Laser is a device that stimulates atoms or molecules to emit light at particular wavelengths and amplifies that light, typically producing a very narrow beam of radiation. Lasers work through three interactions with atoms: absorption of radiation, spontaneous emission, and stimulated emission. Absorption occurs when electrons absorb energy from photons and jump to a higher energy level. Spontaneous emission is when excited electrons return to the ground state and emit photons randomly. Stimulated emission is when an incident photon interacts with an excited electron and forces it to return to the ground state, emitting another photon with the same properties as the incident photon.

1. Laser
REFERENCE: JAYOTI VIDYAPEETH
INNOVATION CENTER
laser, a device that stimulates atoms or molecules to
emit light at particular wavelengths and amplifies that light,

2. typically producing a very narrow beam of radiation. The
emission generally covers an extremely limited range of
visible, infrared, or ultraviolet wavelengths. Many different
types of lasers have been developed, with highly varied
characteristics. Laser is an acronym for “light amplification
by the stimulated emission of radiation.”
Use of laser
1. Medical Laser :- Medical lasers can be used as a scalpel. Since
the laser can be controlled and can have such a small contact area it is ideal
for fine cutting and depth control. Medical lasers can also be used to
reattach retinas and can be used in conjunction with fiber optics to place the
laser beam where it needs to be. Medical lasers can also be used to stitch
up incisions after surgery, by fusing together skin. (LFI).
2. Entertainment :- Laser shows are quite popular and the
special effects are amazing. These use lasers that are in the visible
spectrum along with vibrating mirrors to paint images in the air. Here is an
example of a dance with lasers in the background:
You might noticed the fog in the background, that is what allows the laser
light to reflect and you to view it. Another example of laser entertainment

3. is the use of laser signs at trade shows. Here is an example of a laser
Microsoft sign:
3. Computer and music :- one popular use of lasers is the
reading of CD. CD's function by having a reflective aluminum layer that
has very small pits put in the aluminum. The pits and the lack of are
translated into binary by the computer and then are used for
information. Another use of lasers is in the use of fiber optics. Since
lasers travel very fast they make an ideal way to communicate. The laser is
shot down a fiberglass tube to a receiver. These wires can be very long
with no loss of signal quality. Also modern multiplexing of the line lets
two lasers of different frequencies share the same line.
4. Metal working :- lasers very accurate point and solid state
construction make it ideal or industrial production. Lasers allow better cuts
on metals and the welding of dissimilar metals with out the use of a
flux. Also lasers can be mounted on robotic arms and used in factors. This
is safer then oxygen and acetylene, or arc welding.

4. Principle of Laser
In lasers, photons are interacted in three ways with the atoms:
 Absorptionof radiation
 Spontaneous emission
 Stimulated emission
1. Absorption of radiation :- Absorption of radiation is the process
by which electrons in the ground state absorbsenergy from photons
to jump into the higher energy level.
The electrons orbiting very close to the nucleus are at the lower
energy level or lower energy state whereas the electrons orbiting
farther away from the nucleus are at the higher energy level. The
electrons in the lower energy level need some extra energy to jump

5. into the higher energy level. This extra energy is provided from
various energy sources such as heat, electric field,or light.
Let us consider two energy levels (E1 and E2) of electrons. E1 is the
ground state or lower energy state of electrons and E2 is the excited
state or higher energy state of electrons.The electrons in the
ground state are called lower energy electrons or ground state
electrons whereas the electrons in the excited state are called
higher energy electrons or excited electrons.
In general, the electrons in the lower energy state can’t jump into the
higher energy state. They need sufficient energy in orderjump into
the higher energy state.
When photons or light energy equal to the energy differenceof the
two energy levels (E2 – E1) is incident on the atom, the ground state
electrons gains sufficientenergy and jumps from ground state (E1)
to the excited state (E2).
The absorption of radiation or light occurs only if the energy of
incident photon exactly matches the energy difference ofthe two
energy levels (E2 – E1).

6. 2. Spontaneous emission:- Spontaneous emissionis the
process by which electrons in the excited state return to the ground
state by emitting photons.
The electrons in the excited state can stay only for a short period.
The time up to which an excited electroncan stay at higher energy
state (E2) is known as the lifetime of excited electrons.The lifetime
of electrons in excited state is 10-8
second.
Thus, after the short lifetime of the excited electrons,they return to
the lower energy state or ground state by releasing energy in the
form of photons.
In spontaneous emission,the electrons move naturally or
spontaneously from one state (higher energy state) to another state
(lower energy state) so the emissionof photons also occurs
naturally. Therefore,we have no control over when an excited
electron is going to lose energy in the form of light.
The photons emitted in spontaneous emissionprocess constitute
ordinary incoherent light. Incoherent light is a beam of photons with
frequent and random changes of phase between them. In other
words, the photons emitted in the spontaneous emission process do
not flow exactly in the same directionof incident photons.

7. 3. Simulated emission:- Stimulated emissionis the processby
which incident photon interacts with the excited electron and forces
it to return to the ground state.
In stimulated emission,the light energy is supplied directly to the
excited electron instead of supplying light energy to the ground state
electrons.Unlike the spontaneous emission,the stimulated
emissionis not a natural processit is an artificial process.
In spontaneous emission,the electrons in the excited state will
remain there until its lifetime is over. After completing their lifetime,
they return to the ground state by releasing energy in the form of
light.However, in stimulated emission,the electrons in the excited
state need not wait for completionof their lifetime.An alternative
technique is used to forcefullyreturn the excited electronto ground
state before completion of their lifetime. This technique is known as
the stimulated emission. Whenincident photon interacts with the
excited electron, it forces the excited electron to return to the ground
state. This excited electronrelease energy in the form of light while
falling to the ground state.

8. MADE BY:
SHRIYA