Nonreciprocal Reflection of Elastic Waves from a Free Boundary in a Paratellurite Crystal

Acousto-optics has gained significant attention for its potential to develop innovative devices that control optical beams using ultrasound. The operational parameters of acousto-optic devices depend on the elastic wave propagation geometry in crystals. Paratellurite crystals have exceptional anisotropy of elastic properties and a low speed of sound along specific directions, making them ideal for various applications. Studies have predominantly focused on back-reflection elastic wave configurations, where an acoustic wave is induced in the opposite direction by adding two waves. However, an additional wave is produced upon back reflection, which can be eliminated by correctly combining the phases of the two initial modes. Extensive research has been conducted on the properties of these waves, including their directionality, polarization, and drift angles, with thorough calculations made of their reflection coefficients. Despite the asymmetric reflection geometry in nonreciprocal reflection, the reciprocity condition is satisfied for the energy fluxes. These findings enable the creation of devices that incorporate acoustic beams.