Efficient conversion of a Gaussian beam to a high purity helical beam

Abstract A method for efficiently converting a Gaussian beam into a helical Laguerre–Gaussian (LG) beam is presented. It is based on using a pair of axicons to produce a shifted-Gaussian (doughnut) intensity distribution that is then passed through a spiral phase element. It is shown that the conversion efficiency can be as high as ∼98%, and the calculated far-field intensity distributions of the output beams are very close to those of corresponding pure LG intensity distributions. The principle of the method, the needed optical arrangement, and calculated and experimental results are presented.

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