Intense THz Pulses Research Articles

Coherent transitions between the shallow acceptor levels in germanium using intense THz pulses

Nonlinear transmission spectroscopy was performed on a doped Ge:Ga semiconductor using intense THz pulses with different cycle numbers. When single-cycle pulses were used, non-perturbative phenomena, such as the ionization of shallow impurities, competed with the conventional coherent transition, whereas the coherent transition was dominant when multi-cycle pulses were used.

Application of high intensity THz pulses for gas high harmonic generation

AbstractThe main effects of an intense THz pulse on gas high harmonic generation are studied via trajectory analysis on the single atom level. Spectral and temporal modifications to the generated radiation are highlighted.

High-Field Transport in an Electron-Hole Plasma: Transition from Ballistic to Drift Motion

The time evolution of high-field carrier transport in bulk GaAs is studied with intense femtosecond THz pulses. While ballistic transport of electrons occurs in an n-type sample, a transition from ballistic to driftlike motion is observed in an electron-hole plasma. This onset of friction is due to the holes, which are heated by THz absorption. Theoretical calculations, which reproduce the data quantitatively, show that both electron-hole scattering and local-field effects in the electron-hole plasma are essential for the time-dependent friction.

Molecular Orientation and Alignment by Intense Single-Cycle THz Pulses

Intense single-cycle THz pulses resonantly interacting with molecular rotations are shown to induce field-free orientation and alignment under ambient conditions. We calculate and measure the degree of both orientation and alignment induced by the THz field in an OCS gas sample, and correlate between the two observables. The data presents the first observation of THz-induced molecular alignment in the gas phase.

An intense tunable femtosecond gas-plasma THz source: Application in spectroscopic studies of polycyclic aromatic hydrocarbons

Abstract We present a review on the emission of intense THz pulses from 2-color femtosecond laser filaments in gases. Through the tailoring of the filamentation process tuning of the emitted THz pulses is possible and is described in details. Using these THz pulses as a spectroscopic tool, the absorption spectra of small polycyclic aromatic hydrocarbons and their halogenated compounds are studied. Distinct resonance features for all the examined compounds have been observed, demonstrating the potential of the approach for rapidly discriminating the molecular structure of large organic molecules, in their crystalline form.

ANALYSIS OF TERAHERTZ-INDUCED OPTICAL PHASE MODULATION IN A NONLINEAR DIELECTRIC SLAB

Frequency shift of the spectrum of an incident optical pulse by an intense THz pulse inducing cross-phase modulation (XPM) in a nonlinear dielectric slab is analyzed. The efiect is predicted with a high degree of accuracy using the well-known transmission line matrix (TLM) technique. In this research, to model the THz-induced temporal and spatial variation of the dielectric permittivity of the nonlinear dielectric slab, the transmission lines of the TLM method are loaded with open shunt stubs. The parameters of the stubs are modifled in accordance with the refractive index variation of the dielectric slab, here ZnTe, induced by the strong THz pulse. The obtained numerical results are verifled with a recently reported experimental work.

Spatiotemporal control of ultrashort laser pulses using intense single-cycle terahertz pulses

We demonstrate that the intense electric field of a subpicosecond single-cycle terahertz pulse can control and manipulate the temporal, spectral, and spatial phase of a copropagating ultrashort laser pulse through the Pockels effect in an electro-optic crystal. In the temporal and spectral domains, the single-cycle THz pulse can impart either a positive or a negative quadratic phase modulation to the probe pulse, leading to a spectral shift, broadening, or pulse expansion or compression. While acting in the spatial domain, the THz-induced phase modulation induces a lenslike effect, providing focusing or defocusing of the copropagating probe beam. The experimental results are in good agreement with simulations. Our study gives a comprehensive picture of the nonlinear spatiotemporal dynamics in the high-field regime driven by the intense single-cycle THz pulse.

Femtosecond Terahertz Radiation from Femtoslicing at BESSY

Femtosecond far-infrared radiation pulses in the THz spectral range were observed as a consequence of the energy modulation of 1.7 GeV electrons by femtosecond laser pulses in the BESSY storage ring in order to generate femtosecond x-ray pulses ("femtoslicing"). In addition to being crucial for diagnostics of the laser-electron interaction, the THz radiation itself is useful for experiments where intense ultrashort THz pulses of well-defined temporal and spectral characteristics are required.

Generation of Strong Short Terahertz Pulses via Stimulated Raman Adiabatic Passage-assisted Coherent Scattering

ABSTRACTWe analyzed the efficiency of coherent scattering of infrared radiation in atomic and molecular gases for production of intense short THz pulses, using simulated Raman adiabatic passage (STIRAP). The method is based on excitation of maximal coherence when the system is undergoing through STIRAP in IR-irradiated atomic or molecular gases (for example Rb, methanol, and others) at room temperature. By applying optical pulses in correct sequence one can generate coherence in a system during STIRAP which triggers following coherent scattering of infra-red radiation, and can produce pulses of THz radiation with pulse energies ranging from several nJ to µ-J and pulse durations from several fs to ns.

Few-cycle THZ spectroscopy of semiconductor quantum structures

Optically excited plasma oscillations in n-doped GaAs epilayers emit intense THz pulses. From THz emission experiments in doped superlattices the miniband properties can be revealed. Using a THz-pump and THz-probe technique we observe the response of the intersubband polarization in semiconductor quantum structures. THz cross-correlation measurements of modulation doped semiconductor quantum structures allow to determine the absorption, the dispersion, and the dephasing times of the quantized electrons.

Few-cycle THz spectroscopy of nanostructures

Optically excited plasma oscillations in n-doped GaAs epilayers emit intense THz pulses. Using a THz-pump and THz-probe technique we observe the response of the intersubband polarization in semiconductor quantum structures. THz Cross-correlation measurements of modulation doped semiconductor quantum structures allow to determine the absorption, the dispersion, and the dephasing times of the quantized electrons.