## Laser and properties of a Laser beam

Laser→

LASER is an acronym for Light Amplification by Stimulated Emission of Radiation. It is a device that produces a highly intense monochromatic, collimated, and highly coherent light beam. Laser action mainly depends on the phenomenon of population inversion and stimulated emission.

The first successful Laser is a solid-state laser which was built by TH Maiman in 1960 using Ruby as an active medium.

Note→

The laser has often been referred to as an optical MASER because it operates in the visible spectrum portion of the spectrum. In general, when the variation occurs below the infrared portion of the electromagnetic spectrum, the term MASER will be employed and when stimulated emission occurs in the infrared, visible, or ultraviolet portion of the spectrum the term laser or optical MASER will be used.

Properties of a Laser Beam→

The laser beam has the following main characteristics properties:
1. A laser beam has high directionality and can be emitted only in one direction. The divergence of the laser beam can be less than $10^{-5}$ radian. Due to high directionality, these beams can be focused in very small areas.

2. A leaser beam is very narrow and hence can travel long distances without any spread. The spectral width ($\Delta \lambda$)of a laser beam is of the order of $10^{-6} A^{\circ}$.

3. A laser beam is highly monochromatic. Its monochromaticity is much more than that of any conventional monochromatic source.

4. The laser beam has high intensity and high power levels can produce a temperature of the order of $10^{4} \: ^{\circ}C$.

5. A laser beam has a high degree of coherence. It is high temporally and spatially coherent.