By David F.
Oct. 9, 2001
spectrum consists of the entire range of radiation that is made
of oscillating electrical and magnetic fields. The visible rainbow
produced by a prism is just a sliver of the entire spectrum. It
extends from radio waves, which can be thousands of feet long, to
gamma rays with wavelengths shorter than the diameter of the nucleus
of an atom .
You can think of light as pure energy. It doesn't have any mass
and it travels through space as an electromagnetic wave train. Each
color, or wavelength, is associated with a specific frequency and
amount of energy. The longer the wavelength, the slower the frequency
and the less energy a wave carries. In many cases electromagnetic
radiation acts like a classical wave, such as spreading out after
passing through a pinhole. However, light in its various forms is
also made up of discrete particles, called photons and in many circumstances
acts like a stream of particles.
waves are what AM/FM radio, wireless telephones, and television
stations use to send you popular songs, carry your conversations
and allow you to watch your favorite sitcom. Radio waves are produced
by causing electrons to vibrate back and forth in a metal antenna.
They are the longest waves in the electromagnetic spectrum and can
vary from more than 100,000 feet down to an inch.
radiation is used for radar, transmitting large amounts of information
across the country and warming food and popping popcorn. Microwaves
range from an inch to 1/25th of an inch in length.
radiation is associated with heat, although even objects like
ice, that we consider cold, emit IR waves. Radiant heaters use infrared
light to directly warm objects without heating the air around them.
IR sensors are also used in home security systems to detect intruders.
Vanderbilt's free-electron laser operates in this region of the
spectrum. Infrared waves range from 1/25th of an inch
down to a few millionths of an inch. The standard unit of measurement
in this region is the micron, which is one millionth of a meter,
or 1/25,000th of an inch.
matters most to people because it is what our eyes can see. But
it is a tiny sliver of the entire electromagnetic spectrum. We can
only see wavelengths ranging between 0.4 to 0.7 microns. If you
were building a scale model of the spectrum and set the width of
visible light equal to the width of a human hair, then the entire
spectrum would stretch about a light year, one quarter the distance
to the nearest star!
or UV radiation is produced by the Sun along with visible light.
With wavelengths between a tenth to a thousandth of a micron, UV
carries a greater punch than visible light. That is the reason it
causes sunburn and skin cancer. Fortunately, the atmosphere, including
the ozone layer, filters out much of the ultraviolet radiation before
it reaches the surface.
range from a thousandth to a 100 thousandth of a micron or, in smaller
units, from a nanometer to a hundredth of a nanometer. The smallest
X-ray wavelengths are comparable to the size of an atom. X-rays.
The first medical X-ray in America was taken at Dartmouth College
in 1896. The monochromatic X-ray developed at Vanderbilt holds promise
for significantly improving the quality and safety of medical X-rays.
are even more energetic than X-rays. The only natural sources of
gamma rays on Earth are radioactive materials. However, they are
created artificially by high-energy particle accelerators and nuclear
power plants. Gamma-ray wavelengths vary from a hundredth of a nanometer
down to a few hundred thousandths of a nanometer-lengths comparable
to those found in the nucleus of an atom. Gamma-rays are produced
by the some of the most energetic events in the Universe, such as
stellar explosions and matter falling into massive black holes.