Instructor-Franklin Wong
Kevin Madrigal
David Vasquez
Jovani Alvarez
Salofi Tautua
Topics in Science Research
Light, Lasers, Action!
For our Current topic in Science Research topic we had to study about lasers and
waves, but we will mainly focus on waves because lasers are made of waves of energy. In
this presentation we will explain Light, Electromagnetic Waves; which consist of x-rays,
gamma rays, visible light, UV Rays, Infrared, and Radio waves. We will also be talking
about electromagnetic radiation and black body radiators. When talking about waves you
will need to know the wavelength, frequency, and plank’s constant; you need to know all
these things to find out what the energy of that specific wavelength is. For some waves
you will also need to know what the speed of light is which is C= 3.0 * 10^8 m/s, this is
relating to the equation that Einstein figured out, which is E=mc^2, which means Energy
equals mass times the speed of light squared and you find the energy. We will also talk
about superconductors, which can conduct electricity(a major type of energy). The last
topic we will talk about atoms bonding together with all the type of bonds, covalent and
non-covalent bonds. Our instructor Franklin Wong took us to his lab in the mining and
metalology building and we got to observe how a laser works; we also got a chance to see
a piece of paper burning under the heat of the laser. He also showed us liquid nitrogen
and a glove go through a glass transition that changed its state so that you can throw the
glove to the grown and it will break, as if it was glass. In this class we actually got to
touch liquid nitrogen which is so cold that molecules in the solid take properties of glass
and can break quite easily. Liquid Nitrogen is so cold that you can get hurt by it, but only
if you leave your hand in its presence for a long period of time. Now we will start talking
about photons and wavelength in more detail.
As it turns out, light is made up of particles known as photons. Light is a particle,
and in dark rooms, you can even hear these particles, or photons, traveling through “free
space.” There is a discrete clicking noise, meaning they are separate and distinct clicks.
Basically, in a laser, you have two atoms, and you form a molecule, and each molecule
depends on the color you are trying to make. For example, you put together Gallium,
Aluminum, and Arsenic to create red light. Once you have the molecule corresponding to
the color you want, you run energy through it. With lasers, you use batteries to excite the
molecules from its ground state, and ground state means all of the electrons are in place
and there is no extra energy. When molecules are in their excited state, a few electrons
throughout the entire molecule are out of place. Then, the molecule goes back to its
ground state, and this is where the photon is released. As the electrons are finding their
original spots, they give off energy, and that energy is released in a little particle of light
called a photon. Lasers constantly excite the molecules and let them go back to ground
state, creating a steady beam of light whenever you turn the laser on. The one exception
to this process is green lasers. For a green laser to work, an infrared laser is used to power
it. That infrared laser is powered by a battery, so a green laser is still powered by a
battery, but it’s technically powered indirectly; however, as everything else in the world
it requires energy.
Most things in the entire universe require energy, ranging from a spaceship taking
off, to an ant carrying food back to its colony. Energy is being used and is seen in an
average person’s life. It can be seen as heat, electricity, wind, etc. One form of energy as
heat is a black body radiator. These types of radiators are found inside of light bulbs and
as the heat goes up to about 2500 Celsius, light is produced. Energy is significant to
everything, for example, it supplies people with fuel to go on and live their everyday
lives; however, energy is prodigiously important for making lasers. In the production of
lasers, energy serves as the source of power for the laser in the form of a battery. But, an
exception is the green laser, which is powered by an infrared laser. Through the two
weeks we spent with Franklin, we learned the equation to find Energy (E). The equation
consists of Planck’s constant (h), the speed of light (c), and the Greek letter Lambda, or
wave length (E = h x c/ λ). Energy is given off in the unit of Joules, or electron Volts
(eV), it is converted by the equation: eV = 1.6 x 10E-19. Energy from lasers are released
by radiation, the higher the temperature the shorter the wavelength, but more radiation.
The lower the temperature, the longer the wavelength; and less radiation. Wavelength
classifies the different types of waves or rays, starting from radio waves and ending at
Gamma rays. The higher the temperature, the more compressed the waves or rays are.
The lower the temperature, the longer the waves or rays are. Creating the beautiful and
colorful lasers we have today really depend on the wavelength and energy.
Although blue and green lasers are very expensive compared to a red laser, it isn’t
just because green and blue are prettier than red. Red lasers have a somewhat simple
setup. With the correct combinations of Ga and Al, (GaAl)As efficiently produces
wavelengths of 580-900 nm. Red’s wavelength is about 650 nm and (GaAl)As produces
this wavelength almost as close as we can get it, so this is an ideal molecule to use to
make red lasers. Now, powering this is a 3 step process. The first step is to connect the
(GaAl)As material to an electrical source, preferably a battery. The battery then gives
(GaAl)As energy, putting it into it’s excited state. Finally, (GaAl)As returns to ground
state and gives off energy as red photons. This is what allows (GaAl)As to emit red light.
Green’s wavelength size is about 500 nm. Inside of a green laser there is a yttrium
orthovanadate crystal material with small amounts of Nd. It has this small amount of Nd
because it is doped. Doping can be as low as one out of a million. This is a materials
science challenge to accomplish such control. It has a wavelength of 1064 nm and energy
of 1.2ev. To make green light out of this we actually take two photons and put them
together using second harmonic generation to make one photon of 532 nm and 2.4ev. The
good thing about this crystal material is that it creates photons of 1064 nm efficiently,
meaning that it has very high power and making the process of putting two smaller
photons together to make one very efficient as well. Using this crystal material is quite a
pain. It cannot be directly connected to a battery, meaning we have to use an infrared
laser to give the crystal energy and put it to excite state before green photons can be
created using second harmonic generation. Green lasers still run on batteries, just
indirectly through another laser. This is the same process we make blue lasers with.
Instead of making 400 nm blue lasers, we can make 800 nm infrared photons and use
second harmonic generation to make blue light. But at the moment, we don’t have highly
efficient ways of making 400 nm or 800 nm photons. This is also a materials challenge.
These complications are the reason for blue lasers being up to 900$ more than a red laser.
Although blue lasers are cooler than red lasers, I don’t think that they are worth 1000$
and hopefully one day we will find the materials to make blue lasers inexpensive.