Abstract
We numerically investigate the influence of plasma defocusing in high harmonic generation (HHG) by solving the first-order wave equation in an ionized medium and defining an enhancement factor to quantitatively analyze the influence of plasma defocusing. While degrading the driver pulse intensity, plasma also has a strong impact on HHG phase-matching. Combined with the HHG wavelength scaling law, our results give an estimate of HHG efficiencies with different driver wavelengths and show a limited HHG efficiency in high density media.
Highlights
High harmonic generation (HHG) has become a promising way towards table-top coherent EUV and soft X-ray light sources [1,2,3]
Several groups have already demonstrated HHG results with different IR driver pulses [3,6,7] and keep pushing optical parametric amplification (OPA) systems to higher pulse energy and longer wavelengths in pursuit of more efficient HHG and higher photon energy [8]. Both theory and experiment show a severe drop of the single atom efficiency (SAE) of HHG that is proportional to λ1−(5~6), at a given HHG driver wavelength λ1 [9,10,11]
We numerically investigate plasma defocusing on IR pulse propagation in Ne and He and discuss how it affects HHG by defining an enhancement factor, which is a generalization of the analysis of Ref [17]
Summary
High harmonic generation (HHG) has become a promising way towards table-top coherent EUV and soft X-ray light sources [1,2,3] In recent years, it has been shown theoretically and experimentally, that the maximum available photon energy from HHG based sources can be extended to the water window, and even keV photons are achievable by using longer driver wavelengths [4]. It has been shown theoretically and experimentally, that the maximum available photon energy from HHG based sources can be extended to the water window, and even keV photons are achievable by using longer driver wavelengths [4] Techniques, such as optical parametric amplification (OPA), have been developed to generate high intensity IR pulses with wavelengths longer than the conventional 800nm wavelength from Ti:Sapphire amplifiers [5]. Increasing medium pressure only results in a limited enhancement of the HHG efficiency even if reabsorption is negligible, and it can only partially compensate the loss of SAE when using longer wavelength driver pulses
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