Control of the high-order harmonics cutoff and attosecond pulse generation through the combination of a chirped fundamental laser and a subharmonic laser field

Generation of an isolated sub-40-as pulse using two-color laser pulses: Combined chirp effects

“…To obtain even shorter attosecond pulses, we proposed a scheme of utilizing the combined chirp effects by adding a controlling chirped pulse to the fundamental chirped (β 1 = 6.1) pulse. The idea is enlightened by the fact that adding a subharmonic pulse onto the fundamental chirped pulse will keep extending the cutoff energy and thus reduce the pulse duration of the attosecond pulse [20,21]. line; this is what we find for the optimal value for Ar atom under the present synthesized field).…”

“…More specifically, for an argon atom irradiated by the 5-fs, 800-nm + 10-fs,1600-nm laser pulses, the two chirp parameters of β 1 = 6.1 and β 2 = 4.0, as well as the moderate pulse intensities of ∼10 14 W/cm 2 are the most favorable conditions. As a consequence, the moderate pulse intensities in our proposed scheme are easier to obtain as compared with the former studies (∼10 15 W/cm 2 ) [20,21], and the same chirp form of the two-color field is also beneficial to experimental realization. The present generated ultrashort 5-as pulse with phase compensation may open a new way to the zeptosecond (zs) scale [43], but the phase compensation technique still poses an experimental challenge.…”

“…Using the two-color scheme and from the theoretical side, Zeng et al [19] obtain an isolated 65-as pulse through the combination of an intense 800-nm fundamental field and a weak 400-nm controlling field. Wu et al [20] obtained an isolated 38-as pulse by an intense 800-nm fundamental chirped pulse in combination with a weak 1600-nm controlling field. Xu et al [21] obtained an isolated 11-as pulse through the combination of an intense 800-nm fundamental chirped pulse and a weak 800-nm controlling chirp-free pulse.…”

“…Although the chirp effects on two-color attosecond generation, such as the combination of a chirped pulse and a chirp-free subharmonic pulse [20,21], have been investigated, little study has been reported for the combination effects of the two-color chirped pulses thus far. Due to this, in this paper we theoretically discuss the combined chirp effects by investigating the HHG and isolated attosecond pulse generation when a model Ar is irradiated by an intense 5-fs, 800-nm fundamental chirped pulse combined with a weak 10-fs, 1200-nm controlling chirped pulse.…”

Optimization of three-color laser field for the generation of single ultrashort attosecond pulse

“…The harmonic spectrum is characterized by a rapid drop at low orders followed by a broad plateau where all the harmonics have the same strength and a sharp cutoff around harmonic energy I p + 3.17U p , where I p is the atomic ionization potential and U p is the ponderomotive energy, i.e., the cycle-averaged kinetic energy of an electron gained in a monochromatic laser field. At present, many schemes have been proposed to generate an ultrabroad supercontinuum spectrum and obtain extreme short attosecond pulse, such as using two-color laser fields [11,12], a few-cycle laser pulse [13,3], the chirped laser pulse [14,15], quantum path control [16,17], polarization gating [18,19], and long-wavelength pumping [20,21]. Among them, Sansone et al have reported the generation of a 130 as isolated XUV pulse using the nearinfrared driving pulse.…”