In: Physics
LASER stands for Light Amplification by Stimulated Emission of Radiation. A laser is a device which produces highly directional light. It emits light through a process called stimulated emission of radiation which increases the intensity of light.
Types of lasers
Gas laser:
A gas laser is a laser in which an electric current is discharged through a gas inside the laser medium to produce laser light. In gas lasers, the laser medium is in the gaseous state.
Gas lasers are used in applications that require laser light with very high beam quality and long coherence lengths.
In gas laser, the laser medium or gain medium is made up of the mixture of gases. This mixture 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 lasers wavelength or efficiency.
Solid state laser:
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 a glass or crystalline. The process of adding impurities to the substance is called doping. Rare earth elements such as cerium (Ce), erbium (Eu), terbium (Tb) etc are most commonly used as dopants.
Materials such as sapphire (Al2O3), neodymium-doped yttrium aluminum garnet (Nd:YAG), Neodymium-doped glass (Nd:glass) and ytterbium-doped glass are used as host materials for laser medium. Out of these, neodymium-doped yttrium aluminum garnet (Nd:YAG) is most commonly used.
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 pumping source. Light sources such as flashtube, 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.
Dye laser:
Dye lasers are lasers that use an organic dye as the laser medium. The organic dye laser medium is normally in the liquid form and is continuously circulated through the laser chamber. The dye may be pumped by flash lamps or by another laser such as an argon ion laser.
Rhodamine 6G, commonly referred to as Rh6G is a widely used dye. Dye lasers are commonly used in the dermatology industries.
Excimer laser:
They are pulsed gas discharge lasers that produce UV or ultraviolet light. A chemical reaction with an excimer or an excited dimer is used to power the excimer laser. An excimer can be defined as a heterodimeric or a dimeric molecule which is short-lived formed from two atom species. At least one of the atom species is in the excited electronic state.
There are four commonly used excimer molecules for the excimer laser and are derived from fluorine and chlorine gas. Argon fluoride (ArF) operates in the wavelength of 193 nm; Krypton fluoride (KrF) operates in the wavelength of 248 nm; Xenon fluoride (XeF) operates in the wavelength of 351 nm; and Xenon Chloride (XeCl) operates in the wavelength of 308 nm.
The wavelength output of an excimer laser can be changed simply by changing the gas mixture, the laser mirrors may have to be exchanged to obtain maximum output.
Excimer lasers is well suited to precision micromachining organic material as well as for delicate surgeries such as eye surgery and in semiconductor photolithography.