Optical Bistability with Symmetry Breaking and Its Related Phenomena

本计画是关于一种新型的光学系统，其表现出光破缺分岔。我们提出了这种系统，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金属原子的自旋极化引起的光致法拉第效应。它可以通过光束的单次反馈来实现，而不像其他系统那样使用光学腔。系统的状态可以由原子自旋极化的取向或光在单元中的螺旋度来表征。实验上清楚地证明了自旋破缺分岔的存在，并预言了在外加横向磁场的情况下，系统可能发生连续自旋进动。尽管存在热弛豫，但自旋进动仍由光反馈维持。最近，进动被实验证实。旋进频率与磁场幅值成正比， 关于我们 理论所预期的。频率的上限（~ 10 MHz）被证明是由磁不均匀性的存在限制。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现象。其中的“对称性恢复危机”和“隐藏混沌”是在各种物理系统中普遍存在的现象，我们称之为“对称性恢复危机”和“隐藏混沌”。在无耦合的情况下，很容易看出系统表现出二次稳定性。我们发现，即使在其他情况下，它可以拥有四个稳定的状态，如果我们使用足够强的激光束。我们还可以进一步推广到N-束和二维系统，它们在未来的光学计算机中将起着迫切的作用，我们注意到，在我们提出的利用自旋极化实现光学双稳的建议的刺激下，国际上已经有几个研究组被提出，并取得了许多丰硕的成果。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