X-ray absorption spectroscopy, also known as X-ray absorption fine structure spectroscopy, is a spectral technique to analyze the elemental composition and electronic state of materials by using the signal changes before and after the incident of synchrotron radiation X-ray.

X-ray absorption spectroscopy experiments mainly use transmission method, fluorescence method and full electron yield method.  Tansmission method is the earliest and most used experimental method.

The experimental principle of the transmission method is shown in the figure. After passing through the twin monochromator, the incident X-ray becomes monochromatic light with adjustable wavelength. The transmission method is usually used for samples with a mass percentage of the element to be measured greater than 5%.