ON-LINE WAVELENGTH CALIBRATION OF PULSED LASER FOR CO₂ DIFFERENTIAL ABSORPTION LIDAR

Abstract

Differential absorption lidar (DIAL) remote sensing is a promising technology for atmospheric CO<sub>2</sub> detection. However, stringent wavelength accuracy and stability are required in DIAL system. Accurate on-line wavelength calibration is a crucial procedure for retrieving atmospheric CO<sub>2</sub> concentration using the DIAL, particularly when pulsed lasers are adopted in the system. Large fluctuations in the intensities of a pulsed laser pose a great challenge for accurate on-line wavelength calibration. In this paper, a wavelength calibration strategy based on multi-wavelength scanning (MWS) was proposed for accurate on-line wavelength calibration of a pulsed laser for CO<sub>2</sub> detection. The MWS conducted segmented sampling across the CO<sub>2</sub> absorption line with appropriate number of points and range of widths by using a tunable laser. Complete absorption line of CO<sub>2</sub> can be obtained through a curve fitting. Then, the on-line wavelength can be easily found at the peak of the absorption line. Furthermore, another algorithm called the energy matching was introduced in the MWS to eliminate the backlash error of tunable lasers during the process of on-line wavelength calibration. Finally, a series of tests was conducted to elevate the calibration precision of MWS. Analysis of tests demonstrated that the MWS proposed in this paper could calibrate the on-line wavelength of pulsed laser accurately and steadily.