Lasers have entered many technological products, and you will find them an essential component of CD players, dentist machines, iron cutting and welding equipment, measuring instruments, and other fields. All of these devices use lasers, but what is the laser and what makes the laser distinct from other light sources. In this article, we will explain everything related to laser in a simple and clear way.
The name LASER came from the initial letters of the idea of laser work, represented in the following sentence:
Light Amplification by Stimulated Emission of Radiation
Means Light Amplification by Stimulated Emission of Electromagnetic Radiation. The existence of the laser was predicted by Albert Einstein in 1917, who laid the theoretical basis for the stimulated emission process, and the first laser device was designed in 1960 by the scientist Memman T.H. Maiman uses sapphire crystal known as Ruby laser.
Physics basics about the atom
In the universe there are 100 different types of atoms and everything around us is made of these 100 atoms, but how do atoms combine and bond with each other to form materials such as water consisting of two hydrogen atoms and one oxygen atom, or how a piece of iron or copper was formed. The atoms are in constant motion as the atoms oscillate about their position in the substance, and the atoms have a circular motion or a transitional movement as well. So if you look at a wooden table, for example, and although it is fixed in place, it is the atoms of it that made wood in constant motion.
As a result of the movement of the atoms that they acquire from thermal energy, they exist in different states of excitation, or in other words, that the atoms have different energies. state. The level of excitation depends on the amount of energy supplied by the atom and the energy source is either heat, light or electricity.
The atom contains the nucleus (made up of protons and neutrons) and electrons that orbit the nucleus in different orbits. Each orbit is an energy level.
If the atom is supplied with thermal energy for the first energy from a light or electrical source, then some of the electrons in the atom will transfer from the orbital with a lower energy level to an orbit of energy higher and further away from the nucleus.
Energy absorption
An atom absorbs energy from heat, light, or electricity. The electrons move from a lower energy level to a higher energy level.
This previous idea is simplified about absorbing energy in the atom, but it is considered the basis for the role of the atom in laser production.
When the electron moves to the orbital with a higher energy level, it soon returns and moves to the lower energy level, and then the electron releases energy in the form of a photon (light).
Electrons emit photons when excited, for example when heating a metal such as an electric heater wire, its color turns from a dark color to a glowing color, and this glow is a result of the photons that were released after the atoms of the material of the electric heater wire were excited. Likewise, if we think about the idea of a television screen, it gives the image through the photons produced by the screen material (phosphorous) when excited by an electronic beam.
If we conclude that the light is produced by the photons emitted from the excitation of the electrons of the atom and the photon color (the color of light) depends on the energy of the photon.
The relationship of the atom to the laser
For a simple definition of the laser, we say, based on the previous explanation, that it is a device that controls how atoms release photons.
As we mentioned, the word laser is an abbreviation for the phrase light amplification by stimulated emission of radiation, which means that it explains in detail the idea of laser action, which depends on the fact that the laser is nothing but an amplified light by a process called the excited emission of radiation and this is what we intended to control how the atom emits the photon.
Although there are many types of lasers, they all share the same characteristics. In the laser there is the material that produces the laser that is excited by a pumping process of electrons from the ground level to the excitation level. For electronic pumping, a strong flash light is used or by electric discharge, and this pumping helps to supply the largest possible number of electrons to move to higher energy levels, so the laser material becomes composed of atoms with excited electrons and we call it the excited atom. It is worth noting that it is very necessary to excite a large number of atoms to obtain a laser. This process is called a population inversion, that is, making the number of atoms excited in the laser material greater than the number of atoms that are not excited.
The heart of the enumeration is what makes the light produced by the material laser, and if we do not reach the stage of the enumeration of the population, we will obtain normal light.
Just as the electrons absorbed a lot of energy through the pumping process, these electrons release the energy that they absorbed in the form of photons, i.e. light.
The emitted photons have a specific wavelength (light of a specific color) that depends on the difference in energy levels that the excited electrons have moved between. If the transition of all electrons is between two specific energy levels, then all the emitted protons will have the same wavelength.
