Laser Is An Electromagnetic Wave-Physics-Report, Study Guides, Projects, Research of Physics

Download Laser Is An Electromagnetic Wave-Physics-Report and more Study Guides, Projects, Research Physics in PDF only on Docsity! Laser is an Electromagnetic wave Since electric and magnetic fields are vector quantities, both their magnitude and direction must be specified. But, because these two field directions is always perpendicular to one another in non-absorbing media, the direction of the electric field of a light wave is used to specify the direction of polarization of the light. The kind and amount of polarization can be determined and modified to other types of polarization. If you understand the polarization properties of light, you can control the amount and direction of light through the use of its polarization properties. Laser is an electromagnetic wave, represented by a vector where the electric field E and the magnetic field B are orthogonal to each other, and also orthogonal to the direction of propagation. These 2 fields change with time and space in a sinusoid fashion. Figure 1 In general, to represent light, we only show the electric field and do not show the magnetic field because it is with the electric field that detectors e.g. eye, photographic film, CCD, etc. interact. The wavelength of light lambda is the distance between 2 maxima or 2 minima. docsity.com Figure 2 Laser is in general non-polarized, the electric field is on average oriented in an arbitrary direction, and has a very precise orientation for too short a time to be measured by instruments. So when we detect the direction of electric filed, on detector we found electric filed in every direction so we can not specify the direction of electromagnetic waves as shown in figure. Figure 3 docsity.com represented as a sine wave oscillating equally on each side of the line of travel (electric field vector) of the light energy. 2 Circular Polarization Circular polarization occurs when two linearly polarized light waves of equal amplitude travel perpendicular to each other while 90 degrees out of phase. One wave precedes the other as it moves along the electric field vector. Because of the phase difference, the two electromagnetic components cause the light waves to rotate around the electric field vector. When viewed end-on, a point on the electromagnetic wave follows a circular path, giving this form of polarization its name. EM waves at any polarization angle can be decomposed into two waves at 45 degrees to the original vector, such that the decomposed waves are 90 degrees apart (orthogonal). If one of the orthogonal components is phase shifted exactly 90 degrees, the composite vector will appear to rotate at a fixed time or distance. Figure 6 docsity.com Circular polarization can be left handed (LCP) or right handed (RCP), depending on whether the phase shift between the components is +90 or -90 degrees. 3 Elliptical Polarization Elliptical polarization results when one of the two linear components in circular polarization is greater amplitude than the other. The ratio of the two voltage amplitudes is called the axial ratio. When axial ratio is one, you have circular polarization. One way to look at elliptical polarization is that the two components of circular polarization are not exactly 90 degrees apart. When two perpendicular light waves, which differ in phase by 90 degrees, are of unequal amplitude, they form what is termed elliptically polarized light. If the wave appears to be rotating counter-clockwise when approaching the observer, it is said to be right- elliptically polarized. On the other hand, if the wave appears to be rotating clockwise, it can be termed left-elliptically polarized. If the observer's right thumbs points in the direction of the propagating light, then the electric vector would be rotating in the direction of her fingers. Figure 7 docsity.com How Polarizing Filter Works A circular polarizing filter has two elements. The first element is a linearly polarizing filter. This reduces or blocks scattered light from the sky entering at 90 degrees and light polarized by reflection from water, glass and other shiny surfaces. The second element is a quarter-wave plate. This element serves to convert the linearly polarized light from the first filter into circularly polarized light. Mount the right-sized filter on the camera lens. Then, looking through the view finder, rotate the lens element until the clearest image is seen. Quarter Waveplate The thickness of the quarter waveplate is such that the phase difference is 1/4 wavelength (ture-zero order) or some multiple of 1/4 wavelength (multiple order). If the angle θ (between the electric field vector of the incident linearly polarized beam and the retarder principal plane) of the quarter-waveplate is 45, the emergent beam is circularly polarized. When a quarter waveplate is double passed, i.e. by mirror reflection, it acts as a half waveplate and rotates the plane of polarization to a certain angle. Quarter waveplates are used in creating circular polarization from linear or linear polarization from circular, elliptical, optical pumping, suppressing unwanted reflection and optical isolation. Figure 8 docsity.com 6 Now we put the polarizer at an angle of 30o and rotate the quarter wave plate at 10 o . Record all readings and plot the graph between angle verses intensity as shown in figure. This graph shows that beam is vertically elliptical polarized. -50 0 50 100 150 200 250 300 350 400 0.26 0.28 0.30 0.32 0.34 0.36 0.38 V o lta g e ( m V ) Angle (Degree) Figure 11 7 Now we put the polarizer at an angle of 60o and rotate the quarter wave plate at 10 o . Record all readings and plot the graph between angle verses intensity as shown in figure. This graph shows that beam is horizontally elliptical polarized. docsity.com -50 0 50 100 150 200 250 300 350 400 0.28 0.30 0.32 0.34 0.36 0.38 V ol ta ge ( m V ) Angle (Degree) Figure 12 Table 1 Recoded angles and their corresponding intensities Angle/ degree Intensity at an angle 30 o Intensity at an angle 45 o Intensity at an angle 60 o 0 0.319 0.326 0.311 2 0.32 0.327 0.316 4 0.32 0.331 0.321 6 0.329 0.332 0.322 8 0.334 0.334 0.323 10 0.337 0.334 0.326 20 0.344 0.347 0.339 30 0.352 0.351 0.35 40 0.366 0.356 0.357 50 0.364 0.351 0.366 60 0.368 0.353 0.368 70 0.367 0.345 0.375 docsity.com 80 0.362 0.347 0.368 90 0.358 0.335 0.364 100 0.347 0.324 0.356 110 0.337 0.3 0.348 120 0.318 0.271 0.334 130 0.303 0.21 0.316 140 0.281 0.19 0.297 150 0.274 0.274 0.284 160 0.289 0.319 0.287 170 0.31 0.338 0.307 180 0.325 0.342 0.321 190 0.339 0.348 0.336 200 0.351 0.349 0.351 210 0.356 0.352 0.357 220 0.364 0.349 0.366 230 0.367 0.352 0.371 240 0.361 0.347 0.366 250 0.365 0.359 0.368 260 0.355 0.34 0.361 270 0.35 0.323 0.355 280 0.34 0.313 0.349 290 0.326 0.295 0.336 300 0.312 0.269 0.324 310 0.29 0.143 0.307 320 0.271 0.238 0.29 330 0.272 0.277 0.279 340 0.291 0.304 0.288 350 0.308 0.318 0.302 352 0.315 0.324 0.307 354 0.322 0.324 0.312 356 0.323 0.325 0.317 358 0.323 0.329 0.321 360 0.326 0.331 0.323 docsity.com