Efficient high-charge Laguerre-Gaussian mode conversion by using a periscopic axicon mirror

Laguerre-Gaussian (LG) modes can be converted from fundamental Gaussian mode by using phase optical elements such as spiral phase plates (SPP), but the conversion efficiency is strongly reduced in high charge plates because of the transverse intensity deviation. In this paper, a three-step scheme is proposed to dramatically improve the conversion efficiency. First, a fundamental Gaussian beam is converted to a 1st-order LG beam via a 1st-order SPP and a spatial filtering system. Then, by using a periscopic axicon mirror (PAM), the lst-order LG beam is transformed into an annular beam with larger beam radius. Finally, by using a second high-order SPP, this intensity-matched ring beam can be effectively converted to a high-charge LG0l beam. Through optimization of the PAM's parameter, the total conversion efficiency from fundamental Gaussian beam to LG0l mode as high as 91.85% is obtained, which is much higher than the case without PAM. Numerical simulations are carried out by the particle-in-cell (PIC) code EPOCH to verify the effectiveness of the scheme.