Precision X-ray diffraction system incorporating a laser aligner

A method by which the angle between an atomic plane of a crystal plate and the face of the crystal plate can be determined by means of a goniometer instrument including an X-ray detector arranged to receive that portion of an incident X-ray beam reflected from said crystal plate, said crystal plate being mounted for independent rotation about three mutually perpendicular axes, a first axis being normal to the instrument plane defined by said X-ray beam and the center of said X-ray detector, a second axis being normal to the crystal plate face, and a third axis perpendicular to said first and second axes, comprising the steps of:

• a. directing a collimated optical beam onto the crystal plate face for reflection therefrom onto a position sensing photodetector;
• b. sequentially and controllably adjusting the rotation of said crystal plate about said first and second axes to discrete controlled positions at each of which a peak reading of the X-ray detector is obtained;
• and
• c. adjusting the rotation of said crystal plate about said first and third axes after each of the adjustments about said second axis to obtain a null reading of said photodetector indicating correction of any wobble of said second axis introduced during step (b).