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Fundamental Properties of
Light
Introduction to Physical Optics
Imaging Science Fundamentals
Chester F. Carlson Center for Imaging Science
What is Light?
• To understand
physical optics, let’s
review how we think
about and measure
light, which is part of
electromagnetic
radiation.
Imaging Science Fundamentals
Chester F. Carlson Center for Imaging Science
Electromagnetic Radiation
10-15 m
10-6 m
10-2 m
103 m
• EM radiation is made up of an electric field and a
magnetic field.
• Particle-wave duality of EM radiation.
– Light as a particle
– Light as a wave (physical optics)
• Includes x-rays as well as light, IR (heat) and radio
waves.
Imaging Science Fundamentals
Chester F. Carlson Center for Imaging Science
– Light is an electromagnetic
wave because it requires
two interdependent fields to
propagate.
– Both electrical (E) and
magnetic (B) waves must
exist for light to propagate.
E and B are perpendicular
to each other and to the
direction of motion.
Imaging Science Fundamentals
E
B
Direction of Travel
– The electric field has the
greater effect on materials,
and so we ignore the effect
of the magnetic field from
this point on.
Chester F. Carlson Center for Imaging Science
Optics
• Optics contains two areas of study:
– Geometrical Optics
– Physical Optics
• Geometrical optics, or ray optics, is the
study of light that travels as a “ray,” in
straight lines.
– Light rays passing through lenses and
bouncing off mirrors
Imaging Science Fundamentals
Chester F. Carlson Center for Imaging Science
What is Physical Optics?
• Physical optics, or wave optics, is the
study of how light interacts with objects
similar in size to its wavelength.
– Light energy travels as a wave (not a ray).
– Wave optics concerns the characteristics of
light such as wavelength, intensity, phase,
and orientation.
Imaging Science Fundamentals
Chester F. Carlson Center for Imaging Science
Wavelength

 Wavelength is the distance between two
identical points on a wave. (, lambda)
Imaging Science Fundamentals
Chester F. Carlson Center for Imaging Science
Frequency
time
unit of time
 Frequency is the number of cycles per unit of
time. (, nu)
 It is inversely proportional to the wavelength.
Imaging Science Fundamentals
Chester F. Carlson Center for Imaging Science
Wavelength and
Frequency Relation
 = v/
 Wavelength is proportional to the velocity, v.
 Wavelength is inversely proportional to the frequency.
 eg. AM radio wave has a long wavelength (~200 m), therefore it has
a low frequency (~KHz range).
 In the case of EM radiation in a vacuum, the equation becomes
 = c/
Where c is the speed of light (3 x 108m/s)
Imaging Science Fundamentals
Chester F. Carlson Center for Imaging Science
Photons
 Photons are little “packets” of energy.
 Each photon’s energy is proportional to its
frequency.
 A photon’s energy is represented by “h”
E = h
Energy = (Planck’s constant) x (frequency of photon)
Imaging Science Fundamentals
Chester F. Carlson Center for Imaging Science
Light Wave
• Transverse Wave
– Travels perpendicular to
change of amplitude.
E
B
Direction of Travel
– The case of light:
• Light waves are called electromagnetic waves because they
contain two types of energy that change amplitudes.
• Both electrical and magnetic energy vary perpendicular to each
other.
• Light is a transverse wave because the direction of travel is
perpendicular to the amplitude change of BOTH electrical and
magnetic fields.
Imaging Science Fundamentals
Chester F. Carlson Center for Imaging Science
Light Intensity
• Intensity of a monochromatic light relates
to the brightness of that light.
– The intensity of an electromagnetic wave is
proportional to the amplitude squared.
Higher Intensity
Imaging Science Fundamentals
Lower Intensity
Chester F. Carlson Center for Imaging Science