Research On Stimulated Raman Scattering And Suppression Method In The Process Of Stimulated Brillouin Scattering

In the process of interaction between laser and materials resulting in producing scattering, stimulated Raman scattering(SRS) and stimulated Brillouin scattering(SBS) contend the energy of the pump, it has been an important research topic in recent years.In common used liquid medium, stimulated Brillouin scattering dominates when pumped by single longitudinal mode laser due to the steady state gain of st imulated Brillouin scattering is much higher than that in forward and backward stimulated Raman scattering, and stimulated Raman scattering is suppressed. However, with the increase of pump energy, stimulated Raman scattering will form of exponential growt h. In high power lasers, due to the high pump power density, stimulated Raman scattering become the factors that can not be ignored, it will lead to the reflectivity of stimulated Brillouin scattering energy down, beam quality variation of the pump and may lead to damage optical element.This thesis of stimulated Brillouin scattering of stimulated Raman scattering phenomenon research mainly in the following steps: the basic concept of SBS and SRS and classical electromagnetism theoretical analysis and deduction; in broadband laser pump, the design and experiment of forward SRS gain coefficient measurement in the small Raman frequency shift medium; a simple and effective design and experimental verification of SRS suppression method.Firstly, starting from the classical electromagnetic theory of SBS and SRS respectively, analyzes the SBS and SRS in the interaction process with materials, obtained the SBS steady state and transient conditions of vibration equation, the pump and Stokes coupling equation of SRS, the steady state and transient gain of SRS.Secondly, according to the theoretical result, establish the scheme of the relationship between SBS and SRS from SRS gain coefficient: use broadband laser(532 nm Nd:YAG mode-locked laser) as a pump source, the filtered forward SRS interact with pump light(coaxial direction and pulse waveform peak overlap) to amplify the first-order Stokes, finally using the spectral method to separate the first-order Stokes, measuring the first-order Stokes energy before and after amplification, the pump energy, pump and Stokes’ space-time overlapping effective area and pulse width, by simplified calculation the SRS gain coefficient of the medium is obtained. And on the basis of the results of the experiment of heavy fluorinated carbon materials, analyze the advantages and disadvantages of them as a SBS medium.Finally, through theoretical analysis, design a simple solution that can suppress the SRS, particularly insert a beamspliter in the interaction medium to separate the Stokes. Using this method under the pump of 700 MW/cm2, the forward SRS effect reduced 2.88 times, this method is simple in structure, can be repeatedly used in the media application many times in order to further reduce the phenomenon of the SRS.