受激布里渊散射（SBS）因其广泛应用而受到极大关注，其特性和一些重要参数已经被研究并获得报道。但目前对于发生受激布里渊散射入射激光的阈值并没有一个合理的定义，对于阈值的测量也没有一个统一客观的方式，从而导致不同人对于同一种材料的受激布里渊散射的阈值测量所得的结果不一样。我们的研究就是针对于此而提出来的。 本文首先简要介绍了光散射，特别是受激布里渊散射理论；然后阐述了我们用光强来对介质中受激布里渊散射处于稳态和瞬态时入射激光的阈值进行的新定义；接着根据激光在介质中的传输规律，提出了一种测量阈值的新方法，并用该方法进行了实验；最后对实验结果进行了分析。我们在实验中以较高纯度的水为介质，研究了不同长度水池中，两种不同线宽的激光在不同能量下的衰减情况，讨论了激光在水中的衰减规律，根据其规律提出测量受激布里渊散射的阈值的新方法。实验中的阈值由入射激光的能量来表述。该方法是通过宽带宽和窄带宽激光在水中衰减系数曲线的分离来确定阈值，而不是通过测量背向布里渊散射信号的能量来确定阈值。实验表明，在对介质中能发生受激布里渊散射的入射激光的阈值重新定义后，利用我们所提出的方法确定入射激光在不同长度水池中的入射激光的SBS阈值，既简单方便，又能使对阈值的定义和测量具有统一客观的标准。

Stimulated Brillouin scattering (SBS) has attracted general attention owing to its broad applications. Its characteristics and some important parameters had been investigated and reported. But, at present, there are no suitable definitions of the threshold value of SBS. And, there is no uniform and objective method to measure the threshold value of SBS, too. The result is that different values would be obtained by different people even for the same material. Our study is put forward to settle this problem.In this paper, we first describe the theory of light scattering, especially the stimulated Brillouin scattering. Then we bring forward new definitions of the threshold value of steady state and transient state of SBS in terms of laser-intensity. Then, a new method based on the rule of transmission of laser in medium is suggested to measure the threshold value of SBS experimentally. At last, the results are presented and analyzed.In our experiment, pure water is used as the medium. We study the attenuation of pulsed laser in water cells of different length at different pulse energy, with two kinds of bandwidth. Based on these studies, a new accurate method for measuring the threshold value of stimulated Brillouin scattering (SBS) in terms of laser energy is proposed. In this method, the threshold value of SBS is determined by the deviation of the values of the attenuation coefficients of wide and narrow line width laser in a material rather than determined by the energy of back scattered SBS signal. The results are in good consistency with the theory. This shows that the proposed new definitions and measuring method are clear and simple, and accurate measurement can be achieved.