|What is the difference between the lasers used in
supermarket scanners and those used in laser pens?
First the similarities: Both types of lasers are
called "diode lasers" or "semiconductor lasers"
referring to the main type of materials the make
up the light source. The main features of this
type of laser are their small size (handy for
putting in things like pens and handheld
scanners), and their ability to operate off of
electrical power from the wall or from a battery.
Other kinds of lasers that are not diode lasers
need to be "pumped" by another light source to
Now for the differences: It's possible that the
same exact diode laser can operate in both a laser
pen and in a barcode scanner. In this case, they
would both be the same color--namely both red.
But, if you want a different color for your pen
laser, say blue for example, then you need a
different diode laser made out of a different
semiconducting material. Most red lasers are made
from an alloy of AlInGaP, 4 periodic table
elements, and most blue laser diodes are made out
of alloy of InGaN. The wavelength, or
color, of the laser is determined by the elemental
composition of the laser material.
The red lasers used in both? Absolutely nothing -
they're the same frequency, same laser. The
supermarket scanners also have, well, scanners,
that watch the reflected laser light, but the
lasers are the same.
Note that lasers that aren't that familiar red
hue are different (they use different elements and
different frequencies). There are of course red
lasers that are different as well and are
different shades of red, but the common one is the
same as far as I know.
The earliest barcode scanners and red laser
pens were actually both made using helium-neon gas
lasers. In these lasers, a small capillary tube
containing a mixture of mostly helium and some
neon is excited by an electrical discharge. When
the helium atoms get excited and collide with a
neon atom, the neon gets excited and radiates
light at a wavelength of about 633nm, which is the
wavelength of red light.
With improvements in technology, these gas
lasers were phased out and replaced with laser
diodes. Instead of having a gas as the active
medium, laser diodes have a p-n semiconductor
junction. Using different materials as the
semiconductors results in different bandgaps,
which result in different wavelengths of light
(i.e. different colors) being emitted. Since it's
cheapest to produce laser diodes that emit red
light, barcode scanners typically use red laser
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