Congrats to Shahid Haider of the University of Waterloo – 2014 Norman Edmund Inspiration Award Winner!

 

Glossary

Application Notes | Articles | Tech Tools | FAQs | Glossary | Marketing Literature | Newsletter | Video Resources

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Rack and Pinion

A mating gear pair. The rack is a flat, straight bar (track) with teeth to engage (mate) with the gear teeth of the pinion gear, in order to move in a straight-line orientation. Typically the gear teeth are parallel, however for a helical rack the teeth are angled. The pinion is the smaller gear of the two.

See also Helical Gear

Radiant Sensitivity

The electrical current generated per watt of incident optical power. Expressed in A/W.

Radius of Curvature

The directed distance from the vertex of a surface to the center of curvature.

See also Sag, Effective Focal Length (EFL)

Reference Wavelength

A wavelength, for example 632.8nm, for measuring the accuracy of an optical flat. A 1/20λ flat will have a maximum peak to valley deviation of 632.8/20 or 31.64nm. One wave is 632.8nm.

See also Optical Flat, Surface Accuracy

Reflection

The change in direction of radiation by a surface without a change in the wavelength.

See also Transmission, Parity

Reflection Factor (Pd)

Ratio of the directionally reflected flux to that reflected in the same direction by a perfect reflecting diffuser identically irradiated or illuminated.

Refraction

The term given for the bending of light rays that occurs at the interface between two materials with different indices of refraction. A higher index of refraction results in a lower refracted angle.

See also Index of Refraction (n), Birefringence

Refractometer

An instrument used to measure the refractive index of solids and liquids.

Relative Brightness

A figure of merit corresponding to the amount of light seen by a viewer through binoculars, obtained by squaring the diameter of the exit pupil in millimeters. A higher number indicates a brighter image in low-light situations.

Relative Efficiency

Also referred to as groove efficiency of diffraction gratings, it expresses the energy diffracted into the required order as compared to the efficiency of the coating itself at the same wavelength. For example, a grating that yields 40% diffraction into a specific order at 500nm compared to a mirror with the same coating that reflects 80% of light at 500nm would have a relative efficiency of 50%. Theoretically, the relative efficiency for a grating can appear very high, yet, the actual piece could yield very low diffraction into the desired order if the coating reflectivity is low at the wavelength region of interest.

See also Ruled Grating, Holographic Grating, Groove Density, Diffraction Grating

Relative Illumination (RI)

A measure of a lens's uniformity of sensor illumination across the lens's full image circle for a uniform object illumination, defined radially.

Relay Lens

A lens or combination of lenses used to transfer an image from one point to another at a specified magnification ratio.

Repeatability

In positioning systems, the ability to return to the same position by repeating the same adjustments or by providing the same inputs.

See also Ball Bearing Slide, Ball Bearing Stage

Resolution

The ability to distinguish object detail. It is often expressed in terms of line pairs per millimeter (lp/mm), or microns (μm).

See also Depth of Field (DOF), Contrast, Modulation Transfer Function (MTF)

Resolving Power

The measure of an optical system's ability to produce an image which separates two points or parallel lines on the object.

Responsivity

A measure of the effectiveness of a detector in producing an electrical signal. The product of the light input in Watts and the responsivity result in the predicted output of the detector in Amps. It varies with temperature.

Retardance

The degree of angular shift in the phase of incoming polarized light.

See also Retarder (Waveplate)

Retarder (Waveplate)

A class of materials that exhibit the characteristic of birefringence. Orthogonal components of light that enter a retarder (or waveplate) will experience a relative phase shift upon output. This phase shift is dependent upon the thickness of the retarding medium and the degree of birefringence. The axes of the material exhibit different index characteristics and are generally referred to as the fast (low index) and slow (high index) axes.

See also Circular Polarizer, Retardance

Reticle

A planar, or flat, element located at the image plane of an optical system designed to measure the object imaged. The element is typically made of glass, and can have a wide variety of lines, circles, or patterns either etched or chrome deposited on it. Microscope eyepieces accept reticles while magnifiers or comparators accept contact reticles; the former must be placed close to the eye or sensor, whereas, the latter close to the object under inspection.

Retroreflector

An optical component designed to reflect light back in the direction from which it originated. A trihedral prism is often used as a type of retroreflector.

See also Dove Prism, Trihedral Prism (Corner Cube Retroreflector)

Right Angle Prism

An image reflection prism that deviates the ray path by 90°. It is the most popular type of prism and is often used for image/ beam displacement.

Ring Light Guide

An illumination component comprised of a bundle of optical fibers that terminates in a circular pattern, canted slightly inward towards the axis of the circle. It provides intense, near on-axis directional illumination for shadow-free viewing through the ring.

See also Directional Illumination

Ripple

In relation to rugate notch filters, it is a small variation in the transmission flatness within a specified spectral region.

See also Rugate Notch Filter

Rise Time

The time it takes for a signal to rise from a defined minimum to a fraction of the maximum signal. The low and high points are commonly defined as 10% to 90% of the maximum signal output.

RMS Noise

The unwanted part of electrical output that is not consistent with the radiation signal.

Roll

In relation to movement, it is the angular rotation about the longitudinal axis (plane of translation), typically the X-axis for X-Y-Z configurations.

See also Pitch, Moment Load, Gimbal, Yaw

Rugate Notch Filter

A type of notch filter constructed with a single layer of thin film in which the refractive index varies continuously with position in the direction perpendicular to the substrate plane.

See also Filter, Ripple, Notch Filter

Ruled Grating

A type of diffraction grating with a sawtooth profile that is generated by precision mechanical ruling engines. Replicas are then generated by depositing a coating, an epoxy layer, and polished substrate onto the master. Although the gratings are generally cut from larger pieces and have grooves across the entire face, incident light should be confined to 90% of the full face during use.

See also Holographic Grating, Relative Efficiency, Groove Density, Grating Equation, Diffraction Grating, Blaze Angle

Runout

In a linear stage, any deviation from the desired translation across a flat, straight line.

See also Ball Bearing Stage