Supercontinuum Generation in Atmospheric-Pressure Nitrogen Using a Tightly Focused Intense Femtosecond Laser Beam

Supercontinuum generation in atmospheric-pressure nitrogen by a focused intense femtosecond Ti: sapphire laser was studied at various pulse durations and energies. The generated supercontinuum was greatly blue-broadened due to self-phase modulation in the plasma produced. The measured blue-broadening Δω is proportional to pulse intensity for fixed pulse duration, and values up to 0.7ω (ω being the original laser frequency) was obtained with a pulse energy of 9.5 mJ and minimum duration of 100 fs.