R. Vacher

Photoelastic tensor components of Gd2 (MoO4)3

The whole set of components of the photoelastic tensor has been determined in Gd2(MoO4)3 at room temperature by a combination of ultrasonic and hypersonic wave measurements. The transverse components are found to be connected by relations derived from the theory of Nelson and Lax on the photoelastic effect in anisotropic media. Gd2(MoO4)3 can be considered as a promising acousto‐optical material for intracavity applications like laser mode lockers and cavity dumpers.

Temperature dependence of hypersonic attenuation in NaCl and KCl crystals

Abstract The usual theories of ultrasonic attenuation (Landau-Rumer and Akhiezer) are in disagreement with experiments involving hypersonic phonons (Brillouin scattering). This is shown here by measurements on NaCl and KCl. We observe a T n dependence with n approximately equal to 2.8, and an attenuation increasing with temperature in the low and high temperature range respectively. An extension of the Landau-Rumer and Akhiezer theories to hypersonic frequencies is proposed. Our theoretical expressions give a good account of the temperature dependence of the attenuation in the whole temperature range.

Attenuation and dispersion of longitudinal acoustic waves in α‐sulphur

Velocities and attenuations of longitudinal acoustic waves propagating along the three principal directions of α‐sulphur were measured by means of ultrasonic waves between 20 and 500 MHz and by Brillouin scattering between 4 and 25 GHz. Velocity and attenuation variations plotted versus frequency are continuous along the whole investigated range 20–25 000 MHz. Besides, an important velocity dispersion has been pointed out, with a relative variation of about 1.5%. A phenomenological interpretation involving a loss process with a single relaxation time is given which allows us to account for the whole set of results.

Noise equivalent pressure of a 1550 nm fiber laser as an underwater acoustic sensor dedicated to high depth

High sensitivity and wide dynamic measurement range can be achieved with these detectors These properties make fiber lasers suitable for acoustic detection of seismic risks, tsunami prevention, oil prospection with large deep-sea detectors. But the free running relative intensity and frequency optical noise of the laser can limit the performance of deep-sea detector systems. In this work, the dependence on relative intensity and frequency optical noise versus acoustic frequency is discussed as a function of the acousto-optic sensitivity SAO(nm/Pa).