Gas Purging-free Technique Using Log-ratio Detection in Laser Absorption Spectroscopy

초록

This study presents a theoretical approach and experimental verification for eliminating absorption effects outside the test section using log-ratio detection in laser absorption spectroscopy. In the theoretical approach, a beam path length condition that could cancel the absorption effect external to the test section without purging is derived. To verify that the external absorption effect can be eliminated if the derived beam path length condition is satisfied, gas pressure measurements for the test conditions with a pressure range of 20 to 100 kPa in a gas cell were conducted along the beam path length at varying increments. An absorption feature in the oxygen A-band was used to measure the gas pressure. The gas pressure measurement results experimentally verified that the external absorption effect outside the test section can be eliminated if the beam path length condition is satisfied in the log-ratio detection system. Measurement uncertainty was investigated with an additional experiment if the length condition is not satisfied.

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