Optics 101 Midterm 1 Glossary

University of Rochester Optics 101 Midterm 1 Glossary Flashcards

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.

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.

Irradiance

The power per unit area carried by an optical beam. We often speak of the optical irradiance on a sensor or solar cell, but sometimes view the irradiance as the property of a beam at any given plane of incidence.

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.

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.

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. Scattering can be deterministic as for a diffraction grating, or it can be random, as happens with particles in the atmosphere.

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. For objects of small angular size, the solid angle angle is the cross sectional area divided by the square of the distance. The units of solid angle are Steradians (Sr). We would then say a given object subtends a certain solid angle with respect to the center of the sphere.

Spectral density

A measure of energy, power, or irradiance that is partitioned to represent the spectral energy content of the source. For example, irradiance spectral density 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.

Wavelength

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

Photon

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