1. The problem is to define and derive the laser concept. 2. LASER stands for Light Amplification by Stimulated Emission of Radiation. 3. It is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. 4. The derivation of laser action begins with the concept of atomic energy levels in an atom or molecule. 5. When atoms are energized, electrons jump to higher energy levels (excited state). 6. When these electrons return to a lower energy level (ground state), they emit photons. 7. Stimulated emission occurs when an incoming photon causes an excited electron to drop to a lower energy level and emit a photon coherent with the incoming one. 8. The rate of stimulated emission is proportional to the intensity of the light and the number of excited atoms. 9. The laser medium is placed in an optical cavity with mirrors to reflect photons back and forth, increasing amplification. 10. Population inversion is achieved when more atoms are in the excited state than the ground state, necessary for net amplification. 11. The laser output is coherent, monochromatic, and directional light. Thus, the laser produces a strong, coherent beam of light by stimulated emission under conditions of population inversion in an optical cavity.