Journal
PHYSICAL REVIEW A
Volume 79, Issue 3, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevA.79.033830
Keywords
angular momentum theory; approximation theory; laser beams; light polarisation; optical focusing; optical rotation
Categories
Funding
- Brazilian agencies CNPq
- FAPERJ
- FUJB
- Institutos do Milenio de Nanociencias e de Informacao Quantica
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We investigate in detail the focusing of a circularly polarized Laguerre-Gaussian laser beam [h center dot orbital angular momentum per photon; sigma=1(-1) for left- (right-) handed polarization] by a high-numerical-aperture objective. The diffraction-limited focused beam has unexpected properties resulting from a strong interplay between the angular spatial structure and the local polarization in the nonparaxial regime. In the region near the beam axis, and provided that parallel to center dot parallel to >= 2 and center dot and sigma have opposite signs, the energy locally counterpropagates and the projection of the electric field onto the focal plane counter-rotates with respect to the circular polarization of the incident beam. We explicitly show that the total angular momentum flux per unit power is conserved after focusing, as expected by rotational symmetry, but the spin and orbital separate contributions change.
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