What is Laser?

By BYJU'S Exam Prep

Updated on: September 25th, 2023

Light has always been a primary communication between humans and their surroundings. Still, before the invention of the laser, the light sources available for transmitting information and conducting experiments were generally neither monochromatic nor coherent, and they were of relatively low intensity.

As a source of highly directed, monochromatic, coherent light, the laser has transformed several long-standing optical difficulties while spawning new fundamental and applied optics disciplines. This article gives an overview of LASERs, types of lasers, and their applications.

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What is LASER?

A laser is a device that generates high-intensity light in the form of a laser beam. The output light is generated by stimulated emission of radiation, and the photons emitted by laser light are all in phase.

What is the Full Form of Laser?

The complete form of LASER is Light Amplification by Stimulated Emission of Radiation.

The light waves generated by the laser are of a single wavelength, and the laser beam is very narrow. The total energy is focused on a small narrow area, making these light waves travel a considerable distance.

Population Inversion

For any LASER to operate, population inversion is very much required. Population inversion is when a group of atoms or molecules (essential electrons) are excited and move from the lower energy state to the higher energy state. When these atoms or molecules are in a higher energy state, they can decay and come to a lower energy state.

When a photon hits an electron, two photons are produced, and this is known as stimulated emission. The photons produced in stimulated emission produce coherent light, and significant amplification of light can be achieved by stimulated emission.

Components of LASER

Einstein discovered the principle of LASER in 1917, but the first successful LASER was developed in 1958. LASER comprises three main components, as mentioned below, and these components are much required for the operation of any LASER.

  • An Energy Source: It is also known as the Pumping source, which provides energy to the laser system. Depending on the gain medium, it can be flashlamps, electrical discharges, chemicals, etc. The energy source pumps the atoms or molecules from a lower energy state to a higher energy state and is responsible for achieving population inversion.
  • Gain Medium: It is also known as LASER medium or Active medium in which the laser action takes place. The active medium may consist of solid crystals, gasses, liquid dyes, semiconductors, etc. This component decides the wavelength of any LASER radiation.
  • Resonator: A resonator amplifies the optical gain produced in the gain medium. It consists of two mirrors: a highly reflective mirror and another partially reflective one. The light produced due to stimulated emission will pass through this partially reflective mirror to produce laser light.

Types of LASERS

The laser beam produced can be either continuous or pulsed. Based on the mode of operation, LASERs are of two types, Continuous wave LASERs and Pulsed Lasers. Based on the type of gain medium used as a component of LASER, it can be classified into 6 types as mentioned below:

  • Solid-state lasers
  • Gas lasers
  • Liquid lasers
  • Semiconductor lasers
  • Chemical lasers
  • Metal-vapor lasers

Solid State LASERS

In solid-state lasers, the gain medium uses glass or solid crystalline materials. Ions are introduced as impurities to a host material, and this process is known as doping. Cerium (Ce), terbium (Tb), etc., are dopants. Materials like neodymium-doped yttrium aluminum garnet (Nd: YAG), Neodymium-doped glass (Nd: glass) used as host materials. Examples of solid-state LASERs are Ruby LASER, Nd-YAG LASER, etc.


A ruby laser uses a ruby rod pumped with high energy to achieve population inversion. It is energized through a Xenon flash tube and a three-level solid-state laser.

Diagram of Ruby Laser

The typical construction of a ruby laser is shown below:


Ruby possesses extensive and intense absorption bands in the visible spectrum at 400 and 550 nm and a relatively long fluorescence lifetime of 3 milliseconds. Ruby is one of the few solid-state lasers that emit visible light, lasting at 694.3 nanometers in a deep red hue with an extremely small linewidth of 0.53 nm.


In Nd-YAG Laser, flash tubes or laser diodes are used as an energy source, and an active medium made up of synthetic crystalline material (Yttrium Aluminum Garnet (YAG)) doped with a chemical element (neodymium (Nd)). This laser is a four-level laser system. The typical construction and working of Nd-YAG LASER are shown below:


Both continuous and pulsed output is possible in Nd-YAG LASER. Nd-YAG lasers often produce laser light in the near-infrared portion of the spectrum at 1064 nanometers (nm). It also emits laser light at various wavelengths such as 1440 nm, 1320 nm, 1120 nm, and 940 nm.

Advantages of Solid-State Lasers

The advantages of using Solid-state LASERs are:

  • Construction is simple and economical, and the output light can be continuous and pulsed.
  • Very high efficiency as there is a tiny amount of material loss in the gain medium.

