Optical crystals are transparent in different spectral regions, depending upon the crystal material.

Panels and panel materials are composite structures which consist of multiple layers or skins often bonded to or sandwiching a core material such as multilayer sheets, cored laminates or industrial structural panels.

X-ray fluorescence spectrometers (XRFs) use a spectroscopic technique that is commonly used with solids, in which X-rays are used to excite a sample and generate secondary X-rays.