In this paper we report on the effects of recoil on the steady state response of a three level atomic system in two photon absorption. The strength of the fields and their respective frequencies are arbitrary. The expression we derive reduces to that derived earlier, when recoil is neglected. From numerical calculations we conclude that the inclusion of recoil introduces shifts and asymmetries in the response vs. the detuning. We found how the magnitude of the shift depends on the ratio of the probe frequency to the pumping frequency.
In a previous paper, I have presented a general theory of the optical pumping of atoms by a polarized multimode-laser beam, in the presence of a magnetic field. Equations of motion, valid at arbitrary laser intensities for the density matrix of the atomic system, have been obtained. In this paper, these equations are exactly solved for a linearly $\ensuremath{\sigma}$-polarized laser and levels having small angular momenta. More precisely, I consider the laser transitions ${J}_{b}=1\ensuremath{\rightarrow}{J}_{a}=0$, ${J}_{b}=1\ensuremath{\rightarrow}{J}_{a}=1$, and ${J}_{b}=1\ensuremath{\rightarrow}{J}_{a}=2$. Two particular results are emphasized: (i) For $J=1\ensuremath{-}J=0$ and $J=1\ensuremath{-}J=1$ transitions and for the
J=2 level of a $J=1\ensuremath{-}J=2$ transition, the laser-induced Hanle effects keep a Lorentzian shape, independent of the laser intensity. For the $J=1\ensuremath{-}J=1$ transition, it is shown that the depolarizing relaxation processes play a leading part in the coupling induced by the laser between the transverse alignments of the two levels. On the other hand, the power broadenings of the Hanle effects are shown to be similar. For the
J=1 level of a $J=1\ensuremath{-}J=2$ transition, the Hanle-effect shape presents a departure from the Lorentzian one, owing to a coupling with the laser-induced hexadecapole moment in the
J=2 level. (ii) The populations of the levels exhibit a "zero-field saturation resonance" which is due to the coupling with the Zeeman coherences. These resonances, which reproduce the Hanle effects of the transition, can be observed on the $\ensuremath{\pi}$-polarized fluorescence from the levels. In general, these resonances appear as a saturation effect, i.e., they reduce the laser-induced fluorescence of the levels in zero magnetic field. However, for the ${J}_{b}=1\ensuremath{\rightarrow}{J}_{a}=2$ transition, the ${J}_{a}=2\ensuremath{\rightarrow}{J}_{f}=2 \ensuremath{\pi}$ fluorescence presents an anomalous behavior; the saturation resonance increases the zero-field laser-induced fluorescence. The theoretical study shows the prominent part played by the value of the
Jb=1 level lifetime in the interpretation of this anomaly. Other results, such as the laser-induced depolarization of the fluorescence, are also obtained. All the theoretical predictions have been experimentally checked and will be presented in forthcoming papers.
Summary form only given. Recent advances in laser cooling and trapping have led to a growing interest in laser spectroscopy in cold atomic samples. Examples include the work of Guo et al. and Courtois et al. about the recoil-induced resonance, and Bonifacio et al. and Moore et al. about the collective-atomic-recoil lasers (CARL). At the heart of these applications is the atomic recoil by photon absorption and emission. In the work, we explore a recoil-related phenomenon: hole burning resulting from the momentum redistribution of atoms by spontaneous emission, and its possible application in the precision spectroscopy. In the traditional saturation spectroscopy, the hole in the Doppler profile is created by laser excitation of atoms from the ground to the excited level. By contrast, the hole, is produced by removing the atoms in the velocity group, where the hole is burned, into the neighboring velocity groups of the same ground level. This process is accomplished through optical pumping and momentum redistribution by spontaneous emission. As a result, the requirement on the intensities of the driving laser fields is low, limited only by the interaction time. This is in contrast to the traditional saturation spectroscopy where the driving laser intensity has to be comparable to the saturation intensity determined by the decay rate of the excited level.
The effect of collectivity on the loading of an atom laser via optical pumping is discussed. In our model, atoms in a beam are laser-excited and subsequently spontaneously decay into a trapping state. We consider the case of sufficiently high particle density in the beam such that the spontaneous emission is modified by the particle interaction. We show that the collective effects lead to a better population of the trapping state over a wide range of system parameters, and that the second-order correlation function of the atoms can be controlled by the applied laser field.
We present a wave atom optics theory of the Collective Atomic-Recoil Laser, where the atomic center-of-mass motion is treated quantum mechanically. It extends the previous ray atom optics theory, which treated the center-of-mass atomic motion classically, to the realm of ultracold atoms. For the case of a far off resonant pump laser we derive an analytical solution which gives the linear response of the CARL system for both the quantum and classical regimes. A linear stability analysis reveals significant qualitative differences between these two regimes, which arise from the effects of diffraction on the atomic center-of-mass motion.
The optical pumping of atoms by a multimode gas laser, in the presence of a magnetic field, is studied theoretically. The atoms are described by their density matrix, which is expanded on an irreducible tensorial set. The atomic relaxation is assumed to be isotropic. In order to avoid the usual perturbation theory, we use the so-called "Broad-Line approximation" (BLA). BLA is valid when the width of the "Bennett hole" created by one laser mode in the velocity distribution of the excited atoms is comparable to the spacing between modes; under these conditions, the atomic response does not depend on the velocity and the multimode laser irradiation is equivalent to a broad-line excitation. For the atomic system, BLA leads to a set of coupled equations which is valid at arbitrary intensities of the laser field and which depends on this field through a unique parameter, $\ensuremath{\gamma}$. This parameter can be understood as a laser-induced transition probability. In this article, we analyze the nonlinear effects which can be deduced from this theory, for any value of the angular momenta involved in the laser transition: Hanle-effect broadening, alignment coupling, saturation resonances on the populations are shown. The exact calculations, valid at arbitrary laser intensities for $J=1\ensuremath{\leftrightarrow}J=0$, $J=1\ensuremath{\leftrightarrow}J=1$, and $J=1\ensuremath{\leftrightarrow}J=2$ transitions, and the corresponding experimental results will be presented in forthcoming papers.