A grating has 8000 slits ruled across a width of 4 cm. (5) reduces to m dsin r (8) which is the diraction grating equation for normal incidence. Also notice that the maximum intensity of the double slit is 4 units, the 3-slit case has a maximum intensity of 9 units, and for 4-slits it is 16 units, as we expect when the amplitude increases by one unit with the addition of each slit. n d sin where, n 1, 2, 3,, is an integer known as order of the grating, is the wavelength, d is the distance between the two spectra and is the angle. In this case the grating formulation of Eq. Notice that the bright fringes for any number of slits occur at the same places as for the double slit (provided they have the same slit separation), and that the number of dark fringes between bright fringes goes up by one every time another slit is added. This illustration is qualitative and intended mainly to show the clear separation of the wavelengths of light. Putting these functions into a graphing calculator confirms what we found above, as well as what we suspect about \(n\) slits – that there are \(n-1\) dark fringes between each maximally-bright fringe.įigure 3.3.3 - Comparison of Interference Patterns by Number of Slits A diffraction grating is the tool of choice for separating the colors in incident light. A blazed grating also called echelette grating (from French échelle ladder) is a special type of diffraction grating.It is optimized to achieve maximum grating efficiency in a given diffraction order.
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