Glossary: S

The surface profile of a surface. For spherical surfaces, it is calculated from diameter and radius of curvature. For aspheric surfaces, it is calculated from radial distance from the optical axis, curvature, conic constant, and aspheric terms.

The radial component of the spot (or ray bundle) in the z-plane (perpendicular to image axis) at a given image height.

Condition wherein both image and object planes are tilted with respect to the optical axis, in order to focus over a depth despite the camera being oblique to the object. 

A type of bevel in which the edge of an optical component is cut and conditioned to remove sharp corners. It is less toleranced than a ground edge.

A type of microscope objective with a semi-planar design where roughly 80% of the objective's field of view appears flat.

The size of a camera sensor's active area, specified as the horizontal dimension by the vertical dimension (H x V). It is important in determining the proper lens magnification required to obtain a desired field of view.

Refers to the horizontal nominal inch-based dimension naming scheme for image sensors, not the physical sensor dimensions above 4/3".

The portion of the electromagnetic spectrum from 900 to 1800nm. Definition may differ by application.

A type of filter where the transmission band is a low wavelength range, typically lower than the region blocked.

The effective resistance of a photodiode. It represents the slope of the I-V curve at the origin (V=0).

Corresponds to the "exposure time" of the sensor chip that controls the amount of light incident on it.

The standardization of transmission and reception of analog signals, typically determined by geographical region. Signal parameters include synchronization, number of scanlines, bandwidth, black and blanking levels, frame rate, aspect ratio, etc. Video components of one signal format are not compatible with those of another.

Comparison of signal power to noise power, including dark current and other unwanted/unpredictable fluctuations. In imaging systems, it is expressed in decibel values for analog systems, and "bit" values for digital systems. Industrial cameras have no less than 46dB SNR, yielding 256 steps of contrast in the image. This corresponds to an 8 bit digital signal (2⁸ = 256). Every 6dB of an analog signal converts to 1 bit when digitized.

An electro-optic component that transforms light energy into an electrical current due to the photovoltaic effect.

A lens with only one optical component such as a PCX, DCX, PCV, or DCV lens.

Mechanical method of changing the focus of an optical assembly, such as a laser beam expander or imaging lens, in which optical components are not rotated during translation, which minimizes beam wander and image runout. However, this requires more complex mechanics than rotating focusing mechanisms, which rotate the optical elements during translation, typically increasing the cost of sliding focusing mechanisms. Helicoid barrels are a common type of sliding focusing mechanism.

A mounting thread denoted by M12 x 0.5mm, with no specified flange distance.

Physical law governing the refraction (bending) of light rays at an interface between two regions of different index of refraction.

A laser using a transparent substance (crystalline or glass) as the active medium, doped to provide the energy states necessary for lasing. The pumping mechanism is the radiation from a powerful light source, such as a flash lamp. 

An assembly that is used in conjunction with laser applications to eliminate spatial noise. A pinhole is used to select only the central peak of the intensity pattern from a focused spot. The size of the pinhole is selected based upon the wavelength, objective focal length, and input beam diameter.

Method of quantifying object size by a density (e.g. linepairs per millimeter) rather than a size. Allows for more precise way of describing resolution as it considers the necessary space between defects that allows for their detection, as well as describing lens performance by way of a transfer function. 

The configurations of energy storage, relative to the structure of a laser resonator, that define the relative intensity distribution of the laser beam.

Irradiance per unit wavelength interval at a given wavelength, expressed in watts per unit area per unit wavelength interval.

Measure of a detector's signal during exposure to radiation of a constant power level and varying wavelength.

An optical instrument for forming the spectrum of a light source and recording it on a film. The dispersing medium may be a prism or a diffraction grating.

An optical instrument used to measure and analyze the distribution of radiation in a particular wavelength region.

A reflection which comes from a surface at an angle equal to the angle of incidence. An example is a high quality mirror.

A type of optical aberration in which light rays from the outer portion of a lens focus either in front of (undercorrected) or behind (overcorrected) the focus point of the rays from the center portion of the lens. Unlike most other monochromatic aberrations, spherical aberration appears on-axis as well as off-axis.

A manufacturing specification that tolerances the roundness or deviation from being a perfect sphere of a spherical surface such as a ball lens.

The linear polarization state which is perpendicular to the plane of incidence.  The plane of incidence is normal to the surface or interface upon which light is incident.  If the light is incident upon the interface at an angle, the light will be oscillating in such a way as to appear to be “skipping” across the surface.

The degree to which a laser beam is aligned parallel to the axis of the housing.

A wavelength interval used to denote a spectral region of energy that is not transmitted by a filter.

For ball bearing stages, it denotes error in the horizontal plane (left and right movement in direction of travel).

A measure of linear deviation in a translation stage in the two axes other than the direction of travel. It can be thought of as unintended linear travel in the two axes other than the direction of travel.

Energy outside of the field of view of an optical system that scatters off of the edges of an optical or mechanical component and reaches the sensor in the form of background noise. This can decrease an image's contrast by lightening the background.

The ratio of the illuminance at the peak of an aberrated diffraction pattern to that at the peak of an aberration-free system.

A proportionality constant used to calculate stress birefringence that depends on glass type, wavelength and temperature.

An indication of the peak-to-valley flatness of a surface given in terms of waves (a multiple or part of a reference wavelength). For example, a specification of 1/4 wave means that the flatness of the surface deviates by one quarter of the wavelength used to test the surface. If the wavelength was 550nm, the flatness would be held to within 140nm in order to produce a surface accuracy of 1/4 wave.  Also given in RMS (root mean squared)  where the peak-to-valley values are squared and then the square root is taken of their mean.

A type of surface accuracy specification that measures the deviation of a flat surface such as that of a mirror, window, prism, or plano-lens. This deviation can be measured using an optical flat. The deviations in flatness are often measured in values of waves (λ), which are multiples of the wavelength of the testing source. One fringe corresponds to ½ of a wave. 1λ flatness is considered typical grade, λ/4 flatness is considered to be precision grade, and λ/20 is considered high precision grade.

A specification of allowable flaws in the surface on an optic indicated by a hyphenated number (i.e. 60-40). The first number is referred to as the scratch number and quantifies defects of a long nature, such as scratches; the second number is the dig number and indicates round defects such as pits and dents. Scratch-Dig numbers for surface quality conform to the US government standards MIL-PRF-13830B.

Surface roughness, or high frequency error, is a measure of smoothness, or the quality of the polish on an optic’s surface. Surface roughness can effect scatter and the ability to withstand high laser power on the surface. They are usually an unfortunate by-product of the polishing process. Rough surfaces tend to wear faster than smooth surfaces and may not be suitable for some applications, especially those with lasers or intense heat, due to possible nucleation sites that can appear in small cracks or imperfections. Manufacturing tolerances for surface finish range from 50Å RMS for typical quality, 20Å RMS for precision quality, and 5Å RMS for high quality.