LASER stands for Light Amplification by Stimulated Emission of Radiation, it is a device that produces highly directional light and it emits light through a process called stimulated emission of radiation which increases the intensity of light. A laser is different from conventional light sources in four ways: coherence, directionality, monochromaticity, and high intensity. The light waves of ordinary light sources have many wavelengths. Hence, the photons emitted by ordinary light sources are out of phase. Thus, ordinary light is incoherent.
On the other hand, the light waves of laser light have only one wavelength. Hence, all the photons emitted by laser light are in phase. Thus, laser light is coherent. The light waves from laser contain only one wavelength or color so it is known as monochromatic light. The laser beam is very narrow and can be concentrated on a very small area. This makes laser light highly directional. The laser light spreads in a small region of space. Hence, all the energy is concentrated in a narrow region. Therefore, laser light has a greater intensity than ordinary light.
Lasers are classified into 4 types based on the type of laser medium used:
A solid-state laser is a laser that uses solid as a laser medium. In these lasers, glass or crystalline materials are used.
Ions are introduced as impurities into host material which can be glass or crystalline. The process of adding impurities to the substance is called doping. The first solid-state laser was a ruby laser. It is still used in some applications. In this laser, a ruby crystal is used as a laser medium. In solid-state lasers, light energy is used as a pumping source. Light sources such as a flash tube, flash lamps, arc lamps, or laser diodes are used to achieve pumping. Semiconductor lasers do not belong to this category because these lasers are usually electrically pumped and involve different physical processes.
The optical gain is produced within the semiconductor material.
A gas laser is a laser in which an electric current is discharged through gas inside the laser medium to produce laser light. In gas lasers, the laser medium is in a gaseous state, they are used in applications that require laser light with very high beam quality and long coherence lengths, the laser medium or gain medium is made up of a mixture of gases and is packed up into a glass tube.
The glass tube filled with the mixture of gases acts as an active medium or laser medium.
A gas laser is the first laser that works on the principle of converting electrical energy into light energy. It produces a laser light beam in the infrared region of the spectrum at 1.15 µm.
Gas lasers are of different types: they are, Helium (He) – Neon (Ne) lasers, argon ion lasers, carbon dioxide lasers (CO2 lasers), carbon monoxide lasers (CO lasers), excimer lasers, nitrogen lasers, hydrogen lasers, etc. The type of gas used to construct the laser medium can determine the wavelength or efficiency of the laser.
A liquid laser is a laser that uses the liquid as a laser medium, the light supplies energy to the laser medium. A dye laser is an example of a liquid laser, it is a laser that uses an organic dye (liquid solution) as the laser medium.
A dye laser is made up of an organic dye mixed with a solvent. These lasers generate laser light from the excited energy states of organic dyes dissolved in liquid solvents. It produces a laser light beam in the near-ultraviolet (UV) to the near-infrared (IR) region of the spectrum.
Semiconductor lasers play an important role in our everyday life. These lasers are very cheap, compact in size, and consume low power. Semiconductor lasers are also known as laser diodes.
Semiconductor lasers are different from solid-state lasers. In solid-state lasers, light energy is used as the pump source whereas, in semiconductor lasers, electrical energy is used as the pump source.
In semiconductor lasers, a p-n junction of a semiconductor diode forms the active medium or laser medium. The optical gain is produced within the semiconductor material.