Picosecond ultrasonics signal in biological materials: Comparison between predictions and experiments

Abstract

Picosecond ultrasonics is a non‐destructive method for measuring mechanical properties such as velocity or stiffness coefficients for nanometric materials [1]. This technique uses femtosecond laser pulses for generating and detecting acoustics waves from GHz to THz. Its resolution is about nanometers in depth and a few micrometers laterally. For transparent materials it allows generating the so‐called Brillouin oscillations, which frequencies are determined by the material sound velocity and the light beam wavelength. In this paper this technique is applied to biological cells. Measurements suggest promising perspectives for the imaging inside a single living cell; frequency content is from 5 to 20 GHz. A theoretical model based on Fourier heat and acoustic wave equations has been developed. These equations include heat diffusion and acoustic propagation respectively. It permits numerical simulations in time domain. First experimental results on animal and vegetal cells are presented and confronted with these calculated waveforms. [1] C. Thomsen, H. T. Grahn, H. J. Maris, J. Tauc, Phys. Rev. B 34, 4129, 1986