Laser and its application

Laser | working principle | properties
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1. LASER And Its Application Abdul Ahad Hadi M Rizwan Rizvi Sania Arshad Urooj Fatima

2. History MASER Micro-wave Amplification by Stimulated Emission of Radiation In 1917 Albert Einstein gave the idea of Stimulated Emission of Radiation. Charels H. Townes Inventor of MASER. He thought that molecules in the excited state could be stimulated to emit microwaves when placed in cavity. With the help of his fellows and students he invented a working MASER in 1953. He ,with his team, awarded Nobel Prize in Physics in 1964. Townes began looking beyond the microwave region to shorter wavelength.

3. LASER It was Gordon Gould who first used the word LASER in his research papers. In the mid of 1960, Theodore H. Maiman , demonstrated first LASER. A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. LASER: light amplification by stimulated emission of radiation

4. L Light (not visible only) it also ranges upto x-rays A Amplification (not to increase the amplitude but intensity) S Stimulated E Emission R Radiation

5. Difference between Spontaneous and Stimulated Emission Spontaneous emission:  Electron drops from an excited state to a lower state (no outside mechanism) - emitting a photon. Stimulated emission (lasers): Stimulated emission is the process by which an atomic electron (or an excited molecular state) interacting with an electromagnetic wave of a certain frequency may drop to a lower energy level, transferring its energy to that field. A new photon created in this manner has the same phase, frequency, polarization, and direction of travel as the photons of the incident wave. This is in contrast to spontaneous emission which occurs without regard to the ambient electromagnetic field.

6. Emission of Radiations

7. Basic Principle Of LASER Active Medium LASER Pumping Optical Resonator

8. Active Medium The heart of a laser system is a material capable of emitting radiation of the required energy. This material, known as active medium, may have any form e.g. solid, liquid, or gas but must contain a set of energy levels in which it can absorb or emit energy in the form of optical radiation. Energy Levels Transitions Spontaneous Emission Stimulated Emission Absorption

9. LASER Pumping The population inversion required for light amplification constitutes an abnormal distribution of atoms among the various available energy levels. To understand how light amplification can be achieved in a medium, it is necessary to consider the Boltzmann distribution and then pumping mechanism to achieve the population inversion. Population Inversion The population inversion condition required for light amplification is a non-equilibrium distribution of atoms among the various energy levels of the atomic system. If the energy difference between E1 and E2 is nearly equal to kT (~0.025 eV at room temperature) then the population of the upper level would be 1/e or r 0.37 times of the lower level. For an energy difference large enough to give visible radiation (~2.0 eV), however, the population of the upper level is almost negligible .

10. Four Level Pumping For the analysis of steady-state laser pumping and population, we consider a neodymium laser which is a typical example of four-level laser system. The complicated energy levels of Nd+3 have been simplified into the idealized four-level laser system shown in Figure. This four-level model will in fact provide a simple but surprisingly accurate analytical model for many laser systems

11. Three Level Pumping A three-level system differs from the four-level system in that the lower laser level is the ground level E1. This is a serious disadvantage, since more than half the atoms initially in the ground state must be pumped through the upper pumping level E 3 into the upper laser level E 2 before any inversion at all is obtained on the 2 1 transition. Three-level lasers are, therefore, usually not as efficient as four-level lasers.

12. Optical Resonator A typical optical resonator formed by two curved mirrors with radii of curvature R1 and R2 spaced a distance L apart is shown in Figure. For each mirrors R > 0 implies that the mirror is concave towards the resonator

13. From this similarity (between a curved mirror and a thin lens) we can deduce that the behaviour of a ray upon repeated bounces back and forth between these two mirrors will be exactly the same as the behaviour of a ray passing through a series of lenses spaced at intervals L, with alternate focal lengths f1 = R1/2 and f2 = R2/2.

14. LASER Components

15. LASER Beam Properties MonoChromatic Coherent Directionality Brightness Focusing Property

16. Monochromatic The word monochromatic is derived from Greek language, meaning single color. In the scientific world it is used for electromagnetic waves of single frequency. In fact no light source, including laser, is capable of producing absolutely monochromatic light, we can only make better and better approximations to the ideal. We might begin with a white light source that produces light of all colors of the spectrum, and filter it with a piece of colored glass. The monochromaticity of the filtered light is now as good as the filter. If the radiation from a gas discharge source, such as neon sign or a sodium vapor lamp, is directed through a prism, a series of lines of different colors is seen on a screen.

17. Coherent Coherence probably is the best-known property of laser light. Light waves are coherent if they are in phase with each other, i.e., if their peaks and valleys are lined up at the same point. Two things are necessary for light waves to be coherent. First, the light waves must start out having the same phase at the same position. Second, their wavelengths must be the same, or they will drift out of phase because the peaks of the peaks of the longer wave.

