关于旋光性的一个启发式观点
On a heuristic point of view concerning the optical activity
摘要：
最近的一个发现，菲涅尔的光学活动的手征介质中的唯象描述是不自洽的，我们进行了深入的调查的性质的偏振的平面光波。我们证明了光的偏振是其量子力学性质之一的反映，称为准自旋。出乎意料的是，准自旋在实验室坐标系中是不可观测的。相反，它是相对于动量相关的局部坐标系。准自旋的代表性算子是泡利矩阵。波函数就是琼斯矢量。为了完全确定偏振状态，需要两种不同的自由度。一个是表征准自旋态的自由度。它们是斯托克斯参数，即在琼斯矢量所描述的状态下泡利矩阵的期望值。另一个是指定局部坐标系的自由度，包括传播方向和绕其旋转的角度。因此，存在两个独立的机制来改变偏振态。一种是在固定的局域坐标系中改变准自旋的状态。这是传统的机制，可以表示为琼斯矢量的SU（2）旋转。另一种方法是改变局域坐标系，使准自旋态保持不变，最后我们证明了这是新发现的解释旋光性的机制。
英文摘要：
Motivated by a recent finding that Fresnel's phenomenological description of the optical activity in the chiral medium is not self-consistent, we conduct a thorough investigation into the nature of the polarization of a plane light wave. We demonstrate that the polarization of light is the reflection of one of its quantum-mechanical properties, called the quasi-spin. Unexpectedly, the quasi-spin is not an observable with respect to the laboratory coordinate system. Instead, it is with respect to the momentum-dependent local coordinate system. The representative operators for the quasi-spin are the Pauli matrices. The wavefunction is the Jones vector. In order to completely determine a state of polarization, two different kinds of degrees of freedom are needed. One is the degrees of freedom to characterize the state of quasi-spin. They are the Stokes parameters, the expectation values of the Pauli matrices in the state described by the Jones vector. The other is the degrees of freedom to specify the local coordinate system, including the propagation direction and an angle of rotation about it. Accordingly, there are two independent mechanisms to change the state of polarization. One is to change the state of quasi-spin in a fixed local coordinate system. This is the traditional mechanism that can be expressed as an SU(2) rotation of the Jones vector. The other is to change the local coordinate system with the state of quasi-spin remaining fixed in it. At last, we show that it is the newly-identified mechanism that accounts for the optical activity.
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