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    Add as FriendTYPES OF LASER

    by: ambika

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    1 : TYPES OF PREPARED BY V.REVATHIAMBIKA LECTURER IN PHYSICS
    2 : Introduction OF LASER L – LIGHT A – AMPLIFICATION S – STIMULATED E – EMISSION R - REDIATION A. L. SCHAWLOW and C. H. TOWNES IN 1958 RUBY LASER by T. H. MAIMANN IN 1960 7/3/2012 2
    3 : Basic idea Consider a group of atoms exposed stream of photons, each with energy h?. Let us assume two energy levels E1 and E2 of an atom. During transition from one energy state to another, the light is absorbed (or) emitted by particles. Under this action, 3 processes can occur. They are, Stimulated absorption Spontaneous emission Stimulated emission 7/3/2012 3
    4 : Mechanisms of Light Emission Absorption Spontaneous Emission Stimulated Emission 7/3/2012 4 For atomic systems in thermal equilibrium with their surrounding, the emission of light is the result of: Absorption And subsequently, spontaneous emission of energy There is another process whereby the atom in an upper energy level can be triggered or stimulated in phase with the an incoming photon. This process is: Stimulated emission It is an important process for laser action Therefore 3 process of light emission:
    5 : Laser Fundamentals 7/3/2012 5 The light emitted from a laser is monochromatic, that is, it is of one color/wavelength. In contrast, ordinary white light is a combination of many colors (or wavelengths) of light. 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. The light from a laser is said to be coherent, which means that the wavelengths of the laser light are in phase in space and time. Ordinary light can be a mixture of many wavelengths. These three properties of laser light are what can make it more hazardous than ordinary light. Laser light can deposit a lot of energy within a small area.
    6 : 7/3/2012 6 Incandescent vs. Laser Light Many wavelengths Multidirectional Incoherent Monochromatic Directional Coherent
    7 : Common Components of all Lasers 7/3/2012 7 Active Medium The active medium may be solid crystals such as ruby or Nd:YAG, liquid dyes, gases like CO2 or Helium/Neon, or semiconductors such as GaAs. Active mediums contain atoms whose electrons may be excited to a metastable energy level by an energy source. Excitation Mechanism Excitation mechanisms pump energy into the active medium by one or more of three basic methods; optical, electrical or chemical. High Reflectance Mirror A mirror which reflects essentially 100% of the laser light. Partially Transmissive Mirror A mirror which reflects less than 100% of the laser light and transmits the remainder.
    8 : Laser Components 7/3/2012 8 Gas lasers consist of a gas filled tube placed in the laser cavity. A voltage (the external pump source) is applied to the tube to excite the atoms in the gas to a population inversion. The light emitted from this type of laser is normally continuous wave (CW).
    9 : Lasing Action Energy is applied to a medium raising electrons to an unstable energy level. These atoms spontaneously decay to a relatively long-lived, lower energy, metastable state. A population inversion is achieved when the majority of atoms have reached this metastable state. Lasing action occurs when an electron spontaneously returns to its ground state and produces a photon. If the energy from this photon is of the precise wavelength, it will stimulate the production of another photon of the same wavelength and resulting in a cascading effect. The highly reflective mirror and partially reflective mirror continue the reaction by directing photons back through the medium along the long axis of the laser. The partially reflective mirror allows the transmission of a small amount of coherent radiation that we observe as the “beam”. Laser radiation will continue as long as energy is applied to the lasing medium. 7/3/2012 9
    10 : Lasing Action Diagram 7/3/2012 10 Energy Introduction Ground State Excited State Metastable State Spontaneous Energy Emission Stimulated Emission of Radiation
    11 : PRINCIPLE OF LASER ACTION Due to stimulated emission the photons multiply in each step giving rise to an intense beam of photons that are coherent and moving in the same direction . hence the Light Is Amplified By Stimulated Emission Of Radiation 7/3/2012 11
    12 : PUMPING METHODS OPTICAL PUMPING DIRECT ELECTRON EXCITATION INELASTIC ATOM – ATOM COLLISION DIRECT CONVERSION CHEMICAL PROCESS 7/3/2012 12
    13 : Properties of Laser Monochromatic Concentrate in a narrow range of wavelengths (one specific colour). Coherent All the emitted photons bear a constant phase relationship with each other in both time and phase Directional A very tight beam which is very strong and concentrated.
    14 : Part 2: Laser Hazards 7/3/2012 14
    15 : Types of Laser Hazards Eye : Acute exposure of the eye to lasers of certain wavelengths and power can cause corneal or retinal burns (or both). Chronic exposure to excessive levels may cause corneal or lenticular opacities (cataracts) or retinal injury. Skin : Acute exposure to high levels of optical radiation may cause skin burns; while carcinogenesis may occur for ultraviolet wavelengths (290-320 nm). Chemical : Some lasers require hazardous or toxic substances to operate (i.e., chemical dye, Excimer lasers). Electrical : Most lasers utilize high voltages that can be lethal. Fire : The solvents used in dye lasers are flammable. High voltage pulse or flash lamps may cause ignition. Flammable materials may be ignited by direct beams or specular reflections from high power continuous wave (CW) infrared lasers. 7/3/2012 15
    16 : Laser Class 7/3/2012 16 The following criteria are used to classify lasers: Wavelength. If the laser is designed to emit multiple wavelengths the classification is based on the most hazardous wavelength. For continuous wave (CW) or repetitively pulsed lasers the average power output (Watts) and limiting exposure time inherent in the design are considered. For pulsed lasers the total energy per pulse (Joule), pulse duration, pulse repetition frequency and emergent beam radiant exposure are considered.
    17 : LASER COMPONENTS Laser-Professionals.com 7/3/2012 17
    18 : 7/3/2012 18
    19 : Optical Resonator Two parallel mirrors placed around the gain medium. Light is reflected by the mirrors back into the medium and is amplified . The design and alignment of the mirrors with respect to the medium is crucial. Spinning mirrors, modulators, filters and absorbers may be added to produce a variety of effects on the laser output.
    20 : Comparison chart for all the lasers
    21 : Typical Application of Laser 7/3/2012 21 The detection of the binary data stored in the form of pits on the compact disc is done with the use of a semiconductor laser. The laser is focused to a diameter of about 0.8 mm at the bottom of the disc, but is further focused to about 1.7 micrometers as it passes through the clear plastic substrate to strike the reflective layer. The reflected laser will be detected by a photodiode. Moral of the story: without optoelectronics there will no CD player!
    22 : Difference between a photography & holography
    23 : Common Laser Signs and Labels 7/3/2012 23
    24 : LASER SAFETY EYEWEAR Laser-Professionals.com 7/3/2012 24
    25 : INTERNATIONAL LASER WARNING LABELS Symbol and Border: Black Background: Yellow Legend and Border: Black Background: Yellow Laser-Professionals.com 7/3/2012 25
    26 : CDRH CLASS WARNING LABELS Laser-Professionals.com 7/3/2012 26

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