Definition:
The optical recording of the
object wave formed by the resulting interference pattern of two mutually
coherent component light beams. In the holographic process, a coherent
beam first is split into two component beams, one of which irradiates the
object, the second of which irradiates a recording medium. The diffraction
or scattering of the first wave by the object forms the object wave that
proceeds to and interferes with the second coherent beam, or reference
wave at the medium. The resulting pattern is the three-dimensional record
(hologram) of the object wave.
BACTERIORHODOPSIN
(bR)
Definition:
A light-harvesting protein found in the purple membrane of a micro-organism called Halobacterium halobium. The protein undergoes a photocycle that involves several binary photochemical reactions that can be exploited for optical applications.
PLANE
HOLOGRAM
Definition:
A two-dimensional hologram.
VOLUME
HOLOGRAM
Definition:
A three-dimensional hologram.
ABSORPTION
HOLOGRAM
Definition:
A hologram formed when the light of the illuminating beam is absorbed in correspondence with the recording exposure.
AMPLITUDE
HOLOGRAM
Definition:
A hologram in which diffraction is produced by the silver image, resulting in a dimmer image than in a phase hologram, where diffraction takes place at the gelatin relief image left once the silver has been removed.
PHASE
HOLOGRAM
Definition:
A hologram that is formed on a recording medium by changing the phase of the illuminating wave in correspondence with the recording exposure. It may be formed by contact printing onto a resist material or by silver halide photographic emulsions.
IN-LINE
HOLOGRAPHY
Definition:
The formation of a hologram by single reference-beam interferences with waves that are diffracted or scattered from a small object.
TRANSMISSION
HOLOGRAM
Definition:
A hologram that is illuminated by a source opposite the viewer.
REFLECTION
HOLOGRAM
Definition:
A hologram that is illuminated by a source from the viewer's side.
LENSLESS
FOURIER TRANSFORM HOLOGRAM
Definition:
A hologram formed without lenses and with the object and reference points sharing the same plane. In the initial recording, each object point produces fringes having one spatial frequency across the recording medium. Reconstruction of the hologram, using a diverging illuminating beam, produces primary and conjugate images, both being virtual.
IMAGE
PLANE HOLOGRAPHY
Definition:
A type of holographic process in
which a lens is used to image the subject in the film plane.
FRESNEL
HOLOGRAM
Definition:
A hologram formed with an object located close to the recording medium.
FRAUNHOFER
HOLOGRAM
Definition:
A far-field pattern holographically reproduced image that is categorically considered with three-dimensional lensless photographs.
COMPUTER
POLARIZATION HOLOGRAPHY
Definition:
A technique used to store wavefront information on thin polarization information-recordable materials by controlling the polarization angle of a small illuminating spotlight in each sampling cell on a crystal.
INCOHERENT
HOLOGRAPHY
Definition:
The production of holograms initially from either conventional photographs or incoherent optical equipment.
TEMPORAL
FOURIER HOLOGRAM
Definition:
A technique used to suppress extreme noise amplification during digital image reconstruction that relies on smoothing and differentiation of the data by simplified least squared procedures.
NEAR-FIELD
REGION
Definition:
The area closest to an aperture or source where the diffraction pattern differs substantially from that observed at an infinite distance.
FAR-FIELD
REGION
Definition:
A region far from an aperture or source where the diffraction pattern is essentially the same as that at infinity. Changes in diffraction patterns of points within the far-field region are insignificant.
FRESNEL
DIFFRACTION
Definition:
1. Also known as near-field diffraction. The field of radiation sent through an aperture in an absorbing screen at large distances as compared with the wavelength and the dimensions of the aperture, but small enough to necessitate consideration of the effect of the phase differences between secondary wavelets.
2. The effect of diffraction obtained when the source of radiation and/or the observing screen are at a finite distance from the diffraction aperture or obstacle.
FAR-FIELD
DIFFRACTION PATTERN
Definition:
The diffraction pattern of a source such as a light-emitting diode, injection laser diode or the output end of an optical waveguide observed at an infinite distance from the source.
FRESNEL
NUMBER
Definition:
In a
lens, the square of the radius of its aperture divided by the product of
the focal length and the wavelength. It measures the importance of
diffraction in the image formed by the lens. A small Fresnel number
indicates greater effects of diffraction. The Fresnel number has been used
in lasers with the distance to the following aperture in a resonator
replacing the focal length, and it has proved efficient in determining the
diffraction loss.
CONJUGATE
HOLOGRAPHIC IMAGE
Definition:
Also known as real holographic image. The indistinct, highly distorted image produced on the side of the hologram closest to the observer, in addition to the primary image. When the location of the light source is changed so that all the rays of the reference beam are reversed, a distortion-free, real three-dimensional image appears before the hologram.
WHITTAKER-SHANNON
THEOREM
Definition:
The theorem stating that, when the sampling period in a recorded sample hologram is matched to the object spectrum, the resulting image does not suffer any loss of information content.
RECONSTRUCTION
WAVE
Definition:
The coherent wave used to play back a recorded hologram. It is identical to the reference wave used in the generation of the original hologram; part of it is diffracted by the recording medium and appears in the form of the original object wave.
POLARIZATION
Definition:
With respect to light radiation, the restriction of the vibrations of the magnetic or electric field vector to a single plane. In a beam of electromagnetic radiation, the polarization direction is the direction of the electric field vector (with no distinction between positive and negative as the field oscillates back and forth). The polarization vector is always in the plane at right angles to the beam direction. Near some given stationary point in space the polarization direction in the beam can vary at random (unpolarized beam), can remain constant (plane-polarized beam), or can have two coherent plane-polarized elements whose polarization directions make a right angle. In the latter case, depending on the amplitude of the two waves and their relative phase, the combined electric vector traces out an ellipse and the wave is said to be elliptically polarized. Elliptical and plane polarizations can be converted into each other by means of birefringent optical systems.
