<title>Open path measurements of ozone, water vapor, CO<formula><inf><roman>2</roman></inf></formula>, and atmospheric temperature using intrapuls tuning method of quantum cascade laser</title>

Abstract

We report on application of a distributed feedback (DFB) quantum cascade laser (QCL) for open path spectroscopic monitoring of ozone, water vapor, CO₂ and air temperature. The thermal chirp during a 400 ns long laser pulse at repetition rate of 1 kHz is used for fast wavelength scanning of two water vapor absorption lines, few O₃ lines and a CO₂ line, centered at 1032 cm^-1. A tuning range of 1.7 cm^-1 is achieved. The fast wavelength scanning of the QCL has the advantage of not being affected by atmospheric turbulence, which is essential for long open path measurements. A direct absorption method was adopted in the measurements. Monostatic experimental setup, consisting of a QCL, a retroreflector and a detector is employed. The lowest detection limit for ozone is about 0.2 ppb at 6 km open path. The relative humidity measurements sensitivity depends on the temperature and at 293 K is about 1%. The resolution of the temperature measurements is better than 0.5 K. The column densities and temperature retrieved from the transmittance spectra are obtained, performing averaging of 10 seconds, which is much shorter, compare to other open path techniques.