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Method and apparatus for producing laser radiation following two-photon excitation of a gaseous medium
| Details |
Inventors: Bischel, William K.; Jacobs, Ralph R.; Prosnitz, Donald; Rhodes, Charles K.; Kelly, Patrick J.;
Assignee: The United States of America as represented by the United States (Washington, DC)
Primary Examiner: Sikes; William L.
Assistant Examiner:
Attorney, Agent or Firm: Carlson; Dean E., Gaither; R. S., Simpson; P. Martin
Method and apparatus for producing laser radiation by two-photon optical pumping of an atomic or molecular gaseous medium and subsequent lasing action. A population inversion is created as a result of two-photon absorption of the gaseous species. Stark tuning is utilized, if necessary, in order to tune the two-photon transition into exact resonance. In particular, gaseous ammonia (NH.sub.3) or methyl fluoride (CH.sub.3 F) is optically pumped by a pair of CO.sub.2 lasers to create a population inversion resulting from simultaneous two-photon excitation of a high-lying vibrational state, and laser radiation is produced by stimulated emission of coherent radiation from the inverted level. |
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DETAILED DESCRIPTION The present invention provides a method and apparatus for producing laser radiation by two-photon optical pumping of an atomic or molecular gaseous medium, particularly ammonia or methyl fluoride, to create a population inversion as a result of two-photon absorption by the gaseous medium, followed by stimulated emission of coherent radiation from the inverted level.
Stark tuning is utilized, if necessary, to tune the two-photon transition into exact resonance.
The terms "two-photon absorption" and "two-photon excitation", as generally used in the art and as used herein, refer to the simultaneous absorption, as distinguished from sequential absorption, of two photons of frequencies .
nu.
.
sub.
1 and .
nu.
.
sub.
2 (which may be the same or different) to excite an atomic or molecular state whose energy is equal to the sum of the energies of the two photons.
In simultaneous two-photon absorption, neither .
nu.
.
sub.
1 nor .
nu.
.
sub.
2 is capable, by itself, of exciting a transition in the species, whereas in sequential absorption by two photons, the first photon excites a transition to a first real energy level and the second photon excites a transition between the first energy level and a second energy level.
That is, in sequential absorption of two photons, excitation takes place in two successive stages.
Simultaneous two-photon absorption, on the other hand, involves a transition to an intermediate virtual energy level.
The term "two-photon transition" is used herein to denote the transition corresponding to a two-photon absorption.
The general theory of simultaneous two-photon absorption was initially established by Goppert-Mayer in 1931 (M.
Goppert-Mayer, Ann.
Phys.
Leipz.
9, 273, 1931).
The term "two-photon optical pumping" is therefore used herein to denote optical pumping by means of two photon sources whose frequencies are such that excitation of the gaseous lasing medium to a higher energy level is effected by simultaneous two-photon absorption.
Also, the term "pumping a two-photon transition", when used herein refers to pumping an energy level excited by a two-photon transition as hereinbefore defined
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Fault Detection 
