Development of X-ray ellipsometer and its application

椭偏法在可见光范围内得到了广泛的应用。然而，在x射线光谱范围内的椭偏仍然是前所未有的，因为直到最近才有高质量的偏振敏感光学器件。近年来，包括我们在内的几个研究小组已经研制出了用于x射线的偏振敏感光学元件（偏振器、分析仪和相位延迟器）。如果将这些光学元件小心地与高偏振同步辐射x射线结合使用，则x射线区域的椭偏性应该是可能的。在这项研究中，我们通过将我们开发的可旋转四象限金刚石缓相器系统（由四套金刚石薄晶体组成）和x射线偏振计（由x射线偏振器和x射线分析仪组成）相结合，开发了一种x射线椭偏仪。利用该装置，我们成功地建立了定义明确的x射线任意偏振态，并对透射样品的x射线的偏振态进行了高精度分析。然后，我们通过引入二维扫描（分析仪和偏振器的旋转）精确测量了任意对称晶体样品的圆双折射（CB）和圆二色性（CD）。通过高精度的偏振开关，我们成功地获得了具有单轴的Co(en)_3BrH_2O单晶非光轴的4个光学参数（双折射（LB）、线性二色性（LD）、圆双折射（CB）和圆二色性（CD））。该仪器将用于研究结构的各向异性和材料的电子态。

The method of ellipsometry in the visible-light range has been widely used in many applications. However, the ellipsometry in X-ray spectral range is still unprecedented because until recently the polarization-sensitive optics of good quality was not available. Recently, the polarization-sensitive optical elements (polarizer, analyzer and phase retarder) for X-rays have been developed by several groups including ours. If these optical elements are combined carefully for use with highly polarized synchrotron radiation X-rays, the ellipsometry for the X-ray region should be possible.In this study, we have developed an X-ray elipsometer by combining a rotatable four-quadrant diamond phase-retarder system (consisting of four sets of diamond thin crystals) which we developed and an X-ray polarimeter (consisting of an X-ray polarizer and an X-ray analyzer). With this apparatus, we have successfully created well-defined arbitrary polarization states of X-rays and analyzed the polarization states of X-rays which transmitted the sample with high precision. Then, we have measured circular birefringence (CB) and circular dichroism (CD) precisely for arbitrary symmetry of crystal samples by introducing two-dimensional scans (rotations of the analyzer and the polarizer). We have successfully obtained four optical parameters (birefringence (LB), linear dichroism (LD), circular birefringence (CB) and circular dichroism (CD)) of the non-optic axis of the Co(en)_3BrH_2O single crystal which has a uni-axis by applying a high-precision polarization switching.This apparatus will be applied to studies of anisotropy of structures and electronic state of materials.