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

摘要

We describe a prototype instrument using a Peltier cooled quantum cascade laser for precise measurement of stable carbon (C-13/C-12) 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 parts per thousand (2 sigma standard error of mean of 11 samples) in 10 min of analysis time. The standard deviation of 0.18 parts per thousand 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.