A new concept for sensitive in situ stable isotope ratio infrared spectroscopy based on sample modulation.
Diode-laser absorption spectroscopy finds increasing applications in the emerging field of stable isotope research. To meet the requirements of the water isotopes measurement challenge in environmental research, ways have to be found to cope with the present limitations of spectroscopic systems. In this article, we discuss an approach based on the Stark effect in molecular spectra to reduce the influence of time-dependent, unwanted background structures generally superimposed on the desired signal from the spectral feature under investigation. A road map to high-sensitivity isotopic ratio measurements of water isotopes is presented. On the basis of an Allan Variance analysis of measured data, the detection limits have been calculated as a function of the integration time. To achieve the required optical density of about 6 x 10(-7) for H(2)(17)O measurements, the duty cycle has to be optimized and the implementation of a sample modulation within an optical multipass cell is a promising approach to increase the stability of spectroscopic instrumentation required for ecosystem research and airborne atmospheric platforms.
Werle
Peter
P
National Institute for Applied Optics, Largo E. Fermi, 6, Florence, Italy. pwwerle@inoa.it
Dyroff
Christoph
C
Zahn
Andreas
A
Mazzinghi
Piero
P
D'amato
Francesco
F
D007834:Lasers; D010103:Oxygen Isotopes / Q000032:analysis*; D013055:Spectrophotometry, Infrared / Q000295:instrumentation / Q000379:methods*; D014835:Volatilization; D014867:Water / Q000032:analysis* / Q000737:chemistry
D010103:Oxygen Isotopes; D014867:Water