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| A simple diode produces red laser light |
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| Arguably the most popular use of a laser pointer |
Red Laser Pointers
Why Are Most Laser
Pointers Red?
.
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Excited electrons release energy in the form of photons of specific wavelength,
creating bright monochromatic light |
Research suggests not red, but green lasers to be
the most captivating light source since the human eye is more sensitive to that
particular wavelength. It glows brighter and can reach distances far greater
than a red laser - in order to produce a green laser, the wavelength of the
emergent light must be below 600 nanometers - producing a focused beam of light
at a low wavelength is complicated
Abhishek
Kulkarni
Red lasers are lights of a longer wavelength that can be produced
using a simple diode; this option is cheaper and thus more popularly used in
the market.
All of us, at some point in time, have come across a laser.
Cashiers at the supermarket use them to scan the barcode on your
groceries.
Professors use them to draw students’ attention to specific items
of a presumably mundane presentation.
Cat owners use them to distract their munchkins and turn them into
YouTube sensations.
Basically, we’re all quite familiar with the
little red dot from some area of life, which got me thinking, why red?
We have natural light that splits into seven
of its constituent colors when we pass it through a prism.
Why then, do most laser pointers just give us
one of the seven colors?
Long story short, it’s simply cheaper to
produce laser pointers that emit a red light over any other variations.
Brilliant minds who have developed laser pointers in other colors, but red
laser pointers continue to make the most economic sense.
Therefore, they’re the product of choice for
mass production and thus the most popular item on the shelf.
So, why is it cheaper to produce a red laser
pointer than a laser of any other color? To understand this, let’s look into
what these laser pointers actually are and how they work.
What is a laser?
A laser is essentially a highly focused light
source with amplified brightness.
In fact, the word laser is an acronym that
stands for Light Amplification by Stimulated Emission of Radiation (LASER).
A laser is produced when the electrons of
certain materials, such as glass, crystal, diamond, etc., are energized by the
absorption of energy from an electric current.
Energized electrons jump from lower orbitals
to higher orbitals within the atom. As they return to ‘normal’, i.e. ground
state, these previously energized electrons release energy in the form of
photons.
All of the photons released during this
interaction tend to be ‘coherent’ – the crests and troughs of every light wave
match up precisely, so they’re all of the same color.
As more energy is supplied to the
glass/crystal, several electrons are energized. This is known as pumping.
They move as one to a higher energy state and
then back to the ground state. This phenomenon is called population inversion.
Population inversion leads to a larger burst
of energy, which creates a sort of avalanche of light, known as stimulated
emission. This huge burst of energy, concentrated at a single point, becomes a laser
light.
Who invented the laser?
The first laser was devised by a physicist
named Theodore Maiman while working at Hughes Research Laboratories in Malibu
in 1960.
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| The man who invented the laser beam |
His laser utilized a rod of synthetic ruby,
silvered at the ends, which were cut in such a way that the beam of light would
ricochet inside it, gaining brightness before coming out the other side.
The contraption emitted a narrow, bright beam
of light with a wavelength of 694 nanometers.
Amusingly, when Maiman showcased his findings
to the scientific community, the laser was famously termed “a solution looking
for a problem”.
Clearly, they weren’t looking hard enough for
problems yet, as his research paper was rejected by the popular science
journal, Physical Review Letters.
Subsequently, another equally selective
physics journal, Nature, agreed to publish his findings, which led to what some
might call a “laser boom”.
How do different laser pointers work?
Different methods are utilized to produce
different color lasers. The red laser is produced by using a simple
semiconductor diode to produce light.
This consists of two semiconductors put
together, one on top of the other. On top, we commonly find gallium arsenide, a
material with a shortage of electrons known as a p-type semiconductor.
At the bottom, there’s gallium arsenide with
selenium, a material with an excess electron called an n-type semiconductor.
The two of them stacked together in a diode,
creating what is called a p-n junction.
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electrons from ‘n’ move to ‘p’, creating coherent photons
that eventually emerge as a laser light |
When a current passes through the p-n
junction, electrons from semiconductor ‘p’ get excited and fill the gaps in
semiconductor ‘n’.
The top and bottom of the p-n junction are
coated with a silvered surface.
Excited electrons release photons that get
trapped within this p-n junction and continue to bounce off the silvered
surfaces.
As explained earlier, the p-n junction
eventually experiences a population inversion, leading to stimulated emission;
this emerges from the junction as laser light.
Why are most laser pointers red?
The light that emerges from a simple
semiconductor diode of shelf-bought lasers tends to be in the wavelength range
of 700-800 nanometers, thereby ranging from orange to red in color.
However, research suggests not red, but green
lasers to be the most captivating light source since the human eye is more
sensitive to that particular wavelength.
It glows brighter and can reach distances far
greater than a red laser.
In order to produce a green laser, the
wavelength of the emergent light must be below 600 nanometers. Producing a
focused beam of light at a low wavelength is complicated.
First, a standard semiconductor diode emits a
laser light of about 800 nanometers. This light is focused onto a neodymium
crystal, which converts it into an infrared beam of 1000 nanometers in
wavelength.
Finally, the resultant beam is passed through
a specialized frequency doubling crystal, after which it emerges as a green
light with a wavelength of 530-540 nanometers.
Clearly, producing a green laser light
requires a few more specialized components, so red laser lights are the most
cost-effective to produce and still remain the most popular variety of laser on
the market.
Abhishek Kulkarni is an investment
banker turned writer and standup comedian. After a graduate degree in business
administration and a stint at Citigroup, Abhishek decided to give it all up to
follow his passion for the creative arts. Presently he sits in an armchair
indulging in whimsical thought, writing on topics that tempt his curiosity and
moonlighting as a comic in the city of Bombay
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