Lasers

Laser - History, characteristics, components. principle, types and application.

1. LASERS SAKEENA ASMI MAHATMA GANDHI UNIVERSITY

2. ight mplification by timulated mission of adiation Term coined by Gordon Gould. One of the most influential technological achievements of the 20 th century. Laser is an optical device that generates intense beam of coherent monochromatic light by Stimulated emission of radiation .

3. LASER SPECTRUM Lasers operate in the ultraviolet, visible and infrared region

4. HISTORY OF LASER In 1917, Albert Einstein established the basic fundamentals to built a laser (quantum theory of light and photons & mechanism of stimulated emission). In 1954 , the first maser was demonstrated by Charles Townes, A L Schawlow which worked in the microwave range. The first laser was designed by Theodore Maiman in 1960 and was made by ruby.

5. THEODORE HAROLD MAIMAN

6. WHY ARE LASERS USEFUL ?

7. CHARACTERISTICS OF LASER LIGHT

8. COHERENCE : The light from a laser is said to be coherent , which means that all the light waves have the same frequency and move in phase together. Ordinary light in contrast is out of phase. ORDINARY LIGHT LASER LIGHT

9. 2. DIRECTIONALITY : Lasers emit light that is highly directional, that is, laser light is emitted as a relatively narrow beam in a specific direction. Ordinary light, such as from a light bulb, is emitted in many directions away from the source. ORDINARY LIGHT LASER LIGHT

10. 3. MONOCHROMATICITY : The light emitted from a laser is monochromatic, that is, it is of one colour or wavelength. In contrast, ordinary white light is a combination of many colours or wavelengths of light. 4. HIGH INTENSITY In laser, the light spreads in small region of space and in a small wavelength range. In an ordinary light source, light spreads out uniformly in all directions. Hence, laser light has greater intensity when compared to ordinary light.

11. LASER COMPONENTS

12. LASER MEDIUM ENERGY SOURCE OPTICAL RESONATOR HIGH REFLECTANCE MIRROR (HR) OUTPUT COUPLER MIRROR (OC)

13. 1. Energy source or pump source Part of laser syste m that provides energy to the laser medium. Example of energy source include electric discharges, chemical reactions, light from another laser. Type of energy source depends on laser medium. For eg: Excimer laser uses chemical reactions as energy source Helium laser uses electric discharge etc… 2. Laser medium Also known as active medium or gain medium. System in which population inversion and hence stimulated emission takes place. Laser medium determines the characteristics of laser light emitted. Can be solid(Nd:YAG laser), liquid(dye laser) or gaseous(helium neon laser).

14. 3. Optical resonator Laser medium is surrounded by two parallel mirrors which provide feedback of light. One mirror is fully reflective ( High Reflection mirror ) and other is partially reflective ( Output coupler ). Output coupler will allow some of the light to leave the optical cavity to produce laser output beam. Two mirrors are whole called as OPTICAL RESONATOR .

15. PRINCIPLES OF WORKING OF A LA s ER In lasers, photons are interacted in 3 ways with atoms: 1. Absorption of radiation 2. Spontaneous emission 3. Stimulated emission ABSORPTION OF RADIATION It is the process by which electrons in the lower energy state absorbs energy from photons to jump into higher energy level. It occurs because these electrons in the lower energy state need extra energy to jump into higher energy level. Extra energy is provided from various sources like heat, electric field or light etc.

16. Absorption of light occurs only if the energy of incident photon exactly matches energy difference of the 2 energy levels. This results in POPULATION INVERSION – it is the process of achieving greater number of electrons in higher energy state as compared to lower energy state. ENERGY LOWER ENERGY STATE HIGHER ENERGY STATE

17. 2. SPONTANEOUS EMISSION It is the process by which electrons in the excited state return to the ground state by emitting photons. Electron in excited state can stay only for a short period called as life time of excited electrons which is 10 -8 sec. Here electrons move naturally from one state to another and emission of photons also occur naturally which constitute ordinary incoherent light . ENERGY LOWER ENERGY STATE HIGHER ENERGY STATE PHOTONS

18. 3. STIMULATED EMISSION It is the process by which incident photon interacts with the excited electron and forces it to return to the ground state. Hence light energy is supplied directly to the excited electron, so electrons in the excited state need not wait for completion of their lifetime. Here 2 photons are emitted, one is due to incident photon and another is due to energy release of excited electron. All emitted photons have the same energy same frequency and travel in same direction. Number of photons emitted depends on number of electrons in higher energy level and incident light intensity.

