Pressurized Superfluid 4He Acoustic Microscopy

Abstract

An acoustic microscope has been developed which makes use of pressurized super fluid helium as an acoustic coupling medium. Acoustic micrographs were taken using pure super fluid 4He under saturated vapor pressure at 0.2 K and under 25 atm at 0.2 K and 1.9 K, for the frequency of 400 MHz. By pressurizing liquid 4He, the acoustic attenuation decreases, the efficiency of the antireflection coating increases, and the power level of saturation caused by nonlinearity of the super fluid 4He is raised. A good signal-to-noise ratio of imaging is thus obtained.