Abstract

With current technology, high-intensity lasers can be designed to have pulse widths of 50-100 fs and two groups have now amplified 20–30 fs pulses. We present calculations of single atom harmonic generation spectra from neon and argon atoms in 800-nm fields with pulse durations of 20–100 fs. The rapidly rising and falling intensity profile of the ultrashort pulse modifies both the envelope and phase of the emitted harmonic spectrum, broadening and shifting the harmonic line. Combined with rapid ionization at higher intensities, this pulse envelope effect can lead to asymmetric shifts of the harmonic frequencies (most often blue shifts), which are purely a single atom effect.

© 1996 Optical Society of America