The article describes application of cavity enhanced absorption spectroscopy (CEAS) for detection of nitrogen oxides and vapours of explosives. The oxides are important greenhouse gases that are of large influence on environment, living organisms and human health. These compounds are also markers of some human diseases as well as they are emitted by commonly used explosives. Therefore sensitive nitrogen oxides sensors are of great importance for many applications, e. g. for environment protection (air monitoring), for medicine investigation (analyzing of exhaled air) and finally for explosives detection. In the Institute of Optoelectronics MUT different types of optoelectronic sensors employing CEAS were developed. They were designed to measure trace concentration of nitrogen dioxide, nitric oxide, and nitrous oxide. The sensors provide opportunity for simultaneous measurement of these gases concentration at ppb level. Their sensitivity is comparable with sensitivities of instruments based on other methods, e.g. gas chromatography or mass spectrometry. Our sensors were used for some explosives detection as well. The experiment showed that the sensors provide possibility to detect explosive devices consisting of nitroglycerine, ammonium nitrate, TNT, PETN, RDX and HMX.
The article describes an application of cavity enhanced absorption spectroscopy for nitric oxide and nitrous oxide
detection. Both oxides are important greenhouse gases that are of large influence on environment, living organisms and
human health. These compounds are also biomarkers of some human diseases. They determine the level of acid rain, and
can be used for characterization of specific explosive materials. Therefore the sensitive detectors of these gases are of
great importance for many applications: from routine air monitoring in industrial and intensive traffic areas, to detection
of explosives in airports, finally for medicine investigation, for health care, etc.
Our compact detection system provides opportunity for simultaneous measure of both NO and N2O concentration at ppb
level. Its sensitivity is comparable with sensitivities of instruments based on other methods, e.g. gas chromatography or
Multiwavelength micropulse lidar (MML) designed for continuous optical sounding of the atmosphere is presented. A
specific signal processing technique applying two directional Kalman filtering is introduced in order to enhance signal
to noise ratio. Application of this technique is illustrated with profiles collected in course of COAST 2009 and
WRNP 2010 research campaigns.
Results of measurements of atmospheric aerosol performed with multiwavelength lidar are presented. An approach to
retrieve profiles of aerosol particle size distribution was elaborated. It consists in direct fit of predefined distribution
(usually combination of lognormal functions with a few free parameters) to the experimental signals. The approach was
used for retrieving marine aerosol distributions. Studies of behavior of the particles at the cumulus cloud base were
performed as well. There the assumptions based on Twomey's model of the adiabatic parcel were used to support the
retrieving technique which was adopted to analyze lidar profiles (at 355, 532 and 1064 nm wavelengths) registered in the
region of the base of small warm cumulus clouds. Size distribution profiles and changes of particle effective radius
within the range of 0.5 - 3 μm were discussed.
We report temperature tuning of pulsed operated InGaN LDs (5×500μm stripe,
grown on low-dislocation, high-pressure grown GaN substrates). The devices
are characterized by a rather weak temperature dependence of the threshold
current. A very broad temperature tuning range of 16nm was obtained with
increase of operation temperature by almost 200K. We were able to tune the
diode from the initial wavelength of 415nm at room temperature up to 431nm
at 201°C. After thermally cycling the device no substantial degradation was
noticed. We observed multimode emission and mode hopping with temperature
increase. At 201°C the laser's threshold current doubled and the slope efficiency
of the L-I curve dropped by 35%. These results demonstrate the potential
usage of temperature tuning of nitride-based-LDs for the atomic spectroscopy-related applications.
We present the study of potential application of Cavity Enhanced Absorption Spectroscopy (CEAS) for
construction of fully optoelectronic and portable NO2 detector which could replace the commonly used chemical
detectors. We demonstrate an experiment on detection of NO2 in the ambient air. The concentration of investigated
absorber was found by determination of decay time of pulse radiation trapped in the optical cavity constructed with two
mirrors of a very high reflectivity coefficient (R > 99,99%). As a light source a blue pulsed diode laser was applied. The
output signal was detected by a photomultiplier and analysed by a digital oscilloscope. For this construction the detection
limit better than 1 ppb was obtained. The cavity parameters and it's adjustment were controlled by a beam from a red
laser that is not absorbed by NO2. In order to perform the measurements in two spectral regions the special mirrors have
been developed. Study of influence of another NOx compounds (especially NO3) on final result was investigated as well.
