XUV Transient Absorption Spectroscopy: Probing Laser-Perturbed Dipole Polarization in Single Atom, Macroscopic, and Molecular Regimes

Abstract

Abstract:We employ an extreme ultraviolet (XUV) pulse to impulsively excite dipole polarization in atoms or molecules, which corresponds to coherently prepared superposition of excited states. A delayed near infrared (NIR) pulse then perturbs the fast evolving polarization, and the resultant absorbance change is monitored in dilute helium, dense helium, and sulfur hexafluoride (SF 6 ) molecules. We observe and quantify the time-dependence of various transient phenomena in helium atoms, including laser-induced phase (LIP), time-varying (AC) Stark shift, quantum path interference, and laser-induced continuum structure. In the case of dense helium targets, we discuss nonlinear macroscopic propagation effects pertaining to LIP and resonant pulse propagation, which account for the appearance of new spectral features in transient lineshapes. We then use tunable NIR photons to demonstrate the wavelength dependence of the transient laser induced effects. In the case of molecular polarization experiment in SF 6 , we show suppression of XUV photoabsorption corresponding to inter-valence transitions in the presence of a strong NIR field. In each case, the temporal evolution of transient absorption spectra allows us to observe and understand the transient laser induced modifications of the electronic structure of atoms and molecules.

Non-Adiabatic Electronic and Vibrational Ring-Opening Dynamics resolved with Attosecond Core-Level Spectroscopy

“…Thus, their photochemical dynamics and relaxation processes are of great interest 33 for various applications. The results of our investigation demonstrate that the initially recognized potential of ultrafast x-ray absorption spectroscopy [34][35][36][37][38][39] is now matured with…”

Macroscopic transient absorption in a V-type three-level system

“…Moreover, propagation effects have been referred to in high harmonic generation [24] and four-wave mixing [25]. However, only limited experimental attempts [26][27][28][29][30] have explicitly shed light on their roles in photoabsorption, and most transient absorption studies have been conducted intentionally with either thin or dilute medium to prevent propagation effects from interfering with the results and the breakdown of Beer-Lambert law. Although TAS has emerged as a powerful method to gain amplitude and phase information on the evolution of dilute systems (see, for example, references [3,6,7,31]), whether pronounced spectral features in more general cases can be captured or not after incorporating propagation effects with the retrieved information still remains.…”

Real-Time Reconstruction of the Strong-Field-Driven Dipole Response

“…This usually requires two (or more) controlled events, e.g., a triggering pump and a delayed probe pulse, with timeresolved information gained by controllably varying the interpulse delays. For example, femto-and attosecond timeresolved absorption spectroscopy [3][4][5] were used with great success to access explicitly time-dependent excited-state dynamics to uncover the nonequilibrium electron dynamics of atomic [6][7][8], molecular [9][10][11], and condensed-phase [12][13][14] systems in the presence of additional interactions. Such out-of-equilibrium processes include, e.g., the coupling of multielectron configuration channels [15], strong-field manipulation of autoionization [16,17], or the strong coupling between excited quantum states [18,19].…”