LU monitoring of different acoustic modes

    I initiated and supported the research on linear laser ultrasonics in the cases, when this is the first, not yet accomplished and required, step to the studies of the nonlinear phenomena. For example, I initiated and supported theoretically during my research stay in the Catholic University of Leuven (KUL) (1995-1997) and for several years later, the experiments demonstrating the advantages of laser ultrasonics in generation and detection of wide-frequency-band signals (pulses) of different type of the acoustic waves, which earlier had not been monitored/accessed all optically. The revealed dispersion relations (real and/or imaginary parts) provide opportunity to identify the acoustic modes. Scholte waves guided by different solid/liquid interfaces, leaky Rayleigh waves and the generalized Lamb modes (in the plates loaded by liquids) were studied […]. The motivation was to design the cells/sensors for testing liquids. I also supported theoretically experiments conducted later by Dr. (now Prof.) Christ Glorieux on first monitoring all-optically of nonlinear Scholte pulses. Earlier, I supported theoretically the experiments conducted in the Laboratory of Peter Hess in Heidelberg on the first monitoring by lasers of the nonlinear Rayleigh waves [ Phys. Rev. Let. 79, 1325 (1997) ]. Later, I supported theoretically the first demonstration of the two-dimensional imaging of laser generated surface acoustic waves conducted with femtosecond laser pulses (but at sub-GHz frequencies) in the Laboratory of Oliver Wright in Hokkaido University [ Phys. Rev. Lett. 88, 185504 (2002) ]. In Le Mans University, before the installation of the femtosecond laser systems we did laser ultrasonic monitoring of acoustic modes guided by the liquid layer, confined between two solids (inverse geometry to Lamb waves in liquid-loaded membranes) […] and of propagation of different bulk (longitudinal and shear) and skimming along the solid/solid and solid/liquid interfaces acoustic pulses in diamond anvil cell at high pressure […]. Of course, these experiments were conducted much later than laser-gratings-based experiments in DAC [by Keith Nelson], however, the experiments (with sub-nanosecond lasers for excitation and with different separations of pump and probe) provided opportunity to accumulate sufficient amount of the information for identification of different pure and mode converted signals and, finally, of elastic parameters. Later we were using in Le Mans University sub-nanosecond and nanosecond lasers for monitoring the zero-group-velocity (ZGV) Lamb modes for applications in non-destructive testing […]. The driving engine in these experiments is Assistant Professor Samuel Raetz. I developed the theory of the nonlinear ZGV modes and of the nonlinear black holes (in thickness inhomogeneous plates) in collaboration with the colleagues from Nanjing University of Science and Technology (NJUST) […]. In Le Mans University we are currently slowly and with the temporal gaps (because of the absence of funding or hands, or both) studying the disappearance of the ZGV modes near the cracks and possibilities of their interaction with acoustic modes confined near the cracks or guided by the crack surfaces (including the cases of partially closed cracks) [conferences presentations].