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Bright Idea: The First Lasers

Imagining Ray Devices

Since ancient times, people believed that rays of light carry grand and mysterious powers. Interest in radiation redoubled around the start of the 20th century with the discovery of radio, X-rays and radioactivity. A whole spectrum of radiation opened up, with wavelengths longer or shorter than light. What amazing new uses might be discovered for use in medicine, communications, scientific research — or warfare?

Radio was soon put to use, but the same techniques could not be used with radiation of shorter wavelengths. A method for amplifying light had its origins in an idea Einstein developed in 1916. Looking deeply into the new theory of quantum physics, he predicted that rays could stimulate atoms to emit more rays of the same wavelength. But engineers had little notion how to manipulate atoms, and for decades the idea seemed a theoretical curiosity of no practical interest.

Scientists and engineers pushed radio techniques to ever shorter wavelengths. In the 1930s some hoped they were on the verge of creating a “death ray.” That turned out to be unworkable, but the effort led to something better — radar. By 1940, ingenious devices could generate rays with wavelengths of a centimeter or less. They were swiftly pressed into service to detect enemy airplanes.

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Radiation Spectrum

By the start of the 20th century, scientists understood that light rays could be thought of as electro- magnetic waves — similar to radio waves, but with much shorter wavelengths. A spectrum chart shows various forms of electromagnetic radiation. The only difference between one ray and another is the length of its wave. (We can also say the frequency is different, the frequency being the number of waves that pass a point each second as the ray moves through space.) The spectrum is drawn so that the wavelength is reduced by a large factor at each major division. Thus visible light rays are 1/100,000 the length of "microwave" rays commonly used for radar. Rays with shorter wavelengths can carry more information and more energy.

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Scientists boasted that radar had won the war and the atomic bomb had ended it. What might physicists create next? As the Cold War against the Soviet Union got underway, the US government poured ever larger funds into basic and applied research. Detecting not only military but civilian applications, corporations and entrepreneurs heaped their own money on the pile. Industrial and university laboratories proliferated. It was from this fertile soil that the laser would grow.

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Charles Townes recalls how physicists' war work brought postwar research funding

Of course, the nuclear bomb I think surprised people.... It changed the style, and the amount of money available, and the energy with which physics was pursued. And it made jobs in universities for people. Many of my friends from Caltech had taken jobs [in the 1930s] teaching high school even, teaching in junior colleges certainly — very good men teaching in junior college, working in the oil fields, working in industry. And suddenly after the war, why, there were jobs for them in the universities, and many of them became quite prominent. It wasn't for lack of ability that they were teaching in junior colleges. It's just that there were no jobs.

The laboratory that you turned to at Columbia was funded by the [U.S. Army] Signal Corps, I think you said?

It was a joint services laboratory, but under the responsibility of the Signal Corps primarily... it was a result of the war. That laboratory had been working on magnetrons [for radar] during the war, you see, and they had also started some measurements on the absorption of microwaves by water. They'd made some good measurements, but at high pressure, atmospheric pressure. I'd been working at low pressure where you could get narrow lines.... the laboratory was based on this initial thing, working on magnetrons, which then continued to be supported. After the war of course the ONR [Office of Naval Research, U.S. Navy] particularly but other services stepped in to help the universities and help them keep going, and they were interested in the further development of magnetrons. In a way, that was the job of that laboratory still, after the war, to develop higher frequency magnetrons. The armed services felt that anything in that general area, good physics in that general area was fair game, and that's of course what the university was interested in.

The Maser: First Step to the Laser

Already in the 1930s scientists could have built a laser. They had the optical techniques and theoretical knowledge — but nothing pushed these together. The push came around 1950 from an unexpected direction. Short-wavelength radio waves, called microwaves, could make a cluster of atoms vibrate in revealing ways (a technique called microwave spectroscopy). Radar equipment left over from World War II was reworked to provide the radiation. Many of the world’s top physicists were thinking about ways to study systems of molecules by bathing them with radiation.

