A Solution for Almost Everything: 50 Years of the Laser
Many scientists heralded the invention of the laser five decades ago as a "solution in search of a problem"—but today it is used in most parts of our daily lives
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In perhaps the most famous scene of any Bond film, secret agent 007 lies strapped to a table with his legs spread. Archvillain Auric Goldfinger directs an industrial laser toward Bond’s manhood, and slowly the thick red beam surgically cuts the table in half. The secret agent calmly convinces his foe to shut off the laser in the nick of time.
The scene as described in Ian Fleming’s 1959 book Goldfinger features a large circular saw—not a laser— because the latter was not invented until the following year. The vast majority of Americans who first flocked to the film in 1964 didn’t even known that such a device could exist outside of science fiction films and comic books. But this remarkable invention was already hard at work remaking the world, even if it would take a few more years for awareness to percolate to the average person.
Fifty years after the world’s first laser was built in May 1960, few aspects of daily life don’t involve the use of a laser, whether it’s talking on the phone, surfing the Internet, buying groceries, or even playing with a cat. Although less celebrated, the laser ranks with the airplane, electronic communications, and the personal computer as one of the most influential inventions of the 20th century—even if its exact origins are still disputed.
Although indispensable in modern life today, lasers were first met with a collective shrug. “When lasers were first made, their characteristics and performance seemed so unusual that some scientists not in the field joked, ‘That’s interesting, but what good is it?’” writes Charles H. Townes, the physicist who, with colleague Arthur Schawlow, not only invented the maser (the laser’s predecessor) but also conceived the idea for the amplification of visible light. Townes would win the Nobel Prize for his work in the same year that the film Goldfinger was released, but other scientists continued to describe the laser as “a solution in search of a problem.”
“What that line really reflects is that it was not something invented to solve some specific problem,” notes Jeff Hecht, the historian of science who has written Beam: The Race to Make the Laser and several other related books. “It was not invented to fit a specific set of application requirements. But once you had it, it made a lot of things possible.”
As with many other technologies, the basic concept of the laser seems quite obvious in retrospect, but it languished in the backwaters of speculation and theory for decades before it found practical applications. The word “laser” is an acronym for “light amplification by stimulated emission of radiation.” A laser, says Hecht, is basically “a very well-controlled lightbulb.”
That control comes from the stimulated emission of radiation, a phenomenon first described by Albert Einstein in a 1916 paper. By the early 20th century, physicists already understood that atoms could have different energy levels or states, and that they jump to higher energy levels when stimulated by external energy. Atoms naturally tend to settle at their lowest energy level, so “excited” atoms almost immediately reemit the extra energy in the form of another discrete particle known as a photon—the basic unit of light—in a process known as spontaneous emission. Einstein realized that if an already excited atom were hit by another photon at the right energy, it would shed two photons, a process he called stimulated emission.
As the basics of quantum physics emerged over the following decade, some scientists theorized that stimulated emission could be used to amplify electromagnetic signals. Any practical applications of this idea, however, remained elusive, in part because of the wide gulf that existed then between theoreticians/experimenters and scientists/engineers. “I believe this is one of the cases where the scientific and engineering communities became locked into a particular set of ideas which, while fruitful in other ways, kept quantum electronics and lasers definitely outside the common paths of thought,” Townes wrote in a 2000 journal article.
World War II brought everyone together to turn the theoretical into the practical, from the atomic bomb to radar technology. “Working under intense time pressures, they generated massive advances in electronics . . . and other technologies,” wrote Stanford University electronics engineer and laser expert Anthony E. Siegman, “and at the same time educated themselves in the techniques and the capabilities of these new technologies. As the war ended, many of these scientists returned to their home laboratories, carrying with them not only these new skills and concepts but in many cases pieces of their wartime apparatus . . . which they were eager to apply to more basic scientific pursuits.”
One of these was Charles Townes. After working on radar and microwave technology for Bell Labs during the war, he moved to Columbia University in 1948 and developed microwave spectroscopy for the study of atoms and molecules. On a spring morning in 1951, while sitting on a park bench in Washington, D.C., where he and his colleague and brother-in-law Arthur Schawlow were attending an annual meeting of the American Physical Society, Townes had a eureka moment.
“We shared a room at the Franklin Park Hotel,” recalled Schawlow. Townes had several small children and often got up early out of habit, while the bachelor Schawlow liked to sleep in. One morning Townes arose early, walked outside to enjoy the pleasant morning in Franklin Park, and started musing about a session on microwave generation that he was going to attend that day. “At that point,” wrote Schawlow, “he realized how to use molecules rather than free electrons to generate [microwaves].”
