Scaling isolated-attosecond-pulse duration by controlling a trajectory parameter

Abstract

Reaching an ever shorter duration of isolated attosecond pulses (IAPs) is an ongoing mission in attosecond science. Wide usage of long-wavelength driving lasers has greatly broadened bandwidths for generating IAPs. We propose a strategy to further exploit the ability of a long-wavelength laser in producing short IAPs. We introduce a scaling relationship between IAP duration and a trajectory parameter that is associated with the classical cutoff trajectory of high-order harmonic generation (HHG) in gases. This trajectory parameter can facilitate in shortening IAP duration by shaping laser waveform. We demonstrate the effectiveness of our methods with calculations of HHG from Ne by solving the time-dependent Schrödinger equation. A genetic algorithm is used in search for laser parameters. Macroscopic effects in HHG and attopulse generation are investigated. Our results show that increasing laser intensity and using an additional short-wavelength (e.g., deep ultraviolet) laser pulse together with the infrared are effective ways to shorten IAP duration (from 76 to 47as in our example), for which insightful physical explanations are provided.