Shaped multi-cycle two-color laser field for generating an intense isolated XUV pulse toward 100 attoseconds.

Abstract

The isolated attosecond pulse (IAP) generated from high-order harmonic (HH) radiation has been established as an important technique for the ultrafast optics over past decade. The applications of IAP in ultrafast processes can be greatly extended by further developing the high-intensity IAP. Here, we theoretically propose to shape a two-color field by performing peak amplitude-wavelength analysis. It is found that a 240-as IAP can be generated even without carrier envelop phase (CEP) stabilization using a 25 fs/800 nm fundamental field and a relative weak 25 fs/1330 nm control field, which enables us to markedly relax the requirements of the driving laser fields both in pulse duration and CEP control. On the other hand, if the CEPs of driving laser fields are stabilized, a 65-eV broadband continual harmonic, supporting a 81-as IAP, can be directly produced with the optimized intensity ratio of 0.866 and control wavelength of 1400 nm. Moreover, the propagation effect of two-color field on the macroscopic build-up of HH for generating a high-energy IAP is discussed. We found that the method of phase match still works for the efficient continuous harmonic generation as long as the ionization level and the pressure of gas medium are kept low enough. Since the phase-matched short IAP can be generated with our shaped two-color scheme in combination with a relaxed requirement of driving laser fields, the commercial available high-energy laser source with a loosely focused geometry is promising for scaling up the energy of IAP, showing the potential for the realization of IAP with high focused intensity toward 100 attoseconds.