Townes jotted down some quick notes before the idea slipped away. He had conceived the maser (short for “microwave amplification by stimulated emission of radiation”). He and his graduate students James P. Gordon and Herbert J. Ziegler would build and demonstrate the first working maser in 1954. (A statue of Townes sitting on that park bench now graces a park in his home town of Greenville, South Carolina.)
Townes built upon his maser work, as did others, including Nicholas Bloembergen of Harvard University and Robert Dicke of Princeton University. Similar work was also being done in the Soviet Union by Nikolai Basov and Alexander Prokhorov. Masers soon found applications as highly accurate atomic clocks and as low-noise amplifiers for radio astronomy and deep-space communication with satellites and interplanetary probes.
Scientists realized that the same principles harnessed in the maser could be applied to other electromagnetic wavelengths—such as those of visible light. In 1958 Townes and Schawlow published a paper in <I>Physical Review<$> setting out the concept of an “optical maser,” and the race was on to build one. “Our paper on optical masers attracted considerable interest,” Schawlow wrote in 1976. “Some people had serious doubts that it would even be possible to build an optical maser, and some very plausible arguments were advanced to prove that it would not work. But a number of others seriously sought suitable materials and ways to activate them.”
The key question was just what material would serve as the medium into which energy would be “pumped” to set off the lasing action. Townes’s original 1954 maser used gaseous ammonia, and since then others had built masers using solid materials. But what would lase at the much higher frequencies and shorter wavelengths of optical light?
A year after publication of their paper, almost everyone in the field came together at the first conference in quantum electronics, organized by Townes at Shawanga Lodge in the Catskills. Even Basov and Prokhorov attended, as did a 37-year-old Columbia physics graduate student and inventor named Gordon Gould, who presented his ideas about building an optical maser, for which he logically enough coined the word “laser.”
All the major players were thus present at the conference, and the basic ideas had been proposed and discussed. But it remained to be seen who would actually succeed in building one. The smart money was on Townes at Columbia or perhaps Schawlow, who was still at Bell Labs, but there were other high-powered contenders, including engineers at General Electric, MIT, RCA, Westinghouse, and the Technical Research Group (TRG) in Melville, New York, which Gould had left Columbia to join. Gould had tried to patent his laser ideas in 1959, but the U.S. Patent Office turned him down. The Russians were also continuing their own work, just a step or two behind their American colleagues.
The breakthrough, when it finally occurred only about six months after Shawanga, came from a wholly unexpected source: Hughes Research Laboratories in California, the research and development branch of Hughes Aircraft Company. “In a parquet-floored laboratory on a hillside above Malibu, looking out over Pacific Ocean beaches and movie stars’ homes,” as Siegman described it, physicist Theodore Maiman created the world’s first working laser.
Hughes, of course, was an aerospace company with little immediate use for such a gizmo, so Maiman had done some fancy footwork in gaining permission to work on the problem. He secured a contract with the U.S. Army Corps of Engineers to build a maser, and then convinced Hughes to support his laser research for several months. Having satisfied his contract, he turned his full attention to building a laser in August 1959.
Maiman knew he was entering a particularly competitive world: “It was a little brash for me to enter that race at that time. People with well-funded efforts had already been going for, let’s say, a year. . . . There was not a great deal of enthusiasm or support [at Hughes]. . . . Was it worth the company’s investment to do this work? . . . It became an uphill battle. I got pretty stubborn.”
“Maiman very much marched to his own drum,” observed Siegman. He was a determined, single-minded maverick who ignored both the objections and criticisms of his bosses at Hughes and colleagues who told him he was on the wrong path. “I knew there was something there, and I was determined to follow through on it,” he recalled. “I understood the reasons why it wasn’t supposed to work. I wasn’t daunted by them, though, because I felt that I knew the answers.”
Maiman’s answer involved a ruby crystal and a helical xenon flash-photography lamp. Ruby, a compound of aluminum and oxygen with embedded chromium impurities that impart its reddish color, was already a common material in masers and had been studied extensively, but the general scientific consensus was that it would be too difficult if not impossible to use in a laser. Even Schawlow doubted its suitability. So most of the work had centered around other materials, including potassium vapor and other gases and solid materials.
But Maiman had painstakingly worked through the numbers and the models. “I had a sixth sense that it was going to work,” he remembered. He was also attracted by the prospect that ruby crystals could be made to lase at room temperature, not the cryogenic temperatures that masers required and that most researchers assumed lasers would also need. “If it worked at all, it would be small and compact and operate at room temperature.” Also, “ruby would emit visible light. I would be able to see it.”
