All the remaining parameters are as discussed in the text.The iPhone camera helps you take great photos in any situation-from everyday moments to studio-quality portraits. In all the cases, the buildup of phonons is much slower than that of plasmons, as the vibrations do not reach a steady state during the duration of the pulse. For the largest incident laser intensity, we consider three values of the free-space phonon decay rate: ℏ γ m = 0.07 meV is used for all the solid lines, while ℏ γ m = 0.14 meV (dotted) and ℏ γ m = 0.045 meV (dashed) are also plotted. (b) Phonon population calculated in the same setup, obtained by solving the phonon rate equations. The plasmonic cavity reacts almost instantaneously to the coherent pump, with the plasmon population closely following the shape of the incident pulse.
Γ opt ( t ) is negative, indicating that the system operates in the amplification regime. The shaded area shows normalized optomechanical damping − Γ opt ( t ) / γ m, proportional to the instantaneous intensity of the incident pulse. (a) Evolution of plasmon population for five peak intensities of the incident laser, logarithmically increasing from 6 × 10 2 μ W / μ m 2 (yellow line) to 2.5 × 10 4 μ W / μ m 2 (red line). Reuse & PermissionsĮvolution of the optomechanical SERS system excited by a 1-ps Gaussian pulse. The black dashed lines show a linear response the red line shows Stokes emission calculated from the model in (b). Linear ( R L), superlinear ( R S), and driven-chemical ( R C) regimes are highlighted in blue, orange, and red. Pulsed measurements on two additional particles are also shown (red triangles, squares). (c) Stokes-SERS intensity of 1585 cm − 1 mode for a single NPoM vs peak laser intensity for (red circles) ps-pulsed and (black squares) CW excitation. Zoomed region (inset) highlights the superlinear predicted time-integrated Stokes emission (linear shown dashed). (b) Stokes (orange line) and anti-Stokes (blue line) dependence on the peak intensity of the pulsed illumination. Only for CW illumination does a clear threshold arise from the vanishing effective phonon decay rate (dashed line, normalized to the free-space phonon decay rate), interpreted as the phonon lasing (phasing) or instability regime. In the latter case with 1-ps Gaussian pulses, the peak laser intensity and phonon population are used. (a) Comparison of the nonlinear buildup of incoherent phonon population (solid lines) for CW (black line) or pulsed (red line) illumination. However, we then also observe breaking of molecular bonds in real time.Īlthough this irreversible breaking might ultimately limit how molecules can be used as quantum-mechanical oscillators, our results suggest that novel chemical reactions might be accessed via such tightly confined light. As the intensity of incoming light increases, we show how molecular vibrations increase rapidly above a critical threshold, almost reaching the vibratory equivalent of a laser, or “phaser.” We develop a quantum theory to describe this effect, which suggests how a hundred molecules vibrate together. The appropriate color of light causes molecules placed within these gaps to vibrate. In this configuration, we can trap light in the subnanometric volume between the particle and the substrate, where the particle acts as a sort of nanometer-scale lens, which allows us to enhance and directly observe interactions between the light and molecules. We create the smallest optical cavity in the world, a millionfold smaller than previously used in any optomechanics experiment, by supporting a gold nanoparticle just a few atomic diameters above a metal surface. This work shows that the same behavior underpins how bonds in molecules interact with photons, and it reveals how molecules under short pulses of light can shake themselves apart. The interplay between incoming light and the vibrations it provokes (for example, on a mirror) is exploited by cutting-edge technological systems, from massive gravitational-wave detectors to tiny microdevices that are sensitive to the smallest quantum-mechanical motion. Beams of light inherently produce a mechanical pressure.
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