Fabrication of surface relief gratings (SRGs) on azo dye thin films has been investigated utilizing an interference of evanescent waves. SRGs of approximately 210 nm were inscribed on the photoisomerized azo dye films, that were smaller than a half wavelength of an incidence laser of 488.0 nm. The films were set on a right-angled triangular prism surface and were in the interference of evanescent waves of totally reflected laser beams at the prism surface. The interference at the surface was performed using a laser beam through the one side of the isosceles and the returned beam at the other side of the isosceles where a mirror was set. The SRG patterns of azo dye films due to trans-cis transition of the dyes were observed in situ using an atomic force microscope above the prism surface. (C) 2005 American Institute of Physics.