At the end of the nineteenth century electromagnetic theory and thermodynamics were well developed and therewas the question of reunification of these theories. Blackbody radiation is the emission of electromagnetic radiation from a closed cavity at temperature T through a small hole (Figure 7.1). It was found that the frequency distribution of the emitted radiation was dependent upon the temperature T. M. Planck formulated the famous blackbody radiation law in 1900. He used electromagnetic theory and thermodynamics, but needed an assumption that marked the beginning of quantum theory. Planck’s law involved a fundamental physical constant, now called Planck’s constant. The emission of light from the blackbody was interpreted as quantum emission of light. In the first half of the last century, the quantum emission of atoms and molecules was studiedand in the second half of the century the laser was developed. (“Laser” stands for light amplification by stimulated emission of radiation).
KeywordsGAUSSIAN Beam Spontaneous Emission Atomic Emission Beam Waist Lorentzian Line Shape
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