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Townes recalls why Professor Rabi supported his work at Columbia

Rabi has very strong ideas. Rabi is a very wise man in many ways and I admire him, but he also — he has very strong opinions. And I know perfectly well what Rabi's thinking was. I believe I know perfectly well what his thinking was. He felt molecules were really not very interesting, and not really physics; that's chemistry, and it's not really physics. Real physics is nuclei, high energy physics. And solid state even he felt wasn't very interesting. Columbia never had very much solid state physics. But Columbia had a microwave lab, being well-supported by the armed services and the Signal Corps, and he felt he needed some notable research going on in the microwave lab. This was an active field and interesting a lot of people, but I think he kind of looked down on it as kind of dirty stuff, that molecules are too complicated, and not fundamental and so on. But it's OK, it's pretty good, and so, he needed a person like me. So that's the reason I got hired. Now, it was a good opportunity in that they already had equipment there and a big laboratory and it was well run and well financed, and I could go ahead and work.

Charles Townes of Columbia University had studied molecules as a physicist in the 1930s, and during the war he had worked on radar as an electronics engineer. The Office of Naval Research pressed him and other physicists to put their heads together and invent a way to make powerful beams of radiation at ever shorter wavelengths. In 1951 he found a solution. Under the right conditions — say, inside a resonating cavity like the ones used to generate radar waves — the right kind of collection of molecules might generate radiation all on its own. He was applying an engineer’s insights to a physicist’s atomic systems. Townes gave the problem to Herbert Zeiger, a postdoctoral student, and James P. Gordon, a graduate student. By 1954 they had the device working. Townes called it a MASER, for "Microwave Amplification by Stimulated Emission of Radiation."

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Townes recalls the day he invented the maser

We'd had enough meetings that we had really surveyed everything that was going on, surveyed our own ideas. And so I was beginning to feel that, well, we may be coming to an end as to what we could usefully do immediately. And I was a little discouraged that nobody had turned up... what I felt were new and promising ideas. There were new things, but there was just no clear solution. Then we were having a meeting in Washington. That was the occasion when I sort of tried to think back over things, and what it was that might, might possibly work, and why other things weren't working. And that was where the possibility of the maser occurred to me...

It was in the early morning, before that last meeting, that I was sitting in the park and just thinking it over, with a little bit of a sense of frustration, how we hadn't gotten anywhere, and why was that? The fact that I had surveyed all the field and thought about it overtly and hard and gotten everybody else's ideas, and they had surveyed it and thought about it too, and there weren't any ideas, certainly was part of the reason I decided, "Well, we have to do something drastic. And really, these are the problems, why it hasn't been working. We've got to just find some way of getting around those problems." And the problems were in part just making small things. [There was] already my interest in molecules, and my thoughts back at the Bell Labs about possibly using them as circuit elements. We said, "Well, gee, if you're going to make some small things accurate, that's molecules and atoms are the ways of doing it." But the trouble is, they don't give much energy. And then it suddenly occurred to me: "Well, in principle, they could [produce more intensity] if you get a temperature inversion." And how do you do that? And I just followed up those ideas. So that it was a situation which helped bring about my facing the problem and deciding, well, this is the only way it's going to be done, if we can do it. So in that sense it came out of the committee.

Townes had predicted a remarkable and useful property for the radiation from the device: it would be at a single frequency, as pure as a note from a tuning fork. And so it was. The high degree of order in such radiation would give the maser, and later the laser, important practical uses.

Townes was not alone in his line of thought. Joseph Weber of the University of Maryland expressed similar ideas independently in 1952. And Robert H. Dicke of Princeton worked toward the same goal along a different path. Neither tried to build a device. In Moscow, A.M. Prokhorov and N.G. Basov were thinking in the same direction, and they built a maser in 1955.

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Who Invented the Laser?

Physicists had been working for generations toward controlling ever shorter wavelengths. After radio (meters) and radar (centimeters, then millimeters), the logical next step would be far-infrared waves. Masers had been modestly useful, more for scientific research than for military or industrial applications. Only a few scientists thought an infrared maser might be important and pondered how to make one. Infrared rays could not be manipulated like radar, and indeed were hard to manage at all.

Townes thought about the problems intensively. One day in 1957, studying the equations for amplifying radiation, he realized that it would be easier to make it happen with very short waves than with far-infrared waves. He could leap across the far-infrared region to the long-familiar techniques for manipulating ordinary light. Townes talked it over with his colleague, friend and brother-in-law Arthur Schawlow.