Disadvantages of Solid-State Lasers

The disadvantages of using Solid-state LASERs are:

  • Due to the heating of the rod in the gain medium, there is a power loss.
  • The laser beam produced is not very narrow.

Applications of Solid-State Lasers

The applications of Solid-state LASERs are:

  • Drilling of holes in metals.
  • These lasers are used in the medical field for endoscopy, kidney stone removal, hair removal, etc.
  • These lasers are used in RADARs for target destinations as solid-state lasers use LIDAR technology.


In gas lasers, an electric current is sent through a gas to generate light with the help of population inversion. The active medium consists of one or more gasses or vapors such as carbon dioxide, argon, Helium-neon, etc. Helium-Neon LASER, C02 LASER, etc., are examples of gas lasers.

Helium-Neon (He-Ne) LASER

It contains a mixture of Helium and Neon gasses in the active medium. This is a continuous wave laser in which a DC power supply is used as an energy or pumping source. Helium atoms help to excite the Neon atoms to achieve population inversion. The typical construction of He-Ne LASER is shown below:

The helium-neon laser works in the red region of the visible spectrum at a wavelength of 632.8 nanometers (nm).

Advantages of Gas LASERs

The advantages of using gas LASERs are:

  • Laser beam quality is much narrower than solid-state lasers.
  • The light produced is highly coherent.
  • The wavelength of the light at the output is stable.

Disadvantages of Gas LASERs

The disadvantages of using gas LASERs are:

  • The laser is very bulky hence, not easy to transport.
  • The laser beam produced will have a short lifetime.

Applications of Gas LASERs

The applications of gas LASERs are:

  • Carbon dioxide laser is mainly used for laser cutting and welding.
  • Gas lasers are also used for air pollution measurements, material processing, barcode scanning, etc.
  • Holography and spectroscopy are also applications of gas lasers.


Liquid LASERs or Dye LASERs are lasers that use liquids in the active medium. These liquids are also known as dyes. Materials used as a dye are sodium fluorescein, rhodamine B, and rhodamine 6G.

Working on Liquid LASERs

This laser’s active medium is an organic dye, and the solvent used to dissolve the dye is water, alcohol, or ethylene glycol. The dye is pumped from the storage tank to the capillary tube. With a flash bulb, this dye exits the tubes. The output beam is then routed through a Brewster window to the output coupler, a 50% reflecting mirror. The output wavelength can vary widely, with the maximum output possible at 618 nm.


Advantages of Liquid LASERs

The advantages of using a liquid LASER are:

  • The wavelength of the laser light produced can be varied, and the light beam produced is narrower than solid-state, and gas lasers, and the efficiency of these lasers is higher.

Disadvantages of Liquid LASERs

The disadvantages of using a liquid LASER are:

  • These lasers are very much expensive.
  • Difficult to determine the responsible element used to produce a laser.

Applications of Liquid LASERs

The applications of liquid LASERs are:

  • Since these lasers are very much expensive, these lasers are used as a tool for medical purposes for research and development.

Semiconductor LASERS

Semiconductor lasers use laser diodes which are ordinary PN junction diodes but have a polished intrinsic region between the PN junction. This intrinsic region is responsible for amplifying photons and converting the electric current into laser light. Gallium Arsenide Laser is an example of a semiconductor laser.

Gallium Arsenide Laser

The active medium uses Gallium Arsenide. A semiconductor laser operates similarly to a PN diode when forward-biased. The PN material is coupled to the DC power source through metal connections. Because the current is injected into the junction between P and N materials, the semiconductor laser is known as the Injection Laser.


Electrical energy is used as a pumping source. When forward biased, the electric field produced causes the electrons to move from a lower to higher energy, resulting in population inversion. When electrons decay and move from higher to lower energy, it emits laser light through the polished intrinsic region.

Advantages of Semiconductor LASERs

The advantages of using a semiconductor LASER are:

  • Small size and lightweight.
  • Economical as no mirrors are required, and power consumption is low.

Disadvantages of Semiconductor LASERs

The disadvantages of using a semiconductor LASER are:

  • The output laser beam is not narrow.
  • Sensitive to temperature variations.

Applications of Semiconductor LASERs

The applications of semiconductor LASERs are:

  • Laser printers, scanners, and barcode readers are a few applications where semiconductor lasers are used.

