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Journal of Experimental and Theoretical Physics Letters

Complex resonance and complex-frequency spectroscopy

N. N. Rosanov

Published Nov 1, 2009• 4 citations

Abstract

The response of a medium to radiation with a complex frequency corresponding to an exponential time decrease in the radiation amplitude has been analyzed. The effect of complex resonance has been demonstrated when the real and imaginary parts of the complex radiation frequency approach the real and imaginary parts of the complex frequency of damping natural oscillations of medium oscillators. In resonance itself, the absolute value of the refractive index is divergent and radiation is completely reflected from the medium boundary. It has been shown that scanning of not only the real part, but also the imaginary part of the probe radiation frequency expands the capabilities of spectroscopy and makes it possible to, e.g., distinguish resonances even with coinciding (real) frequencies and close (of the same order of magnitude) widths.

DOI: 10.1134/s0021364009180052

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The response of a medium to radiation with a complex frequency corresponding to an exponential time decrease in the radiation amplitude has been analyzed. The effect of complex resonance has been demonstrated when the real and imaginary parts of the complex radiation frequency approach the real and imaginary parts of the complex frequency of damping natural oscillations of medium oscillators. In resonance itself, the absolute value of the refractive index is divergent and radiation is completely reflected from the medium boundary. It has been shown that scanning of not only the real part, but also the imaginary part of the probe radiation frequency expands the capabilities of spectroscopy and makes it possible to, e.g., distinguish resonances even with coinciding (real) frequencies and close (of the same order of magnitude) widths.

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A. Existence of two types of effects in atom-photon interactionsConsider first a light beam with frequency L propagating through a medium consisting of atoms with resonance frequency A .The index of refraction describing this propagation has an imaginary part and a real part which are associated with two types of physical processes.The incident photons can be absorbed, more precisely scattered in all directions.The corresponding attenuation of the light beam is maximum at resonance.It is described by the imaginary part of the index of refraction which varies with L Ϫ A as a Lorentz absorption curve.We will call such an effect a dissipative (or absorptive) effect.The speed of propagation of light is also modified.The corresponding dispersion is described by the real part n of the index of refraction whose difference from 1, nϪ1, varies with L Ϫ A as a Lorentz dispersion curve.We will call such an effect a reactive (or dispersive) effect.

It is shown that coherent processes of elastic scattering of resonant radiation form a “buffer” electromagnetic field near the boundary of excited media. This part of radiation is not governed by the standard refractive index, but precisely this part of radiation forms the beams reflected and refracted by the excited medium. The presence of the “buffer” field causes the suppression of stimulated emission near the boundary and leads to the appearance of a frequency angular broadening of the beam transmitted through a thin film of excited atoms at an oblique angle.