ISO 17901-2:2015

INTERNATIONAL ISO
STANDARD 17901-2
First edition
2015-07-01
Optics and photonics — Holography —
Part 2:
Methods for measurement of
hologram recording characteristics
Optique et photonique — Holographie —
Partie 2: Méthodes de mesurage des caractéristiques d’enregistrement
holographique
Reference number
ISO 17901-2:2015(E)
©
ISO 2015

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ISO 17901-2:2015(E)

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ISO 17901-2:2015(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 2
5 Principles . 2
6 Measurement methods . 3
6.1 General . 3
6.2 Definition of the Coordinate System. 4
6.3 Hologram recording environment . 4
6.4 Measurement device and apparatus . 4
6.5 Exposure characteristics curve measurement method for recording of the hologram . 6
6.6 Exposure at half-maximum measurement method for recording of the hologram . 6
6.7 Method to measure the R-value of the hologram . 7
6.8 Method to measure the amplitude of refractive index modulation of the hologram . 7
6.8.1 General. 7
6.8.2 Measurement using the transmission hologram . 8
6.8.3 Measurement using the reflection hologram . 8
7 Description of measurement results . 9
7.1 General . 9
7.2 Description of the information concerning the object to be measured . 9
7.3 Description of the measurement results on the exposure characteristics curve and
exposure at half-maximum for hologram recording . 9
7.4 Description of the R-value measurement result of the hologram . 9
7.5 Description of the measurement result of refractive index modulation of the hologram .10
Annex A (informative) Assembly procedure and stability confirmation of hologram
recording optical system based on double-beam interference .13
Annex B (informative) Hologram recording procedure .15
Annex C (informative) Relationship between the hologram and interference fringes due to
double-beam interference .16
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ISO 17901-2:2015(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 on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers
to Trade (TBT) see the following URL: Foreword - Supplementary information.
The committee responsible for this document is ISO/TC 172, Optics and Photonics, Subcommittee SC 9,
Electro-optical systems.
ISO 17901 consists of the following parts, under the general title Optics and photonics — Holography:
— Part 1: Methods of measuring diffraction efficiency and associated optical characteristics of holograms
— Part 2: Methods for measurement of hologram recording characteristics
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ISO 17901-2:2015(E)

Introduction
A hologram is an optical device utilizing interference and applied in numerous fields. In order to
know the exposure characteristics of materials on which the hologram is to be recorded, it is enough
to initially record the hologram under common conditions and subsequently establish the numeral
values representing exposure characteristics by measuring the diffraction efficiency. Though the
hologram-related terms and the measurement method of critical evaluation parameters (diffraction
efficiency, angular selectivity, wavelength selectivity) pertinent to optical characteristics are specified
in ISO 17901-1, there is no stipulation as to the conditions concerning hologram recording or the way to
calculate the numeral values. Therefore, the purpose of this part of ISO 17901 is to provide the terms
and measurement method concerning the hologram exposure characteristics. This part of ISO 17901
does not intend to restrict manufacturing process.
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INTERNATIONAL STANDARD ISO 17901-2:2015(E)
Optics and photonics — Holography —
Part 2:
Methods for measurement of hologram recording
characteristics
1 Scope
This part of ISO 17901 specifies the terms and measurement method concerning exposure characteristics
(exposure characteristic curve, exposure at half-maximum, R-value, amplitude of refractive index
modulation) for the hologram recorded by double-beam interference. The materials of hologram to be
measured are not restricted to any particular ones. This part of ISO 17901 does not intend to restrict
manufacturing process.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 15902, Optics and photonics — Diffractive optics — Vocabulary
ISO 17901-1:2015, Optics and photonics — Holography — Part 1: Methods of measuring diffraction efficiency
and associated optical characteristics of holograms
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 15902, ISO 17901-1, and the
following apply.
3.1
exposure
product of the laser beam irradiance and exposure time on the recording material surface, when the
hologram is to be recorded on the recording material
2
Note 1 to entry: Exposure is represented in Joules per square meter (J/m ) in the SI unit system, but may also be
2 2
expressed in micro-Joules per square centimetre (μJ/cm ) or milli-Joules per square centimetre (mJ/cm ).
Note 2 to entry: If the object wave or reference wave enters the detector obliquely in the course of the measurement
of the irradiance, the value of irradiance might not be measured correctly because of reflection on the surface of
the detector. In such an event, it is enough to allow the object wave or reference wave to enter the detector in an
approximately vertical direction to measure the radiant flux and then to divide the obtained value by the flux
sectional area on the recording material surface.
3.2
exposure characteristics curve
curve of measured values plotted with the exposure taken on the axis of abscissa and
the diffraction efficiency taken on the axis of ordinate, which indicate the characteristics of hologram
recording materials
Note 1 to entry: This curve is also called η -E characteristics curve.
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ISO 17901-2:2015(E)

