nasa facts the laser

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of the microwave port ion o f the electromagneticnd tests of the laser in their efforts to fullyuqderstand its capabilities.

To understand the laser, it i s useful to examinean associated technique called maser (Mic rowaveAmplification by Stimulated Emission of Radi-ation). Masers an d lasers are closely related.Both lasers (concentrated igh t waves) and masers(concentrated microwaves) are electromagnetic

energy differing only in frequency or wavelength.Masers, as amplifiers, pe rform a function simi-

lar t o that fi l led b y certain electron tubes and

semiconducto rs. As generators, masers tak e aplace similar to conventional electronic oscilla-

tor tubes and travelling wave tubes. Lasers, onthe other hand, stand out as the only generatorsof coherent electromagnetic energy at lightfrequencies.

A laser, therefore, i s a maser whose outputbeam fal ls in to the l ight f requency po r t ion ofthe spectrum. Acc ording ly lasers are alsokno wn as optic al masers. The div idin g line be-tween masers and lasers on the electromagnetic

spectrum i s 300 kilomegacycles-the upper end

0pectrum.

Electromagnetic radia tion i s made up of t inypackets of pure energy. It comes naturallyfrom the sun in the fo rm of heat and light. Lightwaves and radio waves are electromagneticenergy, as are microwaves, in fr ar ed rays, u ltra -violet rays, X-rays and gamma rays.

While no one person can be credited with the

invention of the laser technique, a physicist,Charles H. Townes, had much to do with i t sdevelopment. In 19 51 , while searching for away t o make microwaves more useful, he devel-

oped a theory to harness their energy by manip-ulating the no rmal beh avior patterns o f electronsand atoms. In 1954, he devised a technique toforce atoms to em it a stable, coherent level of

energy. Thus, the maser was born. In 196 0,Mr. Townes, together with another scientist,Arthur L. Schawlow, devised a similar techniqueto harness the energy of light waves and thelaser was born.

Basically, the laser i s a device used in the

C O H E R E N T R A D I ATI O N

I N C O H E R E N T R A D I AT IO N

The upper illustration, indicoting o steady, phased radiation,i s such o s that emitted by the laser. The lowe r diogromindicotes the random effect of radiation such as that emiwed

by ordina ry incondescent light.

technique for producing a beam o f light o f suchsmall size and s o closely concentrated that it willno t grea tly increase in size or diffuse, as thelight travels outward from i t s source. Laserlight differs in character fro m o rdinary light inthe same way that a battalion o f well drilled sol-diers differs from a disorganized mob.

aThis i s whot o laser device looks like in action. It i smounted on on 18-inch telescope atop a 60-foot tower neor

N A S As Wallops Island Stotion, Virginia.


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Laser technology i s based on the principle thatlight waves differ from microwaves generated inradio transmission, etc., in th at the crests o fwaves are closer togethe r. Hence, they can befocused or concentrated more intensely. Thismeans the beam of light will travel thousands ofmiles through space before its width increases

significantly. As a result, this beam of light-more properly, energy-is capable of performingmany diversified tasks. Just how many and howwell are st i l l won drou s conjecture. But scien-t i s t s have already discovered that the laser can

effortlessly pierce or cut the hardest of materialssuch as tungsten, steel, or diamond. It offersthe promise of carrying a tremendous number-perhap s millions-of telephone calls or televisionchannels simultaneously. It may measure dis-

tance, alter the atom ic structure of molecules, orbe used in the performance of delicate surgicaloperations. Furthermore, it seems capable ofwelding most anything-fr om delicate human t i s -sues to the toughest of steels produced byindustry.

The laser does not develop ordinary light.0 Light emitted by the incandescent light bulb, for

example, i s produced when the filament (usually

tungsten) within the vacuum of the bulb i s heated.As electric current i s applie d t o the filament, i t smolecules, bat hed in a field of electromagneticenergy, give up their energy t o the field. The

0 Dr. Joseph Randall, of the Astronautics Laborotory a t theNASA Marshall Space Flight Center, inserts a rod of yttriumaluminum garnet doped with ne odym ium into a laser gun

in preparation for an experiment.

