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Physical Review A

Molecular Raman effect in the optical microcavity: QED vacuum confinement of an inelastic quantum scattering process

F. De Martini, Michele Marrocco, C. Pastina, F. Viti

Published Jan 1, 1996• 9 citations
Publisher

Abstract

The spontaneous Raman scattering from liquid samples of ${\mathrm{C}}_{6}$${\mathrm{H}}_{6}$ is investigated in the Casimir topology of a microscopic optical Fabry-P\'erot cavity terminated by Bragg reflectors tuned at the emitted Stokes wavelength. The given general quantum scattering theory is based on a complete set of mode functions describing the cavity-confined field in its vacuum state. The coupling of the field with the normal CH ring stretching mode at \ensuremath{\Delta}\ensuremath{\nu}=3062 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ (totally symmetric species ${\mathit{A}}_{1\mathit{g}}$) of the benzene molecule is given via the related Raman tensor, which leads to the appropriate form of the coupling Hamiltonian. A detailed experimental investigation of the spontaneous Raman scattering for the mode is then reported. The results confirm the relevant predictions of the scattering theory, namely, the effect of the vacuum confinement on the enhancement and inhibition of the total and differential cross sections, on the angular distribution of the scattered radiation, and on the molecular depolarization ratio. \textcopyright{} 1996 The American Physical Society.

DOI
10.1103/physreva.53.471

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The spontaneous Raman effect in ${\mathrm{C}}_{6}$${\mathrm{H}}_{6}$ is investigated in the QED-vacuum confinement condition in the Casimir topology of an optical microcavity as a prototype inelastic quantum-scattering process at optical frequencies. The confinement determines a dramatic enhancement (over a factor of ${10}^{3}$), inhibition, and directional effects on the scattering intensity. Apart from its relevance in atomic and molecular spectroscopy, the work establishes a new perspective in the field of QED scattering involving quantum particles with any energy.

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The quantum theory of the spontaneous emission (SpE) from an active microscopic cavity (microcavity) is given with emphasis on mirror separations of the order of the optical wavelength. The theory is based on a complete set of orthonormal-mode functions that include both transverse polarizations and span the infinite three dimensional space that pervades and surrounds the microcavity. SpE rates for different active-dipole orientations and cavity configurations are calculated. The SpE pulse shape detected outside the cavity is shown to be generally nonexponential. A detailed computer simulation of the process is presented on the basis of the given theory in the perspective of our experiment, for a cavity terminated by mirrors bearing either metal- or semiconductor-multilayered coatings. We then report an extensive experimental verification of the theory by adopting an Eu-dibenzoylmethane complex as active medium with SpE from the $^{5}$${\mathit{D}}_{0\mathrm{\ensuremath{-}}}^{7}$${\mathit{F}}_{2}$ line at \ensuremath{\lambda}=6111 \AA{}, under coherent uv excitation at ${\ensuremath{\lambda}}_{\mathit{p}}$=3547 \AA{}. The results show evidence of ``SpE inhibition'' and ``enhancement,'' of nonexponential decay of SpE signals, and of competition with superradiance and stimulated emission. Finally we report the results of an experimental test of the algorithm adopted in all computer calculations of the optical parameters of the multilayered structures used for cavity confinement.

