Mid-infrared modulated polarization gating for ultra-broadband supercontinuum generation

Weiyi Hong,Peixiang Lu,Qingbin Zhang,Shaoyi Wang,Pengfei Wei

doi:10.1364/oe.18.011308

Abstract

We propose a method to control the harmonic process by a mid-IR modulated polarization gating for the effective generation of an ultra-broadband supercontinuum in the neutral rare-gas media. Using a mid-IR polarization gating pulse modulated by a weaker 800-nm linearly polarized pulse, the ionization, acceleration and recombination steps in the harmonic process are simultaneously controlled, leading to the efficient generation of an ultra-broadband supercontinuum covered by the spectral range from ultraviolet to water window x ray under the low ionization rate. The right phase-matching technique is employed to macroscopically select the short quantum path of the supercontinuum, then isolated sub-100-as pulses with tunable wavelengths are directly obtained. This supercontinuum also supports the pulse duration far below one atomic unit of time.

Highlights

The appearance and development of isolated attosecond pulse pave the way for the study and control of the ultrafast electron dynamics with unprecedented resolutions [1]
Nowadays, isolated attosecond pulses based on the high-order harmonic generation (HHG) have been successfully produced in experiment, and many efforts have been paid to broaden the bandwidth of the supercontinuum and shorten the pulse duration for the potential applications with much higher time resolutions
Lan et al found that the two-color field can restrict the ionization peak within one half cycle and enhance its amplitude, which is dubbed “ionization gating”, the high-efficiency harmonics in the plateau merge to a broadband supercontinuum [6]

Summary

Introduction

The appearance and development of isolated attosecond pulse pave the way for the study and control of the ultrafast electron dynamics with unprecedented resolutions [1]. It has been proposed that the recombination of the electrons can be “gate” into one half-cycle by using the few-cycle polarization gating(PG) technique, a broadband supercontinuum in the plateau region is produced [4] This technique is based on the strong dependence of the HHG on the ellipticity of the driving pulse. Another effective way is to adopt a wave-form-controlled two-color field to significantly enlarge the difference between the highest and the second highest half-cycle photon energies, i.e., “gate” the ionization step, and forms a broadband supercontinuum with several tens eV near the cutoff [5,6,7]. By using a mid-IR PG few-cycle pulse modulated by a weaker near-IR linearly polarized field, a high-efficiency ultra-broadband supercontinuum covered by the spectral range from ultraviolet to water window x ray is successfully produced in the neutral gas

Theoretical model

Findings

Result and discussion

Conclusion