= Temporal coherence from crossed beams
{title2=$I(y)=I_0+\operatorname{Re}\Gamma(\sqrt2y/c)$}
Split one stationary scalar optical field into equal copies travelling at right angles with common transverse <linear polarization>. For wavevectors $k(\widehat{\mathbf x}\pm\widehat{\mathbf y})/\sqrt2$, the relative geometric delay is $\sqrt2y/c$ in <vacuum>, while the delay on the $x$ bisector is zero. The electric-field intensity convention gives the displayed pattern and $I(x)=2I_0$. The mean <Poynting vector> points along $+x$, with magnitude $I(y)/\sqrt2$ in that convention. A transverse detector can record the $y$ profile if it resolves the period $\lambda/\sqrt2$; a longitudinal $x$ profile is not a transverse camera image.
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