An experiment on nonlinear laser spectroscopy and magneto-optics at the Advanced Undergraduate Laboratory at Berkeley is described. The experiment consists of three parts. In the first part, students learn to operate a diode laser system and characterize its performance using a Fabry–Perot spectrum analyzer. In the second part, Doppler-broadened laser-induced fluorescence and Doppler-free saturated absorption spectra of the rubidium D2 line (780 nm) are recorded and analyzed. Finally, in the third part of the experiment, which we describe in greater detail, the near-resonant magneto-optical rotation is investigated. Nonlinear light-atom interaction leads to spectacular manifestations of the resonant Faraday effect—polarization plane rotation in a magnetic field applied along the direction of light propagation radically different from the linear case. In particular, narrow (∼30 Hz) effective line widths are observed in this experiment corresponding to a rotation enhancement by some seven orders of magnitude compared to the linear Faraday rotation.
We theoretically investigate magneto-optical rotation (MOR) of a linearly polarized probe field in the four-level N-type cold atoms. By applying a static magnetic field and a weak coupling field, it is shown that the birefringence enhancement is induced in the system. Moreover, we show that the static magnetic field has a major role in switching the dichroism to enhanced birefringence in the system. We also obtain a large intensity for the output field with nearly perpendicular MOR angle by 88 degrees with subnatural width. It is demonstrated that Doppler broadening has a destructive effect on the MOR of the polarization direction of the probe field. The results of our study can be used for selecting narrow band of wavelengths and polarization converter for efficient switching of TM/TE polarization modes in optical communication, the depolarization backscattering lidar, polarization spectroscopy and precision measurements.
Nonlinear magneto-optical resonances on the hyperfine transitions belonging to the
D2 line of rubidium were changed from bright to dark resonances by changing the laser power density of the single exciting laser field or by changing the vapor temperature in the cell. In one set of experiments atoms were excited by linearly polarized light from an extended cavity diode laser with polarization vector perpendicular to the light's propagation direction and magnetic field, and laser-induced fluorescence was observed along the direction of the magnetic field, which was scanned. A low-contrast bright resonance was observed at low laser power densities when the laser was tuned to the ${F}_{g}=2\ensuremath{\rightarrow}{F}_{e}=3$ transition of
87Rb and near to the ${F}_{g}=3\ensuremath{\rightarrow}{F}_{e}=4$ transition of
85Rb. The bright resonance became dark as the laser power density was increased above 0.6 mW/cm
2 or 0.8 mW/cm
2, respectively. When the ${F}_{g}=2\ensuremath{\rightarrow}{F}_{e}=3$ transition of
87Rb was excited with circularly polarized light in a second set of experiments, a bright resonance was observed, which became dark when the temperature was increased to around 50${}^{\phantom{\rule{0.16em}{0ex}}\ensuremath{\circ}}$C. The experimental observations at room temperature could be reproduced with good agreement by calculations based on a theoretical model, although the theoretical model was not able to describe measurements at elevated temperatures, where reabsorption was thought to play a decisive role. The model was derived from the optical Bloch equations and included all nearby hyperfine components, averaging over the Doppler profile, mixing of magnetic sublevels in the external magnetic field, and a treatment of the coherence properties of the exciting radiation field.
Zeeman splitting in the D 2 line of rubidium atoms ( 87 Rb and 85 Rb) has been studied using 'Doppler broadened' as well as 'saturation absorption spectroscopy'. While a linearly polarized beam was used for the former experiment, in the latter case a (π, σ ± ) polarization configuration was employed for both pump and probe beams. Zeeman lines have been observed by applying a field up to 5 mT. The field variation of relative line intensities in Doppler-broadened spectrum was determined following Tremblay et al and Nakayama's four-level model. For the saturation spectrum, a four-level model was used. Because the enhancement of absorption at the field is as low as 1 mT, the F g = 2 to F e = 3 transition for 87 Rb can be used as the reference for laser locking. Level crossing is observed in 85 Rb at fields less than 5 mT.
We examine the magneto-optical and image state rotation (MOR) of left and right circularly plane-polarized light pulse through a double Λ-type four-level configuration of Rubidium atom via Kerr field and Doppler broadening in the presence of the static magnetic field. The medium’s behavior is different for both orthogonal components of the probe beam, causing linear dichroism or circular birefringence. Enhanced and lossless MOR is obtained by applying the control field through a closed-loop birefringent system. We observe a magnified angle of rotation of probe field in Doppler broadened medium. It is shown that due to the Kerr nonlinearity, the rotation angle of the probe beam is generated and modified through cold and Doppler broadened medium. Moreover, almost complete polarization rotation is observed for a particular set of parameters. The MOR can be effectively utilized in designing new TM/TE polarization modes, optical communication, polarization spectroscopy, lider with backscattering depolarization, precision measurements, and magnetometry.
We present experimental and numerical studies of nonlinear magneto-optical rotation (NMOR) in rubidium vapor excited with resonant light tuned to the
52S1/2→62P1/2 absorption line (421~nm). Contrary to the experiments performed to date on the strong
D1 or
D2 lines, in this case, the spontaneous decay of the excited state
62P1/2 may occur via multiple intermediate states, affecting the dynamics, magnitude and other characteristics of NMOR. Comparing the experimental results with the results of modelling based on Auzinsh et al., Phys. Rev. A 80, 1 (2009), we demonstrate that despite the complexity of the structure, NMOR can be adequately described with a model, where only a single excited-state relaxation rate is used.