Photonics Dictionary: A

An instrument that photographs the spectra of an extraterrestrial object.

The process of using a spectrograph with a telescope to acquire information on an astronomical object's speed and physical characteristics.

An astronomical telescope is a type of optical instrument designed to gather and magnify light from distant celestial objects for observation and analysis. It typically consists of two main optical...

The unit generally used to express distances within the solar system, and sometimes to measure interstellar distances. Technically, one astronomical unit is the mean distance between the Earth and...

The scientific observation of celestial radiation that has reached the vicinity of Earth, and the interpretation of these observations to determine the characteristics of the extraterrestrial bodies...

A glass-ceramic material developed in Russia. Astrosital resembles Zerodur in terms of its ultralow thermal expansion. Other spellings include Astro-Sital and Astro-Sitall.

The real part of the axial propagation constant for a particular mode. The attenuation coefficient for the mode power is twice the attenuation constant.

A means of adjusting the sharpness of an image automatically, with a sensor for estimating distance or contrast and a drive mechanism to adjust the lens. Active systems generate a light source to...

A microscope to which a beamsplitter and illuminated reticle have been added to measure the radius of curvature of a spherical surface by locating both surface and center and calculating the distance...

The number of molecules in one gram mole of a substance, numerically approximated by 6.02 x 1023.

The propagation constant evaluated along the axis of a waveguide, that is, in the direction of transmission. Also called axial propagation wave number.

A thermoplastic or optically transmitting hard plastic produced by applying polymerization initiator and heat to a monomer.

An old name for the rotating arm moving about an axis of rotation over a divided circle used to measure angles. Now the term refers to a small stadia telescope mounted over a ruler for use in...

Commonly known as CR39, this thermosetting plastic is used in the casting of eyeglass lenses because of its toughness and clarity.

An aptamer is a short, single-stranded DNA or RNA molecule that can bind to a specific target molecule with high affinity and specificity. Aptamers are often referred to as chemical antibodies due to...

In the SI system, prefix meaning 10-18.

Image of a uniform source through the sample of a microscope image system. Light from the sample plane is reimaged by the objective into the image plane.

A form of roof prism used to invert an image. The prism has faces cut normal to the optical axis; therefore, the prism may be placed within the optical path of a system and invert the image without...

A departure from ideal paraxial imaging behavior. The distortion of an optical field wavefront as it is propagated through the elements of an optical system. The field distortion is due to the...

Designed for the function of optical wavefront analysis. Shack-Hartmann camera aberration sensors use a lens array to image the wavefront to the CCD image plane. Live feedback may be applied through...

Optical surface damage due to abrasive rubbing. Abrasion damage affects are less than the thickness of the optical coating layers. Surface investigation may be achieved by aluminization of the coated...

An instrument that uses optical filtration in order to measure the transmittance for a discrete range or specific number of wavelengths.

Method of preserving the measured color value and color information as it is translated from differing devices. For example the output of a television display may be measured to have an identical...

The value of the distance of distinct vision, minimum focusing distance or near point, divided by the focal length of the lens. Magnification is produced when the optic is placed at its focal...

Least value of color value combinations which gives white light; minimum purity as determined to be white.

A perfect diffuser that exists only as a concept, or a white with known spectral characteristics used as a reference in measuring absolute reflectance.

The natural log of the ratio of absorbed intensity over the total intensity which gives a constant value assuming a stable volume as well as energy. In optical physics the absorbance may be defined...

A doped or absorbing transparent medium cut or molded into a wedge in order to measure the real and imaginary components of the refractive index. An internally reflected Gaussian beam is interfered...

The transition cross section constant coefficient which defines the transition probability of absorption from ground to a higher level within a given atomic or molecular species. The transition...

A measuring device that uses a light-sensitive cell or detector to determine the amount of light transmitted by a substance.

An absorption peak refers to a sharp increase or spike in the absorption of electromagnetic radiation at a particular wavelength or energy level. It is a distinctive feature in the absorption...

An accelerometer is a sensor or transducer that measures the rate of change of velocity of an object, or in simpler terms, it measures acceleration. Accelerometers are widely used in various...

The range of angle or solid angle values by which light may enter an optical system.

Also cellulose acetate film. The emulsion layer applied to the substrate of a photographic surface. The emulsion layer is composed of small particles suspended in gelatin solution.

Optic surface cleaning liquid that may be applied to glass, crystal, dielectric and metal surfaces; however, may not be applied to plastic and polymer materials.

An achromat, in the context of optics, refers to a type of lens or lens system designed to reduce chromatic aberration. Chromatic aberration is an optical phenomenon where different colors of light...

A lens consisting of two or more elements, usually of crown and flint glass, that has been corrected for chromatic aberration with respect to two selected wavelengths. Also known as achromat.

Stimulating light used for the production of energy through photosynthesis, solar cell or other light senstitive device.

That point in the electromagnetic spectrum at which an optical system focuses the most chemically effective rays.

Glass designed to absorb most infrared and ultraviolet radiation while transmitting most of the visible region.

The creation of a chemical reaction in a substance when radiation is directed to it.