Entrainment and stimulated emission of auto-oscillators in an acoustic cavity

We report theory, measurements and numerical simulations on nonlinear piezoelectric ultrasonic devices with stable limit cycles. The devices are shown to exhibit behavior familiar from the theory of coupled auto-oscillators. Frequency of auto-oscillation is affected by the presence of an acoustic cavity as these spontaneously emitting devices adjust their frequency to the spectrum of the acoustic cavity. Also, the auto-oscillation is shown to be entrained by an applied field; the oscillator synchronizes to an incident wave at a frequency close to the natural frequency of the limit cycle. It is further shown that synchronization occurs here with a phase that can, depending on details, correspond to stimulated emission: the power emission from the oscillator is augmented by the incident field. These behaviors are essential to eventual design of an ultrasonic system that would consist of a number of such devices entrained to their mutual field, a system that would be an analog to a laser. A prototype laser is constructed

Coherent backscattering of ultrasound without a source

Coherent backscattering is due to constructive interferences of reciprocal paths and leads to an enhancement of the intensity of a multiply scattered field near its source. To observe this enhancement an array of receivers is conventionally placed close to the source. Our approach here is different. In a first experiment, we recover the coherent backscattering effect (CBE) within an array of sources and a distant receiver using time correlation of diffuse fields. The enhancement cone has an excellent spatial resolution. The dynamics of the enhancement factor is studied in a second experiment using correlation of thermal phonons at the same ultrasonic frequencies, without any active source

An Ultrasonic analog for a laser

We report measurements on ultrasonic systems analogous to random lasers. One system entails unstable ultrasonic feedback between distinct transducers, another involves a piezoelectric device that emits spontaneously and by stimulation. Both systems are found to exhibit behaviors similar to those of lasers. Over a wide range of parameters we observe narrow single emission lines, sensitivity to linear cavity properties, complex multi-mode emissions, and line narrowing

Non-exponential Dissipation in a Lossy Elastodynamic Billiard, Comparison with Porter-Thomas and Random Matrix Predictions

We study the dissipation of diffuse ultrasonic energy in a reverberant body coupled to a waveguide, an analog for a mesoscopic electron in a quantum dot. A simple model predicts a Porter-Thomas like distribution of level widths and corresponding nonexponential dissipation, a behavior largely confirmed by measurements. For the case of fully open channels, however, measurements deviate from this model to a statistically significant degree. A random matrix supersymmetric calculation is found to accurately model the observed behaviors at all coupling strengths.Comment: 4 pages, 8 figures, figures resized, misprints correcte

An Ultrasonic Analogue for a Random Laser

We describe electro-mechanical auto-oscillator which, when placed in contact with irregular acoustic cavity, can exhibit stimulated emission of ultrasound. Analytic model is constructed describing the device, which we propose as classical analogue of random laser

An Ultrasonic Analogue for a Random Laser

We describe electro-mechanical auto-oscillator which, when placed in contact with irregular acoustic cavity, can exhibit stimulated emission of ultrasound. Analytic model is constructed describing the device, which we propose as classical analogue of random laser

Ultrasound Amplification by Stimulated Emission of Radiation

In his seminal paper1, Albert Einstein introduced the concept of stimulated emission of electromagnetic radiation that led to the invention of masers and lasers. Ever since, there has been a propensity to regard stimulated and spontaneous emission as quantum-mechanical effects. However, these concepts have clear classical (nonquantum) analogues that we demonstrate in experiments with ultrasound. We have designed an electromechanical system consisting of ultrasonic oscillators that emit both spontaneously and by stimulated emission like atoms in an optical laser. The set of nominally independent oscillators lock to each other and produce a high-intensity coherent field. In the absence of stimulated emission, they produce a weak and incoherent field..

Imaging of spherical objects in a reflecting acoustic microscope

An expression is derived for the output signal of a reflecting acoustic microscope in scanning of a spherical object. It is shown that the character of the image of such an object depends significantly on the position of the focal plane relative to the center of curvature of the sphere. The experimental results are in good agreement with the theory