Module 1-1 Continued Nature and Properties of Light.

Module 1-1 ContinuedNature andProperties ofLight

Basic Concepts Section 5Blackbody 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 1-20.

Three thermal radiation—or blackbody radiation—curves are shown, at absolute temperatures of 1600ºK, 2400ºK, and 3200ºK.

K = Kelvin

Basic Concepts Section 5Figure 1.20

Spectraldistributionof blackbodyradiation

Basic Concepts Section 5Note 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.

Basic Concepts Section 5

Basic Concepts Section 5The shift of peak wavelength as a

function of the absolute temperature is given by the so-called Wien displacement law (Equation 1-14):

λmax ⋅ T = 2.898 × 10−3m ⋅ K (1 − 14)where: λmax is the wavelength at which the P(λ) has amaximum value in metersT is the absolute temperature in degrees Kelvin

Basic Concepts Section 5Example 10, page 36

Basic Concepts Section 5Infrared Cameras

Basic Concepts Section 5

Scattering of lightScattering 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.

Basic Concepts Section 5If 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 1-21. 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.

Basic Concepts Section 5Figure 1.21 Rayleigh

Scattering

Basic Concepts Section 5Figure 1.21 Raman scattering

Basic Concepts Section 5Homework

Problems 8, 9 and 10Module 1-1, page 54

Diffraction GratingDiffraction 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.

Diffraction GratingDiffraction 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.

Diffraction GratingTheoryWhen 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)

Diffraction GratingThe 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:mλ = dsinθm where (next slide):

Diffraction Grating

mλ = dsinθm 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, …., andθm is the diffraction angle for a

particular diffraction order m.

Diffraction GratingIf the diffraction angle θm can be

measured for a particular order m and the grating spacing d is known, the wavelength of the light can be calculated.

θm

L

Diffraction GratingExample

Slide 14 and 15 sourcehttp://www.edmundoptics.com/

optics/gratings/