CBSE Class XII, First Year Engineering Lasers

1. Light Amplification by
Stimulated Emission
of Radiation (LASER)
Made By :- Pranav Ghildiyal
Class :- XI B

2. Light Amplification by Stimulated Emission of Radiation LASER’S
What Are Lasers ?
LASER stands for Light Amplification by Stimulated Emission of Radiation. A laser is a device that
produces narrow intense beams of monochromatic coherent light known as laser beams. The emitted beam is nearly
perfect plane wave. These are only of one colour, there are mainly five types of lasers namely Solid-state, Gas Lasers,
Excimer lasers, Dye lasers, Semiconductor lasers. Although today lasers find hundreds of uses like but there many
hazards of laser like damaging of retina, skin burns etc.
How do lasers work ?
A laser generates a light that is rigorously of one colour. Electrons have a property, after being excited
or energized to a higher than normal state they will eventually fall back to their original state. The energy that
they had at that higher level leaks away as light of a specific colour. If we excite a lot of electrons they leak off a
lot of light all of one colour. We can do this a number of ways. A very simple way is to take material that has the
right electrons and flash a strong light on it. The electrons in that material will absorb the energy and spit it back
out as a single colour light. Laser light does not scatter very much thus usually we cannot see it until it hits
something.
In simple language working of laser can be understood by the illustration given below :-
High-voltage electricity causes the quartz flash tube to emit an intense
burst of light, exciting some of the atoms in the ruby crystal to higher
energy levels.
At a specific energy level, some atoms emit particles of light called photons. At
first the photons are emitted in all directions. Photons from one atom stimulate
emission of photons from other atoms and the light intensity is rapidly
amplified.
Mirrors at each end reflect the photons back and forth, continuing this process
of stimulated emission and amplification.
The photons leave through the partially silvered mirror at one end. This is laser
light.
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3. Light Amplification by Stimulated Emission of Radiation LASER’S
How were lasers invented ?
In 1957, a Columbia University student named Gordon Gould designed the first laser device. His mentor, Charles
Townes, had designed and built a device called the maser, which used microwaves, rather than light, to produce a
coherent beam of electromagnetic radiation. Townes' had also designed an optical maser, and thus many people have
credited him with the invention of the laser as well. Gould began a patent war, which lasted until 1977, when he finally
won his first laser patent.
Preceder of laser :- Maser
A maser is a device that produces coherent electromagnetic waves through amplification by stimulated emission.
Historically, the word "maser" is derived from the original upper-case acronym MASER, which stands for "Microwave
Amplification by Stimulated Emission of Radiation". The lower-case usage arose from technological development
having rendered the original definition imprecise, because contemporary masers emit electromagnetic waves not just
at microwave frequencies, but rather across a broader band of the electromagnetic spectrum. Hence, the physicist
Charles H. Townes suggested the usage using "molecular" to replace "microwave" for contemporary linguistic
accuracy.
When the coherent optical oscillator was first imagined in 1957, it was originally called the "optical maser." However,
this was ultimately changed to laser for "Light Amplification by Stimulated Emission of Radiation." Gordon Gould is
credited with creating this acronym in 1957.
Types of lasers
There are many different types of lasers. The laser medium can be a solid, gas, liquid or semiconductor. Lasers are
commonly designated by the type of lasing material employed:
• Solid-state lasers :- These have lasing material distributed in a solid matrix (such as ruby). The
neodymium-Yag laser emits infrared light at 1,064 nano-meters (nm).
• Gas lasers :- These (helium and helium-neon are the most common gas lasers) have a primary output of
visible red light. CO2 lasers emit energy in the far-infrared, and are used for cutting hard materials.
• Excimer lasers :- These (the name is derived from the terms excited and dimers) use reactive gases,
such as chlorine and fluorine, mixed with inert gases such as argon, krypton or xenon. When electrically
stimulated, a pseudo molecule (dimer) is produced. When lased, the dimer produces light in the ultraviolet
range.
• Dye lasers :- These use complex organic dyes, such as rhodamine 6G, in liquid solution or suspension as
lasing media. They are tunable over a broad range of wavelengths.
