Ibm lasers
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The document discusses laser and holography. It defines laser as "Light Amplification by Stimulated Emission of Radiation" and describes the key properties of lasers including being monochromatic, coherent, and directional. It explains the basic concepts of absorption, spontaneous emission, stimulated emission, and population inversion which are necessary for laser operation. The document also provides details about different types of lasers and their applications. It concludes with an overview of holography including the basic principles and techniques for constructing and reconstructing holograms.
![Stimulated Emission
The probability of occurrence of stimulated emission transition from
the upper level 2 to the lower level 1 is proportional to the energy
density u(v) of the radiation and is given by
( P21 ) st = B21 N 2u (v)
where the proportionality constant B21 is known as the Einstein’s
coefficient of stimulated emission of radiation.
Thus the total probability of emission transition from the upper level
2 to the lower level 1 is
P21 = ( P21 ) sp + ( P21 ) st
P21 = N 2 [ A21 + B21u (ν )]](https://image.slidesharecdn.com/ibmlasers-130313213049-phpapp02/85/Ibm-lasers-15-320.jpg)
![Relation between Einstein’s Coefficients
Let N1 and N2 be the number of atoms at any instant in the state 1
and 2, respectively. The probability of absorption transition for
atoms from state 1 to 2 per unit time is
P = N1 B12u (v)
12
The probability of transition of atoms from state 2 to 1,either by
spontaneously or by stimulated emission per unit time is
P21 = N 2 [ A21 + B21u (ν )]
In thermal equilibrium at temperature t, the emission and absorption
probabilities are equal and thus
P = P21
12](https://image.slidesharecdn.com/ibmlasers-130313213049-phpapp02/85/Ibm-lasers-16-320.jpg)
![N1 B12u (ν ) = N 2 [ A21 + B21u (ν )]
N 2 A21
u (ν ) =
N1 B12 − N 2 B21
But Einstein proved thermodynamically that probability of
(stimulated) absorption is equal to the probability of stimulated
emission, So
B12 = B21
N 2 A21
u (ν ) =
N1 B21 − N 2 B21
A21 1
u (ν ) =
B21 ( N1 / N 2 ) − 1](https://image.slidesharecdn.com/ibmlasers-130313213049-phpapp02/85/Ibm-lasers-17-320.jpg)
Ibm lasers
- 1. LASER & Holography
- 2. Laser Light • “LASER” = Light Amplification by Stimulated Emission of Radiation
- 3. What is Laser? Light Amplification by Stimulated Emission of Radiation • A device produces a coherent beam of optical radiation by stimulating electronic, ionic, or molecular transitions to higher energy levels • When they return to lower energy levels by stimulated emission, they emit energy.
- 4. 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.
- 5. Basic concepts for a laser • Absorption • Spontaneous Emission • Stimulated Emission • Population inversion
- 6. Absorption E2 E1 • Energy is absorbed by an atom, the electrons are excited into higher energy state.
- 7. Absorption E2 = E1 + hυ • The probability of this absorption from state 1 to state 2 is proportional to the energy density u(v) of the radiation P = N1 B12u (v) 12 where the proportionality constant B12 is known as the Einstein’s coefficient of absorption of radiation.
- 8. Spontaneous Emission • The atom decays from level 2 to level 1 through the emission of a photon with the energy hv. It is a completely random process.
- 9. Spontaneous Emission The probability of occurrence of this spontaneous emission transition from state 2 to state 1 depends only on the properties of states 2 and 1 and is given by ( P21 ) sp = A21 N 2 where the proportionality constant A21 is known as the Einstein’s coefficient of spontaneous emission of radiation.
- 11. Stimulated Emission hυ = ∆E = E2 − E1 atoms in an upper energy level can be triggered or stimulated in phase by an incoming photon of a specific energy.
- 12. Stimulated Emission The stimulated photons have unique properties: – In phase with the incident photon – Same wavelength as the incident photon – Travel in same direction as incident photon
- 13. E2 E2 E2 hυ hυ hυ h υ In Out hυ E1 E1 E1 (a) Absorption (b) Spontaneous emission (c) Stimulated emission Absorption, spontaneous (random photon) emission and stimulated emission. © 1999 S.O. Kasap, Optoelectronics (Prentice Hall)
- 14. Stimulated emission leads to a chain reaction and laser emission If a medium has many excited molecules or atoms, one photon can become many. Excited medium This is the essence of the laser.
- 15. Stimulated Emission The probability of occurrence of stimulated emission transition from the upper level 2 to the lower level 1 is proportional to the energy density u(v) of the radiation and is given by ( P21 ) st = B21 N 2u (v) where the proportionality constant B21 is known as the Einstein’s coefficient of stimulated emission of radiation. Thus the total probability of emission transition from the upper level 2 to the lower level 1 is P21 = ( P21 ) sp + ( P21 ) st P21 = N 2 [ A21 + B21u (ν )]
- 16. Relation between Einstein’s Coefficients Let N1 and N2 be the number of atoms at any instant in the state 1 and 2, respectively. The probability of absorption transition for atoms from state 1 to 2 per unit time is P = N1 B12u (v) 12 The probability of transition of atoms from state 2 to 1,either by spontaneously or by stimulated emission per unit time is P21 = N 2 [ A21 + B21u (ν )] In thermal equilibrium at temperature t, the emission and absorption probabilities are equal and thus P = P21 12
- 17. N1 B12u (ν ) = N 2 [ A21 + B21u (ν )] N 2 A21 u (ν ) = N1 B12 − N 2 B21 But Einstein proved thermodynamically that probability of (stimulated) absorption is equal to the probability of stimulated emission, So B12 = B21 N 2 A21 u (ν ) = N1 B21 − N 2 B21 A21 1 u (ν ) = B21 ( N1 / N 2 ) − 1
- 18. According to Boltzmann’s law, the distribution of atoms among the energy states E1 and E2 at the thermal equilibrium at temperature T is given by N1 e − E1 / kT = − E2 / kT = e ( E2 − E1 ) / kT N2 e where k is the Boltzmann constant N1 = e hν / kT N2 A21 1 u (ν ) = (1) B21 e hν / kT − 1
- 19. Planck’s radiation formula gives the energy density of radiation u(v) as 8πhν 3 1 u (ν ) = (2) e 3 e hν / kT − 1 from equation (1) and (2) A21 8πhν 3 = B21 e3 This equation gives the relation between the probabilities of spontaneous and stimulated emission.
