- Laser Definition: A laser is defined as a device that amplifies light by stimulating electromagnetic radiation to emit coherent and focused light beams.
- Components of Laser: The three main components of a laser are the active medium, the pump source, and the optical resonator, each playing a crucial role in the amplification and emission of laser light.
- Types of Lasers: Lasers come in various types such as solid-state, gas, dye, excimer, chemical, and semiconductor, each using different materials for the active medium.
- Stimulated Emission: This process involves an incoming photon stimulating an electron to emit a second photon, crucial for creating coherent laser light.
- Practical Applications: Lasers are essential in numerous applications across consumer electronics, medical treatments, industrial processes, and scientific research.
LASER
The acronym LASER stands for Light amplification by stimulated emission of radiation. A laser is a device that produces a unique type of light not found naturally. This light is generated through optical amplification, which relies on the stimulated emission of electromagnetic radiation. It is different from conventional light in three ways. First, the lights from LASER contains only one color or wavelength that is why it is called ‘monochromatic’. Secondly, all the wavelengths are in phase- because of this, it is known as coherent. And thirdly, laser light beams are very narrow and can be concentrated on one tiny spot- this property makes it be known as ‘collimated’. These are also the characteristics of LASER.
For its operation, population inversion is much needed. When a group of atoms or molecules exist with more no electrons in an excited state than in lower energy states, population inversion takes place. Now, when an electron is in an excited state, it may decay to an empty lower energy state. If an electron decays without external influence, emitting a photon, that is known as spontaneous emission.
Stimulated emission occurs when a photon stimulates an electron, causing it to emit a second photon and return to a lower energy level. This process results in the production of two coherent photons. Now, if a significant population inversion exists, then stimulated emission can produce significant amplification of light. Photons which are produced in stimulated emission produce coherent light as they have definite phase relationship.
The principle of laser was first discovered by Einstein in 1917 but it was not until 1958 that laser was successfully developed.
Lasers have a wide range of applications. They are integral to consumer devices like CD and DVD players, and printers. In medicine, they are used for surgeries and skin treatments, while in industry, they assist in cutting and welding materials. They are used in military and law enforcement devices for marking targets and measuring range. Lasers also have many important applications in scientific research.
Components of LASER
Every LASER consists of three basic components. These are –
- Lasing material or active medium.
- External energy source.
- Optical resonator.
- The active medium is energized by an external pump source, creating a population inversion necessary for the spontaneous and stimulated emission of photons, thus achieving optical gain. Semiconductors, organic dyes, gases (He, Ne, CO2, etc), solid materials (YAG, sapphire (ruby) etc.) are usually used as lasing materials and often LASERs are named for the ingredients used as a medium.
- The excitation source, pump source provides energy which is needed for the population inversion and stimulated emission to the system. Pumping can be done in two ways – electrical discharge method and optical method. Examples of pump sources are electrical discharges, flash lamps, arc lamps, light from another laser, chemical reactions etc.
- Resonator guide basically provides the guidance about the simulated emission process. It is induced by high-speed photons. Finally, a laser beam will be generated.
In most of the systems, it consists of two mirrors. One mirror is fully reflective and other is partially reflective. Both the mirrors are set up on optic axis, parallel to each other. The active medium is used in the optical cavity between the both mirrors. This arrangement only filters those photons which came along the axis and others are reflected by the mirrors back into the medium, where it may be amplified by stimulated emission.
Types of LASER
Various types of lasers are available, each suited for specific applications and characterized by the materials used as the active medium.
- Solid State LASER
In this kind of LASERs solid state, materials are used as active medium. The solid state materials can be ruby, neodymium-YAG (yttrium aluminum garnet) etc. - Gas LASER
These LASERs contain a mixture of helium and Neon. This mixture is packed up into a glass tube. It acts as active medium. We can use Argon or Krypton or Xenon as the medium. CO2 and Nitrogen LASER can also be made. - Dye or Liquid LASER
In this kind of LASERs organic dyes like Rhodamine 6G in liquid solution or suspension used as active medium inside the glass tube. - Excimer LASER
Excimer LASERs (the name came from excited and dimers) use reactive gases like Chlorine and fluorine mixed with inert gases like Argon or Krypton or Xenon. These LASERs produce light in the ultraviolet range. - Chemical LASER
A chemical laser is a LASER that obtains its energy from a chemical reaction. Examples of chemical lasers are the chemical oxygen iodine laser (COIL), all gas-phase iodine laser (AGIL), and the hydrogen fluoride laser, deuterium fluoride laser etc - Semiconductor LASER
In these lasers, junction diodes are used. The Semiconductor is doped by both the acceptors and donors. These are known as injection laser diodes. Whenever the current is passed, light can be seen at the output.
