On the temperature dependent characteristics of a photoacoustic water vapor detector for airborne application

A detailed study on the temperature dependent sensitivity of a wavelength modulated diode laser based photoacoustic (PA) water vapor detection system is presented. The temperature dependence of the resonance frequency, the Q-factor of the resonator, the microphone sensitivity and the response time is investigated. It is shown that the overall temperature dependent sensitivity of the system is primarily determined by the temperature dependence of the microphone sensitivity. Effort was made to improve the system’s accuracy for measurements under varying ambient temperature typical in airborne applications, while maintaining the fast response time of the PA system. For this purpose a wavelength-stabilization method is introduced, with which the wavelength instability of the laser can be decreased to be as low as 0.008 nm. Test measurements proved the feasibility of the implementation of the wavelength locking method within the framework of the CARIBIC (civil aircraft for the regular investigation of the atmosphere based on an instrument container) project.     

Measurements of the isotopic composition of water vapor using a DFG-based spectrometer at

We report on absorption measurements of the isotopic composition of water in a demineralized sample by means of wavelength modulation spectroscopy of H₂O lines in the spectral region around . The mid-IR radiation was obtained by difference-frequency mixing of the radiation of an extended cavity diode laser () and that of a diode-pumped monolithic Nd–YAG laser. Preliminary tests indicate the possibility of obtaining a precision for the ¹⁸O/¹⁶O, ¹⁷O/¹⁶O and ²H/¹⁶O isotope ratio measurements of the order of 1 per mil.     

A quartz-enhanced photoacoustic spectroscopy sensor for measurement of water vapor concentration in the air

A compact and highly linear quartz-enhanced photoacoustic spectroscopy(QEPAS)sensor for the measurement of water vapor concentration in the air is demonstrated.A cost-effective quartz tuning fork(QTF)is used as the sharp transducer to convert light energy into an electrical signal based on the piezoelectric effect,thereby removing the need for a photodetector.The short optical path featured by the proposed sensing system leads to a decreased size.Furthermore,a pair of microresonators is applied in the absorbance detection module(ADM)for QTF signal enhancement.Compared with the system without microresonators,the detected QTF signal is increased to approximately 7-fold.Using this optimized QEPAS sensor with the proper modulation frequency and depth,we measure the water vapor concentration in the air at atmospheric pressure and room temperature.The experimental result shows that the sensor has a high sensitivity of 1.058parts-per-million.     

Self-, N2- and O2-broadening coefficients for the CO2 transitions near-IR measured by a diode laser photoacoustic spectrometer

Using a high-resolution tunable diode laser photoacoustic spectrometer, self-, N₂ and O₂ pressure broadening coefficients for the first 11 transitions of ¹²C¹⁶O₂ in the R branch of the (30012) ← (00001) overtone band at the 6348 cm⁻¹ have been revisited at room temperature (∼298 K). Air-broadening parameters have also been calculated from the N₂ and O₂ measurements. The dependence of the broadening on rotational quantum number m is discussed. The recorded lineshapes are fitted with standard Voigt line profiles in order to determine the collisional broadening coefficients of carbon dioxide transitions. The results are compared to our previous measurements and to the values reported in the HITRAN04 database and by other research group with a different spectroscopic technique.     

On the sensitivity to temperature of the threshold current in a strained quantum-well semiconductor laser under a magnetic field

The sensitivity to temperature of the threshold current in a strained quantum-well semiconductor laser under a perpendicular magnetic field is determined quantitatively by means of a suitable merit parameter. The values taken on by this parameter are discussed in terms of changes in the temperature and in the magnetic-field strength.     

A spectroscopic study of water vapor isotopologues H2O, H2O and HDO using a continuous wave DFB quantum cascade laser in the 6.7 μm region for atmospheric applications

A quantum cascade spectrometer was used in the laboratory to study H₂¹⁶O, H₂¹⁸O and HDO line intensities near 6.7 μm. The spectral region ranging from 1483 to 1487 cm⁻¹, which is suitable for the in situ laser sensing of these isotopologues in the atmosphere, was investigated using a continuous-wave distributed feed-back quantum cascade laser. Eight lines of water vapor isopologues were studied—one line of the ν₂ band of H₂¹⁶O, one line of the 2ν₂-ν₂ band of H₂¹⁶O, two lines of the ν₂ band of H₂¹⁸O and four lines of the ν₂ band of HDO were carefully revisited. The measured intensities were thoroughly compared to relevant molecular databases and other experimental and calculated results. We also observe that the H₂O, D₂O, HDO equilibrium constant agrees excellently with previously determined values.