Abstract

An intra-cavity phase element, combined with a passive Q-switch saturable absorber and a suitable intra-cavity aperture, can provide extremely high mode discrimination, so as to obtain laser operation with single, pure, very high order Laguerre-Gaussian mode. With a Nd:YAG laser setup, well controlled and extremely stable Q-switched operation in the degenerate Laguerre-Gaussian TEM04, TEM14, TEM24, TEM34, and TEM44 modes was obtained. The measured output energy per pulse for each of these modes was 5.2mJ, 7.5mJ, 10mJ, 12.5mJ, and 13.7mJ respectively, compared to 2.5mJ for the Gaussian mode without the phase element (more than a five fold increase in output energy). Correcting the phase for these modes, so that all transverse lobes have uniform phase, results in a very bright and narrow central lobe in the far field intensity distribution that can theoretically contain more than 90% of the output energy.

© 2005 Optical Society of America

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References

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Appl. Opt. (1)

Appl. Phys. B (1)

Y. F. Chen, Y. P. Lan and S. c. Wang, �??Generation of Laguerre-Gaussian modes in fiber-coupled laser-diode end-pumped lasers,�?? Appl. Phys. B 72, 167�??170 (2001).
[CrossRef]

Appl. Phys. Lett. (3)

K. M. Abramski, H. J. Baker, A. D. Colly and D. R. Hall, �??Single-mode selection using coherent imaging within a slab waveguide CO2 laser,�?? Appl. Phys. Lett. 60, 2469�??2471 (1992).
[CrossRef]

W. R. Sooy, �??The natural selection of modes in a passive q-switched laser,�?? Appl. Phys. Lett. 7, 36�??37 (1965).
[CrossRef]

N. Davidson, A. A. Friesem and E. Hasman, �??Diffractive elements for annular laser beam transformation,�?? Appl. Phys. Lett. 61, 381�??383 (1992).
[CrossRef]

IEEE J. Quantum Electron. (2)

Y. F. Chen, T. M. Huang, C. F. Kao, C. L. Wang and S. c. Wang, �??Generation of Hermite-Gaussian modes in fiber-coupled laser-diode end-pumped lasers,�?? IEEE J. Quantum Electron. 33, 1025�??1031 (1997).
[CrossRef]

A. A. Ishaaya, N. Davidson, G. Machavariani, E. Hasman and A.A. Friesem, �??Efficient selection of high-order Laguerre-Gaussian modes in a Q-switched Nd:YAG laser,�?? IEEE J. Quantum Electron. 39, 74�??82 (2003).
[CrossRef]

Opt. Commun. (2)

T. Graf and J. E. Balmer, �??Laser beam quality, entropy and the limits of beam shaping,�?? Opt. Commun. 131, 77�??83 (1996).
[CrossRef]

A. Chandonnet, M. Piche and N. McCarthy, �??Beam Narrowing by saturable absorber in a Nd:YAG Laser,�?? Opt. Commun. 75, 123�??128 (1990).
[CrossRef]

Opt. Lett. (6)

Progress in Optics (1)

R. Oron, N. Davidson, E. Hasman and A. A. Friesem, �??Transverse mode shaping and selection in laser resonators,�?? Progress in Optics 42, 325�??386 (2001).
[CrossRef]

Sov. J. Quantum Electron. (1)

A. P. Kolchenko, A. G. Nikitenko and Y. K. Troitskill, �??Control of the structure of transverse laser modes by phase-shifting masks,�?? Sov. J. Quantum Electron. 10, 1013�??1016 (1980).
[CrossRef]

Other (2)

A. E. Siegman, Lasers, p. 1038 (University Science Books, Sausalito, California, 1986).

W. Koechner, Solid-state laser engineering (Springer-Verlag, 5th ed., Germany, 1999, p. 509).

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Figures (10)

Fig. 1.
Fig. 1.

A basic configuration for high-order mode selection in a laser resonator with an intra-cavity phase element and a passive Q-switch saturable absorber.

Fig. 2.
Fig. 2.

Transmission of a typical saturable absorber (see ref. [16]).

Fig. 3.
Fig. 3.

Experimental passive Q-switched Nd:YAG laser arrangement for intra-cavity highorder transverse mode selection.

Fig. 4.
Fig. 4.

Experimental near and far field intensity distributions of the Gaussian TEM 00 mode in passive Q-switched operation. These were obtained with an intra-cavity aperture diameter of 1.8 mm and without an intra-cavity phase element.

Fig. 5.
Fig. 5.

Experimental near and far field intensity distributions of high order modes (degenerate Laguerre-Gaussian TEM 04, TEM 14, TEM 24, TEM 34, and TEM 44 modes).

Fig. 6.
Fig. 6.

Far field intensity distribution of the laser output beam when operated with an active Q-switch, a TEM 04 phase element, and a 4.8 mm intra-cavity aperture diameter.

Fig. 7.
Fig. 7.

Experimental multimode intensity distributions in active Q-switched operation and the corresponding selected modes in passive Q-switched operation. (a) and (b) experimental far field intensity distributions in active Q-switched operation for aperture diameters of 3.5 mm and 4.8 mm; (c) and (d) intensity distributions of (a) and (b) above a threshold of 85% of the maximum intensity; (e) and (f) corresponding calculated LG TEM 04 TEM 44 mode distributions that fit (c) and (d).

Fig. 8.
Fig. 8.

Experimental far field intensity distributions and corresponding temporal pulse shapes in passive Q-switched operation. (a) and (b) far field intensity distribution and corresponding pulse shape for a pure high-order mode selection; (c) and (d) far field intensity distribution and the corresponding pulse shape, for an impure mode selection; (e) and (f) far field intensity distribution and timing sequence for a double-pulse operation.

Fig. 9.
Fig. 9.

Calculated energy percentage as a function of radius in the far field intensity distribution for the TEM 00 mode, and for several high-order LG modes with uniform phase.

Fig. 10.
Fig. 10.

Calculated and experimental far field intensity distributions for a laser operating with a LG TEM 04 mode. (a) for typical TEM 04 with alternating 0 and π phases for adjacent lobes; (b) for TEM 04 with uniform phase.

Tables (1)

Tables Icon

Table 1. Calculated effective transmission through the saturable absorber for each LG mode distribution, assuming the induced transmission patterns shown in Figs. 7(c) and 7(d). With T eff = T ( x , y ) · I mode · ( x , y ) · dxdy I mode ( x , y ) · dxdy . .

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