Measurements of Nitrogen Concentration using Raman-Induced Polarization Spectroscopy (RIPS) at STP Conditions

摘要

We report measurements of molecular nitrogen via pulsed Raman-Induced Polarization Spectroscopy (RIPS) using probe-laser radiation at ～532 nm and pump-laser radiation at ～607 nm. The pump and probe beams are crossed so as to obtain a maximum overlap length, thus generating higher Raman signals. The signal is passed through a polarizer and detected using a photomultiplier tube. Atmospheric mixtures of N{sub}2-Ar are studied with concentrations varying from 0% to 79% N{sub}2 to determine the detection limit. Pump and probe energy levels are varied independently to study signal dependence on laser irradiance. These pulsed measurements are compared to those obtained via RIPS using a cw-probe laser. A comparison between cw-probe RIPS and pulsed-probe RIPS shows potential for improvement in the detection limit when using the latter technique. Detection limits using the two RIPS techniques are analyzed to suggest their applicability for measuring other species in practical combustion systems.