LASER Fall 2022/2023 Handout PDF

Faculty of Applied Health Science 11/20/2022 Technology Physics by Dr. Ahmed Yassin...

Faculty of Applied Health Science 11/20/2022 Technology Physics by Dr. Ahmed Yassin Fall 2022/2023 in ss Ya ed hm r-A Topics D  What is LASER ?  Difference between LASER and ordinary light.  Lasing action.  Population inversion.  Pumping process.  LASER operation.  Types of LASER.  Applications of laser. Dr./ Ahmed Yassin..... Physics 1 Faculty of Applied Health Science 11/20/2022 Technology What is LASER ?  is an acronym for “ Light Amplification By Stimulated Emission of Radiation ”.  Laser devices stimulate atoms or molecules to emit light at particular wavelengths and amplifies that light, typically producing a very narrow beam of radiation. The emission generally covers an extremely limited range of visible, infrared, or in ultraviolet wavelengths. ss Ya ed hm r-A Difference between LASER and ordinary light D Dr./ Ahmed Yassin..... Physics Dr./ Ahmed Yassin..... Physics 2 Faculty of Applied Health Science 11/20/2022 Technology Stimulated emission Spontaneous emission Highly energized Poorly energized in Monochromatic Polychromatic ss Ya ed hm r-A Lasing action D  The laser is an outgrowth of a suggestion made by Albert Einstein in 1916 that: “Under the proper circumstances atoms could release excess energy as light, either spontaneously or when stimulated by light”. Dr./ Ahmed Yassin..... Physics 3 Faculty of Applied Health Science 11/20/2022 Technology LASING ACTION  According to Einstein, the interaction of radiation with matter could be explained in terms of three basic processes: 1. Absorption, 2. Spontaneous emission, and in 3. Stimulated emission. ss Ya ed hm r-A D Absorption  In the equilibrium position, atom is initially lying in the ground level of energy E1.  Atom raises to the upper excited level E2 , when it absorbs a photon with energy = ΔE. ∆𝑬 𝑬𝟐 𝑬𝟏 𝒉𝝊 Dr./ Ahmed Yassin..... Physics 4 Faculty of Applied Health Science 11/20/2022 Technology Spontaneous Emission  Atom (or molecule) is in the excited state E2.  The atom will tend to spontaneously decay to the ground state E1.  A photon with energy (hυ) will be released in a random direction. in ss Ya ed hm r-A Stimulated Emission D  Atom (or molecule) is in the excited state E2.  The atom will be hit by another photon.  So, it decays to the ground state E1.  Two photons with energy (2hυ) will be released.  The two photons will have the same energy, direction, phase and polarization. Dr./ Ahmed Yassin..... Physics 5 Faculty of Applied Health Science 11/20/2022 Technology Population inversion  Population inversion is the process of achieving greater population of higher energy state as compared to the lower energy state.  Population inversion technique is mainly used in for light amplification. ss Ya ed hm r-A Pumping Process D  Let us assume that initially the majority of electrons will be in the lower energy state or ground state (E1) and only a small number of electrons will be in excited states (E2 and E3).  When we supply light energy which is equal to the energy difference of E3 and E1, the electrons in the lower energy state (E1) gains sufficient energy and jumps into the higher energy state (E3).  This process of supplying energy is called pumping. Dr./ Ahmed Yassin..... Physics 6 Faculty of Applied Health Science 11/20/2022 Technology Pumping Process in ss Ya ed hm r-A  We also use other methods to excite ground state electrons such as electric discharge and chemical reactions. The flow of D electrons from E1 to E3 is called pump transition. Common types of pumping 1- Optical pumping by light in case of solids, 2- Excitation by electric discharge in case of gases. 3- Thermal pumping, and 4- Chemical reactions. Dr./ Ahmed Yassin..... Physics 7 Faculty of Applied Health Science 11/20/2022 Technology LASER operation The LASER device should contain: 1- Pump, which is an external source of energy that produces a population inversion. 2- Amplifying medium, which is a material or substance of solid, liquid, or gaseous nature that is able to produce a laser light. 3- Resonator, which consists of a pair of aligned plane or curved mirrors. One of them is of 100 % reflectivity, while the other in mirror is partially reflected. ss Ya ed hm How does LASER work ? r-A D Dr./ Ahmed Yassin..... Physics 8 Faculty of Applied Health Science 11/20/2022 Technology How does LASER work ? in ss Ya ed hm r-A Types of LASER D Lasers are classified into 4 types based on the type of LASER medium used: 1- Solid-state laser such as: ruby laser and neodymium- doped Yttrium Aluminum Garnet (Nd:YAG) laser. 2- Gas laser such as: CO2 laser. 3- Liquid laser. 4- Semiconductor laser. Dr./ Ahmed Yassin..... Physics 9 Faculty of Applied Health Science 11/20/2022 Technology 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.  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 in are used to achieve pumping. ss Ya ed hm r-A Solid-state laser D Dr./ Ahmed Yassin..... Physics 10 Faculty of Applied Health Science 11/20/2022 Technology 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.  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 in wavelength or efficiency. ss Ya ed hm r-A Gas laser D Dr./ Ahmed Yassin..... Physics Dr./ Ahmed Yassin..... Physics 11 Faculty of Applied Health Science 11/20/2022 Technology Semiconductor laser  Semiconductor lasers play an important role in our everyday life. These lasers are very cheap, compact 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 in produced within the semiconductor material.ss Ya ed hm r-A Semiconductor laser (laser diode) D Dr./ Ahmed Yassin..... Physics 12 Faculty of Applied Health Science 11/20/2022 Technology Applications of LASER The most significant applications of lasers include: Lasers in medicine Lasers in communications Lasers in industries Lasers in science and technology Lasers in military in ss Ya ed hm r-A D Dr./ Ahmed Yassin..... Physics 13