Abstract-Two-dimensional terahertz spectroscopy of condensed-phase molecular systems

 

 

The Journal of Chemical Physics

Klaus Reimann,  Michael Woerner. Thomas Elsaesser, 

Setup for three-pulse measurements. BS are beam splitters, Q are quartz glass windows for the vacuum chamber, NL are nonlinear crystals for THz generation (GaSe), ZnTe is the electro-optic crystal, λ/4 is a quarter-wave plate, WP is a Wollaston polarizer, and PD1 and PD2 are silicon photodiodes. The detected signal is the difference of the outputs of PD1 and PD2.

https://aip.scitation.org/doi/full/10.1063/5.0046664

Nonlinear terahertz (THz) spectroscopy relies on the interaction of matter with few-cycle THz pulses of electric field amplitudes up to megavolts/centimeter (MV/cm). In condensed-phase molecular systems, both resonant interactions with elementary excitations at low frequencies such as intra- and intermolecular vibrations and nonresonant field-driven processes are relevant. Two-dimensional THz (2D-THz) spectroscopy is a key method for following nonequilibrium processes and dynamics of excitations to decipher the underlying interactions and molecular couplings. This article addresses the state of the art in 2D-THz spectroscopy by discussing the main concepts and illustrating them with recent results. The latter include the response of vibrational excitations in molecular crystals up to the nonperturbative regime of light–matter interaction and field-driven ionization processes and electron transport in liquid water.

Abstract-Mid-infrared beam splitter for ultrashort pulses

Carmine Somma, Klaus Reimann, Michael Woerner, Thomas Kiel, Kurt Busch, Andreas Braun, Mathias Matalla, Karina Ickert, and Olaf Krüger

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-42-15-2918&origin=search

A design is presented for a beam splitter suitable for ultrashort pulses in the mid-infrared and terahertz spectral range consisting of a structured metal layer on a diamond substrate. Both the theory and experiment show that this beam splitter does not distort the temporal pulse shape.

© 2017 Optical Society of America

Abstract-Strong Local-Field Enhancement of the Nonlinear Soft-Mode Response in a Molecular Crystal

Giulia Folpini, Klaus Reimann, Michael Woerner, Thomas Elsaesser, Johannes Hoja,  Alexandre Tkatchenko,

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.097404

The nonlinear response of soft-mode excitations in polycrystalline acetylsalicylic acid (aspirin) is studied with two-dimensional terahertz spectroscopy. We demonstrate that the correlation of ${\mathrm{CH}}_3$rotational modes with collective oscillations of $\pi$ electrons drives the system into the nonperturbative regime of light-matter interaction, even for a moderate strength of the THz driving field on the order of $50\mathrm{kV}/\mathrm{cm}$. Nonlinear absorption around 1.1 THz leads to a blueshifted coherent emission at 1.7 THz, revealing the dynamic breakup of the strong electron-phonon correlations. The observed behavior is reproduced by theoretical calculations including dynamic local-field correlations.

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Abstract-Strong local-field enhancement of the nonlinear softmode response in a molecular crystal

Giulia Folpini, Klaus Reimann, Michael Woerner, Thomas Elsaesser, Johannes Hoja, and Alexandre Tkatchenko

https://journals.aps.org/prl/accepted/ae076Yc0Mb51db56829d2d3865649318b071feee8

The nonlinear response of softmode excitations in polycrystalline acetylsalicylic acid (aspirin) is studied with two-dimensional terahertz spectroscopy. We demonstrate that the correlation of CH3 rotational modes with collective oscillations of \pi electrons drives the system into the nonperturbative regime of light-matter interaction, even for a moderate strength of the THz driving field on the order of 50~kV/cm. Nonlinear absorption around 1.1~THz leads to a blueshifted coherent emission at 1.7~THz, revealing the dynamic breakup of the strong electron-phonon correlations. The observed behavior is reproduced by theoretical calculations including dynamic local-field correlations.

Abstract-Phase-resolved two-dimensional terahertz spectroscopy including off-resonant interactions beyond the χ(3) limit

Carmine Somma1, Giulia Folpini1, Klaus Reimann1, Michael Woerner1,a) and Thomas Elsaesser1


1 Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, 12489 Berlin, Germany
a) Electronic mail: woerner@mbi-berlin.de
J. Chem. Phys. 144, 184202 (2016); http://dx.doi.org/10.1063/1.4948639

http://scitation.aip.org/content/aip/journal/jcp/144/18/10.1063/1.4948639

We present the first two-dimensional (2D) terahertz (THz) experiment with three phase-locked THz pulses and a fully phase-resolved detection of the nonlinearly emitted field by electrooptic sampling. In a prototype experiment we study the ultrafast dynamics of nonlinear two-phonon and two-photon interbandcoherences in the narrow-gap semiconductor InSb. Due to the extraordinarily large optical interband dipole of InSb the experiments were performed in the strongly nonperturbative regime of light-matter interaction allowing for impulsive off-resonant excitation of both two-phonon coherences and two-photoninterband coherences, the ultrafast dynamics of which is experimentally observed as a function of the waiting time in the three-pulse 2D experiment. Our novel three-pulse 2D THz spectroscopy paves the way for the detailed investigation of nonlinear quantum coherences in solids and holds potential for an extension to other systems.

Abstract-Ultra-broadband terahertz pulses generated in the organic crystal DSTMS

Carmine Somma, Giulia Folpini, Jyotsana Gupta, Klaus Reimann, Michael Woerner, and Thomas Elsaesser
https://www.osapublishing.org/ol/abstract.cfm?uri=ol-40-14-3404#Abstract

Electric-field transients covering the extremely wide frequency range from 0.5 to 26 THz are generated in the organic nonlinear crystal 4-N,N-dimethylamino-4′-N′-methylstilbazolium 2,4,6-trimethylbenzenesulfonate (DSTMS). Parametric difference frequency mixing within the spectrum of 25-fs amplified pulses centered at 800 nm provides a highly stable broadband output with an electric-field amplitude of up to several hundred kilovolts/cm. The high stability of the terahertz pulse parameters allows for sensitive phase-resolved broadband spectroscopy of optically thick crystalline samples.

© 2015 Optical Society of America

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Abstract-Ultrafast two-dimensional terahertz spectroscopy of elementary excitations in solids

Michael Woerner, Wilhelm Kuehn, Pamela Bowlan, Klaus Reimann and Thomas Elsaesser
http://iopscience.iop.org/1367-2630/15/2/025039

Recent experimental progress has allowed for the implementation of nonlinear two-dimensional (2D) terahertz (THz) spectroscopy in the ultrafast time domain. We discuss the principles of this technique based on multiple phase-locked electric field transients interacting in a collinear geometry with a solid and the phase-resolved detection of the THz fields after interaction with the sample. To illustrate the potential of this new method, 2D correlation spectra of coupled intersubband-longitudinal optical phonon excitations in a double quantum well system and a study of ultrafast carrier dynamics in graphene are presented.