Second-order cascading-assisted controllable supercontinuum generation in birefringent media

The propagation of intense ultrashort light pulses in transparent dielectric media gives rise to one of the most spectacular nonlinear optical phenomenon — supercontinuum generation (SC). The nature of this process is fairly well understood and involves intricate coupling between temporal and spatial effects leading to filamentation and an explosive growth of the pulse spectrum [1]. In recent years the rapidly growing field of applications has seen a rising demand for achieving broadband radiation with desired temporal and spectral properties. However, the spectral extent of the SC is essentially determined by the input wavelength and the linear or nonlinear properties of the medium such as material dispersion, bandgap and the nonlinear refractive index [2], all of which remain fixed in an isotropic medium for a given input wavelength. On the other hand, the use of birefringent nonlinear media, which possess both, quadratic and cubic nonlinearities, may provide the desired degree of control. The second-order cascading, which results from the phase-mismatched second harmonic (SH) generation [3] produces a cascaded-quadratic Kerr-like nonlinearity, ncasc 2 ∝ −d2 eff /Δk, which contributes to the nonlinear index of refraction. By setting an appropriate phase mismatch, Δk = k 2ω − 2k ω , the interplay between the cascaded and cubic nonlinearities may be exploited to either enhance or suppress the nonlinear effects [4, 5] and to access qualitatively different regimes of nonlinear propagation.