Introduction to Lasers [Year-1]

[Music] introduction to laces at the end of this lesson you will be able to we find the characteristics of laser on comparison with ordinary light explain the basic principle and conditions for working of laser explained absorption spontaneous and stimulated emission in a two-level system list the properties of laser the field for darkness vanished when man discovered fire till then man knew only the natural sources of light later light sauce evolved into different artificial forms physicists had work to create devices for producing powerful beam of light this resulted in the invention of lasers lasers are an important milestone in the field of engineering in science from a barcode scanner to include a detection in high-security areas from a projection pointer to Printers from optical tweezers for handling delicate matter to cutting off eye strength materials from removing body art or complicated I searchable lasers are simply everywhere lasers have unique characteristics different from ordinary light this enables to produce highly intense light focus to a small point next let us discuss the basic principles characteristics and working of a laser the term laser is an acronym of light amplification by stimulated emission of radiation it is a device which produces an intense beam of monochromatic and coherent light invention has some history so indeed lasers the basic principle of laser is based on the einstein's theory of light proposed in 1916 which was later developed by god and gold in 1957 in 1960 the order may man invented the first working Ruby laser which was also the first optical laser apart from solids such as Ruby researchers have analyzed that some materials like xenon helium or semiconductors can also be used as laser mediums different types of lasers have been developed which enhanced the scope of their applications the working and principle of the laser is based on some important features let us discuss about them the working principle of lasers is based on spontaneous absorption spontaneous emission stimulated emission and population inversion absorption an atom consists of different energy states let us consider two different states of an electron such as ground state he not an excited state e^x electromagnetic energy falls on an atom in the form of photon of frequency is from the principle of conservation of energy the electromagnetic energy is given as the difference of e^x and e not when the photon energy falls on the electron it jumps from the ground inor to the excited state eh by absorbing the energy this process of absorbing energy from photons is known as absorption of radiation spontaneous emission it is known that electron absorbs energy and moves from lower energy level e not to the higher energy level e X but the excited electrons that had jumped to the higher energy state does not remain in the same state for a long period and comes back to its original ground state he not by losing its energy in the form of photons these photons are considered as in coherent light as they do have any correlation in phase thus the electrons in the excited atoms are released on their own from their higher energy state to the ground state emitting photons this is called as spontaneous emission the mean life or lifetime of the excited atom is the time for which it stays in that state this is about 10 to the power minus eight seconds the for spontaneous emission however the mean life for some excited states is 10 to the power of five times longer and such states are called as metastable state and they play an important role in laser operation stimulated emission in this process the atomists initially present in its excited state e^x a photon of energy H s can stimulate the atom to move to its ground state he not during this process the atom emits an additional photon with the same energy HF this process is called as stimulated emission as it is triggered by an external photon population inversion generally in any atomic system the number of atoms in the ground state is more than that in the excited state this is because of the tendency of electrons to stay in the ground state but in order for more photon to be emitted there should be more electrons in the excited state this process is achieved through optical pumping and this occurrence is known as population inversion the transition electrons do not stay in an excited state for a longer time but in some systems the electrons remain in an excited state for longer period these systems are called as active systems or media generally these active systems are compounds or mixtures of different elements consider the ecosystem containing a large number of atoms in thermal equilibrium condition at a temperature T before the system is subjected to any radiation there are n naught number of atoms present in their ground state with energy e naught and a number and X are in a state of higher energy X according to Ludwig Boltzmann annex can be given in terms of and not Y and X is equal to n naught into e to the power of minus of e X minus T naught divided by K T as the temperature increases due to thermal agitation mode number of atoms move to the higher energy state e^x since X is greater than T naught the Boltzmann equation requires NX to be lesser than and naught means there will be less number of atoms in the excited state compared to the ground state thus only by thermal agitation the populations of e^x can exceed that of Enoch suppose the atoms are flooded with the photons of energy X minus T naught then by absorption by ground state atoms the photons will disappear and atoms move through excited state leading to population inversion thus through stimulated emission of excited state atoms most number of photons will be generated showed that the probability is per attend for absorption and stimulated emission processes are identical thus the net if it will be absorption of photons when more atoms are in the ground state when stimulated emission dominates that is when more photons are emitted than the absorbed photons the laser light is produced the lasers have certain unique characteristics that enable the laser light to be focused hundred times better than the ordinary light these characteristics are mono chromaticity coherence directionality and sharp focus let us discuss these in detail laser lights are highly monochromatic it means the laser beam is made up of a single color or a single wavelength in contrast the ordinary white light from an incandescent light bulb is a combination of many colors or wavelengths and is certainly not monochromatic the laser is highly coherent means a wavelength of the laser light is in phase in space in time this is because of the orderly electronic transitions that take place in laser the laser-light can travel several hundred kilometers long in space without any destruction whereas the corresponding coherence length for wave trains emitted by ordinary light is typically less than a meter laser emits light that are highly directional which means the light emitted by the laser are relatively a narrow beam in a specific direction without dispersion moreover the laser beam spreads very little and thus can be focused sharply but if you observe the ordinary light bulb it emits light in many directions away from the source thus lasers with a unique characteristics illuminate investigate repaired transfer here and we take certainly it is interesting to know about the fundamentals of laser technology as always you could connect it in some form of application in day-to-day life this lesson we have learned laser or light amplification by stimulated emission of radiation is a device which produces an intense beam of monochromatic light the working of lasers is based on absorption spontaneous emission stimulated emission and population inversion crystals of lasers are mono chromaticity coherence directionality and sharp focus

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Length: 11min 11sec (671 seconds)

Published: Mon Apr 10 2017