Optics 101 Midterm 3 Glossary (copy)

University of Rochester Optics 101 Midterm 3 Glossary Flashcards

Absorption

For a propagating wave, process by which optical power or irradiance decreases on propagation, leaving energy in the material.

Angular Size

For a distant object, it is given by the angle between the rays at opposite edges of the object that pass through the center of the aperture (chief rays).

Aperture Stop

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

Bragg Grating

Periodic variation in material composition that produces a strong optical reflection at a specific wavelength.

Cladding

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

Conduction Band

A range of allowed electronic energy levels in which electrons are free to move.

Constructive Interference

The superposition 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 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.

Diffraction Limited Spot Size

The smallest focal spot permitted by the wave nature of light. Equal to the ratio of the wavelength to the numerical aperture.

Dispersion

The variation of the velocity of a wave with frequency or wavelength. 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.

Fluorine

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 of a wave.

Germania

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

Holes

Vacant energy states in the valence band of a solid.

Holography

A method of wavefront reconstruction that makes use of a recorded interferogram.

Interference

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

Interferogram

An irradiance pattern that reveals the phase variations in a wavefront under test.

Iridescence

The appearance of color due to optical interference or diffraction.

Irradiance

The power per unit area carried by an optical beam.

Jacket

A protective coating over an optical fiber.

Magnification

In an imaging system, 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 caused by particular microscopic properties of an optical material.

Numerical Aperture

Product of the external refractive index and sine of the maximum axial ray angle.

Objective Lens

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

Optical Cavity

An arrangement of mirrors that confines light waves by recirculating optical energy either in the form of continuous waves or optical pulses.

Optical Path Length (OPL)

The product of the geometric length of the light path 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.

Photopolymer

A light sensitive material in which light absorption initiates a polymeric chemical reaction.

Planck’s Constant

The constant of proportionality relating photon energy to its frequency.

Population Inversion

When an assembly of atoms, molecules, or electronic band states contains a larger population in the excited state than in the ground state or the lower lasing level.

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.

Semiconductor

A material whose valence band is completely occupied at low temperatures and whose conductivity increases at high temperatures.

Solid angle

A two dimensional measurement of angle. 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.

Spectral density

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

Spontaneous Emission

The process by which an atom, molecule, semiconductor crystal, nanocrystal or nucleus in an excited state undergoes a transition to a state with a lower energy and emits a photon.

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.

Stimulated Emission

The emission of electromagnetic radiation in the form of photons of a given frequency, triggered by photons of the same frequency.

Traveling wave

A displacement that moves in time without changing shape.

Valence Band

A range of electronic energy levels in which electrons are in covalent bonds and are not free to move through the solid.

Visual Magnification

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

Waveguide

The trapping and directing of light by a mechanism such as total internal reflection.

Wavelength

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

Responsivity

The ratio of the photocurrent in a detector to the input optical power.

Quantum Efficiency

The average number of photon generated charge carriers for each photon absorbed in a detector.