Twist deformation response of a holographic volume grating in flexible photopolymer

Twist deformation of flexible photopolymer using a diffraction spectrum of a holographic volume grating is explored. Twist deformation can be categorized into transverse shear and macroscopic twist deformations. At a small twist angle, the transverse shear deformation can be considered as a tiny unit of twist deformation. In a transmission grating, the peak wavelength shift exceeds 150 nm, which provides a large linear measurement range of ±20<i>d</i><i>e</i><i>g</i> and 0.08 deg/nm angular sensitivity for sensing shear deformation. The sensitivity of the reflection grating is significantly lower than that of the transmission grating. The obvious change in the color of the diffraction spot provides an important basis for visualization of twist deformation. At a large twist angle, the macroscopic twist deformation is characterized. The linear peak wavelength shift exceeds 120 nm, and the twist angle exceeds 100 deg. The optimal angular sensitivity approaches 0.55 deg/nm. The relative parameters confirm the applicability of a holographic grating reflecting the macroscopic twist deformation. This research can promote the practical application of holographic sensors in sensing mechanical deformation of material, such as the measurement of the pre-tightening force of bolts and other fields.