Illustration 37.2: Dielectric Mirrors

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For applications that require mirrors with very high reflectance (such as a laser mirror), several dielectric layers are used to build the mirror. A typical mirror uses alternating indices of refraction to increase the reflectance to more than 98%. In the following example the mirror is made of alternating layers of zinc sulfide (n = 2.3) and magnesium fluoride (n = 1.35) film. The table shows the electric field. The intensity of the wave is n*E*E, which is proportional to the square of the electric field (and the energy of the wave). Restart.

When the animation is in its initial state, the incident light encounters only empty space. The data table shows you that, of the incident light (represented by E), all is transmitted (Etrans = E) and none is reflected (Eref = 0). This is an obvious result because there is nothing to reflect from. Now add a layer of film by clicking on "add film." A layer of zinc sulfide and a layer of magnesium fluoride are added. What happens to the intensity of the transmitted and reflected light?

Now add several more layers. Notice that as each layer is added, more light is reflected and less escapes. By building a substance of alternating layers of carefully chosen materials you have constructed a mirror!

Physlets were developed at Davidson College and converted from Java to JavaScript using the SwingJS system developed at St. Olaf College.

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