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Updated: Jul 14, 2026

Infrared Degenerate Four-wave Mixing with Upconversion Detection for Quantitative Gas Sensing
Published on: March 22, 2019
Real-time, ultralow concentration detection of analytes in solution by infrared intracavity laser absorption
Untzizu Elejalde1, John M Girkin
1Institute of Photonics, University of Strathclyde, SUPA, Wolfson Centre, Glasgow, UK. untzizu.elejalde@strath.ac.uk
Abstract:
Two intracavity laser absorption techniques for ultralow concentration detection of chemicals in solution are compared. The first consists of a laser diode in a grating extended cavity, which produces a linear calibration curve for parts in 10(9) (ppb) concentrations corresponding to 17 nM. By replacing the grating with a highly reflective mirror, parts in 10(12) (ppt) concentration detection is achieved, which corresponds to 340 pM. We report, to our knowledge for the first time, ppt detection of analyte concentration in liquid solution demonstrating good agreement between theory and experiment.
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