Abstract-Generalized framework for determining time origin in terahertz emission spectroscopy on the basis of causality

Takeya Unuma and Kaishu Minami

Fig. 1 Analysis of THz emission data simulated for a damped cosine current. (a) Temporal waveform of THz electric field E(t) convolved with a resolution of τres = 0.30 ps. (b) Fourier spectra of amplitude ρ(ω) and phase θ(ω). (c) Causality-based functions K(δt) versus possible time-origin misplacement δt (curves 1–3) computed with the three different sets of anchor points (ω0/2π, ω1/2π, ω2/2π) = (0.98, 1.22, 2.06), (0.98, 1.50, 2.06), and (0.98, 1.79, 2.06) THz. (d) Magnified view of (c) around the point where causality is best satisfied.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-4-5136

We develop a generalized causality-based framework for determining the time origin in terahertz emission spectroscopy. Our framework is formulated in terms of a multiply subtractive Kramers-Kronig relation and can treat all major mechanisms of terahertz emission, which include the occurrence of a delta-function-like instantaneous polarization observed typically in nonlinear optical processes. We show that a function derived within our framework properly determines the positions of t = 0 both for simulated terahertz waveforms and for a measured one obtained in biased conjugated polymers. This function will be useful for an in-depth understanding of ultrafast phenomena involving terahertz emission in various optoelectronic materials.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement