NDLI: Generation of near diffraction free beams in Yb:YAG laser using an intracavity lens with spherical aberration

Content Provider	IEEE Xplore Digital Library
Author	Senatsky, Yu. Shirakawa, A. Ueda, K.
Copyright Year	2009
Description	Author affiliation: Institute for Laser Science, University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan (Shirakawa, A.; Ueda, K.) \|\| P.N.Lebedev Physical Institute of the Russian Academy of Sciences, Moscow, Russia (Senatsky, Yu.)
Abstract	The methods of near diffraction free (ndf) light beams generation in lasers are paid attention in a view of many interesting applications. An annular mirror [1], an intracavity axicon [2], or a diffractive mirror [3] were used for ndf Bessel-Gauss beams formation in argon and Nd:YAG lasers [1–3]. The present work offers a scheme where a simple plano-convex intracavity lens with a strong spherical aberration was used in Yb:YAG laser for the generation of ndf beams. A 9.8% at. Yb:YAG ceramics plane-parallel plate (9×11×1.1 mm) mounted on a copper cooler was end-pumped by a cw fiber-coupled laser diode at room temperature. The pump radiation (power 0.1–1.5W) was focused into the plate to a circular spot with a bell-shaped intensity profile of ≈100µm halfwidth. One of the planar surfaces of the Yb-doped plate was high-reflection (HR) coated for the wavelength λ ≈1030nm and anti-reflection (AR) - for the pump light. The other surface was AR coated for λ ≈1030nm. The resonator was formed by the HR surface of the plate and the plane output coupler with the reflectance ≈95%. The length of the resonator, L was varied from 26 to 66cm. A glass lens of 25mm diameter without any coating and with the focus (for paraxial rays) f ≈ 25mm was placed inside the resonator with its spherical surface being turned towards the Yb-doped plate. The spacing between the lens apex and HR mirror was d ≤ f. The lens could be moved along the resonator axis. The Yb-laser operated in a cw regime (power 1–30mW) at the transition ≈1030nm and emitted multiringed beams with diameters up to 11mm. Different beam intensity profiles (depending on d and L) were registered. At d ≈ f the generation of several concentric rings with a deep and narrow (200–400 µm) minimum at the beam axis was observed. Under shifting the lens towards the HR mirror, one could observe other multiringed patterns alternating from a central minimum to a narrow central maximum. The comparison of the images obtained with the data taken from literature [1–4] allows one to classify the beams as Bessel-Gauss modes of zero and higher orders. Modes of Laguerre-Gauss (LGp1) type [4–6] were observed at d ≈ f as well. The angular divergence of radiation estimated using the central peak or minimum widths in the far field has yielded $2–4×10^{−4}$ rad, while the diffraction limit, associated with these widths is 3–6 × $10^{−3}$ rad. Fig.1 illustrates output beam images monitored by a CCD-camera.
Starting Page	1
Ending Page	1
File Size	346829
Page Count	1
File Format	PDF
ISBN	9781424440795
DOI	10.1109/CLEOE-EQEC.2009.5192544
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2009-06-14
Publisher Place	Germany
Access Restriction	Subscribed
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Laser theory Diffraction Optical propagation Surface emitting lasers Focusing Laser modes Laser beams Mirrors Lenses Fiber lasers
Content Type	Text
Resource Type	Article

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