Tight focusing and blue shifting of millijoule femtosecond pulses from a conical axicon amplifier.
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.
Wood
W M
WM
Focht
G
G
Downer
M C
MC