LASER LIGHT

Laser is an acronym for Light Amplification by Stimulated Emission of Radiation.
The term light is used in a broad sense to include radiation at frequencies in the
infra-red, visible or ultraviolet regions of the electromagnetic wave spectrum. In
common parlance the term laser refers more to a device based on this principle
than to the principle itself. The term laser action is often used when referring to
the process. Lasers are devices that generate coherent light.
The physical principle (stimulated emission) responsible for laser action was introduced
by Albert Einstein in 1916. A device called MASER (microwave amplification
by stimulated emission of radiation) based on this principle was first operated in
the microwave regime. The laser is an extension of this principle to the visible part
of the electromagnetic spectrum.
A summary of principal developments in the field of laser follows.
1916: A. Einstein introduces stimulated emission as a fundamental process
of light-matter interaction in addition to the already known processes of absorption
and spontaneous emission of light.
1924: Richard Tolman discusses “negative absorption” i.e. amplification,
and explains that the emitted radiation would be coherent with the input
radiation.
928: Rudolph W. Landenburg confirms existence of stimulated emission.
V.A 1940: Fabrikant suggests method for producing population inversion in
his PhD thesis. Population inversion is required for maser/laser operation.
1950: Alfred Kastler suggests a method of ”optical pumping” for orientation
of paramagnetic atoms or nuclei in the ground state. This was an important
step on the way to the development of lasers for which Kastler received the
1966 Nobel Prize in Physics.
1951: Edward Purcell and Robert Pound observe inverted populations of
states in a nuclear magnetic resonance experiment. Population inversions is a
necessary condition for maser and laser action.
—bf 1952: Nikolay Basov and Alexander Prokhorov describe the principle of
the maser (Microwave Amplification by Stimulated Emission of Radiation).
1954: C. H. Townes, J. P. Gordon, and H. J. Zeiger realize the first maser
utilizing a beam of excited ammonia molecules to produce amplification of
microwaves by stimulated emission at a frequency of 24 gigahertz (GHz).
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2 Laser Physics
1958: Charles H. Townes and Arthur L. Schawlow introduce concept of the
laser.
1959: Gordon Gould introduces the term laser in a paper, ”The LASER:
Light Amplification by Stimulated Emission of Radiation”
1960: Laser action observed by T. H. Maiman in Ruby [Nature 187, 493
(1960)]. It is now known to be one of the most difficult laser systems to
operate. Sorokin and Stevenson develop first four-level solid-state laser at
IBM. Ali Javan, William Bennett, and Donald Herriott at Bell Labs develop
first helium neon (He:Ne) gas laser.
1961: Elias Snitzer reports the operation of a neodymium glass laser, currently
the prime candidate as a laser source for fusion. In the first medical use
of the laser, Charles Campbell and Charles Koester destroy a retinal tumor
with the ruby laser. In the first example of efficient nonlinear optics, P. A.
Franken, A. E. Hill, C. W. Peters and G. Weinreich demonstrate generation
of second harmonic light by passing the pulses from a ruby laser through a
quartz crystal, transforming red light into green.
1962: Scientists at Bell Labs report the first yttrium aluminum garnet (YAG)
laser, which continues to dominate material processing applications. Scientists
at General Electric, IBM, and MIT Lincoln Laboratory develop a gallium
arsenide laser that converts electrical energy directly into infrared light. F.
J. McClung and R. W. Hellwarth develop laser Q-switching technique to produces
laser pulses of short duration and high peak powers. Four groups in
the US (M. I. Nathan et al., R. N. Hall et al, T. M. Quist et al, N. Holonyak
and S. F. Bevacqua) nearly simultaneously make first semiconductor diode
lasers, which operate pulsed at liquid-nitrogen temperature. Semiconductor
diode lasers are the first important step in the development of optical communication,
optical storage, optical pumping of solid-state lasers and many
other applications.
1963: L. E. Hargrove, R. L. Fork, and M. A. Pollack report the first modelocked
operation of a laser in a helium-neon laser with an acousto-optic modulator.
Mode locking is the basis for the femtosecond pulsed laser. Herbert
Kroemer and the team of Rudolf Kazarinov and Zhores Alferov independently
propose ideas to build semiconductor lasers from heterostructure
devices, which lead to their receiving the 2000 Nobel Prize in Physics. C. K.
N. Patel develops first carbon dioxide laser at Bell Labs.
1964: C. H. Townes, N. G. Basov and A. M. Prokhorov awarded the Nobel
prize for their fundamental work in Quantum Electronics; Townes for demonstrating
the ammonia (NH3) maser and subsequent work in masers and lasers
and Basov and Prokhorov for contributing to the development masers and
lasers. William B. Bridges develops first noble gas ion laser. J. E. Geusic,
and H. M. Marcos, and L. G. Van Uitert develop neodymium-doped yttrium
Laser Light 3
aluminum garnet (Nd: YAG) laser. This is the most widely used solid state
laser; from cutting and welding to medical applications and nonlinear optics.
C. J. Koester and E. Snitzer develop neodymium-doped fiber amplification.
Fiber amplifiers are used in communication and for high power lasers. Arno
Penzias and Robert Wilson use maser amplifier to observe 3K cosmic background
radiation proving the existence of the Big Bang. They are awarded
the Nobel Prize in Physics in 1978.
1965: George C. Pimentel and Jerome V. V. Kasper demonstrate the first
chemical laser. With output currently reaching megawatt levels, chemical
lasers get their energy from chemical reactions and are some of the most
powerful lasers in the world. James Russell invents the laser compact disk
(CD player). Anthony J.DeMaria, D. A. Stetser, and H. A. Heynau report
the first generation of picosecond laser pulses using a neodymium glass laser
and a saturable absorber.
1966: Peter Sorokin and John R. Lankard built the first widely tunable organic
dye laser, now used in ultrafast science and spectroscopy. Charles K.
Kao and George Hockham of Standard Telecommunications Laboratories in
England publish landmark paper demonstrating that optical fiber can transmit
laser signals and reduce loss if the glass strands are pure enough. Alfred
Kastler is awarded the Nobel Prize in Physics ”for the discovery and development
of optical methods for studying Hertzian resonances in atoms”.
1968: NASA launches the first satellite equipped with a laser.
1969: Led on Earth by American physicist Carroll Alley and using retroreflectors
placed on the moon by Neil Armstrong and Buzz Aldrin, NASA’s
Lunar Laser Ranging experiments begin. Using these mirrors, scientists on
Earth bounce lasers off the moon, measuring its orbital motions, and in the
process determining fundamental gravitational and relativistic constants with
extraordinary precision. D. J. Spencer, T. A. Jacobs, H