CC BY
18LM-I-20
Scattering and self-healing of terahertz high-order Bessel beams transmitting through randomly inhomogeneous
media and obstacles
B.A. Knyazev1,2, V.S. Pavelyev1, K.N. Tukmakov1, A.S. Reshetnikov1, V.V. Gerasimov2,
N.D. Osintseva2
1- Samara National Research University, Moskovskoe Shosse 34, Samara, Russia, 443086
2- Budker Institute of Nuclear Physics of SB RAS, Pr. Lavrentyeva 11, Novosibirsk, Russia,
630090
b.a. knyazev@inp. nsk.su
Bessel beams with orbital angular momentum are considered as one of the possibilities for creating multiplex communication lines in the atmosphere [1]. At the Novosibirsk free electron laser (NovoFEL) facility [2], experiments were being carried out in the terahertz range to study the propagation of Bessel beams (BB) of orders from zero to fourth through randomly inhomogeneous phase media and amplitude obstacles. The beams were created using binary silicon axicons with spiral zones, the period of which was 3.2 mm, and the height of the diffractive relief was calculated for a wavelength of 141 ^m and was equal to 29.1 ^m. A well-formed "diffraction-free" Bessel beam with such parameters existed at distances from 150 to 350 mm from the axicon [3].
The laser generated monochromatic linearly polarized radiation with a pulse duration of 100 ps and a repetition rate of 5.6 MHz. The value of the mode radius of the Gaussian beam of the NovoFEL in the plane of the axicons was 12.1 mm. The intensity distribution was recorded by a Pyrocam IV pyroelectric detector with a matrix size of 25.6 x 25.6 mm2. Obstacles were installed whether directly behind the axicon or at the beginning of the Bessel beam formation region at a distance of about 150 mm. The intensity distribution of the beam passing through the obstacle was recorded at different distances from the axicon up to the beam decay region (350 mm). To study the degree of conservation of the fraction of radiation containing the initial Bessel mode, we used the property of the BB to form a narrow ring at the focus of the lens, containing, in the case of non-disturbed BB, all the energy of the initial beam. An example of the measurement results for a Bessel beam with a topological charge f_ =4 is shown in Fig. 1. Knowing the properties exhibited by Bessel beams with orbital angular momentum when passing through the lens cascade, it can be argued that the results shown in Fig. 1 demonstrate a high content of the corresponding Bessel mode in the reconstructed beam.
This work was supported by the Russian Science Foundation, grant 19-72-20202. Experiments were carried out at the Novosibirsk free electron laser, which is a part of the Shared Research Facility "Siberian Synchrotron and Terahertz Radiation Center."
[1] I.P. Lukin, E.Kh. Tanier. Formation of a Bessel beam with conical focusing in a turbulent atmosphere. Bulletin of the Tomsk Polytechnic University. v. 318, No. 2, 63-67 (2011).
[2] G.N. Kulipanov, E.G. Bagryanskaya, E.N. Chesnokov, et al. Novosibirsk free electron laser—facility description and recent experiments. IEEE Trans. THz Sci. Techn, vol. 20, 798-809 (2015).
[3] Y.Y. Choporova, B.A. Knyazev, G.N. Kulipanov, V.S. Pavelyev, M.A. Scheglov, N.A. Vinokurov, B.O. Volodkin, V.N. Zhabin. Highpower Bessel beams with orbital angular momentum in the terahertz range. Phys. Rev. A. vol. 96, 023846 (2017).
Fig. 1. Top row: images of the Bessel beam recorded at distances of 85, 141, and 197 mm from the axicon in the absence of obstacles. Middle row: images obtained after installing an 8 mm thick polyethylene foam sheet after the axicon. Bottom row: Image taken in the focal plane of a silicon lens with a focal length of 100 mm, mounted at the distances indicated above.
