The liquid-crystal (LC) alignment properties of surface relief gratings (SRGs) of different azo polymers and their correlations with grating parameters and polarizations of writing beams were studied.Three azo polymers with different kinds of azo chromophores and different chromophore densities were used in this study.The contrasts (Tmax/Tmin) and optical photographs of different liquid crystal cells were compared to determine the alignment properties.For the gratings with a period of 800 nm recorded by p+p interfering Ar+ laser beams on the epoxy based azo polymer containing 4-cyanoazobenzene chromophores (BP-AZ-CN) films

the ability for aligning liquid crystal increased with the increase of grating depths.For gratings of the epoxy based azo polymer containing 4-carboxylazobenzene chromophores (BP-AZ-CA) with a period of 800 nm and the gratings of the polyacrylate based azo polymer containing 4-carboxylazobenzene chromophores (PA-AZ-CA) with a period of 1200 nm

the liquid crystal showed uniform alignment when the grating depth was in a range from 16 to 100 nm.For the BP-AZ-CA gratings with a similar depth

the liquid crystal showed better alignment on the gratings with a period of 800 nm than gratings with a period of 1200 nm.Compared with BP-AZ-CA and PA-AZ-CA gratings with a period of 1200 nm

liquid crystal shows a better alignment on the PA-AZ-CA gratings.For the PA-AZ-CA gratings inscribed by RCP+LCP interfering Ar+ laser beams

no unidirectional alignment was observed even for the gratings depths over 100 nm.Above results can offer a better understanding of the effect of polymer structures and grating parameters on the liquid crystal alignment performance.