Systematic errors in diode-laser measuring the relative content of 13CO2 and 12CO2

Systematic errors appearing during measurements of the relative content of carbon dioxide gas isotopic isomers ¹²CO₂ and ¹³CO₂ with the help of mid-IR diode lasers tunable in the 4.35-μm region. The main sources of such errors are the luminescent component in the diode laser radiation, interference of analytic CO₂ absorption lines, as well as temperature and concentration variations of the gaseous medium being analysed. Based on simulations an analytic expression is obtained describing the systematic errors, which can be used to compare the parameters of analytic pairs of lines applied for isotopic analysis.