Diffraction of picosecond bulk longitudinal and shear waves in micron thick films
- 40 Downloads
Investigation of thin metallic film properties by means of picosecond ultrasonics [C. Thomsen et al., Phys. Rev. Lett. 53, 989 (1984)] has been under the scope of several studies. Generation of longitudinal and shear waves [T. Pézeril et al., Phys. Rev. B 73, 132301 (2006); O. Matsuda et al., Phys. Rev. Lett. 93, 095501 (2004)] with a wave vector normal to the film free surface has been demonstrated. Such measurements cannot provide complete information about properties of anisotropic films. Extreme focusing of a laser pump beam (≈0.5 μm) on the sample surface has recently allowed us to provide evidence of picosecond acoustic diffraction in thin metallic films (≈1 μm) [C. Rossignol et al., Phys. Rev. Lett. 94, 166106 (2005)]. The resulting longitudinal and shear wavefronts propagate at group velocity through the bulk of the film. To interpret the received signals, source directivity diagrams are calculated taking into account material anisotropy, optical penetration, and laser beam width on the sample surface. It is shown that acoustic diffraction increases with optical penetration, so competing with the increasing of directivity caused by beam width. Reflection with mode conversion at the film-substrate interface is discussed.
KeywordsShear Wave Longitudinal Wave EUROPEAN Physical Journal Special Topic Mode Conversion Laser Spot Size
Unable to display preview. Download preview PDF.
- C. Thomsen et al., Phys. Rev. Lett. 53, 989 (1984) Google Scholar
- T. Pézeril et al., Phys. Rev. B 73, 132301 (2006) Google Scholar
- O. Matsuda et al., Phys. Rev. Lett. 93, 095501 (2004) Google Scholar
- C. Rossignol et al., Phys. Rev. Lett. 94, 166106 (2005) Google Scholar
- G. Tas et al., Phys. Rev. B 49, 15046 (1994) Google Scholar
- D.A. Hutchins et al., J. Acoust. Soc. Am. 70, 1362 (1981) Google Scholar
- J.D. Aussel et al., Ultrasonics 26, 245 (1988) Google Scholar
- M. Perton, Ph.D. thesis, University of Bordeaux 1, No. 3294, 2006 Google Scholar