5a. Lasers.pptx.Detailed description about LASER-Light Amplification by Stimulated Emission of Radiation

LASER- Light Amplification by Stimulated Emission of Radiation

1. WHAT IS A LIGHT? 1 Light is a form of electromagnetic radiation that can be seen by a human eye. Light is a type of energy that makes it possible for us to see the world around us. We need light to see things Wavelength ( λ ) Frequency

2. LASER 2 (Light Amplification by Stimulated Emission of Radiation)

3. INTRODUCTION ON LASER (Light Amplification by Stimulated Emission of Radiation) 3 LASER is an acronym for: L – Light A – Amplification (by) S – Stimulated E – Emission (of) R - Radiation

4. INTRODUCTION ON LASER (Light Amplification by Stimulated Emission of Radiation) 4 The LASER (Solid state Ruby LASER) was invented by the physicist Theodore Harold Maiman in 1960 One of the most technical achievements of 20 th Century Stimulated emission was postulated by Einstein in 1917 In 1961, a gas state He-Ne laser is developed by Ali Javan and others in Bell Telephone Laboratory In 1964, CO 2 laser is developed by Kumar Patel of Bell labs in 1964

5. DIRECTIONALITY ( Highly pointed, one direction & narrow distribution) INTENSITY ( focus over a small area & penetrate long depth) MONOCHROMATICITY (Emit single (only one) wavelength) COHERENCE (wavelength and frequency ar all in same phase) 5 CHARACTERISTICS OF LASER Laser Source LASER Ordinary light Wall

6. PRINCIPLE OF LASER Stimulated Absorption Spontaneous Emission Stimulated Emission 6

7. PRINCIPLE OF LASER 7 EXCITED STATE Light Energy GROUND STATE STIMULATED ABSORPTION PHOTON SPONTANEOUS EMISSION STIMULATED EMISSION

8. Stimulated Absorption Atom in ground state with energy E 1 absorbs a photon of energy h υ and goes to excited state (higher energy state) with energy E 2 . This process is called Stimulated absorption . Condition Incident photon energy h υ ≥ Energy difference (∆E = E 2 – E 1 ) 8 EXCITED STATE E 2 Light Energy, h υ GROUND STATE E 1

9. Spontaneous Emission Atom in excited state with energy E 2 emits the absorbed photon of energy h υ and return to ground state with energy E 1 spontaneously without any external influences. This process is called Spontaneous emission . 9 EXCITED STATE E 2 Emitted photon energy h υ = E 2 – E 1 GROUND STATE E 1

10. Stimulated Emission Atom in excited state with energy E 2 interact with the photon of energy h υ and this photon stimulate (trigger) the atom to make transition to the ground state with energy E 1 . This process is called Stimulated emission . By this process, two photons in phase are emitted and thus, photons are amplified by stimulation 10 EXCITED STATE E 2 Emitted photon energy h υ = E 2 – E 1 GROUND STATE E 1 Incident Light Energy h υ Incident Light Energy h υ 2 h υ

11. Stimulated Emission 11 EXCITED STATE E 2 GROUND STATE E 1 Incident Light Energy h υ Amplified photons energy 4 h υ

12. Photons Amplification/ Lasing action/ Laser action EXCITED STATE E 2 GROUND STATE E 1 Incident Light Energy h υ Amplified photons energy 8 h υ Conditions to achieve lasing action: 1. Minimum two energy levels should be present 2. Population inversion should be achieved. 3. Continuous supply of input of energy to raise the atoms to excited state

13. 13 Population Inversion Normal Population Population Inversion The state of achieving more number of atoms in the excited state compared to the ground state GROUND STATE GROUND STATE EXCITED STATE EXCITED STATE

14. Pumping Methods Process of achieving population inversion Types Optical Pumping Electric discharge method Direct conversion In elastic atom atom collision   14 Pumping

15. 15 Electrical Discharge Method (excitation by e - s) Optical Pumping (excitation by photons) Inelastic collision between atoms Direct Conversion EXCITED STATE EXCITED STATE Semiconductor EXCITED STATE Light Energy GROUND STATE Electrical Energy Light Energy A A* B B* e* e* EXCITED STATE

16. 16 Optical pumping When atoms are exposed to photon energy h υ , atoms in lower energy state absorb the photon energy and excited to higher energy state and create population inversion. This method of pumping is called Optical pumping . Solid state laser Ruby Laser – xenon flash lamp Nd -YAG Laser – krypton flash tubes

17. 17 Electrical discharge method In this method, electrons are produced in electrical discharge tube Electrons are accelerated to high velocity by electric field Accelerated electrons collide with the gas atoms Gas atoms gain energy from electrons and get excited to higher energy state and create population inversion. This method of pumping is called electrical discharge method . In equation form, A = gas atom in ground state, e* = e - with high KE, A* = same gas atom in excited state and e = same e - with low KE Gas laser CO 2 Laser Argon Laser

18. 18 Direct Conversion In this method, electrical energy is applied to direct band gap semiconductor like GaAs Recombination of electrons and holes takes place, and electrical energy is directly converted to optical light energy and thus, create population inversion Semiconductor diode laser GaAs Laser Electrical energy  Semiconductor diode  Optical light energy

19. 19 Inelastic atom-atom collision In this method, a combination of two gases say A and B are used Excited states of A and B nearly coincides in energy First, atoms of gas A are excited to higher energy state by electrical discharge method Now A* at higher energy state collide with atoms of gas B which are in lower energy state Due to inelastic collision, B atoms gain energy and get excited to higher energy state and thus creating population inversion Mixed Gas laser He-Ne gas Laser

20. Active medium: It is the basic material in which atomic or molecular transitions takes place leading to laser action. It is the medium (solid, liquid, gas, dye, semiconductor) in which population inversion takes place Pumping source: With the help of external energy source , the system can be pumped to higher energy state and more number of atoms are generated and thus, population inversion is achieved. Optical Resonator: Consists of a pair of reflecting surfaces in which one is fully (100%) reflecting R 1 and other is partially reflected R 2 . Active material is placed between the two reflecting surfaces. Photons generated are bounced back and forth, thereby, induce more and more stimulated emissions leading to laser action. Components of LASER Active Medium Fully silvered mirror (100%) Partially silvered mirror

21. Laser in Communication In fiber optic communication laser bandwidth is very high compared to the radio and microwave communications As it has large bandwidth, more amount of data can be sent Lasers are used in communications Laser in Industry Lasers can be used to blast holes in diamonds and hard steel Laser can be used to drill, weld and cut metal from surfaces It is used in Laser printing and in computer storage devices Surface defects can be detected using Lasers without damaging them 21 Applications of LASER

22. Laser in Medicine Laser is used in drilling minute holes in cell walls of the human body Cancer treatment can be done using Laser Laser is used in Endoscopic application It is used in the treatment of tissue in Skull and spine Skin imperfections can be removed by Laser Argon and CO 2 laser are used in the treatment of liver and lungs Lasers are used in bloodless surgery and in destroying kidney stones and gall stones Laser is used in the eye treatment. 22 Applications of LASER

23. Laser in Military A Laser beam can be bounced off a target such as enemy air plane or ship, to determine its distance and speed Laser can serve as war weapon High energy lasers are being employed to destroy enemy air crafts and missiles Other Applications Laser is used in air pollution to determine the size of dust particles Laser is used in CD s, barcode scanners, thermometers, laser pointers and hologram 23 Applications of LASER