Almost everyone working on the laser problem had been trying to build a continuous-wave device, another idea Maiman discounted. “I didn’t see any reason why I had to do this continuous-wave—pulsed mode was perfectly fine. People do a lot of things purposely with pulses, for example, radar. Besides, I was just trying to demonstrate that this could be done, not find the ultimate system.”
Maiman’s calculations indicated that an intensely bright light source would be necessary to pump the required energy into the ruby to achieve stimulated emission. He found only three bulbs that would do the trick, all helically shaped, and bought the smallest, a General Electric FT506, capable of emitting a flash with a brightness temperature of about 8,000 Kelvin. (In comparison, the sun’s brightness temperature is only about 5,500 K.) At first Maiman couldn’t figure out how to focus the bulb’s light onto his ruby; given the bulb’s odd shape, a simple set of reflectors wouldn’t capture all the light energy. Then he realized that he could simply place the cylindrical crystal inside the helical bulb, thus surrounding it with light, and put the entire assembly inside a highly polished aluminum cylinder that would reflect everything back onto the ruby. He coated each end of the crystal with silver to turn it into an optical cavity, in which the additional energy generated in the lasing process would be contained. He left a small hole in the coating at one end so that he could measure what was going on inside.
On May 16, 1960, Maiman assembled his device and fired up the xenon bulb. Inside the crystal, the sudden flood of photons excited some of the chromium atoms to higher energy levels, causing them to emit photons, which were reflected back into the optical cavity by the silvered ends of the crystal to strike and excite still more chromium atoms. Soon more chromium atoms were in a higher energy state than in the normal ground state—a “population inversion” had been achieved. The cascade of high-energy photons bounced back and forth inside the optical cavity, but some of the photons found their way out of the tiny hole provided, through which Maiman could detect and measure a stream of these emerging in a coherent beam—the first laser light produced on Earth.
The beam was hardly visible, mostly because Maiman had set up the experiment with only a tiny hole in the cavity and a synthetic crystal of fairly poor optical quality. Shortly afterward, with better-quality crystals and one end of the crystal only half-silvered, to allow more photons to exit instead of being endlessly bounced around inside, “bright red spots from ruby laser beams hitting the laboratory wall were seen and admired,” Townes later wrote.
Ever the careful and methodical researcher, Maiman wrote up the results. But his paper was rejected by the first journal to which he submitted, Physical Review Letters, whose editors failed to realize its significance and dismissed it as another routine bit of maser research. Maiman sent a shorter version to Nature, which agreed to publish it. To beat the lag time before the publication and at the urging of Hughes Research, which wanted his accomplishment on record before they could be scooped by Bell Labs or someone else, Maiman held a press conference on July 7. The day afterward, no doubt to his amusement, he found himself being hailed by the nation’s newspapers as the discoverer of a “science-fiction death ray.”
Some were still dubious about Maiman’s accomplishment, in part because the paper in Nature was so short—only four paragraphs, one of which consisted solely of acknowledgments. Townes later called it “the most important per word of any of the wonderful papers in Nature over the past century.” But it galvanized the research community. Almost immediately, ruby laser experiments were repeated everywhere, including by Townes and Schawlow at Bell Labs, which served to silence any remaining skepticism. Only a few months later, Peter Sorokin and Myrek Stevenson had built rare-earth solid-state lasers at IBM; by the end of 1960, Ali Javan, William Bennett Jr., and Donald Herriott at Bell Labs had created both the first continuous-wave laser and the first gas laser, using a mixture of helium and neon.
And despite the witticisms about “a solution in search of a problem,” the device soon became useful not just for scientific research but in practical applications as well. In December 1961 a ruby laser destroyed a retinal tumor at Columbia-Presbyterian Hospital in New York. As researchers continued to build ever more varied types whose diverse materials created beams of different wavelengths and power, ever more scientific, industrial, and even artistic applications emerged. In possibly the most exotic example, the Apollo astronauts set up reflectors on the lunar surface that bounced back beams sent from Earth, providing a precise measurement of the distance between the two worlds.
Although no one seriously disputes that Theodore Maiman built the first working laser in May 1960, the question of who should be credited with “inventing” the device remains a matter of some contention. “The problem with trying to say something like the laser was invented is that technology really evolves,” Hecht pointed out. “Progress is by a series of steps. . . . Each one of those steps was important, and some years back I finally stopped trying to say anybody ‘invented’ the laser.”