19. ENERGY LOWER ENERGY STATE HIGHER ENERGY STATE PHOTONS

20. ENERGY SOURCE LASER MEDIUM

21. ENERGY SOURCE LASER MEDIUM

22. LASER MEDIUM OPTICAL RESONATOR HIGH REFLECTANCE MIRROR (HR) OUTPUT COUPLER MIRROR (OC)

23. LASER MEDIUM OPTICAL RESONATOR HIGH REFLECTANCE MIRROR (HR) OUTPUT COUPLER MIRROR (OC)

24. LASER MEDIUM OPTICAL RESONATOR HIGH REFLECTANCE MIRROR (HR) OUTPUT COUPLER MIRROR (OC)

25. (Based on type of laser medium used)

26. 1. Solid state laser Uses solid as a laser medium – glass or crystalline materials are used. Materials such as Sapphire (Al 2 O 3 ), Neodymium doped yttrium aluminium garnet (Nd:YAG), Neodymium doped glass ( Nd:Glass ) etc are used as materials for laser medium. Nd:YAG is the most commonly used. The first solid state laser was Ruby laser – here ruby crystal is the medium. RUBY LASER Nd:YAG LASER

27. 2. Gas laser Laser medium is in the gaseous state. Type of gas used can determine the laser efficiency. Types : Helium Neon laser, Argon laser, carbon monoxide laser, Excimer lasers etc. Helium Neon laser CO 2 laser

28. 3. Liquid laser Uses liquid as laser medium. Most common is Dye laser – organic dye as laser medium. DYE LASER

29. 4 . Semiconductor laser Also known as LASER DIODE. Play an important role in our everyday life. These lasers are very cheap, compact size, and consume low power.

30. APPLICATIONS OF LASERS

31. LASERS IN MEDICINE Bloodless surgery Fiber optic endoscope to detect ulcers in the intestine . Lasers are used extensively in the treatment of eye diseases particularly to reattach a detached retina.

32. Used to remove caries or decayed portion of teeth. Liver and lung diseases could be treated using lasers. To destroy cancerous and precancerous cells. Used to study internal structure of microorganisms and cells .

33. To break up gall stones and kidney stones. To remove plague clogging human arteries. Lasers are used in cosmetic treatments such as acne treatment, hair removal etc…

34. LASERS IN INDUSTRY # For precision measurements and leveling Latching tool Milling tool

35. Laser light is used to collect the information about the prefixed prizes of various products in shops and business establishments from the barcode printed on the product. Welding and cutting of metal

36. LASERS IN SCIENCE AND TECHNOLOGY Lunar laser ranging

37. LASERS IN COMMUNICATION Laser communication systems are wireless communications through the atmosphere. Eg: Optical fiber communications, used particularly for long distance optical data transmission, Free space optical communications for inter satellite communications etc…

38. LASERS IN MILITARY Thermal imaging Night vision Laser guns

39. LASERS IN HOLOGRAPHY Holography is the production of holograms by the use of lasers.

40. BIOLOGICAL EFFECTS OF LASER RADIATION The unprotected human eye is extremely sensitive to laser radiation and can be permanently damaged from direct or reflected beams. The area of the eye damaged by laser energy is dependent upon the wavelength of the incident laser beam. The retina, cornea and lens are the areas most commonly damaged. 1. Laser effects on eye

41. 2 . Laser effects on skin Thermal (burn) injury is the most common cause of laser induced skin damage. Thermal damage is generally associated with laser operating at exposure time greater than 10 microseconds and the wavelength region near UV to infrared region. Retina : laser light in the visible to infrared spectrum can cause damages to retina. These wavelengths are also known as “retinal hazard region” Cornea and lens : laser light in the UV or far infrared spectrum can cause damage to cornea and lens.

42. NOBEL PRIZE IN PHYSICS 2018 DONNA STRICKLAND GERARD MOUROU ARTHUR ASHKIN “For groundbreaking inventions in the field of LASER PHYSICS ” (Inventing optical tweezers and high power laser pulses)

43. THANKYOU…