Abstract

We propose and demonstrate the adaptive conversion of a multimode beam into a near-diffraction-limited flattop beam in the near field based on a combination of dual-phase-only liquid-crystal spatial light modulators (LC-SLMs) and the stochastic parallel gradient descent (SPGD) algorithm. One phase-only LC-SLM redistributes the intensity of the multimode beam, and the other compensates the wavefront of the output beam. The SPGD algorithm adaptively optimizes the phase distributions of dual-phase-only LC-SLMs to reduce the variance between the actual beam shape and the target beam shape. The experimental results on a fiber multimode beam show that the system is capable of adaptively creating square and rectangle flattop beams with desired parameters. Beam quality can be greatly improved by this system. The power in the main lobe of the far-field spot is about 4 times larger than that of the input multimode beam.

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References

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2010 (2)

2009 (2)

2008 (2)

2005 (2)

2003 (1)

2002 (1)

2000 (1)

1998 (1)

Barty, C. P. J.

Beach, R. J.

Becker, M. F.

Bulte, H.

Davidson, N.

Dawson, J. W.

Eckhouse, V.

El-Agmy, R.

Fridman, M.

Friesem, A. A.

Greenaway, A. H.

Hasman, E.

Heebner, J. E.

Heinzen, D. J.

Hoffnagle, J. A.

Ishaaya, A. A.

Jefferson, C. M.

Kliner, D. A. V.

Kohn, R. N.

Koplow, J. P.

Liang, J.

Liu, Z.

Ma, H.

Ma, Y.

Machavariani, G.

Marciante, J. R.

Messerly, M. J.

Moore, S. W.

Pax, P. H.

Reid, D.

Rockwell, D. A.

Roides, R. G.

Shimshi, L.

Shkunov, V. V.

Shverdin, M. Y.

Siders, C. W.

Sivokon, V. P.

Sridharan, A. K.

Stappaerts, E. A.

Teodoro, F. D.

Vorontsov, M. A.

Wang, X.

Xi, F.

Xu, X.

Zhou, P.

Appl. Opt. (2)

J. Opt. Soc. Am. A (1)

Opt. Express (3)

Opt. Lett. (6)

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Figures (7)

Fig. 1
Fig. 1

Experimental setup for conversion of multimode fiber laser beam into near-diffraction-limited flattop laser beam in the near field.

Fig. 2
Fig. 2

Near-field and far-field intensity distributions of the input multimode beam. (a) Near- field intensity distribution recorded by CCD1. (b) Far-field intensity distribution recorded by CCD2.

Fig. 3
Fig. 3

Intensity distribution of the output beam and evolution of the fit error as the algorithm proceeds. (a) Intensity distribution. (b) Evolution of the fit error.

Fig. 4
Fig. 4

Far-field intensity distribution of the output beam without being compensated by LC-SLM2.

Fig. 5
Fig. 5

Far-field intensity distribution of the output beam being compensated by LC-SLM2 and evolution of the relative phase error metric during the SPGD algorithm execution. (a) Far-field intensity distribution (solid line corresponds to experimental result and dashed line corresponds to ideal result).(b) Evolution of the relative phase error metric.

Fig. 6
Fig. 6

PIB curves of the far-field intensity distribution of the input multimode beam, output beam without being compensated by LC-SLM2, and output beam compensated by LC-SLM2.

Fig. 7
Fig. 7

Adaptive conversion of multimode beam into rectangle flattop beam with desired parameters: (a) target beam profiles (top row corresponding to flattop beam with parameters a = 0.0035, b = 0.0055, p = 6, q = 6; bottom row corresponding to flattop beam with parameters a = 0.0055, b = 0.0035, p = 6, q = 6). (b) Experimental results of the rectangle flattop beam. (c). Corresponding evolutions of the fit error as the algorithm proceeded.

Equations (4)

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ϕ j = i = 2 n a i Z i ( r , θ ) ,
J f i t e r r o r = x y [ I t arg e t ( x , y ) I c a m e r a ( x , y ) ] 2 ,
I t arg e t ( x , y ) = exp { [ a ( x x o ) ] 2 p [ b ( y y o ) ] 2 q } ,
J c o m p e n s a t i o n = I f a r f i e l d ( x , y ) 2 d x d y ,

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