Open-path ozone detection by quantum-cascade laser

Open-path ozone measurements performed by mid-IR differential absorption spectroscopy are reported. Ozone spectrum was taken by fast repetitive sweeping of a quantum-cascade laser wavelength over a spectral feature from the ν3 absorption band of ozone, centered at 1031.2cm-1. Short (100ns) sweeping times were essential to prevent line-distortions caused by atmospheric turbulence. For fast wavelength sweeping, a technique that employed the thermal chirp during 140ns excitation pulses was used. The lowest detection limit of 0.3ppm.m was estimated from the minimum detectable differential absorption. We present the results from cell and open-path measurements over 440 and 5800m, together with experimental data regarding the tuning range, the tuning rate and the tuning linearity of the QCL while operated with 140ns excitation pulse

Ozone detection by differential absorption spectroscopy at ambient pressure with a 9.6μm pulsed quantum-cascade laser

We report direct absorption spectroscopic detection of ozone at ambient pressure with a pulsed, DFB quantum-cascade laser (QCL) tuned within 1044-1050cm-1 by temperature scanning. Wavelength calibration curves were derived from FTIR and CO2 spectra and interpreted with respect to the heat transfer from the heterostructure to the sink. The laser linewidth (∼0.13cm-1 FWHM) was found to decrease with temperature, probably as a result of operation at constant current. Spurious spectral features due to baseline inaccuracies were successfully filtered out from the QCL O3 spectra using differential absorption. Reference O3 concentrations were obtained by applying the same method to UV spectra, simultaneously measured with a differential optical absorption spectrometer (DOAS). Column densities retrieved from QCL spectra are in fairly good agreement (±20%) with the DOAS values above 28ppm m. The estimated QCL lowest detectable, absolute and differential absorptions, (7×10-3 and 2×10-3, respectively), entail effective detection limits of 14 and 25ppm m, respectively. Ongoing improvements in the acquisition system should allow the achievement of detection limits at the level of commercial open-path DOAS systems (∼2ppm m) in the near future. Our results demonstrate the applicability of the differential absorption method to QCL spectroscopy at ambient pressure, and encourage its use for open path detectio

Ozone detection by differential absorption spectroscopy at ambient pressure with a 9.6 mu m pulsed quantum-cascade laser

We report direct absorption spectroscopic detection of ozone at ambient pressure with a pulsed, DFB quantum-cascade laser (QCL) tuned within 1044-1050 cm(-1) by temperature scanning. Wavelength calibration curves were derived from FTIR and CO2 spectra and interpreted with respect to the heat transfer from the heterostructure to the sink. The laser linewidth (similar to0.13 cm(-1) FWHM) was found to decrease with temperature, probably as a result of operation at constant current. Spurious spectral features due to baseline inaccuracies were successfully filtered out from the QCL O-3 spectra using differential absorption. Reference O-3 concentrations were obtained by applying the same method to UV spectra, simultaneously measured with a differential optical absorption spectrometer (DOAS). Column densities retrieved from QCL spectra are in fairly good agreement (+/-20%) with the DOAS values above 28 ppm m. The estimated QCL lowest detectable, absolute and differential absorptions, (7x10(-3) and 2x10(-3), respectively), entail effective detection limits of 14 and 25 ppm m, respectively. Ongoing improvements in the acquisition system should allow the achievement of detection limits at the level of commercial open-path DOAS systems (similar to2 ppm m) in the near future. Our results demonstrate the applicability of the differential absorption method to QCL spectroscopy at ambient pressure, and encourage its use for open path detection

Line-of-sight data transmission system based on Mid IR quantum cascade laser

We report on an application of a pulsed distributed feedback quantum cascade laser (QCL) for an open path data transmission. A pulse QCL in the 1046 cm(-1) range (28.7 THz) is used as a carrier signal source. The QCL is modulated with 50 ns pulses at repetition rate of 100 kHz, used as a sub-carrier. This sub-carrier is frequency modulated with a low frequency signal with bandwidth of 20 kHz (high quality sound signal)