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Reflection Grating

Reflection grating consists of an array of $ N$ equally spaced, identical narrow reflecting grooves or ridges on a non-reflecting surface. The spacing between the grooves is $ d=10^{-6}$ m. Light from a distant source falls normally (that is, perpendicularly to the surface) on the grating. A distant observer observes light reflected at angle $ \theta$, see Fig. 2.

(a)
If the source emits blue light (wavelength $ \lambda=450$ nm), what values of the angle $ \theta$ correspond to principal maxima? Does the answer depend on $ N$?

(b)
If the source emits red light (wavelength $ \lambda=700$ nm), what values of $ \theta$ correspond to principal maxima?

(c)
Using the above results, explain why the surface of a compact disc looks ``rainbow-colored'' when seen from an angle.

HINT: Natural light is a mixture of waves with wavelength spanning the whole spectrum from blue to red.

Figure: Reflection grating.
\includegraphics[scale=1.0]{grating.eps}



Tomas Arias 2003-11-09