Charles H. Townes invented the microwave-emitting maser in
the early 1950s at Columbia University, with the help of Herbert
Zeiger and James Gordon. Masers began proliferating in the last
half of the 1950s, but even before then a few physicists were
looking at prospects for amplifying stimulated emission at wavelengths
much shorter than microwaves. In the Soviet Union, V. A. Fabrikant
and his students filed a patent application dated June 18, 1951
on amplifying electromagnetic radiation from the ultraviolet through
the radio spectrum, but their idea had little direct effect on
laser research, even in the Soviet Union. In the United States,
Robert H. Dicke developed in 1954 proposed the "optical bomb,"
in which a short excitation pulse would produce an inverted population,
which would then generate an intense burst of spontaneous emission.
In 1956, he filed a patent on using a pair of parallel mirrors,
forming a Fabry-Perot interferometer, as a resonant optical cavity.
However, the first detailed proposal for building a laser -- which
at the time they called an "optical maser" -- was published
by Townes and Arthur L. Schawlow. Schawlow had been a postdoctoral
fellow under Townes at Columbia until leaving to join Bell Labs
in 1951, and they continued working together on a book on microwave
spectroscopy, although not on masers. The two also maintained
close personal ties -- Schawlow married Townes' younger sister
-- and Townes consulted at Bell Labs. In 1957 both began thinking
about the possibility of "infrared and optical masers,"
and after discussing the idea over lunch at Bell Labs, decided
to collaborate. They spent several months working on the problem,
as described in their interviews, which led to their famous paper
"Infrared and Optical Masers," published in the December
1958 Physical Review.
That paper had a profound impact on American laser development.
Preprints circulated at Bell Labs and Columbia before the journal
came out, and formal publication was the starting gun for the
great laser race that culminated in completion of the first laser.
Not everyone realized its importance, however. Bell Labs attorneys
did not think the idea was worth patenting, and filed a patent
application only after Townes insisted. That led to U. S. Patent
No. 2,929,922, issued in 1960.
Meanwhile, similar ideas were running through the mind of a 37-year
old Columbia graduate student, Gordon Gould. At the time, Gould
was doing doctoral thesis research under Polykarp Kusch, who shared
the 1955 Nobel Prize in Physics with Willis Lamb. Gould was hardly
a typical establishment scientist of the placid 1950s. He and
his first wife joined a Marxist study group in the mid 1940s.
After the 1947 Soviet takeover of Czechoslovakia he left both
the group and his wife, but that background haunted him during
the anticommunist witch hunts of the 1950s. He had begun taking
graduate courses at Columbia while teaching at the City College
of New York, but lost that teaching job in 1954 after he refused
to identify other members of the study group to a special committee
of the New York board of higher education. That incident incensed
Kusch, who secured a research assistantship so Gould could become
a full-time graduate student.
Gould wrote down his laser ideas -- including a definition of
"laser" as Light Amplification by the Stimulated Emission
of Radiation -- in late 1957, and had them notarized by a candy
store owner named Jack Gould (no relation) in what he hoped was
the first step to getting a patent.
The path from maser to laser was far from obvious, because
of the large physical differences between microwaves and visible
light. Optical photon have thousands of times more energy, and
microwaves are thousands of times longer. Among the trickier problems
was developing a resonant cavity for laser oscillation.
Resonance occurs when a wave travels an integral number of wavelength
as it makes a round-trip of the cavity. The simplest resonant
cavity is a half-wavelength long, so a round trip equals one wavelength.
Microwaves are measured in centimeters, and microwave cavities
typically are on the order of a wavelength across, and enclosed
on all sides. Visible light has wavelengths under a micrometer,
so analogous cavities are obviously impractical.
The solution to that problem, recognized both by Townes and Schawlow
and by Gould, was an optical device known as a Fabry-Perot interferometer.
The Fabry-Perot is simply two flat mirrors mounted parallel to
each other, separated by many thousands of wavelengths. Light
bounces back and forth between them, through the laser medium,
stimulating the emission of more light. In practice, one mirror
reflects all incident light, while the other transmits some light
to form the laser beam.
The allocation of credit for "inventing" the laser concept
remains controversial. Townes and Schawlow have been widely honored
by the scientific community, separately receiving Nobel Prizes
in 1964 and 1981. Their Physical Review paper had a profound
impact, and was the single biggest event triggering many research
efforts that led to early lasers. Gould's notebooks and their
offspring -- his patent applications and proposals for research
funding -- had only minimal circulation, and essentially no impact
on most of the scientific world.
Gould made less-important but nonetheless solid contributions
in lasers and fiber optics, but by the mid-1970s he had become
almost invisible in the laser world. However, he quietly continued
pursuing his patent applications, and after a court in 1973 invalidated
a patent issued to Townes and Schawlow, he was able to secure
a series of patents on laser concepts and applications, starting
in 1977. The delay made them far more valuable, with Gould and
his legal team collecting many millions of dollars in royalties.
Publication of the Schawlow-Townes paper was the starting gun
for the race to build lasers. Some researchers, such as Townes,
Theodore Maiman, and Nicolaas Bloembergen, had worked on microwave
masers. Others, such as Peter P. Sorokin, Robert Hall, and C.
Kumar N. Patel, came from other fields of physics after becoming
intrigued with the laser concept.
