Efficient frequency upshift of 10fs laser pulsespropagating in a 5-cm length birefringent photonic crystal fibre

This paper reports that a 5-cm length birefringent photonic crystal fibre is used to tune the output frequency of unamplified 10-fs Ti:sapphire pulses. The zero dispersion of the fibre is at 823~nm and 800~nm for slow and fast fundamental modes, respectively. It is demonstrated that efficient upshift of the output frequency can be achieved when the pumped radiation is polarized along the slow axis of the fibre. When the average input power reaches 320~mW, about 60% of the output energy is located in one peak at 600~nm and is accompanied by depletion of the pulse inside the anomalous dispersion region.