Two-photon above-threshold ionization using extreme-ultraviolet harmonic emission from relativistic laser–plasma interaction

Abstract

We report on the observation of energy-resolved photoelectron (PE) spectra produced via two-extreme-ultraviolet-(XUV)-photon above-threshold ionization (ATI) of argon atoms. The XUV radiation consists of higherorder harmonics generated by the process of the relativistic oscillating mirror (ROM) in high-peak-power laser-pulse interaction with solid targets. The energetic XUV radiation is focused into an argon gas target at intensities high enough to induce two-photon ionization at yields that allow the recording of energy-resolved PE spectra. A clear two-XUV-photon ATI PE peak structure is observed in shot-to-shot measurements. This work is a first step towards a frequency-resolved optical gating-type characterization of attosecond pulse trains emanating from relativistic laser-plasma interactions and thus is important for XUV-pump-XUV-probe applications of these harmonics.

Generation of Attosecond Light Pulses from Gas and Solid State Media

“…Grazing incidence focusing optics are usually toroidal [52,144] or parabolic [92] mirrors with high reflectivity in a broadband XUV spectral range, while normal-incidence focusing optics are unprotected metal coated or multilayer spherical mirrors with high reflectivity in a more confined (compared the toroidal mirrors) XUV spectral range. Although, both configurations can deliver asec structure in the XUV interaction region, the advantages and disadvantages of each of them is a matter under investigation.…”

“…[144], while recently a system of toroidal mirrors (in a Wolter configuration [149]) with reflectivity 40%-50%, has been used for focusing an XUV beam of~60 eV photon energy down to ≈ 13 µm reaching intensities in the range of~10 12 W/cm 2 [52]. Parabolic mirrors have been used for focusing solid surface harmonics of~20 eV photon energy in a focal spot diameter of ≈ 16 µm reaching in this way intensities in the range of~10 12 W/cm 2 [92]. Normal incidence spherical mirrors with reflectivity 10%-20% have been used for focusing an XUV beam of~20 eV photon energy in the sub-4 µm level reaching intensities >10 13 W/cm 2 [150] while multilayer mirrors have been used for focusing an XUV beam of~90 eV photon energy [29].…”

“…So far the two photon ionization of He [43] and N 2 [186] that have been used are not applicable at higher photon energies because the target will be single photon ionized. Candidate processes for this extension are two-photon multiple ionization [156] and two-photon ATI [92]. Such types of developments are currently designed and will be soon implemented in asec laboratories.…”

“…Due to the experimental obstacles mentioned before, the solid surface harmonics as a robust asec source (that can be utilized for further experiments) is still in the development phase and applicability up to now is mainly dedicated to the studies of the ultrafast dynamics of laser-plasma interaction [82][83][84][85][86]. Nevertheless, recent experiments performed in the non-linear XUV regime [54,92] and recent progress in the laser pulse engineering and solid target technology [5,6,[35][36][37]67] verifies the feasibility of using solid surface harmonics in ultrafast XUV spectroscopy and attosecond science.…”

Single-shot autocorrelator for extreme-ultraviolet radiation

“…In the first category is the so-called RABITT (reconstruction of attosecond beating by interference of two-photon transitions) method for a train of attosecond pulses [5][6][7][8] and the "streaking" or the XFROG method for isolated pulses [9][10][11][12]. The second category includes the IVAC (intensity volume auto correlation) [13][14][15][16] and the XUV-FROG techniques [17,18]. All these methods have been frequently applied, but are in fact relatively cumbersome.…”