Lasers are intense beams of concentrated light. These beams are powerful enough to cut through lumps of metal and zoom miles into the sky. Although laser technology seems new, it has been with us for nearly six decades: the first practical laser was developed in 1960. Since then, lasers have continued to grow and flourish.
The term LASER is an acronym for ‘Light Amplification by Stimulated Emission of Radiation’. It means a laser device emits light using an optical amplifier based on the stimulated emission of electromagnetic radiation.
A laser is an advanced light source, which is very different from a light bulb and a flashlight. Below, we have explained how does a laser work and where exactly different types of laser are used. Let’s start with a basic question.
What Is A Laser?
Definition: A laser is a small yet powerful device that produces a narrow beam of radiation. This radiation falls within a broad range of the electromagnetic spectrum, from gamma rays to radio waves.
The intense beams of light produced by lasers have three main characteristics: they are
- Monochromatic (the wavelength of laser light is extremely pure)
- Coherent (all photons that make up a laser beam have a fixed phase relationship with respect to one another)
- Highly collimated (rays of light are accurately parallel).
How Is It Different From Conventional Light Source?
Light travels as a wave, and distance between two successive peaks of a wave is known as wavelength. The color of the light depends on its wavelength. For instance, red light has a longer wavelength than green light.
The rays coming from the Sun consist of several different wavelengths. Human eyes perceive this blend of wavelengths as white light. Similarly, a bulb emits light of different wavelengths.
A laser, however, is a completely different device. It doesn’t exist in nature. Instead, it is artificially created to produce an intense light beam in which all waves have one color (single wavelength), and they all move together in the same phase (peaks of the waves are lined up).
That’s the reason laser beams are very bright and narrow. Unlike a flashlight, they can travel very long distances and focus on a tiny spot.
How Does A Laser Work?
Molecules and atoms usually move with a given specific energy. When they receive energy from an external source, they move with relatively higher energy. This is what call an excited state.
Molecules and atoms can release this additional energy and return to their initial energy state. They often release this extra energy in the form of light, and this phenomenon is known as spontaneous emission.
When other high-energy molecules are atoms collide with this light, they emit light with the same characteristics (wavelength and phase). This process is known as stimulated emission.
When the number of high-energy molecules and atoms (within a confined space) is low, the emitted light is quite weak. A process called light amplification is used to keep a large number of molecules and atoms in a high energy state. This results in an avalanche effect of stimulated emission, and thus intense light is emitted.
To further strengthen and amplify the light in a specific direction, two mirrors are placed facing each other. Let’s understand this principle step by step.
I. A high-intensity flash lamp is switched on and off to inject energy (in the form of photons) into the ruby crystal.
II. Atoms in the crystal soak up this external energy, and their electrons jump to a higher energy level.
III. After a few milliseconds, the electrons return to their ground state (initial energy level), ejecting a photon. This is called spontaneous emission.
IV. The ejected photons move at the speed of light inside the ruby crystal. They excite other electrons into heightened states, causing more photons to be emitted via the process of stimulated emission.
Basically, the light (photons) has been amplified by stimulated emission of radiation in this step. Hence the name LASER.
V. Mirrors at both ends of the crystal keep the photons bouncing back and forth. One mirror is made slightly less reflective to let some of the photons escape.
VI. The escaping photons find their way out into the world as an intense beam of laser light.
Different Types of Laser
Since different atoms can be brought to excited states in many different ways, we can build various types of lasers. While thousands of kinds of lasers are known to exist, most of them are used only in research and experiments. We have listed the seven most common types of lasers developed in the past half-century.
1. Gas Laser
Helium-neon laser at the University of Chemnitz, Germany
In a gas laser, an electric current is discharged through a specific gas to create coherent light. Developed in 1960, it was the first laser to work on the principle of transforming electricity into laser light.
Gas lasers can be further categorized into chemical, excimer, ion, and metal-vapor lasers. They all are based on different gases and are used for many different purposes.
