ISO/TR 16743:2013
(Main)Optics and photonics — Wavefront sensors for characterising optical systems and optical components
Optics and photonics — Wavefront sensors for characterising optical systems and optical components
ISO/TR 16743:2013 gives terms and definitions and describes techniques for the characterization of wavefronts influenced by optical systems and optical components. It describes basic configurations for a variety of wavefront sensing systems and discusses the usefulness of tests in different situations.
Optique et photonique — Capteurs de front d'onde pour caractérisation des systèmes optiques et des composants optiques
General Information
Standards Content (Sample)
TECHNICAL ISO/TR
REPORT 16743
First edition
2013-03-15
Optics and photonics — Wavefront
sensors for characterising optical
systems and optical components
Optique et photonique — Capteurs de front d’onde pour
caractérisation des systèmes optiques et des composants optiques
Reference number
©
ISO 2013
© ISO 2013
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ii © ISO 2013 – All rights reserved
Contents Page
Foreword .iv
1 Scope . 1
2 Introduction to wavefront sensing techniques . 1
3 Foucault knife-edge test . 2
3.1 The knife-edge test . 2
3.2 Variations on the knife-edge test . 3
3.3 Application of knife-edge test to diode lasers . 3
3.4 The pyramid sensor . 3
4 Screen testing . 4
4.1 General . 4
4.2 Hartmann test . 4
4.3 The development of automated wavefront sensing . 5
4.4 Shack-Hartmann test . 6
4.5 Measurements with a Shack-Hartmann sensor . 7
5 Wavefront curvature sensors . 8
5.1 General . 8
5.2 Wavefront curvature sensing and phase diversity techniques . 8
5.3 Phase diversity wavefront sensor with diffraction grating . 9
6 Wavefront sensing by interferometry .10
6.1 General .10
6.2 Self-referencing interferometry .11
6.3 Electronic detection and phase measurement .12
6.4 Shearing interferometry .12
6.5 Point-diffraction interferometers with error-free reference wavefronts .17
6.6 Lateral shearing and the Ronchi test .20
6.7 Lateral shearing with a double frequency grating .21
7 Summary of wavefront sensing methods .22
Bibliography .25
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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International
Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies
casting a vote.
In exceptional circumstances, when a technical committee has collected data of a different kind from
that which is normally published as an International Standard (“state of the art”, for example), it may
decide by a simple majority vote of its participating members to publish a Technical Report. A Technical
Report is entirely informative in nature and does not have to be reviewed until the data it provides are
considered to be no longer valid or useful.
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.
ISO/TR 16743 was prepared by Technical Committee ISO/TC 172, Optics and photonics, Subcommittee
SC 1, Fundamental standards.
iv © ISO 2013 – All rights reserved
TECHNICAL REPORT ISO/TR 16743:2013(E)
Optics and photonics — Wavefront sensors for
characterising optical systems and optical components
1 Scope
This Technical Report gives terms and definitions and describes techniques for the characterization of
wavefronts influenced by optical systems and optical components. It describes basic configurations for
a variety of wavefront sensing systems and discusses the usefulness of tests in different situations.
The aim is to cover practical instruments and techniques for measuring the wavefronts produced by
optical systems and optical components. This Technical Report includes various implementations of
the Hartmann method, the curvature sensor and applications of the knife-edge method. The use of
interferometers is discussed. This Technical Report also includes techniques such as phase diversity
and pyramid sensors, currently used in astronomy and being developed for other areas.
NOTE More information on interferometry can be found in ISO/TR 14999-1, ISO/TR 14999−2 and
ISO/TR 14999−3.
This Technical Report explains briefly how these techniques work and includes diagrams illustrating
the use of this type of equipment for making the measurements required for ISO 10110-5, ISO 10110-8,
ISO 10110-12 (slope requirements) and ISO 10110-14.
