The quadrupole magnetostatic field (QMF), together with 3 pairs of laser beams, known as the magneto-optical trap, has been widely used for cooling and trapping atoms. This report concerns itself with some new phenomena observed in fluorescence emitted by Rb atoms in QMF under the circumstances of a single /spl sigma/ laser beam. A circularly polarized laser traveling-wave tuned to D/sub 2/-line is passed through a vacuum chamber along the central axis of two anti-Helmholtz coils. The fluorescence emitted by Rb atoms excited by the circularly polarized light in the direction at right angle to the direction of the incident laser beam is collected and imaged with all polarized directions taken into account. From the camera picture we can see that, around the zero-field point, there exists a dark region, the size of which is inversely proportional to the field gradient and is not sensitive to the detuning. The dark region corresponds to a dip in the profile of the fluorescence intensity versus the space. An attempt is made to explain the origin of this dark region.
Nonlinear magneto-optical resonances occurring for near-zero magnetic field are studied in Rb vapor using light-noise spectroscopy. With a balanced detection polarimeter, we observe high contrast variations of the noise power (at fixed analysis frequency) carried by diode laser light resonant with the $5{\mathrm{S}}_{1∕2}\phantom{\rule{0.2em}{0ex}}(F=2)\ensuremath{\rightarrow}5{\mathrm{P}}_{1∕2}\phantom{\rule{0.2em}{0ex}}(F=1)$ transition
87Rb and transmitted through a rubidium vapor cell as a function of magnetic field
B. A symmetric resonance doublet of anticorrelated noise is observed for orthogonal polarizations around
B=0 as a manifestation of ground-state coherence. We also observe sideband noise resonances when the magnetic field produces an atomic Larmor precession at a frequency corresponding to one-half of the analysis frequency. The resonances on the light fluctuations are the consequence of phase to amplitude noise conversion owing to nonlinear coherence effects in the response of the atomic medium to the fluctuating field. A theoretical model (derived from linearized Bloch equations) is presented that reproduces the main qualitative features of the experimental signals under simple assumptions.
We observe a narrow secondary dispersive feature nested within conventional nonlinear magneto-optical rotation (NMOR) signals obtained with a laser-cooled rubidium vapor. A similar feature has been previously named a "twist" by Budker et. al., in the context of warm vapor optical magnetometry [Phys. Rev. A. 81, 5788-5791 (1998)], and was ascribed to simultaneous optical pumping through multiple nearby hyperfine levels. In this work the twist is observed in a cold atom vapor, where the hyperfine levels are individually addressable, and thus is due to a different mechanism. We experimentally and numerically characterize this twist in terms of magnetic field strength, polarization, and optical intensity and find good agreement between our data and numerical models. We find that the twist width is proportional to the magnetic field in the transverse direction, and therefore two independent directions of the magnetic field can be measured simultaneously. This technique is useful as a simple and rapid in-situ method for nulling background magnetic fields.
We present a modified scheme for detection of the magneto-optical rotation (MOR) effect, where a linearly polarized laser field is interacting with cold
87Rb atoms in an integrating sphere. The rotation angle of the probe beam's polarization plane is detected in the experiment. The results indicate that the biased magnetic field, the probe light intensity and detuning, and the cold atoms' temperature are key parameters for the MOR effect. This scheme may improve the contrast of the rotation signal and provide an useful approach for high contrast cold atom clocks and magnetometers.
We report our study of the magneto-optical effect in a strictly linear regime on spin-polarized cold cesium atoms. Due to the low intensity and the short illumination period of the probe beam, less than 7.5% of the sample atoms change their states by absorbing probe photons. We produce a medium of atoms at rest in either the
6S1∕2,F=3,mF=0 or
6S1∕2,F=3,mF=3 state by optically pumping atoms trapped in a magneto-optical trap. We use the
D1 resonance with large lower and upper state hyperfine splittings as a probe transition to avoid hyperfine mixing from the Zeeman interaction. Under this idealized situation we measure the Stokes parameters in order to find the polarization rotation and circular dichroism experienced by the probe light. We find that there are qualitative differences between the results for the
mF=0 and
mF=3 cases. While dispersion and consequent Faraday rotation play a dominant role when the atoms are in the
mF=0 state, it is dissipation and circular dichroism that are important when they are in the
mF=3 state. Similarly, while the size of the Faraday rotation and the circular dichroism for the
mF=0 case scales linearly with the applied magnetic field, for the
mF=3 case it is the shift of the probe polarization change versus frequency that is linearly proportional to the magnetic field strength.