Abstract
In recent years, the manipulation of Fano resonances in the time domain has unlocked deep insights into a broad spectrum of systems' coherent dynamics. Here, inelastic scattering of light with coherent acoustic phonons is harnessed to achieve complex Fano resonances. The sudden change of phonon momentum during reflection leads to a transition from anti-Stokes to Stokes light scattering, producing two different resonances that interfere in the measurement process. We highlight the conditions necessary to achieve such interference, revealing an underlying symmetry between photons and phonons, and verify the theory experimentally. Then, we demonstrate the possibility to characterize energy and coherence losses at rough interfaces, thus providing a mechanism for nondestructive testing of interface quality. Our results describe numerous unexplained observations in ultrafast acoustics and can be generalized to the scattering of light with any waves.
Highlights
In recent years, the manipulation of Fano resonances in the time domain has unlocked deep insights into a broad spectrum of systems’ coherent dynamics
These time-domain investigations of Fano resonances have showcased the mapping of the Fano parameters q in the frequency domain to a phase φ in the time domain [18]
In this Letter, we investigate the formation of Fano resonances due to the interaction of light with coherent acoustic phonons (CAPs) reflecting at an interface
Summary
The complex plane as a function of the laser wavelength, enabling nondestructive characterization of the roughness of surfaces and buried interfaces. For both experimental setups, the absorption of the femtosecond laser pulse leads to the generation of longitudinal CAPs, η(z − vt ), that propagates in the sample [29,30]. The CAPs propagate to the bottom of the thin film, are reflected towards the surface, and re-enter the probe’s penetration region This time, the probe light is anti-Stokes scattered, corresponding to the absorption of a phonon at the frequency B, as shown in the lower part of Fig. 1(b). The probabilities of Stokes and anti-Stokes (a) z=0 z>0
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