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Arthur Schawlow recalls how Rabi inspired him to make discoveries

My lab [at Columbia] was right next door to a lab occupied by one of Rabi's students, or some of Rabi's students, and in fact, there was a whole block of rooms occupied by Rabi's students, and this one of Townes' was at the end of them. And so, Rabi would come around once in a while, and of course, I was much intimidated by the great man, Nobel Prize winner and all that. He went off to Japan for a month, then he came around and he stuck his head in my door, and said, "Well, what have you discovered?" And this really struck me, because I never thought I could discover anything, you know. I might do something, but to discover something! It just sort of helped to raise your standards, and raise your sights, and so on: let's see if I can't pick out what's important to do, and not just do something.

Schawlow found the key — put the atoms you wanted to stimulate in a long, narrow cavity with mirrors at each end. The rays would shuttle back and forth inside so that there would be more chances for stimulating atoms to radiate. One of the mirrors would be only partly silvered so that some of the rays could leak out. This arrangement (the Fabry-Pérot etalon) was familiar to generations of optics researchers.

The same arrangement meanwhile occurred to Gordon Gould, a graduate student at Columbia University who had discussed the problem with Townes. For his thesis research, Gould had already been working with "pumping" atoms to higher energy states so they would emit light. As Gould elaborated his ideas and speculated about all the things you could do with a concentrated beam of light, he realized that he was onto something far beyond the much-discussed "infrared maser." In his notebook he confidently named the yet-to-be-invented device a LASER (for Light Amplification by Stimulated Emission of Radiation).

Gordon Gould recalls his creative moment

I had tried two different techniques without success, and finally, Professor Rabi, who was a sort of guru — Dr. I. I. Rabi, one of the many Nobel Laureates to come out of Columbia — came back from Europe from a conference and he was all excited about what was called "optical pumping," using light from one source to excite another medium, in this case for the purpose of getting a population up in an excited state for making measurements. So he came back and said, "Well, I see you that haven't succeeded yet in what you were trying to do (which was to thermally excite [the molecules] — Why don't you try this?" So, being a lowly graduate student, next naturally I tried it. And that got me into optical pumping, and later on I saw how to use that, first to excite a maser — microwave amplifier — and then later on, laser media. And that was the beginning of it all.

So the beginning of it all actually had its start long, long ago, in some sense. To invent anything important or exciting, obviously you have to have a lot of building blocks in your head to do it. So if I say that on a certain night in November, 1957, suddenly, when I couldn't get to sleep, the idea for the laser popped into my head, the way to make that beam — yes, it popped into my head, but only after my head had been working away on all the materials for all those years.

Everybody who does anything creative at all has that feeling, that moment that happens from time to time, where suddenly something comes into your head full blown, almost, whether it's a painting or an idea for a book or a laser or anything else, or maybe a way of making money.... I believe that the mind has been churning away, subconsciously, on all the materials that are necessary to go into it. That stretched back to Yale, where I specialized in optics and spectroscopy there, Yale was a big optical laboratory. Columbia was not, but Columbia had all this microwave spectroscopy, and the maser was first thought of and demonstrated there by Townes and his students. It was really the combination of those things: familiarity with optical techniques, and also being in an atmosphere where all these new things were developing in the microwave area. That combination was needed to come up with something like the laser. Plus the added impetus of working on my thesis using optical pumping.

Peter Franken recalls hearing Gould's exciting ideas

The pivotal event for me actually was when I learned of Gordon Gould's — or the notion I attributed to Gordon Gould—of using a Fabry-Pérot resonator. Up until then I was thinking along the lines of my toilet training at Columbia, which would have suggested just building a microwave cavity with a hole in it, and trying to get it to resonate at optical frequencies. But when Gordon at some conference (I always forget the date) told me he was going to use a Fabry-Pérot, it was like a blinding light bulb; I realized, my God, you could get parallel light as well as monochromatic light, and the full significance of it then occurred to me. And so I was excited about it, and indeed in the late fifties I lectured on the subject. We didn’t have lasers then but I could still give lectures about them, and I was one of the cadre of young atomic physicists, spectroscopist types in the fifties, the late fifties, because of the work I was doing at Michigan, who were really very excited and interested in the potential of having a laser.

