ISO 18115-3:2022

INTERNATIONAL ISO
STANDARD 18115-3
First edition
2022-06
Surface chemical analysis —
Vocabulary —
Part 3:
Terms used in optical interface
analysis
Analyse chimique des surfaces — Vocabulaire —
Partie 3: Termes utilisés dans l'analyse des interfaces optiques
Reference number
ISO 18115-3:2022(E)
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ISO 18115-3:2022(E)
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Published in Switzerland
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ISO 18115-3:2022(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
3.1 General terms . 1
3.2 Terms related to properties of light. 5
3.3 Terms related to optical properties due to interactions with media . .12
3.4 Terms related to ellipsometry . 18
3.5 Terms related to Raman spectroscopy . 20
3.6 Terms related to nonlinear optical technique terms . 25
Bibliography .31
Index .33
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ISO 18115-3:2022(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 201, Surface chemical analysis,
Subcommittee SC 1, Terminology.
A list of all parts in the ISO 18115 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
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ISO 18115-3:2022(E)
Introduction
Optical spectroscopies and surface chemical analysis, in general, are important areas which involve
interactions between people with different backgrounds and from different fields. Those conducting
optical spectroscopy on surfaces can be materials scientists, chemists, physicists or biologists and
might have a background that is primarily experimental or primarily theoretical. Those making use of
the data and results extend beyond this group into other disciplines.
ISO 18115-1 extend from the techniques of electron spectroscopy and mass spectrometry to general
spectrometry terms and X-ray analysis. The terms covered in ISO 18115-2 relate to scanning-probe
microscopy.
This document covers terms used in optical spectroscopies. This includes terms related to general
terms, properties of light and optical properties of materials. In terms of techniques, there is a focus on
terms related to Raman spectroscopy, ellipsometry and nonlinear optical techniques.
The wide range of disciplines and the individualities of national usages have led to different meanings
being attributed to particular terms and, again, different terms being used to describe the same concept.
To avoid the consequent misunderstandings and to facilitate the exchange of information, it is essential
to clarify the concepts, to establish the correct terms for use, and to establish their definitions.
The terms are given in alphabetical order, classified under 3.1 general terms, 3.2 properties of light,
3.3 optical properties of materials, 3.4 ellipsometry terms, 3.5 Raman spectroscopy terms and 3.6
nonlinear optical technique terms. The terms in each clause are not always mutually exclusive and
some terms placed in one clause can equally belong in another.
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INTERNATIONAL STANDARD ISO 18115-3:2022(E)
Surface chemical analysis — Vocabulary —
Part 3:
Terms used in optical interface analysis
1 Scope
This document defines terms for surface chemical analysis in the area of optical interface analysis
including ellipsometry, Raman spectroscopy and nonlinear optical techniques as well as general optical
terms.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1 General terms
3.1.1
background signal
signal present at a particular position, energy, mass or wavelength due to processes or sources other
than those of primary interest
3.1.2
CCD detector
semiconductor device that converts light into an electrical signal
Note 1 to entry: When a photon is absorbed by the detector, a single electron is released. Electrodes covering
the chip surface hold these electrons in place in an array of wells, or pixels, such that during exposure to light, a
pattern of charge builds up that corresponds to the pattern of light.
3.1.3
compensator
retardation plate of fixed or variable optical path length difference used for introducing a light path
difference between two beams or to compensate the optical path length that can cause unwanted
dispersion or time-delay
Note 1 to entry: See also retardation plate/wave plate (3.1.34).
[SOURCE: ISO 10934:2020, 3.1.27, adapted]
3.1.4
confocal optical microscopy
optical microscopy in which, light is suppressed from out-of-focus planes using one or more pinholes
such that only light from a confocal volume is detected
Note 1 to entry: An image of an extended area is formed via scanning.
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ISO 18115-3:2022(E)
Note 2 to entry: The confocal principle leads to improved contrast and axial resolution by suppression of light
from out-of-focus planes.
3.1.5
confocal volume
effective volume that is in focus around a point in the object which gives rise to the detected signal or
image in confocal microscopy
[SOURCE: ISO 10934:2020, 3.3.10.8, modified — The phrase “detected signal or” has been added.]
