Superfocusing of high-M2 semiconductor laser beams:experimental demonstration

Sokolovskii, G.S., Melissinaki, V., Dudelev, V.V., Losev, S.N., Soboleva, K.K., Kolykhalova, E.D., Deryagin, A.G., Kuchinskii, V.I., Viktorov, E.A., Farsari, M., Sibbett, W. and Rafailov, E.U. (2014). Superfocusing of high-M2 semiconductor laser beams:experimental demonstration. IN: Semiconductor lasers and laser dynamics VI. Panajotov, Krassimir; Sciamanna, Marc; Valle, Angel and Michalzik, Rainer (eds) SPIE proceedings . SPIE.


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.

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Divisions: Engineering & Applied Sciences > Institute of Photonics
Additional Information: G. S. Sokolovskii ; V. Melissinaki ; V. V. Dudelev ; S. N. Losev ; K. K. Soboleva ; E. D. Kolykhalova ; A. G. Deryagin ; V. I. Kuchinskii ; E. A. Viktorov ; M. Farsari ; W. Sibbett and E. U. Rafailov, "Superfocusing of high-M2 semiconductor laser beams: experimental demonstration", Proc. SPIE 9134, Semiconductor Lasers and Laser Dynamics VI, 91341N (May 2, 2014). Copyright 2014. Society of Photo-Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited. DOI:
Event Title: Semiconductor lasers and laser dynamics VI
Event Type: Other
Event Dates: 2014-04-14 - 2014-04-17
Uncontrolled Keywords: Bessel beam,diffraction limit,superfocusing,Applied Mathematics,Computer Science Applications,Electrical and Electronic Engineering,Electronic, Optical and Magnetic Materials,Condensed Matter Physics
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Published Date: 2014
Authors: Sokolovskii, G.S.
Melissinaki, V.
Dudelev, V.V.
Losev, S.N.
Soboleva, K.K.
Kolykhalova, E.D.
Deryagin, A.G.
Kuchinskii, V.I.
Viktorov, E.A.
Farsari, M.
Sibbett, W.
Rafailov, E.U. ( 0000-0002-4152-0120)



Version: Accepted Version

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