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Basics of Optics
by Ron Kurtus (25 June 2006)
Optics is the branch of physics that studies the physical properties of light. This includes visible light, as well as other electromagnetic wavelengths such as infrared and x-rays. The three main parts of optics consist of the generation of electromagnetic waves, controlling the propagation of the waves, and detection of the energy.
Questions you may have include:
- How are the various electromagnetic waves generated?
- How is the propagation of the waves controlled?
- How is the energy detected and processed?
This lesson will answer those questions.
Generation
Long electromagnetic waves such as radio and television are usually created through the movement or oscillation of electrons. The shorter microwaves use a special very-high frequency oscillation of electrons to create their radiation.
Heated matter is a major source of radiation in the visible and near visible regions (infrared and ultraviolet). Atomic orbital effects, such as electrons changing orbits when stimulated or struck by other electrons, also can cause visible light emission. A fluorescent bulb and laser are examples.
Very short wavelength radiation such as x-rays are created when high energy electrons collide with atoms. Gamma rays are caused by nuclear collisions and reactions.
Controlling propagation
Goals in controlling the propagation of electromagnetic radiation include selectively filtering wavelengths, reducing the amplitude of the radiation, and controlling the direction of the waves.
Lenses and mirrors can be used to direct and focus the electromagnetic waves. Glass lenses can be used for visible light, but other materials and methods must be used for wavelength regions outside the visible.
Your eye has a lens that focuses light to your retina. A major purpose of controlling propagation is to focus the radiation on a detector for image or information processing.
Detection
Detection of electromagnetic waves can be by chemical, mechanical and/or electrical reactions caused by the radiation. There are also some nuclear reactions used to detect radiation.
Your eye detects visible light on the retina, through an electro-chemical reaction. Older cameras detect light through a chemical reaction on the photographic film. Newer digital cameras have arrays of small detectors that create electrical charges when radiated. X-rays can be detected by photographic film or special digital cameras.
Infrared is often detected by its property of heating matter. The heat is used to create an electrical current or can be detected through increased electrical resistance. Microwaves heat matter but also can be detected by directly causing a current. Radio waves require an antenna that creates a current when the waves strike it.
Summary
Optics concerns the study of physical properties of electromagnetic radiation, including visible light, infrared and x-rays. The three main parts of optics consist of the creation of electromagnetic waves, controlling the propagation of the waves, and detection of the energy.
See the light
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