We present an experiment on detection of nitrogen dioxide in free air using cavity enhanced spectroscopy. As a light source a blue pulsed diode laser was applied, while the output signal was detected with a photomultiplier. The absorber concentration was found by investigation of the optical resonator quality. It was done by determination of decay time of radiation pulse trapped in the cavity. Also the measurement of the phase shift between the output signal and modulation signal was used as the alternative method. The detection limit better than 1 ppb was demonstrated. The aim of this experiment was to study potential application of cavity enhanced absorption spectroscopy for construction of fully optoelectronic NO2 detector which could replace the commonly used chemical detectors.
Construction of a polichromator assigned to 9-wavelength lidar is presented. Combining the technique of narrowband interference filters and dispersion due to diffraction gratings the bandwidth of several nanometers as well as a relatively high transmission for each wavelength of interest has been achieved.
A new method of retrieving of the aerosol size distribution from the signals of a multiwavelength lidar is presented. The method allows to reconstruct the distribution without assuming the lidar ratio. The method was tested on artifical data. A good agreement with the assumed distribution was shown.
A prototype of multiwavelength lidar system for investigation of atmospheric aerosol particles distribution is presented. This technique consists on relation between of the cross section for the light scattering and the particle size as well as the scattered radiation wavelength. Our lidar working simultaneously on several wavelengths is based on the system with a Ti:Sa laser, generating the light pulses at λ=850 and λ=750 nm, which are also frequency doubled and tripled. Additionally a Nd:YAG laser, working on the fundamental and on its second harmonics (λ=1064 and λ=532 nm), is also used. Special algorithms for retrieving the aerosol particles size distribution from the lidar signals were elaborated. The system was applied during a field campaign in Karkonosze Mountains.
The growth of aerosol and ozone concentrations in the troposphere stimulates development of monitoring techniques allowing their detection. DIAL (Differential Absorption Lidar) is one of the most promising methods. It allows the remote measurements of selected pollutants within the range of few kilometers and with spatial resolution of few meters. We introduce the basic principles of the DIAL method and describe shortly our mobile lidar system. We present and comment selected registrations of ozone and aerosol concentration distributions obtained during summer field campaigns of 1997 and 1998.
We describe a mobile LIDAR laboratory designed to detect and to determine the concentration distribution of several pollutants, such as NO2, SO2, O3, toluene and benzene, as well as dust and aerosol. We present the principles of its operation and the basics of the construction. FInally we give the operational characteristics and the main parameters of the system.
The complexity of processes occurring in the atmosphere requires a continuous improvement of methods used for better understanding and predicting various atmospheric phenomena. The paper is dedicated to the atmospheric pollution, the important environmental problem on both global and local scale. Measurement techniques dealing with emission and emission processes as well as with creation, migration and distribution of pollutants are described. Because of high dynamics of these processes, conventional monitoring methods, even if performed in many local stations, are not able to satisfy the needs. Laser remote sensing, allowing to measure atmospheric contaminations spatially resolved over distances and altitudes of several kilometers, has recently become one of the leading techniques in environmental studies. We review the conventional as well as LIDAR techniques of atmosphere monitoring indicating their advantages and limitations. We concentrate on the DIAL method explaining its principle of operation, describing its features and showing examples of applications.
A novel construction of grazing incidence pulsed dye laser is presented. In this laser light beam passes two times through diffraction grating. Due to that the output laser spectrum is characterized by a narrow line and a very low background caused by amplified spontaneous emission.
A new method of rate constants for electron impact induced transitions between excited atomic levels
determination is presented. The results for 3P→4P and 3P→5S transitions in sodium atom are in
good agreement with Gryzinski's theory.