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Strong Selective Anti-Stokes Raman Scattering Enhancement in Plasmonics Using Photon Density of States Engineering

2021; American Chemical Society; Volume: 125; Issue: 50 Linguagem: Inglês

10.1021/acs.jpcc.1c08445

1932-7455

С. В. Гапоненко, Д. В. Гузатов, Natalia Strekal,

Advanced Thermodynamics and Statistical Mechanics

We demonstrate theoretically the possibility to achieve domination of anti-Stokes Raman scattering enhancement over the Stokes one by means of photon local density of states (LDOS) engineering in model plasmonic nanostructures. The theory predicts anti-Stokes over Stokes scattering enhancement domination when both anti-Stokes and Stokes secondary photons energies correspond to the descending long-wave wing of extinction spectra of metal nanoparticles. The photon LDOS effect is proposed as a rationale for anti-Stokes anomalies reported for surface enhanced Raman spectroscopy, and the model of a dimer formed by two nanospheres is found to provide the reasonable agreement with experimental data explaining both promotion and inhibition of anti-Stokes scattering depending on the laser wavelength used. Our consideration means that evaluation of local temperature based on the anti-Stokes/Stokes ratio in Raman scattering for plasmonic structures cannot be performed. The simple models of isolated and coupled spheres and isolated spheroids, though offering strong anti-Stokes/Stokes enhancement asymmetry, do not promise absolute domination of anti-Stokes process versus the Stokes one, which is necessary for laser cooling effects. In a more general context, photon DOS engineering can be purposefully used to highlight anti-Stokes versus Stokes scattering even in the case of inhibited Raman scattering, provided that d(LDOS)/dω ≫ 1 holds, that is, DOS sharply grows with frequency.