Fundamentals of Lasers
Light
Amplification by
Stimulated
Emission of
Radiation
LASERS
Laser Fundamentals
•
A laser is a device that generates light by a process called
STIMULATED EMISSION.
•
The acronym LASER stands for Light Amplification by Stimulated
Emission of Radiation.
•
The light emitted from a laser is monochromatic.
•
Laser emit light that is highly directional.
•
The light from a laser is said to be coherent.
Laser Operation:
Excited State
Energy
Introduction
Metastable State
Spontaneous
Energy
Emission
Stimulated
Emission of
Radiation
Ground State
Lasing Action Diagram
Necessary conditions for a lasing transition:
-population inversion
-metastable states
Absorption:
An incoming photon excites the atomic system from a lower energy state into a higher energy state. This is called absorption or sometimes stimulated absorption.
E2
(Absorption)
E1
Spontaneous Emission:
Once the atom or molecule goes in its excited state, there is a probability that it will emit radiation again and return to a lower energy state thus a photon is emitted.
In this emission process, where the atoms spontaneously goes to a lower energy state through the emission of a photon is called spontaneous emission. This emission process is a random one and the emitted light goes off in all directions and thus the light is incoherent. E2
(spontaneous emission)
E1
Metastable States:
Normally the average lifetime for spontaneous emissions by excited atoms is around 10-8 seconds (that is, the atom or molecule will usually take around
10-8 seconds before emitting the photon). However, there are states for which the lifetime is much longer i.e, around 10-3 seconds. These states are called metastable States.
Stimulated emission:
Stimulated emission is the process by which an incoming photon of a specific frequency can interact with an excited atomic electron, causing it to drop to a lower energy level. The incident and emitted photon have the same wavelength and phase and hence two
Amplification by
Stimulated
Emission of
Radiation
LASERS
Laser Fundamentals
•
A laser is a device that generates light by a process called
STIMULATED EMISSION.
•
The acronym LASER stands for Light Amplification by Stimulated
Emission of Radiation.
•
The light emitted from a laser is monochromatic.
•
Laser emit light that is highly directional.
•
The light from a laser is said to be coherent.
Laser Operation:
Excited State
Energy
Introduction
Metastable State
Spontaneous
Energy
Emission
Stimulated
Emission of
Radiation
Ground State
Lasing Action Diagram
Necessary conditions for a lasing transition:
-population inversion
-metastable states
Absorption:
An incoming photon excites the atomic system from a lower energy state into a higher energy state. This is called absorption or sometimes stimulated absorption.
E2
(Absorption)
E1
Spontaneous Emission:
Once the atom or molecule goes in its excited state, there is a probability that it will emit radiation again and return to a lower energy state thus a photon is emitted.
In this emission process, where the atoms spontaneously goes to a lower energy state through the emission of a photon is called spontaneous emission. This emission process is a random one and the emitted light goes off in all directions and thus the light is incoherent. E2
(spontaneous emission)
E1
Metastable States:
Normally the average lifetime for spontaneous emissions by excited atoms is around 10-8 seconds (that is, the atom or molecule will usually take around
10-8 seconds before emitting the photon). However, there are states for which the lifetime is much longer i.e, around 10-3 seconds. These states are called metastable States.
Stimulated emission:
Stimulated emission is the process by which an incoming photon of a specific frequency can interact with an excited atomic electron, causing it to drop to a lower energy level. The incident and emitted photon have the same wavelength and phase and hence two