Seed laser frequency stabilization for Doppler wind lidar

Abstract

We demonstrate a tunable wavelength-locked seed laser source with high-frequency stability to realize the precise measurements of global atmospheric wind field. An Nd:YAG laser at 1 064 nm is used as the master laser (ML). Its frequency is locked to a confocal Fabry-Perot interferometer by using the Pound-DreverHall method, which ensures the peak-to-peak value of its frequency drifts less than 180 kHz over 2 h. Another Nd:YAG laser at 1 064 nm, as the slave laser, is offset-locked to the above ML using optical phase locked loop, retaining virtually the same absolute frequency stability as the ML. The tunable ranges of the frequency differences between two lasers are up to 3 GHz, and the tuning step length was an arbitrary integral multiple of 200 kHz. The researched seed laser source is compact and robust, which can well satisfy the requirement of the Doppler wind lidar.OCIS Wind field, as an important parameter of the atmospheric dynamics and climate variability, can be used to obtain the rule and tendency of atmospheric changes. Doppler wind lidar (DWL) is not only able to obtain the wind field distribution information, but can also measure cloud top height, vertical distribution of cloud, aerosol properties, and changes of the wind field. Currently, DWL is the only tool appropriate for realizing the direct measurements of global three-dimensional (3D) wind profile [1,2] . According to the principle of detection, DWL can be divided into two kinds: coherent DWL, which uses the heterodyne method to detect the aerosol backscatter spectrum, and incoherent DWL, which directly detects both aerosol and molecular backscatter spectra. Very low aerosol concentrations are present in the free troposphere over the mid-oceanic regions and large regions of the southern hemisphere. Consequently, incoherent DWL has incomparable advantages relative to coherent DWL. Meanwhile, the wind profiles over large parts of the tropics, as well as the major oceans, are difficult to measure using ground-based DWL. Therefore, space-borne incoherent DWL is required to measure the whole global wind field. In the system of the space-borne incoherent DWL, the detection unit will falsely treat the frequency jitters of the laser source as the Doppler shifts caused by wind. The speed of spacecraft can also bring the Doppler shifts into the DWL, thereby seriously affecting the measuring accuracy of wind speed [3,4] . As a result, the laser source in space-borne incoherent DWL must have high-frequency stability and large tuning range.The most common approach for laser stabilization is to use a single laser locked to a stable external reference, and then directly diffracting it with an acousto-optic modulator (AOM) or an electro-optic modulator (EOM). However, this method is not feasible when the tuning range goes up to several gigahertz or higher. In order to solve the above problem, the approach of using two individual lasers to separate the requirements of frequency stability and large tuning range is introduced. The master laser (ML) is locked to...

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