Intense attosecond has attracted a lot attention due to its potential applications in nonlinear opitcs in XUV regime and atttosecond pump/attosecond probe experiment. Typically, a high energy driving laser source is focused to a rare gas and then the radiated harmonic spectrum are selected for producing an intense isolated attosecond pulse. However, the main technical challenge is that the pulse duration of a high-energy commercial available femtosecond laser source is limited to 25 fs, which is not enough to generate isolated attosecond pulse down to 100 as. In this case, the application of an intense attosecond pulse is significantly limited.
To overcome this limitation, the group headed by Professor Peixiang Lu in WNLO proposes to use a shaped two-color driving laser source. By analyzing the ratio between the highest and second highest laser peaks of the shaped two-color field, the best laser shape is theoretically predicted. The simulation results show that, using the synthesized 800-nm fundamental field and1400-nm control field with intensity ratio of 0.866, the 105-as isolated pulse can be directly produced with driving pulse duration up to 25 fs. Moreover, the carrier envelop phase of the driving fields don’t need to be stabilized, which has significantly relaxed the requirements on laser system. For this reason, the commercial available high-energy source can be used as driving laser source for obtaining the intense isolated attosecond pulse. Furthermore, we also perform analysis on the group velocity mismatching and variation of the intensity ratio introduced by propagation of the two-color field on producing phase-matched attosecond pulse. It is found that the attosecond pulse still builds up as long as the gas pressure is kept low enough. At the phase-matched condition, the predicted pulse energy of the produced attosecond pulse is up to 0.5 uJ with 1J pump energy, which has readily reached the intensity of 1014 W/cm2. We believe that this result will pave the way for further application of the atttosecond pulse in attosecond pump/attosecond probe experiment.
This work was supported by NNSF （11204095, 11234004 , 61275126）and 973 program （2011CB808103）and published on Optics Express 22, 13213–13233（2014）