An excited red electron moves to a lower energy level (the electron is blue) and loses its energy as a photon
Laser light:
Laser light differs from ordinary light as it has the following properties:
The emitted light is monochromatic, meaning it has one wavelength. The wavelength determines the color of the light produced as well as its energy.
The light emitted by the laser is coherent, meaning that all the photons are in the same phase, which makes the intensity of the light great, so the photons do not fade each other due to the phase difference between them.
The emitted light has a one-way direction, where the laser beam is a beam of photons in a straight path, while ordinary light is scattered and scattered throughout the space.
Responsible for these characteristics is the process of stimulated emission, while in ordinary light the emission is automatic, as each photon is randomly emitted, unrelated to the other.
An important factor in laser production is the mirrors installed on both sides of the laser production material. Mirrors help to reflect some of the photons into the laser material several times, so that these photons induce other excited electrons to emit more photons of the same wavelength and the same phase, and this is the process of light amplification. One of these women is designed to be less than 100% reflective to allow some photons to escape through it, which is the laser beam that we get.
Ruby Laser
The components of the sapphire laser are a flash light source, a sapphire stem, and two mirrors installed at the ends of the leg. One of these women has a reflectance of 90%. The light source is responsible for the pumping process and the sapphire stem is the laser production material.
(1) Sapphire laser components
(2) A high voltage difference that provides the flash with sufficient power to generate light of high intensity for a short period of time. This light excites the atoms in the sapphire crystal to higher energy levels.
(3) Some atoms release photons
Photons shot parallel to the axis of the sapphire stem, collide with the mirror and are reflected back into the sapphire several times, prompting other electrons to emit photons.
(5) Photons of one wavelength and of the same phase and grouped in a beam that passes from the mirror to give the laser light.
Types of lasers
Lasers come in different types according to the uses and the diversity of the laser comes from the diversity of the material used to produce it. There are solid, liquid and gaseous materials, and the type of material is the most used basis to distinguish between the different types. The laser is called by the type of material used, for example the He-Ne laser means that the material used is a mixture of helium and neon, and the sapphire laser means that the material that produces the laser is sapphire, and so on for the rest of the other types. Let's take some examples of different types of lasers:
A solid-state laser is a laser that is produced by a substance or mixture of solid materials such as ruby or a mixture of aluminum, yttrium-aluminum and neodymium: yttrium-aluminum. It is called the TAG laser for short, and its wavelength is in the infrared region.
Gas laser, which is based on a gaseous substance such as helium, neon and carbon dioxide, and its wavelengths are in the infrared range, and it is used in cutting solid materials of high energy.
Excimer laser is a type of laser that uses inert gases such as chlorine, fluorine, krypton or argon. These gases produce laser beams with wavelengths in the ultraviolet range.
Dye lasers, which are complex organic materials such as rhodamine 6G, are dissolved in an alcohol solution to produce a laser that can control its wavelength.
Semiconductor laser, sometimes called diode lasers, depends on semiconductor materials and has a small laser size and consumes little energy and therefore is used in delicate devices such as CDs and laser printers.
The laser is characterized by its wavelength, for example the wavelength of the sapphire laser is 694nm, and the laser material is chosen based on the required wavelength as in the illustrative table below, for example the carbon dioxide gas laser is used in cutting solid metals because its wavelength is in the infrared range, which are thermal rays if It fell concentrated on the surface of the metal being melted.
Laser classifications
Lasers are classified into four categories based on their danger to live cells. When dealing with a laser, you must pay attention to the sign that indicates its classification.
Class I This means that the laser beam is of low power and is not dangerous.
Class IA This classification indicates that the laser is harmful to the eye if we look in the direction of the beam and is used in the supermarket as a scanner. The laser power that falls under this rating is 4mW.
Class II This refers to a visible optical laser with an energy of less than 1mW.
Class IIIA: Medium laser power, 1-5mW, and hazardous to the eye if direct beam enters the eye. Most pens marked fall in this category.
Class IIIB This laser has more power than average.
The fourth classification, Class IV, which are types of high-energy lasers and reach 500mW for the continuous beam, while for pulsed lasers, its energy is estimated at 10 J / cm2 and is dangerous to the eyes and the skin. The use of this laser requires many equipment and prevention measures.
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