Two-photon resonance with combined amplitude and frequency modulation

N. D. Voropaev, А. Н. Ораевский

Stephanos Papademetriou, Stephen H. Chakmakjian, Carlos R. Stroud

We report the observation of the first six subharmonic resonances of the Rabi frequency in the absorption of a 100% amplitude-modulated laser beam by a two-level atom. The amplitude-modulated field is formed by combining two separate cw lasers; one is held fixed in frequency, and the other, of equal amplitude, is scanned in frequency. We present data and theory for several values of the detuning between the fixed field and the atomic resonance. The experimental results are in good agreement with theory.

Edward J. Robinson

This paper generalizes some recent results of F. T. Hioe [Phys. Rev. A 30, 2100 (1984)]. It is found that a two-level system driven by a resonant pulse with temporally symmetric amplitude modulation and antisymmetric frequency modulation may be completely inverted. In addition, it is shown that certain amplitude-modulated-- frequency-modulated combinations may be mapped into Hioe's (hyperbolic cosecant and hyperbolic tangent) solution.

Andrei I. Maimistov, Edward A. Manykin

Sergiy I. Zub, A. S. Kleiman

Mark A. Kramer, Robert W. Boyd, Lloyd W. Hillman +1 more

The propagation of a weakly modulated light beam through a nonlinear material is treated. The optical field representing such a beam consists of a strong carrier-frequency component and two weak, symmetrically displaced sidebands that combine to form a field, which may be purely amplitude modulated (AM), frequency modulated (FM), or some combination of these two modulation forms. It is shown that, for any optical nonlinearity, two modulation forms exist that have the property that the form of modulation is invariant under propagation of the beam. If a modulation form other than one of these natural modes is injected into the nonlinear medium, the modulation form will change as the beam propagates, asymptotically approaching the natural mode that experiences the lower attenuation. Explicit expressions for these natural modes are presented for the case in which the nonlinear medium can be modeled as a collection of two-level atoms. For the special case of an on-resonance pump beam, the natural modes correspond to pure amplitude modulation and pure frequency modulation. This formalism provides a general description of saturation spectroscopy for both AM and FM fields. Formulas are derived for the rate at which a pure FM beam is converted to an AM beam owing to its interaction with a two-level atomic medium. We also consider the variation that is due to propagation of the depth of modulation of an AM wave interacting resonantly with two-level atoms. The formalism predicts the existence of spectral features whose shape depends sensitively on the internal relaxation processes of the material. Experimental spectra are presented for ruby, alexandrite, and fluorescein in glass and are interpreted.