Propagation of beams with orbital angular momentum through 1D and 2D periodic grating (an analogue of the Talbot effect)
- Mr. Oleg KAMESHKOV
- Ms. Yulia CHOPOROVA
- Prof. Boris KNYAZEV (Budker Institute of Nuclear Physics)
Talbot effect (self-imaging of periodic gratings) attracted attention for 170 years that have passed since its discovery. The invention of lasers generating coherent beams caused a new impetus to these studies. Commissioning of the Novosibirsk free electron laser facility, which generates powerful coherent monochromatic radiation in the terahertz range, enabled us to demonstrate recently the Talbot effect in this region of the spectrum. Large wavelength of the terahertz radiation enables performing experiments with gratings, fabricated using LIGA technology at synchrotron radiation source VEPP-4, the structural elements of which are close to the wavelength. In this paper we describe first observation of diffraction patterns in the free space region behind the periodic structures illuminated with beams carrying orbital angular momenta with topological charges equal to plus-minus 1 or 2. The images observed did not reproduce images of the gratings exactly, but manifested some periodicity inherent to the Talbot effect with distorted spots related to individual grating openings. The numerical simulation of the electromagnetic field behind the gratings, carried out in a frame of the Fresnel-Kirchhoff model, is compared with the experimental data.