エバネッセント場
f ^ c u t ( k x ) = { 1 ( | k x | < k c ) 0 ( | k x | > k c ) {\displaystyle {\hat {f}}_{\mathrm {cut} }(k_{x})={\begin{cases}1&(|k_{x}|<k_{c})\\0&(|k_{x}|>k_{c})\end{cases}}}
これを、空間表示に戻すと、
f c u t ( k x ) = 1 2 π ∫ − ∞ ∞ d k x f ^ cut exp  ( i k x x ) = sin  ( k c x ) π x {\displaystyle {\begin{aligned}f_{\mathrm {cut} }(k_{x})&={\frac {1}{2\pi }}\int _{-\infty }^{\infty }\mathrm {d} k_{x}{\hat {f}}_{\text{cut}}\exp(ik_{x}x)\\&={\frac {\sin(k_{c}x)}{\pi x}}\end{aligned}}}