Coherent combination of microsecond-pulse tapered amplifiers for a water-vapor differential absorption lidar
Résumé
Remote sensing techniques are critical in atmospheric research, such as the monitoring of the low tropospheric temperature and the water vapor distribution. Lidar is one type of remote sensing technique that can deliver an atmospheric measurement with high spatial and temporal resolutions 1. In this paper, we describe a diode-laser-based laser source at 828 nm in a master oscillator power amplifier (MOPA) architecture designed to be compatible with a water-vapor differential absorption lidar (DIAL). Two tapered amplifiers with a pulse duration of 1 µs and a repetition rate of 10 kHz are injected by a single-frequency DBR seed laser diode and coherently combined. The performance of the seed DBR laser diode and the tapered amplifiers are characterized. The phase dynamics during the pulse are analyzed, and we demonstrate that they do not significantly reduce the combining efficiency. The combined power is stabilized by a hill-climbing algorithm which actively corrects the low-frequency environmental noise. The average combined pulse energy is highly stable with relative fluctuations σon = 0.4%. The combined pulse energy reaches 10.3 µJ at the maximal operation current of 8.1 A with a combining efficiency above 82% ± 5%. This work demonstrates the coherent beam combination of micropulse tapered amplifiers and the interests of these techniques in lidar applications.
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