Differential optical absorption spectroscopy (DOAS) has become a widely used method to measure trace gases in the atmosphere. The concentrations of trace gases can be retrieved by fitting differential absorption spectra with standard differential absorption cross-section using the linear least-square method. The basic principle of DOAS is introduced. The construction of DOAS on-line monitoring system is designed and the retrieval method of trace gases concentration based on the principle of least-squares is discussed. The properties of DOAS system are tested by experiments. The advantages of DOAS system used in atmosphere quality monitoring are shown.
White Cell is a typical multiple-path absorption cell for absorption spectroscopy. For multi-path enhanced absorption
application, we should make sure that the input light of the multiple-path cell can be output as much as possible to
enhance absorption signal. Thus the astigmatism of the White cell should be analyzed for optimization as a key factor. In
White cell, the astigmatism is difficult to be calculated as the meridian and sagittal planes of the beam would rotate with
a different angle while at each reflection. In this article, the White cell is presented by defined 4×4 optical matrices as a
nonsymmetrical system. The astigmatic difference would then be obtained from the eigenvalues of the partitioned
matrices. The numerical computation and ray-tracing simulation results presented have proved the efficiency of this
method. The astigmatism can be improved by properly choosing the distance h between the two rows of image spots on
the field mirror.
Dual-wavelength method is a research focus in nonvolatile holographic storage. However, both theoretical analysis and experimental demonstration that nonlinear enlargement is inevitable during dual-wavelength readout. By analyzing the speciality of nonlinear enlarge factor, a method of choosing the suitable retrieving angle is proposed, which can prove the uniform enlarge factor and a least efficiency of 44% at a thin thickness such as 10 um to that of Bragg match. In this paper, At last, a novel scheme which achieves simultaneous dual-wavelength readout of two polarization multiplexed holograms is proposed and demonstrated by the experiment.
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