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Ultra-short Pulses
The cubic nonlinear Schrödinger equation (NLSE) is the standard approximation for nonlinear Maxwell's equations in optics. Its derivation assumes a slowly varying amplitude approximation. For ultra-short pulses, when the width of the pulse is only a few cycles, this approximation breaks down. In the recent years, together with Gene Wayne (Boston) , Yeojin Chung (Los Alamos), and Chris Jones (North Carolina), I have investigated other possible approximations to nonlinear Maxwell' s equations in the regime of ultra-short pulses. In 2004, Gene and I derived a new equation, the so-called short-pulse equation (SPE) and we were able to show that the SPE is an excellent approximation to Maxwell's equations for ultra-short pulses. Many questions, though, remain open as
  • Integrability of the SPE (there is a claim that the SPE is strongly related to the Sine-Gordon equation)
  • Regularization of the SPE using nonlocal terms and nonlocal solitons
  • Extension of the SPE to more complicated geometries and media

Read more (selected publications):

Y. Chung, C. K. R. T. Jones, T.Schäfer, C. E. Wayne: Ultra-short pulses in linear and nonlinear media, Nonlinearity 18 (2005) 1351-1374.

T. Schäfer and C. E. Wayne: Propagation of ultra-short optical pulses in nonlinear media, Physica D 196 (2004)  90-105.