High-order harmonics extension and isolated attosecond pulse generation in three-color field: Controlling factors

In the present Letter, we theoretically discuss the optimum conditions for generating ultrashort attosecond pulse in three-color field with a model He exposed to the intense 5 fs, 800 nm fundamental field and the two weak control fields of 25 fs, 400 nm and 25 fs, 1600 nm. Through investigating the controlling factors in HHG spectra generation via manipulating the laser parameters of the three fields, we demonstrate that properly increasing the pulse intensity of 800 nm and 1600 nm fields at the same time with zero phase effects is an effective way to generate short attosecond pulses. Finally, an isolated pulse of 7 as is predicted by Fourier transforming an ultrabroad XUV continuum of 393 eV with phase compensation.

► Single isolated attosecond pulse generation in three-color scheme. ► A synthesized field of an intense 5 fs/800 nm and two weak 25 fs/400 nm and 25 fs/1600 nm pulses. ► Solution of time-dependent Schrödinger equation for He interacting with external laser filed. ► Properly increase of the intensities of 800 nm and 400 nm pulses and zero phase effect. ► Generation of 7 as pulse under the optimized conditions of the laser parameters.