Lasers and Their Uses (1983) / Chapter Skim
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Lasers and Their Uses
Lasers and Their Uses
Pages 11-26
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From page 11... ...
In 1958, when Charles Townes and I published a paper in the Physical Review showing that it would be possible to build what is now known as a laser, nobody had ever heard of any such device. Yet a few years later it was such a common part of everyone's vocabulary that we could even find the music critic of the London Times writing, "Solti's performance deals more completely with the great moments than wildest dreams may have imagined: the first violin and viola statement of the passionate E flat theme in part two sawing through you like a beneficent laser beam.
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From page 12... ...
In ordinary light sources, such as a neon sign, atoms are excited somehow, perhaps by thermal agitation or by collisions with electrons in an electrical discharge. The excited atoms store energy for a brief interval, perhaps a millionth of a second, then spontaneously emit light.
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From page 13... ...
Some of the light energy stored between the mirrors leaks out through the partial mirror at the end and produces a very highly directional beam. This structure, which practically all lasers use, determines the properties of laser light.
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From page 14... ...
That is enough to burn a small amount of absolutely anything. For instance, when a ruby laser was fired at the surface of a block of carbon, a little of the material not only melted but actually vaporized violently enough to produce a white hot jet of carbon vapor.
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From page 15... ...
The deep red light goes easily through the clear outer balloon but is absorbed by the dark blue inner balloon. The inner balloon then gets a hot spot and breaks.
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From page 16... ...
Since laser light has a pure color, some substances, such as white paper, just reflect the light while others, such as dark ink, absorb it and become hot. Thus when a 1joule flash of light from a laser strikes a typewritten letter, the ink becomes white hot and vaporizes, while the paper remains unaffected.
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From page 17... ...
As in the process of ablation, which cools spacecraft nose cones during reentry, it all happens so quickly that there is no time for conduction, so the balloon stays cool. FIGURE 5 Balloon after the laser eraser has erased a spot from the letter N
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From page 18... ...
Then the laser could vaporize only a little bit from the surface before the plasma layer prevents any further damage. It has even been suggested that under intense laser light there may be phase transitions to a nonmetallic form, and that there can be hot electrons out of thermal equilibrium with the rest of the metal.
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From page 19... ...
As the prism rotates, the laser beam goes around in a horizontal fan. The grading machine carries a little photocell on the top of a pole.
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From page 20... ...
Everyone knew, of course, that light can be guided around corners by fiber optics light pipes. The principle is shown by the curved plastic rod in Figure 7, which is guiding the light beam by total internal reflection at the surfaces.
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From page 21... ...
changes the brightness drastically, and much less than that can be detected. It is worth noting that it is totally against all ordinary experience to produce a dark spot by bringing together two light beams, even from different parts of the same source.
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From page 22... ...
Some commercial lasers used for research have a spread in wavelength of less than one part in a hundred million, and others have been built with at least a thousand times narrower bandwidth. With such lasers, very high resolution laser spectroscopy is possible.
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From page 23... ...
The beam from a tunable laser can be sent through a cell that is carefully designed with baffles to prevent any scattered light from the walls reaching a photodetector at one side of it. However, when the laser is tuned to a resonance of the gas in the cell, light is scattered from the atoms and detected by the photocell.
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From page 24... ...
Fairbank, Jr., was able to measure the relative vapor density of sodium atoms at various temperatures by scattering light tuned to one of the orange-yellow resonance lines of the sodium atom. He could detect the scattered light at temperatures as low as - 30°C, when there were only about 100 sodium atoms per cubic centimeter.
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From page 25... ...
Even at power levels much less than that, the response of transparent substances to the light's electric field is nonlinear, and the light is altered as an overdriven loudspeaker distorts sound. True optical harmonics or overtones can be generated in this way, having frequencies of two times or even higher multiples of the light frequency.
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From page 26... ...
It is gratifying to observe that lasers are also being used for artistic ends. Not only are the colored light patterns forming the basis of light shows, but lasers are also being used to carve artistic objects of wood.
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