Photonics Dictionary: O

The distance between the object and the cornea, or the first surface of the objective in an optical device.

Distance between the front vertex of a lens and the object.

A family of specialized instruments used by ophthalmologists and optometrists to study a patient's eyes and prescribe spectacles. It includes the ophthalmoscope to observe and photograph the retina;...

Directing an optical beam in varying directions by varying reflection, refraction, focusing and diffraction methods.

The phenomenon that can render an optical resonator the equivalent of a semiconductor flip-flop. A bistable device will remain stable in two optical states, one of high transmission and another of...

Optical coherence tomography (OCT) is an imaging technique used in medical diagnostics and biomedical research to obtain high-resolution, cross-sectional images of biological tissues. An OCT imaging...

A system of modular mechanical components for building precision optical systems. The basic equipment includes a variety of modules for mounting, supporting and accurately positioning lenses and...

The storage of information via optical means, primarily employing a low-power laser to inscribe data on a photosensitive surface as pits or phase differences and to read such data via reflected light...

The physical length of the light path in a substance divided by the refractive index of that substance. See also equivalent air path.

A dome-shaped structure used for some optical instruments in place of a flat window. The transparent material should be of good quality and the hemispherical surfaces should be concentric.

Optical phase distortion refers to a phenomenon where the phase of an optical wavefront is altered as it propagates through a medium. This distortion can result from variations in the refractive...

With respect to microscopy, also called dispersive staining, optical staining the projection of colors through areas of a colorless specimen by color filters that are constructed to fit over the...

Optical strain sensors are devices that utilize optical principles to measure the deformation or strain experienced by a material under mechanical stress. These sensors convert changes in strain into...

A group of lenses, or any combination of lenses, mirrors and prisms, so constructed as to refract or reflect light to perform some definite optical function.

Refers to a variety of methods and tools used to determine the surface contour and performance of optical components and systems.

An optical testing instrument is a device or system used to evaluate and measure the performance, quality, and characteristics of optical components, systems, and devices. These instruments play a...

One of a class of crystalline substances belonging to triclinic, monoclinic and orthorhombic systems that have two optic axes. Two polarizations are allowed for any given direction of propagation,...

A variable focal length lens system that retains the object in focus as one or more lenses move as a unit along its optical axis.

A transparent crystalline substance that displays the same optical properties (i.e. refractive index) in all directions such that all light rays behave the same in all directions of propagation and...

A transparent crystalline substance in which the refractive index of the optic axis (extraordinary axis) is different from the other two crystal axes. Two polarization directions are allowed for any...

Optoacoustic, or photoacoustic, refers to a phenomenon and related techniques that involve the generation of acoustic waves in a material induced by the absorption of light. The term "optoacoustic"...

A transistor that uses an electro-luminescent source, a transparent base and a photoelectric collector.

A crystal having the axes of its grains aligned so that they have directional magnetic characteristics.

The system of color classification and description produced by Wilhelm Ostwald.

The physical distance, measured along the optical axis, from the object to the image. Also called overall length.

The figure seen through or imaged by an optical system. It may contain structures, natural or artificial, or it may be the real or virtual image of an object formed by another optical system. In...

In an optical system, the space between the object being viewed and the system entrance pupil.

The optical element that receives light from the object and forms the first or primary image in telescopes and microscopes. In cameras, the image produced by the objective is the final image. In...

A coarse diffraction grating that is used to form a scale of intensities to determine the relative magnitudes of stars. The grating is placed over the objective of a telescope to form a diffraction...

1. A prism used in some instruments to bend light 90° before it enters the objective. 2. A dispersing prism located in front of an astronomical telescope objective to produce spectra of all...

The image error that results from astigmatism, coma, oblique spherical aberration, lateral color and distortion.

A common technique in microscopy, oblique illumination is one in which the object is illuminated by a light source that is at an oblique angle (on the side) to the optical axis. This technique is...

An acid-resistant, lustrous volcanic glass, usually black or banded.

A device that completely or partially restricts the amount of light reaching the eye.

Refers to the characteristic hue of the ocean according to the presence and concentration of specific minerals or substances, such as chlorophyll. Atmospheric aberrations of color must be corrected...

The physical adaption of the eye lens, by means of ciliary muscle contraction, in order to maintain a clear, in focus image of light and other objects and surroundings at a given distance onto the...

The eye's involuntary reaction in the process of accommodation. This reflex is most dramatic in response to looking at a distant object after having previously been focused on a near object or vice...

The prism used in a rangefinder to bend the lines of sight through the instruments into the eyepieces.

That surface of a lens located nearest to the eye.

An electro-optical infrared tracker consisting of a beamsplitter, an illuminating source, an image dissector tube and an electronics unit, that automatically acquires and tracks particular eye...

Off-axis paraboloid and ellipsoid mirrors are specialized optical components used in various optical systems, particularly in applications requiring precise focusing, collimation, or imaging of...