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4. Light Amplification by Stimulated Emission of Radiation LASER’S
• Semiconductor lasers :- These sometimes called diode lasers, are not solid-state lasers. These
electronic devices are generally very small and use low power. They may be built into larger arrays, such as the
writing source in some laser printers or CD players.
• Chemical lasers :- These are powered by a chemical reaction permitting a large amount of energy to
be released quickly. Such very high power lasers are especially of interest to the military, however continuous
wave chemical lasers at very high power levels, fed by streams of gasses, have been developed and have some
industrial applications. As examples, in the Hydrogen fluoride laser (2700–2900 nm) and the Deuterium
fluoride laser (3800 nm) the reaction is the combination of hydrogen or deuterium gas with combustion
products of ethylene in nitrogen trifluoride.
• Free electron lasers:- These generate coherent, high power radiation, that is widely tunable,
currently ranging in wavelength from microwaves, through terahertz radiation and infrared, to the visible
spectrum, to soft X-rays. They have the widest frequency range of any laser type. While FEL beams share the
same optical traits as other lasers, such as coherent radiation, FEL operation is quite different. Unlike gas,
liquid, or solid-state lasers, which rely on bound atomic or molecular states, FELs use a relativistic electron
beam as the lasing medium, hence the term free electron.
Uses of laser
1. In medicine
 To break up gallstones and kidney stones,
 To weld broken tissue (e.g. Detached retina),
 To remove plaque clogging human arteries,
 Bloodless surgery,
 Laser healing,
 Surgical treatment,
 Kidney stone treatment,
 Eye,
 Dentistry.
2. In industries
 To drill tiny holes in hard materials,
 For welding and machining.
3. In everyday life
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5. Light Amplification by Stimulated Emission of Radiation LASER’S
 As bar-code readers,
 In compact disc players,
 To produce short pulses of light used in digital communications.
4. In holography
Holography is the production of holograms by the use of laser. A hologram is a 3D image recorded in a
special photographic plate. The image appears to float in space and to move when the viewer moves.
5. Other Uses
 Law enforcement: - used for latent fingerprint detection in the identification field.
 Research:- Spectroscopy, laser ablation, laser annealing, laser scattering, LIDAR, laser capture micro
dissection, fluorescence microscopy.
 Laser lighting displays: - Laser light shows.
 In communication :- Lasers are used to send signals over long distances through optical fibres. They
allow sending of thousands of signals at the time due to narrow band width.
 In measuring long distances: - Being highly coherent these can travel long distances without any loss
their intensity e.g. to measure distance of moon.
Hazards of laser
• Eye: Acute exposure of the eye to lasers of certain wavelengths and power can cause corneal or retinal burns
(or both). Chronic exposure to excessive levels may cause corneal or lenticular opacities (cataracts) or retinal
injury.
• Skin: Acute exposure to high levels of optical radiation may cause skin burns; while carcinogenesis may occur
for ultraviolet wavelengths (290-320 nm).
• Chemical: Some lasers require hazardous or toxic substances to operate (i.e., chemical dye, Excimer lasers).
• Electrical: Most lasers utilize high voltages that can be lethal.
• Fire: The solvents used in dye lasers are flammable. High voltage pulse or flash lamps may cause ignition.
Flammable materials may be ignited by direct beams or specular reflections from high power continuous wave
(CW) infrared lasers.
Properties of laser beam
• A laser beam is a powerful, narrow, monochromatic and directional beam of electromagnetic radiation.A laser
device excites the atoms in a lasing medium. The electrons of these atoms move to a higher orbit, then release
photons, creating a laser beam.
• The emitted beam is nearly perfect plane wave.
