Abstract-Varying pre-plasma properties to boost terahertz wave generation in liquids

                                                        Communications Physics

Evgenia A. Ponomareva, Azat O. Ismagilov, Sergey E. Putilin, Anton N. Tsypkin, Sergei A. Kozlov,  Xi-Cheng Zhang,  

https://www.nature.com/articles/s42005-020-00511-1

Laser-driven nonlinear phenomena can both reveal the structural features of materials and become the basis for the development of various translated technologies, including highly intense terahertz sources. Here we realize a modified single-color double-pulse excitation scheme for enhancing the terahertz wave generation in flat liquid jets, and we show that the pre-ionization effect is crucial for finding the optimal input conditions. The experimental results, being supported by numerical simulations, reveal the preference for longer pre-pulses to induce the effective ionization process and shorter signals for the strong laser-plasma interaction. In addition to the identified features of the terahertz wave energy enhancement with respect to the duration change for both pulses and their ratio variation, we state the possibility of achieving the optical-to-THz conversion efficiency value up to 0.1% in the case of double-pulse excitation of an α-pinene jet.

Abstract-Optimized design for a terahertz parametric oscillator based on degenerate four-wave mixing in silicon nitride

Tahereh Amini and Fazel Jahangiri

https://www.osapublishing.org/josab/abstract.cfm?uri=josab-37-9-2725

We propose terahertz wave generation using a parametric oscillator based on phase-matched and non-phase-matched degenerate four-wave mixing processes within a silicon nitride Fabry–Perot microcavity. The central frequency of the generated terahertz waves would be tunable over the frequency range of 3.6–5.73 THz by varying the wavelength of the pump wave. The best phase-matching condition is achieved at a frequency of 5 THz, and an optimum peak power of 329 W is obtained at a frequency of 4.29 THz.

© 2020 Optical Society of America

Abstract-Terahertz-wave generation from surface phonons at forbidden frequencies of lithium niobate

Jun-ichi Shikata, Seigo Ohno, Hiroaki Minamide,

https://www.jstage.jst.go.jp/article/elex/advpub/0/advpub_17.20200133/_article

This paper describes terahertz (THz)-wave generation within forbidden bands in polar crystals, focusing on the A1 phonon modes in lithium niobate. This material exhibits two negative-permittivity frequency ranges at 7.4-12.7 THz and 18.8-25.6 THz for the lowest and highest A1 modes, respectively. Exploiting the finite-difference time-domain simulations, we demonstrate that both the surface phonon modes can be radiative with a structured grating. Fourier analyses of the radiative fields reveal the relevant peaks in the spectrum as well as the dispersion relations. Our results provide a novel method for coherent THz-wave sources at unexplored THz frequencies.

Abstract-Terahertz wave generation from liquid nitrogen

Alexei V. Balakin, Jean-Louis Coutaz, Vladimir A. Makarov, Igor A. Kotelnikov, Yan Peng, Peter M. Solyankin, Yiming Zhu, and Alexander P. Shkurinov

Fig. 1. Experimental setup. M–dielectric mirror; MM–metallic mirror; BS–beam splitter; 𝜆/2$\lambda /2$–half-wave phase plate; L–lens; PM–off-axis parabolic mirror; BBO–β$\mathrm{\beta }$-barium borate crystal.

https://www.osapublishing.org/prj/abstract.cfm?uri=prj-7-6-678

We present the results of research carried out for the first time, to the best of our knowledge, on the generation of terahertz radiation under the action of “single-color” and “dual-color” high-power femtosecond laser pulses on liquefied gas–liquid nitrogen. Our experimental results supported by careful theoretical interpretation showed clearly that under femtosecond laser radiation, liquid and air emit terahertz waves in a very different way. We assumed that the mobility of ions and electrons in liquid can play an essential role, forming a quasi-static electric field by means of ambipolar diffusion mechanism.

© 2019 Chinese Laser Press

Abstract-Terahertz wave generation element, terahertz wave detection element, and terahertz time domain spectroscope device

Ouchi, Toshihiko (Machida, JP) 
United States Patent 9304373
http://www.freepatentsonline.com/9304373.html

A terahertz wave generation element is provided, which includes: an optical waveguide including a core of electro-optic crystal; an optical coupler for extracting a terahertz wave generated from the optical waveguide when light propagates in the optical waveguide to a space; and a reflecting layer disposed on the opposite side to the optical coupler with respect to the core of the optical waveguide, so as to reflect the generated terahertz wave. According to the element, it is possible to provide a generation element that can generate a relatively high intensity terahertz wave efficiently by photoexcitation or generate a terahertz wave having a relatively narrow pulse width, so as to flexibly control waveform shaping of the generated terahertz wave.

Abstract-Evaluation of polarized terahertz waves generated by Cherenkov phase matching

Takuya Akiba, Yasuhiro Akimoto, Koji Suizu, Katsuhiko Miyamoto, and Takashige Omatsu  »View Author Affiliations

Applied Optics, Vol. 53, Issue 8, pp. 1518-1522 (2014)
http://dx.doi.org/10.1364/AO.53.001518

http://www.opticsinfobase.org/ao/abstract.cfm?uri=ao-53-8-1518

We report terahertz (THz) wave generation by satisfying Cherenkov phase-matching condition in both s and ppolarizations. A dual-wavelength optical parametric oscillator is constructed from two potassium titanium oxide phosphate crystals pumped by a frequency-doubled Nd:YAG laser. By rotating the orientation of both a lithium niobate crystal (LiNbO3) and the polarization of the pump waves, the polarization of the THz wave changes. Due to the difference in the refractive index and absorption, the output power for p polarization is one tenth that for s polarization. A tuning range from 0.2 to 6.5 THz is obtained for s polarization, and from 0.2 to 4.2 and 5.4 to 6.9 THz for p polarization. The extraction efficiency is improved by changing the angle of prism for p polarization, and a large phase change occurs at total internal reflection. Consequently, p-polarized THz waves are optimal for spectroscopic applications.

© 2014 Optical Society of America