Optics 101 Midterm 2 Glossary

University of Rochester Optics 101 Midterm 2 Glossary Flashcards

Absorption

Absorption

For a propagating wave, a process by which optical power or irradiance decreases on propagation, leaving energy in the material. It can also refer to the fraction of optical energy converted into electrical or thermal energy in a material as light passes through.

Angular Size

For a distant object, the angular size is given by the angle between the rays at opposite edges of the object that pass through the center of the aperture (chief rays). This is the ‘apparent’ size of the object.

Aperture Stop

The surface in an optical system that limits the size of an axial ray bundle.

Cladding

The region of an optical fiber just outside the core. It has a lower refractive index than the core. 

Constructive Interference

The superposition (addition) of two or more waves such that the local irradiance is greater than the sum of the irradiances of the waves.

Core

The inner region of an optical fiber. It usually has a higher refractive index than the cladding.

Critical Angle

The angle of incidence, measured from inside a material of high refractive index, beyond which light will totally reflect.

Destructive Interference

The superposition (addition) of two or more waves such that the local irradiance is less than the sum of the irradiances of the waves.

Diffraction

Change in the directions and intensities of a wave or group of waves after passing by an obstacle, through an aperture, through a collection of apertures, or passing by an assembly of obstacles.

Diffraction Limited Spot Size

The smallest focal spot permitted by the wave nature of light. It is approximately equal to the ratio of the wavelength to the numerical aperture.

Dispersion

The variation of the velocity of a wave with frequency or wavelength. It is usually measured as a variation in index of refraction with wavelength.

Eyepiece

In a visual instrument, the lens or group of lenses just in front of the eye, whose function is to create a virtual image at a comfortable viewing distance.

Fluorine

A chemical used as a dopant to lower the refractive index of an optical fiber. It is usually used in the cladding.

Frequency

The number of oscillations or vibrations per unit time (e.g. seconds) of a wave.

Germania

A chemical term for germanium dioxide, a common constituent of an optical fiber core.

Holography

A method of wavefront reconstruction that makes use of a recorded interferogram. The interference is usually between an object wave and a reference wave. The recording medium can be photographic emulsion, a photopolymer, or a nonlinear crystal.

Interference

The superposition (addition) of two or more waves such that the local irradiance is not equal to the sum of the irradiances of the waves.

Iridescence

The appearance of color (often quite vivid) due to optical interference or diffraction.

Irradiance

The power per unit area carried by an optical beam. Often spoke of on a sensor or solar cell, but sometimes viewed as the property of a beam at any given plane of incidence.

Jacket

A protective coating over an optical fiber.

Magnification

In an imaging system, the magnification is the ratio of the transverse size of the image to that of the object.

Material dispersion

The variation of the refractive index/phase velocity with frequency (or wavelength) caused by particular microscopic properties of an optical material.

Numerical Aperture

In an optical system, the product of the external refractive index and sine of the maximum axial ray angle that can enter or exit an optical system. For an optical fiber, the maximum axial ray angle that can be trapped in the fiber by total internal reflection.

Objective Lens

The first light collection element in an optical system such as a camera, microscope, or telescope.

Optical Path Length (OPL)

The product of the geometric length of the path light follows through the system, and the index of refraction of the medium through which it propagates.

Phase

An angular measure of the fractional shift of a harmonic wave.

Phase velocity

The speed at which a wave front travels (propagates) through space.

Photon

The elementary particle of light and other electromagnetic radiation. A photon carries energy proportional to the optical frequency and has zero rest mass.

Photopolymer

A light sensitive material in which light absorption initiates a polymeric chemical reaction (usually forming polymer chains from monomers). Photopolymers often have two components that are sensitive to different wavelengths of light.

Planck’s Constant

The constant of proportionality relating photon energy to its frequency. In standard international (SI) units, h=6.626*10^-34 Js.

Radiant intensity

Power per unit solid angle measured at a distance much larger than the size of the source.

Scattering

For a propagating wave, the tendency for material inhomogeneities to redirect the light.

Solid angle

A two dimensional measurement of angle (or angular subtense), in which the cross sectional area of an object is projected on to a sphere. The solid angle is then the area on the sphere divided by the square of the radius of the sphere. The units of solid angle are Steradians (Sr).

Spectral density

A measure of energy, power, or irradiance that is partitioned to represent the spectral energy content of the source. It would be measured in Watts per meter squared per nanometer.

Standing wave

A displacement that does not travel through space, but oscillates in time with a fixed spacial pattern. In optics, it is often formed by the interference of two counterpropagating waves.

Traveling wave

A displacement (or disturbance) that moves in time without changing shape. A periodic or harmonic traveling wave is represented by a periodic function that moves, usually with a fixed velocity.

Visual Magnification

The ratio of the apparent (angular) size of an object with an optical system to that without the optical system.

Wavelength

The period of oscillation (in space) of a harmonic wave.