Littrow configuration
= Littrow configuration
{c}
In the Littrow configuration the selected diffracted ray retraces the incident ray, so $\alpha=\beta$ and the <grating equation> becomes $m\lambda=2d\sin\alpha$.
= Littrow configuration
{c}
In the Littrow configuration the selected diffracted ray retraces the incident ray, so $\alpha=\beta$ and the <grating equation> becomes $m\lambda=2d\sin\alpha$.