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hot glow of light thus provided i s a spontaneousor ran dom emission of energy. Because of therand om emission, ordin ary lig ht contains allcolors of the spectrum, diffuses quickly, radiatesdifferent wave lengths and frequencies at thesame time, and cannot be precisely or accuratelydirected. Moreover, it has an inherently lo w

quality of brightness.The laser produces a beam o f light possessing

opposite qualities. The laser beam i s monochro-matic (sing le frequ ency ). Research scientistsfor some years have noted that as certain mate-

rials begin to cool after being heated (in technical

language, stimulated), their atoms emit energy inthe form of ligh t waves. This Stimulated Emis-sion provides a part of the acronym IaSEr.

This schematic dia gr am of a laser i s indicative of t he g r w tsimplicity of the device. The laser has man y applicationpossibilities. Considerab le emphasis i s being placed on laserdevelop ment in the fields of communications, radars, medicine

and welding.

Scientists observed also that when the atoms arestimulated they emit their li ght precisely in unisonor, aga in in technical language, in phase. Fur-ther, it was observed tha t their light waves movei n one precise direction. Scientists describe thisone-way action of the light as coherent.

If you have ever focused a lighted flashlightinto a mirror in a darkened room, youve un-

doubtedly noticed how the reflected light seems

to amp lify in intensity an d lighten the whole room.In a manner of speaking, this i s exactly what thelaser device does to Amplify the Light emitted

by the atoms. Thus, we have li g h t Amp lifica-

tion-two more letters of our acronym LAser.A pencil-size ro d of synthetic r uby was used

in ma king the first lasers, in ea rly 1960. Thero d ends, squared off a nd silver coa ted (one end

more heavily silvered than th e other), served astwo facing mirrors.


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Aroun d the ro d was placed a coil of Xenonflash-tube (a tube containing the heavy inert gas-eous element Xenon). Wh en this tube wasmade to flash, (electrically fired ) the intenseflash of light (energy) fed into the ruby rod.This energy caused a few of the chromium atomspresent as an impurity in synthetic r uby t o be-

come highly excited. The energy thus producedsought to escape through one end of the ruby

rod. Instead, the energy was trapped by a mir-rored end of the rod and reflected directly back

to the opposite end. Enroute, the energy causeds t i l l more ions to become excited. So, to -


Then, when the reac tion ha d bu ilt up enougti,Radiation forced throu gh the less silvered end ofthe ro d as a powerful, pencil-thin beam of in-tense, coherent red light. Rad iation contrib-utes the fifth letter in the acronym IaseR.

An attribute of the laser i s its singular color.

As mentioned earlier, ordin ary light contains all

colors of the spectrum. Laser ligh t i s more one-colored than ordina ry light. I t s single-color light,

depending upon the m aterial used in the laser

technique, theoretically can be of any singlecolor. Light emitted from the ruby rod i s a bril-liant deep red.

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These are ruby rods, iust as they are grown, and before they have been ground, polish ed and s ilvered. To gro w one, scientistsDuring the heat ing process, chromium ions,

When the proper temperature is reached, the fused and nearly liquidThe m elt of crystal, tu rned slow ly t o give it a general rod-like shape, i s taken

The penny

place calcium tungs tate crystals in a crucible and he at them to about 2,800 degrees F.t a act as impurities, are introduced into the crystal melts.

crystal i s pink i n color from the chromium ions.from the crucible with a platinum wire. While these rods look light pink, in laser use, t hey deve lop a deep red light.

in the photograph illustrates t h e comparative s i r e of the rods.

gether-in unison-the energy moved tow ard theopposite mirror where again, it was caught andreflected anew, towards the other m irrored rod-end. Finally, bounce d back and for th between

the facing mirror-ends of the ruby rod, and caus-in g additional ions to join the crowd marchingi n unison, the energy became so -highlywampli-fied that the ro d could contain it no more.

