This paper is concerned with the history, properties, development, application, and prospects of soft X-ray (2 – 300 ) VLS spectrometers, i.e., spectrometers with reflection diffraction gratings whose spacing varies monotonically across the aperture according to a prescribed law (so-called Varied Line-Space (VLS) gratings). An important feature of grazing-incidence VLS spectrometers is that the spectrum is formed on a nearly flat surface perpendicular (or slightly inclined) to the diffracted beams, making them perfectly compatible with modern CCD detectors. VLS spectrometers are employed for the spectroscopy of laboratory and astrophysical plasmas, including the diagnostics of relativistic laser-produced plasmas, for measuring the linewidth of an X-ray laser, for recording the high-order harmonics of laser radiation, and for recording the emission of fast electric discharges and other laboratory X-ray sources. Instruments with VLS gratings are employed to advantage in reflectometry/metrology, X-ray fluorescence analysis, and microscopy with the use of synchrotron, free-electron laser, and laser-produced plasma radiation, as well as in SXR emission spectroscopy, combined with an electron microscope (SXES). Recent years have seen the active development of VLS spectrometers dedicated to the investigation of the electronic structure of different materials and molecules by resonant inelastic X-ray scattering (RIXS) spectroscopy with synchrotron radiation. Among recent trends is the development of VLS gratings with a multilayer reflective coating and extension of the operating spectral range towards ‘tender’ X-rays (ℏω ∼ 1.5 – 6 keV), some projects aiming to achieve a resolving power λ/δ λ ∼ 10⁵ in the region ℏω ∼ 1 keV.

本文关注的是软 X 射线 (2 – 300 ) VLS 光谱仪的历史、性质、发展、应用和前景，即具有反射衍射光栅的光谱仪，其间距根据规定的规律在孔径上单调变化（所以-称为变线距 (VLS) 光栅）。掠入射 VLS 光谱仪的一个重要特征是光谱形成在与衍射光束垂直（或略微倾斜）的近乎平坦的表面上，使其与现代 CCD 探测器完美兼容。VLS 光谱仪用于实验室和天体物理等离子体的光谱分析，包括相对论激光产生的等离子体的诊断，用于测量 X 射线激光器的线宽，用于记录激光辐射的高次谐波，以及记录快速放电和其他实验室 X 射线源的发射。带有 VLS 光栅的仪器在反射计/计量学、X 射线荧光分析和显微术中使用同步加速器、自由电子激光和激光产生的等离子体辐射，以及 SXR 发射光谱学，结合电子显微镜（SXES）。近年来，VLS 光谱仪的积极发展，致力于通过共振非弹性 X 射线散射 (RIXS) 光谱和同步辐射来研究不同材料和分子的电子结构。最近的趋势之一是开发具有多层反射涂层的 VLS 光栅，并将工作光谱范围扩展到“柔和”X 射线。ℏω ∼ 1.5 – 6 keV)，一些项目旨在在ℏω ∼ 1 keV区域内实现分辨率λ / δ λ ∼ 10 ⁵。