Development of CO2 Cavity Ring-Down Spectroscopy for Medical Applications

Abstract

A compact cavity ring-down spectroscopy setup for detection of CO2 has been developed. First tests using solid carbon as well as liquid glucose samples with either natural isotopic or 13C enriched composition have been performed. The samples are first converted to CO2 gas using a commercial elemental analyzer and then injected into the optical ring-down cavity along a flow of helium buffer gas. The CO2 concentration in the buffer gas as well as first estimates of the 13C/12C carbon isotope ratio are evaluated. While the fast flow through the cavity is sufficient for determination of the partial pressure of CO2, isotope ratios require a scan of the laser frequency and thus stopping and trapping of the sample at the correct timing.