2054Lecture14 - Introduction to Optics Introduction Topics...

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Unformatted text preview: Introduction to Optics Introduction Topics of Discussion Topics Optical Systems & the Paraxial Optical Approximation Approximation The Laws of Optics The Optical System The An optical system is composed of a An optical collection of flat or curved mirrors, convex or concave lens, diffraction grating and polarizers. polarizers. The Paraxial Approximation The Light travels along straight lines, called rays, that Light rays that are perpendicular to the wave fronts. are As rays travel through an optical system, rays As may be “bent” by an optical component. may Rays that are not “bent” are said to travel along Rays the principal axis of the optical system. principal The paraxial approximation only consider rays The paraxial that travel close to the principal axis of the optical system. optical Objects & Images Objects The distance from an object to the optical The system is called the object distance. object The distance from the image to the optical The system is called the image distance. The image image The of an object may be viewed at an image point. image When rays pass through an image point, we call it a real image. When rays do not pass through real When the image point, we call it a virtual image. virtual The location where all rays pass through the The image point is called the focal point. focal Law of Reflection Law The angle of incidence θi is the angle a The angle ray makes relative to the normal of the incident surface. incident The angle of reflection θr is the angle a ray The makes relative to the normal of the exiting surface. surface. The angle of incidence coincides with the The angle of reflection, that is θI = θr. Types of Reflection Types Specular reflection occurs when the reflected light rays travel parallel to one another – a smooth surface. another Diffuse reflection occurs when the reflected light rays travel in random directions relative to one another – a rough surface. rough Refractive Index Refractive Each optical material has a physical Each constant, called the refractive index n, refractive which describes its ability to “bend” light. which The index of refraction n depends on The wavelength and temperature. wavelength The index of refraction is given by The n = c / v, where v is the speed of light in where the material. the Law of Refraction Law Let a material of refractive index n1 and material Let of refractive index n2 share a common boundary. A ray, called the incident ray, travels in a ray, incident travels material of refractive index n1 at an angle of θ1 relative to the surface normal at the boundary. relative A ray, called the refracted ray, travels in a ray, refracted travels material of refractive index n2 at an angle of θ2 relative to the surface normal at the boundary. relative The law of refraction is given by The law n1 sin θ1 = n2 sin θ2. sin Total Internal Reflection Total Light reflected at all angles greater than Light the critical angle θc is called total internal critical reflection, and is given by reflection and θc = sin (n2 / n1) -1 -1 Brewster’s Law Brewster’s Let light travel in a material of refractive Let index n1. Then the angle θB, called Then called Brewster angle, iis the angle of reflection s Brewster from a polarizing material of refractive index n2, and is given by tanθB = n2 / n1. Dispersion Dispersion A llight source composed of a single ight wavelength is called monochromatic. A monochromatic light source composed of many wavelengths is called polychromatic. polychromatic Since the index of refraction is wavelength Since dependent, each wavelength “bends” differently according to Snell’s Law. We call this phenomenon dispersion. dispersion ...
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