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Speckle field is a relatively common phenomenon. But the speckle has special application value in nonlinear optical domain because it can be used to suppress different nonlinear processes that are caused by high power laser. To enhance the suppression capability, it is necessary to reveal the basic mechanism of the speckle parameter nonlinear optical interaction process. In this work, the coupling wave equation under the wave number mismatch condition is used to analyze the parameter process of speckles field. The solving process of the coupling wave equation is introduced in detail. And the wave number or phase matching condition is fully discussed. Furthermore, the threshold of the nonlinear gain is analyzed when the wave number does not fully meet the matching condition. To describe the solution of the coupling wave equation more clearly, the undetermined coefficient of the exact analytical solution is discussed. Since the boundary field will affect the confirmation of the undetermined coefficient, the characteristic of boundary field should be analyzed first. The nonlinear process of the speckle field is a three-wave interaction process. The different boundary conditions will affect the three-wave interaction process. And it is found that if the complex amplitudes of the three waves at the boundary are not zero, the undetermined coefficient will be changed with the phrase parameters of the three waves. To achieve the maximum value, the boundary waves must meet the phase matching condition. The wave number of the speckle filed is not an invariant, because of its random distribution characteristic. Therefore, during the analysis of the three-wave interaction process, the segment handling method is used to ensure the effective solving of the first order coupling wave equation. On the other hand, the randomly fluctuation of the wave number destroys the phase matching condition of the boundary. It is just through the basic mechanism that the speckle field can be used to suppress the nonlinear gain of high-power optical field. Both the theoretical analyses and the numerical calculation results show that the speckle field has good suppression effect for some typical nonlinear parameter process, such as stimulated Brillouin scattering.
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Keywords:
- speckles /
- parametric process /
- phrase match condition
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Google Scholar
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图 1 CPP产生散斑的光路示意图和CPP面型
Fig. 1. The speckles generated light path by CPP and the Surface shape of a CPP.
图 2 散斑场的纵向振幅和波数(差)变化. 蓝色虚线是散斑场的振幅, 红色实线是波数(差)
Fig. 2. Amplitude and wavenumber of speckles in longitudinal. The blue dot line is amplitude and the red solid line is wavenumber.
图 3 散斑的波数差(a)和增益曲线(b)对比
Fig. 3. The wavenumber difference of speckles (a) vs. the gain curve (b) of parametric process.
图 4 SBS后向散射光沿z轴的增长 (a) 增益系数g = 5×103/m的情况; (b) 增益系数g = 2×104/m的情况
Fig. 4. Gain curves of SBS backscatter light along axis z: (a) Gain coefficient g = 5×103/m; (b) gain coefficient g = 2×104/m
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[1] 叶佩弦 2007 非线性光学物理 (北京: 北京大学出版社) 第91页
Ye P X 2007 Nonlinear Optical Physics (Beijing: Beijing University Press) p91
[2] Divol L 2007 Phys. Rev. Lett. 99 155003
Google Scholar
[3] 约瑟夫. 古德曼著(曹其智, 陈家璧 译) 2007 光学中的散斑现象理论与应用 (北京: 科学出版社) 第1页
Goodman J W (translated by Cao Q Z, Chen JB) 2009 Speckle Phenomena in Optics-Theory and Applications (Beijing: Beijing Science Press) p1
[4] Froula D H, Divol L, London R A, Berger R L, Dppner T, Meezan N B, Ross J S, Suter L J, Sorce C, Glenzer S H 2009 Phys. Rev. Lett. 103 045006
Google Scholar
[5] Neumayer P, Berger R L, Callahan D, Divol L, Froula D H, London R A, MacGowan B J, Meezan N B, Michel P A, Ross J S, Sorce C, Widmann K, Suter L J, Glenzer S H 2008 Phys. Plasmas 15 056307
Google Scholar
[6] 项江, 郑春阳, 刘占军 2010 59 8717
Google Scholar
Xiang J, Zheng C Y, Liu Z J 2010 Acta. Phys. Sin. 59 8717
Google Scholar
[7] Wang Y, Yuan C X, Gao R L, Zhou Z X 2012 Phys. Plasmas. 19 103109
Google Scholar
[8] Rosenbluth M N 1972 Phys. Rev. Lett. 29 565
Google Scholar
[9] Liu C S, Rosenbluth M N, White R B 1974 Phys. Fluids 17 1211
Google Scholar
[10] 汪卫星, 常铁强, 苏秀敏 1994 43 766
Google Scholar
Wang W X, Chang T Q, Shu X M 1994 Acta. Phys. Sin. 43 766
Google Scholar
[11] McKinstrie C J, Li J S, Giacone R E, Vu H X 1996 Phys. Plasmas 3 2686
Google Scholar
[12] Eliseev V V, Rozmus W, Tikhonchuk V T, Capjack C E 1996 Phys. Plasmas 3 2215
Google Scholar
[13] Kruer W L, Wilks S C, Afeyan B B, Kirkwood R K 1996 Phys. Plasmas 3 382
Google Scholar
[14] Follett R K, Edgell D H, Froula D H, Goncharov V N, Igumenshchev I V, Shaw J G, Myatt J F 2017 Phys. Plasmas 91 031104
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