10.1 Introduction

LASER stands for Light Amplification by Stimulated Emission of Radiation. Laser light is different from conventional light. In conventional light sources [such as tube light or electric bulb], there is no coordination among different atoms emitting radiation. Whereas in lasers, all atoms act together and produce highly directional, monochromatic, coherent and stimulated radiation. In conventional light source, different atoms emit radiation at different times and in different directions so that there is no phase relation between the emitted photons. The photons emitted by different atoms of laser are in phase or they maintain constant phase relationship and they move in the same direction. Lasing has been extended ...

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