![]() ![]() While light travels at about \(3 x 10^ m/s\) in a vacuum, it travels slower through any medium, depending on the optical density. The higher the optical density of a material, the slower light is able to pass through it. Refractive materials are described by their optical density, which is a measure of how much of the light gets absorbed by atoms in the material. They refract again once they leave the prism due to the differences in refractive properties between air and the prism. Shorter wavelengths (violet) get refracted more than the longer wavelengths (red). When white light hits the refracting surface, the different colors of light separate because of their differing wavelengths. Let’s take a look at each of them separately.ĭispersion occurs when light of different wavelengths, such as white light, hits a refracting surface, like a prism. Let’s get started!ĭispersion and diffraction are each descriptions of light interacting with matter in different ways, and both can be used to separate light of multiple wavelengths. In effect, a pinhole in a wire grid polarizer will act like an ordinary pinhole for light whose E vector is parallel to the wires, and will act like a sheet of glass for light whose E vector is perpendicular to the wires.Hi, and welcome to this video on the diffraction of light waves! In this video, we will compare and contrast diffraction and dispersion and take a look at how diffraction gratings work. The portion that has its E vector perpendicular to the wires will pass right through the wire grid polarizer. The portion of the scattered light that has its E vector parallel to the wires in the grid will be absorbed. Scattered light, though, will hit the material of the wire grid polarizer. So, light that gets through the pinhole basically never touches the material that the pinhole has been punched into.Īs a result, if you make a pinhole in a wire grid polarizer and use the pinhole the way a pinhole is usually used, then most of the light, regardless of polarization, will go through the pinhole. The pinhole removes the scattered light, leaving a "clean" beam. The only portions of the beam that hit the material outside the pinhole are portions due to light that has been scattered upstream by, e.g., dirt on the optics. Due to the geometry of the light beam and the lens, the beam waist is usually in the range from 5 to 40 microns in diameter, and the size of the pinhole is chosen to be slightly bigger than the beam waist. When a pinhole filter is used, it is typically at the focus of a lens, so a light beam is as small as it can be when it encounters the pinhole. Essentially none of the photons whose E vector is parallel to the wires can get through, even though there seems to be space between the wires. ![]() For all practical purposes, photons whose E vector is perpendicular to the wires just go through as if the wires were not there. However, only the photons whose E vector is aligned with the wires can induce current in the wires and be absorbed. That's not the way it works.Įach photon is effectively much wider than the distance between the wires, so every photon that hits the wire grid polarizer "sees" the wires. You are imagining that some of the light hits the wires and some goes between the wires, and that the polarization filtering occurs only between the wires. ![]()
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