|Posted: Oct 28, 2015
A new physical mechanism allows 'phonon lasing' driven by optical forces at ambient conditions
(Nanowerk News) Last years have witnessed a steady and fast increase in the number of research reports dealing with full control of phonons . The word "phononics" is slowly entering the scientific vocabulary to indicate a platform where coherent phonons can be generated, harnessed and detected. In the field of photonics, the key element to fully enable the technology was the invention of lasers; yet, a full spread and development was not achieved until lasers were made easy to build and control. Likewise, despite the so-called "phonon laser" has been demonstrated in several publications, the high device quality (narrow linewidth) and strict experimental conditions (vacuum, low temperature) necessary for the effect to be observed, let alone used, make it simply too complex a source for a rapid diffusion of the technology.
A work recently published in Nature's Scientific Reports ("A self-stabilized coherent phonon source driven by optical forces"), headed by the Phononic and Photonic Nanostructures Group led by ICREA Prof Clivia M. Sotomayor-Torres and with Dr Daniel Navarro-Urrios as its first author, reports "phonon lasing" in a one-dimensional opto-mechanical crystal in response to an anharmonic modulation of the intracavity radiation pressure force.
The latter comes as a consequence of the spontaneous triggering in the optical cavity of a self-pulsing regime, i.e., a stable dynamic competition between thermo-optic (TO) effects and free-carrier-dispersion (FCA). The feedback exerted by the coherent mechanical oscillations on the self-pulsing makes the coupled system a frequency-entrained, self-stabilized oscillator. The wide dynamical frequency tuning of the self-pulsing enables a manifold of frequency-entrained regions associated to the coherent amplification of different mechanical modes up to hundreds of MHz. The self-pulsing dynamics could be readily engineered, enabling the scaling of the phonon lasing frequency up to the tens of GHz.
Commonly, the phonon lasing regime in optomechanical systems is achieved by means of dynamical back-action. In this case, compensating intrinsic mechanical losses demands rather restrictive conditions, and the requirements for the optical and mechanical modes in terms of quality factors and inter-coupling strengths are not easy to fulfil. Our findings show a new physical mechanism that allows phonon lasing underfar more relaxed configurations and moreover, opens new research avenues in the field of non-linear opto-mechanics. The system operates at ambient conditions of pressure and temperature in a silicon platform, which enables its exploitation in sensing, intra-chip metrology or time-keeping applications.