Optical Bistability with Symmetry Breaking and Its Related Phenomena

这个项目是关于一种新型的光学双稳系统，它表现出对称破缺的分叉。我们提出了该系统，并对其静态和动态行为进行了理论和实验研究。这种双稳态是基于碱原子中的自旋极化引起的光致法拉第效应。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取向或细胞中的光的螺旋度来表征。实验清楚地证明了对称性破缺分叉的存在。我们还预言了当施加横向磁场时，连续自旋进动是可能的。尽管存在热弛豫，但自旋进动仍由光学反馈来维持。最近，这种进动得到了实验证实。进动频率与磁场幅值成正比，如ex…更多的是被理论所期待的。结果表明，频率的上限(-10 MHz)受到磁性不均匀性的限制。我们还研究了该系统中可以看到的混沌行为。通过数值计算，我们发现了许多有趣的奇怪吸引子和分支。其中“对称性恢复危机”和“隐藏混沌”是各种物理系统中普遍存在的现象。作为我们的系统的推广，我们分析了一个两束系统，其中两部分通过原子扩散耦合。在无耦合的情况下，很容易看到系统表现出四次稳定性。我们发现，即使在其他情况下，如果我们使用足够强的激光，它也可以拥有四个稳定状态。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迫不及待的作用。我们注意到，在我们提出的利用自旋极化来实现光学双稳的激励下，世界上已经有几个小组被提出并取得了许多丰硕的成果。较少

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