Fast fabrication of optical vortex generators by femtosecond laser ablation

Fast fabrication of micro-optical elements for generation of optical vortex beams based on the q-plate design is demonstrated by femtosecond (fs) laser ablation of gold film on glass. Q-plates with diameter of 0.5mm were made in similar to 1 min using galvanometric scanners with writing speed of 5 mm/s. Period of gratings of 0.8 mu m and groove width of 250 nm were achieved using fs-laser ablation at lambda = 343 nm wavelength. Phase and intensity analysis of optical vortex generators was carried out at 633 nm wavelength and confirmed the designed performance. Efficiency of spin-orbital conversion of the q-plates made by ablation of 50-nm-thick film of gold was 3%. Such gratings can withstand thermal annealing up to 800 degrees C. They can be used as optical vortex generators using post-selection of polarisation.