Nonresonant Light Research Articles

Steady propagation of pulses in resonant media

Steady propagation of pulses of radiation in a resonant medium is studied by taking into account the loss for the case in which pulse duration is small as compared to the relaxation time of the resonant atoms. Expressions for the amplitude profile, chirped frequency, envelope velocity, propagation number and the atomic variables are evaluated in terms of the known quantities. For negligible loss, we get a nonchirped hyperbolic-secant 2π-pulse of arbitrary frequency and duration and the results agree with those of Eberly and Matulic. For nonzero loss, we get chirped 2π-pulses of arbitrary frequency and duration and a small asymmetry which depends on the pulse duration and detuning. If the medium is inverted, we can also get exactly resonant chirped π-pulses of duration greater than a critical value and having an arbitrary small asymmetry. The expression for the pulse area in this case is different from that given in the literature. Exactly resonant nonchirped hyperbolic-secant π-pulses of duration equal to this critical value and having the usual expression for pulse area obtained by Arecchi and Bonifacio and by Lamb are a special case of our results obtained by taking asymmetry equal to zero and pulse duration equal to the critical value. For π-pulses the product of the envelope and mean phase velocities is almost equal to the square of the velocity of nonresonant light. Consideration of nonlinear Kerr effect leads to an extra term in chirping.

Chirped Steady π-pulses of Light of an Arbitrary Duration in a Lossy, Exactly Resonant Inverted Medium

It is shown that the steady π -pulses of light in a lossy, resonant inverted medium can have an arbitrary duration greater than a critical value and are in general chirped. The non-chirped π -pulses of fixed duration (for a given population inversion) obtained by Arecchi and Bonifacio and by Lamb is a special case of our results when the pulse duration is set equal to the critical value. We find expressions for the pulse profile, propagation number, envelope velocity and atomic variables, and show that the expression for the area of the pulse in this case is different from that used commonly, and that the product of the envelope and mean phase velocities is equal to the square of the velocity of non-resonant light.

Optically-induced energy level shifts for intermediate intensities

We report measurements of optically-induced energy level shifts produced by nonresonant light at intermediate intensities in atomic sodium vapor. The intensity dependence of the shifts departs substantially from the linear behavior predicted by 2nd order perturbation theory. The behavior is in good agreement with more exact calculations and yields a value of 0.10 for the 3P 3 2 −4D oscillator strength.

Experimental Study of Zeeman Light Shifts in Weak Magnetic Fields

According to the quantum theory of the optical-pumping cycle, one can describe the effect of a nonresonant light beam on the different Zeeman sublevels of an atomic ground state by an effective Hamiltonian ${\mathcal{H}}_{e}$ which depends on the polarization and spectral profile of the incident light. In order to check the structure of ${\mathcal{H}}_{e}$, we have performed a detailed experimental study of the ground-state energy sublevels of various kinds of atoms perturbed by different types of nonresonant light beams. Attention is paid to the modification of the Zeeman structure due to ${\mathcal{H}}_{e}$. We have been able to obtain experimentally in the ground state of $^{199}\mathrm{Hg}$, $^{201}\mathrm{Hg}$, and $^{87}\mathrm{Rb}$, Zeeman light shifts that are larger than the width of the levels due to the thermal relaxation. The removal of the Zeeman degeneracy in zero external field, due to a nonresonant light irradiation, is observed by different optical-pumping techniques; the full Zeeman diagram of the perturbed atoms is also determined when a static field ${\stackrel{\ensuremath{\rightarrow}}{\mathrm{H}}}_{0}$ is added. We have checked that the effect of ${\mathcal{H}}_{e}$ can be described in terms of fictitious static electric or magnetic fields. These fictitious fields can be used to act selectively on a given atomic level.