Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: 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 ~0.5 mm were made in
~1 min using galvanometric scanners with writing speed of 5 mm/s. Period of
gratings of 0.8 micrometers and groove width of 250 nm were achieved using
fs-laser ablation at 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 800C. They can be used as optical vortex
generators using post-selection of polarisation.

30
The categories of this paper are: q-alg
5
The categories of this paper are: gr-qc
28
The categories of this paper are: alg-geom
17
The categories of this paper are: q-fin
6
The categories of this paper are: astro-ph
4
The categories of this paper are: cond-mat
1
The categories of this paper are: cs
22
The categories of this paper are: chao-dyn
20
The categories of this paper are: acc-phys
31
The categories of this paper are: ao-sci
2
The categories of this paper are: math
9
The categories of this paper are: nlin
19
The categories of this paper are: eess
12
The categories of this paper are: nucl-th
33
The categories of this paper are: plasm-ph
15
The categories of this paper are: nucl-ex