We will describe ultrasonic facilities at low temperatures which have been built up over the last ten years at Sherbooke and give examples of some of our results. More recently, we have initiated research and development program on acoustic microscopy in the range 30-500 MHz. Our facilities include lens guiding and polishing equipment for both spherical and cylindrical lenses as well as ZnO fabrication unit by RF sputtering. Much of our work in acoustic microscopy has been at low temperatures. An instrument has been built for imaging in liquid nitrogen and we observe a significant increase in resolution as compared to water. We have also built a V(z) apparatus for measurements as a function of temperature between 80 and 200 K using liquid propane. We used a cylindrical lens of the type invented by Prof. Chubachi and coworkers. We have also built and exploited an acoustic micrpscope operating in liquid Helium at RF- frequencies (30-90 MHz). Images have been obtained in reflection and transmission at 1.9 K, where the transmission method is a new one in which the detecting transducer is placed at the focal plane. Finally a ^3He cryostat is being built for imaging at 0.3 K in ^4He under a pressure of about 25 bars with a quick change top loading system. In this cryostat it should be possible to do very high resolution imaging.

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