title: Tight focusing and blue shifting of millijoule femtosecond pulses from a conical axicon amplifier.
abstract: We focus millijoule femtosecond pulses to a spot radius of 2 microm after amplification free of phase-front distortion in a Nd:YAG-pumped conical axicon dye cell. Peak focal intensities reach 10(16) W/cm(2) , creating an intense spark that is caused by air breakdown at the focus. Intensity-dependent blue shifts of the pulse spectrum as large as 11 nm are observed as a result of temporally asymmetric self-phase modulation in the air-breakdown plasma.
authors.forename: W M
authors.initials: WM
authors.lastname: Wood
authors.forename: G
authors.initials: G
authors.lastname: Focht
authors.forename: M C
authors.initials: MC
authors.lastname: Downer