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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