18. Directionality We think of laser beams as tightly focused and straight, but once they go for enough from the laser, they actually spread out slightly with distance. The spreading is called beam divergence. Laser beams, in general, have very low divergence. Brightness The primary characteristic of laser radiation is that lasers have a higher brightness than any other light sources. We define brightness as power emitted per unit area per unit solid angle. The relevant solid angle is that defined by the cone into which the beam spreads. Hence, as lasers can produce high levels of power in well-collimated beams, they represent sources of great brightness. The brightness of Sun is ~ 1.3x106 W m-2 sr-1 .

19. Focusing Property The minimum spot size to which a laser beam can be focused is determined by diffraction. A single mode beam can be focused into a spot, which has dimensions of the order of the wavelength of light. The imperfections in the optical system may mean that we cannot achieve this in practice. A useful relation for estimating the spot size is that the radius r, at the focal plane of a lens of focal length f is given by r = f.ϴ

20. Applications of LASER Laser light is different from an ordinary light. It has various unique properties such as coherence, monochromacity , directionality, and high intensity. Because of these unique properties, lasers are used in various applications. The most significant applications of lasers include: Lasers in medicine Lasers in industries Lasers in science and technology Lasers in military

21. Removal of Tissue by Laser Surgery Laser has very high intensity (power/area) and can produce intense heat on a specific spot. Today most laser surgery makes use of this heat primarily because its destructive effects can be extremely selective and precisely controlled. To have an idea about the removal of tissue using lasers, one must know that how laser light interacts with the tissue. Tissue like any other material absorbs light differently at different wavelengths. If the wavelength of a laser is matched very closely with the absorption band of the target structure; the laser light will be absorbed by and therefore damage that structure.

22. LASER In Dermatology Dermatology is the medical field concerned with diseases of the skin. Laser has given dermatologists an improved new tool to treat some conditions. This technology was easily introduced in dermatological therapeutic because dermatologists have long been used ordinary light for skin treatments. Lasers can be used to treat port-wine stains, tattoos, seborrhea, warty keratoses, basal cell carcinomas, warts, freckles, nevi, acne and various growths both benign and malignant. Generally the laser is used to remove some sort of growth or colored area in the skin and in general the results are comparable to conventional modes of therapy.

23. Treatment of Port-Wine Stains Dark-red birthmarks called port-wine stains often appear on the face or neck. Networks of abnormal blood vessels just under the surface of the skin cause port-wine stains as shown in Figure 9.12. Because port-wine stains are dispersed on the surface of the skin, conventional surgery can't remove them effectively. Laser can treat this condition

24. Shattering of the Stones Delivery of light from a dye laser through optical fiber can shatter kidney stones and gall stones into pieces small enough to pass freely from the body. The laser is tuned to a wavelength strongly absorbed by the stones. Prospects for this treatment look very good.

25. Cancer Treatment Lasers are an integral part of a new treatment for cancer called photodynamic therapy. Scientists noted that cancerous tissue concentrated some of the body's own pigments, particularly porphyrin, in the brownish-red pigment of blood. The treatment relies on a dye, called hematopophyrin derivative ( HpD ) which cancer cells retain much longer then healthy cells.

26. Treatment of Detached Retina Figure shows the structure of the human eye. Retina is the light sensitive layer at the back of the eye. Sometimes the retina can become torn and detached from the back of the eyeball.

27. The damage can spread, and without treatment the entire retina can come loose from the back of the eye causing blindness. A laser pulse focused on the retina can stop the detachment from the eyeball. An instrument that has the opportunity of working closer to the macula is shown

28. LASER I n I ndustry A nd C ommercial Levelling of ceramic tiles floor with a laser device

29. Lasers used for visual effects during a musical performance.

30. Bird Deterrent Laser beams are used to disperse birds from agricultural land, industrial sites, rooftops and from airport runways. Birds tend to perceive the laser beam as a physical stick. By moving the laser beam towards the birds, they get scared and fly away.

31. LASER In Military

32. References Gould, R. Gordon (1959). "The LASER, Light Amplification by Stimulated Emission of Radiation". In Franken, P.A.; Sands R.H. (Eds.). The Ann Arbor Conference on Optical Pumping, the University of Michigan, 15 June through 18 June 1959. p. 128. OCLC 02460155. "laser". Reference.com. Retrieved May 15, 2008. "Four Lasers Over Paranal". www.eso.org. European Southern Observatory. Retrieved 9 May 2016. Conceptual physics, Paul Hewitt, 2002 "Schawlow and Townes invent the laser". Lucent Technologies. 1998. Archived from the original on October 17, 2006. Retrieved October 24, 2006. Chu, Steven; Townes, Charles (2003). "Arthur Schawlow". In Edward P. Lazear (ed.),. Biographical Memoirs. vol. 83. National Academy of Sciences. p. 202. ISBN 0-309-08699-X Laser and optics Habiba Arain (laser and its applications) www.slideshare.net