Gould, Schawlow and Townes now understood how to build a laser — in principle. To actually build one would require more ideas and a lot of work. Some of the ideas were already in hand. Other physicists in several countries, aiming to build better masers, had worked out various ingenious schemes to pump energy into atoms and molecules in gases and solid crystals. In a way they, too, were inventors of the laser. So were many others clear back to Einstein.

The Patent War

In 1957 Townes talked over some ideas about pumping light-energy into atoms with Gordon Gould, a graduate student who had been thinking along similar lines. Worried that he might be scooped, Gould wrote down his ideas for the record. He developed many more ideas of how lasers could be built and used, and in April 1959 he filed patent applications with his employer, the high-tech research firm TRG. Nine months earlier Schawlow and Townes had applied for a patent on behalf of Bell Laboratories, which employed Schawlow on staff and Townes as a consultant.

When the Bell patent was granted, Gould sued, claiming he was first to conceive the device. Legal battles raged for the next thirty years. If Gould’s patents were valid, everyone who built or used a laser would owe him money—and the longer the patents were undecided, the more valuable they became as the laser industry grew. In 1987 Gould and his backers began to win settlements. One of the greatest patent wars in history was over.

The historical question of how to assign credit for inventing the laser remains controversial. Most of the ideas were patented by someone, but that tells little about how the ideas actually arose and spread among scientists.

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Robert Dicke recalls patenting his ideas

Of course, as soon as the maser was developed, it was clear that there was a possibility of doing this optically — and I remember a Physical Society meeting in Washington, I can't say when, but it was certainly after my patent was issued, because I saw Charlie [Townes] and I said, "How are things going?" He mentioned that, well, he’d got a good way of building a resonator for this, I don't know whether he called it "laser" or not, but a maser to operate with... optical maser, something like that. He says, "All you have to do is put a couple of mirrors on it." I said, "That's great, Charlie, but it's not new, because I've got it in a patent."...

I was consulting with RCA at the time, and it seemed like a kind of cute idea. I didn't have anything specifically in mind to do with it. You know, it was hard for me to convince RCA that this was an important invention. I actually wrote up three separate patent disclosures on various aspects of this thing, and they thought, well, it might be worth patenting but they would combine all three in one. So, the result is that the patent application's a great mess, because they put too many things in it.

Ali Javan comments on credit for discoveries

I think at the end priority does not establish, really, achievement to be recognized as any major contribution of any one person. It cannot really. Who said what first. What is important is originality, and carrying the work through beyond even the original conception. That is what is important. Even the original conception, it can have only — get you so much towards, really, an achievement. Beyond the conception — making it happen...

Charlie Townes, I think his work in masers is original. As original as could be. And not only his suggestion is what one puts the value towards his achievement, but the fact that he went ahead and did it and then carried on to the next step, and the next step and the next step and the one that led to lasers. That is what counts.

The Race to Build a Laser

The race was on! When Schawlow and Townes published their ideas in 1958, physicists everywhere realized that an "optical maser" could be built. Teams at half a dozen laboratories set out, each hoping to be the first to succeed.

Columbia University: Schawlow left it to Townes to make the first attempt. Townes decided to start with potassium gas, since its properties were well understood. But one of these properties is that it is corrosive. The gas attacked the seals on Townes’s glass tubes and darkened the glass.

TRG Corporation: When Schawlow and Townes published their work, Gould told his employers that he was working along the same lines. They got funding for a project from the US Department of Defense. The project was classified "secret," and Gould was barred from working on it because he had briefly participated in a Marxist study group during the war.

Westinghouse Research Laboratories: Masers were being made not just from gas but from crystals — synthetic ruby, for one example. Perhaps a crystal might be stimulated to emit visible light. Irwin Wieder and collaborators tried pumping energy into a ruby using a tungsten lamp. The system was hopelessly inefficient — they couldn’t get nearly enough energy into the atoms to make a laser.