Physical Review A•Mar 1, 1991•231 citations
The spontaneous Raman scattering from liquid samples of {\mathrm{C}}_{6}$${\mathrm{H}}_{6} is investigated in the Casimir topology of a microscopic optical Fabry-P'erot cavity terminated by Bragg reflectors tuned at the emitted Stokes wavelength. The given general quantum scattering theory is based on a complete set of mode functions describing the cavity-confined field in its vacuum state. The coupling of the field with the normal CH ring stretching mode at \ensuremath{\Delta}\ensuremath{\nu}=3062 cm\ensuremath−1{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}cm\ensuremath−1 (totally symmetric species A1g{\mathit{A}}_{1\mathit{g}}A1g​) of the benzene molecule is given via the related Raman tensor, which leads to the appropriate form of the coupling Hamiltonian. A detailed experimental investigation of the spontaneous Raman scattering for the mode is then reported. The results confirm the relevant predictions of the scattering theory, namely, the effect of the vacuum confinement on the enhancement and inhibition of the total and differential cross sections, on the angular distribution of the scattered radiation, and on the molecular depolarization ratio. \textcopyright{} 1996 The American Physical Society.
The spontaneous Raman effect in C6{\mathrm{C}}_{6}C6​H6{\mathrm{H}}_{6}H6​ is investigated in the QED-vacuum confinement condition in the Casimir topology of an optical microcavity as a prototype inelastic quantum-scattering process at optical frequencies. The confinement determines a dramatic enhancement (over a factor of 103{10}^{3}103), inhibition, and directional effects on the scattering intensity. Apart from its relevance in atomic and molecular spectroscopy, the work establishes a new perspective in the field of QED scattering involving quantum particles with any energy.
Spontaneous Raman scattering is investigated theoretically by considering a completely classical description of the process that takes place within the mirrors of a microscopic Fabry-P\'erot cavity. This analysis is based on the image method within the framework of the classical theory of light scattering. In order to account for the finite reflectivities of the mirrors, the result for the scattered field is presently determined analytically only in the limit of low finesse of the optical cavity. This leads to a general expression for the cross section of the Stokes transition that explains the results recently reported in the literature [F. De Martini, M. Marrocco, C. Pastina, and F. Viti, Phys. Rev. A 53, 471 (1996)]. Therefore, in the limit of low finesse of the cavity, one must accept that this effect has a fundamentally classical nature. \textcopyright{} 1996 The American Physical Society.
Several experimental schemes of vacuum-confinement in electromagnetic-bounded structures are presented together with related results involving Spontaneously Emitting (SE) molecules. Striking anomalies in the SE spatial-distribution and decay-times are detected. In addition, an anomalous "zero-threshold-laser" behaviour of molecular Stimulated Emission (StE) in a single-mode Casimir-type microscopic cavity is reported. This novel effect is due to an unexpected collective molecular process taking place at an exceedingly low excitation level in the optical-pumping scheme. In the framework of "Phase-transition" theory this effect corresponds to an order-disorder transition taking place at a critical-temperature T c which is virtually infinite.
A description is given of several novel experimental methods for quantum-electrodynamic vacuum confinement of emission modes close to a single electromagnetic boundary and in a microscopic Fabry–Perot optical cavity of length of the same order of magnitude as the wavelength of the recorded radiation. Strong anomalies (Purcell effect) of the spontaneous emission process and of a phase transition with spontaneous–stimulated decay of states in the stimulated emission process are demonstrated experimentally. It is shown that in the context of the phase transition theory an active microscopic cavity behaves as a superconductor with an extremely high critical transition temperature. This unusual behavior can be interpreted as a manifestation of a perturbation induced in a quantum system by "measurement apparatus" of dimensions comparable with the de Broglie wavelength of a test particle.
The quantum theory of the spontaneous emission (SpE) from an active microscopic cavity (microcavity) is given with emphasis on mirror separations of the order of the optical wavelength. The theory is based on a complete set of orthonormal-mode functions that include both transverse polarizations and span the infinite three dimensional space that pervades and surrounds the microcavity. SpE rates for different active-dipole orientations and cavity configurations are calculated. The SpE pulse shape detected outside the cavity is shown to be generally nonexponential. A detailed computer simulation of the process is presented on the basis of the given theory in the perspective of our experiment, for a cavity terminated by mirrors bearing either metal- or semiconductor-multilayered coatings. We then report an extensive experimental verification of the theory by adopting an Eu-dibenzoylmethane complex as active medium with SpE from the 5^{5}5${\mathit{D}}_{0\mathrm{\ensuremath{-}}}^{7}$F2{\mathit{F}}_{2}F2​ line at \ensuremath{\lambda}=6111 \AA{}, under coherent uv excitation at ${\ensuremath{\lambda}}_{\mathit{p}}$=3547 \AA{}. The results show evidence of ``SpE inhibition'' and ``enhancement,'' of nonexponential decay of SpE signals, and of competition with superradiance and stimulated emission. Finally we report the results of an experimental test of the algorithm adopted in all computer calculations of the optical parameters of the multilayered structures used for cavity confinement.