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Polarization switching with sodium vapour

M. W. Hamilton, Weston J. Sandle

Published Jan 1, 1984• 0 citations
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Abstract

Results are given of an experiment which demonstrates switching of the polarization state of the output of a near-concentric Fabry-Perot containing sodium vapour, excited via the homogeneously broadened Dl transition. An example of the output, for linearly polarized laser input, at 1.5 GHz below line center shows switching with hysteresis at high input power (approximately 400 mW) due to saturation, as well as the switching at lower power (approximately mW) due to optical pumping effects. Purely absorptive polarization switching at approximately 50 mW input power was observed. Polarization switching has been predicted in the context of three state atoms in an optical cavity, and the lower power switchin has been previously observed using the inhomogeneously broadened Dl transition of sodium in a Fabry-Perot with the laser detuned above line center. By using argon buffer gas at up to 100 torr, importance of hyperfine structure and inhomogeneous broadening was reduced so as to make the transition approximate a J + 1/2 to J - 1/2 transition.

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Optical pumping-induced spatio-temporal modifications to propagation, polarization and intensity of laser beams in sodium vapour

R. Holzner, S. Dangel

Circularly polarized laser beams propagating through sodium vapour and tuned to the buffer-gas-broadened atomic transition can optically pump sodium atoms into a non-absorbing ground state. This causes an intensity-dependent refractive index gradient along as well as transverse to the laser beam propagation direction, giving rise to a number of nonlinear spatio-temporal intensity and polarization pattern creating processes. In the case of a single circularly polarized laser beam we have observed self-focusing and defocusing, the transformation of the incident Gaussian beam intensity profiles into ring profiles, a large shift of about 5 GHz of the maximum of the absorption profile when suitable magnetic fields are applied and the deflection of a beam by the inhomogeneous transverse magnetic field of a current-carrying wire. When two beams of opposite circular polarization are superimposed, astonishing effects such as the mutual deflection of both beams (beam bouncing), the mutual extinction of both beams (beam switching), the separation of initially overlapping beams (beam splitting) and the mutual attraction of both beams (beam attraction) can be observed. While most of the effects can be well described for the stationary state by a to atomic transition model, the correct description of the dynamics requires the consideration of all hyperfine states.

Quantum and Semiclassical Optics Journal of the European Optical Society Part B•Feb 1, 1998•5 citations
Results are given of an experiment which demonstrates switching of the polarization state of the output of a near-concentric Fabry-Perot containing sodium vapour, excited via the homogeneously broadened Dl transition. An example of the output, for linearly polarized laser input, at 1.5 GHz below line center shows switching with hysteresis at high input power (approximately 400 mW) due to saturation, as well as the switching at lower power (approximately mW) due to optical pumping effects. Purely absorptive polarization switching at approximately 50 mW input power was observed. Polarization switching has been predicted in the context of three state atoms in an optical cavity, and the lower power switchin has been previously observed using the inhomogeneously broadened Dl transition of sodium in a Fabry-Perot with the laser detuned above line center. By using argon buffer gas at up to 100 torr, importance of hyperfine structure and inhomogeneous broadening was reduced so as to make the transition approximate a J + 1/2 to J - 1/2 transition.
Experimental investigations of optical bistability (OB) for systems with degenerate lower states have up to now relied principally on atomic sodium [1-4]. The study of the influence of lower level coherence effects in OB [5] is greatly aided by the use of a nonlinear medium having a transition with integral electronic angular momentum character. A suitable choice upon which we report here is the 4f6 6s2 (7F1) to 4f6 6s6p (7Foo) 570.68-nm transition in SmI, driven by linearly polarized laser excitation in a near-concentric Fabry-Perot cavity. Unlike the case of the Na J = 1/2 to J = 1/2 D1 transition, for which polarization asymmetry in switching (PS) develops spontaneously [1-4], for the above transition we find that the symmetry in the polarization is conserved. No polarization differences of σ+ with respect to σ− develop in the output from the optical cavity. This behaviour accords with the theoretical expectation [6] that PS is suppressed by transverse optical pumping.
The interaction of left- and right-hand circularly polarized narrow-band cw laser beams that copropagate through sodium vapor and are tuned to the homogeneously broadened D1 transition can lead to the mutual extinction of both beams. Such beam switching is caused by an intensity- and polarization-dependent refractive index due to optical pumping even at low intensities. The dynamics of beam switching is investigated experimentally and explained qualitatively by the conventional J = 1/2 to J = 1/2 transition model. The accurate quantitative description, however, is only achieved by an extended model comprising hyperfine ground states in spite of homogeneous line broadening by argon buffer gas, which is larger than the hyperfine splitting.
Experiments on the steady-state, nonlinear behavior of the 7F1^{7}\mathrm{F}_{1}7F1​${\mathrm{\ensuremath{-}}}^{7}$F0o{\mathrm{F}}_{0}^{\mathrm{o}}F0o​ 570.68-nm transition of atomic samarium in a laser-driven, near-concentric Fabry-Perot cavity are reported. For zero applied magnetic field, only simple optical bistability, symmetric in both ${\ensuremath{\sigma}}^{+}$ and ${\ensuremath{\sigma}}^{\mathrm{\ensuremath{-}}}$ transmitted polarizations, is observed for a linearly polarized excitation beam. However, for a magnetic field applied parallel to the propagation direction, polarization-sensitive switching appears, with lowest power threshold near the edge of the Doppler-broadened region. Subsidiary measurements of atomic parameters are also given to enable the transition to be experimentally well characterized.
We report on the observation of critical slowing down and of self-pulsing in a Fabry-Perot resonator (FP) filled with sodium atoms under conditions of transverse optical pumping /1/. The experimental set-up (see Fig.1) is similar to the one used in steady-state bistability studies reported before /2/. The dye laser, optically isolated from the FP by means of a Faraday rotator (FR) is detuned from the Na D1-line by 10 to 20 GHz. The sodium sample (N ≃ 1013 cm–3, buffer gas: argon, p=200 mbar) is placed in a near confocal Fabry-Perot (Beam waist: 1 20 μm) and can be subjected to a transverse magnetic field B. The intensity of the laser beam can be switched by means of an electro-optic modulator(EOM), thus providing input-steps of variable height (power:5 – 50 mW). A polarizer P1 is used to either circularly or linearly polarize the input beam. The right– and left circular polarization components of the resonator output beam can be separated by means of a λ/4-plate and a polarizing beam splitter P2. A pair of photodiodes PDi is used for detection.
Circularly polarized laser beams propagating through sodium vapour and tuned to the buffer-gas-broadened atomic transition can optically pump sodium atoms into a non-absorbing ground state. This causes an intensity-dependent refractive index gradient along as well as transverse to the laser beam propagation direction, giving rise to a number of nonlinear spatio-temporal intensity and polarization pattern creating processes. In the case of a single circularly polarized laser beam we have observed self-focusing and defocusing, the transformation of the incident Gaussian beam intensity profiles into ring profiles, a large shift of about 5 GHz of the maximum of the absorption profile when suitable magnetic fields are applied and the deflection of a beam by the inhomogeneous transverse magnetic field of a current-carrying wire. When two beams of opposite circular polarization are superimposed, astonishing effects such as the mutual deflection of both beams (beam bouncing), the mutual extinction of both beams (beam switching), the separation of initially overlapping beams (beam splitting) and the mutual attraction of both beams (beam attraction) can be observed. While most of the effects can be well described for the stationary state by a to atomic transition model, the correct description of the dynamics requires the consideration of all hyperfine states.