Minor Species Detection Using Infrared Cavity Ringdown Laser Absorption Spectroscopy with a Rapidly Tunable Compact Laser System

摘要

The capabilities of a compact gas-phase spectrometer based on infrared cavity ringdownrnlaser absorption spectroscopy (CRLAS) are demonstrated. This system, with some minorrnmodifications, will be shown to have the sensitivity and resolution to measure stablernspecies (reactants and products) as well as trace radical species (such as CH3) inrncombustion systems. The laser source consists of a cascaded optical parametric generatorrn(OPG), a frequency filter consisting of a miniature tunable Fabry-Perot etalon, and arnoptical parametric amplifier (OPA). The OPG and OPA stages are based on periodicallyrnpoled lithium niobate (PPLN), where the gain is large enough to allow the crystals to bernpumped with a compact, high repetition rate micro-laser. The system described here isrnshown to tune continuously in 200 cm~(-1) segments in the 2900-3100 cm~(-1) spectral regionrn(6500-6300 cm~(-1) for the signal output) with a resolution of 0.3 cm~(-1). With the selectionrnof additional (or more capable) PPLN crystals and frequency filters, the system isrncapable, in principle, of continuous tuning in 300 cm~(-1) segments, with a resolution ofrn0.05 cm-1, anywhere in the entire PPLN transparency region of 2220-7690 cm~(-1).