A Long Path Differential Optical Absorption Spectrometer (LP-DOAS) system has been developed to measure simultaneously atmospheric trace gases concentration and spectral extinction coefficient in the visible region over a few hundred meter. Concentrations of atmospheric gases; SO2, NO2, and O3 are evaluated from the differential optical absorption spectra measured by system. Performance of the system was tested in the field over a 1500 m path length. The Differential Optical The field measurements were carried out and compared with those of a fixed monitoring system. The results show very good correlation, R2 > 0.7, for two gas species: NO2, and O3. Atmospheric visibility is estimated by integrating the measured spectral extinction coefficient over the visible region, at 550 ± 3 nm by considering the stability of xenon lamp and transmitted light intensity. During the measurement, average exctinction is 0.51/km and average visual range is 10.1 km. The amount of PM10 and the relative humidity affect the extinction. Because of the alignment of the optic system in DOAS system all measured data did not have quantitatively significant extinction coefficients.
Differential optical absorption spectroscopy (DOAS) is the method widely used to measure trace gases in the atmosphere. The key procedures in the retrieval algorithms of the recorded DOAS spectra are the separation of the absorption into two parts that represent respectively broad and narrow spectral features and the evaluation of absorption spectra. The linear least-squares fitting routines were used to evaluate absorption spectra in the past when the atmospheric spectra were modeled with a linear combination of known laboratory reference spectra to derive the concentrations. In this paper, a new analysis method to derive the concentrations was developed. The method is based on the data correlation and can get the simultaneous linear equations with unknowns of the concentrations (formula available in paper). Solving this n order linear equations can determinate the concentrations of trace gases. This new method considers the fingerprint features of the various trace gases in the same range of wavelength and reduces the influence caused by the detector noise and photon statistics.
The polyisocyanate random copolymer containing an asymmetric chiral carbon center and Disperse-Red-1 nonlinear optical chromophores is synthesized. The optical activity is measured at the visible and near infrared spectral ranges, confirming the existence of the induced optical chirality in the copolymer film. Upon the application of a Corona field to the slab waveguide copolymer film, the polarization rotation at the wavelength of 1.3 micrometers is found to be changed, opening the possibility of the chiral electro-optic modulation in a chiral polymeric waveguide thin film.