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Proceedings Paper

Superfocusing of high-M2 semiconductor laser beams: experimental demonstration
Author(s): G. S. Sokolovskii; V. Melissinaki; V. V. Dudelev; S. N. Losev; K. K. Soboleva; E. D. Kolykhalova; A. G. Deryagin; V. I. Kuchinskii; Evgeny A. Viktorov; M. Farsari; W. Sibbett; E. U. Rafailov
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Paper Abstract

The focusing of multimode laser diode beams is probably the most significant problem that hinders the expansion of the high-power semiconductor lasers in many spatially-demanding applications. Generally, the ‘quality’ of laser beams is characterized by so-called ‘beam propagation parameter’ M2, which is defined as the ratio of the divergence of the laser beam to that of a diffraction-limited counterpart. Therefore, M2 determines the ratio of the beam focal-spot size to that of the ‘ideal’ Gaussian beam focused by the same optical system. Typically, M2 takes the value of 20-50 for high-power broad-stripe laser diodes thus making the focal-spot 1-2 orders of magnitude larger than the diffraction limit. The idea of ‘superfocusing’ for high-M2 beams relies on a technique developed for the generation of Bessel beams from laser diodes using a cone-shaped lens (axicon). With traditional focusing of multimode radiation, different curvatures of the wavefronts of the various constituent modes lead to a shift of their focal points along the optical axis that in turn implies larger focal-spot sizes with correspondingly increased values of M2. In contrast, the generation of a Bessel-type beam with an axicon relies on ‘self-interference’ of each mode thus eliminating the underlying reason for an increase in the focal-spot size. For an experimental demonstration of the proposed technique, we used a fiber-coupled laser diode with M2 below 20 and an emission wavelength in ~1μm range. Utilization of the axicons with apex angle of 140deg, made by direct laser writing on a fiber tip, enabled the demonstration of an order of magnitude decrease of the focal-spot size compared to that achievable using an ‘ideal’ lens of unity numerical aperture.

Paper Details

Date Published: 2 May 2014
PDF: 7 pages
Proc. SPIE 9134, Semiconductor Lasers and Laser Dynamics VI, 91341N (2 May 2014); doi: 10.1117/12.2052483
Show Author Affiliations
G. S. Sokolovskii, Ioffe Physical-Technical Institute (Russian Federation)
V. Melissinaki, Foundation for Research and Technology-Hellas (Greece)
V. V. Dudelev, Ioffe Physical-Technical Institute (Russian Federation)
S. N. Losev, Ioffe Physical-Technical Institute (Russian Federation)
K. K. Soboleva, St. Petersburg State Polytechnical Univ. (Russian Federation)
E. D. Kolykhalova, Ioffe Physical-Technical Institute (Russian Federation)
A. G. Deryagin, Ioffe Physical-Technical Institute (Russian Federation)
V. I. Kuchinskii, Ioffe Physical-Technical Institute (Russian Federation)
Evgeny A. Viktorov, Univ. Libre de Bruxelles (Belgium)
National Research Univ. of Information Technologies, Mechanics and Optics (Russian Federation)
M. Farsari, Foundation for Research and Technology-Hellas (Greece)
W. Sibbett, Univ. of St. Andrews (United Kingdom)
E. U. Rafailov, Aston Univ. (United Kingdom)

Published in SPIE Proceedings Vol. 9134:
Semiconductor Lasers and Laser Dynamics VI
Krassimir Panajotov; Marc Sciamanna; Angel Valle; Rainer Michalzik, Editor(s)

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