CC BY
7THz-I-4
NONLINEAR AND TERAHERTS PHOTONICS
THz emission from single metallic microdroplet targets irradiated with
femtosecond laser pulses
A. V. Balakin1, P. M. Solyankin2, M. S. Krivokorytov3'4, A. P. Shkurinov1
ALT'22
1-Faculty of Physics, Lomonosov Moscow State University, Moscow 119991, Russia 2- Institute on Laser and Information Technologies of the Russian Academy of Sciences—Branch of the Federal Scientific Research Center "Crystallography and Photonics" of the Russian Academy of Sciences, Shatura,
140700, Russia
3- Moscow Institute of Physics and Technology, Dolgoprudny, Moscow Oblast 141701, Russia 4 - Institute for Spectroscopy, Russian Academy of Sciences, Troitsk, Moscow 108840, Russia
a.v. balakin@physics.msu.ru
Here we present results of investigation of THz generation in liquid metal eutectic alloy (48% Sn, 52% In) microdroplets irradiated with femtosecond laser pulses. The single liquid-metal microdroplets with a diameter around 50 um were produced with special dispenser device as it has been described in our previous paper [1]. These microdroplets were falling down into vacuum chamber and their flowing was synchronized with the laser pump pulses from Ti:Sa regenerative amplifier. It provides possibility to supply a new microdroplet coming across each laser pulse, and to eliminate registration of any cumulative effects. A double-pulses excitation scheme with low-energy prepulse and more powerful second pulse, which was discussed indetails in [1], was applied to get efficient THz generation from the droplet.
In particular, one of worthwhile phenomenon investigated in our experiments was a study of the radiation pattern of THz emission from the single metallic microdroplet excited by ultra-short laser pulses. A special vacuum chamber made of a polypropylene tube transparent in THz, was designed to measure the THz radiation pattern in a wide range of angles (0°-150° relative to the laser pump beam direction). X-ray signal from the microdroplet target was measured simultaneously with the THz one in our experiments as well. A typical view of dependence of the THz signal from a microdroplet on the detection angle and energy of X-ray radiation is depicted in Fig.1. As one may see, it demonstrates a complicated multi-lobe structure with clear strong lobe directed in 60 degrees relative to the optical pump. We believe that observed behavior of the THz radiation pattern could be associated with an interference of contributions from the dipole and quadrupole currents, and the presence of opaque thick droplet could lead to effective decreasing of forwardly directed contribution into the THz signal. Also we compare this case with previously studied radiation pattern of THz emission from gas cluster jet irradiated with intense femtosecond laser pulses [2].
Fig. 1. Dependence of the THz signal from a microdroplet on the detection angle and energy of X-ray radiation. Droplet diameter is 50 ^m.
This work was funded partly by RFBR and ROSATOM according to the research project № 20-21-00143, partly by the Ministry of Science and Higher Education within the State assignment FSRC "Crystallography and Photonics" RAS and in part by the Ministry of Science and Higher Education of the Russian Federation in framework of Agreement № 075-15-2022-830from 27May 2022.
[1] Solyankin P. M. et al. Single free-falling droplet of liquid metal as a source of directional terahertz radiation //Physical Review Applied, vol. 14, №. 3, p. 034033 (2020)
[2] Balakin A. V. et al. Directional terahertz beam generation under interaction of an intense femtosecond laser pulse with a cluster
jet //JOSA B, vol. 38, №. 11, p.. 3515-3522 (2021).
