1. Diffraction Gratings, and Interference in Thin Films
From soap bubbles to solar panels

2. What are diffraction gratings?
So far, we have discussed and learned about single and double slit interference. What happens when there are multiple slits?
Diffraction gratings are devices that have large numbers of equally spaced parallel slits that act as individual light sources. The diffraction patterns produced by these devices resemble those produced by double slits. As such, their minima and maxima can be calculated using

3. About Cont’d
So, what are some of the differences between double slit and a multiple slit interference patterns?
Multi-slit sources deliver more light energy; i.e. higher intensity. This produces brighter patterns.
Multi-slit sources have much sharper and narrower maxima.
The distance between successive maximums are greater on account of smaller slit separations, enhancing the resolution.

4. Types of diffraction gratings
There are two common types of gratings:
Transmission: The spaces between the diffraction lines (opaque) transmit light.
Reflected: The spaces between the gratings reflect the light as opposed to transmitting it. Metals can also be used.
Another type, although not
as common, is the crossed
grating. The image to the
left is a pattern produced by
such a grating

5. Application: Spectroscope
A well known example of an application of a diffraction grating is the spectroscope. Spectroscopes are used perform spectral analysis.
Recall that with a diffraction grating, the central maximum was mainly white light. However, as we went further out from the central maximum, we had a more pronounced distribution of colours.
Why do you think this is so?

6. Tomorrow: Interference in Thin films
What do soap bubbles and solar panels have in common?