3.3
exposure at half-maximum
smallest exposure that can achieve 50 % of the highest diffraction efficiency in the
exposure characteristics curve
Note 1 to entry: This term is a measure to indicate the sensitivity of the hologram recording material. The smaller
the exposure at half-maximum, the smaller the light quantity required for hologram recording.
3.4
R-value
diffraction efficiency of the hologram that has recorded the interference fringes of a certain spatial frequency
Note 1 to entry: For the spatial frequency of interference fringes, the value measured in air is used.
Note 2 to entry: This is an index to indicate the resolution of a recording material in terms of the fine detail
of the interference fringes identified spatially in the hologram. For the finer interference fringes, the recording
material that can achieve the high R-value (diffraction efficiency) can be the recording material that ensures the
high resolution in the hologram. For example, R (1000) is equal to 30 when the diffraction efficiency of hologram
recorded with the spatial frequency of interference fringes being 1 000 lines/mm is assumed to be 30 %.
3.5
spatial frequency
number of interference fringes per unit length
Note 1 to entry: This indicates the density of a periodic pattern of interference fringes and is expressed by the
number of interference fringes repeated per unit length (lines/mm). This is proportional to the reciprocal of the
spacing of interference fringes.
3.6
amplitude of refractive index modulation
amount of modulation of the refractive index and equivalent to the contrast of
interference fringes and the mean refractive index in the recording material of a phase hologram in which
the phase is modulated according to the difference in the refractive indices of the recording material.
Note 1 to entry: This is an index to indicate the phase modulation capacity of recording material and expressed
also in Δn.
4 Symbols and abbreviated terms
NA Numerical aperture of objective
λ Laser wavelength in air (μm)
η Diffraction efficiency (%)
T Thickness of hologram (μm)
θ’ Bragg diffraction angle (angle inside the hologram) (radian)
B
5 Principles
Holograms are recorded through mutual double-beam interference of plane waves. Examples of hologram
recording optical systems are shown in Figure 1. The measurement is made of the diffraction efficiency
of each hologram according to any one of measurement methods specified in ISO 17901-1:2015, 6.5. The
exposure characteristics curve, exposure at half-maximum, R-value, or amplitude of refractive index
modulation is derived from the relationship between the measured diffraction efficiency value and
exposure conditions.
To derive the exposure characteristics curve or exposure at half-maximum, multiple holograms
are recorded while changing the exposure and the diffraction efficiency is then measured for each
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ISO 17901-2:2015(E)

