Experimental generation of adjustable partially coherent optical vortices from coherent and incoherent light sources

Abstract

Adjustable spatial coherence systems allow the possibility to make different intensity distributions using one source. Most common adjustable sources are based on the Collet–Wolf system. However, it is also possible to adjust the spatial coherence of the illumination field from white light sources by spatially filtering the source mutual intensity spectrum. We implement the Collet–Wolf source and the LED-based system to experimentally contrast a variety of partially coherent optical vortices that can be generated with spatial light modulation. We experimentally study the effects of changing the transverse coherence in partially coherent optical vortices, using a proposed metric of vortex contrast depth that quantifies the change of the vortex hollowness. To expand the analysis, we use a Michelson interferometer to reconstruct the spiral wavefronts using phase shifting. We found that the LED system at lower spatially correlated light produces truncated triangular distributions (a 50 µm pinhole is used), and with higher correlated light, it produces partially coherent optical vortices (a 10 µm pinhole is used). The Collet–Wolf system generates partially coherent optical vortices up to 0.5 mm of focal shift in the diffuser. Our results provide an experimental understanding and instrumental methodology capable of steering the optical transverse coherence, producing adjustable partially coherent optical vortices that can be obtained using incoherent and coherent sources.