A Brillouin lidar for remote sensing of the temperature profile in the ocean: Towards the laboratory demonstration

The oceans cover more than 70% of the Earth´s surface and have a large influence on the world´s climate. The knowledge of their water temperature profile is a key to a deeper understanding of the climate system as it can provide valuable input to climate studies, weather forecast and physical oceanography. Concerning the upper-ocean mixed layer, a remote sensing lidar technique is a promising approach due to its flexibility and low cost. Based on the detection of spontaneous Brillouin scattering, we are currently developing such a rugged system for operation from a mobile platform. It consists of a pulsed laser system to generate spontaneously Brillouin scattered light and a detector to deduce the temperature from a frequency analysis of the backscattered light. The light source is a pulsed, three stage Yb-doped fiber amplifier with subsequent frequency doubling. Using this laser system we performed first range resolved temperature measurements in our laboratory setup. The setup involved a slow scanning Fabry-Pérot interferometer as a detector, which is not capable of real-time measurements. Switching to an edge filter based on an Excited State Faraday Anomalous Dispersion Optical Filter (ESFADOF) will provide this capability. So far, the amplifier generates laser pulses with an energy of up to 131μJ at 532nm. We currently switch its operating wavelength to render it compatible with the ESFADOF, providing the desired steep transmission edges with very low fluctuations. We are on the verge of demonstrating first temperature measurements with the ESFADOF under laboratory conditions.