• Laser light show. Image courtesy of author.
  • Gérard Mourou, Arthur Ashkin, Donna Strickland, who won the 2018 Nobel Prize in Physics "for groundbreaking inventions in the field of laser physics." -The Nobel Prize

Lasers: A Gift from Quantum Physics

Lasers are everywhere. Want to remove unwanted hair? Try laser hair removal. Tired of wearing glasses? Laser vision correction procedures are available. Laser therapy is even used to remove unwanted body fat. (This doesn't sound like such a bad idea post-Thanksgiving...)

Have you ever gone to a laser light show? Laser light shows use colored laser beams to project beautiful images synchronized to music. Look around town, and you’ll notice colorful Christmas decorations that are now done with laser light projectors.

It is hard to believe that the laser was invented only in 1960.  Many people don’t realize that the term "laser" originated as an acronym for "light amplification by stimulated emission of radiation." The acronym is now so common it’s no longer written in capital letters.

So what’s the science behind lasers? And how do they really work?

The laser is one of the most unique and useful technologies of modern times and is a gift of quantum mechanics. Developed in 20th century, quantum mechanics studies the smallest scales of energy of atoms and subatomic particles. Quantum theory states that electrons in an atom have different energy states, and the lowest energy state is called ground state.

When electrons are in an excited higher energy state, their time there is very short. Almost immediately, they jump to their normal or “ground” state, giving off photons, tiny particles of light. This process is generally random and is called spontaneous emission, but it doesn’t produce a laser. Instead, this process gives us the light in an ordinary neon light bulb.   

 

Spontaneousemission.png

                                              [Spontaneous emission]

Lasers depend on the coherent emission of light by many atoms, all at the same frequency. In a laser, an atom undergoes a transition and emits a photon in the presence of many other photons that have equal energies. A process known as stimulated emission causes the light emitted by this atom to propagate in the same direction and with the same phase as surrounding light waves.  

 

Stimulated Emission.svg

                                         [Stimulated emission]

 

These photons are all at the same wavelength and are “coherent,” meaning the crests and troughs of the light waves are all in lockstep. In contrast, ordinary visible light comprises multiple wavelengths and is not coherent.

 

Laser light is different from normal light in other ways as well. First, a laser’s light contains only one wavelength (one specific color). The particular wavelength of light is determined by the amount of energy released when the excited electron drops to a lower orbit. Secondly, laser light is directional. Whereas a laser generates a very tight beam, a flashlight produces light that is diffuse. Because laser light is coherent, it stays focused for vast distances, even to the moon and back.

https://lh5.googleusercontent.com/_368zaPrnCsLgkSdI07g_iix9ox8lD_McsJZZT8x4-4Aa5WdU31IL41lkeBHouIq6--AaYqCQ1mZUqbHape3J0935B6QQcPjqWeg-HEE4oTeKElJCHY0dTnKvFiEkzgbM1Ti4vuf https://lh6.googleusercontent.com/eIJ40RLcBwhWs94VKdOwtjI80ELVSf1hG_3HQiKrLf8qY-ap3-c5jNgYHInjJlag5hB9vJoSHOC50TSBJDQOhXsOO9g9IFP79P1pHsHo38XHm_iVwgacvhoZC97upHAXF7nUpmtE

The design of many lasers is similar to that of a neon light bulb, but there are mirrors at the end of the tube.  Light emitted by the gas atoms is reflected by the mirrors and travels back and forth along the tube. The excited atoms emit photons that stimulate the emission of more photons with the same energy and all these photons are repeatedly reflected to amplify the final laser light.

Laser come in large variety of sizes, power output and beam colors. The destructive power and the accuracy of laser weapons are the key features that make them attractive for video games. With impressive designs and over-the-top characteristics, the cannons with laser power are often included in video games to give the extra flavor of progress and innovation.