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Application of stimulated rotational Raman scattering technique in NO2-DIAL system

Differential Absorption Lidar (DIAL) for detecting atmospheric pollution is used extensively for its high precision and spatial resolution. The selection of the suitable absorption wavelength and the stimulation and modulation of the corresponding laser source are of key importance for DIAL system. This literature presents first a new approach for attaining the specific absorption wavelength in design of the new type NO2-DIAL. The third harmonic of Nd:YAG laser itself is taken as the selected λon (354.7 nm), and is converted to the circularly or elliptically polarized laser to pump the D2 Raman cell, acquiring plentiful frequency spectrum of stimulated vibrational and rotational Raman scattering light, among which the first-order pure stimulated rotational Raman scattering light nearest to the pumping laser wavelength is taken as the λoff (359.9 nm) for DIAL. The polarization state of the pumping laser can be conveniently modulated by using a λ/4 wave-plate. It is of large advantages in raising the technical performance and the economical efficiency. The technique will be very useful for DIAL to detect other constituents of atmospheric pollution.