Editorial
The holographic fraternity has been
saddened by the unexpected death of Emmett Leith, one of the
founding fathers of holography, at the age of 78. This issue
contains tributes from people who knew him, and a copy of a
letter of condolence I sent to his wife on behalf of both myself
and the Group. Many members will remember Emmett’s address to
the Group on the occasion of his visit to the UK to receive the
Society’s Progress Medal, and many others will have met him at
various conferences on holography. Ironically, he had just
celebrated his formal retirement, though he had no intention of
severing his research connections. He had been due to co-chair
the forthcoming 7th International Symposium on Display
Holography (see From the Chairman). His paper will now be
presented by Nick Phillips.
There is more cheerful news,
however. It is an open secret that Fuji has been field testing a
proposed panchromatic holographic emulsion. First reports say
that results are comparable with Agfa material in speed and
image brightness, and that both resolution and signal-to-noise
ratio are superior. The material is now coming on the market,
and technical details are available from Fuji Hunt, whose
address is Orchard Court V, Binley Business Park, Coventry CV3
21Q; the website is
www.fujihunt.com/europe. We shall hear
more about it at St Asaph. It is to be hoped that its ready
availability may bring about a resurgence of interest in
holography as a creative medium.
Another piece of good news is that
Spatial Imaging has set up a teaching centre for holography,
with courses going from complete beginnings up to professional
standard. Details are available from The London School of
Holography, 6 Marlborough Road, Richmond, Surrey TW10 6JR,
tel.020 8332 1948, e-mail
school@holograms.co.uk. The website is
www.holographyschool.com.
Finally, our long-time Chairman
Kevin Brown has decided to call it a day. He is going to live in
southern Spain – but he tells us he intends to keep up his
connections with holography. Spain is by no means a backwater in
this respect: there is a thriving holography research facility
at Alicante University, close to where Kevin is going to live.
We all wish him well in his new life. His place has been taken
by Professor Hans Bjelkhagen, well known as a pioneer of
full-colour holography and a leading light in the revival of
Lippmann photography. Hans’s address to members appears in this
Newsletter.
Graham Saxby
From the Chairman
At the RPS Holography Group
Committee meeting held on 16 December 2005 I was appointed the
new Chairman. No doubt many of you already know me and my work
in holography. However, much has happened over the past few
years. My Department has moved from De Montfort University in
Leicester to OpTIC Technium in St Asaph, North Wales, where our
new Centre for Modern Optics is situated. This laboratory is
designed for research and development in optics and holography;
we are also equipped for the small-scale manufacture of silver
halide emulsions, and there is a lab for recording full-colour
holograms. I hope that some of the Holography Group members will
visit OpTIC this summer to participate in the 7th International
Symposium on Display Holography, which will take place from
10–14 July. This is a continuation of the triennial conferences
initiated by Professor Tung H Jeong at Lake Forest College,
Illinois, in 1982, the most recent of which was the Millennium
Conference, held six years ago at St Pölten in Austria; this
year’s symposium is thus overdue. I am sure it will be an
important event for people interested in display holography, and
well worth attending.
At the end of last year we received
the tragic news of the death of Emmett Leith. When I met him
last year he was preparing to come to Wales and give an invited
paper at our conference. In the event, we are planning to honour
his memory at the conference, as well as that of Stephen Benton,
who died in 2003.
I hope that 2006 will turn out to be
an important year for display holography, considering all the
exciting things currently going on in the field, such as
large-format images, full-colour digitally printed holograms,
new improved silver halide recording materials and advances in
holographic data storage.
Hans I Bjelkhagen
Emmett Leith: A Pioneer of
Holography
The following is taken from an
obituary by Jo Collins Mathis, News Staff Reporter with the Ann
Arbor News, with the author’s permission.
Emmett Leith, Schlumberger Professor
of Electrical Engineering and Computer Science at the University
of Michigan, was widely known for his work with lasers and
holography. After falling ill at his home in Canton, he died on
23 December at St Joseph Mercy Hospital, at the age of 78. Only
three weeks earlier he had been honoured at his retirement
party. He had worked at the University for 52 years.
