P. Pääkkönen, J. Lautanen, M. Honkanen, M. Kuittinen, J. Turunen, S. N. Khonina, V. V. Kotlyar, V. A. Soifer, A. T. Friberg,
Rotating optical fields: experimental demonstration with diffractive optics Journal of Modern Optics. ,vol. 45, pp. 2355- 2369 ,(1998) ,
10.1080/09500349808231245