Generation of UV light from microstructural fibers pumped with a femtosecond 800 NM oscillator.

Microstructured fibers have been shown to be an excellent media for nonlinear optical interactions due to small core size, long interaction length and unusual dispersion properties. Supercontinuum generation with just oscillator pumping is one of the manifestations of such properties [l]. The supercontinuum is typically observed in the fundamental mode even in the multimode PCFs. Another interesting observation is the generation of distinct frequency bands when pumping the PCF at 1550 nm [2]. The color generation was observed in the visible region exiting the fiber in single higher-order modes different for each color. Here we report the observation of the upconversion of the femtosecond 800 nm pulses from a commercial Ti:Sapphire oscillator to the UV frequency range, Fig. 1. It is unambiguously observed that the nonlinear mechanism is distinct from that of the supercontinuum generation and the UV generation occurs starting from the higher-order mode at the fundamental wavelength and yielding a very high-order mode in the UV