Ruby lasers in use generally are able to giveout only short pulses of l ight -for about1 /1,000,000th of a second. And these flashescan be generated only ab out once or tw ice eachsecond. Oth er solids substitute d for the rub yro d have served to increase the length of timein continuous operation. Most such solids, but

not all, however, produce infr are d light.

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Another type of laser i s generated f ro m amixture of helium an dh eo n gases. Gas lasers

0 can be used for a ny desire d length of time, butare characteristically lower in power than thepulsed solid lasers. However, the gas laser canproduce bot h visual and inf ra re d beams. But,the characteristics of neither gas nor solid lasers

are ful ly understood as yet. Science teams in

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government and industry jo intly believe thesefields of laser research to h old gre at promise.

It i s possibk to focus the laser's concentratedbeam into a spot measuring no more than

5 / 100,000ths of an inch. In fact, a laser canb e directed s o sharply that i t s accuracy i s limitedonly by the precision of the telescope used in

aiming it.

Close up view of the NASA Explorer X X l l (the B e a c o n satellite). Quartz refkctors, 360 of them, are mou nted an an eight-sidedfiat-top p y r a m i d Tw o s d o r p o n d s s h o w n in left and right forefront of the picture are designed to catch the sun's rays fo r con-

T h e 116-lb windm i l l - shapd spacaraft i s equippe d to mak e surveys of Earth's ionosphere and to evaluateersion into electricity.lase r techniques.


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A boom of loser light i s so concentrated tho t it will spread only one-third of on inch for each mile thot it travels from its trans-mitter. Thus, if w e aimed a laser b w m at o

moon torge t a s diogranm ed in the photo at left, our boom, on skiking the moon, would illuminate an areo obout one mile in diom-eter as illustrated in the photo ot righ t. If we were oble to build CI search light, using ordinary electric light, powerful enough

to tmvel the distonco to the moon, it s rays would prob ably cover on areo equ ol to six times the diameter of the moon.

The moon is 238,357 miles awa y from earth and has a diameter of 2,160 miles.

N A S A i s using laser in connection w ith theExplorer XXII, XXVll and XXlX (the Geodetic Ex-plorer) satellites which were launched October10, 1964, Apri l 29, 1965, and November 6,1965, respectively. These sate llite experim entsprovide a means to investigate the uses andtechniques o f space communications and track-

ing. The satellites carry equipment fo r laser

tracking, the laser device being mounted on anIntercept Ground Optical Recorder (IGOR) tele-scope at N ASA's Godd ard Space Flight Center,Greenbelt, Maryland.

With this arrangement, the laser i s aimedal on g a predicted pat h of the satell ite. Thelaser beam i s flashed when the orbiter appearsover the station. A reflector assembly on thespacecraft returns th e l i gh t beam to a pho to -multiplier tube in the groun d telescope. The

time for the round trip of the laser beam enablesthe trackers t o pinp oint the distance of the satel-lite within 10 feet-f or a satellite more than 600miles away. By add ing an azimuth or angular

measurement of the beam, the direction of thesatellite can be obtained.

The reflec tor assem bly consists of fused silicaprisms mounted on the satellite. When a light

ra y hits the face of any prism, it will be reflecteddirectly back to i ts source. Explorer XXlX i s

stabilized in i t s flight s o as to keep the reflectorassembly pointing earthward at all times.

The reflector assembly i s composed of 36 0fused silica corner reflector prisms each coatedwith aluminum t o make them highly reflective.Then, each prism i s finally coated with a silicon

oxide -a convention al prote ctive process usedon the front face of any optical quality glass.

Fused silica, a fo rm of glass, was used in thereflector assembly instead of more conventionalglass because the latter would have turned blackafter two months of exposure to radiation in freespace. Fused silica wi ll remain highly reflectivefor a longer time than ordinary glass.

