Superfocusing of high-M2 semiconductor laser beams:experimental demonstration


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.

Publication DOI:
Divisions: Engineering & Applied Sciences > Aston Institute of Photonics Technology
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
ISBN: 978-1-628-41082-2
Full Text Link: http://proceedi ... ticleid=1868170
Related URLs: http://www.scop ... tnerID=8YFLogxK (Scopus URL)
PURE Output Type: Conference contribution
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. (ORCID Profile 0000-0002-4152-0120)



Version: Accepted Version

Export / Share Citation


Additional statistics for this record