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Laser System for Measurements of Gas Concentrations in Mixtures of Gases

IP.com Disclosure Number: IPCOM000080197D
Original Publication Date: 1973-Nov-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Smith, JE: AUTHOR

Abstract

A system has been devised for increasing the signal-to-noise ratio in a gas detection Rnman scattering system.

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Laser System for Measurements of Gas Concentrations in Mixtures of Gases

A system has been devised for increasing the signal-to-noise ratio in a gas detection Rnman scattering system.

In conventional Raman scattering sensing techniques for analyzing gas spectra, laser light is sent through a cell housing the gas sample to be analyzed, and a suitable monochromator senses the Raman scattered light produced in the cell. In the system to be described below, the cell is placed within the laser cavity, rather than outside the cavity, to obtain enhancement of the Raman scattered light.

Gases which occur in molecular, as opposed to atomic, forms have discrete vibrational spectra which can be measured by Raman spectroscopy. The Raman spectrum of a particular gas is, in general, unique for each gas specie so that each gas specie can be detected and identified. Furthermore, the intensity is linearly proportional to the partial pressure of the particular gas in the sample, so that it is possible to measure concentration.

In the practice of a Rnman scattering sensing system, the sample gas is placed into a transparent cell 2 (see Fig. 1) and the active medium is in tube 4, wherein both the tube and cell are aligned in the optical cavity bounded by mirrors 6 and 8. The active medium is pumped to produce lasing, which laser beam 10 is scattered by the gas in the sample cell 2. Monochromator 12 detects the Raman scattered light.

In Fig. 2, a dummy cell 2', identical to gas-conta...