2. Solid-State Lasers
Nd:YAG laser with frequency-doubled 532 nm green light
This type of laser uses a solid medium to produce laser light, instead of gas as in gas lasers. Usually, the medium contains a crystalline or glass ‘host’ material, which is doped with ions to provide the needed energy states.
Perhaps the most commonly used solid-state laser is neodymium-doped yttrium aluminum garnet (Nd:YAG). These lasers emit light with a wavelength of 1064 nm (in the infrared) and are used for several applications, including medicine, manufacturing, and fluid dynamics.
3. Free-Electron Lasers
A Free Electron Laser named FELIX at The FOM Institute for Plasma Physics Rijnhuizen | Wikimedia
In free-electron lasers, the lasing medium contains high-speed electrons moving freely through a magnetic structure. Its wavelength of operation can be changed in a controlled manner, and it has the broadest frequency range of any laser type — it can operate in wavelengths ranging from microwaves and infrared to ultraviolet and X-ray.
Since these lasers can produce light with a very short-wavelength (down to a few tenths of a nanometer), they will become an essential tool for atomic-level material characterization.
4. Dye Laser
The top view of dye rhodamine 6G, emitting at 580 nm (yellow).
As the name suggests, a dye laser uses an organic dye (a liquid solution) as the lasing medium. Unlike most solid-state and gas lasers, it can be used for a much broader range of wavelengths, extending from 50 nm to 100 nm.
For instance, the dye rhodamine 6G can be configured from 560 nm (greenish-yellow) to 635 nm (orangish-red), and generate pulses as short as 16 femtoseconds. Dye lasers are very versatile. They are used in several applications, including medicine, spectroscopy, and atomic vapor laser isotope separation (ALVIS).
5. Semiconductor Lasers
Semiconductor lasers emitting different wavelengths
Semiconductor lasers are similar to light-emitting diodes that directly convert electrical energy into light. They operate by recombining electrons and holes via voltage. The wavelength of the emitted beam depends on the semiconductor material used.
Modern laser diodes can emit light from ultraviolet to infrared spectrum. They are the most common type of lasers produced and are used in various devices, including barcode readers, laser printers, and fiber optic communication equipment.
6. Fiber Lasers
3 fiber disk lasers
In a fiber laser, the active lasing medium is an optical fiber doped with rare-earth elements, such as dysprosium, ytterbium, thulium, and erbium. The light is guided due to a phenomenon called total internal reflection.
Compared to other types of lasers, the fiber laser delivers a high output power and can provide high optical gain over several kilometers. Due to its large surface area to volume ratio (that enables efficient cooling), it can support kilowatt levels of continuous output power. Also, they are reliable and exhibit vibration stability and extended lifetime.
7. Nuclear Pumped Lasers
The working principle of nuclear-pumped lasers is based on the energy of fission fragments. The lasing medium (tube) consists of uranium-235, which is subjected to high neutron flux in a nuclear reactor core.
In the near future, this technology may achieve high excited rates with smaller laser volumes. So far, three uses of nuclear-pumped laser have been proposed: propulsion (launch objects into orbit), manufacturing (deep-cut welding), and weapon programs.
Lasers have a ton of applications that affect our daily lives, and most of them fall into three broad categories:
- Transmission and processing of information
- Precise delivery of energy
- Alignment, measurement, and imaging
These categories cover various applications, from the mundane alignment of suspended ceiling and heavy-duty welding to pinpoint energy delivery for delicate surgery and laboratory measurements of atomic properties.
LaWS aboard USS Ponce | Wikimedia
Militaries are also heavily investing in laser technologies and using them for their weapons and advanced missile systems. The United States Navy, for example, has installed the AN/SEQ-3 Laser Weapon System (LaWS) in battleships. It’s a solid-state laser array that can be configured to low output to warn/cripple the sensors of a target or high output to destroy the target at an impressive distance.
According to the report, the laser technology market is expected to grow to $16.9 billion by 2024. The major factors that are expected to drive the market are growing demand from healthcare vertical, enhanced performance of laser over conventional material processing methods, and shift toward production micro- and nanodevices.