Abstract-THz generation from laser-induced breakdown in pressurized molecular gases: on the way to terahertz remote sensing of the atmospheres of Mars and Venus

Petr M. Solyankin, Irina A. Nikolaeva, Andrew Angeluts, Daniil E. Shipilo, Nikita Minaev,  Nikolay A. Panov, Alexey V. Balakin, Yiming Zhu, Olga Kosareva,  Alexander P. Shkurinov

https://iopscience.iop.org/article/10.1088/1367-2630/ab60f3/meta

The present paper studies the generation of terahertz (THz) radiation in CO2 in comparison with atmospheric air at a wide range of pressures. We established experimentally and explained theoretically that for these gases there are optimal pressures at about 1 bar for air and 0.5 bar for CO2 under which the efficiency of conversion from near-infrared to THz frequencies is the highest. We consider the possibility of applying femtosecond laser-induced THz generation for the study of the atmosphere of Mars and found that the overall THz yield near the surface of Mars is just a factor of 6 lower than on Earth. Comparable THz energy on the two planets is associated with underdense plasma on Earth (~10% of neutrals) and full double ionization of carbon dioxide on Mars (~200% of neutrals), the latter opening great perspective for THz remote sensing of trace gases in the Martian atmosphere.

Abstract-Terahertz Switching Focuser Based on Thin Film Vanadium Dioxide Zone Plate

Petr M. Solyankin, Mikhail N. EsaulkovIgor,  A. ChernykhIvan,  V. Kulikov, Maxim L. Zanaveskin, Andrey R. Kaul, Artem  M. Makarevich, Dmitrii I. Sharovarov, Oleg E. Kameshkov, Boris A. Knyazev, Alexander P. Shkurinov, 

https://link.springer.com/article/10.1007/s10762-018-0540-0

In this paper, we propose a switchable focuser device based on a Fresnel zone plate (FZP) structure for terahertz (THz) applications. Each FZP contains seven rings, etched in thin VO2film with the designed focal lengths of 50 and 100 mm for 3.7-THz frequency. Temperature-induced VO2 phase transition leads to the change in dielectric susceptibility of the material, which allows one to switch on and off the focusing properties of the device. The devices were tested with radiation of 3.1 and 3.7 THz emitted by quantum cascade lasers. Experimental results were compared with numerical simulations. In this article, we compare the FZP based on VO2 films with different properties and show that a thicker VO2 film reveals higher focusing efficiency, while a thinner one reveals a higher modulation ratio for the peak intensity at the focal point of FZP. We demonstrate experimentally the near-diffraction-limited size of the beam in the focal point of the device. Switching between two phase states of the VO2 films results in up to the 38-fold change of intensity in the focal point.