A

Aberration – An optical aberration is when an image is distorted after passing through one or more optical components.

Absorption - When the energy of electromagnetic radiation is transferred to matter, often becoming thermal energy.

Achromatic Lens – A corrective lens that aims to reduce the effects of chromatic and spherical aberrations. The most common type of achromat is a doublet.
See also: Doublet Lens, chromatic abberrations

Anamorphic Prism Pair - Anamorphic Prism pairs are primarily used to correct the asymmetric beam shape of a Laser Diode from elliptical to near circular shape. This is done by expanding (or contracting) the beam in one direction only while the other direction remains unchanged.

Angle of Incidence (θ) –The angle between an incoming light ray and the normal (perpendicular) line of a medium,
See also: Snell’s Law, Angle of Reflection

Angle of Reflection – The angle between a reflected ray and normal (perpendicular) line.                          
See also: Angle of Incidence

Anodizing – An electrolytic method of controlled oxidation that adds a new finish to a metal surface. This is commonly done on aluminum to make it more corrosion resistant as well as lower reflectance. Many of Ealing’s opto-mechanics are anodized for this reason.

Anti-Reflection Coating – Applied to optical components to reduce reflection. Coating types are chosen based on the operating requirements of a particular component.

Aperture – A small opening through which light passes. The narrower the aperture, the more collimated the light must be to pass through. There are various types of apertures used in optics including slits, pinholes, and iris diaphragms.
See also: Collimate, Rectangular Aperture

Aspheric Lens - Aspheric lenses have at least one surface that is not a true sphere. The aspheric profile used is frequently a conic surface of revolution about the lens axis, matched in design to the shape of the second surface. The shape of this lens produces a dramatic reduction of the spherical aberration, even for very low f-numbers.

Attenuation – Electromagnetic waves can lose power, or become attenuated, by travelling through matter. Common forms of attenuation are absorption and scattering.
See also: Absorption

B

Back Focal Length (BFL) – The distance from the rear focal point to the optical surface.

Bandpass Filter – An optic that allows only a certain range of frequencies to be transmitted while attenuating others.

Band Stop Filter (Notch Filter) – An optic that allows most light to be transmitted will attenuating a small range of frequencies.

Bandwidth – A range of wavelengths in the optical spectrum. In the context of an optical filter, the bandwidth refers to the wavelengths that are can pass through the filter.

Beamsplitter – An optic that splits an incident beam of light into multiple beams of light.
A common cubic beamsplitter is made with two isosceles triangular prisms glued together creating a 45^o divide. An incoming light beam perpendicular to a face of the cube will be split into a beam of into parts that are transmitted through the interface and that which is not.

Beer Lambert Law – The relationship between transmittance (T) and optical depth (τ).

BiConcave Lens (Equi-Concave) - A symmetrical lens that is concave on both sides. It will cause incident light beams to diverge.

BiConvex Lens (Equi-Convex) - A lens that is convex on both sides. It focuses light by causing incident beams to converge.  

Brewster’s Angle – The angle at which light is completely transmitted through a surface without reflection.

Brewster Prism - Brewster Prisms are designed to have an apex angle such that a p-polarized ray incident at Brewster’s angle will pass through the prism parallel to the base at minimum deviation, and exit also at Brewster’s angle.

C

Chromatic Aberration - The presence of material dispersion causes the refractive index to vary with wavelength.
More Info
See also: Achromatic Lens

Coherent Light – Photons with the same frequency and phase.

Collimated – Electromagnetic waves propagating parallel to each other. Light can have varying levels of collimation.

Concave Lens – The surface of the lens curves inward.
See also: Bi-Concave

Convex Lens – The surface of the lens curves outward.
See also: Bi-Convex

Cutoff Wavelength (CWL) –Commonly used in the description of optical filters, the CWL is the wavelength corresponding to 50% of the maximum transmission.
Ealing Filters

D

Decibel – A logarithmic unit used to express ratio between power or intensity. In optics, decibels (dB) can be used to describe the power of electromagnetic waves. While dB are unitless, the power ratio can be referenced to 1 millaWatt (mW) with the unit dBm which allows values for EM waves to be expressed in short form.

Dichroic Filter – A type of bandpass filter tuned to allow only a small range of colors while reflecting others.

Diffraction – When a light ray is bent around a corner of an object or slit. This demonstrates the wavelike properties of light.

