Retrieving the susceptibility from time-resolved terahertz experiments

Abstract

We present an analytical expression for the observed signal in time-and phase-resolved pump-probe studies, with particular emphasis on terahertz time-domain spectroscopy. Maxwell's equations are solved for the response of damped, harmonic oscillators to a driving probe field in the perturbative regime. Our analytical expressions agree with the one previously reported in the literature ͓Nemec et al., J. Chem. Phys. 122, 104503 ͑2005͔͒ in the Drude limit; however, they differ in the case of a vibrational resonance.

Simultaneous ultrafast probing of intramolecular vibrations and photoinduced charge carriers in rubrene using broadband time-domain THz spectroscopy

“…34, will be detailed in a separate publication. 33 In brief, the treatment takes into account the spatial variations of the pump intensity along the direction of excitation ͑determined by the optical absorption coefficient͒, ground-state sample dispersion with multiple resonant features, dispersion between the group velocity of the pump, and the THz phase velocity. The detector response function is also accounted for.…”

“…The detector response function is also accounted for. 33 The parameters describing the ground-state absorption are taken from a fit to the Fourier transform infrared ͑FTIR͒ spectrum shown in Fig. 1͑b͒, while the Drude scattering rate ͑which hardly influences the results͒ is taken as 105ϫ 10 12 rad s −1…”

Non-equilibrium Dynamical Mean-Field Theory

“…To describe the experimental signals of time-resolved optical spectroscopy one has to know how electromagnetic pulses of finite length propagate through a material which is driven out of equilibrium by means of the pump pulse [225,226,227]. When the probe field is weak, its effect can be calculated as a linear response δj of the current j to the external electrical field δE β (r, t),…”

“…Provided that σ(t, t ′ ) is known, one can calculate the reflected and transmitted pulses from Maxwell's equations, taking the induced current inside the sample from Eq. (8.1) [225,226,227]. However, the solution of those equations, and the coprresponding derivation of generalized reflection and transmission coefficients is more complicated than for samples that are in equilibrium.…”

Theory of time-resolved optical spectroscopy on correlated electron systems

“…However, if the optical conductivity ͑t , tЈ , r͒ depends on t and tЈ separately, then there is no simple relation to the reflection coefficient r͑t , tЈ͒. 41 This is evident from the definition ͑4͒, which shows that a sample which is not in equilibrium can modulate the pulse frequency. From now on we use an approximate form for r͑t , tЈ͒, which is valid for reflection from a very thin slab ͑with thickness L → 0͒, such that the phase lag between the borders is negligible and the conductivity is constant throughout the sample.…”