Extended Data Fig. 1: Photoacoustic excitation of particle’s vibrations.
From: Single-particle photoacoustic vibrational spectroscopy using optical microresonators
a, Light absorption of a short laser pulse excites mechanical resonances of the particle. Top panel: the laser pulse; Bottom panel: the particle’s surface displacement (Curve: theoretical model; Circles: three-dimensional finite-element method). b, Simulated temperature map when the particle is irradiated by a short laser pulse. c, Excited oscillation shapes of breathing, even and odd vibrational modes when the laser pulse is irradiated from the top as shown in b. d, Vibrational spectrum of the spherical particle at the contact site (blue dot in b) is obtained from the theoretical displacement evolution. The frequency is normalized to the natural frequency of the (1,0) mode. The parameters of the spherical particle used in both theoretical and simulation model: 500 nm in radius, E = 500 MPa, ρ = 1.0 g cm−3, Poisson’s ratio σ = 0.35, refractive index n = 1.75 + 0.005i, heat capacity Cp = 1300 J/(kg ⋅ K), and thermal expansion coefficient αth = 2.4 × 10−4. The heat conductivity coefficient κh = 0.08 W/(m ⋅ K) is used in the simulation.
