Introduction to LASER

Introduction to LASER.

The term LASER is a short form of Light Amplification by Stimulated Emission of Radiation the name signifies that in this amplification of light takes place by forced emission of radiations. The laser is one of the most important discoveries of the century.

T.Maiman was the first man who does the first successful operation of the laser in 1960 using a ruby crystal in the USA. after this the first gas laser was fabricated by Ali Javan and coworkers. from this time different types of lasers started to come forward, lasers using solids, liquids, and gases have been developed. The immense use of lasers from toys to warfare and from welding to surgery has made it very popular.

The LASER light is basically an electromagnetic wave but it has some special characteristics which make it different from ordinary light ;

Directionality: The laser beam is highly directional having almost no divergence (except the diffraction effect ). 

Note: For a typical laser beam divergence is less than 0.01 milliradian, i.e., for a meter of propagation, the spread is less than 0.01mm. 

Monochromaticity: The laser light is nearly monochromatic in nature. In reality, no light is perfectly monochromatic means they can not be defined by single wavelengths instead they are characterized by the spread in frequency and for the laser lights, it is very less than ordinary light so compared to the ordinary light we can say that the LASER light is monochromatic in nature.

Monochromaticity is also taken as a measure of spectral purity. Smaller the value of monochromaticity, the higher the purity of the spectrum.

Coherence: LASER radiation is characterized by a high degree of coherence, both spatial and temporal.In other words, a constant phase relationship exists between the radiation field of laser and light sources at different locations and times. 

It is possible to observe interference effects from two independent laser beams. It is the main feature that distinguishes LASER from ordinary light other characteristics are related to a high degree of coherence.

In general, the coherence or phase between two light waves can vary from point to point (in space) or change from instant to instant( or time ). Thus, these are two types of coherence,

Temporal Coherence: if coherency is maintained with respect to time by source.

Spatial Cohrence: If the two waves maintain a constant phase relationship over any time at different points in space.

Intensity: The laser is highly intense compared to an ordinary source of light.Since the power is concentrated in the small diameter of LASER light so even a small LASER can deliver very high intensity at the focal plane of the lens.