[1] Z. Zhou, Q. Tan, and G. Jin, Chin. Opt. Lett. 7, 938(2009).
[2] B. Richards and E. Wolf, Proc. R. Soc. Lond. A 253, 358 (1959).
[3] K. S. Youngworth and T. G. Brown, Opt. Express 7, 77(2000).
[4] S. Quabis, R. Dorn, M. Eberler, O. Gl¨ockl, and G. Leuchs, Appl. Phys. B 72, 109 (2001).
[5] M. Rashid, O. M. Marag`o, and P. H. Jones, J. Opt. A: Pure Appl. Opt. 11, 065204 (2009).