14-07-2014, 03:31 PM
LASER RADIATION
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Introduction
A laser is a device that emits light (electromagnetic radiation) through a process of optical amplification based on the stimulated emissionof photons.
Laser is expressed through the output being a narrow beam which is diffraction-limited, often a so-called "pencil beam." Laser beams can be focused to very tiny spots.
Lasers actually produce radiation in several modes having slightly different frequencies (wave lengths)
These lasers having slightly different frequencies are called “single wavelength lasers “.
Laserphysiscs
Electrons and how they interact with electromagnetic fields are important in our understanding of LASER physics.
Stimulated emission:
the energy of an electron orbiting an atomic nucleus is larger for orbits further from the nucleus of an atom.
. The quantum mechanical effects force electrons to take on discrete positions in orbital
The light emitted
The light generated by stimulated emission is very similar to the input signal in terms of wavelength, phase, and polarization.
This gives laser light its characteristic coherence, and allows it to maintain the uniform polarization.
The helium-neon laser shows from earth to moon it will spread up to 500 kms.
The unique property of laser light is it can’t be replaced using standard light sources
Continuous and pulsed modes of operation
A laser can be classified into two types based on power output.
i.e continuous and pulsed operations.
A laser whose output is normally continuous can be intentionally turned on and off at some rate in order to create pulses of light.
. Most laser diodes used in communication systems fall in that category
Pulsed operation
Pulsed operation of lasers refers to any laser not classified as continuous wave, so that the optical power appears in pulses of some duration at some repetition rate.
. This encompasses a wide range of technologies addressing a number of different motivations.
. Some lasers are pulsed simply because they cannot be run in continuous mode.
Q-switching
In a Q-switched laser, the population inversion is allowed to build up by introducing loss inside the resonator which exceeds the gain of the medium.
this can also be described as a reduction of the quality factor or 'Q' of the cavity.
Then, after the pump energy stored in the laser medium has approached the maximum possible level.
This results to absorps high peak power.
Mode-locking
A mode-locked laser is capable of emitting extremely short pulses on the order of tens of picoseconds down to less than 10 femtoseconds.
These pulses will repeat at the round trip time, that is, the time that it takes light to complete one round trip between the mirrors comprising the resonator.
As weapons
Laser beams are famously employed as weapon systems in science fiction, but actual laser weapons are still in the experimental stage.
The extreme handicap that laser-induced blindness represents makes the use of lasers even as non-lethal weapons morally controversial, and weapons designed to cause blindness have been banned by the Protocol on Blinding Laser Weapons.