• Laser light is concentrated in a narrow range of wavelengths (Mono chromaticity)
• All the emitted photons bear a constant phase relationship with each other in both time and phase
(Coherence)
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6. Light Amplification by Stimulated Emission of Radiation LASER’S
• Laser light is usually low in divergence(Directionality)
• Light possesses high radiant power per unit area (High Irradiance)
Safety
Warning symbol for lasers Laser warning label
Even the first laser was recognized as being potentially dangerous. Theodore Maiman characterized the first
laser as having a power of one "Gillette" as it could burn through one Gillette razor blade. Today, it is accepted that
even low-power lasers with only a few milliwatts of output power can be hazardous to human eyesight, when the
beam from such a laser hits the eye directly or after reflection from a shiny surface. At wavelengths which
the cornea and the lens can focus well, the coherence and low divergence of laser light means that it can be focused
by the eye into an extremely small spot on the retina, resulting in localized burning and permanent damage in seconds
or even less time.
Lasers are usually labelled with a safety class number, which identifies how dangerous the laser is:
• Class 1→ Is inherently safe, usually because the light is contained in an enclosure, for example in CD players.
• Class 2 → Is safe during normal use; the blink reflex of the eye will prevent damage. Usually up to 1 mW power,
for example laser pointers.
• Class 3R→ Lasers are usually up to 5 mW and involve a small risk of eye damage within the time of the blink
reflex. Staring into such a beam for several seconds is likely to cause damage to a spot on the retina.
• Class 3B → Can cause immediate eye damage upon exposure.
• Class 4 →Lasers can burn skin, and in some cases, even scattered light can cause eye and/or skin damage. Many
industrial and scientific lasers are in this class.
Infrared lasers with wavelengths beyond about 1.4 micrometres are often referred to as "eye-safe", because the
cornea strongly absorbs light at these wavelengths, protecting the retina from damage. The label "eye-safe" can be
misleading, however, as it only applies to relatively low power continuous wave beams; a high power or Q-
switched laser at these wavelengths can burn the cornea, causing severe eye damage, and even moderate power
lasers can injure the eye.
An important real life application of laser:- in medical field
Different kinds of lasers have different uses when it comes to the field of medicine, the convenience and ease that
these gadgets provide are a definite leap when it comes to the advancement of healing, surgery and cure.
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7. Light Amplification by Stimulated Emission of Radiation LASER’S
A common incorrect notion is that basic high power green lasers have the application for healing or treating small cuts
and notch. The fact is, if the laser is powerful enough, the only thing it can do is cauterize if not bum it, this actually
reduces the possibility of infection but when it bums the area, there could be more harm than good that it can do.
Now another wonder in the field of lasers is that infrared laser pointers provide advancement in the treatment of soft
tissue injuries like bruises and strains which can be called bio-stimulation. With bio-stimulation, infrared lasers are able
to penetrate below the skin and vitalize cells which enhances the process of microcirculation, inflammation, immune
response and reduction of pain.
These are few of the new breakthroughs that has touched the field of lasers:
 Surgery: Back in the day, when the word surgery is mentioned, the first thing that comes into mind is the
shiny stainless blade cutting through the skin, but nowadays lasers provide a bloodless and germ free wound
when it penetrates through the skin. The total and highly accepted of lasers in surgery is that it dramatically
reduces if not irradicates the risk for infection thus speeding up the process of healing.
 Tattoo Removal: There was a time when the average joe who would have his tattoo removed would suffer
the scarring and loss of the skin's integrity. Thanks to the new technology that these lasers provide, pulsed
versions provide short but intense burst of lights through the skin that goes to the pigment of the tattoo. In
the process the pigment is broken down and removed naturally through the use of the body's immune system.
Tattoo removal has never been these easy, it removes the tediousness of the process and better yet, you
would know that when you decide to remove or change your tattoo, your skin would stay scar-free, intact and
healthy.
 Acne: Pimples or acne is 30% fat in composition, therefore when fat is removed, there is a big possibility of
acne reduction. Lasers can break down the specific chemical bonds in the fat that is found in acne, these
process allows the body to absorb that fat that has been broken down.
 Cancer: Although a lot of controversy has risen when it comes to the benefits of lasers, doctors and medical
practitioners alike claimed the many significant progress that lasers contribute to the treatment of cancer
specially in areas where conventional medicine and methods have proven futile. As of the moment researches
has yet to be explored to further support the claims of benefit that these lasers provide.
Bibliography
www.google.com
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8. Light Amplification by Stimulated Emission of Radiation LASER’S
www.wikipedia .com
www.Answers.com
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