Laser & Optical Fiber

INTRODUCTION:

LASER stands for Light Amplification by Stimulated Emission of Radiation. Laser

technology started with Albert Einstein in 1917, he has given theoretical basis for the

development of Laser. The technology further evolved in 1960 when the very first laser

called Ruby Laser was built at Hughes Research Laboratoriesby T.H. Mainmann.

CHARACTERISTIC OF LASER RADIATION:

The laser beam has the properties given below which distinguish it from an ordinary beam of

light. Those are

1. Highly directional

2. Highly monochromatic

3. Highly intense

4. Highly coherence

1. Highly directional:

A conventional light source emits light in all directions. On the other hand, Laser

emits light only in one direction. The width of Laser beam is extremely narrow and hence a

laser beam can travel to long distances without spreading.

The directionality of laser beam is expressedin terms of divergence

Δ𝜃 =

𝑟2 − 𝑟1

𝑑2 − 𝑑1

Where r1and r2are the radii of laser beam spots at distances of d1 and d2 respectively from

laser source.

2. Highly monochromatic:

A monochromatic source is a single frequency or single wavelength source of light.

The laser light is more monochromatic than that of a convectional light source. This may be

due to the stimulated characteristic of laser light. The band width of convectional

monochromatic light source is 1000A0. But the band width of ordinary light source is 10 A0.

For high sensitive laser source is 10-8 A0.

3. Highly intense:

Laser light is highly intense than the conventional light. A one milli-Watt He-Ne laser

is highly intense than the sun intensity. This is because of coherence and directionality of

laser. Suppose when two photons each of amplitude ‘A’ are in phase with other, then young’s

principle of superposition, the resultant amplitude of two photons is 2A and the intensity is

4a2. Since in laser many numbers of photons are in phase with each other, the amplitude of

the resulting wave becomes ‘nA’ and hence the intensity of laser is proportional to n2A2. So

1mw He-Ne laser is highly intense than the sun.

4. Highly coherence:

A predictable correlation of the amplitude and phase at any one point with other point

is called coherence.In case of conventional light, the property of coherence exhibits between

a source and its virtual source where as in case of laser the property coherence exists between

any two sources of same phase.

There are two types of coherence

i) Temporal coherence

ii) Spatial coherence.

    Temporal coherence (or longitudinal coherence):

    The predictable correlation of amplitude and phase at one point on the wave train w .r.

    t another point on the same wave train, then the wave is said to be temporal coherence.

    Spatial coherence (or transverse coherence):

    The predictable correlation of amplitude and phase

    at one point on the wave train w. r .t another point on a

    second wave, then the waves are said to be spatial

    coherence (or transverse coherence).Two waves are said to

    be coherent when the waves must have same phase & amplitude.

This information is for knowledge only, not to hurt anyone's feelings.