7.23 Development of Lasers
249
7.23 Development of Lasers
In 1917, Albert Einstein 36 showed that stimulated emission of light was possible.
Einstein deduced that excited electronic states can be stimulated to release their
energy by light passing by. Any passing light which has about the frequency of the
light that would be released by an electron transition will stimulate that release.
However, no serious thought emerged on how to apply the idea until the 1950s.
In 1953, searching for a good source for intense microwaves near one frequency,
Charles Townes, at Columbia University, acting on an idea of Joseph Weber, at the
University of Maryland, developed the first MASER (Microwave Amplification by
the Stimulated Emission of Radiation) by ‘pumping’ excited ammonia molecules
into a microwave cavity with a resonant frequency of 24.0 GHz. 37 Townes recognized that a LASER (Light Amplification by the Stimulated Emission of Radiation)
could be built, and helped develop the technology. Theordore H. Mariman at Hughes
Research Lab in Malibu California built the first operational Laser in 1960.
By populating electronic metastable states in a material placed between two
parallel mirrors, light waves spontaneously released by a few of the excited atoms
will stimulate others, amplifying the wave. If the wave happens to be heading
perpendicular to the parallel mirrors, it will reflect back and forth, amplifying on
each pass, continuing in this manner as long as there is energy to maintain the
‘population inversion’ of the metastable states, i.e. more than half should be excited
at any one time. (See Fig. 7.20.)
Fig. 7.20 Laser operation: The atom depicted as a dot, initially in a metastable excited state, is
stimulated to emit light by a passing wave at just the emitting wavelength. The device shown
has waves reflected back and forth between two parallel mirrors, with the mirror on the left only
partially reflecting, letting some waves pass through
36 A. Einstein, The Quantum Theory of Radiation Phys Zeits 18, 121–128 (1917).
37 J. Gordon, H. Zeiger, C. Townes, The Maser—A New Type of Microwave Amplifier, Frequency
Standard, and Spectrometer, Phys Rev 99:4, 1264–1274 (1955).
249
7.23 Development of Lasers
In 1917, Albert Einstein 36 showed that stimulated emission of light was possible.
Einstein deduced that excited electronic states can be stimulated to release their
energy by light passing by. Any passing light which has about the frequency of the
light that would be released by an electron transition will stimulate that release.
However, no serious thought emerged on how to apply the idea until the 1950s.
In 1953, searching for a good source for intense microwaves near one frequency,
Charles Townes, at Columbia University, acting on an idea of Joseph Weber, at the
University of Maryland, developed the first MASER (Microwave Amplification by
the Stimulated Emission of Radiation) by ‘pumping’ excited ammonia molecules
into a microwave cavity with a resonant frequency of 24.0 GHz. 37 Townes recognized that a LASER (Light Amplification by the Stimulated Emission of Radiation)
could be built, and helped develop the technology. Theordore H. Mariman at Hughes
Research Lab in Malibu California built the first operational Laser in 1960.
By populating electronic metastable states in a material placed between two
parallel mirrors, light waves spontaneously released by a few of the excited atoms
will stimulate others, amplifying the wave. If the wave happens to be heading
perpendicular to the parallel mirrors, it will reflect back and forth, amplifying on
each pass, continuing in this manner as long as there is energy to maintain the
‘population inversion’ of the metastable states, i.e. more than half should be excited
at any one time. (See Fig. 7.20.)
Fig. 7.20 Laser operation: The atom depicted as a dot, initially in a metastable excited state, is
stimulated to emit light by a passing wave at just the emitting wavelength. The device shown
has waves reflected back and forth between two parallel mirrors, with the mirror on the left only
partially reflecting, letting some waves pass through
36 A. Einstein, The Quantum Theory of Radiation Phys Zeits 18, 121–128 (1917).
37 J. Gordon, H. Zeiger, C. Townes, The Maser—A New Type of Microwave Amplifier, Frequency
Standard, and Spectrometer, Phys Rev 99:4, 1264–1274 (1955).