Self-organization in a phonon laser (original) (raw)
Related papers
The operation threshold of a double barrier phonon laser
Solid State Communications, 2000
We make an adaptation of laser modeling equations to describe the behavior of a phonon laser (saser). Our saser consists of an AlGaAs/GaAs double barrier heterostructure designed to generate an intense beam of transversal acoustic (TA) phonons. To study our system, we begin with a Hamiltonian that describes the decay of primary longitudinal optical phonons (LO 1 ) into secondary (LO 2 ) and TA (LO 1 3 LO 2 ϩ TA) and its inverse process (recombination). Using this Hamiltonian, a set of coupled equations of motion for the phonons is obtained. We also consider the interaction between the phonons and its reservoirs. These interactions are introduced in the equations of motion leading to a set of coupled Langevin equations. In order to obtain an expression to describe our saser, we apply, in the Langevin equations, an adiabatic elimination of some variables of the subsystem. Following the method above we obtain the value of the injection threshold for the operation of our phonon laser. At this threshold occurs a phase transition from a disordered to a coherent state. It is shown that a big "optical" pumping is not necessary to get a sasing region. ᭧
The coherence of the AlGaAs–GaAs phonon laser
Physica B-condensed Matter, 2002
To study the emission properties of an AlGaAs–GaAs phonon laser we develop a formalism similar to that used to describe a laser. The device studied here consist of a double-barrier resonant tunneling diode tailored to generate an intense rate of primary LO1 phonons. These phonons are confined in the well and they decay into a pair of secondary LO2 and TA phonons. The TA phonons are generated by stimulated emission and they are partially reflected in the well walls. A combination of these two processes leads, for injection rates greater than the threshold, to the selection of a single phonon mode. Finally, the TA phonons escape through the barriers forming an intense coherent phonon beam. We start with a Hamiltonian that takes into account the electrons, the three phonon branches, the electron–phonon interaction and the phonon–phonon interaction. The last one is responsible for the TA phonon generation. From this Hamiltonian we get a set of five coupled Heisenberg–Langevin equations that are solved making an expansion in coherent states and doing the usual adiabatic approximation. The threshold for phonon lasing is calculated. The results show that it is not necessary to have a big pumping to get a single mode operation. This confirm our previous results obtained using rougher approximations. The phonon laser studied here has a very short wavelength. The mean free path of TA phonons is of the order of 2 mm. Therefore, it could be useful to perform acoustic nanoscopy and other applications.
GaAs-AlxGa1-xAs double-barrier heterostructure phonon laser: A full quantum treatment
Physical Review B, 2001
The aim of this work is to describe the behavior of a device capable to generate high-frequency (~THz) acoustic phonons. This device consists in a GaAs-AlxGa1-xAs double-barrier heterostructure that, when an external bias is applied, produces a high rate of longitudinal optical (LO) phonons. These LO phonons are confined and they decay by stimulated emission of a pair of secondary longitudinal optical (LO~) and transversal acoustic phonons. The last ones form an intense beam of coherent acoustic phonons. To study this effect, we start from a tight-binding Hamiltonian that takes into account the electron-phonon and phonon-phonon interactions. We calculate the electronic current through the double barrier and obtain a set of five coupled kinetic equations that describes the electron and phonon populations. The results obtained here confirm the behavior of the terahertz phonon laser, estimated by rougher treatments [S.S. Makler et al., J. Phys.: Condens. Matter 10, 5905 (1998).]
Stimulated decay of nonselectively pumped optical phonons in GaAs
Physical Review B
We have considered the processes determining the steady-state population of longitudinal optical ͑LO͒ phonons being intensively produced in GaAs by electrons optically excited or accelerated in strong external electric field. The emitted LO phonons pass their energy to acoustic phonon systems through anharmonic decay into longitudinal acoustic ͑LA͒ phonons. The latter emerge as almost monoenergetic and concentrated in a narrow layer in the reciprocal space. Had the occupation numbers of k states within this layer grown to unity, the decay process would have become stimulated, effectively desolating the built-in LO states and giving rise to various nonlinear phenomena. We show that this is actually the case by tracing LA phonon kinetics and calculating the number of phonons in each k state available for feedback. The results obtained substantially clarify the physical picture of energy transfer processes mediating heat removal in GaAs. ͓S0163-1829͑99͒02131-1͔
Self-pulsations in phonon-assisted lasers
Journal of the Optical Society of America B, 1998
The observation of stable self-pulsing of a single-transverse-mode alexandrite laser with a Fabry-Perot cavity is reported. This process occurs many times above threshold and depends on the pump wavelength. The novel theoretical model, in which the dynamics of the host lattice phonons is taken into account, is shown to explain this phenomenon. The border of the Hopf bifurcation is found in the plane of two parameters: the intensity and the frequency of the pump laser. In the region where self-pulsations occur they are proved to be the result of the photon-phonon energy pulling.
