Based on absorption spectroscopy, Cavity Ring­down Spectroscopy (CRDS) works by attuning light rays from a Continuous Wave (CW) laser to a wavelength within the IR spectrum where a contaminant absorption peak occurs. By measuring the time it takes for the light to fade, or “ring­down” an accurate molecular count is calculated that is not pressure sensitive. The time of light decay, in essence, provides an exact, non­invasive, and rapid means to detect contaminants in gases.