A high-flux high-order harmonic source

Abstract

We develop and implement an experimental strategy for the generation of high-energy high-order harmonics (HHG) in gases for studies of nonlinear processes in the soft x-ray region. We generate high-order harmonics by focusing a high energy Ti:Sapphire laser into a gas cell filled with argon or neon. The energy per pulse is optimized by an automated control of the multiple parameters that influence the generation process. This optimization procedure allows us to obtain energies per pulse and harmonic order as high as 200 nJ in argon and 20 nJ in neon, with good spatial properties, using a loose focusing geometry (\documentclass[12pt]{minimal}\begin{document}$f_\# \approx 400$\end{document}f#≈400) and a 20 mm long medium. We also theoretically examine the macroscopic conditions for absorption-limited conversion efficiency and optimization of the HHG pulse energy for high-energy laser systems.

Multi-μJ harmonic emission energy from laser-driven plasma

“…However, due to intrinsic processes associated with this generation mechanism, there is a maximum laser pulse intensity that can be used with the consequence of limiting their brightness and severely restricting the scope of applications [2,3]. Techniques like the loose-focusing [4][5][6][7] or the double optical gating [8] have been implemented to enhance the XUV flux and exploit higher laser energies from modern laser systems. More recently using these techniques, a tabletop source delivering 2.6 GW power in a single attosecond pulse was reported [9].…”

Resonant third harmonic generation of KrF laser in Ar gas

“…(2), and also the free electron contribution due to the redistribution of the ionization rate along the gas jet. 23 An interesting consequence of the strong sensitivity of the dispersive contribution to wavelength and atomic number was the observed oscillating property of harmonic conversion on the particle density for 247.7-nm wavelength. As illustrated in Fig.…”

Macroscopic study and control of high-order harmonic and attosecond pulse generation in noble gases

“…In summary it can be said, that for phase-matching to be achieved several linear and nonlinear contributions to phase-mismatch have to be finely balanced, which depend on the type of gas, pressure, focusing geometry, cell position, length of trajectory and laser intensity. These sources define the phase-matching conditions in HHG, and methods to balance them are still researched today [77,80,41]. A summary of different contributions is presented in Figure II.18, where contributions to the XUV wavevector (k q ) and polarization wavevector (κ q ) are listed.…”

“…However, for these trajectories non-collinear phase-matching is achievable before the focus [64]. In most phase-matching calculations, however, only short trajectories are taken into account, which have a weak intensity dependent phase, and this contribution sometimes is considered negligible [77].…”

“…The generation geometry and ionization rate now also define the optimal pressure, which maximizes the coherence length [81,82,77]:…”