3.1.6
depth of field
region where the sharpness of the edges of the images reaches a pre-set optimum
[SOURCE: ISO 26824:2013, 8.16, modified — "the" has been replaced by "a" prior to "pre-set optimum".]
3.1.7
depth of focus
axial depth of the space on both sides of the focal plane, within which the image or signal appears
acceptably sharp, while the positions of the object plane and of the objective are maintained
Note 1 to entry: The method to determine when the image or signal is acceptably sharp depends on the microscopy
or spectroscopy method. For example, in confocal Raman microscopy, the depth of focus can be determined as
2
when the signal does not decrease by more than 87 % (1/e ) compared to the maximum signal exactly at the
object position.
[SOURCE: ISO 19262:2015, 3.68, modified — Note 1 to entry has been added.]
3.1.8
diffraction grating
set of regularly repeating structures which, when illuminated, produce, by reflection or transmission,
maxima and minima of intensity as a consequence of interference
Note 1 to entry: These maxima and minima vary in position according to wavelength. Radiation of any given
wavelength may thus be selected from interference pattern allowing the grating to be used for producing
monochromatic light.
[SOURCE: ISO 10934:2020(en), 3.1.42, modified — "diffraction" has been deleted as a consequence and
Note 1 has been reworded slightly.]
3.1.9
dipole moment
vector quantity describing the separation of electric charges where the direction is from negative to
positive charge
Note 1 to entry: When an atom or molecule interacts with an electromagnetic wave, it can undergo a transition
from an initial to a final state of energy difference through the coupling of the electromagnetic field to the
transition dipole moment. When this transition is from a lower energy state to a higher energy state, this results
in the absorption of a photon. A transition from a higher energy state to a lower energy state results in the
emission of a photon.
3.1.10
edge filter
optical filter that rejects light above or below a specific wavelength but transmits light outside that
criterion
Note 1 to entry: Depending on whether the transmitted part contains the longer or shorter wavelengths, the
edge filter is called a long wave pass (LWP) or a short-wave pass (SWP) filter, respectively.
Note 2 to entry: In Raman spectroscopy, an edge filter is used to reject Rayleigh scattering (3.3.38) but permit
measurement of either Stokes (3.5.25) or anti-Stokes (3.5.1) Raman scattering.
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Note 3 to entry: In reality, edge filters have a narrow transition width. Edge filters with a very narrow transition
width are also available and are known as razor edge filters.
3.1.11
fluorophore
molecular entity that emits fluorescent light when excited by a specific range of wavelengths of light
3.1.12
goniometer
instrument that either measures an angle or allows an object to be rotated to a precise angular position
3.1.13
half-wave plate
half-wave compensator
optical device which alters the polarization state of light travelling through the device by π
3.1.14
Jones matrix
two by two matrix that is used to represent the operation of an optical element such as a polarizer on
the polarization state of light
Note 1 to entry: Fully polarized light is represented by a Jones vector (3.2.17).
3.1.15
lock in amplifier
type of amplifier that extracts a signal from a complex waveform at the same frequency as that of a
second carrier wave
3.1.16
monochromator
optical device that transmits a light beam with a certain wavelength within a wider range of
wavelengths available at the input
Note 1 to entry: The bandwidth is defined by the spectral purity (3.1.33)
3.1.17
neutral density filter
filter having uniform absorption throughout the range from near ultraviolet to near infrared radiation,
thus reducing the light intensity without altering spectral distribution
[SOURCE: ISO 6196-6:1992, 06.01.13]
3.1.18
notch filter
optical filter that attenuates light with a specific narrow frequency range while passing all other
frequencies unalterated
Note 1 to entry: In Raman spectroscopy, a narrow notch is used to reject Rayleigh scattering (3.3.38) but permit
measurement of both Stokes (3.5.25) and anti-Stokes Raman scattering (3.5.1).
3.1.19
numerical aperture
NA
product of the refractive index of the medium in which the lens is working, n, and the sine of one-half of
the angular aperture of the lens, θ
Note 1 to entry: The numerical aperture is given by NA = nsinθ, where 2θ is the full angular aperture of the lens.
[SOURCE: ISO 18115-2:2021, 5.93, modified — Note 2 has been deleted.]