- 20. Condition for the laser operation If N1 > N2 • radiation is mostly absorbed • spontaneous radiation dominates. if N2 >> N1 - population inversion • most atoms occupy level E2, weak absorption • stimulated emission prevails • light is amplified Necessary condition: population inversion
- 21. Population Inversion This situation in which the number of atoms in the higher state exceed that in the lower state (N2 > N1) is known as population inversion. Pumping The process of moving the atoms from their ground state to an excited state is called pumping. The objective is to obtain a non- thermal equilibrium. Optical Electrical Pumping Pumping
- 22. Optical Pumping The atoms are excited by bombarding them with photons example: Ruby Laser Electrical Pumping The atoms are excited by Electron collision in a discharge tube. example: He-Ne Laser
- 23. Lasers that maintain a population inversion indefinitely produce continuous output – termed CW (for continuous wave) lasers Lasers that have a short-lived population inversion produce pulsed output – these are pulsed lasers
- 24. Ruby Laser (Three Level Laser) Ruby (Al2O3) monocrystal, Cr doped. Xenon Flash Light tube Partially silvered mirror
- 25. Ruby Laser Short-live state 10-8sec E3 Radiation-less Transition Optical Pumping Metastable state 10-3sec E2 5500 Å Stimulated 6943 Å Spontaneous 6943 Å Emission Emission 6943 Å E1 Ground State
- 26. He-Ne Laser Energy 20.61 eV Metastable state 20.66 eV Transfer 6328 Å 6328 Å 6328 Å Electron Impact 18.70 eV c Spontaneous Emission c Radiation-less Transition Ground He State Ne
- 27. Ruby Laser Solid –State Laser Three Level Laser Pulsed Laser He-Ne Laser Gas Laser Four Level Laser Continuous Laser
- 28. Ruby Laser Optical Pumping Coolent required High Power of 10 kW He-Ne Laser Electronic pumping Coolent not required Low Power of about 0.5 – 5 mW
- 29. Applications of Laser Laser beams are very intense so are used for welding, cutting of materials. Lasers are used for eye surgery, treatment of dental decay and skin diseases. Lasers are used for barcode scanners in library and in super markets. Laser is used in printers (Laser printers). Lasers are used for Nuclear Fusion. Laser are used in CD/DVD Player Laser is used in Holography. Laser torch are used to see long distant objects.
- 30. Holography Holography is the production of three-dimensional images of objects. The physics of holography was developed by Dennis Gabor in 1948. He was awarded the 1971 Nobel Prize. The laser (1960s) met the requirement of coherent light needed for making holographic images.
- 31. Holography In Holography both the amplitude and phase components of light wave are recorded on a light sensitive medium such as a photographic plate. Holography is a two step process. In First step is the recording of the Hologram where the object is transformed into a photographic record. Second step is the reconstruction in which the Hologram is transformed into the image.
- 32. Principle of Holography Holography is the interference between two waves, an object wave which is the light scattered from the object and the reference wave, which is the light reaching the photographic plate directly. The film records the intensity of the light as well as the phase difference between the scattered and reference beams. The phase difference results in the 3-D perspective.
- 33. Conventional vs. Holographic photography • Conventional: – 2-d version of a 3-d scene – Photograph lacks depth perception or parallax – Phase relation (i.e. interference) are lost
- 34. Conventional vs. Holographic photography • Hologram: – Freezes the intricate wavefront of light that carries all the visual information of the scene – Provides depth perception and parallax – Gives information about amplitude as well as phase of an object. – The hologram is a complex interference pattern of microscopically spaced fringes
- 35. Construction of Hologram Mirror Reference Beam Incident Laser Object Beam Object Beam Photographic Plate (Hologram)
- 36. Reconstruction of Hologram Laser Beam Hologram Virtual Image Real Image
- 37. Holography A hologram is best viewed in coherent light passing through the developed film. The interference pattern recorded on the film acts as a diffraction grating. By looking through the hologram, we see virtual image.
- 38. National Geographic • First major publication to put a hologram on its cover • March 1984 issue carried nearly 11 million holograms around the world
- 39. Applications of Holography • Design of containers • Improve design of to hold nuclear aircraft wings and materials turbine blades • Credit cards carry • Used in aircraft “heads-up display” monetary value • Art • Supermarket • Archival Recording of scanners fragile museum • Optical Computers artifacts
- 40. Holography goes Hollywood • Holodeck from Star Trek Holodeck Clip • Star Wars Chess Game • Body Double in Total Recall • The Wizard in Wizard of Oz