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Applied Optics

Population Inversions Produced by Chemical Depletion of Ground States

Michael L. Seman

Published Jan 1, 1965• 2 citations
Publisher

Abstract

A discussion is given on the possibility of creating population inversions in gas systems by chemical removal of the lower of the two states between which inversion is desired. The requirements which have to be met for closed and flow systems are indicated. The minimum requirement in all cases is that the reaction rate of the lower state be faster than that of the upper state. Possible systems are suggested.

DOI
10.1364/ao.4.s1.000181

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A discussion is given on the possibility of creating population inversions in gas systems by chemical removal of the lower of the two states between which inversion is desired. The requirements which have to be met for closed and flow systems are indicated. The minimum requirement in all cases is that the reaction rate of the lower state be faster than that of the upper state. Possible systems are suggested.
We propose a new scheme for lasing without population inversion that utilizes interferences in double-quantum-well intersubband transitions. In contrast to the previous inversionless laser schemes based on atomic systems, the new proposal permits us to use band-gap engineering to choose the subband energies, coupling strengths, and decay rates, as desired, and permits us to create a laser system that does not require population inversion. We present detailed calculations on a specific scheme and discuss possible extensions.
[6]. This state is called trapped state or nonabsorbingstate. Therefore, if one managed to prepare all atoms at lower levels in such trapped state any small amount ofatoms at upper level should be sufficient for amplification since there should be transitions from the upper state tothe state which is orthogonal to the trapped one. Apparently, such inversionless amplification implies some hiddeninversion, namely, with respect to the empty untrapped state. In general, population inversion is required between
When an atomic system interacts with light, it can amplify the electromagnetic radiation when gain exceeds loss. This requires that transitions from the upper level to the lower level prevail over the transitions from the lower level to the upper level. If one deals with a two-level system, the only way to obtain amplification is to create a state of population inversion, i.e. the upper level must be more densely populated that the lower level. "Lasing without inversion" may be possible when part of the atoms are trapped, which removes them from the subspace of states with which the upper level can have transitions. This chapter determines to what extent population inversion is necessary to achieve amplification. Independently, amplification without inversion and lasing without inversion were predicted by Harris using a different type of atomic interference. The amplification threshold has a number of features that are reminiscent of the laser threshold.