CIRCULARLY
POLARIZED LIGHT
Definition:
A light beam whose electric vectors can be broken into two perpendicular elements that have equal amplitudes and that differ in phase by l/4 wavelength.
CIRCULAR
DICHROISM (CD)
Definition:
The optical phenomenon in which planar polarization is converted to elliptical polarization when plane-polarized light traverses an active medium.
ANGULAR
APERTURE
Definition:
The angle between the most divergent rays that can pass through the lens to form an image. In a birefringent crystal light modulator or Pockels cell, the maximum angle in the incident light rays that gives a nominal 100:1 contrast ratio with applied half-wave voltage is a function of the crystal thickness.
WAVE
PLATE
Definition:
An optical element having two principal axes, slow and fast, that resolve an incident polarized beam into two mutually perpendicular polarized beams. The emerging beam recombines to form a particular single polarized beam. Wave plates produce full-, half- and quarter- wave retardations. Also known as retardation plate.
AIRY
DISC
Definition:
The central peak (including everything interior to the first zero or dark ring) of the focal diffraction pattern of a uniformly irradiated, aberration-free circular optical element or system.
RAYLEIGH
CRITERION OF RESOLVING POWER
Definition:
When a lens system with a circular aperture is free of aberrations, the image of a point object will appear as a disc of finite size surrounded by concentric rings. When two points are separated such that the center of the image of one falls on the first minimum of the second, the points are said to be resolved according to the Rayleigh criterion. This condition exists when the angular separation of the point objects, viewed from the objective lens of the instrument, is:
where l is the light wavelength and a the diameter of the objective lens.
MINIMUM
SPOT SIZE
Definition:
The
smallest linear diameter to which a laser or other beam of radiant energy
is capable of being focused, depending on the quality of the focusing
optics, aperture and focal length, beam irradiance distribution (whether
uniform or Gaussian), wavelength and other factors.
HALF-WAVE
PLATE
Definition:
A plate of electro-optical material that serves to rotate the plane of polarization of a light beam.
QUARTER-WAVE
PLATE
Definition:
A plate made of a
double-refracting crystal having such a density that a phase difference of
one-quarter cycle is formed between the ordinary and extraordinary
elements of light passing through.
NUMERICAL
APERTURE (NA)
Definition:
The sine of the vertex angle of the largest cone of meridional rays that can enter or leave an optical system or element, multiplied by the refractive index of the medium in which the vertex of the cone is located. Generally measured with respect to an object or image point, and will vary as that point is moved.
F-NUMBER
(f/#)
Definition:
The
expression denoting the ratio of the equivalent focal length of a lens to
the diameter of its entrance pupil.
LAW
OF BREWSTER
Definition:
The law stating that when light
strikes a surface at such an angle that the reflected and refracted rays
are perpendicular to each other, the maximum polarization of the light
occurs in both reflected and refracted rays. The maximum polarization in
the reflected ray is perpendicular to the plane containing the ray and
normal to the surface, and therefore perpendicular to the refracted ray
that lies in this plane.
BRAGG’S
LAW
Definition:
The law expressing the condition under which a crystal will reflect a beam of x-rays with the greatest amount of distinction or resolution and, at the same time, denoting the angle at which the reflection occurs. For x-ray reflection, the angle formed by the incident or the reflected beam and the crystal planes is the one generally used. If this Bragg angle is represented by q, if d represents the distance between the planes or layers of atoms, and if l is the wavelength of the x-rays, the law may be expressed by the equation:
assuming that n must be a whole number.
COSINE
Definition:
A formula indicating that, for an imaging lens system, the image brightness for off-axis points will fall off at a rate proportional to the cos4 of the off-axis field angle.
INVERSE
SQUARE LAW
Definition:
The law
stating that the illuminance (or irradiance) from a point source varies as
the inverse square of the distance between the source and the receiver.
LAMBERT
(l)
Definition:
A unit
of luminance equal to 1/p
candela per square centimeter.
PARAXIAL
Definition:
Characteristic
of optical analyses that are limited to infinitesimally small apertures.
Also called first-order or Gaussian optics.
PARTIAL
COHERENCE THEORY
Definition:
Totally
coherent radiation is produced by a purely monochromatic point source. In
the real world the energy will have a limited bandwidth and the point
source will subtend some angle resulting in partially coherent radiation.
COHERNENCE
LENGTH
Definition:
That
length over which energy in two separate waves remains constant. With
respect to a laser, the greatest distance between two arms of an
interferometric system for which sufficient interferometric effects can be
obtained.
DEGREE
OF COHERENCE
Definition:
A
quantitative measurement of the coherence of a light source; equal to the
visibility (V) of the fringes of a two-beam interference test:
where Imax equals the intensity at a maximum of the
interference pattern and Imin equals the intensity at a
minimum. A value greater than 0.88 indicates highly coherent light.
SPATIAL
COHERENCE
Definition:
The
maintenance of a fixed-phase relationship across the full diameter of a
cross section of a laser beam.
TEMPORAL
COHERENCE
Definition:
A
characteristic of laser output, calculated by dividing the speed of light
by the linewidth of the laser beam. The temporal coherence length of
different lasers thus varies from a few centimeters to many meters.
Text originated from www.photonic.com