Strong smog penetrating capability of quantum cascade laser at 8.9 micrometre

Abstract

To solve the problem that existing near-infrared (NIR) target recognition system cannot penetrate the dense smog, in long-wave infrared (LWIR) target recognition system the smog penetrating capability of quantum cascade laser (QCL) at 8.9 micrometre has been studied. A normalized multiple-particle distribution model has been built firstly and increase threshold values have been derived. According to the calculation, the LWIR scattering and extinction parameters are lower than NIR corresponding parameters. Moreover, the echo power of LWIR detection laser is 2–3 orders of magnitude higher than that of NIR detection laser in dense smog, and the echo signal-to-noise ratio (SNR) is higher 40 dB–80 dB than that of NIR laser. Finally, The strong penetration capability of the 8.9μm QCL is also demonstrated experimentally by comparing it with 0.65μm laser, the maximum value of the its penetration distance is up to 36 m by using 30 mirrors with the total optical path of 71.3 m, and its attenuation parameter is less than <1%/m in the dense smog. Based on the presented results, the application of LWIR QCL in dense smog will be broadened.