IBM: At IBM’s Thomas J. Watson Research Center, Peter Sorokin realized that you didn’t need mirrors if you used a crystal with the right properties. He had a calcium fluoride crystal polished to have square sides. A ray striking an edge at a 45-degree angle would be reflected toward the next edge and continue to go round and round the inside. A trace of uranium atoms sprinkled through the crystal could act like a gas in a cavity. But they couldn't get laser action, that is, amplification of light.

Bell Labs: Bell Labs had a good supply of rubies for maser research, and Schawlow decided to try that route. Meanwhile, Ali Javan, a former student of Townes, tried another route. Like Townes, Javan preferred the simple medium of a gas, and he settled on a combination of helium and neon in a long glass tube. An electric discharge through the gas would energize the helium, and collisions would transfer that energy to the neon. They too couldn't get laser action.

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Schawlow recalls how he set out to make a ruby laser

After we finished the paper, I knew that Townes and Cummins and later Abella and Heavens were going to work on trying to make a potassium optical maser at Columbia. And I never want to do what anybody else is doing, because I haven't much confidence in my ability to compete, and I don't like competing. And being at Bell Labs in the trasistor era, you felt that if you could do anything in a gas, you could do it better in a solid. And so I started trying to learn about solids. And in fact, in that one paragraph in our paper that mentions that solids have broad bands for absorbing light and sharp lines to emit it, I had just learned that much; I knew that ruby was that way.

Now, ruby was a common material around there because a lot of people were working on microwave masers. So you could go down the hall and find somebody who had a drawer full of rubies of various concentrations, and could borrow a few samples which you'd never return. So I just thought well, I'll get my feet wet, I'll try and learn something about this stuff, what's it all about. I had no idea of the theory, or anything at all about it. And I got hold of a copy of Pringsheim's book on Fluorescence and Phosphorescence. Which was one of these wonderful, thoroughly Germanic books that had all the references back to the early 1800s. It was very complete, but it didn't have the answers we wanted. At that time, I asked [lab director Al] Clogston if Icould work on that, and he said "Fine." Then later there was another incident in the fall of 1958 after — the fall of 1960, rather, after Maiman had published the pink ruby laser, I was thinking about the dark ruby, and I really knew quite a lot about it, and I knew that those satellite [dark ruby spectrum] lines, or "N" lines, were really very strong, stronger than the [pink ruby’s]"R" lines, and I just felt that that dark ruby maser that I had proposed really ought to work. So I asked Clogston if he thought I ought to try it out, and he said, "You owe it to yourself." So, we did, and it worked. Right away. And of course, I should have done it sooner.

Javan recalls starting work on a gas laser

After I did come up with the idea and really convinced myself that helium-and-neon was the best medium to proceed, there were a lot of non-believers. A lot of non-believers. And the non-believers were telling me that gaseous discharges were really too chaotic. You could not have anything, you know, that you could control. And there were a lot of uncertainties.

Hughes Laboratories: Theodore Maiman made calculations and measurements that convinced him Wieder was wrong in saying it was impossible to pump much energy into a ruby. Even so, you would need an extraordinarily bright energy source. One day, Maiman realized the source did not have to shine continuously, which was what Schawlow and others were trying. A flash lamp would do. Scouring manufacturers’ catalogs, he found a very bright lamp with a helical shape. Just right, he thought, for fitting a ruby inside. He assembled the components with the aid of an assistant, Irnee d’Haenens, and on May 16, 1960 they observed pulses of red light. It was the world’s first laser.

Other teams moved quickly when they heard of Maiman's work. Within a couple of weeks of the press conference that announced the discovery in July, groups at Bell Labs and TRG had bought flashlamps like the one shown in Maiman's publicity photo, reproduced his device and studied it in detail. Schawlow, who had joined the Bell group, with his technician George Devlin made a laser out of a different type of ruby crystal. Wieder with Lynn Sarles independently got the same result. When Sorokin heard of Maiman’s achievement, he realized that he had been too pessimistic. He and Mirek Stevenson had their calcium fluoride crystals recut into cylinders silvered at their ends, and got laser action from them in November. The input power required was less than 1 percent of that needed for the ruby laser. Back at Bell Labs, Ali Javan with Donald Herriott and William Bennett continued on their original path, and in December produced a continuous beam of infrared rays — the first gas laser. Altogether, by the end of 1960 three quite different types of laser had been demonstrated.

