By Stimulated Brillouin Scattering Signal Detection And Processing

The Brillouin scattering technique is not only able to detecting the sound speed, the salinity and the depth of the sea, but also can be applied to identifying target, i.e. identifying whether there are torpedo and submarine etc underwater, which has great sense and importance for us to understand ocean and solidify our national defence. The primary characteristic of Stimulated Brillouin scattering is that the scattering light has a frequency shift relative to the incited light. When the stimulated Brillouin scattering technique applying in underwater detection, if the intensity of laser reaches the threshold value, the stimulated Brillouin scattering occur, and if there are objects underwater, for the absorption and scattering of light by the object, the stimulated Brillouin scattering will disappear, so we can identify the object underwater by detecting the Brillouin scattering light. The detecting, processing and identifying of stimulated Brillouin scattering signals and the measuring of the Brillouin frequency shift are important steps in underwater detecting by using stimulated Brillouin scattering.The Brillouin frequency shift in water divided by the frequency of the incidence light is in 10"5 magnitude, which can be identified by Fabry-Perot interferometer. Circular interference fringes are produced after incidence light and scattering light go through the Fabry-Perot interferometer. For the relationship between the Brillouin frequency shift and the space-between-rings, the Brillouin frequency shift can be calculated by measuring the space-between-rings. For the characteristic of the Fabry-Perot interference fringes, this paper introduced a new method to obtain the center and the diameter of Fabry-Perot interference fringes, and a set of software is written with this method using Visual C++ , which can obtain the center and the diameter of Fabry-Perot interference fringes, then the Brillouin frequency shift can be calculated.The laser underwater detection technique detect underwater object by identifying the existence of Brillouin scattering signals. For the laser underwater detection technique, this paper introduced two experiment programs to identify the Brillouin scattering signals. In the first experiment program, we use CCD to get the image of Fabry-Perot interference fringes, which can be identified by the software. In the second experiment program, for the difference of the time-delay of the scattering light signal and the reflected light signal, the wave crest which present different light signals will appear at different position in oscillograph. Through the detection of the wave crest, we will know the existence of underwater object and the depth of the object in water. In the program, a set of software is written using Visual basic, which can be used to control the communication between oscillograph and computer, identify the signals and calculate the depth. This paper completed all the work in the two experiment programs, and got excellent result in experiment.