| Abstract [eng] |
Supercontinuum generation is a phenomenon that occurs when an intense ultrashort laser pulse propagates in a transparent dielectric medium and during which temporally and spatially coherent light with an ultrabroadband spectrum is observed. Supercontinuum generation occurs due to complex interplay between self-focusing, self-phase modulation, multi-photon absorbtion, shock formation and dispersion. So far, supercontinuum generation was only investigated in isotropic materials, which do not afford sufficient control over the generated supercontinuum spectrum. On the other hand, materials possessing quadratic nonlinearity allow us to control the effective nonlinear refractive index by simply varying the phase mismatch parameter. In this work we demonstrate the generation of supercontinuum and the control of its spectral extent and generation threshold in an anisotropic non-centrosymmetric material with normal group velocity dispersion. It is shown that the supercontinuum generation threshold is highly dependent on the angle between the pump wave and the optical axis of the crystal and that the use of cascaded-quadratic nonlinearity offers a straightforward way of reducing the supercontinuum generation threshold. Furthermore, the tunability of the supercontinuum spectra is explained to occur due to the interplay between the cascaded quadratic nonlinearity and phase matched second harmonic generation. Finally, the measurements performed using the method of frequency resolved optical gating (FROG) were used to confirm that pulse-splitting occurs before the onset of supercontinuum generation. |
