## 3 Results
Also in this case, for modulation along \(\mathbf{n_{0}}\), the value of \(\Delta\Lambda/\Lambda\) increases with increasing strain, while for modulation perpendicular to \(\mathbf{n_{0}}\), it decreases with increasing strain. However, a decrease observed in the latter case has nearly the same magnitude as the increase observed in the former case, which signifies an asymmetry in the transversal shrinking process. Further studies of grating structures with different values of \(\Lambda\) are needed to resolve the details of this interesting process. The values obtained during increasing (solid symbols) and decreasing strain (open symbols) are quite similar, but they exhibit some hysteresis. The hysteresis is even more evident in the dependence of the diffracted intensity \(I_{\mathbf{d}}\) of the first-order diffraction peaks on \(\varepsilon_{\perp}\) shown in Figure 5a. The diffracted intensity observed after a full cycle of stretching and contraction of the sample is also about 10% lower than in the beginning. However, the most evident observation of this experiment is that the value of \(I_{\mathbf{d}}/I_{\mathbf{d}0}\) strongly decreases with increasing strain, and drops for about a factor of five during straining from \(\varepsilon_{\perp}=0\) to \(\varepsilon_{\perp}=0.17\). Another interesting observation is that with increasing strain, the form of the diffraction peaks is transformed from a nearly circular spot to an elongated cloud. This is attributed to the formation of shear-stripe domains that accompany the reorientation process of the director field [33; 34]. The stripes are oriented perpendicular to \(\mathbf{n_{0}}\), and typically have a thickness of around 10 \(\upmu\)m. Consequently, they cause strong light scattering in the direction parallel to \(\mathbf{n_{0}}\) (see insets in Figure 5a), and therefore, the outgoing peaks become elongated. In determination of the diffraction efficiency, this effect was taken into account by integrating the diffracted intensity in the elongated regions marked as rectangles in the inset of Figure 5a. The results obtained for the grating with grating lines parallel to \(\mathbf{n_{0}}\) are shown in Figure 5b. In this case, the two effects mentioned above are superimposed on each other (see inset of Figure 5b) and for \(\varepsilon_{\perp}\geq 0.12\), it is practically impossible to separate the diffraction from holographic grating from the diffraction from the strain-induced striped structure. For that reason, the measurements of \(I_{\mathbf{d}}/I_{\mathbf{d}0}\) as a function of \(\varepsilon_{\perp}\) were limited to \(\varepsilon_{\perp}<0.12\). A profound hysteresis is observed during the stretching-contraction cycle. Besides this, opposite to the situation in Figure 5a, the value of \(I_{\mathbf{d}}/I_{\mathbf{d}0}\) strongly increases with increasing strain. The increase for a factor of 10 is obtained for straining  
Figure 4: Relative modification of grating periodicity \(\Lambda\) of a one-dimensional line grating as a function of the tensile strain \(\varepsilon_{\perp}\) applied in the direction perpendicular to the alignment direction \(\mathbf{n_{0}}\). Solid symbols correspond to the increasing strain, and open symbols correspond to the decreasing strain. The drawings illustrate orientation of the grating lines with respect to \(\mathbf{n_{0}}\). The arrows indicate the direction of strain. from \(\varepsilon_{\perp}=0\) to \(\varepsilon_{\perp}=0.12\). Also in this case, the data shown are already renormalized for the decrease associated with the _cis_-to-_trans_ back-isomerization. For a square holographic grating with the lattice distance \(a=13.5\)\(\upmu\)m, the scattering from stripe domains smears out the diffraction from the grating structure already for \(\varepsilon_{\perp}\geq 0.03\), which prevents reasonable measurements of the strain-induced effects on the holographic pattern. Consequently, this grating structure was not investigated in the configuration in which the strain is applied perpendicular to \(\mathbf{n_{0}}\).