Single laser-based differential absorption lidar (DIAL) for remote profiling atmospheric oxygen

Abstract

Recently, we have demonstrated a longitudinally pumped tunable dual-wavelength Ti:sapphire laser that can operate at simultaneous dual-wavelength (765.0, 771.3 nm), (763.9, 772.2 nm), (763.5, 772.2 nm) and (762.4, 773.7 nm) with a pulse width of ∼20 ns and a maximum average power of ∼2.98 W at 1-kHz pulse repetition rate, corresponding to a slope efficiency of ∼34.7% [1]. In this paper, the feasibility of the contactless differential absorption lidar (DIAL) equipped with the dual-wavelength laser emitting at 762 nm (on-wavelength) and 773 nm (off-wavelength) on remote 3D-measurement of molecular oxygen, O2, has been investigated. Absorption by atmospheric oxygen A-band at 761.9 nm corresponds to the magnetic dipole transition b1Σb+(v′=0)←X3Σg−(v″=0) with absorption cross section of 5.749 × 10−3 cm−2 atm−1 at STP. The accuracy and dynamic range of the DIAL measurement can be extended by simultaneous transmission and detection the spectrally close “on” and “off” wavelengths generated in a compact single laser, in addition to reduce the cost, volume, and weight of the system. The results demonstrate that a concentration of less than 1 ppm by volume is detectable by the system if a path length of 1 km is used. It is noticeable that the wavelengths 762 nm and 773 nm in the near-infrared window spectral range (650–950 nm) allow lidar system to monitor dissolved oxygen in ambient water. This system can also be used from a satellite to quickly characterize O2 in H2O matrices in the outer solar system bodies.