The structure of biological molecules is determined most commonly by use of x-ray diffraction. why use x-rays instead of more readily available (and brighter! ) light, like lasers

The use of X-ray crystallography permits the viewing of the biological molecules in its 3-D structure since the diffracting rays from the crystal will form the diffraction pattern on the periodic film, therefore allowing the further study of the structure.On the other hand, the use of lasers allows for the viewing of the biological processes as the sample is tagged with the fluorescing substance called fluorophore which illuminates upon exposure to light of shorter wavelength hence facilitating visibility and also in obtaining high resolution images.