Photonics Dictionary

A reticle, also known as a reticule or graticule, is a pattern or set of markings placed in the focal plane of an optical instrument, such as a microscope, telescope, riflescope, or camera, to...

The formation of a distinct, irregular surface pattern on a photographic emulsion due to differential swelling of the gelatin.

The retina is a light-sensitive tissue layer located at the back of the eye, opposite the lens. It plays a crucial role in the process of vision by converting light into neural signals that are sent...

A special-purpose camera used by ophthalmologists to photograph the retina of the eye. The optical system operates through the eye pupil, and the illuminant must be able to send light into the eye...

The study of the quality of the image formed on the retina by the measurement of the flux reflected from the eye when the image of a grating or line is produced on the retina.

Also known as reversed telephoto lens. A lens consisting of an ordinary objective with a negative component near its front focal point. Thus, the back focus is large, relative to its focal length....

Two lenses, separated by a distance equal to the sum of their focal lengths, and retroreflecting mirror assemblies, one of which is coaxial with the lenses and the other slightly translated off-axis.

Retroreflection is a phenomenon in optics where light is reflected back toward its source, typically in a direction nearly parallel to the direction from which it originated. This occurs due to the...

Retroreflectivity refers to the property of a surface or material to reflect light back to its source, regardless of the angle of incidence. Unlike most surfaces that scatter light in various...

A retroreflector is an optical device or structure that reflects incident light or electromagnetic waves back to their source, regardless of the direction from which the light approaches. Unlike...

Voltage that produces current flow in the direction of greater resistance to the steady-state direct current; i.e., from the cathode to the anode.

A prism made of two elements cemented together that, depending on its orientation, inverts or reverts an image. It may be used in converging or diverging light. Sometimes referred to as a K prism.

The characteristics of a material that determine its tendency to flow.

Rhodamine refers to a family of fluorescent organic dyes that are widely used in various fields, including biology, chemistry, medicine, and materials science. These dyes are known for their bright...

A reflecting prism that is rhomboidal in shape. It has two parallel transmitting faces, and two parallel reflecting faces; the latter are oblique to the former (usually but not necessarily at...

A cable that incorporates multiple fibers, jacketed side by side in a ribbonlike form.

A photodiode having a conducting grid that covers the surface of the photodiode junction and intercepts and wastes some of the light. In this way, efficient optical- and microwave-frequency design...

A small erect-image telescope for use as a sighting device on a rifle. The chief requirement is a long eye relief to avoid damage to the eye due to recoil. The power may lie anywhere between 1 and...

A wave that is polarized elliptically or circularly polarized and in which the electric field vector — observed while looking in the direction of propagation — rotates in a right-hand or...

The formation of a block by attaching optical elements to a plate with a ring of pitch or other thermoplastic material.

A toric lens generated by rotating a specific cross section about an axis beyond its area and used in the formation of annular images.

A system of local area networking in which each node or station is connected to two others, ultimately forming a loop. Data are passed in one direction only, being received by each node and then...

A ring laser gyroscope (RLG) is a type of gyroscope that uses laser light to detect and measure changes in orientation. It operates based on the Sagnac effect, which is a fundamental principle of...

A circular lamp or bundles of optical fibers placed around the perimeter of an objective lens to illuminate the object field below it.

The approximately concentric waves that form on a surface that has been polished without an oscillation of the polishing lap.

A Risley prism, also known as a Risley prism pair or Risley rotating prism, is an optical device used for controlling the direction of a laser beam or other optical beam by independently rotating two...

Robotic arms, also known as robot arms or manipulator arms, are mechanical devices designed to mimic and perform the functions of human arms. They consist of multiple articulated segments, joints,...

A polarizing prism assembly made up of two cemented calcite halves. The prism transmits the ordinary ray without deviation, while the extraordinary ray is deviated to accomplish the polarization.

Rockwell hardness (Rc) refers to a method for measuring the hardness of a material, primarily metals, using an indentation test. It is named after the Rockwell scale, which was developed by Stanley...

An obsolete term once used to describe a unit of radiation dosage.

The study of x-rays, their biological effects and technology. Named for W.C. Roentgen, who discovered x-rays in 1895.

Conductor element for use in integrated electro-optic systems that measures current flowing through it.

A transparent plate ruled with black lines and equal, clear spaces. It is used as a multiple knife-edge for testing a concave mirror.

A statistical method of dealing with a series of values where each value is squared, the mean of these squares is calculated, and the square root of that mean is then taken.

A statistical method of dealing with a series of values where each value is squared, the sum of these squares is calculated and the square root of that sum is then taken.

A corrective lens system that is placed near the focal plane of a Newtonian telescope to increase its effective field of view by correcting for coma formed by the telescope's paraboloidal mirror.

A camera system used for microphotography that has a structure, such as a cylinder or surveyor belt, to rotate the documents to be recorded. The image is fixed relative to film motion and exposure is...

A disc composed of a series of holographic optical elements that diffract light at various angles. When spinning, a raster scan may be generated.

Developed for use in military reconnaissance systems, it consists of a polygonal mirror, drive motor, interface between motor and mirror, and control electronics. Also used in broadband video...