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Optical Measurement of Gas Constituents using Double Quantum Absorption

IP.com Disclosure Number: IPCOM000082738D
Original Publication Date: 1975-Jan-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Hodgson, RT: AUTHOR [+3]

Abstract

A system has been devised that is suited for measuring pollutants in a gas, dopant atoms in an evaporation chamber, or very minute constituents in a vapor, wherein a spacial resolution of approximately one micron and a density resolution of 100 atoms/(micron)/3/ can be obtained.

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Optical Measurement of Gas Constituents using Double Quantum Absorption

A system has been devised that is suited for measuring pollutants in a gas, dopant atoms in an evaporation chamber, or very minute constituents in a vapor, wherein a spacial resolution of approximately one micron and a density resolution of 100 atoms/(micron)/3/ can be obtained.

The system relies upon the double-quantum absorption of two focused tunable laser beams crossed at a point within the gas, vapor, or the like being sensed. As seen in Fig. 1, a first tunable dye laser emits a beam 2 at a first frequency u(2) and its light is focused at point P through lens 4. A second tunable laser emits a beam 6 that is focused through lens 8 at the same point P within the gaseous substance of interest. Such gaseous substance could be housed in a transparent container or be present in the open air.

Each laser beam is transmitted by the gaseous substance with no attenuation, until it reaches the common focal volume at P. At point P, one photon from each beam is absorbed to excite a double-quantum resonance in the gas, which double-quantum resonance is detected by observing fluorescence, the latter being focused by lens 10 onto a wide-band photodetector
12.

Fig. 2 is an energy diagram for the element sodium. Assume that the first dye laser beam has a frequency u(2) which emits at 6173 angstroms (in the red) and the second dye laser beam has an emission frequency u(2) of 5882 angstroms (in the orange)....