Oblique incidence response of photoelastic coatings

A novel surface angle measurement technique is described using an LPC for surface inclinations between 20° and 70°. The technique utilizes the Fresnel transmission equations and a similar experimental setup for measuring strain. Measurement of the optical Fresnel response is necessary for accurate strain measurements. Additionally, the oblique angle intensity responses between a luminescent and reflective photoelastic coating are compared. The LPC exhibits a considerably more diffuse emission characteristic than the RPC. At 30° and 60°, respectively, the LPC normalized intensity retains 88% and 49% compared to 25% and 4% for the RPC, enabling more accurate strain measurements at higher surface inclinations.