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The lasing threshold is the lowest excitation level at which a laser's output is dominated by stimulated emission rather than by spontaneous emission. Below the threshold, the laser's output power rises slowly with increasing excitation. Above threshold, the slope of power vs. excitation is orders of magnitude greater.
From level 4, the atoms again decay by a fast, non-radiative transition Ra into the level 3. Since the lifetime of the laser transition L is long compared to that of Ra (τ 32 ≫ τ 43), a population accumulates in level 3 (the upper laser level), which may relax by spontaneous or stimulated emission into level 2 (the lower laser level).
The special condition > is known as a population inversion, a rather unusual condition that must be effected in the gain medium of a laser. The notable characteristic of stimulated emission compared to everyday light sources (which depend on spontaneous emission) is that the emitted photons have the same frequency, phase, polarization, and ...
Light is generated in a semiconductor laser by radiative recombination of electrons and holes. In order to generate more light by stimulated emission than is lost by absorption, the system's population density has to be inverted, see the article on lasers. A laser is, thus, always a high carrier density system that entails many-body interactions.
A laser normally produces a very narrow beam of light in a single wavelength, in this case, green. Photons, the quanta of electromagnetic radiation are released and absorbed from energy levels in atoms and molecules. In a lightbulb or a star, the energy is emitted from many different levels giving photons with a broad range of energies.
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The laser damage threshold (LDT) or laser induced damage threshold (LIDT) is the limit at which an optic or material will be damaged by a laser given the fluence (energy per area), intensity (power per area), and wavelength. LDT values are relevant to both transmissive and reflective optical elements and in applications where the laser induced ...
After 18 weeks, the NFL playoffs are finally here. Over the next three days we’ll have six wild-card games to decide who will move on to the divisional round.