Understanding Nd:YAG Laser and Its Applications

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LASER
LASER
&
&
IT’S APPLICATIONS
IT’S APPLICATIONS
(CO-4 Part-III)
 
 
Dr. Prabodh Sahai Saxena
Prof & Head
Deptt of Physics
LNCT BHOPAL
 
Construction and working of Nd:YAG laser
Advantages of Nd:YAG laser
Applications of Nd:YAG laser
Construction and working of CO
2
 laser
Advantages of CO
2
 laser
Disadvantages of CO
2
 laser
Applications of CO
2
 laser
 
 
 
Nd: YAG laser is a 
four-level laser system
, which
means that the four energy levels are involved in laser
action. These lasers operate in both pulsed and
continuous mode.
Nd: YAG laser is a 
solid state laser 
in which Nd: YAG
crystal is used as a laser medium.Nd
+3
 ions are the
active centers.
Nd: YAG stands for 
Neodymium 
(Nd
+3
) doped 
Yttrium
Aluminum Garnet 
(Y
3
Al
5
O
12
).
Nd: YAG laser generates laser light commonly in the
near 
IR region 
(infrared region) of the spectrum at 1064
nanometers (nm).
It also emits laser light at 
several different wavelengths
including 1440 nm, 1320 nm, 1120 nm, and 940 nm.
 
 
 
Nd:YAG laser consists of three important elements:
an 
energy source, active medium, and optical
resonator 
.
The 
energy source 
or pump source supplies energy to
the active medium to achieve population inversion. In
Nd: YAG laser, light energy sources such as  Krypton
(Kr) arc lamp used as energy source.
The 
active medium 
or laser medium of the Nd:YAG
laser is made up of a synthetic crystalline material
Yttrium Aluminum Garnet (YAG) doped with a
chemical element  neodymium (Nd).
The Nd:YAG crystal is placed between two mirrors.
One mirror is fully silvered whereas, another mirror
is partially silvered.
 
The energy level E
1
 is known as ground state, E
2
 is the
next higher energy state or excited state, E
3
 is the
metastable state or excited state and E
4
 is the pump
state or excited state. Let us assume that initially, the
population will be N
1
 > N
2
 > N
3
 > N
4
.
When flashtube or laser diode supplies light energy to
the active medium (Nd:YAG crystal), the lower energy
state (E
1
) electrons in the neodymium ions gains
enough energy and moves to the pump state or higher
energy state E
4
.
The lifetime of higher energy state E
4
 is very small
(10
-8
 sec). After this short period, the electrons will fall
into the next lower energy state or metastable state
E
3
 by releasing non-radiation energy (releasing energy
without emitting photons).
 
 
 
 
The lifetime of 
metastable state 
E
3
 is high as compared
to the lifetime of pump state E
4
. Therefore, the electrons
reach E
3
 much faster than they leave E
3
. This results in an
increase in the no of electrons in the metastable E
3
 and
hence population inversion is achieved.
After some period, the electrons in the metastable state
E
3
 will fall into the next lower energy state E
2
 by releasing
photons. The emission of photons in this manner is called
spontaneous emission.
 
When photon emitted due to spontaneous emission is
interacted with the other metastable state electron, it
stimulates that electron and makes it fall into the lower
energy state by releasing the photon. As a result, two
photons are released. The emission of photons in this
manner is called stimulated emission of radiation.
 
 
When these two photons again interacted with the
metastable state electrons, four photons are released.
Likewise, millions of photons are emitted. Thus,
optical gain is achieved.
In this way, several electrons on stimulation produce
photons thereby generating a coherent laser beam of
10,640Å.
 
 
Nd:YAG laser offers high gain.
Low power consumption.
The efficiency of Nd:YAG laser is very high as
compared to the ruby laser.
Nd:YAG laser has good thermal properties.
Nd:YAG laser has good mechanical properties.
It is much easy to achieve population inversion
.
 
Nd:YAG lasers are used in laser designators and laser
rangefinders. A laser designator is a laser light source,
which is used to target objects for attacking. A laser
rangefinder is a rangefinder, which uses a laser light to
determine the distance to an object.
Nd:YAG lasers are used for cutting and welding steel.
It finds many medical applications such as endoscopy,
urology, neurosurgery, ENT, gynecology, dermatology,
dental surgery and general surgery.
Nd:YAG lasers are used to remove skin cancers.
 
CO
2
 was the first 
molecular gas laser 
developed by
Indian born American scientist  Prof. C. K. N. Pillai.
It is a 
four level gas laser 
and it operates at 10.6 μm
in the far IR region. It is a very efficient laser.
Laser action is achieved by transitions between
vibrational
 and 
rotational levels 
of molecules.
Its construction is simple and the output of this laser
is 
continuous
.
The active medium is a gas mixture of CO
2
, N
2
 and
He.
 
