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Laser light is: Coherent Monochromatic Directional Polarized 1. Lasing a. Apply energy to a substance to excite the electrons b. As electrons “decay,” they emit energy as light of certain energy E c. Emitted energy = energy needed to excite other electrons up to the same energy level d. These electrons decay, emit light energy E, E absorbed by other electrons, ... e. “Stimulated Emission” – predicted by Einstein in 1917 as a consequence of quantum theory 2. Monochromatic a. All waves/particles are close to the same frequency b. Same frequency => same color of light i. Is a yellow laser possible? c. Same frequency => same energy d. Same energy => same size “jump” down energy levels. 3. Coherent z E x, y,z,t Acos 2 t a. Predictability of light wave: Where E(x, y, z, t) = energy of the electromagnetic (light) wave at some place (x, y, z) and time ( t ); A = amplitude of the wave; = the frequency,in Hz; = the wavelength of the wave; = phase constant (shifts the wave along x-axis) b. Marching Band: all in step; time & place of any marcher can be predicted 4. Directionality a. Light contained between two highly reflective mirrors; only small portion is transmitted through the mirrors. b. Wave is reflected many times. c. Multiple reflections increase the distance the light travels, but confining it to the region between the mirrors. d. Because of long distance traveled, curvature of waves is very small, so light waves emerging from the laser are nearly planer. e. EX: two mirrors at the barber/beauty shop – object appears much farther away, multiple reflections f. Some divergence present g. Diffraction – spreading of wavefront, a wave-like property of light. i. SHOW Young’s double slit experiment – sin = n/D ii. Measure spot diameter at various distances for 1/r^2 h. Speckling i. As you move your head, the pattern moves. ii. Fringes 5. Polarization a. Brewster surface/angle b = tan-1 (n2/n1) i. Where n2 & n1 are indices of refraction of materials ii. If incident light is air, then n1 ~ 1, and b = tan-1 n2