Application of Quasi-Phase Matching Concept for Enhancement of High-Order Harmonics of Ultrashort Laser Pulses in Plasmas

R A Ganeev,A S Alnaser,S Y Stremoukhov,A V Andreev

doi:10.3390/app9081701

Abstract

Novel methods of coherent short-wavelength sources generation require thorough analysis for their further amendments and practical implementations. In this work, we report on the quasi-phase matching (QPM) of high-order harmonics generation during the propagation of single- and two-color femtosecond pulses through multi-jet plasmas, which allows the enhancement of groups of harmonics in different ranges of extreme ultraviolet. The role of the number of coherent zones; sizes of plasma jets and the distance between them; plasma formation conditions, and the characteristics of the fundamental radiation on the harmonic efficiency at quasi-phase matching (QPM) conditions are analyzed. We demonstrate the ~40× enhancement factor of the maximally-enhanced harmonic with respect to the one generated at ordinary conditions in the imperforated plasma.

Highlights

The interaction of ultrashort laser pulses with gases, plasmas, surfaces, and solids allows the conversion of longer-wavelength laser sources towards the extreme ultraviolet (XUV) region.This approach took special attention due to relative easiness in generating coherent short-wavelength radiation
We report the role of the number of coherent zones, sizes of plasma jets, plasma formation conditions, and the characteristics of fundamental radiation on the high-order harmonic generation (HHG) efficiency at quasi-phase matching (QPM)
QPM allows tuning a group of enhanced harmonics in the XUV range

Summary

Introduction

The interaction of ultrashort laser pulses with gases, plasmas, surfaces, and solids allows the conversion of longer-wavelength laser sources towards the extreme ultraviolet (XUV) region.This approach took special attention due to relative easiness in generating coherent short-wavelength radiation. Increasing the length of laser-matter interaction to attain stronger nonlinear optical response from extended media is one of the methods that has been applied to enhance the coherent XUV yield during high-order harmonic generation (HHG). To diminish the effect of phase mismatch in laser-produced plasmas (LPP) on the HHG efficiency, the concept of quasi-phase matching (QPM) using the modulated shape of the LPP, was employed to minimize the difference between the phases of two waves This modulation is based on the division of extended plasma into a set of equidistantly-separated plasma jets either by inserting multi-slit mask (MSM) in front of ablating surface [1], or by using perforated targets [2]

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Conclusion