Almost 60 years since their discovery, lasers were famously described as “a solution looking for a problem”. Theorized around 1958 and first built two years later in 1960, lasers were exciting cutting-edge science only used by Bond villains and outer space explorers.
Today we have incorporated lasers into our daily lives, and use them in more ways that we realize; used in CD and DVD players, laser printers, medical procedures, barcode scanners, fibre optic connection cables and so much more.
Lasers are highly “concentrated” light beams that irradiate in a single wavelength, powerful enough to reach the vast deepness of space or cut through thick pieces of metal. Used in most areas of research, lasers are used as tools for ground breaking discoveries and inventions; like using lasers to secure rare raw materials or more famously detect gravitational waves.
The theory behind lasers goes back to one of history’s most famous physicists, Albert Einstein. When in 1917 he proposed a theory of stimulated light emission; he had previously demonstrated that light was made up of photons, tiny packets of wave energy with specific wavelengths depending on the amount of energy. Both concepts fundamental for the science behind lasers. But it was until four decades later that the first practical laser was built.
Coined by Gordon Gould in 1957, LASER stands for Light Amplification by Stimulated Emission of Radiation. Gould was a graduate student of Charles Townes, who alongside Arthur Schawlow invented masers. Masers are similar to lasers but produce micro and radio waves instead of visible light. Townes and Schawlow won Nobel Prizes in 1964 and 1981 respectively for their work in masers and maser communication systems. Although Townes and Schawlow are often recognized as the inventors of lasers, it was until years later that Theodore Maiman created the first ever working practical visible light laser using a ruby as a lasing medium.
After the race for the creation of lasers in the early 60’s, laser research saw an immense expansion that lead to the development of high-power gas lasers, chemical lasers and semiconductor lasers.
Einstein had theorized that if the atoms that make up a material are given excess energy, they will emit photons (light particles); those photons can then stimulate other atoms nearby in order to emit further photons, creating a cascade effect with photons of the same energy, wavelength and direction.
In short in the words of Chris Woodford, a laser is effectively a machine that makes billions of atoms pump out trillions of photons all at once so they line up to form a really concentrated light beam.
To make a laser work, there must be a medium and a source of energy to stimulate the atoms. A medium in either solid, liquid or gas is the source of atoms with electrons to stimulate (shown in the diagram as the grey area). The energy required to stimulate said electrons usually in the form of a flash tube or another laser (shown in the diagram as the yellow arrow).
Normally a red laser, will have a ruby crystal for a medium and a flash tube wrapped around it. To create a laser beam, a voltage makes the tube flash on and off. With every flash, the tube “injects” energy into the crystal as photons i.e. the tube “pumps” the crystal with energy time it emits light. Then, the atoms in the crystal absorb the energy and can now jump to a higher energy level; after a few milliseconds the atoms fall back to their original ground state by releasing a photon. This is called spontaneous emission. The full mirror at the end of the laser tube keeps the photons bouncing back and forth inside the crystal. And every now and then one of those photons will stimulate an already excited atom, which will then give off another photon apart from the original one . This is called stimulated emission. In other words, one photon has produced two thus amplifying the light!
Which is the basic theory behind lasers! Light Amplification (increase in the amount of light) due to Stimulated Emission by Radiation.
The partial mirror at the other end, reflects some of the photons but allows the others to escape. Those escaping photons form a highly concentrated beam of powerful laser light.
Laser beams are coherent and of one wavelength therefore one colour; usually green, red, blue or infrared. In theory, since we are able to excite many kinds of atoms, we should be able to make lasers out of many different things but there are only 4 commonly used lasers: semiconductor, solid-state, fiber and gas lasers.
Semiconductor lasers are cheap, small and chip-like devices that are commonly used in CD and DVD players and barcode scanners. Working like a mix between Light Emitting Diodes (LED) and traditional lasers; they make light when electrons and missing electrons hop join together like LED’s and generate coherent monochromatic light like lasers.
Like the laser explained above, they work using ion-doped crystals or glasses that are pumped with discharge lamps or laser diodes. They can produce high powered beams in brief pulses, or lower powers with high beam quality.
Using a doped fiber-optic cable as the amplifying medium, fiber lasers can produce extremely high output powers with high beam quality and wide wavelength tunable operation.
Gas lasers use compounds of noble gases or carbon dioxide as their medium, and are pumped by electricity. They give off a continuous bright beam. They are powerful, efficient and used in industrial cutting and welding.
Less common lasers are the chemical and nuclear pumped lasers. Lasers today are used in information technology, telecommunications, medicine, manufacturing, measurement and analysis and scientific research.
Lasers have quickly become a multi-billion dollar industry as they have proven in their short life span of 50 years to be one of the most important technologies developed. Lasers drive our modern communication and economic world through the storage and transfer of data across the internet. Lasers are an indispensable tool for research that has allowed us to progress and to explore beyond what we thought previously possible.