## 3 Results
For a specific measurement in the selected sample region, the uncertainty of the experimental data shown in Figures 2-5 is within the size of the data points. However, when measurements are performed in different sample regions, the variations might be larger, as some imperfections and inhomogeneities are usually present within the sample structure. At temperatures in the vicinity of \(T_{0}\) (81.6 \({}^{\circ}\)C), the _cis_-to-_trans_ back-isomerization of the azomesogens is so fast that systematic measurements of the effect of strain on diffraction properties, as described above, are not possible. Hence, at these temperatures we used another setup, in which the sample was clamped to the frame with two sides and consequently had a fixed length, and we performed in situ monitoring of the tensile force and diffraction intensity during recording and relaxation of the holographic patterns. Before clamping, the sample was slightly prestrained. Also in this case, the measurements were performed in two configurations: for clamping along \(\mathbf{n_{0}}\) and for clamping perpendicular to \(\mathbf{n_{0}}\). Figure 6 shows the results obtained for clamping along \(\mathbf{n_{0}}\) at \(T=75\)\({}^{\circ}\)C. One-dimensional UV interference pattern with \(\Lambda=9.5\)\(\upmu\)m was recorded. Figure 6a shows relative modifications of the force \(\Delta F/F_{0}\) as a function of time obtained for three different prestraining forces \(F_{0}\) applied to the film. The value \(F_{0}=1\) mN corresponds to the tensile stress of \(\sigma\sim\)2 kPa. The exact value of \(\sigma\) is difficult to be determined, because clamping affects the cross-section of the film. The tensile force \(F\) increases during the recording process (0 < t < 5 min), while after switching off the UV light, it decreases back to the  
Figure 5: (**a**) Relative modification of intensity of first-order diffraction peaks \(I_{\mathrm{d}}\) for a one-dimensional grating with grating lines parallel to \(\mathbf{n_{0}}\). The insert in the lower left corner shows the far-field diffraction pattern observed at \(\varepsilon_{\perp}=0\). The transmitted beam was blocked, so that only the first-order diffraction peaks can be seen. The insert in the upper right corner shows the far-field diffraction pattern observed at \(\varepsilon_{\perp}=0.1\). Elongation of diffraction peaks due to light scattering from striped domains can be noticed. Squares denote the regions of integration that are used to determine the intensity of the diffraction peaks. (**b**) Relative modification of \(I_{\mathrm{d}}\) for a one-dimensional grating structure with grating lines perpendicular to \(\mathbf{n_{0}}\). The inserts in the upper left and lower right corners show far field diffraction patterns at \(\varepsilon_{\perp}=0\) and \(\varepsilon_{\perp}=0.1\), respectively. The elongation of diffraction peaks due to light scattering from striped domains can again be noticed. Squares denote regions of integration that have been used to determine the intensity of diffraction peaks. initial value. The relaxation process is monotonic, and takes place in two stages: a fast one on a time scale of seconds, which is attributed to thermal effects, and a slower one on a time scale of minutes, which is attributed to _cis_-to-_trans_ back isomerization. Figure 6b shows the temporal dependence of diffracted intensity \(I_{\mathrm{d}}\) of the probe beam. Despite the sample being clamped at two opposite edges and hence being unable to be shrunk due to UV illumination, the value of \(I_{\mathrm{d}}\) strongly fluctuates during the recording process. The fluctuations differ from one recording process to another, and are in general larger at larger clamping forces. They are attributed to inhomogeneous modifications of the material structure during the illumination. Regions of film that are slightly softer than the surrounding expand on behalf of the harder regions. If the structure is fully homogeneous, contraction cannot happen due to clamping.