TRANSPORT OF TERAHERTZ NONEQUILIBRIUM ACOUSTIC PHONONS IN DENSE CORUNDUM CERAMICS

The propagation of nonequilibrium terahertz acoustic phonons in dense alpha-Al2O3 ceramics with grain size similar to 10 mu m was studied. P honons were generated by the heat pulse technique and optical detectio n of 29 cm(-1) (0.874 THz) phonons via the Cr3+ impurity ions fluoresc ence was used. The diffusive propagation of phonons from heater to opt ical detector was observed with mean free path of phonons (l) over bar = 150 mu m which is significantly larger than the grain size. This va lue is in agreement with the result of computer calculation of (l) ove r bar taking into account reflection and refraction at interfaces of d isoriented alpha-Al2O3 single-crystalline grains in the framework of a coustic mismatch model.