F. D'Amato

Tunable diode lasers and two-tone frequency modulation spectroscopy applied to atmospheric gas analysis

In this paper, we discuss the main features of a class of gas analyzers based on spectroscopic techniques with the aim of realizing fully automated systems which can be used for practical purposes. The technique we deal with is based on semiconductor diode laser as sources, emitting in the near infrared region of the electromagnetic spectrum, and the two-tone frequency modulation spectroscopy as the detection technique. We will describe the main features of a typical device and two particular apparata for industrial and biological applications.

Temperature dependence of foreign gas broadening and shift of the aQ(9,9) transition line of ammonia

N2, Air, O2, H2, Ar, and He broadening and shift of the aQ(9,9) transition line of ammonia have been measured in the temperature range 180–380 K with errors of ∼2 and 10%, respectively. All the measurements have been fitted with the well-known power law, which holds very well in the temperature range considered here. N2 pressure effects have also been compared with calculations based on the Anderson–Tsao–Curnutte (ATC) theory with mixed results, anyway much more satisfactory for broadenings than shifts.

Temperature dependence of self-shift of ammonia transitions in the ν2 band

Abstract Pressure-induced lineshift has been measured as a function of temperature, in the range 200–400 K, for five transitions of the ν2 band of ammonia lines near 937 cm−1. Results are compared with semiclassical calculations that rely on the impact approximation. In general the theory does not agree very well with the experimental values of the shift, but the sign and the order of magnitude are confirmed. The present work shows that extensive and detailed measurement of the lineshifts is feasible and reliable, even when their absolute values in ammonia as a function of temperature are very small.

Pressure broadening in the second overtone of NO, measured with a near infrared DFB diode laser

Abstract Fundamental spectroscopical parameters of the second overtone band (3←0) of NO are reported using a high resolution, direct absorption spectrometer, based on a distributed feedback diode laser emitting at 1.8 μm. Line intensity, self- and nitrogen-line broadening coefficients have been measured with high accuracy in the second overtone of NO, for 7 groups of lines belonging to the R branch, from R(6.5) up to R(13.5) of the two electronic states 2 Π 1/2 and 2 Π 3/2 . The results for this band have been compared with available data on the fundamental band and the first overtone.

Variations in the sign of the pressure-induced lineshifts in the ν2 band of ammonia with temperature

The self-collisional shift of the aP(6,0) and aP(6,1) lines of the infrared ν2 ammonia band was measured as a function of temperature in the range 200–400 K. In agreement with theoretical predictions, the shift goes from negative (red shift) to positive (blue shift) with increasing temperature. Such a result must be taken into account in modelling the temperature dependence of pressure shift.

Measurement of atmospheric CO concentration with tunable diode lasers

Abstract The atmospheric concentration of CO at the Laboratories of ENEA in Frascati (Rome) has been investigated by measuring the optical absorption at ≈2077 cm−1 over a path of 104 m with a tunable diode laser apparatus developed in Russia and implemented in Italy.

High power pulsed millimeter laser Raman generation in CH3F

Abstract This work reports about the production of millimeter Raman pulsed emission obtained in CH 3 F by means of a high pressure continuously tunable CO 2 laser. Some new strong lines are observed with peak power up to the kW range. The results are in agreement with the Raman scattering theory. The emissions are observed by tuning the CO 2 laser over several GHz.

Emission of simultaneous tunable off-resonance and line centre FIR Raman lines in NH3 and CH3F

Abstract By pumping with a continuously tunable CO2 laser we have analysed the FIR emission of the sR(3,0) ammonia line and the λ=2 mm emission of the R(1) CH3F absorption line. The simultaneous emission of an off-resonance tunable Raman frequency and an untuned line centre one has been observed. The results agree with the theory. In addition about 8% tuning of the mean FIR frequency was observed at 150 GHz.

A midinfrared laser spectrometer for the in-situ measurement of stratospheric nitrous oxide

In this paper, mid-infrared spectrometer based on a liquid nitrogen cooled lead-salt diode laser, emitting at 2190 cm/sup -1/ for the in-situ measurement of stratospheric nitrous oxide is developed. The system operates unattended for several hours under changing ambient conditions: during flight, the pressure is ranging from 1000 down to 30 mbar, temperature ranges from +70/spl deg/C to -90/spl deg/C. Typical flight measurements are performed between 10000 and 22000 m of altitude and at an aircraft speed of 160-190 m/s.

A compact near-infrared diode-laser analyser for the measurement of atmospheric methane profiles on an airborne platform

In this paper, compact near-infrared distributed feedback diode-laser, emitting at 1.651 micron for the measurement of atmospheric methane profiles on an airborne platform is developed. The detection technique is based on two-tone frequency modulation spectroscopy. The calibration procedure for the analyser with respect to pressure changes during the flight mission is also discussed.