Optical parametric oscillators with pumping by femtosecond pulses for broadband lidar gas analysis of atmosphere

摘要

The middle IR or so-called "fingerprint" region of atmospheric gases is most attractive for multicomponent remote gas analysis of the atmosphere. Femtosecond lidars can be applied to this purpose. In recent years compact powerful laser systems have been developed, which emit the pulses of femtosecond duration. First of all, those are solid-state lasers based on wide-band active media: Ti~(3+):Al_2O_3 (λ = 0.75-1 μm) and Cr~(3+):MgSiO_4 (1.2-1.32 μm). Frequency conversion of these quite promising and basic sources of super-short pulses into other spectral ranges using non-centrosymmetrical nonlinear crystals seems to be quite attractive, especially if preserving duration of the transformed radiation. Usually to overcome the problem middle IR femtosecond pulses are generating with two- or three-stage low efficiency frequency converters with nonlinear crystals. High efficiency middle IR semiconductor crystals are not suitable for one-stage generation because high optical loss at near IR.rnThis study was aimed at search and investigation of nonlinear crystals, in which effective single-stage optical parametric oscillators. The investigation includes estimation of phase- and group-velocity matching conditions, phase-matching spectral and angular widths, and potential efficiencies. The possibilities of using a hyper broadband nonlinear-optical frequency converter of femtosecond pulse radiation for design of multicomponent mixture analyzers are investigated. The method of broadband lidar sensing of atmospheric gases by the DOAS - technique (Differential Optical Absorption Spectroscopy) is described. The numerical simulation of DOAS sensing of atmospheric gas components using the frequency-converted femtosecond radiation is carried out.