New ways to miniaturize mechanical oscillators. Improved light-modulated communication systems. Dramatic amplifications to weak mechanical and electrical signals. Sensitive sensors for the motion of nanoparticles.

These are some of the promises of a new system created by researchers at the National Institute of Standards and Technology (NIST). It relies on the collective oscillations at the surface of a metal nanoparticle, also known as plasmons, to induce sustained vibrations in a mechanical device that are 50 times larger. The entire system, which is no bigger than a red blood cell, is known as a plasmomechanical oscillator, or PMO.

To create their system, the researchers used a gold nanoparticle about 100 nanometers in diameter embedded in a tiny cantilever made of silicon nitride. Beneath these components and separated by an air gap is a gold plate. When a voltage is applied, an electrostatic actuator sitting atop the cantilever bends toward the plate and controls the size of the air gap. In turn, the gap's size affects the resonant frequency of the nanoparticle — just as tuning a guitar string changes the frequency of the string's reverberation. By shining laser light on the system, electrons in the resonator are made to oscillate, and the temperature of the resonator rises. This sets the stage for a complex interchange between light, heat and mechanical vibrations that offers several desirable properties.

A small, direct-current voltage applied to the electrostatic actuator, for instance, alters the optical frequency at which the resonator vibrates and the intensity of the laser light the system reflects. Such optomechanical coupling can modulate and control the flow of light on silicon chips and shape the propagation of light beams traveling in free space.

A second property relates to the heat generated by the resonator when it absorbs laser light. The heat causes the thin gold film actuator to expand, narrowing the gap and decreasing the frequency at which the embedded resonator vibrates. Conversely, when the temperature decreases, the actuator contracts, widening the gap and increasing the frequency of the resonator.

Force exerted by the actuator always kicks the cantilever in the same direction in which it's already traveling. If the incident laser light is powerful enough, these kicks can cause self-sustaining oscillations with amplitudes thousands of times larger than those of the device due to the vibration of its own atoms at room temperature.

The team also demonstrated that if the electrostatic actuator delivers a small mechanical force to the PMO that varies in time while the system undergoes these self-sustaining oscillations, the PMO can lock onto that tiny variable signal and greatly amplify it.

The research appears in a recent issue of Optica.