hologram. To derive the R-value, one or multiple holograms are recorded while adjusting the incident
angle of double beams in such a manner that the interference fringes with specific spatial frequency
are obtained and subsequently, the diffraction efficiency of each hologram is measured. To derive the
amplitude of refractive index modulation, the diffraction efficiency is measured according to any one
of measurement methods specified in ISO 17901-1:2015, 6.5. Finally, the amplitude of refractive index
modulation can be obtained from the Formula (2) or Formula (3) described in 6.8 to substitute values
of the wavelength of light used for the measurement of diffraction efficiency, volume of the hologram,
double-beam incident angle, mean refractive index of hologram, and the measured diffraction efficiency.
a) Transmission hologram b) Volume reflection hologram
Key
1 laser 7 mirror 2
2 objective 8 mirror 3
3 pinhole 9 hologram recording material
4 collimating lens 10 holder
5 mirror 11 reference wave
6 half mirror 12 object wave
Figure 1 — Example of optical arrangements for hologram recording
6 Measurement methods
6.1 General
The exposure characteristics (exposure characteristics curve, exposure at half-maximum, R-value, and
amplitude of refractive index modulation) as specified in this part of ISO 17901 are measured as follows
on the basis of the diffraction efficiency as specified in ISO 17901-1. It should be noted that, according to
this part of ISO 17901, the exposure characteristics during a hologram recording is derived by measuring
the diffractive efficiency of holograms recorded through double-beam interference of plane waves.
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ISO 17901-2:2015(E)

6.2 Definition of the Coordinate System
The axis of coordinate and the angle of wave are defined as follows.
a) The recording material (or hologram) plane shall be the xy-plane while the axis vertical to the plane
shall be the z-axis.
b) For the z-axis, the advance direction of the object (or reconstructed) wave shall be positive.
c) As shown in Figure 2, the angle of incidence, θ, is formed between the z-axis in positive direction and
the extension of the incident wave; the positive symbol indicates a counter-clockwise direction).
a) Wave advancing in the +z direction b) Wave advancing in the –z direction
Key
1 light wave
2 recording material or hologram
Figure 2 — How to establish the coordinate system and wave angle in measurement of exposure
characteristics of hologram
6.3 Hologram recording environment
Hologram recording shall be made inside a dark room at stable room temperature and humidity and
under conditions with thorough countermeasures against mechanical vibration and air turbulence.
For example, mechanical vibration can be prevented by mounting all of the equipment, including a laser,
on a vibration-isolation optical table. In order to prevent air disturbance, the whole optical table may
be enclosed in the plastic cover or blackout curtain to shut off the air flow from the air conditioner, etc.
When the laser is of either air-cooling or a water-cooling type, due care should be taken on air turbulence
or vibration generated from the laser itself.
6.4 Measurement device and apparatus
The optical system as shown in Figure 1 shows an example of an optical system that can be used for the
measurement of the exposure characteristics of hologram recording materials. This system consists of
the following components:
NOTE Refer to Annex A for the recommended assembly procedure and stability confirmation method for
the hologram recording optical system, Annex B for the hologram recording procedure, and Annex C for the
relationship between the spacing of hologram interference fringes of double-beam interference based hologram
and the incident angle of object (and reference) waves.
a) Laser
The laser should ensure high temporal stability of the output (for example, ±5 % or less in output
fluctuation over 30 min).
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ISO 17901-2:2015(E)

