LASER DIODE

LASERBy-Pranav Patel(13PGEC027)

IntroductionL - LIGHT A - AMPLIFICATION BY S - STIMULATED E - EMISSION OFR - REDIATIONDefinition of laser

A laser is a device that generates light by a process called STIMULATED EMISSION .

Semiconducting lasers are multilayer semiconductor devices that generates a coherent beam of monochromatic light by laser action. A coherent beam resulted which all of the photons are in phase.Mechanisms of Light Emission

When the atom makes a transition from higher energy state E2 to E1 lower energy state a photon is emitted. This emission process can occur two ways:Spontaneous emission-when atom return to ground state in a random fashion.Stimulated emission-when a photon with energy e2 - e1 interacts with another atom in the higher energy state sending it to lower energy state with the creation of another atom.Therefore 3 process of light emission:AbsorptionSpontaneous EmissionStimulated EmissionABSORPTIONThe atom is initially in a lower energy state E1.When a photon with energy E2 - E1 is incident on the atom, it gets excited to higher level E2.This is absorption.

E2E1SPONTANEOUS EMISSIONSpontaneous emission is the process by which an atom in an excited state undergoes a transition to ground state and emits a photon by itself without the help of external radiation.

E2E1STIMULATED EMISSION Consider the atom present in the excited state. After the certain time period this atom falls due to spontaneous process and it emits a photon; but before the occurrence of this spontaneous emission process, if the incident photon is allowed to strike this excited atom then there is no chance for this atom to go to the further higher energy level. In this case once the external photon strikes this excited atom, this atom leaves its position form this higher energy level and emits the photon.Thus we are getting twos photons at the output. This process is shown in fig.The emitted photon is in phase with the incident photon and the emission is known as stimulated emission.E1E2Thank you