OPT 101 Vocab 2

Aperture Stop

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

Cladding

The region of an optical system that limits the size of an axial ray bundle

Constructive Interference

The superposition (addition) of two of more waves such that the local irradiance is greater than the sum of the irradiance 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 effects are most obvious when the obstacle or aperture size
is approximately the same as the wavelength of the waves.

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. 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

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 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

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.

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 the photon energy to its
frequency. In standard international (SI) units, h = 6.626 x 10-34 J-s

Radiant Intensity

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

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 to electronic 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 rays at
opposite edges of the object that pass through the center of the aperture stop (chief rays). This
is the ‘apparent’ size of the object

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 spatial 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

Photon

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