Properties and behaviours of light Single-slit diffraction and diffraction grating interference patterns.

2. Properties and behaviours of light • Single-slit diffraction and diffraction grating interference patterns. • Operation of spectroscope and the interferometer in terms of the wave properties of light. • Application of the wave properties of light. • Basic concept of holography • Electromagnetic waves

4. Plane-polarized: a wave that vibrate in only one plane. • Unpolarized : a wave that vibrates in all directions perpendicular to the direction of travel. • Polarization: confining the vibration of a wave to one direction. • Polarizer: a natural (e.g., clouds) or artificial (e.g., filters) means to achieve polarization. • Double refraction: the property of certain crystals to split an incident beam of light into two.

5. Monochromatic: of one colour, or one wavelength. • Scattering: a change in direction of particles or waves as a result of collisions with particles.

6. Edwin Land (1909- 1991) was an American physicist and inventor. Land became interested in polarized light while a freshman ay Harvard University, in 1926. In his senior year, at the age of 19, he terminated his studies to found a laboratory near the university. With other young scientists, he applied the principles of polarization to various areas of optics, including filtering and cinematography. In 1948, the company he founded, the Polaroid Corporation , introduced the first model of its most successful product, the Polaroid Land camera for instant photography.

7. A light wave which is vibrating in more than one plane is referred to as unpolarized light. • Light emitted by the sun, by a lamp in the classroom, or by a candle flame is unpolarized light. • Such light waves are created by electric charges which vibrate in a variety of directions, thus creating an electromagnetic wave which vibrates in a variety of directions. The beam is made up of waves vibrating in all directions, as shown by the white arrows in this diagram.

8. It is possible to transform unpolarized light into polarized light. • Polarized light waves are light waves in which the vibrations occur in a single plane. • The process of transforming unpolarized light into polarized light is known as polarization.

9. Polarization by Transmission Polarization by Reflection P 3. Polarization by Refraction 4. Polarization by Scattering

10. Polaroid filters are made of a special material which is capable of blocking one of the two planes of vibration of an electromagnetic wave. • When unpolarized light is transmitted through a Polaroid filter, it emerges with one-half the intensity and with vibrations in a single plane; it emerges as polarized light.

11. The spaces between the pickets of the fence will allow vibrations which are parallel to the spacings to pass through, while blocking any vibrations which are perpendicular to the spacings. • If two picket fences are oriented such that the pickets are both aligned vertically, then vertical vibrations will pass through both fences. • if the pickets of the second fence are aligned horizontally, then the vertical vibrations which pass through the first fence will be blocked by the second fence.

12. Unpolarized light can undergo polarization by reflection off of non-metallic surfaces. • The extent to which polarization occurs is dependent upon the angle at which the light approaches the surface of the material/ element. • A person viewing objects with light reflecting off of a non-metallic surfaces will see a glare if the extent of polarization is large. • Light reflected off a lake is partially polarized in a direction parallel to the water's surface.

13. Polarization can occur by the refraction of light. • Refraction occurs when a beam of light passes from one material into another material. • At the surface of the two materials, the direction of the beam changes direction, where the refracted beam gains some degree of polarization. • Both refracted light beams are polarized - one in a direction parallel to the surface and the other in a direction perpendicular to the surface. • Since these two refracted rays are polarized with a perpendicular orientation, a polarizing filter can be used to completely block one of the images.

14. Polarization also occurs when light is scattered while traveling through a medium. • When light strikes the atoms of a material, it sets the electrons of those atoms into vibration. The vibrating electrons then produce their own electromagnetic wave which is radiated outward in all directions. • This newly generated wave strikes neighboring atoms, forcing their electrons into vibrations at the same original frequency. These vibrating electrons produce another electromagnetic wave which is once more radiated outward in all directions. • This absorption and reemission of light waves causes the light to be scattered about the medium. This scattered light is partially polarized. • Polarization by scattering is observed as light passes through our atmosphere. The scattered light often produces a glare in the skies.

16. The diffraction of light through a single slit is also called Fraunhofer diffraction, after Munich born Joseph von Fraunhofer (1787-1826). Interest in light and optics led the 22-year-old Fraunhofer to become the first to measure the spectrum of sunlight and identify the absorption lines.

17. Central maximum: the bright central region in the interference pattern of light and dark lines produced in diffraction. • Secondary maxima: the progressively less intense bright areas, outside the central region, in the interference pattern. • Resolution: The ability of an instrument to separate two images that are close together.

18. Light passing through a single slit creating a diffraction pattern. • The pattern consist of a bright central region with dark regions of destructive interference, alternating with progressively less intense areas of bright constructive interference. • The smaller the slit width, the larger the distance between maxima and minima.

19. Formula for the minima of fringes • Sinθ = nλ / w • θ is angle of the fringe • λ is the wavelength of light • w is the width of the slit • n is the order of the minimum

20. The distance between the first minima on either side of the center line • Sinθ = λ / w • Sinθ = Y1 / L • Y1 is the length between the minimums • L is the length from the slit to the object

21. In order to determine the width of the central maximum in degrees we found the angle between the center line to one of the minimums beside it. We then multiplied that angle by 2 because the central maximum is made up of 2 minimums, one on either side. • To find length we used the properties of central maximum (shown in previous slide) to find the length between the minimums. Then multiplied by 2 once again because its made up of two minimums.

23. Diffraction grating: device whose surface is ruled with close, equally spaced parallel lines for the purpose of resolving light into spectra; transmission grating are transparent; reflection grating are mirrored. • Spectroscope: an instrument that uses a diffraction grating to visually observe spectra.

24. Diffraction Grating: device used for wave analysis. Splits and diffracts light into several beams • The direction of the beams depends on the spacing of the gratings and the wavelength of the light • Gratings are commonly used in spectrometers, an instrument used to visually observe spectra

25. If the vertical grating is perpendicular to light it gives a horizontal pattern • If the horizontal grating is parallel to light it gives a vertical pattern • Crossed grating gives crossed pattern

26. Formula for waves passing through slits in a diffraction grating • Sinθ = mλ / d • m = order of maximum • λ is the wavelength • d is the distance between the grating lines • θ is the angle of the order of maximum

27. A 4000 line/cm grating produces a second order bright fringe at an angle of 23 degrees. Calculate the wavelength of the light. • Formula: Sinθ = mλ / d • λ = ? • d = (1/ 4000cm) / 100 = 2.5 x 10^-06 m • θ = 23.0 • Second order so m = 2 • Sin 23 = 2 λ / 2.5 x 10^-06 • Rearrange to solve for λ • λ = 4.88 x 10^-07

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