b) Objective
An adequate objective to be selected should be the one capable of expanding the beam diameter so
that the irradiance of the laser beam irradiating the collimating lens becomes approximately even
within the effective diameter of the collimating lens (for example, the magnification of ×10 to ×40).
c) Pinhole
The pinhole to be used should have the adequate hole diameter (for example, 5 approximately
25 μm) relative to the laser wavelength and the objective focal length.
NOTE The theoretical formula for the beam diameter, d, at the focal point of the objective is given by
Formula (1). The value twice as large as the value given by Formula (1) can be used as a rough standard for
the pinhole diameter.
44fλ λ
d=≈ (1)
πω π NA
where
f is the focal length of objective (µm);
2
ω is the beam diameter of incident light (the width at which the beam intensity becomes 1/e of
the maximum value (µm);
NA is the numerical aperture of objective.
d) Collimating lens
Lens as attached to the lens mount which has its spherical aberration corrected relative to the
wavelength of the laser to be used.
e) Mirror
The mirror should have a sufficiently high surface flatness (for example, better than the wavelength
level of about 1/10). The stage on which the mirror is to be mounted should be capable of fine motion
of rotation and tilting and is best achieved using a micrometre controlled mount.
f) Half-mirror
The half mirror should be capable of achieving the reflected light/transmitted light ratio of 1:1.
NOTE Such half-mirrors include, for example, those with multi-layer derivative or chromium coating,
those shaped like wedges with the wedge angle of 1 deg [=π/180 (rad) to avoid interference noise caused by
backside reflection, and those provided with the anti-reflection coating.
g) Test-piece holder
The holder should be capable of moving within a range approximately equal to the test piece size
while holding the hologram recording material. In this situation, the holder should have anti-
vibration characteristics.
Removal or attachment of recording materials has to be done in a dark room and therefore, the
holder should be configured to enable easy removal and attachment. For example, the holder may
be an edged metal frame of a size approximately equivalent to the test piece (a frame with a width
of about 10 mm, and matte-black coated), with the test piece clamped with leaves (clamps).
h) Detector
The detector should have a sufficient dynamic range and responsivity to the light intensity to be
measured and should have been calibrated.
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ISO 17901-2:2015(E)

6.5 Exposure characteristics curve measurement method for recording of the hologram
The exposure characteristics are defined by the exposure characteristics curve illustrated in Figure 3.
The exposure characteristics curve (a η-E characteristics curve representing the relationship between
the exposure and diffraction effects) is plotted as follows.
a) The wavelength of the light source and the incident angle of object and reference waves for a
hologram recording shall be determined as required. Using the optical system shown in Figure 1,
the processing specified for each recording material (development, bleach, etc.) shall be done for the
recording material that has been exposed under different exposure conditions.
b) The diffraction efficiency shall be measured according to any of the measurement methods specified
in ISO 17901-1:2015, 6.5.
The diffraction efficiency can be divided into several types and generally, the corresponding values
vary. Therefore, measurement of diffraction efficiency requires selection of the measurement method
appropriate to the object to be measured. For the volume reflection hologram, it is recommended to
use either the spectral transmission diffraction efficiency measurement or the spectral diffraction
efficiency measurement by reflectance according to ISO 17901-1:2015, 6.5.4 and 6.5.5, respectively.
c) To obtain the exposure characteristics curve, the measurement results shall be plotted by taking
2
the exposure (µJ/cm ) along the abscissa and the diffraction efficiency (%) along the ordinate.
Key
η diffraction efficiency in (%)
2
E exposure in (mJ/cm )
NOTE The curve showing a peak (left) and the curve asymptotic to the saturation value (right) are shown
above as typical examples.
Figure 3 — Example of exposure characteristics curve (η - E characteristics curve)
6.6 Exposure at half-maximum measurement method for recording of the hologram
2
For the exposure at half-maximum, the lowest exposure among those (µJ/cm ) equivalent to 1/2 of the
highest diffraction efficiency in the exposure characteristics curve (Figure 3) obtained according to 6.5
(or 1/2 of the diffraction efficiency assumed to be saturated) shall be read from the graph of Figure 4.
The smaller number means the smaller exposure required for hologram recording. The exposure at half-
maximum can be used as a measure to represent the sensitivity of the material for hologram recording.
It should be noted here that this exposure at half-maximum is simply a rough standard to determine the
exposure and is not necessarily the optimum exposure during hologram recording.
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ISO 17901-2:2015(E)

