p _ = ℏ k _ {\displaystyle {\underline {p}}=\hbar {\underline {k}}}
| k _ | = 2 π λ = ω c 2 | v _ | {\displaystyle \left|{\underline {k}}\right|={\frac {2\pi }{\lambda }}={\frac {\omega }{{c}^{2}}}\left|{\underline {v}}\right|}