In this paper, a novel photoacoustic viscoelasticity imaging (PAVEI) technique that provides viscoelastic information of biological tissues is presented. We deduced the process of photoacoustic (PA) effect on the basis of thermal viscoelasticity theory an
It is well known that a light spot of sub-wavelength will diverge in all directions. In this letter, A method is presented for generating sub-wavelength (0.44\lambda) longitudinally polarized beam, which propagates without divergence over lengths of abou