Photo by Pixabay: https://www.pexels.com/photo/assorted-color-laser-lights-417458/
How does a laser work? By focusing light into a narrow beam.
LASER is actually an acronym, and it stands for Light Amplification by Stimulated Emission of Radiation. They have been around since the 1960s when the first laser was built by Theodore H Maiman, although the theory behind them goes all the way back to 1917.
So, how does a laser work? We need to look at how atoms release energy first. An atom consists of a nucleus and a cloud of electrons. The electrons are arranged in different planes around the nucleus and each plane has a different energy level. Electrons are always in the plane that matches their energy level. If energy is applied to the electrons, they can move up an energy level, but then they will be unstable. If the electrons lose energy, they move an energy level and the energy they lost gets released as a photon.
The photon that is released carries the energy that has been emitted by the electron as it jumps down a plane. This energy corresponds to the wavelength of the photon and we can see this wavelength of light. For example, when sunlight hits a tomato, the atoms in the skin of the tomato absorb the thermal energy. The electrons get excited and jump to a higher plane. They are unstable, so they fall back down to the original plane and they release the energy. The energy they release is about 650 nanometers, which our eyes and brain see as red.
A laser works in the same way except the released energy is controlled. When the energy is released from the tomato, it can go in any direction and several different wavelengths might be released. This is the same as happens with a flashlight. When the light is switched on, the photons coming out of the flashlight are directed to go in one general direction, but they spread out pretty quickly and get scattered. The photons in a laser beam are all in sync so they stay together.
A laser starts with a source of atoms and electrons that can be excited. Ruby is a common material. Energy is pulsed into a ruby tube using concentrated light. The wavelength of the light is controlled to give the ruby atoms just the right amount of energy. The light excited the ruby atoms and their electrons jump to higher planes. The electrons are unstable at this higher energy plane and they cannot stay there for very long. When they drop back down to their previous plane, they release photons.
Each end of the ruby tube is blocked with a mirror. The photons released by the electrons fly along, hit the mirror and get reflected back. They bounce back and forth between the two mirrors. Each time one of these photons hits an electron that is still at the higher energy plane, they stimulate the electron to release its energy, increasing the number of photons flying back and forth. Because all of these photons have been released from electrons with exactly the same amount of energy, they all have exactly the same wavelength, which means they fly in parallel. This process continues and the number of photons in sync rapidly increases.
One of the mirrors at the end of the ruby tube is a half-silvered mirror. A half-silvered mirror is a mirror that stops some wavelengths but lets other wavelengths through. The decided wavelength of light passes through that mirror and the laser beam is emitted.
There are many different types of laser and some can be very powerful. It all depends on the wavelength of photon that is released. The principle behind how the laser beam is formed is the same, but a different material is used, in this case gas. Then, the laser beam that is produced is focused through a lens. The beam with a carbon dioxide laser is infrared light, which means it is basically heat. A gas is released along with the laser to increase its effectiveness. The gas is either oxygen, which burns through the thing being cut, or nitrogen, which melts through the thing being cut. These lasers can be used in factories for cutting metal, but they are also used in more delicate processes, such as surgery.
So, how does a laser work? Energy is released from an electron in the form of a photon. Mirrors combine these photons to make a beam of light. And this is what I learned today.
Sources
https://spaceplace.nasa.gov/laser/en/
https://lasers.llnl.gov/education/how-lasers-work
https://science.howstuffworks.com/laser.htm
https://en.wikipedia.org/wiki/Laser
https://en.wikipedia.org/wiki/Carbon-dioxide_laser