A high precision pulsed quantum cascade laser spectrometer for measurements of stable isotopes of carbon dioxide

We describe a prototype instrument using a Peltier cooled quantum cascade laser for precise measurement of stable carbon (13C/12C) isotopologue ratios in atmospheric CO2. Using novel optics and signal processing techniques in a compact instrument, we are able to detect the difference between sample and reference with a precision of 0.1‰ (2σ standard error of mean of 11 samples) in 10min of analysis time. The standard deviation of 0.18‰ for individual 30 s measurements shows that this prototype instrument already approaches the best reported literature values using continuous wave lead alloy tunable diode lasers. The application of pulsed near room-temperature quantum cascade lasers to this demanding problem opens the possibility of field worthy rapid response isotopic instrumentation and attests to the maturity of these lasers as spectroscopic sources.