Investigation of non-radiative relaxation dynamics under pulsed excitation using photon absorption remote sensing: a proof-of-principle study in mechanical sensing

In this study, we present Photon Absorption Remote Sensing (PARS) microscopy as a method for mechanical sensing of single micro-objects. PARS employs probe beam scattering to capture the non-radiative relaxation process following the absorption of a light pulse. When operated at gigahertz-range bandwidth, PARS resolves sub-nanosecond dynamics, tracing both photoacoustic (PA) pressure propagation and thermal diffusion. Coupled with a developed descriptive model, this GHz-range measurement enables retrieval of minimally distorted PA temporal profiles, which encode the ratio between the absorber’s sound speed and diameter. Proof-of-principle experiments with polystyrene microspheres demonstrate the ability to assess elastic properties at the single-particle level.