The generation of Terahertz (THz) waves via two-color plasma in gas has captured the interest of the research community due to its capability to create intense waves characterized by a wide and adjustable spectrum. Efforts aimed at improving the performance of THz radiation for particular applications entail examining and adjusting several variables. In this study, we introduce a simple method for manipulating THz polarization through the adjustment of chirp and wavelength dispersion. Specifically, we will show that by managing these characteristics, it is possible to produce THz waves with polarizations that can be elliptical, circular, or resemble a "flower" pattern. The implications of these changes on the spatiotemporal path of THz radiation will also be examined.
The generation of Terahertz (THz) radiation using two-color plasma in gases has garnered significant interest within the scientific community for its ability to produce powerful waves with very broad and tunable spectra. Understanding how to modify the characteristics of the generated THz radiation paves the way for optimizing its performance for targeted applications. To achieve this, various approaches have been explored, however, the combined impact of chirp and wavelength dispersion has not yet been thoroughly investigated. Our study aims to understand how the laser chirp and the phase difference caused by air dispersion influence the shape of the THz pulse. The findings highlight that these factors significantly alter the shape of the THz pulse. Specifically, the nature of the chirp (positive or negative) in the pump laser distinctly affects the pulse shape. For instance, a pump laser with positive chirp results in a THz waveform with a negative monopolar configuration, while a laser with negative chirp generates a THz pulse with a positive configuration.
We present the application of THz monocycles to the Atom Probe Tomography (APT), an analytical microscope that allows the three-dimensional mapping of chemical heterogeneities in a material at the atomic scale. When a positive electric field of several volts per angstrom is applied to the surface of a material, the surface atoms evaporate as ions even at cryogenic temperatures, this is the work principle of APT. We prove that THz transient can induce the controlled evaporation of surface atoms due to the strong increase in the THz field in the near field of the sample. In addition, the use of THz pulses reduces the thermal effects reported when using laser pulses in the visible or near ultraviolet domain. We are also studying the effect of the THz pulses on the energy of the evaporated ions.
We present findings on High Harmonic Generation (HHG) in solids utilizing a high-energy fiber laser system operating at 1550 nm. The driving laser source comprises an Erbium-Doped Fiber chirped pulse Amplifier (EDFA) combined with a post-compression stage employing a hollow-core photonic crystal fiber (HC-PCF) filled with noble gases. Nonlinear self-compression in the HC-PCF enables the generation of ultrashort pulses with a duration of 50 fs and energy of 0.91 μJ at a repetition rate of 660 kHz. In a first step, harmonics up to H7 were observed when focusing the laser into small bandgap materials such as Zinc Oxide (ZnO). Subsequently, the system was enhanced to measure high harmonics in the extreme ultraviolet (XUV) range, with harmonics up to H25 observed using a large bandgap material, magnesium oxide (MgO). To the best of our knowledge, this represents the first solid-state HHG source driven by a high-energy few-cycle fiber laser in the telecom region.
We studied polarization-resolved photoluminescence originating from a ZnO-(Mg,Zn)O quantum well heterostucture embedded within an atom probe tip, i.e. a nanoscale needle-shaped sample with apex radius of several tens of nm, prepared by focused ion beam. The study was carried out within a photonic atom probe before the atom probe analysis of the sample. This setup allows for the analysis of the polarization of the photoluminescence emitted by the tip and for its orientation around its axis. While the photoluminescence emitted by bulk ZnO and by the (Mg,Zn)O alloy is strongly polarized along the tip axis, coinciding with the crystal [1-100] axis, the ZnO/(Mg,Zn)O quantum well luminescence appears to be strongly polarized along its in-plane direction, perpendicular to the crystal [1-100] axis. Finite-difference time domain calculations provide a key for the interpretation of these results in terms of selection rules and of effects related to the waveguide effect of the tip.
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