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ISO 18115-3:2022(E)
3.1.20
objective lens
combination of several lenses in a common mounting which, together with the focusing lens, projects a
real reversed image of the object in the image plane
[SOURCE: ISO 9849:2017, 3.2.20]
3.1.21
optical modulator
optical device that imposes modulation on a light beam
Note 1 to entry: This modulation can be for example in phase, frequency or amplitude.
Note 2 to entry: Examples include electro-optical modulator or photo acoustical modulator.
3.1.22
peak height
distance between the peak maximum and the background
Note 1 to entry: The method used to determine the background should be carefully considered and specified.
[SOURCE: ISO 7941:1988, 4.3.2, modified — Reworded slightly.]
3.1.23
peak shape
form of a spectral feature that can typically be described by a mathematical function and parameters
such as spectral position, height, and width
Note 1 to entry: Examples of the mathematical function include Gaussian, Lorentzian, PearsonVII and Voigt
functions.
3.1.24
peak width
width of a peak at a defined fraction of the peak height
Note 1 to entry: Any background subtraction method used should be specified.
Note 2 to entry: The most common measure of peak width is the full width of the peak at half maximum (FWHM)
intensity.
Note 3 to entry: For asymmetrical peaks, convenient measures of peak width are the half-widths of each side
of the peak at half maximum intensity. Other parameters that can be measured are skewness, the amount and
direction of skew or departure from horizontal symmetry and kurtosis which is a measure of how tall and sharp
a peak is.
3.1.25
photobleaching
loss of optical fluorescence (3.2.15) in a fluorescent molecule due to overexposure with irradiating light
3.1.26
photodetector
device that converts light into an electrical signal
Note 1 to entry: Examples include photodiode, photomultiplier, CCD and CMOS.
3.1.27
photomultiplier tubes
photomultipliers
PMTs
electronic device for amplifying and converting light pulses into measurable electrical signals
Note 1 to entry: They can be used for the collection of, for example, confocal Raman, CARS (3.5.3), two photon
fluorescence, TPEF (two photon excitation fluorescence) (3.2.46) and second harmonic generation (3.6.27).
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ISO 18115-3:2022(E)
[SOURCE: ISO 772:2011(en), 1.163, modified — Note 1 has been added.]
3.1.28
polarizer
material which only transmits the component of a light wave which is oscillating in a particular
direction
[SOURCE: ISO 23713:2005, 3.2, modified]
3.1.29
quarter-wave plate
optical device which changes the polarization state of light travelling through the device by π/2
3.1.30
selection rules
set of restrictions governing the allowedness of transitions of a system from one quantum state to
another
Note 1 to entry: The selection rules may differ according to the technique used to observe the transition for
example between infrared spectroscopy and Raman spectroscopy.
3.1.31
silicon diode detector
photodiode that converts the light into electrical current
Note 1 to entry: These types of detectors can be used for SRS (3.5.24) and it is a type of photodetector (3.1.26).
3.1.32
solid angle
2
Ω = A/r
where
A is the area of the included surface of a sphere in a cone with its apex at the centre of the sphere;
r is the radius of the sphere
Note 1 to entry: The solid angle is the three-dimensional angle, e.g. the cone of light from a point source.
Note 2 to entry: Solid angles are expressed in steradians (sr).
[SOURCE: ISO 80000-3:2006, 3-6 and notes adapted from ISO 4007:2018, 3.4.13
3.1.33
spectral purity
indication of the monochromaticity of a given light sample
3.1.34
wave plate
retardation plate
optical device generally consisting of a piece, or pieces, of optically anisotropic material with plane
faces, to produce a specific polarization state change of the light when travelling through the device
Note 1 to entry: Waveplates are constructed out of a birefringent material (for example quartz, mica, or certain
polymers), for which the index of refraction is different for light linearly polarized along one or the other of two
certain perpendicular crystal axes.
3.2 Terms related to properties of light
3.2.1
airy disc
central spot of light in the diffraction pattern of a point light source
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ISO 18115-3:2022(E)
3.2.2
bandwidth
range of frequencies within a given band
Note 1 to entry: A common way to calculate bandwidth is to use the full width at half maximum. It is typically
measured in hertz.
3.2.3
beam diameter
diameter of an electromagnetic beam along any specified line that is perpendicular to the beam axis
and intersects it.
Note 1 to entry: The beam diameter can be defined in several ways, such as full-width at half-maximum (FWHM),
2
1/e, 1/e or 4σ based on the measured intensity as a function of lateral distance.
