Bragg diffraction from a cubic crystal lattice.  Plane waves incident on a crystal lattice at angle <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \theta }"><semantics><mrow class="MJX-TeXAtom-ORD"><mstyle displaystyle="true" scriptlevel="0"><mi>θ<!-- θ --></mi></mstyle></mrow><annotation encoding="application/x-tex">{\displaystyle \theta }</annotation></semantics></math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/6e5ab2664b422d53eb0c7df3b87e1360d75ad9af" class="mwe-math-fallback-image-inline" aria-hidden="true" style="vertical-align: -0.338ex; width:1.09ex; height:2.176ex;" alt="\theta "></span> are partially reflected by successive parallel crystal planes of spacing <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle d}"><semantics><mrow class="MJX-TeXAtom-ORD"><mstyle displaystyle="true" scriptlevel="0"><mi>d</mi></mstyle></mrow><annotation encoding="application/x-tex">{\displaystyle d}</annotation></semantics></math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/e85ff03cbe0c7341af6b982e47e9f90d235c66ab" class="mwe-math-fallback-image-inline" aria-hidden="true" style="vertical-align: -0.338ex; width:1.216ex; height:2.176ex;" alt="{\displaystyle d}"></span>.  The superposed reflected waves interfere constructively if the Bragg condition <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle 2d\sin \theta =n\lambda }"><semantics><mrow class="MJX-TeXAtom-ORD"><mstyle displaystyle="true" scriptlevel="0"><mn>2</mn><mi>d</mi><mi>sin</mi><mo>⁡<!-- ⁡ --></mo><mi>θ<!-- θ --></mi><mo>=</mo><mi>n</mi><mi>λ<!-- λ --></mi></mstyle></mrow><annotation encoding="application/x-tex">{\displaystyle 2d\sin \theta =n\lambda }</annotation></semantics></math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/2edaffe141f9aea021b76c5ecdaffdccfd405c4c" class="mwe-math-fallback-image-inline" aria-hidden="true" style="vertical-align: -0.338ex; width:12.947ex; height:2.176ex;" alt="{\displaystyle 2d\sin \theta =n\lambda }"></span> is satisfied.
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