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Celebrating the 50th Anniversary of the Laser:
|Key parts of 1961 ruby laser:
flashlamp and ruby rod (quarter
shown for scale).
Credit: K. Martin/NIST
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1961—Shortly after the invention of the ruby laser, Don Jennings built and operated the first ruby laser at NIST. The lasing effect was achieved with a small ruby crystal, 1/4 inch in diameter and 1 and 1/4 inches long. The ends were optically polished flat and parallel and coated with silver. The crystal was optically excited from the sides by a xenon flash lamp built by George Unger in the NIST chemistry glass shop.
|1963 ruby laser with ruby red
encased in xenon lamp.
Credit: Jan Hall
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1963—NIST scientists Don Jennings and Jan Hall designed a ruby laser that could be focused down to an intense, uniform, pinpoint beam just 20 micrometers in diameter. They used this laser to conduct one of the first nonlinear absorption experiments, using anthracene crystals. Nonlinear absorption is a process in which two particles of light (photons) are absorbed simultaneously, exciting an atom by an amount of energy equal to the sum of the two photon energies. When the crystals were excited by ruby laser light, they emitted intense blue fluorescence (a shorter wavelength of light). The revolutionary result broke Stokes Law, which held that the fluorescence wavelength was always longer than the excitation wavelength.
1965—The first quantitative and predictable "two-photon detachment" was performed by NIST scientist Jan Hall working with Lewis Branscomb using a ruby laser and a beam of negative iodine molecules. The experiment provided a clear validation of the new technique of detaching electrons from atoms using two photons of laser light. The technique has led to advances in a wide range of technology areas, from radar performance to quantum cryptography, the most secure method known for protecting the privacy of a communications channel.
Mid-1960s—NIST researchers made many groundbreaking laser-based distance measurements, which eventually led to a number of world-record measurements of the speed of light and redefinition of the meter in terms of the speed of light. The work began in the Poorman’s Relief Gold Mine in Colorado, which offered a steady temperature and a 40-meter-long straight path enabling accurate laser frequency measurements. A stable 30-meter-long vacuum interferometer was built to study the interference patterns created by light waves. This led to the invention of a way to stabilize lasers by locking them to a frequency that induced a transition between specific energy levels in molecules such as methane and iodine. In addition, the laser-based distance measurements made in the gold mine were converted by NIST researcher Judah Levine into measurements of the Earth’s movement, which turned out to be one way of supporting the detection and measurement of underground nuclear tests by the United States and Russia. Levine also obtained new data about the state of the Earth's liquid core by monitoring the stretching of the Earth produced by the tidal effects of the sun and moon.
|Jan Hall at Poorman's Relief Gold Mine.
Credit: Lindy Hall
1967—NIST provides its first calibration of laser power for an industrial customer.
Early laser pioneer Don Jennings.
1969—James Faller of NIST first suggested that astronauts place reflectors on the moon. Faller also provided the initial designs for the first reflector array and two subsequent arrays. By measuring the round-trip travel time for a laser pulse sent to the moon and reflected back (about 2.5 seconds), other scientists measured the distance between the Earth and moon to better than 2.5 cm (1 inch). Experiments with lunar laser ranging instruments are still active today and are credited with dramatically increasing understanding of Earth and moon geophysics and dynamics as well as gravitational physics.
|Reflector deployed on the
surface of the moon by the
astronauts of Apollo 14.