The Analyzing Of Laser's Monochromatic And Stable Frequency Indexes In Lidar Based On Brillouin Signal Detecting

Lidar based on brillouin signal detecting is a new detecting technique that can acquire the underwater information. It not only be applied to detecting the depth of the sea, the temperature of the sea, the shoal and red tide, but also be able to identifying whether there are torpedo and submarine underwater, it's flexible, high-efficiency and real time, so it is one of the most perfect detecting technique for fast and large area ocean research.Detecting the small Brillouin frequency shift accurately is the key of Brillouin lidar underwater detection system to achieve real time and accurate detecting of underwater target and ocean circumstance parameters. Brillouin scattering is a phenomenon which is caused by the interaction of incited light and elastic sound wave of the medium, the primary characteristic of Brillouin scattering is that the scattering light has a frequency shift relative to the incited light.For brillouin signal detecting, double-edges detecting technique that based on Molecular absorption filter is an effective way of measuring the small Brillouin frequency shift. The detecting precision of Brillouin scattering frequency shift direct influence the detecting ability of the system and the detecting precision of the ocean parameters. The laser's central frequency will drift while working, if the excursion of the central frequency is too big, it will influence the measuring precision of Brillouin scattering frequency shift. By the method of simulating and calculating, we gain the absorption spectrum of molecule iodine absorption cell from 470nm~550nm, then combine with the requirement of edge technique, we choose the most perfect absorption line for underwater detecting system and ascertains the center emission frequency of laser emitter.The theory of using Brillouin lidar for sea detecting is analyzed, the relationship of Brillouin scattering frequency shift detecting precision and measuring precision of temperature and sound speed is gained. The relationship of the error of the resulting signals ratio△S and the frequency drift of the laser△v is given. The proper monochromatic and stable frequency indexes that satisfy the detecting system's precision demand are ascertained. These may have great contribution to the design of the practical Brillouin lidar system and emendation of the error.