which could reach up to 99 percent reflectivity, but that was
barely enough—and the coatings would have to be exposed to
the laser discharge. Further problems came from the need to
align the two flat mirrors forming the Fabry-Pérot resonator
without a laser interferometer to assure their parallelism.
Javan and Bennett worked long hours on gas-discharge
physics and enlisted the help of Donald Herriott, one of Bell’s
few in-house optics experts, who had worked with multilayer
coatings at Bausch & Lomb. Progress was slow because they
wanted to measure gain before trying to demonstrate oscillation. Experimental malfunctions caused further delays.
Javan thought that microwave frequencies of 2 to 4 GHz
would excite the gas more efficiently than the 10-MHz radio
source used in their gain experiments, but the microwaves
melted the laser tube. When they tried baking out impurities
in a tube with their best mirrors installed, the heat destroyed
the reflective coatings. Department head Al Clogston assured
upper management that progress was being made.
Bennett, Herriot and Javan mounted their second-best
mirrors on an 80-cm tube and tried a milder bake-out process.
Although the mirrors showed crazing, they remained intact.
On December 13, 1960, they filled the tube with a helium-neon mixture and fired up the discharge. Having seen no sign
of lasing by 4 p.m., they stopped, discouraged, and discussed
what to do next. As Herriott fiddled with a mirror, Javan spotted
something new on their oscilloscope. They had finally hit the
sweet spot and generated a beam. Bennett later estimated that
Bell Labs had spent a million dollars on instrumentation and
equipment. It was the kind of project that, as Bloembergen had
foreseen, was beyond the reach of any university laboratory.
Bell colleagues also contributed new ideas. Gary Boyd and
Jim Gordon showed that curved cavity mirrors could make
stable resonators that greatly relaxed mirror alignment requirements, easing development of low-gain lasers. Alan White and
Dane Rigden of Bell’s exploratory development group built
an enhanced copy of the original 1.15-µm helium-neon laser
for the Army Signal Corps, then demon-
strated laser action on the now-standard
632.8-nm helium-neon line in 1962.
Peter Sorokin (left) and Mirek
Stevenson at IBM, adjusting
their uranium laser.
Courtesy of IBM
microwave resonances in solids but switched to optically-pumped solid-state lasers after they saw the Schawlow-Townes paper.
Expecting low gain, Sorokin devised a square resonator
based on total internal reflection to avoid losses. They chose
calcium fluoride as a host material because its refractive index
was just above the square root of two; thus, it would have total
internal reflection at a 45° angle. They dug through the literature to identify uranium and samarium as suitable light emitting ions. The crystals were custom-grown, cut into squares,
and polished. When they heard the news about Maiman’s
laser, they were stunned.
They quickly ordered their own flashlamps and had spare
crystals cut and polished into rods. Their crystals required
cryogenic cooling to act as four-level lasers, so they put a
uranium-doped rod into a special dewar
with a window on the bottom and fired
the flashlamp. “It worked the first time,”
Sorokin recalls. “Bill Smith supported us
with anything we needed, but we didn’t
spend a lot of money.” IBM already had
much equipment, including the special
Bell Labs and the gas laser
Deep pockets and strong management
support were crucial to Bell Labs’ success
in developing the helium-neon laser.
The helium-neon system posed huge
challenges. Gain was low, so the laser
would need a long tube to develop enough
gain to offset cavity losses. The best cavity
mirrors were multilayer dielectric coatings,
Those first diode
lasers required high-current pulses and
to reach threshold.
The problem was
that they were
devices, with nothing
to keep carriers near
The dawn of diode lasers
Semiconductors were hot after the invention of the transistor, and through the
1950s, developers explored new materials, moving from the initial germanium
devices to silicon and later III-V compounds such as gallium arsenide. In early
1962, Sumner Mayburg at the General
Telephone and Electronics Laboratories
in Bayside, N. Y., and Jacques Pankove
at RCA Labs separately reported strong
recombination radiation from GaAs
junctions. But it took a report of nearly
100 percent emission efficiency from a
24 | OPN Optics & Photonics News