LASERS
PRESBYTERIAN BOYS SECONDARY
SCHOOL, LEGON
GROUP WORK BY SCIENCE 24
STUDENTS ON
LASERS
TEACHER : MR. OBED ACKOM
(PASCAL)
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LASERS
A laser is an optical device for producing a very intense beam of coherent monochromatic
light. A laser is an amplifier of light.
The word LASER is an acronym for Light Amplification by the Stimulated Emission of
Radiation.
"Light amplification" means that the ‘lingir’ is strengthened, or given more energy -
Stimulated emission" means that the atoms emit light when exposed to radiation.
A laser converts input energy (usually electrical) into a very concentrated beam of light. A
laser is therefore a device that produces a special kind of concentrated light energy.
A laser works on the principle of stimulated emission of radiation from a system of atoms.
Electricity is made to pass through a gas and the gas glows. This is because the atoms of the
gas get excited because of the energy they absorb. The excited atoms later de-excite by
giving off energy in the form of a light wave. If this light wave hits an already excited atom
then this atom also gives out light. This is referred to as "stimulated emission". The light
emitted laser beam has been amplified and is brighter.
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LASERS
Characteristics of a Laser Beam
A laser beam has three characteristics:
1. A laser beam is monochromatic. This means that a laser beam consists of waves that
all have the same wavelength and colour.
2. The waves are coherent, or in step with each other. This means that all the crests of
the waves align with each other, as do all the troughs that is, all the waves are exactly in step
or “in phase") and all move in the same direction at the same time.
PRINCIPLE OF OPERATION OF LASERS
In a solid, liquid, or gaseous state, each atom possesses an amount of internal energy and
remains in its lowest configuration known as the ground state. The atom can move to occupy
a well-defined configuration of higher energy levels than the ground state called the excited
state.
In a lamp, for example, energy is pumped into the reacting atoms near the filament and are
said to be in an excited state. Each excited atom can drop back spontaneously to the ground
state, emitting the absorbed energy in the form of a randomly directed photon (particle of
light). The photons in the emitted stream have no particular phase relationship so they are
incoherent, and vary in phase.
Under some circumstances, an atom in an excited state can be stimulated to drop to a lower
energy state when hit by a photon.
When the atom drops to the lower energy state, a photon identical to the incident photon is
released.
If the near-by atoms are also in an excited state, a chain reaction will be set off, with released
photons going on to stimulate the release of even more photons. This process where the
excited atoms are triggered into photon emission by the presence of electromagnetic radiation
(light) is known as stimulated emission. In this process all the photons will be identical, or
coherent, meaning they will have the same wavelength, phase, polarization, and direction of
travel. If the chain reaction can be maintained, a beam of laser light is obtained.
TYPES OF LASERS
Lasers are generally classified according to the material called the medium they use to
produce the laser light; gas, solid state, liquid, semi-conductor and free electrons are all
common types of lasers.
The Gas Laser
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LASERS
In the gas laser, light is amplified or made brighter each time it passes through a special
crystal or gas which is stimulated into producing more light of the same colour by passing
through a gas-filled tube with highly reflective mirrors facing inward at each end. As the
photon bounces between the two parallel mirrors they trigger further stimulated emission and
the light gets brighter with each passage through the excited atoms. One of the mirrors is
partially silvered, allowing a small amount of light to pass through, rather than reflecting it
all. The escaped light forms the laser beam.
Solid State Laser
Solid state lasers produce light by means of a solid medium. The most common solid laser
media are rods of ruby crystals and neodymium-doped glasses and crystals (Fig. 34.8). Solid-
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LASERS
state laser offers the highest power output. They are usually pulsed to generate a very brief
burst of light. They are useful for studying physical phenomena of very brief duration.
Liquid Lasers
The most common liquid laser media are inorganic dyes contained in glass vessels. They are
pumped by intense flash lamps in a pulse or by a separate gas laser in the continuous wave
mode. Some dye lasers are tunable, meaning that the colour of the laser light they emit can be
adjusted with the help of a prism located inside the laser cavity.
Semi-conductor Lasers
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LASERS
They are the most compact lasers. It consists of gallium arsenide. One layer is treated with an
impurity whose atoms provide an extra electron and the other with an impurity whose atoms
are one electron short. Semi-conductor lasers are pumped by the direct application of electric
current across the junction. They can be operated in the continuous wave mode with better
than 50% efficiency. Only a small percentage of the energy used to excite most other lasers is
converted into light. Scientists have developed extremely tiny semi-conductor lasers, called
quantum-dot vertical-cavity surface-emitting lasers. These lasers are so tiny that more than a
million of them can fit on a chip, the size of a fingernail. Semi-conductor lasers are used in
compact disc (CD) players and form the heart of fibre optics communication systems.
APPLICATION OF LASERS
- In Industry
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LASERS
Powerful laser beam can be focused on a small spot to generate enormous temperatures.
Consequently. the focused beams can readily and precisely heat, melt, or vaporize materials.
Lasers have been used, for example, to drill holes in diamonds, to shape machine tools, to
trim microelectronics, to cut fashion patterns to synthesize new material, and the attempt to
induce controlled nuclear fusion. Laser light is used by surveyors to measure distances and to
guarantee that segments of bridges and tunnels are in line.
Lasers are used in the entertainment industry and are often used in light shows.
- Barcode scanners
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LASERS
Supermarket scanners typically use helium-neon lasers to scan the universal barcodes to
identify products. The laser beam bounces off a rotating mirror and scans the code, sending a
modulated beam to a light detector and then to a computer which has the product information
stored.
- Scientific Research
Molecular structures of matter can be studied by measuring the scattering and colour shifts.
Lasers are used to detect certain types of air pollution.
- Range Finding
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LASERS
Scientists use lasers to make extremely accurate measurements. Lasers have been used for
precise determination (to within an inch) of the distance between the Earth and the moon.
Scientists have used laser to determine the speed of light to an unprecedented accuracy.
- Communications
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LASERS
Laser light is used in communications. Laser light can travel a large distance in outer space
with little reduction in signal strength. High-energy laser light can carry 1000 times the
television channels today carried by microwaves. Lasers are therefore ideal for space
communications. Low-loss optical fibres have been developed to transmit laser light for
earthbound communication in telephones and computer systems. Lasers are used to play
audio CDs and video discs.
- Medicine
Lasers have a wide range of medical uses. Intense narrow beams of laser light can cut certain
body tissues (tumours, especially of the brain and spinal cord) in a small fraction of a second
without damaging surrounding healthy tissues. Lasers have been used to "weld" the retina
(Fig. 34.9), bore holes in the skull, vaporize lesions and cauterize blood vessels. It is also
used in surgery for eye disorders.
LASER SAFETY
Because the eye focuses laser light just as it does to other light, the chief danger in working
with lasers is eye damage. Therefore, laser light should not be viewed either directly or when
reflected. Lasers have been divided into groups depending on their power output, their
emission duration and the energy of the photons they emit. The classification is: the higher
the laser's energy, the higher its potential to injure.
High-powered lasers generate a beam of energy that can start fires, burn flesh and cause
permanent eye damage whether the light is direct, reflected, or diffused.
Goggles blocking the specific colour of photons that a laser produces are mandatory for the
safe use of
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lasers. Even with goggles, direct exposure to laser light should be avoided.
GROUP MEMBERS
1. Ethan Nartey
2. Joseph Amankwah
3. Gati Wilberforce
4. Kweku Adotey Appiah
5. Enam Cobblah
6. Benjamin Cameron Appiahene
7. Daniel Ekpale
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LASERS
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