2 Introduction to wavefront sensing techniques
Interferometry is a well-established technique for comparing a test wavefront with a reference
wavefront, usually spherical or planar, and requires a degree of coherence between the two wavefronts
to produce an interference pattern. Some interferometers for wavefront characterization are self-
referencing, such as shearing interferometers. These reveal the slope of the wavefront at various points
with values deduced from the interferogram and integrated to calculate the phase profile.
More recently non-interferometric techniques have been developed, partly driven by the needs of
adaptive optics, and it is possible to apply these to wavefronts with limited coherence. The majority of
these techniques are based on measuring the wavefront slope values.
Many of the non-interferometric techniques can be categorized as screen tests. A screen test is a general
term for the test of a beam with an opaque plate placed or moved in the focusing beam and the irradiance
pattern transmitted by the opaque plate analysed. The screen may have one or more holes, slits or edges
to transmit part of the beam while blocking with the opaque part.
Non-interferometric techniques include focused waist (image of source) measurements and wavefront
sampling which gives slope measurements. The knife-edge is a simple test that isolates regions of the
wavefront to reveal aberrations. The Hartmann test uses a perforated screen to isolate bundles of rays
and the direction of these bundles is measured to calculate the wavefront slopes. The Shack-Hartmann
test uses an array of small lenses to sample the wavefront. The wavefront slopes are deduced from the
positions of the focal spots generated by the lens array and the slope values are integrated to calculate
the phase profile.
Wavefront curvature sensing and phase diversity techniques are a class of wavefront retrieval
mechanisms that infer the wavefront from measurements of the intensity of the light as the beam
propagates. Typically this involves the measurement of two images along the beam path, from which
the intensity gradient is derived. Two standard approaches are to measure the intensity either side of
a focus or either side of a pupil plane in an optical system. Phase diversity techniques use calculation
algorithms for the retrieval of wavefront phase. Once the intensity data are collected, a processing step
is required to calculate the wavefront. This can be achieved using the intensity transport equation,
[11]
and solved by direct integration or iteratively using Fourier transform techniques. Phase diversity
methods are finding more use with faster phase retrieval methods as computation speeds increase.
3 Foucault knife-edge test
3.1 The knife-edge test
a) Test set-up
b) typical intensity pattern seen by observer
Key
1 mirror
2 knife-edge
3 source
Figure 1 — Knife-edge test for wavefront from a concave mirror
The knife-edge test is one of a family of techniques in which elements of a deformed wavefront are detected
by blocking with an opaque mask that has an edge that clearly defines the boundary between the opaque
and transmitting regions of the mask. The mask is placed in the plane of best focus of the wavefront.
The knife-edge test was reported by Foucault in 1858 as a method for examining the form of a concave
[12]
mirror surface. The mirror is used to form an off-axis image of a pinhole source placed in a plane
containing the centre of curvature of the mirror and a blade with a knife-edge as shown in Figure 1a).
The mirror is observed from the vicinity of the image and the knife-edge is moved across the line of
sight until a shadow is seen to cross the mirror. The direction of movement of the shadow will depend on
whether the image is formed in front of or behind the knife-edge. If the centre of curvature lies exactly in
the plane of the pinhole and the knife-edge, the whole aperture of the mirror will darken simultaneously
revealing imperfections in the image. When the knife-edge is scanned across, imperfections in the image
will be revealed as dark and bright regions, simulated in Figure 1b).
Knife-edge scanning is a relatively simple method for measuring spot sizes but inaccuracies can occur
due to uncertainties in the location of the knife-edge. The method has been applied to the measurement
of spot diameters to a precision of better than 50 nm using interferometry to monitor the knife-edge
2 © ISO 2013 – All rights reserved
[13]
position. In applications such as optical data recording, the size and structure of the smallest possible
focused spot is important. These parameters are described by the point-spread function, a measure of
[14-16]
the quality of the optical system.
3.2 Variations on the knife-edge test
The Foucault knife-edge test can be used to make precise measurements of zonal errors in near-spherical
[17]
wavefronts and is useful as a null test. It is not, however, so useful for testing aspherical wavefronts.
The asymmetry of the single knife-edge allows sys
...
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