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APPLICATIONS

X-ray

Because they are much higher in frequency and energy levels, x rays are even shorter in wavelength than

visible light waves. Hence, for x-ray diffraction, it is necessary to have gratings in which lines are separated by

infinitesimal distances. These distances are typically measured in units called an angstrom, of which there are 10

million to a millimeter. Angstroms are used in measuring atoms, and, indeed, the spaces between lines in an x-ray

diffraction grating are comparable to the size of atoms.

When x rays irradiate a crystalin other words, when the crystal absorbs radiation in the form of x rays

atoms in the crystal diffract the rays. One of the characteristics of a crystal is that its atoms are equally spaced, and,

because of this, it is possible to discover the location and distance between atoms by studying x-ray diffraction

patterns. Bragg's lawnamed after the father-andson team of English physicists William Henry Bragg (1862-1942)

and William Lawrence Bragg (1890-1971)describes x-ray diffraction patterns in crystals.

Though much about x-ray diffraction and crystallography seems rather abstract, its application in areas such

as DNA research indicates that it has numerous applications for improving human life. The elder Bragg expressed

this fact in 1915, the year he and his son received the Nobel Prize in physics, saying that "We are now able to look

ten thousand times deeper into the structure of the matter that makes up our universe than when we had to depend on

the microscope alone." Today, physicists applying x-ray diffraction use an instrument called a diffractometer, which

helps them compare diffraction patterns with those of known crystals, as a means of determining the structure of

new materials.

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HOLOGRAMS

A holograma word derived from the Greek holos, "whole," andgram, "message"isa three-dimensional (3-D) impression of an object, and the method of producing these images is

known as holography. Holograms make use of laser beams that mix at an angle, producing an

interference pattern of alternating bright and dark lines. The surface of the hologram itself is asort of diffraction grating, with alternating strips of clear and opaque material. By mixing a laser

beam and the unfocused diffraction pattern of an object, an image can be recorded. An

illuminating laser beam is diffracted at specific angles, in accordance with Bragg's law, on the

surfaces of the hologram, making it possible for an observer to see a three-dimensional image.

Holograms are not to be confused with ordinary three-dimensional images that use only

visible light. The latter are produced by a method known as stereoscopy, which creates a singleimage from two, superimposing the images to create the impression of a picture with depth.

Though stereoscopic images make it seem as though one can "step into" the picture, a hologram

actually enables the viewer to glimpse the image from any angle. Thus, stereoscopic images canbe compared to looking through the plate-glass window of a store display, whereas holograms

convey the sensation that one has actually stepped into the store window itself.

SOURCES:

http://www.scienceclarified.com/everyday/Real-Life-Physics-Vol-2/Diffraction-Real-life-applications.html

http://www.icdd.com/resources/axa/vol47/v47_02.pdf