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Physical Review Letters

Light Polarization of a Quasi-isotropic Laser with Optical Feedback

Guy Michel Stéphan, D. Hugon

Published Aug 12, 1985• 41 citations
Publisher

Abstract

The light of a quasi-isotropic, single-mode gas laser is linearly polarized for a line ${J}_{a}=1\ensuremath{\rightarrow}{J}_{b}=2$. However, the azimuth of polarization can vary inside the line. Among the many different effects which cause these variations, we describe the role played by the detector optical feedback. We show experimentally that its amplitude and phase can be varied in a controlled manner in order to obtain abrupt switches between two perpendicular polarization states. Polarization bistability and hysteresis effects can then be commanded and studied from the outside of the laser.

DOI
10.1103/physrevlett.55.703

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The light of a quasi-isotropic, single-mode gas laser is linearly polarized for a line Ja=1\ensuremath→Jb=2{J}_{a}=1\ensuremath{\rightarrow}{J}_{b}=2Ja​=1\ensuremath→Jb​=2. However, the azimuth of polarization can vary inside the line. Among the many different effects which cause these variations, we describe the role played by the detector optical feedback. We show experimentally that its amplitude and phase can be varied in a controlled manner in order to obtain abrupt switches between two perpendicular polarization states. Polarization bistability and hysteresis effects can then be commanded and studied from the outside of the laser.
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A quasi-isotropic CO2{\text{CO}}_{2}CO2​ laser near the resonant condition can present bistability in the polarization state, with spontaneous flips between two orthogonal linear polarization eigenmodes. In this work, we explore the role of the pump and noise on the polarization dynamics, showing a transition from stable to bistable states and the presence of coherent resonance.
We have studied microscopic effects leading to mode competition in an inhomogeneously broadened medium of a gas laser with a weakly anisotropic cavity. The polarization bistability observed in some lasers, which is believed to be caused by hole burning, we attribute to microscopic coherent effects induced by two light fields. Due to these effects one field can be coupled with another. Hole burning is found to be important, but not crucial. The exact solution of the equation of motion for field amplitudes is compared with the third order approximation of perturbation theory. The role of four wave mixing, important for bistability of axial modes in a homogeneously broadened medium, is discussed.
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