lasers SOLID STATE LASERS .

INSTITUTE OF
SCIENCE
DEPARTMENT OF CHEMISTRY
Name – Sana shaikh
Roll no – 3
Sub – Physical Chemistry (P-3)
Topic – Solid State Lasers

LASER
 The acronym laser stands for "light
amplification by stimulated emission of
radiation.“
 A laser is a coherent and focused beam
of photons; coherent, in this context, means
that it is all one wavelength, unlike ordinary
light which showers on us in many
wavelengths.

HOW IS LASER PRODUCED?
 Light is emitted in the form of tiny package called
‘quanta’/photon.
 Each photon has a characteristic frequency and
its energy is proportional to its frequency.
 Three basic ways for photons and atoms to
interact:
 Absorption .
 Spontaneous Emission .
 Stimulated Emission.

COMMON COMPONENTS OF
ALL LASERS.
Active Medium -
 The active medium may be solid crystals such as ruby or Nd:YAG,
liquid dyes, gases like CO2 or Helium/Neon, or semiconductors
such as GaAs. Active mediums contain atoms whose electrons may
be excited to a metastable energy level by an energy source.
Excitation Mechanism -
 Excitation mechanisms pump energy into the active medium by one
or more of three basic methods; optical, electrical or chemical.
High Reflectance Mirror-
 A mirror which reflects essentially 100% of the laser Partially
Transmissive Mirror
 A mirror which reflects less than 100% of the laser light and
transmits the remainder.

Characteristics & application
 Laser radiation has five striking characteristics each of them opens up
interesting opportunities in spectroscopy, giving rise to ‘laser spectroscopy’.

SOLID STATE LASER
 A solid-state laser is a laser that uses a gain
medium that is a solid, rather than
a liquid such as in dye lasers or a gas as
in gas lasers.
 Semiconductor-based lasers are also in the
solid state, but are generally considered as a
separate class from solid-state lasers .

 The active medium of a solid-state laser consists of
a glass or crystalline "host" material to which is added a "dopant"
[ neodymium, chromium, erbium ,thulium or ytterbium]
 Many of the common dopants are rare earth elements, because the
excited states of such ions are not strongly coupled with the thermal
vibrations of their crystal lattices (phonons), and their operational
thresholds can be reached at relatively low intensities of laser
pumping

CONSTRUCTION
 A laser is constructed from three principal
parts:
 An energy source (usually referred to as
the pump or pump source),
 A gain medium or laser medium, and
 Two or more mirrors that form an optical
resonator.

 PUMP SOURCE
 1. The pump source is the part that provides
energy to the laser system.
2. Examples of pump sources include electrical
discharges, flashlamps, arc lamps, light from
another laser, chemical reactions and even
explosive devices.
3. The type of pump source used principally
depends on the gain medium, and this also
determines how the energy is transmitted to the
medium.

 GAIN MEDIUM
1. The gain medium is the major determining factor of the
wavelength of operation, and other properties, of the laser.
2. Gain media in different materials have linear spectra or wide
spectra.
3. Gain media with wide spectra allow tuning of the laser
frequency.
4. The gain medium is excited by the pump source to produce
a population inversion, and it is in the gain medium that
spontaneous and stimulated emission of photons takes place,
leading to the phenomenon of optical gain, or amplification.

 OPTICAL RESONATOR
 1. The optical resonator, or optical cavity, in its simplest form is two parallel
mirrors placed around the gain medium which provide feedback of the light.
2. The mirrors are given optical coatings which determine their reflective
properties.
3. Typically one will be a high reflector, and the other will be a partial reflector.
4. The latter is called the output coupler, because it allows some of the light to
leave the cavity to produce the laser's output beam.
5. Some lasers do not use an optical cavity, but instead rely on very high optical
gain to produce significant amplified spontaneous emission(ASE) without
needing feedback of the light back into the gain medium , Such lasers are said
to be superluminescent, and emit light with low coherence but high bandwidth.

Solid state lasers
 Ruby laser.
 The first laser, one that is still
used.
 Ruby is synthetic aluminum
oxide, Al2O3, with 0.03 to
0.05% of chromium oxide,
Cr2O3, added to it. The Cr3+
ions are the active ingredient;
the aluminum and oxygen
atoms are inert.
 Pumping is by light from a
xenon flash tube.

Solid state lasers •
 Neodymium: YAG laser. •
The active ingredient is
trivalent neodymium, Nd3
added to an yttrium
aluminum garnet, YAG,
Y3Al5O12.
 The Nd-YAG laser has a
vary high radiant power
outpt at 1064nm.

ADVANTAGES AND DISADVANTAGES.
 ADVANTAGES
1. No chance is of wasting material in the active
medium because here material used is in the form
of solid.
2. construction of solid state laser is
comparatively simple.
3. cost of solid state laser is economical.
 DISADVANTAGES
1. output power is not very high as in CO2 laser.
2. efficiency of solid state laser is less compared
to CO2 laser.

APPLICATIONS
 Nd:YAG solid state lasers are usually used
when drilling holes in metals.
 Nd:YAG pulsed type solid state lasers can
be used in medical applications such as
endoscopy.
 As military applications, Nd:YAG is used to
target destination system.

REFERENCES
 Physical Chemistry by P. W. Atkins.
 Molecular Structure and Spectroscopy by G.
Aruldhas.

lasers SOLID STATE LASERS .

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