X-ray and ultraviolet (UV) observations of the outer solar atmosphere have been used for many decades to measure the fundamental parameters of the solar plasma. This review focuses on the optically thin emission from the solar atmosphere, mostly found at UV and X-ray (XUV) wavelengths, and discusses some of the diagnostic methods that have been used to measure electron densities, electron temperatures, differential emission measure (DEM), and relative chemical abundances. We mainly focus on methods and results obtained from high-resolution spectroscopy, rather than broad-band imaging. However, we note that the best results are often obtained by combining imaging and spectroscopic observations. We also mainly focus the review on measurements of electron densities and temperatures obtained from single ion diagnostics, to avoid issues related to the ionisation state of the plasma. We start the review with a short historical introduction on the main XUV high-resolution spectrometers, then review the basics of optically thin emission and the main processes that affect the formation of a spectral line. We mainly discuss plasma in equilibrium, but briefly mention non-equilibrium ionisation and non-thermal electron distributions. We also summarise the status of atomic data, which are an essential part of the diagnostic process. We then review the methods used to measure electron densities, electron temperatures, the DEM, and relative chemical abundances, and the results obtained for the lower solar atmosphere (within a fraction of the solar radii), for coronal holes, the quiet Sun, active regions and flares.

几十年来，人们一直使用太阳外层大气的 X 射线和紫外线 (UV) 观测来测量太阳等离子体的基本参数。本综述重点关注太阳大气层的光学薄发射，主要发现于紫外线和 X 射线 (XUV) 波长，并讨论了一些用于测量电子密度、电子温度、差分发射测量 (DEM) 的诊断方法。 ）和相对化学丰度。我们主要关注从高分辨率光谱获得的方法和结果，而不是宽带成像。然而，我们注意到最好的结果通常是通过结合成像和光谱观察来获得的。我们还主要关注从单离子诊断获得的电子密度和温度的测量，以避免与等离子体电离状态相关的问题。我们首先对主要的 XUV 高分辨率光谱仪进行简短的历史介绍，然后回顾光学薄发射的基础知识以及影响谱线形成的主要过程。我们主要讨论平衡等离子体，但简要提及非平衡电离和非热电子分布。我们还总结了原子数据的状态，这是诊断过程的重要组成部分。然后，我们回顾了用于测量电子密度、电子温度、DEM 和相对化学丰度的方法，以及针对低层太阳大气（在太阳半径的一小部分内）、日冕洞、安静的太阳、活跃的太阳所获得的结果。区域和耀斑。