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Franken recalls how the laser discoveries excited physicists

Let me tell you about the OSA [Optical Society of America] meeting. It was held in Pittsburgh, in 1961 in Pittsburgh.... That was Panic City. The halls were packed. Normally with an invited paper at the Optical Society, you might draw a hundred people. There might be two or three click-click-clicks of cameras taking pictures of the slides. These halls were packed, the ballroom was packed, for this invited paper. I remember as a high point Charlie [Townes] — I'm sorry, Art Schawlow getting up, giving a talk: every slide he projected, there was a veritable staccato machine gun fire of Minoltas going off. It was unbelievable! Panicville. Everybody wanted to get in on it.

What's it Good For?

Fifty years after the first laser, there are few people in modern society who have not been affected by the invention.

Revolutionizing Communications: In the 1980’s telecommunication systems relied on bulky copper cable, which was at the limits of its signal-carrying capacity and had filled the duct space under city streets with no room for expansion. Laser light beamed through a single strand of glass optical fiber, thinner than a human hair, can carry more than half a million telephone conversations, or thousands of computer connections and TV channels. Without fiber optics the internet that brings you this exhibit would not exist.

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Improving Commerce, Industry and Entertainment: One of the earliest uses of lasers was in surveying. For example, to tunnel under the English Channel, separate tunnels were started from the English and French sides of the Channel. Laser surveying brought the two together with a misalignment of only a few inches over 15 miles. Today, supermarket checkout scanners, CDs, DVDs, laser holograms for security on credit cards, and laser printers are just a few of the countless consumer products that rely on lasers. Industrial lasers cut, drill and weld materials ranging from paper and cloth to diamonds and exotic alloys, far more efficiently and precisely than metal tools.

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Pain free Surgery: Used in millions of medical procedures every year, lasers reduce the need for general anesthesia. The heat of the beam cauterizes tissue as it cuts, resulting in almost bloodless surgery and fewer infections. For example, detached retinas cause blindness in thousand of people each year. If caught early, a laser can "weld" the retina back in place before permanent damage results. Optical fibers can also deliver laser beams inside the body to reduce the need for more invasive surgery.

Advancing Science: Before any other application, lasers were used for scientific research. At first, like masers, they were used to study atomic physics and chemistry. But uses were soon found in many fields. For example, focused laser beams are used as "optical tweezers" to manipulate biological samples such as red blood cells and microorganisms. Five researchers have shared Nobel Prizes for using lasers to cool and trap atoms and to create a strange new state of matter (the Bose Einstein condensate) that probes the most fundamental physics. Over the long run, none of the uses of lasers is likely to be more important than their help in making new discoveries, with unforeseeable uses of their own.

Everyday Lasers: From cat toys to computer mice, lasers play important (and fun) roles in our daily lives. The average red laser pointers, for example, are great tools for presentations and giving your cat some exercise. But did you know high grade laser pointers, preferably green, can be used in astronomy? Brighter and easier to see, a well-powered green laser can be used to point out planets and constellations in the night sky. The primary reason a green laser stands out so well, is because it delivers at least 5 milliwatts of power.

Laser pointers have also taken on a political role in recent history. At a 2019 Chilean protest, a coordinated effort using hundreds of common laser pointers resulted in the take down of a surveillance drone.

Pop Culture and Not-So-Fiction Science-Fiction: After the invention of the laser, science fiction audiences witnessed a boom in laser-inspired weapons. In 1977, “Star Wars Episode IV, A New Hope,” fans saw the Death Star use laser power to destroy an entire planet. In some early episodes of Star Trek, such as “The Cage” and “Where No Man Has Gone Before,” the laser pistol was the weapon of choice. In “Goldfinger” (1964), James Bond must escape death by laser beam, and in “Tron” (1982), the laser beam acts as a transporter for main protagonist, Kevin Flynn to enter a digital world.

Currently, these weapons remain in the world of research and development, but several countries are working on how to harness lasers for defense. For example, beams of light are used in military applications for targeting and passive surveillance.

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