We demonstrate the adaptive generation of a near-diffraction-limited flattop laser beam in the near field based on the stochastic parallel gradient descent algorithm and dual-phase-only liquid crystal spatial light modulators (LC-SLMs). One LC-SLM redistributes the intensity, and the other compensates the wavefront of the output beam. The experimental results show that approximately 69% of the power is enclosed in a region with less than 6% rms intensity variation. The 5mm diameter near-diffraction-limited output beam retains a flattop intensity distribution without significant diffraction peaks for a working distance of more than 30cm.

© 2010 Optical Society of America

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2010 (1)

2009 (3)

2007 (1)

2005 (1)

2000 (1)

1998 (1)

1997 (1)

Artal, P.

Becker, M. F.

Bulte, H.

Burnham, R. L.

El-Agmy, R.

Fernández, E. J.

Greenaway, A. H.

Heinzen, D. J.

Hoffnagle, J. A.

Jefferson, C. M.

Kasinski, J. J.

Kohn, R. N.

Liang, J.

Liu, Z. J.

Ma, H. T.

Ma, Y. X.

Oliker, V.

Prieto, P. M.

Reid, D.

Sivokon, V. P.

Vorontsov, M. A.

Wang, X. L.

Xi, F. J.

Xu, X. J.

Zhou, P.

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Figures (4)

Fig. 1
Fig. 1

Experimental configuration of the beam-shaping system. The configuration shows the feedback loop formed by phase-only LC-SLMs, CCD cameras, and the control computer.

Fig. 2
Fig. 2

Beam-shaping results for super-Gaussian profile ( w o = 1.55 mm , m = 12 ): (a) input beam profile, (b) output beam profile (solid curve) and target profile (dashed curve), (c) evolution of the relative rms error during the SPGD algorithm execution, and (d) relative rms variation of the output intensity on efficiency: measured value (solid curve) and target value (dashed curve).

Fig. 3
Fig. 3

Wavefront compensation results: (a) far-field intensity profile not being compensated by LC-SLM 2, (b) far-field intensity profile being compensated by LC-SLM 2, and (c) evolution of the relative phase error metric during the SPGD algorithm execution.

Fig. 4
Fig. 4

Intensity profiles of the output beam after propagating a certain distance in the near field: (a) at 15 cm from LC-SLM 2, (b) at 30 cm from LC-SLM 2, and (c) at 50 cm from LC-SLM 2.