Temporal and spatial distribution of temperature eld was studied in operating acousto-optic devices on base of large-size paratellurite crystals. The study was carried out in real time by means of thermal imaging technique. Dynamics of heat release in a hot deector and a hot tunable lter was examined at dierent frequencies and driving electric power levels applied to piezoelectric transducers. The study was also based on measurements of standing wave ratio and analysis of the Smith charts.