The Inner Workings of a Ruby Laser
Introduction
Lasers are used in everyday life whether it is in a DVD or CD player, a grocery scanner, or a
laser pointer. Many people know what a laser is and how to use it, but not many people know
how a laser works. The internal structure of a laser is fairly simple, but the science behind it is
rather complicated. The scope behind this paper is to describe the components of a laser pointer
and what exactly what each component does. There are four main components to a standard
laser; a power source, flash lamp, an amplifying medium, and a mirrored tube. These parts are
shown are in figure 1.
Lasing Process
A basic laser consists of four
major parts. First there is a
flash lamp that is a excitation
energy that is pumped into an
amplifying medium. The
excitation energy is a light,
usually a flash lamp, which is
powered by an energy supply,
such as a battery. A flash
lamp is basically a florescent
light that is formed into a
spiral; this lamp is what
creates the light of the laser.
The amplifying medium is the
type of material in the laser
that increases the intensity of
the light that passes through it.
This medium can be a solid
liquid or a gas, for the typical
red laser pointer it is normally
a ruby. The final parts are the mirrors which are on both ends of the laser. The light from the
lamp then bounces back and forth between the mirrors until the wavelengths of the light become
equal and travel out of a tiny hole on one mirror. Figure 1 clearly illustrates the components of
the laser.
What is a Laser?
A laser (light amplification by stimulated emission of radiation) is a light that is concentrated
into a single wavelength. A wavelength is the distance from one crest of a wave to the crest of
the wave next to it. Figure 2 shows all the types of light and their wavelengths. As shown in
figure 2 the human eye can only see a very small amount of light, this light is called visible light.
Since only certain
range wavelengths of
light are visible to
humans the wavelength
of a laser must be
within that range. The
wavelength of that laser
will determine the color
of the laser, for
example a red laser, the
most common colored
laser, has a wavelength
of about 650
nanometers (1.0 nm =
1.0x10-9 m) to 750
nanometers.
Power Source
The power source is exactly what it sounds like. Since the laser is a beam of light it
needs electricity to be able to light up the bulb that is inside of the laser. This power
source is typically a battery that will discharge a burst of energy to the flash lamp (the
light bulb), that will feed energy to the laser.
Flash Lamp
The flash lamp is what feeds the laser the energy needed to emit a beam. The lamp emits
a burst of intense light that excites atoms that are in the ruby. This causes the atoms in
the ruby to jump to a higher energy level. Once the atoms reach a certain energy level
the atoms emit photons. Photons are particles of light that are emitted by atoms. When
one photon is emitted it bounces back and forth between the mirrors, and eventually that
photon will hit an atom which will then give off two photons, this is called stimulated
emission, and since one photon makes two photons the light is being amplified. This
stimulated emission only allows one wavelength to exist in the laser chamber.
Amplifying Medium
The amplifying medium in the red laser is actually a synthetically grown ruby crystal.
The reason that a ruby is used is because it has a broad absorption band in the 400nm to
500nm of visible light. It also allows the flash tube to pump high amounts of energy into
it creating a more powerful laser.
Mirrored Tube
The mirrored tube is another important aspect of any laser. The tube is how the atoms
become excited and jump energy states. The light is flashed inside the tube and the
atoms bounce back and forth between the mirrors until they give off phonons from being
excited.
Laser Beam
As said earlier the beam is emitted in a single wavelength. This wavelength is what makes it
possible to be able to direct the laser to a single point. Normal light, like the light from a lamp
on a desk, is called white light. This light is called white light because all the colors in the
spectrum are present; when all colors of light are present the color appears white. All the colors
in the spectrum each have their own wavelength as shown in figure 2. So with white light all the
wavelengths spread out therefore not being able to be concentrated to a single beam. White light
can be directed to an area, like a flashlight, but since it has multiple wavelengths it spreads out
too quickly to be able to be concentrated. Since a laser beam is a single wavelength it can be
directed to a single point at a very long distance. Depending on the quality of the laser it can
travel different distances. For example a simple ruby laser can travel about twenty mile before
the light dissipates too much to be able to be seen. A more expensive laser like a YAG (yttrium
aluminum-garnet) laser can travel to the moon and back and the diameter of the laser will not
change much noticeably.
Conclusion
A laser is simple to build but the science behind it is quite complicated. The laser consists of a
light source (flash lamp), a mirrored cylinder, an amplifying medium, and a power source (such
as a battery). The trick to creating a laser beam is to get all the emitted light to become one
wavelength, and once this has occurred all the light will be traveling in the same path and will
result in a beam of light. Lasers are a good way to help teachers to more effectively teach a
class.