Inscription of holographic gratings using circularly polarized light:: influence of the optical set-up on the birefringence and surface relief grating properties

The polarization properties of the optical setup used for holographic recording of diffraction gratings on azopolymer thin films are analyzed. The state of polarization of circularly polarized light is fully analyzed after reflection on a mirror at various incidences (Lloyd-mirror set-up). The Stokes analysis is performed using a photopolarimeter and the phase shift, the ellipticity and the azimuth orientation are compared with those calculated from Fresnel formulae. At large angles of incidence, an initially right circularly polarized (RCP) beam becomes elliptically polarized with an azimuth of nearly +45degrees. From these results, holographic diffraction gratings are recorded on an azobenzene-containing polymer thin film using (i) co- and contra-circularly polarized beams and (ii) a right circularly polarized beam interfering with a +45degrees linearly polarized light beam. Using Jones-matrix formalism, the polarization states of the diffracted orders from the birefringence (Deltan) and the surface-relief (2Deltad) gratings are derived and compared with experimental measurements. Finally, the induced local birefringences and surface-relief amplitudes are discussed in connection with atomic force microscopy measurements. The diffraction efficiencies obtained under the (+45degrees + RCP) and (LCP + RCP) (where LCP = left circularly polarized) configurations are thus compared and discussed.