16-fs, 1-microJ ultraviolet pulses generated by third-harmonic conversion in air

We describe a simple method for generating sub-20-fs ultraviolet light pulses with useful average powers, using a kilohertz Ti:sapphire laser system. By focusing a 22-fs, 1-mJ laser pulse in air, we obtain ultraviolet pulses with an energy of 1 microJ and at a wavelength of 266 nm and with an average power of 1 mW. The pulse duration of the ultraviolet pulses was measured to be 16 fs with frequency-resolved optical gating.