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Module 1-1 Continued Nature and Properties of Light.

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1 Module 1-1 Continued Nature and Properties of Light

2 Basic Concepts Section 5 Blackbody radiation The spectrum of electromagnetic radiation emitted by an object at some absolute temperature T—generally referred to as thermal radiation or blackbody radiation—is shown in Figure Three thermal radiation—or blackbody radiation—curves are shown, at absolute temperatures of 1600ºK, 2400ºK, and 3200ºK. K = KelvinKelvin

3 Basic Concepts Section 5 Figure 1.20 Spectral distribution of blackbody radiation

4 Basic Concepts Section 5 Note that as the temperature rises, the amount of light (area under the curve) increases and the peak radiant power, P( λ ), shifts towards shorter wavelengths. The shift in wavelength of the emitted radiation of a thermal source, as it is heated, is familiar to most of us. We see an object become “red-hot” as the temperature increases.

5 Basic Concepts Section 5

6 The shift of peak wavelength as a function of the absolute temperature is given by the so- called Wien displacement law (Equation 1-14): λ max ⋅ T = × 10 − 3 m ⋅ K (1 − 14) where: λ max is the wavelength at which the P( λ ) has a maximum value in meters T is the absolute temperature in degrees Kelvin

7 Basic Concepts Section 5 Example 10, page 36

8 Basic Concepts Section 5 Infrared Cameras

9 Basic Concepts Section 5 Scattering of light Scattering is the redirection of light caused by its interaction with matter The scattered light may have the same or longer wavelength (lower energy) compared with the incident radiation, and it may have a different electric field polarization.

10 Basic Concepts Section 5 If the dimensions of the scatterer are much smaller than the wavelength of light, like a molecule, for example, the scatterer can absorb the incident light and quickly reemit the light in a different direction. See Figure If the reemitted light has the same wavelength as the incident light, the process is called Rayleigh scattering. If the reemitted light has a longer wavelength, the molecule is left in an excited state, and the process is called Raman scattering.

11 Basic Concepts Section 5 Figure 1.21 Rayleigh Scattering

12 Basic Concepts Section 5 Figure 1.21 Raman scattering

13 Basic Concepts Section 5 Homework Problems 8, 9 and 10 Module 1-1, page 54

14 Diffraction Grating Diffraction Gratings are optical components used to separate light into its component wavelengths. Diffraction Gratings are used in spectroscopy, or for integration into spectrophotometers or monochromators.

15 Diffraction Grating Diffraction Gratings consist of a series of closely packed grooves that have been engraved or etched into the Grating’s surface. Diffraction Gratings can be either transmissive or reflective. As light transmits through or reflects off a Grating, the grooves cause the light to diffract, dispersing the light into its component wavelengths.

16 Diffraction Grating Theory When a beam of light is incident on a diffraction grating, part of the light will pass straight through. Part of the light is diffracted to paths that diverge at different angles on both sides of the original path. (revisit Course 1 Module 1-1 part 4) (Interactive 1.5 Young’s Double Slit Experiment, page 30)

17 Diffraction Grating The angle θ at which the light diverges is related to the wavelength and spacing of the lines on the grating. The relationship is described by: m λ = dsin θ m where (next slide):

18 Diffraction Grating m λ = dsin θ m where: λ is the wavelength of the incident light in meters, d is the spacing between lines on the grating in meters, m is an integer that takes on the values 0, 1, 2, …., and θ m is the diffraction angle for a particular diffraction order m.

19 Diffraction Grating If the diffraction angle θ m can be measured for a particular order m and the grating spacing d is known, the wavelength of the light can be calculated. θm θm L

20 Diffraction Grating Example

21 Slide 14 and 15 source ings/


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