Nonlinear XUV signal generation probed by transient grating spectroscopy with attosecond pulses

Abstract

Nonlinear spectroscopies are utilized extensively for selective measurements of chemical dynamics in the optical, infrared, and radio-frequency regimes. The development of these techniques for extreme ultraviolet (XUV) light sources facilitates measurements of electronic dynamics on attosecond timescales. Here, we elucidate the temporal dynamics of nonlinear signal generation by utilizing a transient grating scheme with a subfemtosecond XUV pulse train and two few-cycle near-infrared pulses in atomic helium. Simultaneous detection of multiple diffraction orders reveals delays of ≥1.5 fs in higher-order XUV signal generation, which are reproduced theoretically by solving the coupled Maxwell–Schrödinger equations and with a phase grating model. The delays result in measurable order-dependent differences in the energies of transient light induced states. As nonlinear methods are extended into the attosecond regime, the observed higher-order signal generation delays will significantly impact and aid temporal and spectral measurements of dynamic processes.

Self-heterodyned detection of dressed state coherences in helium by noncollinear extreme ultraviolet wave mixing with attosecond pulses

“…Cross sectiondependent resonant pulse propogation effects further distort the absorption profile of the 1s2p state [35][36][37]. Additional absorption features corresponding to LISs, which can be simplistically described as virtual states in a two-photon Raman-like transition to a dark state involving an XUV and a NIR photon, appear at energies distinct from the bright states [31,34,[38][39][40][41]. As shown in Table 1, LISs appear in energy either one NIR photon above (+) or below (-) their corresponding dark states.…”

“…The experimental apparatus employed for XUV wave-mixing measurements has been described previously and is shown in Fig. 1a [30][31][32]. Briefly, 22 fs duration NIR pulses produced by a 2 mJ, 1 kHz Ti:Sapphire multipass µm at full width half maximum (FWHM), which is substantially larger than the estimated ~20 µm XUV beam waist.…”

“…These measurements provide evidence of four-wave mixing interactions in the form of quantum beat oscillations [22][23][24][25][26], but they lack the selectivity of higher-order wave-mixing techniques to disentangle complex spectra [27]. Capitalizing on the phasematching conditions inherent in wave-mixing processes, recent experiments employed a noncollinear beam geometry between an XUV attosecond pulse train and either one [28,29] or two [30][31][32] moderately intense NIR pulses to measure transient spectra of spatially isolated XUV wave-mixing signals. These time-dependent wave-mixing signals were utilized to characterize a dark state in N2 [30], to measure ultrafast lifetimes of autoionizing states in krypton [32], and to construct the first multidimensional spectrum in the XUV by implementing NIR pulse shaping techniques [33].…”

Autoionization dynamics of (2P1/2)ns/d states in krypton probed by noncollinear wave mixing with attosecond extreme ultraviolet and few-cycle near infrared pulses

“…The apparatus utilized for background-free attosecond wave-mixing measurements has been described previously 20,22 and is shown in Fig. 1a.…”

“…21 In a recent study, the nonperturbative nature of noncollinear wave-mixing with these ultrashort, intense pulses was explored in He, revealing that the accumulation of the AC Stark phase over the NIR pulse duration leads to delays in higherorder signal generation. 22 However, all of these experiments were performed on systems containing only long-lived Rydberg states, and the generation and time dependence of nonlinear signals from XUV-excited states that decay on ultrafast timescales has yet to be established.…”