Azopolymers are materials that exhibit photoinduced anisotropy, enabling the direct holographic recording of diffraction gratings with selective polarization. The use of nanocomposite materials, in particular the doping of azopolymers with gold nanoparticles, can alter the properties of the azopolymers. One of the most significant effects is the enhancement of photoinduced birefringence, which leads to increased diffraction efficiency. The spectral photosensitivity of the fabricated nanocomposites enabled the use of the blue-green region of the laser spectrum for recording holographic diffraction gratings, while the red wavelength, lying within the transparency region of the material, was used for monitoring the grating recording kinetics and measuring the diffraction efficiency. This paper presents a study on the kinetics of diffraction efficiency and polarimetric parameters (azimuth and ellipticity) of diffraction gratings in thin films of azopolymer Poly-n-epoxypropylcarbazole – Solvent Yellow 3 (PEPC-SY3) doped with gold nanoparticles (0–1 μg/mL). Holographic diffraction gratings were recorded using laser radiation with a wavelength of 473 nm and various polarizations of the recording beams, including linear (P:P, ±45°) and circular (LCP:RCP) polarizations. Significant variations in azimuth and ellipticity were also observed, indicating local changes in the refractive index caused by the formation of periodic surface and volume structures in the nanocomposite film. This work presents results on the dynamic changes in the polarization of a beam transmitted through the material during holographic recording of diffraction gratings. It allows one to observe the processes that occur due to photo-induced anisotropy—specifically, changes in the azimuth and ellipticity of the transmitted beam—as well as to practically optimize and control polarization-sensitive holograms. This opens pathways for the development of advanced diffractive optical elements and high-density data storage systems.