Abstract

Multimode laser operation is usually characterized by high output power, yet its beam quality is inferior to that of a laser with single TEM 00 mode operation. Here we present an efficient approach for improving the beam quality of multimode laser resonators. The approach is based on splitting the intra-cavity multimode beam into an array of smaller beams, each with a high quality beam distribution, which are coherently added within the resonator. The coupling between the beams in the array and their coherent addition is achieved with planar interferometric beam combiners. Experimental verification, where the intra-cavity multimode beam in a pulsed Nd:YAG laser resonator is split into four Gaussian beams that are then coherently added, provides a total increase in brightness of one order of magnitude. Additional spectral measurements indicate that scaling to larger coherent arrays is possible.

© 2005 Optical Society of America

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References

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Appl. Opt.

Appl. Phys. B

D. Sabourdy, V. Kermene, A. Desfarges-Berthelemot, M. Vampouille and A. Barthelemy, �??Coherent combining of two Nd:YAG lasers in a Vernier-Michelson-type cavity,�?? Appl. Phys. B 75, 503�??507 (2002).
[CrossRef]

Appl. Phys. Lett.

J. R. Leger, M. L. Scott and W. B. Veldkamp, �??Coherent addition of AlGaAs lasers using microlenses and diffractive coupling,�?? Appl. Phys. Lett. 52, 1771�??1773 (1988).
[CrossRef]

M. J. DiDomenico, �??A single-frequency TEM00-mode gas laser with high output power,�?? Appl. Phys. Lett. 8, 20�??22 (1966).
[CrossRef]

A. A. Ishaaya, N. Davidson, L. Shimshi and A. A. Friesem, �??Intra-cavity coherent addition of Gaussian beam distributions using a planar interferometric coupler,�?? Appl. Phys. Lett. 85, 2187�??2189 (2004).
[CrossRef]

CLEO 2004

A. Shirakawa, K. Matsuo and K. Ueda, �??Power summation and bandwidth narrowing in coherently coupled fiber laser array,�?? CThGG2, Conference on Lasers and Electro-Optics (CLEO), San Francisco, California, USA (2004).

J. Opt. A: Pure Appl. Opt.

M. Tondusson, C. Froehly, V. Kermene and M. Vampouille, �??Coherent combination of four laser beams in a multi-axis Fourier cavity using a diffractive optical element,�?? J. Opt. A: Pure Appl. Opt. 3, 521�??526 (2001).
[CrossRef]

Opt. Express

Opt. Lett.

Phys. Rev. A

L. Fabiny, P. Colet, R. Roy and D. Lenstra, �??Coherence and phase dynamics of spatially coupled solid-state lasers,�?? Phys. Rev. A 47, 4287�??4296 (1993).
[CrossRef] [PubMed]

Proc. SPIE

A. E. Siegman, �??New developments in laser resonators,�?? Optical Resonators: Proc. SPIE 1224, 2�??14 (1990).
[CrossRef]

Other

W. Koechner, Solid-state laser engineering (Springer-Verlag, 5th ed., Germany, 1999, p. 209).

N. Hodgson and H. Weber, Optical resonators, fundamentals, advanced concepts and applications (Springer-Verlag London, Great Britain, 1997, p. 319).

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Figures (7)

Fig. 1.
Fig. 1.

Laser resonator configurations. (a) a basic multimode laser resonator; (b) a laser resonator with four incoherent laser beam distributions; (c) a laser resonator with two interferometric combiners resulting in phase locking and coherent addition of the four beam distributions.

Fig. 2.
Fig. 2.

Intra-cavity aperture array for generating multiple channels within the resonator. (a) A 2×2 spaced aperture array; (b) a single square aperture for generating a tightly packed 2×2 array.

Fig. 3.
Fig. 3.

Experimental resonator configuration. A 2×2 coherent phased array of Gaussian distributions is generated within the gain medium using four apertures and two interferometric beam combiners. Coherently adding the beams in the array produces a single output beam with high brightness.

Fig. 4.
Fig. 4.

Measured output pulse energy as a function of the pump power for a single Gaussian channel laser operation (oe-13-7-2722-i001), and for intra-cavity coherent addition of four Gaussian channels (oe-13-7-2722-i002).

Fig. 5.
Fig. 5.

Experimental near and far field intensity distributions of the single and four channels output beam. (a) a single Gaussian channel without an intra-cavity interferometric beam combiner; (b) four Gaussian channels that are coherently added with two intra-cavity interferometric combiners.

Fig. 6.
Fig. 6.

Experimental near and far field intensity distributions of the multimode output beam and the Gaussian output beam after tight packing. (a) square multimode beam output distributions without an intra-cavity interferometric beam combiner; (b) Gaussian beam output distribution after coherently adding a tightly packed 2×2 array of Gaussian distributions with two intra-cavity interferometric combiners.

Fig. 7.
Fig. 7.

Experimental power spectrum measurements. (a) The power spectrum of the output beam with a single Gaussian channel resonator configuration (without beam combiners); (b) the power spectrum of the coherently combined output beam with a four-channel resonator configuration.

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