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A future laser flight experiment may be a two-way communication link-up in which a satellite

would receive a laser beam from a ground sta-tion, modulate the beam, an d relay it to another

groun d station. Labo ratory tests and experi-ments under way in the N AS A pro gram ran gefrom basic research (for lea rning the nature of

lasers and th e forces b ehind them) to advancedapplied projects in their uses.

The Explorer satellites involve two major po ten-tial peaceful uses of the laser for which NASA

established the program: ( 1 optical radar, and( 2 ) pace tracking.

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This i s a loser stripped of i t s outer covering t o i l lustrate the posit ioning of the ruby r od (center) and the flash tube (right) .A single pulse of lig ht, lasting for 1 1,000,000th

I t would us e about the same amount ofNote the com paro tive size of the laser w ith th e technicians hand which holds it.

of a second i s powerfu l enough t o voporize a hole completely through a rozor blode.energy as would be required by the batteries of a hand flashlight to operate i t s light bulb for two seconds.

Samples of potenti al uses of lasers by privateindustry include advance warning to aircraftpilots of ai r turbulence; dri lli ng and welding ofmachine and electronic parts; erasure of type-written letters with the split-millisecond pulses ofheat vaporiz ing the typewri ter ink. There are

In medicine, a laser has been used at Columbiamany others.

Presbyterian Hospital in New York City to spotweld a detached retina in a human eye. Simi-l a r surgical techniques now appear very prom-ising for b rain and nerve operations, according

t o medical authorities.Chemists, too, have an interest in the laser,

whose beams may be used to create chemicalreactions never befor e possible, or even to p ro-


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Research and developm ent work in the field of losers has developed rapid ly. Scientist n o wunderstand the principles of laser action and understand qua lity of materials wh ich produceefficient losers. Wh ile an imp ortan t num ber of loser applications have been discovered, scien-

t i s t s fee l that possible applications of the loser hove barely been tapped. Shown obove i s a

por tab le bs er he ld in th e l e f t hand of Dr. C. F. Luck of th e Ray theon Company. He i s checkingthe power supply that runs it.

vide a tool to manipulate a single atom withinthe molecule.

Laser beams have also demonstrated promise

i n the metall urgy field-to cut, weld, and piercematerials such as tungsten, diamonds, an d steel.

O ne of the most dramatic demonstrations oflaser possibilities was pr ovid ed b y researchers of

the Massachusetts Institute of Technology andthe Raytheon Company. They shot laser beamsat the moon and detected their reflections backon earth. Each of the 1 3 short bursts of thered laser beam made the half-million-mile round

trip in 2 % seconds. Ma n ha d illuminated a

celestial body for the first time with an opticaldevice.

Private industry and the Department of

NASA FACTS format i s designed for bulletin-board displayuncut, or for 8 x 1 0 % looseleof notebook insertion whenCut alon g do tte d lines ond fold ed along solid l ines. Fornotebo ok r ing insertion, punch at solid dots in the margins.

Defense are also among the enthusiasts in laserdevelopment and are hard at work in their re-spective fields on commercial and military appli-

cations o f the technique. The laser a l so holdsgreat promise in space and especially for com-munications, tracki ng an d naviga tion. For ex-ample, the laser shows great promise in detectingand measuring high alt itude cosmic dust; and theuse of laser gyroscopes in the gu idance systemsof rocket launch vehicles i s now undergoing tests.

Much advanced work i s being conducted atNASAs Marshall and Goddard Space FlightCenters. However, NA SA expects to stimulate

and carry out a great many promising researchprojects with lasers at its new Electronics Re-search Center in Cambridge, Massachusetts.

_ _ _ ~~-NASA FACTS i s an educa tional pub licatio n of NASAs Educo- ?tionol Progroms and Services Office. It w i l l be moiled toaddresses wh o reque st it from: NASA, Educational Pub lico-tions D istribution Center, FAD-1, Washington, D.C. 20546. /

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