METR 415. Wed 1/30/2013

Transcription

1 METR 415 Wed 1/30/2013

2 Agenda M415 1/30/13 Review of concepts: speed, wavelength, frequency, wavenumber (1/wavelength) and index of refracjon New material: InteracJon of electromagnejc waves with mamer The spectrum of electromagnejc radiajon ReflecJon RefracJon AbsorpJon ScaMering

3 EM spectrum - 1

4 EM spectrum - 2

5 Hyperphysics as a resource hmp://hyperphysics.phy- astr.gsu.edu/hbase/phyopt/polarcon.html#c1

6 ReflecJon

7 Specular and diffuse reflecjon Specular reflecjon: mirror- like. Angle of incidence = angle of reflecjon Diffuse reflecjon: incoming light is reflected in a broad range of direcjons. An example of the disjncjon between specular and diffuse reflecjon would be glossy vs. mame paints

8 Specular reflecjon

9 RefracJon

10 RefracJon and Snell s Law The index of refracjon is defined as the speed of light in a vacuum divide by the speed of light in the medium

11 Snell s Law

12 Index of refracjon RaJo of speed of electromagnejc waves in a vacuum to electromagnejc waves speed of electromagnejc waves of the same frequency travelling through a medium O]en varies by wavelength

13 Index of refracjon of various media

14 Absorp'on EM radiajon passing through an opjcal system can be amenuated by absorpjon and by scamering. The exponenjal law of absorpjon is the basic working relajonship, but specific terms such as absorbance, absorpjvity, and transmimance are widely used. To the extent that electromagne/c radia/on is absorbed by a medium, it transfers energy to the medium

15 AbsorpJon

16 ScaMering

17 ScaMering Rayleigh scamering refers to the scamering of light off of the molecules of the air, and can be extended to scamering from parjcles up to about a tenth of the wavelength of the light. Responsible for blue sky

18 Blue sky

19 ScaMering (Hyperphysics link) hmp://hyperphysics.phy- astr.gsu.edu/hbase/atmos/scamercon.html#c1

20 Rayleigh ScaMering

21 Hyperphysics Snell s Law calculator hmp://hyperphysics.phy- astr.gsu.edu/hbase/geoopt/refr.html#c3

22 PolarizaJon

23 Key Facts about polarized light If the electric field vectors are restricted to a single plane by filtrajon of the beam with specialized materials, then the light is referred to as plane or linearly polarized with respect to the direcjon of propagajon, and all waves vibrajng in a single plane are termed plane parallel or plane- polarized. The human eye lacks the ability to disjnguish between randomly oriented and polarized light, and plane- polarized light can only be detected through an intensity or color effect, for example, by reduced glare when wearing polarized sun glasses.

24 Linear polarizers

25 What produces polarizajon in nature Polarized light can be produced from the common physical processes that deviate light beams, including absorpjon, refracjon, reflecjon, diffracjon (or scamering), and the process known as birefringence (the property of double refracjon).

26 PolarizaJon by reflecjon Light that is reflected from the flat surface of a dielectric (or insulajng) material is o]en parjally polarized, with the electric vectors of the reflected light vibrajng in a plane that is parallel to the surface of the material. Common examples of surfaces that reflect polarized light are undisturbed water, glass, sheet plasjcs, and highways. In these instances, light waves that have the electric field vectors parallel to the surface are reflected to a greater degree than those with different orientajons

27 PolarizaJon by reflecjon

28 ScaMering of sunlight Gas and water molecules in the atmosphere scamer light from the sun in all direcjons, an effect that is responsible for blue skies, white clouds, red sunsets, and a phenomenon termed atmospheric polariza'on. The amount of light scamered (termed Rayleigh sca9ering) depends upon the size of the molecules (hydrogen, oxygen, water) and the wavelength of light, as demonstrated by Lord Rayleigh in Longer wavelengths, such as red, orange, and yellow, are not scamered as effecjvely as are the shorter wavelengths, such as violet and blue

29 PolarizaJon by scamering

30 PolarizaJon and scamering

31 Minerals that polarize light The first clues to the existence of polarized light surfaced around 1669 when Erasmus Bartholin discovered that crystals of the mineral Iceland spar (a transparent, colorless variety of calcite) produce a double image when objects are viewed through the crystals in transmimed light

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33 Brewster s angle When considering the incidence of non- polarized light on a flat insulajng surface, there is a unique angle at which the reflected light waves are all polarized into a single plane. This angle is commonly referred to as Brewster's angle

34 IllustraJon of Brewter s angle

35 Polar orbijng satellites List of polar orbijng satellites, their sensors, and the parts of the electromagnejc spectrum they sample: hmp://psbcw1.nesdis.noaa.gov/terascan/home_basic/ polarsats_sensors_tables.html#avhrr

36 Some satellites measure polarizajon Scanning MulJ- channel Microwave Radiometer (SMMR)

37 How polarizing glasses work

38 Polarizing filters

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