I'm sure you've seen a LASER, I mean almost everyone has. you may have teased a cat with it (Don't feel sorry cats they probably don't care about us either, at least I feel that way. I love cats btw, please don't hate me.)
If you haven't seen a laser its kinda like a source of light, but way more intense and organized, they have many other useful applications too. but for now let's move on.
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So Basically the word "LASER" is an acronym for Light Amplification by Stimulated Emission of Radiation.
Don't worry I will try to explain all those terms as easy as possible. and also there's no usage of Math in this post. I Promise.
Difference between a LASER beam and normal light.
How is the laser different you ask? well like I said laser is a beam of light but its more organized than light.
- The rays of light from a laser travel in the same direction (almost parallel) .
- The line-width of lasers is very low, hence they are monochromatic(single color).
- The light beam emitted by a laser is coherent light, meaning the waves are in phase to each other and polarized in the same direction, hence they are more intense than normal light.
- The light beam emitted from a laser is much more powerful than normal light.
Components
the Laser consist of mainly three parts.
Energy Source
The energy source is usually a high-intensity light source powered by electricity.Active Medium
The active medium provides the environment for stimulated emission(Term explained ahead) like a crystal.Optical Cavity
An optical cavity is basically an arrangement of the mirrors in a way that light-beam is reflected back and forth a large number of times, without losing much flux intensity.
The working process
the process for creating a laser beam can be divided into four parts as below.
1. Stimulated Absorption
We know how the electrons are located around the nucleus in a probability cloud called orbitals.
(read more about orbitals and atomic structures in my previous article.)
The electrons can only exist in certain energy states, and it can not exist in-between.
So when a photon with a certain energy collides with the electron in the ground state, the photon is annihilated in the process and all of its energy is used in getting the electron to the excited state, also for the excitation to occur the energy of the photon has to be equal to the energy required.
2. Spontaneous Emission
As everything in nature wants to be in a lower state, so do the electrons, and the excited state is very unstable.
After a tiny fraction of time the electron returns to its original state, releasing a photon with a certain amount of energy.
If the energy(frequency) of the photon is in visible spectrum then we see a single color light.
What causes the electron to fall back down? well, the empty space is never so empty, the particles are continuously popping in and out of existence, all the time, which causes the unstable electrons to fall back to ground state.
3. Stimulated Emission
So after the spontaneous emission, we have a photon that will be able to interact with the electrons in the excited state and make them fall to the ground state.
but there's a problem, the electrons get excited for a short amount of time, meaning that the electrons get back to the ground state before the photon is able to interact.
In order to create another photon with same coherence and polarization, the excited electron has to be disturbed by the newly created photon.
To overcome this obstacle we use material which allows so-called "Metastable state"
Metastable states are the level of energy slightly lower than the excited states. which gives our photons enough time to reach the electron just in time.
And now the identical photons are created, and these two identical photons create more photons by interacting with other excited electrons.
So the number of photons increase exponentially. kinda like one zombie bites a human and creates another zombie(but faster).
4. Light Amplification
The mirror in the one end of the laser is semi-reflective, which means that some of the photons exit out and some of them bounce back, and travel back and forth from one mirror to another, which creates a standing wave due to interference.
All the photons excited from the process are in phase and have the same polarity.
Applications
Daily applications of lasers involve CD, Blue-Ray, DVD, and HD-DVD players, Barcode readers, Laser pointers (to play with cats).
lasers are also used in welding metals marking(producing visible patterns such as letters).
Military applications like range-finding, target designation, and illumination, weapons.
Medical applications like laser surgery of the eye, therapeutic and diagnostics applications.
And the most important application of the lasers nowadays is in Quantum computers.
Quantum computers require very low temperature to work, thanks to laser cooling we can now achieve the temperatures in fractions of absolute zero.
Maybe I'll do a post about laser cooling, but for now, Thank you so much for reading. Don't forget to upvote, resteem, and follow me for more interesting stuff like this one.
References: A Textbook of Engineering Physics, By Dr. M.N Avadhanulu and Dr. P.G Kshirsagar, all the images in the post are self-created unless stated otherwise.
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