Table-top extreme ultraviolet second harmonic generation

Abstract

The lack of available table-top extreme ultraviolet (XUV) sources with high enough fluxes and coherence properties has limited the availability of nonlinear XUV and x-ray spectroscopies to free-electron lasers (FELs). Here, we demonstrate second harmonic generation (SHG) on a table-top XUV source by observing SHG near the Ti M2,3 edge with a high-harmonic seeded soft x-ray laser. Furthermore, this experiment represents the first SHG experiment in the XUV. First-principles electronic structure calculations suggest the surface specificity and separate the observed signal into its resonant and nonresonant contributions. The realization of XUV-SHG on a table-top source opens up more accessible opportunities for the study of element-specific dynamics in multicomponent systems where surface, interfacial, and bulk-phase asymmetries play a driving role.

Extreme Ultraviolet Second Harmonic Generation Spectroscopy in a Polar Metal

“…The χ eff (2) spectrum was then extracted using eq after binning and averaging spectra based on the photon energy and intensity of the driving fundamental pulse. The inherent jitter of the XFEL, both in frequency and intensity, allowed for a high-fidelity extraction of χ eff (2) ( 2ω) with significantly more data points, compared to refs − . For the T = 62 K set of measurements, a quadratic function was fit to a plot of I (ω) vs I (2ω), at each energy where the second-order fit coefficient is modulo |χ eff (2) (2ω)| 2 , with χ eff (2) (2ω) a rank-three tensor of four independent components (χ zzz (2) ,χ xxz (2) , χ zxx (2) , and χ xxy (2) ), because of point group symmetry (Figure e).…”

“…Such effects were not visible in XUV-SHG at 160 K, but may have been below the detection limit of this experiment. Through complementary theory calculations, Helk et al 23 noted that resonant and nonresonant contributions to SHG can be of the same order of magnitude in the XUV regime, because of allowed transitions from the valence band to high-energy continuum states. Further development of SHG methodology in the XUV and SXR regimes will be essential to deconvolute these contributions and to fully characterize element-specific responses.…”

“…To gain insight into the nature of the polar phase, we turn to extreme ultraviolet second harmonic generation (XUV-SHG) spectroscopy, which is a newly developed method viable for studying bulk-phase noncentrosymmetric masterials, surfaces, , and buried interfaces in the XUV or the soft X-ray (SXR) regimes, where the objective is to perform SHG under resonant conditions, and in the hard X-ray regime, where a nonresonant approach is usually taken. − In SXR- or XUV-SHG spectroscopy, the incident X-ray beam is resonant or half-resonant with a core-to-valence transition, such that the resulting resonantly enhanced, background-free signal is sensitive to core levels in the electronic structure. By energetically resolving the SHG emission, the symmetry breaking can be correlated to particular spectral features.…”

Element-specific electronic and structural dynamics using transient XUV and soft X-ray spectroscopy

“…In addition to linear X-ray absorption spectroscopy, novel nonlinear X-ray methods are emerging as a promising field for both fundamental light-matter interaction and material characterization. 57 Recent developments of intense X-ray sources at larger facilities are now making nonlinear X-ray measurements possible. X-ray transient grating spectroscopy 58 can directly give element-specific measurements of vibrational, magnetic, or electronic transport.…”

Intense narrowband XUV pulses from a compact setup

“…Ultrashort, intense extreme-ultraviolet (XUV) pulses are used in a growing number of applications, which include nonlinear multiphoton ionization of atoms [1][2][3][4][5][6], molecules [7,8] and clusters [9][10][11], second-harmonic generation in thin films [12] and the study of XUV strong-field physics [13,14]. Intense XUV pulses are also a prerequisite for performing XUV-pump XUV-probe experiments where XUV pulse durations down to the attosecond regime have already been used [15][16][17].…”