and also in Bessel beams, the narrow focal is accompanied by high amplitude side lobes. The lens presents high gain, around 30 dB. Thus, nonlinear effects can mainly activated locally at the focal spot. The field of the second harmonic maintain the excellent beam-width of the Fresnel lens, while its side-lobes are strongly reduced. The proposed lens in the weakly nonlinear regime is suitable for second harmonic imaging techniques: the excellent beam spatial resolution of the second harmonic is maintained, while the side-lobe amplitude, responsible of signal-to-noise ratio, is reduced.

@other{phdc5,
 author = {Noé Jiménez},
 pages = {133-154},
 title = {Chapter 5 - Nonlinear Focused Beams by Axisymmetric Gratings},
 year = {2015}
}