Note 2 to entry: This usually refers to a beam of circular cross section, but not necessarily so it can be, for
example, elliptical in which case the orientation of the major and minor axis needs to be specified.
3.2.4
beam divergence
angular measure of the increase in beam diameter or radius with distance from the optical aperture or
antenna aperture from which the beam emerges
Note 1 to entry: As the wavevector, k (3.2.49) is a vector it is dependent on both the spectral purity and angular
divergence of a source.
3.2.5
candela
luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency
12
540 × 10 hertz and that has a radiant intensity in that direction of 1/683 W per steradian (a unit of
solid angle)
Note 1 to entry: Candela (cd) is the unit of luminous intensity in the International System of Units (SI).
3.2.6
chromaticity
property of a colour stimulus defined by its chromaticity coordinates, or by its dominant or
complementary wavelength and purity taken together
Note 1 to entry: Chromaticity coordinates specifies a colour regardless of its luminance.
[SOURCE: ISO 9241-302:2008(en), 3.3.9, modified — Note 1 to entry has been added.]
3.2.7
circular polarization
polarization state in which, at each point, the electric field of the wave has a constant magnitude, but its
direction rotates with time at a steady rate in a plane perpendicular to the direction of the wave
Note 1 to entry: Circularly polarized light can be produced by passing linearly polarized light through a quarter-
wave plate at an angle of 45° to the optical axis of the plate.
Note 2 to entry: As the electric field can rotate clockwise or anti-clockwise as it propagates, circularly polarized
waves exhibit chirality.
3.2.8
coherence
characteristic of a beam of electromagnetic radiation where there is a deterministic (not random) phase
relationship between each pair of points in the beam
Note 1 to entry: There are two types of coherence; spatial coherence (3.2.40) and temporal coherence (3.2.45)
[SOURCE: ISO 11145:2018, 3.11.1, modified — Note 1 has been added.]
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ISO 18115-3:2022(E)
3.2.9
coherence length
propagation distance in a dispersive medium over which an electromagnetic wave maintains a specified
degree of coherence
Note 1 to entry: Practically, it is used for quantifying the degree of temporal coherence (3.2.45) as the propagation
length (and thus propagation time) over which coherence degrades significantly.
3.2.10
colour temperature
temperature of a Planckian radiator whose radiation has the same chromaticity as that of a given
stimulus
[SOURCE: ISO 9241-6:1999, 3.5]
3.2.11
depolarization
act of randomizing the polarization of an electromagnetic wave
Note 1 to entry: A depolarizer is the device used to depolarise light regardless of the input wave. In reality a
depolariser will produce a pseudo-random output.
3.2.12
diffraction limit
maximum spatial resolution achievable for an optical system, governed by diffraction phenomena
Note 1 to entry: The Abbe diffraction limit, is defined as λ/ (2 NA) in which λ is the wavelength of the illuminating
light and NA is the numerical aperture (3.1.19).
3.2.13
elliptical polarization
polarization state in which, the electric field vector describes an ellipse in any fixed plane intersecting,
and normal to, the direction of propagation
Note 1 to entry: An elliptically polarized wave may be resolved into two linearly polarized waves in phase
quadrature, with their polarization planes at right angles to each other. Circular and linear polarization can be
considered to be special cases of elliptical polarization.
Note 2 to entry: As the electric field can rotate clockwise or anti-clockwise as it propagates, elliptically polarized
waves exhibit chirality.
3.2.14
extinction coefficient
imaginary part of a complex refractive index of a material which describes the amount of attenuation
when the electromagnetic wave propagates through the material
3.2.15
fluorescence
phenomenon in which absorption of light of a given frequency by a substance is followed by the emission
of light at a lower frequency (longer wavelength) from the excited states with the same degeneracy
Note 1 to entry: Generally, the emission is from singlet excited state to singlet ground state.
Note 2 to entry: In the case of multiphoton fluorescence, the emitted light may be of a shorter wavelength.
3.2.16
frequency
reciprocal of the period
Note 1 to entry: The unit of frequency is the hertz (Hz), which corresponds to one cycle of periodic motion per
second.
