action, recalls Colin Webb, who worked
with Gordon.
Bennett made a long-pulse argon
laser, and when he described it at a New
York conference, he said CW operation
would require impossible amounts of
power. Gordon, who was in the audience,
stood up to announce that Bell had made
its own argon-ion laser pulsed with a
one-in-three duty cycle. “We switch it
on in the morning and switch it off at
night,” he said. Bridges then used the
Bell design with a larger power supply to
generate 80-m W CW from krypton and
xenon at Hughes.
The argon laser was off and running.
However, commercial development was
a challenge for an ion laser with transitions so far above the ground state that
only about 0.05 percent of the input
energy emerges in the beam. Jarrett,
who developed a segmented graphite
bore for a white-light krypton-ion laser
as a co-founder of Coherent, recalled
that initial tests were discouraging:
“There were signs of erosion and graphite
powder everywhere: The disks looked
like nothing so much as burned barbecue briquettes.” Indeed, the graphite had
burned, because it hadn’t been degassed
properly, but that was solved by induction heating in a high vacuum.
The brightness of ion lasers at visible
wavelengths earned ion lasers some
important applications, but their tough
design requirements caused problems. At
Hughes, Bridges developed argon lasers
for an Air Force night reconnaissance
system; the results were good, but it
never went into production because the
cooling system didn’t meet requirements
for installation in military planes.
Eye surgeon Francis L’Esperance
ran into a different problem when he
ordered one of the first commercial
argon lasers from Raytheon. At more
than two meters in length, it was too big
to fit into the elevators at the Columbia-Presbyterian Medical Center in New
York. They hired a rigger to hoist the
massive laser through a window, but he
dropped it. When Raytheon shipped a
A giant 1.5-k W carbon-dioxide laser built by Hughes Research Laboratories, sitting on top of big sheets of plywood. Courtesy of Bill Bridges
replacement, L’Esperance paid $25 to
a nearby crane operator, who slipped
it flawlessly inside, where the surgeon
used it to develop a laser treatment that
has preserved the vision of millions of
people with diabetic retinopathy.
Metal vapor lasers
The helium-mercury laser also inspired
the discovery of other metal-vapor
lasers by Fowles and Silfvast at Utah.
They first tried to make a bismuth laser
to study hyperfine structure, which is
particularly strong in the heavy metal.
Silfvast developed a simple quartz tube
apparatus to vaporize bismuth and test
the vapor for pulsed laser action, but he
grew discouraged after a few months of
tests found no laser lines. In early 1965,
he decided to try zinc and cadmium,
which looked like good laser prospects
because of their electron configurations.
He tried zinc first. “The very first
time I turned it on I got this turquoise,
blue-green transition at 492.4 nm to
lase,” he recalled. Overjoyed, he hunted
