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Experimental investigation of the energy backflow in the tight focal spot
V.V. Kotlyar 1,2, S.S. Stafeev 1,2, A.G. Nalimov 1,2, A.A. Kovalev 1,2, A.P. Porfirev 1,2

IPSI RAS – Branch of the FSRC "Crystallography and Photonics" RAS,
443001, Samara, Russia, Molodogvardeyskaya 151,
Samara National Research University, 443086, Samara, Russia, Moskovskoye Shosse 34

 PDF, 1355 kB

DOI: 10.18287/2412-6179-CO-763

Pages: 863-870.

Full text of article: Russian language.

Using two identical microobjectives with a numerical aperture NA = 0.95, we experimentally demonstrate that the on-axis intensity near the tight focal spot of an optical vortex with a topological charge 2 is zero for right-handed circular polarization and nonzero for left-handed circular polarization. This serves to confirm that in the latter case there is a reverse energy flow on the optical axis, as testified by a very weak local maximum (the Arago spot) detected at the center of the measured energy flow distribution, caused by diffraction of the direct energy flow by a 300 nm circle (the diameter of a reverse energy flow tube). The comparison of numerical and experimental intensity distributions shows that it is possible to determine the diameter of the reverse energy flow "tube", which is equal to the distance between the adjacent intensity nulls. For NA = 0.95 and a 532 nm incident wavelength, the diameter of the on-axis reverse energy flow "tube" is measured to be 300 nm. It is also experimentally shown that when an optical beam with second-order cylindrical polarization is focused with a lens with NA = 0.95, there is a circularly symmetric energy flow in the focus with a very weak maximum in the center (the Arago spot), whose distribution is determined by diffraction of the direct energy flow by a 300 nm circular region, where the energy flow is reverse. This also confirms that in this case, there is a reverse energy flow on the optical axis.

energy backflow, tight focusing, optical experiment, Richards-Wolf formulae, FDTD-method, optical vortex, cylindrical vector beam.

Kotlyar VV, Stafeev SS, Nalimov AG, Kovalev AA, Porfirev AP. Experimental investigation of the energy backflow in the tight focal spot. Computer Optics 2020; 44(6): 863-870. DOI: 10.18287/2412-6179-CO-763.

The work was partly funded by the Russian Science Foundation under project # 18-19-00595 (Section "An experimental detection of the reverse energy flow in the tight focus of a circularly polarized optical vortex"), the Russian Foundation for Basic Research under project # 18-29-20003 (Section "An experimental detection of the reverse on-axis energy flow in the focus of a second-order polarization vortex"), and the Russian Federation Ministry of Science and Higher Education within a state contract with the "Crystallography and Photonics" Research Center of the RAS under agreement 007-ГЗ/Ч3363/26 (section "Forces exerted upon a nanoparticle in the reverse energy flow").


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