An interference pattern is created that is very similar to the one formed by double-slit diffraction (see Figure 17.8 and Figure 17.9). Such an arrangement of slits is called a diffraction grating.
No, a laser would have two excited atoms.Is that the case for a real laser? Explain. In the animation there is only one excited atom. Change the excitation level and try to match it to the incoming photon energy. Change the energy of the incoming photons, and see if you can match it to an excitation level that will produce pairs of coherent photons. This animation allows you to examine the workings of a laser. A laser beam is used to change the shape of the lens of the eye, thus changing its focal length. Laser eye surgery has improved the vision of many people, without the need for corrective lenses.One of the advantages of using a laser as a surgical tool is that it is accompanied by very little bleeding.A holographic image is produced by constructive and destructive interference of a split laser beam. Holograms take advantage of the wave properties of light, as opposed to traditional photography which is based on geometric optics. A viewer can move around the image and see it from different perspectives. The name hologram means entire picture (from the Greek holo-, as in holistic), because the image is three-dimensional. Laser beams are used to produce holograms.The time it takes for the light to make the round trip can be used to make precise calculations of the Earth-Moon distance. Lasers are bounced off reflectors that astronauts left on the Moon.Lasers are used in industry to cut steel and other metals.Some barcode scanners use a laser beam.
CDs are read by interpreting variations in reflections of a laser beam from the surface. Those audio and data-storage devices began replacing cassette tapes during the 1990s. This chapter began with a picture of a compact disc (see Figure 17.1).These properties lead to a number of applications in industry and medicine.
Laser beams are directional, very intense, and narrow (only about 0.5 mm in diameter). You get the word laser (see Figure 17.2 (a)), which is the name of the device that produces such a beam of light. Take the first letters of all the words (except by and “of”) and write them in order. Some four decades later, Einstein’s idea found application in a process called, light amplification by stimulated emission of radiation. Such a light stream is said to be coherent. Those photons could go on to hit other excited atoms, and soon you would have a stream of in-phase photons. The exciting part is that you would have two photons with the same energy and they would be in phase. He suggested that the atom would emit a photon with that amount of energy, and it would be accompanied by the original photon. He considered an atom excited by a certain amount of energy and what would happen if that atom were hit by a photon with the same amount of energy. In 1917, Albert Einstein was thinking about photons and excited atoms. There will always be some blurring of images, no matter what the size of the aperture or the wavelength of light used to make an image.
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