Diffraction Grating – An optic that splits a beam of light into several beams of different wavelength. It is commonly used to split white light into various colors.

Diffusion – Light being scattered and spread over a wide angle.

Distortion - Distortion is produced when the chief rays intersect the image surface at heights different from those predicted by the paraxial approximation.
More Info (pg 12)

Doublet Lens – Doublets are composed of two lenses. They typically incorporate one concave lens with high dispersion and one convex lens with low dispersion. Doublets are ideal for imaging applications.
See also: Achromatic Lens

Dove Prism - Dove Prisms are a truncated form of right angle prism. They use total internal reflection to produce an inverted image which emerges without any beam deviation. The main application for these prisms are as image rotators.

 

E

Electromagnetic Wave – A wave consisting of with orthogonal oscillating electric and magnetic fields. EM waves are able to propagate through vacuum, unlike sound waves, which require material to travel through. In a vacuum, EM waves travel at a speed of 3x10⁸ m/s. Depending on it’s wavelength, EM waves can be categorized as radio waves, microwaves, infrared, visible light, ultraviolet, X-rays or gamma rays.

Equilateral Prism -  Equilateral Prisms are used routinely as dispersing elements where spectral separation is required. They provide better brightness (lower stray light) than diffraction gratings. They also have greater power handling capabilities and avoid possible confusion when trying to interpret overlapping spectral orders.

 

F

Filter -  An optic that only allows certain frequencies to be transmitted while absorbing or rejecting others.

Focal Length- The distance between a lens and its focal point. 

Focal Point (also Focus): The point in which light rays passing through a lens converge.
See also: focal length

Frequency – The number of waves per period of time (often seconds). For light, the frequency (f) is equal to the speed of light (c) divided by wavelength (λ). 

f=c/ λ

G

H

HeNe Laser – This gas laser uses a medium composed of 10 parts Helium and 1 part Neon. It is typically constructed to emit red light at a wavelength of 632.8 nm.
Learn more about HeNe lasers with our HeNe Teaching Kit.

I

Illuminance – Luminous flux per surface area.

Index of Refraction (n) – A unitless value that describes how much light is refracted went entering a medium. The value of n is found by dividing the speed of light (c) by the speed of light in the particular medium (v).
The index of refraction in a vacuum (i.e. no refraction) is 1.0 and rises for more refractive mediums. For example, air has an index of refraction of 1.000277 while water has 1.3. This is why submerging a pencil part way into water reveals a disconnect at the edge of the two mediums.
See also: Refraction, Snell’s Law

J

K

Kinematic Mount – A optical mount with a frame or platform that is moveable by multiple fine-thread screws. This is alows for fine adjumsent of the optic's position.
See also: Kinematic Mirror Mounts,  Kinematic Prism/Beamsplitter Mount,  Kinematic Platform for Prisms and Beamsplitters

L

Lambertian Reflector – An ideal reflective surface with a luminance that is the same in all directions.

Laser – “Light Amplification by Stimulated Emission of Radiation.” Lasers emit coherent electromagnetic beams generated by stimulated emission.

Littrow Prism - They are normally used in a laser cavity or prism spectrometer to select a particular wavelength. In general, the beam is incident on the hypotenuse and is reflected back from the rear surface. It exits from the hypotenuse dispersed into its constituent wavelength components. Tuning is accomplished by tilting.

Longpass Filter – An optic that only allows higher light frequencies to pass while rejecting lower frequencies.

Luminous Flux – The measure of the power of light adjusted with respect the sensititvity of human eyes to certail wavelengths.
See also: Illuminance

Lux – The SI united of illuminance.

M

Meniscus Lens – Characterized by one concave and one convex side. This type of lens is commonly used in corrective eyewear. Meniscus lenses can either be converging or diverging depending on their relative curviture.

Monochromatic – Consisting of one color.

 

N

Neutral Density Filter - Filters that are used to control the intensity level without affecting the spectral response of the system.

Near Infrared (NIR) – The part of the electromagnetic spectrum ranging from approximately 700 to 2500 nm.

Noise – Unwanted electromagnetic waves existing alongside the desired signal.

 

O

Optical Fiber – A fiber that employs the rules of total internal reflection to transmit light. Fiber optic cables can transmit more data at long distances than copper wire cables.