Key
η diffraction efficiency in (%) η highest diffraction efficiency
max
2
E exposure in (mJ/cm ) η /2 exposure at half maximum
max
Figure 4 — Typical exposure characteristics curve and the way of reading the exposure at half-
maximum
6.7 Method to measure the R-value of the hologram
The R-value is an index to indicate the resolution of the hologram material and is defined as follows.
a) The holograms shall be recorded by changing the incident angle, θ, of the collimated double-beam.
In the double beam transmission hologram case, it is assumed that the incident angle of the object
wave is θ and that of the reference wave is 2π − θ. In the double beam reflection hologram case, it is
assumed that the incident angle of the object wave is θ and that of reference wave is π.
The incident angle θ shall be set so that the spatial frequency of interference fringes in air (n = 1,0)
at the position of recording material becomes, for example, 500 lines/mm, 1 000 lines/mm,
2 000 lines/mm, 3 000 lines/mm, and 4 000 lines/mm (refer to Formula (C.4) for the transmission
type and Formula (C.8) for reflection type).
b) The diffraction efficiency of each hologram shall be measured according to any of the measurement
methods specified in ISO 17901-1:2015, 6.5.
c) The diffraction efficiency at each spatial frequency of, for example, 500 lines/mm, 1 000 lines/mm,
2 000 lines/mm, and 3 000 lines/mm, in air shall be assumed to be the R-value.
EXAMPLE Assuming that the diffraction efficiency when the transmission hologram of spatial frequency of
1 000 lines/mm in air is recorded to a certain recording material is 30 %, the R-value at the spatial frequency of
1 000 lines/mm is 30, which is represented as R (1 000) = 30.
6.8 Method to measure the amplitude of refractive index modulation of the hologram
6.8.1 General
The amplitude of refractive index modulation of volume phase holograms shall be derived from the
measurement of the diffraction efficiency of the transmission or reflection hologram. Formula (2) and
Formula (3) are applicable only to sinusoidal index modulation.
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ISO 17901-2:2015(E)

6.8.2 Measurement using the transmission hologram
The amplitude of refractive index modulation is measured using the transmission hologram as follows.
a) Using a collimated double-beam, the hologram shall be recorded while assuming the incident angle
of object wave as θ and the incident angle of reference wave as 2π − θ.
b) The highest diffraction efficiency value (or the diffraction efficiency value recognized for saturation)
shall be determined in the exposure characteristics curve (see Figure 3) derived in 6.5.
c) The amplitude of refractive index modulation (Δn) shall be calculated from Formula (2):
λ η
′
Δn= cosaθ rcsin (2)
B
πT 100
The value of arcsin shall be calculated in radians.
NOTE The relationship between the Bragg diffraction angle, θ’ , and double-beam incident angle, θ, can be
B
expressed as follows according to the Snell’s law:
sinθ
 
′
θ =arcsin
 
B
n
 
where
is the mean refractive index of hologram.
n
For the mean refractive index of hologram, it is recommended to use the value measured on the recorded
hologram. Since the correct measurement is not easy generally, the value calculated on the basis of
composition of materials of hologram may be used.
EXAMPLE The hologram is recorded using the 7 µm thick silver-halide photosensitive material with the
wavelength of 0,532 µm and θ = π/8 (radian) and the diffraction efficiency of 50 % were achieved. The amplitude
of refractive index modulation in this case is estimated to be Δn = 0,018 when n¯ is taken to be 1,63. Note that
this value represents the amplitude of refractive index modulation when the diffraction efficiency reaches 40 %
for the first time in an example of transmission hologram as shown in the left figure of Figure 3 concerning the
diffraction efficiency, exposure characteristics.
6.8.3 Measurement using the reflection hologram
The amplitude of refractive index modulation is measured using the reflection hologram as follows.
a) Using the collimated double-beam, the hologram shall be recorded while assuming the incident
angle of object and reference waves as 0 (radian) and π (radian) or θ (radian) and π − θ (radian),
respectively.
b) The exposure characteristics curve (see Figure 3) shall be plotted on the basis of the diffraction efficiency
measured according to ISO 17901-1:2015, 6.5.4. On this curve, the highest diffraction efficiency value
(or the value of diffraction efficiency that can be recognized as saturated) shall be determined.
c) The amplitude of refractive index modulation (Δn) shall be calculated from Formula (3):
1+ η/100
λ
′
Δn= coslθ ⋅ og (3)
B
2πT
1− η/100
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