利用低频场控制轨道直接产生低于50阿秒的单个脉冲

提出一种直接得到脉宽小于50as的单个脉冲的新方法.利用波长为800nm脉宽为5fs的超短脉冲叠加上波长为10μm，强度为超短脉冲强度的10％且脉宽足够长的低频场脉冲驱动氦原子，谐波谱可以拓展到I_p+8.2U_p，同时，高于4.2U_p的谐波几乎是连续的.如果继续调节超短脉冲的载波包络相位，超连续谱可以继续拓宽，从而可以得到低于50as的单个脉冲. 关键词： 阿秒脉冲 超连续谱

Direct generation of isolated sub-50 attosecond pulse via controlling quantum paths by a low frequency field

We propose a new method to directly generate an isolated sub-50 attosecond pulse. The combination of a 5fs driving laser pulse with the wavelength of 800nm and a low frequency field with the wavelength of 10μm is adopted. The intensity of the low frequency field is 10% that of the driving pulse. It is shown that the harmonic spectrum is extended to I_p+8.2U_p and the harmonics above I_p+4.2U_p become continuous. By adjusting the phase of the carrier-envelope of the few-cycle pulse，the bandwidth of the supercontinuum can be further broadened and a close-to-Fourier-limit sub-50as pulse is directly obtained.