Thermal Fluctuations of the Optical Properties of Nanomechanical Photonic Metamaterials

Abstract

The combination of optical and mechanical resonances offers strong hybrid nonlinearities, bistability, and the ability to efficiently control the optical response of nanomechanical photonic metamaterials with electric and magnetic field. While optical resonances can be characterized in routine transmission and reflection experiments, mapping the high‐frequency mechanical resonances of complex metamaterial structures is challenging. Here, it is reported that high‐frequency time‐domain fluctuations in the optical transmission and reflection spectra of nanomechanical photonic metamaterials are directly linked to thermal motion of their components and can give information on the fundamental frequencies and damping of the mechanical modes. This is demonstrated by analyzing time‐resolved fluctuations in the transmission and reflection of dielectric and plasmonic nanomembrane metamaterials at room temperature and low ambient gas pressure. These measurements reveal complex mechanical responses, understanding of which is essential for optimization of such functional photonic materials. At room temperature the magnitude of the observed metamaterial transmission and reflection fluctuations is of order 0.1% but may exceed 1% at optical resonances.

Photonic metamaterial analogue of a continuous time crystal

“…This coupling between mechanical and optical properties of the lattice provides opportunity for detecting the state of the lattice optically by monitoring its transmissivity. Indeed, it was shown recently that even picometric thermomechanical fluctuations in such structures can measurably modulate scattered and transmitted light 18 . At low laser power (≤tens of μW), the transmissivity spectrum contains several overlapping peaks of small amplitude at frequencies just below 1 MHz corresponding to oscillations of the individual illuminated nanowires.…”

“…The pronounced dependence of the frequency of transmissivity oscillation on incident power below 120 μW (Fig. 4c) is due to thermal contraction of the nanowires induced by decreasing laser illumination 18 .…”

Ballistic dynamics of flexural thermal movements in a nanomembrane revealed with subatomic resolution

“…Flexural deformations and modes of oscillation are now understood to be of fundamental importance to the thermal, optical, electrical, and mechanical properties of graphene and other two-dimensional (2D) materials (1)(2)(3)(4)(5) and to the optical properties of photonic metamaterials through near-field coupling among resonators and mechanochromic effects (6,7). In contrast to a classical Brownian particle in a fluid that is thermally perturbed by external collisions with ambient atoms, thermal movements under vacuum are driven internally by momentum transfer from the annihilation and creation of the flexural phonons.…”

Optical Control of Nanomechanical Brownian Motion Eigenfrequencies in Metamaterials

“…The metamaterial structure supports a near-infrared closed mode optical resonance at a wavelength of 1542 nm (see Supplementary Figure S1), underpinned by the excitation of antiparallel displacement currents in adjacent dissimilar silicon nanobricks by incident light polarized parallel to the long axis of the bricks. In the vicinity of this optical resonance, thermal (Brownian) motion of the nanowires, mutual positional fluctuations of pico- to nanometric amplitude, translate to fluctuations of metamaterial transmission (of order 0.1%) at their few MHz natural mechanical resonance frequencies. , These thermomechanical oscillations are detected as peaks in frequency spectra of transmission amplitude spectral density (Figure b,c): the metamaterial is mounted in a vacuum chamber at a pressure of 4 × 10 –3 mbar to exclude air damping of mechanical motion. (It should be noted here that while a classical Brownian particle in a fluid is thermally perturbed by “external” collisions with ambient atoms, the thermal motion of objects under vacuum is driven “internally” by momentum transfer from the annihilation, creation, and interference of phonons.)…”