|What is the difference between one of those
lasers they use to scan food at the supermarket
and a laser that can burn through metal?
|Question Date: 2002-01-11|
That's a really great question. One of the
more significant differences between the two
lasers is the power that they emit. Since the
laser that is used at the grocery store does not
burn (or even heat up) the items it scans, it may
be obvious that there is a lower amount of power
in the "laser beam". Here is a little analogy I
like to think of. Imagine taking 2 identical
pieces of garden hose. One of them is connected
to your kitchen sink, and the other is connected
to a fire hydrant. The hose connected to the fire
hydrant will have quite a bit more water flowing
through it, and thus feel more
"powerful". Another difference between the
lasers is the kind of light they emit. You may
have noticed that when the groceries are scanned
you can see a red light on the side (note: you
should never look into any sort of laser, even
those at the grocery store... they can cause
serious and permanent damage to your eyes). The
lasers that are used to cut metal can be a
different color (I have seen blue, red, and a few
other colors). Each 'color' of light has a
different energy. There are verified theories
that light comes in small particles which are
called photons. Meaning, one can think of a 'beam'
of light as being a bunch of really small marbles,
instead of a stream of water. The photons that
are blue have more energy than photons that are
An understanding of how lasers function is
necessary to explain the last difference, which
has to do with the different materials the lasers
are made from. Lasers work by having some
sort of source of a single color of light that is
placed inside of a "resonating cavity". The
simplest form of resonating cavity is two mirrors.
Light that gets trapped inside the mirrors will
bounce back and forth, and every time it passes
through the light source it creates more light.
If one of the mirrors lets a small amount of light
out of it, the light that comes out the end is
what is seen as the 'laser beam'. In the case
of the laser at the grocery store the light source
that is used is something called a 'semiconductor
laser diode'. Essentially it is a material that
when electricity is passed through it, light gets
emitted at a certain wavelength (color). It is a
solid material. In the case of a high-power
that cuts through metal, the material that is used
is a gas. When electricity is passed through the
gas item there is a certain wavelength.
the chemical composition of the semiconductor
versus the gas lead to fundamental differences in
the maximum output power of the laser.
There are two big differences. One is how
laser is. Grocery scanner lasers (and laser
pointers) are about 5 milliwatts, which is enough
to make a spot of light that can be seen. A dim
light bulb is about 50 watts, or 50 thousand times
more energy, but it shines in all directions, not
just on one spot like a laser. An industrial
laser for cutting and welding can be around 1 to
10 kilowatts. A portable heater usually produces
1 kilowatt, so imagine that much heat put on the
size of a laser spot. That's how the big lasers
can cut through metal.
The other difference
is the color of the light that the laser produces.
Grocery scanners make red light, so the black and
white stripes can be detected easily. Cutting and
welding lasers make all sorts of colors, when a
person is putting together a factory which will
use lasers like this they choose one that will be
absorbed well by what they want to cut. One
example of this is in medicine, where lasers are
used in surgery sometimes to keep people from
bleeding. By using a blue laser, the blood
absorbs the light and heats up so that the cut
stops bleeding (the same way fried egg doesn't
run). Since other parts of the patient (nerves,
bones,etc.) reflect the laser, they aren't hurt.
The red lasers used to scan bar codes at the
checkout counter are just a few milliwatts (1/1000
of a watt). The lasers that can burn through metal
are 1000's of watts. Even a 1-watt laser, if you
shine it on your hand (NEVER EVER LOOK DIRECTLY AT
IT) starts to feel a bit warm.
are also at different energies of light. The red
lasers you see in markets are Helium-Neon ("HeNe"
for short) lasers. Some lasers produce UV
radiation, and are so powerful you must wear
protective eye coverings just to work in the same
room with them. I don't know off hand what lasers
you are talking about, but I suspect it would be a
very high-energy, high-power laser.
a good place to read about
I think the main difference is the amount of
the laser emits. You can have lasers that are
different wavelengths (colors) but if the laser is
powerful enough, I don't think it really matters
what wavelength it operates at. It looks like
there are a couple different types of lasers that
are sold for cutting; the more powerful one uses
carbon dioxide gas. In this case, it is the
technology that provides enough power and is
readily available that determines the wavelength
of the laser beam used.
If you search on
the internet for "cutting lasers"
you should find lots of neat info. Here's one
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