Measurements of Acoustic Velocities and Thickness of Iron Film in High-Pressure Diamond Anvil Cell by Laser Ultrasonics Technique
Résumé
The study of elastic properties of the materials under high pressures is important for the industrial, geophysical and astrophysical projects. The technique, based on diamond anvil cell (DAC), provides excellent opportunities for this purpose. Meanwhile, direct use of piezoelectric ultrasonic transducers in DAC is quite complicated task due to high pressures, relatively small volume of the sample under study and the presence of confining medium, i.e. diamond anvils. For this reason, contactless laser optoacoustic technique [1], allowing the excitation and the detection of ultrasound directly in the sample under high pressure, looks very promising [2]. We present the results of opto-acousto-optic experiments with iron at high pressures. The experimental data are obtained through the excitation of acoustic pulses by sub-nanosecond laser. Contactless detection of acoustic pulse, for the following visualisation with rapid oscilloscope of 3 GHz bandwidth, is achieved using 1 GHz bandwidth photo-detection of reflected ultra-stable CW probe laser radiation. Loading of the sample surfaces by diamond increases both the efficiency of laser-induced thermoelastic generation of acoustic waves and the efficiency of their acousto-optic detection at iron/diamond interfaces. In comparison with picosecond laser ultrasonics [3], laser ultrasonic technique provides easier opportunities in measurements of the velocities of shear acoustic waves and of the sample thickness. [1] C. B. Scruby and L. E. Drain, Laser Ultrasonics Techniques and Applications (Hilger, Bristol, 1990).[2] N. Chigarev, P. Zinin, L. C. Ming, G. Amulele, A. Bulou and V. Gusev V, Appl. Phys. Lett. 93,181905 (2008).[3] F. Decremps, L. Belliard, B. Perrin, M. Gauthier, Phys. Rev. Lett 100, 035502 (2008).