Technology Guide Principles – Applications – Trends - hhimawan

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Laser
Related topics
5 Optical technologies
5 Optics and information
technology
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5 Sensor systems
5 Nanobiotechnology
5 Joining and production
technologies
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medicine
Principles
Since they first appeared in 1960, lasers as a light
source have established themselves in a growing
number of applications in industry and in everyday
life. Laser light differs from other light sources, such as
light bulbs or neon lamps, by its very narrow spectral
bandwith as well as its high temporal and spatial stability
and consistency.
“Laser” stands for Light Amplification by Stimulated
Emission of Radiation, whereby radiation in this
context refers to a stream of light particles (photons).
Light amplification depends on the existence of a laseractive
medium – a material in which a discrete amount
of energy can be deposited (absorption) and subsequently
released (emission) at an atomic level. Emission
can be spontaneous, being either induced by the
medium itself, or stimulated by other photons, as is the
case for lasers. The newly generated photons have the
same properties as those already existing, in terms of
colour of light or wavelength.
The wavelength of the generated photons can be
modified according to the condition of the laser-active
medium, which can be either a gas, a liquid or a crystal
to which specific atoms have been added. This
means that each laser can typically only emit photons
within a small defined wavelength range. Since the
wavelength not only represents the colour of the light
particles but also their energy, photons of different
wavelengths also possess different amounts of energy.
Thus, light particles with a wavelength in the blue
spectral range possess greater energy than photons
with a wavelength in the red spectral range.
pumping
end mirror output mirror
laser-active
medium
laser
beam
� Laser setup: The mirrors serve to generate a light field from
identical photons by backcoupling already generated photons. To
maintain the laser beam, energy must be deposed continuously
in the laser­active medium by “pumping”.
wavelength
� Categorisation and characterisation of some laser types
Aside from the energetically loaded laser-active
medium – the crystal, liquid or gas – it is necessary to
feed back the generated photons into the medium using
a resonator, so that a resonant field of laser light
comprising a large amount of identical photons builds
up by further stimulated emission. Typically, the resonator
consists of two oppositely positioned mirrors for
each wavelength. One of the resonator mirrors is highly
reflective to laser light. The other mirror allows part of
the laser light to exit the resonator. Energy must be deposited
continuously in the laser-active medium, in a
process known as “pumping”. This ensures that sufficient
stimulated emission is generated on a continuous
basis to maintain constant laser operation. The pumping
of the laser-active medium can be accomplished in
several ways, such as generating an electrical field in
the laser-active medium or by irradiating the medium
with light.
Lasers are categorised in different ways, i. e. according
to their operating mode (continuous-wave or
pulsed) or the type of the laser-active medium (solid
state laser, gas laser, diode laser, etc.).
Continuous-wave lasers are systems that emit laser
light continuously. These systems are most easily char