A carbon dioxide molecule has a carbon atom at the
center with two oxygen atoms attached, one at both
sides.
CO
2
 molecule exhibits three independent modes of
vibrations. They are
 
(a)Symmetric stretching mode
(a)Symmetric stretching mode
:- In this mode of
vibration, carbon atoms are at rest and both oxygen
atoms vibrate simultaneously along the axis of the
molecule departing or approaching the fixed carbon
atoms.
 
 
 
 
 
 
 
(b)Bending mode:- 
(b)Bending mode:- 
In this mode of vibration, oxygen
atoms and carbon atoms vibrate perpendicular to
molecular axis.
 
(c)Asymmetric stretching mode
(c)Asymmetric stretching mode
:- In this mode of
vibration, oxygen atoms and carbon atoms vibrate
asymmetrically, i.e., oxygen atoms move in one
direction while carbon atoms in the other direction.
 
It consists of a quartz tube 5 m long and 2.5 cm in the
diameter. This discharge tube is filled with gaseous
mixture of CO
2
, helium and nitrogen with suitable
partial pressures.
The terminals of the discharge tubes are connected to
a D.C power supply. The ends of the discharge tube are
fitted with NaCl Brewster windows so that the laser
light generated will be polarized.
Two concave mirrors one fully reflecting and the
other partially form an optical resonator.
 
Electrical discharge method is used for Pumping action.
When an electric discharge occurs in the gas, the electrons
collide with nitrogen molecules and they are raised to
excited states.
 Now N
2
 molecules in the excited state collide with
CO
2
 atoms in ground state and excite to higher electronic,
vibrational and rotational levels.
Since the excited level of nitrogen is very close to the
E
5
 level of CO
2
 atom, population in E
5
 level increases.
 
As soon as population inversion is reached, any of the
spontaneously emitted photon will trigger laser action
in the tube. There are two types of laser transition
possible.
 
Transition E
5
  to E
4
 : This will produce a laser beam of
wavelength 10.6μm.
Transition E
5
  to E
3 
 :This transition will produce a
laser beam of wavelength 9.6μm. Normally 10.6μm
transition is more intense than 9.6μm transition.
The power output from this laser is 10kW.
 
It has high efficiency.
The output of this laser is continuous.
It has very high output power.
The construction of CO
2
 laser is simple.
The output power can be increased by extending the
length of the gas tube.
 
The operating temperature plays an important role in
determining the output power of laser.
The corrosion may occur at the reflecting plates.
Accidental exposure may damage our eyes, since it is
invisible (infra red region) to our eyes.
The contamination of oxygen by carbon monoxide
will have some effect on laser action.
 
 
High power CO
2
 laser finds applications in
material processing, welding, drilling, cutting
soldering etc.
The low atmospheric attenuation (10.6μm makes
CO
2
 laser suitable for open air communication.
It is used for remote sensing
It is used for treatment of liver and lung diseases.
It is mostly used in neuro surgery and general
surgery.
It is used to perform microsurgery and bloodless
operations.
 
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Nd:YAG laser is a solid-state laser system used in various applications due to its ability to generate laser light in the near-infrared region. This laser operates in a four-level system, with Nd:YAG crystal as the active medium. The construction, working principles, advantages, and applications of Nd:YAG and CO2 lasers are discussed in detail. By achieving population inversion through an energy source and optical resonator, Nd:YAG laser efficiently emits laser light at different wavelengths. Population inversion is crucial for the laser's functionality, leading to the emission of photons and efficient laser operation.


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  1. LASER & IT S APPLICATIONS (CO-4 Part-III) Dr. Prabodh Sahai Saxena Prof & Head Deptt of Physics LNCT BHOPAL

  2. Construction and working of Nd:YAG laser Advantages of Nd:YAG laser Applications of Nd:YAG laser Construction and working of CO2 laser Advantages of CO2 laser Disadvantages of CO2 laser Applications of CO2 laser

  3. Nd: YAG laser is a four-level laser system, which means that the four energy levels are involved in laser action. These lasers operate in both pulsed and continuous mode. Nd: YAG laser is a solid state laser in which Nd: YAG crystal is used as a laser medium.Nd+3 ions are the active centers. Nd: YAG stands for Neodymium (Nd+3) doped Yttrium Aluminum Garnet (Y3Al5O12). Nd: YAG laser generates laser light commonly in the near IR region (infrared region) of the spectrum at 1064 nanometers (nm). It also emits laser light at several different wavelengths including 1440 nm, 1320 nm, 1120 nm, and 940 nm.

  4. Nd-YAG laser

  5. Nd:YAG laser consists of three important elements: an energy source, active medium, and optical resonator . The energy source or pump source supplies energy to the active medium to achieve population inversion. In Nd: YAG laser, light energy sources such as Krypton (Kr) arc lamp used as energy source. The active medium or laser medium of the Nd:YAG laser is made up of a synthetic crystalline material Yttrium Aluminum Garnet (YAG) doped with a chemical element neodymium (Nd). The Nd:YAG crystal is placed between two mirrors. One mirror is fully silvered whereas, another mirror is partially silvered.

