We study localized light bullets and X-waves in quadratic media and show how the notion of nonlocality can provide an alternative simple physical picture of both types of multi-dimensional nonlinear waves. For X-waves we show that a local cascading limit in terms of a nonlinear Schrodinger equation does not exist - one needs to use the nonlocal description, because the nonlocal response function does not converge towards a delta-function. Also, we use the nonlocal theory to show for the first time that the coupling to second harmonic is able to generate an X-shape in the fundamental field despite having anomalous dispersion, in contrast to the predictions of the cascading limit.
Bibliographical noteCopyright 2006 American Physical Society
- Nonlocal description
- Nonlinear optics
- Quadratic nonlinear materials