Glazov M M, Zapasskii V S
Opt Express. 2015 May 4;23(9):11713-23. doi: 10.1364/OE.23.011713.
Spin noise spectroscopy (SNS) is a new method for studying magnetic resonance and spin dynamics that has gained, in the last several years, a considerable popularity. The method is based on measuring magnetization noise of a paramagnet using the Faraday rotation technique. In strong contrast with methods of nonlinear optics, the spectroscopy of spin noise is considered to be essentially nonperturbative. At the same time, presently, it became clear that the SNS, as an optical technique, demonstrates abilities lying far beyond the bounds of conventional linear optics. Specifically, the SNS allows one to penetrate inside an inhomogeneously broadened absorption band and to determine its homogeneous width, to realize a sort of pump-probe spectroscopy without any optical nonlinearity, to probe a bulk inhomogeneous medium by focal point of a probe beam, etc. This may seem especially puzzling when taken into account that SNS can be considered just as a version of Raman spectroscopy, which is known to be deprived of such abilities. Understanding of these paradoxical features of SNS technique is required for the present-day applications of SNS and its further development. In this paper, we present a general analysis of this apparent inconsistency from the viewpoint of distinction between spectroscopy of the light intensity and of the light field and provide its resolution.
自旋噪声光谱学（SNS）是一种研究磁共振和自旋动力学的新方法，在过去几年中颇受关注。该方法基于利用法拉第旋转技术测量顺磁体的磁化噪声。与非线性光学方法形成强烈对比的是，自旋噪声光谱学被认为本质上是非微扰的。同时，目前已经清楚，作为一种光学技术，SNS展现出的能力远远超出了传统线性光学的范畴。具体而言，SNS能够深入到非均匀展宽的吸收带内部并确定其均匀宽度，能够在没有任何光学非线性的情况下实现一种泵浦 - 探测光谱学，能够通过探测光束的焦点探测体相非均匀介质等。考虑到SNS可以被视为拉曼光谱学的一种形式，而拉曼光谱学并不具备这些能力，这似乎尤其令人困惑。为了SNS在当今的应用及其进一步发展，需要理解SNS技术的这些矛盾特性。在本文中，我们从光强光谱学和光场光谱学的区别角度对这种明显的不一致进行了全面分析并给出了解决方案。
