| Picosecond ultrasonics is a non-destructive method for measuring mechanical and thermal properties such as sound velocity or heat conductivity at sub-micron scale. This technique uses femtosecond laser pulses for generating and detecting GHz acoustics waves. Its resolution is about nanometers in depth and a few micrometers laterally dictated by the optical diffraction limit. In this paper, the technique is applied to biological single in-vitro living cells. 1D mapping in a cell with a lateral resolutions of 2μm is presented; 3 organelles are detected: nucleus, vacuole and membrane. From a set of cells, sound velocities and attenuations are deduced from the acoustic signals measured in the vacuole and the nucleus. Photoacoustic responses calculated according to thermoelastic generation mechanism and reflectometric detection model are presented and compared to the measurements. Measurements achieved in different varieties of the Allium Cepa cell illustrate the sensitivity of the technique. |