Abstract: An X-ray window of an X-ray diffractometer diffraction chamber is provided. The X-ray window can include: a plurality of unidirectional carbon fiber sheets stacked one over another, wherein carbon fibers in adjacent carbon fiber sheets are disposed at an angle relative to one another; and a binding material that binds the plurality of unidirectional carbon fiber sheets together, the binding material being at least partially transparent to X-ray radiation. The X-ray window can also or alternatively include: at least one carbon fiber sheet, the X-ray window having a carbon fiber content of at least 50 wt % and a thickness between about 0.2 mm and about 5 mm to be adapted for use at a pressure greater than atmospheric pressure.