Two-Dimensional Polarization Holographic Gratings in Azopolymer Thin Films: Polarization Properties in the Presence or Absence of Surface Relief

Abstract

During polarization holographic recording in azopolymer thin films, usually together with the volume anisotropic grating, a surface relief grating (SRG) is also formed. By using two consecutive exposures, it is possible to obtain a two-dimensional (2D) grating. To the best of our knowledge, the polarization properties of such gratings have not been studied yet. To determine the influence of the surface relief on the polarization selectivity of the 2D gratings, we propose two methods to suppress the SRG formation: by varying the recording conditions or varying the sample structure. In these experiments we have used the commercially available azopolymer PAZO, poly[1-4-(3-carboxy-4-hydrophenylazo) benzene sulfonamido]-1,2-ethanediyl, sodium salt] to perform the polarization holographic recording using a 442 nm He-Cd laser. As indicated by our results, when the surface relief is present, it strongly dominates the response of the 2D grating and it behaves almost as a scalar polarization insensitive grating. Conversely, when the SRG formation is suppressed, the polarization properties of the 2D grating in all four diffracted orders are very well pronounced. In this way, we demonstrate that we can easily control SRG formation and, if desired, obtain 2D grating with high surface relief modulation, or alternatively record polarization-selective 2D gratings with virtually no surface relief.

Polarization Diffraction Gratings in PAZO Polymer Thin Films Recorded with Digital Polarization Holography: Polarization Properties and Surface Relief Formation

“…The recording is performed either through the substrate side (case 1 in Figure 1), or from the azopolymer film side of the sample (case 2). As shown by our earlier studies [18,33], in case 1, the intensity of the recording beam is significantly reduced before reaching the free surface of the azopolymer film (due to the absorbance within the film itself), and this allows us to suppress the formation of the surface relief grating. In contrast, in case 2, the intensity of the recording beam is maximal on the free surface of the azopolymer layer, and this results in high amplitude surface relief grating.…”

“…#346411, Sigma Aldrich, Burlington, MA, USA). Its chemical structure and absorbance spectrum are presented in our earlier work [33]. The thin film samples were prepared by dissolving the azopolymer PAZO in methanol, and then spin-coating the solution with a concentration 100 mg/mL on cleaned and polished glass substrates (BK7) at 1000 rpm for 30 s. The thickness of the azopolymer layers is approximately 1800 ± 20 nm, as measured by the F20 Optical Thin-Film Analyzer (Filmetrics, San Diego, CA, USA).…”

“…It allows us to set any desired value of the azimuth or of the ellipticity of the probe beam. A similar optical scheme was employed in our recent work [33]. We use a linearly polarized probe beam from a He-Ne laser at 633 nm, and, with a half-wave plate and a quarter-wave plate, we vary the polarization of the input beam and monitor the polarization state of the light diffracted in the ±1 orders.…”

“…Over the years, this phenomenon has been studied by many groups [23,[27][28][29]. The SRGs are of great interest because of their numerous applications in photonics, biophysics, and other fields [30][31][32][33][34].…”