Early efforts concentrated on materials whose energy-level structures
already were well-known from spectroscopic studies. Ali Javan
started working on the helium-neon gas laser at Bell Labs even
before the Schawlow-Townes paper was published. At Columbia, Townes
and two graduate students, Herman Z. Cummins and Isaac Abella,
investigated a potassium-vapor scheme discussed in the Physical
Review paper. In the Soviet Union, Basov studied semiconductors.
With a few exceptions, such as Bell Labs, most of the research
was modestly funded.
The largest research program was sponsored by the Advanced Research
Projects Agency of the Department of Defense, the agency chartered
to support risky research with high potential rewards. It had
a peculiar history. As he developed his laser ideas, Gordon Gould
realized that he could not continue pursuing both them and his
graduate work. He left Columbia to work for a small company on
Long Island, TRG Inc., and soon interested his employer in lasers.
The company used Gould's ideas as the basis for a $300,000 research
proposal to ARPA. Pentagon officials, dazzled by visions of laser
weapons, were so excited that they gave TRG a contract for $1
million. Such increases are extremely rare.
Gould, like Townes, initially concentrated on alkali metal vapors.
The generous Pentagon funding let TRG investigate many laser candidates,
but the program was ill-starred from the beginning, as Gould describes
in his interview. Security restrictions came with the military
money. Although the worst anticommunist hysteria had passed, the
Marxist skeleton in Gould's closet was enough to prevent him from
getting a security clearance. TRG scientists trying to build lasers
could consult with Gould, but they could not tell him details
about classified research. Moreover, alkali metal vapors would
prove to be very difficult to make into lasers.
Among the maser materials considered for use in lasers was
synthetic ruby, aluminum oxide doped with chromium atoms. The
chromium lines were useful in masers, and their spectroscopy was
well known. At Bell Labs, Schawlow considered ruby as a laser
material, but in 1959 he publicly dismissed it as unsuitable.
That opinion was based on inadequate data, and before long it
was proved wrong.
Meanwhile, Theodore Maiman was trying to use his knowledge of
ruby masers to make a laser at Hughes Research Laboratories in
Malibu, California. He began working with ruby because it was
well-known, at first thinking he could switch to a better material
later, when he better understood laser requirements. However,
he eventually convinced himself that Schawlow was wrong, and that
ruby would make a good laser. It could not generate a continuous
beam, but he decided pulses were good enough to demonstrate laser
action. As he relates in his interview, he forged ahead, working
alone, while Hughes management grew skeptical. By the time he
succeeded in making the ruby laser work for the first time, on
May 16, 1960, he was not supposed to be working on the program.
Maiman's laser, was small and elegant: a ruby rod, with its ends
silvered to reflect light, which he placed inside a spring-shaped
flashlamp. His success is undisputed, but he almost immediately
ran into problems. The then-new Physical Review Letters
summarily rejected his report of making an "optical maser"
as "just another maser paper." The journal's founding
editor Samuel Goudsmit, a theoretician best known as the co-discoverer
of electron spin, had grown tired of the glut of maser papers
arriving at his office, and decided that they no longer merited
rapid publication in his journal. Moreover, the journal had just
published another paper by Maiman on the spectroscopy of ruby
-- work that led to his laser demonstration.
Hughes management reacted enthusiastically once the laser worked,
and sponsored a full-fledged press announcement in early July.
However, the public-relations photographer commissioned to immortalize
the first laser on film wasn't satisfied with it. He thought the
device was too small, and insisted that Maiman pose with a bigger
flashlamp and ruby rod. Today Hughes is still distributing those
pictures, showing Maiman with what isn't really the first ruby
laser.
Maiman hurriedly prepared a concise 300-word report which was
immediately accepted by the British weekly Nature. When
efforts to convince Goudsmit of his error failed, the Nature
paper, published August 6, 1960, became the first report of
a working laser. Maiman later published a more detailed analysis
in Physical Review.
In their interviews, some laser pioneers recall when and how they
heard the news of Maiman's laser. Other laboratories soon made
their own ruby lasers -- although some used the flashlamp shown
in the press release, rather than the one Maiman actually used.
Schawlow's group at Bell Labs was among the first to get one working,
but theirs was considerably larger than Maiman's. Soon afterwards,
laser action on slightly different lines in "dark" or
"red" ruby, which has a higher concentration of chromium
ions than in the "pink" ruby used by Maiman, was reported
by Bell Labs and another group at Westinghouse in Physical
Review Letters.
Although Maiman had beat everyone else hands down in the great
laser race, Townes, Basov and Aleksandr Prokhorov received the
1964 Nobel Prize for their work on laser theory. Understandably
annoyed, Maiman points out that none of the theorists were able
to make a working laser before he did. However, he has received
the Japan Prize and been inducted into the National Inventors'
Hall of Fame.
of laser history, a bibliography, and interviews or profiles of Charles Townes,
Arthur Schawlow, Nicolaas Bloembergen, Gordon Gould, Theodore Maiman, Peter
Sorokin, Ali Javan, Robert Hall, C. Kumar N. Patel, William Bridges, William
Silfvast, James J. Ewing, John Madey, and Dennis Matthews. Order ISBN 0-12-336030-7
from your bookstore,