There’s little question that Townes, along with Basov and Prokhorov, had developed and published the first theoretical ideas, and the three shared a Nobel Prize for it in 1964. But when the U.S. Patent Office awarded a patent to Bell Labs in March 1960 based on Townes’s and Schawlow’s work—two months before Maiman had built the first operational example—Gould contested the claim. He would finally win patents on a number of his innovations after an almost 30-year legal battle. Siegman had perhaps the best answer to the entire controversy: “The technology develops, and when the technology’s ripe, things are going to emerge eventually.”
Whoever one credits as inventor of the laser, there is no denying its ubiquity and usefulness in the modern world. Perhaps no other device exists in so many different variations and has so many applications. “It’s an enormously varied technology,” observed Siegman. “If you set up an ‘electronic Olympics’ [for] what electronic device has the greatest frequency stability, the highest peak power, the highest average power—a whole bunch of records to beat—the laser would win over transistors, vacuum tubes, whatever, in essentially every category.”
Lasers may be building-sized or microscopic semiconductor diodes, and they can do everything from shooting down missiles, as with the military’s current Airborne Laser Test Bed aboard a converted Boeing 747-400F, to performing the most painstakingly delicate eye surgery. Laser “tweezers” can even unravel strands of DNA or manipulate individual atoms. Many thousands of handheld laser pointers are used every day to enhance PowerPoint presentations. Even within the same general sphere of activity, lasers can have multiple uses. “At one end of the transportation chain, powerful laser beams weld your auto bodies together, and at the other end of the chain, the police use laser radars to catch you speeding,” Siegman noted. Over a dozen Nobel Prizes have already been awarded to work either directly related to or made possible by lasers, and more are sure to come.
Margaret Murnane, an optical physicist at the University of Colorado, has been using lasers to create ultrafast pulses of light—as fast as less than one femtosecond (one millionth of a billionth of a second). Such pulses are “really faster than anything in our natural world,” she says. Ultrafast lasers not only enable scientists to capture and study phenomena that occur quickly in small places, such as the movement of electrons through semiconductors, but also to generate radiation in certain parts of the electromagnetic spectrum that are otherwise difficult or impractical to access.
One of these is the terahertz range of frequencies, which lies between high-frequency microwaves and the lowest frequencies of infrared light. “We can use that to find out different things about materials that people couldn’t look at before, because there’s just no way to generate large intensities of light in that region,” reports Jason Baxter of Drexel University. He uses terahertz-pulse laser spectroscopy to study the properties of semiconductor materials with the aim of creating more efficient solar cells. Such work might be done at a huge synchrotron, Baxter explains, with all the cost and time constraints endemic to such a facility, but “we’re doing it on the benchtop now. Forty years ago, there was just no way that you could study something like that.”
Another long-awaited scientific milestone may soon be passed thanks to the laser. At the National Ignition Facility at Lawrence Livermore National Laboratory in California, 192 high-powered lasers, creating a several-nanosecond-long burst with a combined energy of about 500 terawatts, will be focused on a pellet of deuterium and tritium fuel, initiating—scientists hope—the world’s first controlled nuclear fusion reaction.
Lasers are also one of the main driving forces of the technology economy: in 2004 alone, well more than 700 million semiconductor diode lasers, the most common type, were sold for use in printers, CD and DVD players, supermarket barcode scanners, and many other devices.
The laser also serves at the heart of today’s broadband communications revolution, in both the military and civilian realms. “Charles Kao’s work on fiber optics, which requires laser sources, led to today’s broadband communications systems, the Internet, and the huge capacity we have for telecommunications today,” notes Hecht.
Laser applications 50 years from now seem almost beyond conjecture. Certainly lasers will be even more numerous, cheaper, and engaged in far more exotic and varied uses. A laser can pretty much be custom-made for almost any conceivable job, large or small. Just as computers have steadily increased in speed, power, and memory while dropping in size and price, lasers have benefited from a similar manifestation of Moore’s law.
And as for establishing the original inventor of the laser? Perhaps the definitive answer has already been found: in 1965 natural masers were discovered in interstellar hydrogen clouds, pumped by the light of nearby stars; in the 1970s natural lasers activated by sunlight were also found in the atmospheres of Mars and Venus.
So while Theodore Maiman certainly built humankind’s first operating laser, and despite whether it was Townes, Gould, or someone else who first came up with the idea, it doesn’t really matter. They’d already been scooped millions of years earlier. For 50 years now, humans have been merely devising and perfecting endless variations on a theme first composed by Mother Nature. The symphony continues.