Power-modulated integrated path differential absorption lidar for probing benzene concentration

Abstract

Aimed at the regional open-path detection of benzene (C6H6) in the atmosphere, a power-modulated integrated path differential absorption (PM-IPDA) lidar is introduced and demonstrated. Two tunable interband cascade lasers (ICLs) with about 3.2 µm wavelength are utilized to generate the required PM optical signal. These two operation central wavelengths (CWs) of the PM-IPDA lidar are, respectively, 3236.6 and 3187.1 nm, which can mitigate the influence of significant gases such as H2O, CH4, and HCl on the detection performance. In this work, the fast Fourier transform algorithm is used to retrieve the measured values with the time resolution of 0.1 s corresponding to 104 sampling bins at the sampling rate of 100 kSps/s. The modulated frequency of the PM-IPDA lidar is selected as 10 kHz by laboratory experiments. The slow fluctuation characteristic of the benzene absorption spectrum within the vicinity region of 3.2 µm reduces the impact of small wavelength fluctuations on the performance of PM-IPDA lidar, although a scheme modulated only the driving current causes wavelength fluctuations of ∼±0.2nm. These laboratory experiments also indicate the PM-IPDA lidar can reduce the error resulting from 1/f noise. Open-path observation experiments show that the detection limit is about 0.60mg⋅m−3 and that the PM-IPDA lidar can be used for the regional open-path real-time detection of benzene.