Dual-wavelength locking technique for coherent 2-µm differential absorption lidar applications

A dual-wavelength locking technique for coherent 2-µm differential absorption lidar (DIAL) applications has been developed for simultaneously measuring water vapor (${{\rm{H}}_2}{\rm{O}}$) and radial wind velocity profiles. The two wavelengths for DIAL measurement were stabilized by sidebands of an electro-optic modulated laser, which was locked to the ${{\rm{CO}}_2}$ R30 absorption line. We selected wavelengths of 2050.550 and 2051.103 nm to minimize the effects of height-dependent temperature and pressure variations. The long-term wavelength stability of the two locked lasers of ${\lt}{0.2}\;{\rm{pm}}$, which corresponds to 14 MHz, was achieved. The DIAL instrument using the developed technique meets the requirement of measuring the ${{\rm{H}}_2}{\rm{O}}$ concentration with a systematic error ${\lt} {{5}}\%$ below an altitude of 5 km.