[SOURCE: ISO 2041:2018, 3.3.33]
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ISO 18115-3:2022(E)
3.2.17
Jones vector
two by one matrix that describes the polarization state of light where the two parts represent the
amplitude and phase of the electric field in the x and y directions
Note 1 to entry: An optical element is represented by a Jones matrix (3.1.14).
3.2.18
irradiance
power of electromagnetic radiation incident on a surface per unit surface area
−2
Note 1 to entry: The SI unit is watt per square metre (Wm ).
Note 2 to entry: This can also be expressed as the incident flux per area incident on a given surface.
[SOURCE: ISO 29464:2017, 3.6.7, modified — Note 1 has been modified. Note 2 to entry has been added.]
3.2.19
linear polarization
plane polarization
polarization state in which, the electric field vector is confined to a given plane along the direction of
propagation
Note 1 to entry: The two orthogonal linear polarization states that are most important for reflection and
transmission are referred to as p- and s-polarization.
3.2.20
lumen
SI derived unit of luminous flux (3.2.22), whereby one lumen is the luminous flux emitted within a unit
solid angle (one steradian) by a point source having a uniform luminous intensity of one candela
Note 1 to entry: If a light source that emits one candela of luminous intensity uniformly across a solid angle of one
steradian, the total luminous flux emitted into that angle is one lumen (1 cd·1 sr = 1 lm).
Note 2 to entry: Lumen (symbol: lm) is the SI derived unit of luminous flux, a measure of the total quantity of
visible light emitted by a source.
3.2.21
luminescence
emission, of optical radiation by atoms, molecules or ions in a material, which for certain wavelengths
or regions of the spectrum is in excess of the radiation due to thermal emission from that material at the
same temperature, as a result of these particles being excited by energy other than thermal agitation
[SOURCE: IEC 60050 845:1987, 04-18, modified — Reordered the text of the definition.]
3.2.22
luminous flux
quantity derived from the radiant flux, by evaluating the radiation in accordance with its action upon
the CIE standard photometric observer
[SOURCE: ISO 4007:2018,3.4.4]
3.2.23
luminous intensity
quantity of visible light that is emitted in unit time per unit solid angle
Note 1 to entry: The candela (one of the SI base units, abbreviation cd), is the unit of luminous intensity.
Note 2 to entry: The unit for the quantity of light flowing from a source in any one second (the luminous power, or
luminous flux) is called the lumen.
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ISO 18115-3:2022(E)
3.2.24
monochromatic radiation
radiation consisting of only a single wavelength, or of only a very narrow band of wavelengths of which
the central wavelength is quoted
[SOURCE: ISO 10934:2020, 3.1.123.2]
3.2.25
optical constants
quantities that describe the optical behaviour of a substance for a specified wavelength
Note 1 to entry: Typical properties are refractive index (3.3.43), absorption coefficient (3.3.1), or reflectivity
(3.3.41).
3.2.26
period
smallest interval of time for which a periodic function repeats itself
Note 1 to entry: If no ambiguity is likely, the fundamental period is called the period.
[SOURCE: ISO 2041:2018, 3.3.32]
3.2.27
phosphorescence
photoluminescence (3.2.28) delayed by storage of energy in an intermediate energy level
Note 1 to entry: The emission is generally from triplet excited state to singlet ground state.
[SOURCE: ISO 17724:2003, 53]
3.2.28
photoluminescence
luminescence (3.2.21) caused by absorption of optical radiation
[SOURCE: IEC 60050 845:1987, 04-19]
3.2.29
photometry
method for the measurement of light, in terms of electromagnetic radiation weighted by the human
eye's response
Note 1 to entry: This response changes with wavelength, and to an extent, from person to person. Internationally
agreed standard observer functions are therefore used in order to provide a consistent measurement base for
photometry.
Note 2 to entry: The word 'luminous' is used to indicate that measurements have been made using a detection
system (called a photometer) that has a spectral response similar to that of a human eye.
3.2.30
photon
particle representing a quantum of light or other electromagnetic radiation that carries energy
proportional to the radiation frequency, has zero rest mass and travels at the speed of light in a vacuum
3.2.31
polarizability
ratio of induced dipole moment of a material to the electric field that induces it
Note 1 to entry: Polarizability is a measure of how easily an electron cloud is distorted by an electric field.
2 −1
Note 2 to entry: The SI units of polarizability are C m V .
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