Generation of high intensity speckles in overlapping laser beams

Liang Hao; Jie Qiu; Wen Yi Huo

doi:10.1063/5.0123585

Journals >Matter and Radiation at Extremes >Volume 8 >Issue 2 >Page 025903 > Article

Matter and Radiation at Extremes
Vol. 8, Issue 2, 025903 (2023)

Generation of high intensity speckles in overlapping laser beams

Liang Hao, Jie Qiu, and Wen Yi Huo^a)

Author Affiliations

Laboratory of Computational Physics, Institute of Applied Physics and Computational Mathematics, Beijing 100094, China

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DOI: 10.1063/5.0123585 Cite this Article

Liang Hao, Jie Qiu, Wen Yi Huo. Generation of high intensity speckles in overlapping laser beams[J]. Matter and Radiation at Extremes, 2023, 8(2): 025903 Copy Citation Text

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Abstract

A new mechanism for the generation of high intensity speckles by coupling of overlapping beams is discovered and studied in detail. Using three-dimensional simulations, the coupling of overlapping beams smoothed by phase plates and by polarization smoothing are investigated in the regime relevant to inertial confinement fusion studies. It is found that the intensity distribution of the laser beam spot can be changed by nonuniform spatial phase modulation, and the speckles formed by the phase plate can be split into smaller speckles with higher intensities, which is favorable for the generation of laser plasma instabilities. Stimulated Brillouin scattering is compared in simulations with and without coupling of the overlapping incident beams, and the results confirm the enhancement of stimulated Brillouin scattering due to this mechanism.

{\vec{A}}_{α} = (\frac{1}{2} A_{α x} e^{i Ψ_{α}} + c . c .) {\vec{e}}_{x} + (\frac{1}{2} A_{α y} e^{i Ψ_{α}} + c . c .) {\vec{e}}_{y},

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{\vec{A}}_{B} = (\frac{1}{2} A_{B x} e^{i Ψ_{B}} + c . c .) {\vec{e}}_{x} + (\frac{1}{2} A_{B y} e^{i Ψ_{B}} + c . c .) {\vec{e}}_{y},

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\begin{align} δ n & = δ n_{⊥} + \frac{1}{2} \sum_{α \neq β} (δ n_{α β} e^{i (Ψ_{α} - Ψ_{β})} + c . c .) \\ + \frac{1}{2} \sum_{α} (δ n_{α}^{B} e^{i (Ψ_{α} - Ψ_{B})} + c . c .), \end{align}

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\begin{align} (\frac{\partial}{\partial z} + \frac{ν_{α}}{v_{g α}} + \frac{\partial k_{α}}{2 k_{α} \partial z} - \frac{i \nabla_{⊥}^{2}}{2 k_{α}} + \frac{i ω_{p e}^{2}}{2 k_{α} c^{2}} \frac{δ n_{⊥}}{n_{e}}) A_{α x} \\ = - \frac{i ω_{p e}^{2}}{4 n_{e} k_{α} c^{2}} (\sum_{β \neq α} δ n_{α β} A_{β x} + δ n_{α}^{B} A_{B x}) \end{align}

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\begin{align} (\frac{\partial}{\partial z} + \frac{ν_{α}}{v_{g α}} + \frac{\partial k_{α}}{2 k_{α} \partial z} - \frac{i \nabla_{⊥}^{2}}{2 k_{α}} + \frac{i ω_{p e}^{2}}{2 k_{α} c^{2}} \frac{δ n_{⊥}}{n_{e}}) A_{α y} \\ = - \frac{i ω_{p e}^{2}}{4 n_{e} k_{α} c^{2}} (\sum_{β \neq α} δ n_{α β} A_{β y} + δ n_{α}^{B} A_{B y}), \end{align}

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\begin{align} (\frac{\partial}{\partial z} - \frac{ν_{B}}{v_{g B}} + \frac{\partial k_{B}}{2 k_{B} \partial z} + \frac{i \nabla_{⊥}^{2}}{2 k_{B}} - \frac{i ω_{p e}^{2}}{2 k_{B} c^{2}} \frac{δ n_{⊥}}{n_{e}}) A_{B x} \\ = \frac{i ω_{p e}^{2}}{4 n_{e} k_{B} c^{2}} \sum_{α} δ n_{α}^{B *} A_{α x} \end{align}

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\begin{align} (\frac{\partial}{\partial z} - \frac{ν_{B}}{v_{g B}} + \frac{\partial k_{B}}{2 k_{B} \partial z} + \frac{i \nabla_{⊥}^{2}}{2 k_{B}} - \frac{i ω_{p e}^{2}}{2 k_{B} c^{2}} \frac{δ n_{⊥}}{n_{e}}) A_{B y} \\ = \frac{i ω_{p e}^{2}}{4 n_{e} k_{B} c^{2}} \sum_{α} δ n_{α}^{B *} A_{α y}, \end{align}

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\begin{align} δ n_{α β} & = - K \frac{{(k_{α} - k_{β})}^{2}}{8 π m_{e} c^{2}} (A_{α x} A_{β x}^{*} + A_{α y} A_{β y}^{*}) \end{align}

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\begin{align} δ n_{α}^{B} & = - K \frac{{(k_{α} - k_{B})}^{2}}{8 π m_{e} c^{2}} (A_{α x} A_{B x}^{*} + A_{α y} A_{B y}^{*}), \end{align}

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\frac{\partial A_{α x}}{\partial z} = i K \frac{ω_{p e}^{2} {(k_{α} - k_{β})}^{2}}{32 π n_{e} m_{e} k_{α} c^{4}} {|A_{β x}|}^{2} A_{α x} .

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f_{α i} (z) = \frac{{⟨| A_{α i} (x, y, z) |^{2}⟩}_{x, y}}{\sum_{i} {⟨| A_{α i} (x, y, 0) |^{2}⟩}_{x, y}},

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Liang Hao, Jie Qiu, Wen Yi Huo. Generation of high intensity speckles in overlapping laser beams[J]. Matter and Radiation at Extremes, 2023, 8(2): 025903

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