This year is the 50th anniversary of the laser, a device used in applications from performing precise surgical procedures to measuring gravitational waves. In 1917, Albert Einstein proposed that a photon hitting an atom in a high energy state would cause the atom to release a second photon identical in frequency and direction to the first. In the 1950s, scientists searched for a way to achieve this stimulated emission and amplify it so that a group of excited atoms would release photons in a chain reaction. In 1959, American physicist Gordon Gould publicly used the term “light amplification by stimulated emission of radiation” for the first time. A year later, scientists demonstrated the first working optical laser.
Shortly after its demonstration, Bell Labs researchers invented the gas laser (above, with Ali Javan, one of the inventors). The first gas laser used an electric current to excite helium and neon atoms, producing a continuous beam of light.
In 1954, Charles H. Townes, James P. Gordon (both above), and Herbert J. Zeiger built the precursor to the laser—the maser, which emits microwaves instead of visible light.
Their device used excited ammonia molecules to amplify the energy. Hydrogen masers (above) are still used for atomic clocks, because the microwave pulses emitted by hydrogen gas are extremely regular.
Soon after Maiman’s demonstration, scientists proposed inducing nuclear fusion by concentrating laser beams on a tiny capsule of fuel to set off an atomic chain reaction, mimicking the conditions inside the sun. The resulting energy could be used in weapons or as a power source. The University of Rochester’s Laboratory for Laser Energetics was one of the first facilities to explore using lasers, such as this one from 1972, for fusion energy.
The Nova laser at Lawrence Livermore National Laboratory in California, completed in 1984, was the world’s largest working laser until its retirement in 1999. With 10 laser beams, it was used for experiments on x-rays, astronomical phenomena, and fusion energy. In 1996, it was made into a petawatt laser, in which a short, intense pulse produced the highest power yet achieved: about 1.3 petawatts, or 1.3 quadrillion watts.
Nova’s parts have been used in other lasers, such as the petawatt laser at the University of Texas at Austin; said to be the most powerful working laser, it produces about 1.1 petawatts. Above, at UT Austin, an infrared beam and a green amplifying beam zigzag back and forth across a table. The infrared beam then travels through amplifiers (blue) recycled from Nova.
The Laser Interferometer Gravitational-¬Wave Observatory comprises two observatories, in Louisiana (above) and Washington, that are seeking the first direct evidence of gravitational waves—distortions in the curve of space-time. At each, a laser beam is split into two beams that travel back and forth along 2.5-mile mirrored arms many times before recombining. A gravitational wave would distort the space inside the arms by less than a thousandth the diameter of an atomic nucleus, forcing the beams slightly out of sync.
Researchers at the University of California, Berkeley, have created the smallest semiconducting laser, which could eventually be used for optical computing. A cadmium sulfide wire 50 nanometers in diameter generates visible light and holds it in a five-nanometer space.
The first laser, demonstrated by Theodore Maiman at the Hughes Research Laboratories, was a ruby crystal rod with mirrored ends, resting in the center of a coiled quartz flash tube. The tube lamp flashed an intense white light, which energized chromium atoms in the ruby. As the atoms lost energy, released photons bounced between the mirrors, stimulating more atoms, before finally escaping out of one end of the rod in short pulses of red light.