Pulsed slit jet cavity ring-down spectroscopy with a midinfrared lead salt diode laser

Abstract

We report the design, construction, and evaluation of a midinfrared continuous wave cavity ring-down spectrometer based on a lead salt diode laser. A pulsed molecular beam assembly with a homemade slit nozzle was constructed and incorporated into the spectrometer. A computer program was developed to automate and to synchronize the timing of the cavity ring-down experiments with the pulsed molecular beam. To initiate a cavity ring-down event, a frequency detuning scheme is exploited to effectively block the laser from entering the ring-down cavity by rapidly shifting the laser frequency. The standard deviation of the experimental ring-down time, i.e., σ(τ)∕⟨τ⟩, was 0.63%, corresponding to a noise-equivalent absorption of 8.0×10−7 at a fixed laser frequency with an evacuated cavity with ten averaging cycles. A room temperature infrared spectrum of methane and a jet cooled infrared spectrum of propylene oxide at 3.3μm are presented.