Characterization of photoelastic materials by combined Mach-Zehnder and conoscopic interferometry: Application to tetragonal lithium tetraborate crystals

•Combined Mach-Zehnder and conoscopic interferometry are used to explore photoelastic properties of anisotropic crystal materials.•The performance of such combined approach is demonstrated on tetragonal lithium tetraborate (LTB) single crystals, as an example.•By exploring different geometries of piezooptic coupling full sets of piezooptic and photoelastic tensor constants of LTB have been precisely characterized.•The acoustooptic efficiency of LTB has been evaluated using the magnitudes of photoelastic constants derived from piezooptical measurements.•LTB demonstrates quite large acoustooptic performance becoming advanced material for deep-ultraviolet applications.