Catastrophic transition between dynamical patterns in a phonon laser
Physical Review Research
The bifurcations or transitions of the classical nonlinear systems with finite degrees of freedom exhibit some dynamical behaviors that are similar to those in the phase transitions of many-body systems. A dynamical type of them in the form of a sudden transition of the amplitudes between two harmonic oscillations, which are stable under periodically driving force, is not so common to see. We show that a sudden transition of this type can be realized in a system of coupling a microresonator that supports a mechanical vibration to another microresonator, and the system was experimentally demonstrated as a phonon laser. If the pump laser power or the intercavity coupling strength is adjusted to a critical value, the cavity field patterns will suddenly change, together with a jump of the stabilized mechanical amplitude. Such transition can be applied to a precise measurement of the optomechanical coupling constant, which is hard to measure due to its proportion to a tiny zero-point mechanical fluctuation amplitude.
The terahertz phonon laser: a full quantum treatment
Physical Review B, 2001
The aim of this work is to describe the behavior of a device capable to generate high frequency (~THz) acoustic phonons. This device consists in a GaAs-AlGaAs double barrier heterostructure that, when an external bias is applied, produces a high rate of longitudinal optical LO phonons. These LO phonons are confined and they decay by stimulated emission of a pair of secondary longitudinal optical (LO_2) and transversal acoustic (TA) phonons. The last ones form an intense beam of coherent acoustic phonons. To study this effect, we start from a tight binding Hamiltonian that take into account the electron-phonon (e-ph) and phonon-phonon (ph-ph) interactions. We calculate the electronic current through the double barrier and we obtain a set of five coupled kinetic equations that describes the electron and phonon populations. The results obtained here confirm the behavior of the terahertz phonon laser, estimated by rougher treatments.
Ab initio theory of coherent phonon generation by laser excitation
2010
We show that time-dependent density functional theory (TDDFT) is applicable to coherent optical phonon generation by intense laser pulses in solids. The two mechanisms invoked in phenomenological theories, namely impulsively stimulated Raman scattering and displacive excitation, are present in the TDDFT. Taking the example of crystalline Si, we find that the theory reproduces the phenomena observed experimentally: dependence on polarization,
Dynamics of Non-equilibrium Short-wave-length Phonons in Semiconductor Heterostructures
VLSI Design, 2001
The behavior of short-wave-length acoustic phonons in the vicinity of a quantum well in a GaAs/A1GaAs heterostructure has been investigated. Hot two-dimensional electrons in the well produce longitudinal optical phonons, which decay into almost monoenergetic short-wave-length longitudinal acoustic (LA) phonons. The latter undergo elastic scattering and down-conversion into transverse acoustic (TA) phonons. The distribution of the LA and TA phonons over frequency and distance to the well have been found by solving semi-analytically a system of two kinetic equations with nontrivial boundary conditions and nonlinear dispersion. The distribution functions have essentially non-temperature form even at substantial distance from the well.
Nature Communications, 2020
Efficient generation of phonons is an important ingredient for a prospective electrically-driven phonon laser. Hybrid quantum systems combining cavity quantum electrodynamics and optomechanics constitute a novel platform with potential for operation at the extremely high frequency range (30–300 GHz). We report on laser-like phonon emission in a hybrid system that optomechanically couples polariton Bose-Einstein condensates (BECs) with phonons in a semiconductor microcavity. The studied system comprises GaAs/AlAs quantum wells coupled to cavity-confined optical and vibrational modes. The non-resonant continuous wave laser excitation of a polariton BEC in an individual trap of a trap array, induces coherent mechanical self-oscillation, leading to the formation of spectral sidebands displaced by harmonics of the fundamental 20 GHz mode vibration frequency. This phonon “lasing” enhances the phonon occupation five orders of magnitude above the thermal value when tunable neighbor traps ar...