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Photonics Dictionary

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law of reversibility

In physics, the law of reversibility is often associated with the concept of reversibility in thermodynamics. The law asserts that any process that occurs in a closed system can, in theory, be...

Lawson criterion

Defines the minimum operational standards for a self-sustaining fusion reactor as equivalence between energy released per volume unit and kinetic energy per unit volume.

lay length

In a fiber optic cable, the longitudinal length required for the transmission media, wrapped around a central member, to complete one helical wrap. Also called pitch.

layout

In the optical shop, the process of positioning and marking a blank or lens before surfacing, cutting and edging.

lbf

pound-force

lead zirconate titanate

A ferroelectric polycrystalline ceramic material used in optical memories for computers and as a piezoelectric transducer.

leaky mode

In an optical waveguide, a mode whose field decays monotonically for a finite distance in the transverse direction but which becomes oscillatory everywhere beyond that finite distance.

leaky ray

In an optical waveguide, a ray for which geometric optics would predict total internal reflection at the core boundary, but which suffers loss by virtue of the curved core boundary.

least circle of confusion

The circle of confusion is a defocused or aberrated image of a point. Focus is generally set where the diameter of this circle is minimized or least.

LED -> light-emitting diode

An LED, or light emitting diode, is a semiconductor device that emits light when an electric current passes through it. LEDs are widely used in various applications due to their energy efficiency,...

legacy fiber

Older fiber optic cable that may not be suitable for state-of-the-art applications and that is difficult for suppliers to sell.

lens bench -> optical bench

A support for optical parts comprising a solid bed that permits precise longitudinal movement of one component relative to the others, and a number of sliders equipped with holders for lenses, lamps,...

lens blank

A lens blank is a piece of optical material in a raw, unfinished state, typically in the form of a disk or block, from which lenses are eventually fabricated. Lens blanks are made from various...

lens disc

A rotating disc that holds several lenses of differing focal length about a diameter. Used to switch lenses in a system while maintaining focus.

lens molding

The production of rough glass lens blanks that are pressed while red-hot to the approximate size and shape of the finished lens, ready for fine grinding and polishing. Large companies often do their...

lens mount

The metal tube that maintains the optical components of a lens in proper relationship. Some lenses are mounted in metal cells, which in turn are screwed to the front and rear of a shutter or lens...

lens speed

Also known as f number, lens speed is commonly represented as the ratio of the focal length to the diameter of the lens. Lower f numbers produce brighter images.

lens testing equipment

Lens testing equipment refers to a range of specialized tools and instruments used to evaluate the optical performance, quality, and characteristics of lenses. These instruments are essential for...

lens transmission

The ratio of the intensities of a light bundle before and after passing through the lens.

lens

A lens is a transparent optical device that focuses or diverges light, allowing it to pass through and form an image. Lenses are commonly used in optical systems, such as cameras, telescopes,...

lensless microscopy

Lensless microscopy, also known as computational or holographic microscopy, is an imaging technique that captures and reconstructs microscopic images without the use of traditional lenses. Instead of...

lenslets

A matrix of miniature lenses, molded or formed onto a common base.

lensometer

An ophthalmic instrument used to measure the magnitude and direction of the maximum and minimum powers of a spectacle lens, and mark the optical center of the lens by an ink dot. When the lens to be...

lenticular

An array or mosaic of optical surfaces. May be a number of lenses closely packed to form multiple images or many parallel cylinders used as a projection screen.

lenticular color photography

A type of additive color photography using a lenticular structure impressed on a film base and a camera lens with a filter having three sectors of red, blue and green. Exposure of the film through...

lenticular screen

A rear or front projection screen composed of minute optical surfaces that introduce a spread to the light beam that conforms approximately to the light distribution requirements of the application.

lenticular stereo photography

A type of stereoscopic photography in which a pair of lenses focuses a pair of images, relative to the positions of the two eyes, onto film through a lenticular screen, which records the images as an...

leukocyte

Leukocytes, commonly known as white blood cells, are a crucial component of the immune system in vertebrates, including humans. These cells are responsible for defending the body against infections...

LFM

laser feedback microscope; lateral force microscope; longitudinal field modulator

lidar

Lidar, short for light detection and ranging, is a remote sensing technology that uses laser light to measure distances and generate precise, three-dimensional information about the shape and...

Liebmann effect

The visual perception of contrasting forms is more difficult if the forms have the same luminance but different chromaticities, than if the forms have the same chromaticity but different luminances.

light chopper -> optical chopper

A mechanical or electrical-electromagnetic device for periodically interrupting or blocking abeam of light for a brief known interval. The three most common chopper types include the tuning fork...

light diffusion

Light diffusion refers to the process by which light is scattered or spread out in various directions as it interacts with a medium or material. Unlike direct transmission through a transparent...

light fidelity

LiFi, short for light fidelity, is a wireless communication technology that utilizes visible light or infrared light to transmit data. Developed as an alternative or complementary technology to...

light field

The term light field refers to the spatial distribution of light rays traveling in all directions through a given space. It includes information about the intensity and direction of light rays at...

light filament

Phenomenon caused by an ultrashort and ultra-intense light pulse propagating in a Kerr medium, such as air or water. When the pulse's power exceeds the critical power (approximately 3 GW in air),...

light frame

The term for an image captured by a detector and from which a dark frame, bias frame and/or flat-field frame can be subtracted during image processing.

light pen

A handheld, light-sensitive device that is used with a display console to directly change, measure or erase the visual information presented. Interfaced with the computer that is generating the...

light sectioning

Technique for measuring the volume bulk of materials as they move along a conveyor with an accuracy of better than 1 percent. Based on the use of high-resolution arrays of solid-state detectors, the...

light sheet fluorescence microscopy

Also known as single plane illumination microscopy (SPIM), this process was designed for imaging of sensitive samples and fast biological processes in vivo. In this method, a light sheet illuminates...

light source efficiency -> luminous efficacy

Quotient of total luminous flux divided by total radiant flux; lumens per watt. (For a source, quotient of total luminous flux divided by lamp power input.)

light source power

The electrical power used to stimulate any light source. Power supplies may be step-up or step-down transformers; rectifiers to convert AC to DC; ammeters and voltmeters to observe the input to the...

light-activated silicon-controlled rectifier

A PN-PN device with incident light taking the place of gate current; three of the four semiconductor regions are available for circuit connections.

light-activated silicon-controlled switch

Similar to LASCR, except that all four regions are available.

light-emitting diode

An LED, or light emitting diode, is a semiconductor device that emits light when an electric current passes through it. LEDs are widely used in various applications due to their energy efficiency,...

lightguide -> fiber optic lightguide

A bundle of optical fibers arranged randomly for the purpose of transmitting energy, not an image.

line scan

Line scan refers to a method of capturing images or data by scanning a single line at a time, as opposed to capturing the entire image simultaneously. This technique is commonly used in various...

line source

In the spectral sense, an optical source that emits one or more spectrally narrow lines as opposed to a continuous spectrum. In the geometric sense, an optical source whose active (emitting) area...

line spectrum

A spectrum formed by radiation whose energy values of the property being measured cluster about at least one discrete value, as opposed to a continuous spectrum. The actual width of the spectral line...

line-scan camera

A line-scan camera, also known as a line-scan image sensor or linear array camera, is a type of digital camera designed to capture images one line or row of pixels at a time, rather than a full...

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