Optical Bistability with Symmetry Breaking and Its Related Phenomena

本课题研究的是一种具有对称破缺分岔的新型光学双稳系统。提出了该系统，并对其静态和动态特性进行了理论和实验研究。双稳性是基于碱原子自旋极化引起的光诱导法拉第效应。它可以通过光束的单一反馈来实现，而不像其他系统那样使用光学腔。系统的状态可以通过原子自旋极化的方向或细胞内光的螺旋度来表征。实验清楚地证明了对称破缺分岔的存在。我们还预测，当我们施加横向磁场时，可以实现连续的自旋进动。尽管存在热弛豫，但自旋进动仍由光反馈维持。最近，进动在实验上得到了证实。进动频率与磁场幅值成正比，这是理论所期望的。频率的上限（-10MHz）被证明受到磁不均匀性存在的限制。没有这一点，更快速的振荡是可能的。我们还研究了该系统的混沌行为。通过数值计算，我们发现了许多有趣的奇异吸引子和分岔。其中我们命名的“对称恢复危机”和“隐藏混沌”，被发现是各种物理系统中普遍存在的现象。作为我们系统的扩展，我们分析了一个双光束系统，其中两个部分通过原子扩散耦合。在不耦合的情况下，很容易看出系统表现出正交稳定性。我们发现，即使在其他情况下，如果我们使用足够强的激光束，它也可以拥有四种稳定状态。我们可以进一步将分析扩展到n束和二维系统，这将在未来的光学计算机中发挥重要作用。我们注意到，在我们提出的利用自旋极化实现光学双稳的启发下，世界上已经有几个小组研究出来，并取得了许多卓有成效的成果。少

This project was on a new type of optically bistable system which exhibits symmetry-breaking bifurcations. We proposed this system and studied theoretically and experimentally on its static and dynamical behavior. The bistability is based on the optically induced Faraday effect due to the spin polarization in alkali atoms. It can be achieved by a single feedback of the light beam without the use of an optical cavity unlike other systems. The states of the system can be characterized by the orientation of atomic spin polarization or by the helicity of the light in the cell. The symmetry-breaking bifurcation was clearly demonstrated experimentally.We also predicted that continuous spin precession can be possible when we apply a transverse magnetic field to the system. The spin precession is sustained by the optical feedback despite the thermal relaxation. Recently, the precession was confirmed experimentally. The precession frequency was proportional to the magnetic field amplitude as ex … More pected by the theory. The upper limit of the frequency (-10MHz) turned out to be limited by the presence of magnetic inhomogeneity. Without this, more rapid oscillation can be possible.We also studied on chaotic behavior which can be seen in this system. With use of numerical calcurations, we found many interesting strange attractors and bifurcations. Among them "symmetry recovering crises" and "hidden chaos", which we named, was found to be universal phenomena seen in various physical systems.As an extension of our system, we analysed a two-beam system, where the two parts are coupled through the atomic diffusion. In the no-coupling case, it is easy to see that the system shows quadrastability. We found that, even in other cases, it can possess four stable states, if we use laser beams intense enough. We can further extend the analysis to N-beam and two-dimensional systems, which will play an impatient role in optical computers in future.We note that stimulated by our proposal to utilize spin polarization for optical bistability, several groups in the world have been worked out and obtained many fruitful results. Less