Chemical LASERS

In chemical LASERs, chemical reaction works as the pumping system. These are continuous wave lasers with a massive power output of megawatts. Chemical oxygen-iodine laser (COIL), all gas-phase iodine laser (AGIL), and the hydrogen fluoride (HF) and deuterium fluoride (DF) lasers are examples of chemical lasers. The typical construction of chemical lasers is shown below:


Advantages of Chemical LASERs

The advantages of using a chemical LASER are:

  • The output power is very high, and they generate less amount of heat.

Disadvantages of Chemical LASERs

The disadvantages of using a chemical LASER are:

  • The gasses used are highly reactive (Fluorine), and these lasers can explode if not operated satisfactorily.

Applications of Chemical LASERs

The applications of chemical LASERs are:

  • For cutting and drilling purposes in industry.

Metal-vapor LASERS

Metal-Vapour LASERs are a kind of gas laser that uses a metal Vapour in the laser medium. Metal vapors are generally metal atoms or metal ions. These lasers require incredibly high temperatures, achieved by intense arc discharge. These lasers generally work in the pulsed mode of operation. Copper-Vapour Laser, Helium-cadmium lasers, etc., are some examples of Metal-Vapour LASERs. Typical construction of Metal-Vapour lasers is shown below:


Advantages of Metal-Vapour LASERs

The advantages of using Metal-Vapour LASERs are:

  • The output light beam is too narrow, and the laser beam appears continuous because of the high repetition rate.

Disadvantages of Metal-Vapour LASERs

The disadvantages of using Metal-Vapour LASERs are:

  • These lasers operate at a very high temperature, affecting nearby instruments.
  • These lasers are very costly.

Applications of Metal-Vapour LASERs

The applications of Metal-Vapour LASERs are:

  • High-speed photography and imaging, Modern telecommunications equipment, etc.

Characteristics of Laser

There are 9 different types of Characteristics of a Laser, which are mentioned below:

  • Wavelength
  • Gain Bandwidth
  • Monochromaticity
  • Coherence
  • Polarization
  • Directionality
  • Output power
  • Collimation
  • Spatial and Temporal Profiles

Advantages of Laser

Due to the different characteristics of lasers, they differ from other light sources. These characteristics of lasers provide some significant advantages over conventional light sources. The advantages of laser are:

  • Laser data carrying capacity is very high, so it is used for space transmissions.
  • Lasers can penetrate through any obstacle, so they are used to find cracks and voids in metal, and stone detectors, remove kidneys, etc.
  • The beam width of the laser is narrower than other light sources, making them travel large distances.
  • Laser-based fiber optic communications are utilized as they are free from electromagnetic interference.
  • It is less damaging compared to X-rays, and leakage is minimal.

Disadvantages of Laser

As the characteristics of a laser make it different from other light sources and provide significant advantages, lasers also have some drawbacks, making them difficult to use. The disadvantages of laser are:

  • Lasers are expensive; hence, they are more costly for medical management.
  • Laser beams should be delicately handled, as a slight mistake leads to burning.
  • Some laser beams are harmful to humans as they provide unfavorable thermal characteristics.
  • Cooling and power stabilization tools and equipment are required.

Applications of Laser

Besides its advantages and disadvantages, lasers are used in almost every industry for several purposes. Based on the application, different types of lasers are used. Some typical applications of laser are:

  • Laser in Medical: Lasers are used for photocoagulation of the retina to stop hemorrhaging and tacking of retinal tears. Higher intensity lasers are employed if the supporting membrane around the implanted lens turns milky following cataract surgery. For delicate surgery, a concentrated laser can behave as an exceedingly sharp scalpel.
  • Lasers for Welding and Cutting: Carbon dioxide lasers with energies up to several kilowatts are widely used in the automotive sector for computer-controlled welding on vehicle assembly lines. CO2 lasers are used for fusing stainless steel handles to copper cooking pots.
  • Surveying and Ranging: Helium-neon and semiconductor lasers are now standard components of field surveyor equipment. To calculate the distance, a rapid laser pulse is directed to a corner reflector at the spot to be measured, and the time of reflection is measured.
  • Lasers in Communication: Fiber optic cables are a popular means of communication because light traveling through the fibers allows many signals to be transferred with high quality and minimal loss. Light signals can be modified with data sent via light-emitting diodes or lasers.
  • Heat Treatment: Heat treatments for hardening or annealing have been used in metallurgy for a long time. However, lasers open new avenues for selective heat treatment of metal objects.

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