Enhanced Amplification of Attosecond Pulses in a Hydrogen-like Plasma-Based X-ray Laser Modulated by an Infrared Field at the Second Harmonic of Fundamental Frequency

Ilias R Khairulin,Olga Kocharovskaya,Vladimir A Antonov,Mikhail Yu Ryabikin

doi:10.3390/photonics9020051

Abstract

In a recent work (Antonov et al., Physical Review Letters 123, 243903 (2019)), it was shown that it is possible to amplify a train of attosecond pulses, which are produced from the radiation of high harmonics of the infrared field of the fundamental frequency, in the active medium of a plasma-based X-ray laser modulated by a replica of the infrared field of the same frequency. In this paper, we show that much higher amplification can be achieved using the second harmonic of the fundamental frequency for modulating of a hydrogen-like active medium. The physical reason for such enhanced amplification is the possibility to use all (even and odd) sidebands induced in the gain spectrum in the case of the modulating field of the doubled fundamental frequency, while only one set of sidebands (either even or odd) could participate in amplification in the case of the modulating field of the fundamental frequency due to the fact that the spectral components of the high-harmonic field are separated by twice the fundamental frequency. Using the plasma of hydrogen-like C5+ ions with an inverted transition wavelength of 3.38 nm in the water window as an example, it is shown that the use of a modulating field at a doubled fundamental frequency makes it possible to increase the intensity of amplified attosecond pulses by an order of magnitude in comparison with the previously studied case of a fundamental frequency modulating field.

Highlights

The beginning of the 21st century was marked by the emergence and rapid development of attosecond physics—an interdisciplinary field of research aimed at probing and controlling the ultrafast dynamics of charge carriers in atoms, molecules, and solids on their own time scales [1,2,3,4,5,6,7]
In recent work [19], we proposed a method for amplifying a train of attosecond pulses formed by a set of high-order harmonics of the infrared (IR) field in a hydrogen-like active medium of a plasma-based X-ray laser, which is simultaneously irradiated with a replica of the fundamental-frequency IR field used to generate the high harmonics
We show that if the second harmonic of the fundamental field is used for modulation of an active medium, all gain components induced by that field participate in amplification of a train of attosecond pulses produced by the HHG of the fundamental IR field frequency

Summary

Introduction

The beginning of the 21st century was marked by the emergence and rapid development of attosecond physics—an interdisciplinary field of research aimed at probing and controlling the ultrafast dynamics of charge carriers in atoms, molecules, and solids on their own time scales [1,2,3,4,5,6,7]. The main instrument of attosecond physics is attosecond X-ray and vacuum ultraviolet (VUV) pulses produced due to high-order harmonic generation under the action of optical laser field on a gas medium in the tunneling ionization regime [8,9,10]. Such sources make it possible to generate a spectrum of harmonics with a width of more than 1 keV and up to 12 octaves [11], as well as to generate pulses with a duration of down to 40–50 as [12,13,14]. If the active medium exhibits strong plasma dispersion at the frequency of the modulating field, harmonics of different orders are amplified independently of each other, and their relative phases are preserved

Results

Discussion

Conclusion