부산대학교 도서관

With the development of lasers, self-trapping and self-focusing of intense light due to the intensity-dependent change in the refractive index of certain media was predicted [1]. For a medium with a sufficiently large, negative Kerr coefficient (n 2 ), self-focusing of the incident light takes place when the power exceeds a critical value [2]. For cw and short pulse regimes (∼100fs) the phenomenon is well modelled by the Nonlinear Schrödinger equation (NLS): ∂E/∂Z = i/2 ▿ 2 ⊥ E − β/2 ∂ 2 E/∂t 2 − γf(|E| 2 )E (1) where E is the slowly varying envelope of the electric field, ß is the group velocity dispersion (GVD) parameter and γ is the nonlinear coefficient. f(|E| 2 ) = |E| 2 gives a cubic, and f(|E| 2 ) = |EΊ 2 / (1 + σ|E| 2 ) gives a saturating nonlinearity with σ the saturation parameter. The terms on the right hand side of (1) describe respectively: diffraction, GVD and nonlinear effects. By achieving a balance between these terms, self-focusing of light takes place even beyond the diffraction limit.