How Lasers work.(Physics principle explained)

Every physics nerd, children, and most people would have probably heard of the word LASER. Laser stands for Light Amplification by Stimulated Emission of Radiation. You would be wondering that there's even an acronym for the word laser. Nowadays LASERS are used in various fields including industrial. medical, cosmetic, or just playing with it on the dark rooftop. You might have thought that who would have built such a cool and amazing thing and it was none other than Albert Einstein who laid the physics and mathematical groundwork and principles for the working of the LASER but it would take another 43 years to be built properly and available for consumer use which it is today.

So how do these things work and what's the principle that lies in it. We are going to find out but first, we will have to understand something else.

Atoms as we all know are the building blocks of the universe. These really small particles are constantly in motion. An atom consists of a specific configuration of protons, electrons, and neutrons, making every element unique. We would be focusing on the electron part of the atom. An atom can also be distinguished based on its excitation states or the energy levels of its electrons. So what happens is, inside atom electrons are located in certain specific energy levels( Orbits) and each electron can jump to a higher energy level but it needs a specific amount of energy to do so. So when we strike light or a photon of specific energy strikes an atom, the electrons inside it absorb that photon of light. Now, if the energy of the photon is exactly equal to the amount of energy that the electron requires to jump to a higher energy level, it absorbs that energy doing so. This is called excitation of the atom but this excitation is short-lived as the electron loses this energy by giving off the light is absorbed and the electron hence returns to its original energy level. 

This was the groundwork for the working of laser and what lies ahead is the pure brilliance of Einstein that enables us to use this concept in making lasers. So what happens is if we take a ton of these atoms and provide them energy by current or any other method, some of the atoms would absorb this energy and radiate the light of specific energy that we just talked about earlier. So when this radiated light strikes other atoms, it causes them to do the same ( radiate the light of the same energy) and this causes a cascade of atoms radiating light. This is the light amplification of the radiation. To amplify this light more and more we make sure to bounce this light between a pair of mirrors that are some distance apart which stimulates other atoms to release energy in the form of light.

To make sure this light energy is released as a LASER we make sure of some other things as well:

1. The light or photon released by the de-excitation of atoms must be of the same energy meaning the same wavelength and ultimately meaning the same color. ( that's why LASERS are monochromatic)

2. We make sure this light comes out as a fine beam of light that is very dense and energetic.

3.The rays of light are coherent which means that the crests and troughs of these light waves are aligned properly without any phase difference.

LASERS are also of various types such as gas lasers, ruby lasers, excimer lasers, and semiconductor lasers. etc.