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Adaptively controlled supercontinuum generation in a microstructure fiber

Efficient confinement of laser radiation in the core of a photonic crystal fiber (PCF) enhances the nonlinear processes resulting in supercontinuum generation. The technique of adaptive pulse shaping using an evolutionary algorithm provides a method to gain control over nonlinear processes. Adaptive pulse shaping of the driving laser radiation passing through the photonic crystal fiber was employed to modify the shape and composition of the output supercontinuum. Amplified pulses of a Ti:Sapphire laser system were coupled into a high air fill factor (cobweb) PCF sample. Alternatively a Cr:Forsterite master oscillator was used as the pump source. Supercontinua acquired with unshaped pulses are compared for both pump sources. Amplitude and phase shaping of the amplified Ti:Sapphire pulses was then used to optimize the emission between 500 and 700 nm, as well as a soliton centered at 935 nm. The originally separated spectral regions near 700 nm eventually merged into a smoother and broader supercontinuum. The intensities of the broadband emission and of the soliton driven by a shaped laser pulse increased in comparison to unshaped pulses by factors of 4 and 3, respectively. In addition, the suppression of self-steepening effects in supercontinuum spectra was demonstrated using a shaped laser pulse.