 

P

Paraxial Ray – A light ray that is sufficiently close to the axis of an optical setup. The following approximations can be made for the angle (θ) between the ray and optical axis

Sinθ ≈ θ           Tanθ ≈ θ            Cosθ ≈ 1

Where θ is in radians
More info on Paraxial Optics

Peak Transmittance – The highest ratio of radiant energy that is able to pass through an optic.
See also: Transmittance, Beer-Lamber Law

Pellicle Beamsplitter - These beamsplitters are ideally suited to high-energy laser sampling, interferometry, and theodolite alignment applications.

Penta Prism – A 5-sided prism that deviates an incident beam through 90° without inverting or reversing it.
See Image here

Photodiode – A semiconductor that converts photons into electrical current. Photodiodes are traditionally used in solar cells.

Plano-Concave – A concave lens with one flat side.

Plano-Convex – A convex lens with one flat side.

Plate Beamsplitter - These thin film beamsplitters are designed to work at 45 degrees incidence and to provide an equal split between the transmitted and reflected beams.

Polarizer – An optical filter that only allows a certain direction of polarized light to pass through it.
See also Sheet Polarizer, Laser Polarizer

Power (Optics) - Optical power is the measure of how much an optical component diverges or converges incoming light. Power is related to focal length by the equation.

P=1/f

Prism – Prisms are blocks of optical material having flat polished faces. They have no optical power and cannot act on a beam to form images. They can, however, be used to change an incident beam, which may or may not be carrying image information, in one of five ways: Inversion, Reversion, Deviation, Displacement, or Dipsersion.

Q

 

R

Reflection – A light wave is reflected when it reaches a new medium but returns to the medium from which it came. The law of reflection dictates that the angle with respect to normal is the same for incoming light as it is for the reflected light. 

Refraction – The bending of an electromagnetic wave as it passes between mediums.
See also: Index of Refraction, Snell’s Law

Resolutions – For an optical system, the resolution is the amount of detail that is resolved for the object being imaged.

Retardance – The amount of phase shift in incoming polarized light.
See also: waveplate

Right Angle Prism - A Right Angle Prism is used to turn or deflect a beam through 90° or 180°. In either case this is achieved by total internal reflection and produces a very efficient broadband reflector.
Images: 90°, 180°

 

S

Shortpass Filter – An optic that transmits the wavelengths short of cut-off while attenuating the longer wavelengths.

Seidel Aberrations - The most important aberrations in the majority of  applications are the Seidel (also known as Primary or Third order) aberrations. These are the first aberrations to have an impact on the image quality as the aperture and field angles are increased beyond the point at which the paraxial approximation ceases to remain accurate.
More Info
See also: Distortion

Signal-to-Noise Ratio: The ration between the amount of desired light in a signal to the amount of light noise. 

Snell’s Law – A formula relating the index of refraction and angle of incidence (θ) of two mediums. n₁/n₂ = sin(θ₂)/sin(θ₁). Snell’s law can be used to calculate how much light will refract when entering a new substance.

Stimulated Emission – A photon can interact with an atom’s electron to bring it from an excited state to the ground state. This results in the release of energy as a new photon with the same frequency as the incident photon.

Surface Quality - The quality of a lens uses scratch/dig numbers based on standards established by the U.S. Military. The lower the scratch & dig, the higher quality the optic surface is.

 

T

Transmittance – A measure of the amount of light energy that is able to pass through an optical component.  It is often given as a percentage of the total incoming light. Transmittance can be lowered due to scattering, absorption, and/or reflection.

Triplet Lens - An optical component consisting of 3 lenses combined to overcome optical aberrations.

 

U

Ultraviolet - An electromagnetic wave ranging from approximately 400 nm to 100 nm.

Unpolarized – Light that consists of rays with inconsistent polarizations patterns.

 

V

Visible Light (VIS) - An electromagnetic wave ranging from approximately 390 to 700 nm. This contains the colors that can be seen by the human eye.

 

W

Wavelength – The distance at which a wave repeats. This can be the distance between two wave peaks, for example.
See also: frequency

Waveplate (Retarder): An optic that alters the polarization of a light wave that passes through it.
Half Waveplate  - shifts direction of linearly polarized light
Quarter Waveplate – converts linear polarized light to circularly polarized light
See also: Retardance

X

X-Ray – An electromagnetic wave ranging from approximately 0.01 to 10 nanometers. X-rays have a shorter wavelength compared to visible light, which means they also have a higher energy.