  6. The energy level E1is known as ground state, E2is the next higher energy state or excited state, E3is the metastable state or excited state and E4is the pump state or excited state. Let us assume that initially, the population will be N1> N2> N3> N4. When flashtube or laser diode supplies light energy to the active medium (Nd:YAG crystal), the lower energy state (E1) electrons in the neodymium ions gains enough energy and moves to the pump state or higher energy state E4. The lifetime of higher energy state E4is very small (10-8 sec). After this short period, the electrons will fall into the next lower energy state or metastable state E3by releasing non-radiation energy (releasing energy without emitting photons).

  7. The lifetime of metastable state E3is high as compared to the lifetime of pump state E4. Therefore, the electrons reach E3much faster than they leave E3. This results in an increase in the no of electrons in the metastable E3and hence population inversion is achieved. After some period, the electrons in the metastable state E3will fall into the next lower energy state E2by releasing photons. The emission of photons in this manner is called spontaneous emission.

  8. When photon emitted due to spontaneous emission is interacted with the other metastable state electron, it stimulates that electron and makes it fall into the lower energy state by releasing the photon. As a result, two photons are released. The emission of photons in this manner is called stimulated emission of radiation.

  9. When these two photons again interacted with the metastable state electrons, four photons are released. Likewise, millions of photons are emitted. Thus, optical gain is achieved. In this way, several electrons on stimulation produce photons thereby generating a coherent laser beam of 10,640 .

  10. Nd:YAG laser offers high gain. Low power consumption. The efficiency of Nd:YAG laser is very high as compared to the ruby laser. Nd:YAG laser has good thermal properties. Nd:YAG laser has good mechanical properties. It is much easy to achieve population inversion.

  11. Nd:YAG lasers are used in laser designators and laser rangefinders. A laser designator is a laser light source, which is used to target objects for attacking. A laser rangefinder is a rangefinder, which uses a laser light to determine the distance to an object. Nd:YAG lasers are used for cutting and welding steel. It finds many medical applications such as endoscopy, urology, neurosurgery, ENT, gynecology, dermatology, dental surgery and general surgery. Nd:YAG lasers are used to remove skin cancers.

  12. CO2 was the first molecular gas laser developed by Indian born American scientist Prof. C. K. N. Pillai. It is a four level gas laser and it operates at 10.6 m in the far IR region. It is a very efficient laser. Laser action is achieved by transitions between vibrational and rotational levels of molecules. Its construction is simple and the output of this laser is continuous. The active medium is a gas mixture of CO2, N2 and He.

  13. A carbon dioxide molecule has a carbon atom at the center with two oxygen atoms attached, one at both sides. CO2 molecule exhibits three independent modes of vibrations. They are (a)Symmetric stretching mode:- In this mode of vibration, carbon atoms are at rest and both oxygen atoms vibrate simultaneously along the axis of the molecule departing or approaching the fixed carbon atoms.

  14. (b)Bending mode:- In this mode of vibration, oxygen atoms and carbon atoms vibrate perpendicular to molecular axis. (c)Asymmetric stretching mode:- In this mode of vibration, oxygen atoms and carbon atoms vibrate asymmetrically, i.e., oxygen atoms move in one direction while carbon atoms in the other direction.

  15. It consists of a quartz tube 5 m long and 2.5 cm in the diameter. This discharge tube is filled with gaseous mixture of CO2, helium and nitrogen with suitable partial pressures. The terminals of the discharge tubes are connected to a D.C power supply. The ends of the discharge tube are fitted with NaCl Brewster windows so that the laser light generated will be polarized. Two concave mirrors one fully reflecting and the other partially form an optical resonator.

  16. Electrical discharge method is used for Pumping action. When an electric discharge occurs in the gas, the electrons collide with nitrogen molecules and they are raised to excited states. Now N2molecules in the excited state collide with CO2atoms in ground state and excite to higher electronic, vibrational and rotational levels. Since the excited level of nitrogen is very close to the E5level of CO2atom, population in E5level increases.

  17. As soon as population inversion is reached, any of the spontaneously emitted photon will trigger laser action in the tube. There are two types of laser transition possible. Transition E5 to E4: This will produce a laser beam of wavelength 10.6 m. Transition E5 to E3 :This transition will produce a laser beam of wavelength 9.6 m. Normally 10.6 m transition is more intense than 9.6 m transition. The power output from this laser is 10kW.

  18. It has high efficiency. The output of this laser is continuous. It has very high output power. The construction of CO2laser is simple. The output power can be increased by extending the length of the gas tube.

  19. The operating temperature plays an important role in determining the output power of laser. The corrosion may occur at the reflecting plates. Accidental exposure may damage our eyes, since it is invisible (infra red region) to our eyes. The contamination of oxygen by carbon monoxide will have some effect on laser action.

  20. High power CO2laser finds applications in material processing, welding, drilling, cutting soldering etc. The low atmospheric attenuation (10.6 m makes CO2laser suitable for open air communication. It is used for remote sensing It is used for treatment of liver and lung diseases. It is mostly used in neuro surgery and general surgery. It is used to perform microsurgery and bloodless operations.

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