Emmett Leith was born in Detroit,
and received his doctorate from Wayne State University. He
uncovered the principles of holography while working on a
military radar programme at the UM Institute of Science and
Technology in the mid 1950s. During 1961–4 he and fellow
researcher Juris Upatnieks presented [ground-breaking papers] to
the Optical Society of America, in which they described three
major advances in holography.
A number of his former colleagues
paid tribute to his achievements at the funeral service. Among
them fellow professor Kim White noted his many honours,
including the National Medal of Science, and membership of the
National Academy of Engineering. He had been responsible for the
supervision of more than forty doctoral students, and had
intended to keep on working even though officially retired. His
daughter Kim Leith stressed his humility and modesty, and his
sense of humour.
He is survived by his wife June, two
daughters and a son, and three grandchildren.
Emmett Leith remembered
Peter Waddell
In 1967 Strathclyde University
prepared to hold the first ever international holography
conference. I was fortunate enough to obtain a Caird Travelling
Scholarship, and for six weeks travelled throughout the USA by
Greyhound bus, visiting all the leading American holographers in
the hope of persuading them to attend. Top of the list was
Professor Emmett Leith, inventor of the laser transmission
hologram. During the week I spent with him we became close
friends. Many of those I had contacted did come to our
conference, which thus was able to cover the scene in
contemporary applied holography comprehensively. Emmett had told
me he was eager to trace his Aberdeenshire origins, so while he
was here I made arrangements for him to visit the land of his
ancestors. He did so a few years later, and the experience
thrilled him.
In 1975, 1977 and 1979 I spent the
summer period in the USA as an optics consultant, working mainly
on an optical device for stabilising the image of a spinning
object. My final stay was with the Ford Motor Corporation, at a
location not far from Emmett’s place of work. He and his team
took a keen interest in our research. I met him again when Chris
Morris and I gave a lecture at Ann Arbor, and found that both of
our teams were working on a similar project. From an idea at
Fords, back at Strathclyde I began to develop imaging mirrors
constructed of stretchable membranes. From 1994 to 1947 Ford
funded research into the use of these mirrors in car body
design. Mirrors 1.25 m in diameter with an aperture of f/0.5
were producing visually superb 3–D images. Emmett’s team was
working along similar lines. In 1995 Steven Mason built four
such mirrors at Strathclyde University, and over the next few
years Bob Andrews organised demonstrations at Ford in the USA,
producing sharp images up to eight metres in front of the
mirror. A demonstration in 1998, involving Emmett and myself,
used a pair of cameras to send a live stereo pair of images, to
be observed via a large mirror in Michigan. Filmed in Glasgow,
the image of my arm appeared more than two metres in front of
this mirror, apparently shaking hands with Emmett: a world
first! Emmett declared to the audience (and to me by phone) that
he had never seen a finer 3–D image. Optimistic predictions were
made as to its possible uses; so far, nothing has appeared on
the commercial scene. Emmett was subsequently able to arrange an
appointment for me as visiting professor, working with him on
the mirror project. It was here that I really came to know him
and to appreciate his brilliance. We played with wild snakes in
the garden, walked in the woods and parks, and enjoyed wonderful
meals home cooked by his wife June. Incidentally, although I
have since retired, the mirror research is continuing at
Strathclyde under Stuart McKay and Steven Mason.
I was shocked and saddened to hear
of Emmett’s sudden death, following so soon after his retirement
party at the University. Like many others I feel that, with Yuri
Denisyuk, he should have been awarded a share in the Nobel Prize
for Physics along with Denis Gabor. He always supported our
projects enthusiastically, and to me he was both mentor and
friend. My professional attitude was largely shaped by Emmett’s
thoughts and actions. Goodbye, old friend: you will never be
forgotten.
Peter Waddell
Henry Nebrensky tells the Group all
about marine holography
After the AGM on 25 February, Dr
Henry Nebrensky of the School of Engineering and Design, Brunel
University, gave an illustrated lecture to members on recent
work in underwater holography. Although much of the earlier work
in this field had been concerned with the examination of oil rig
structures, as early as 1966 work in the USA was concerned with
the holography of marine creatures, by 1969 even including cine
holography. This work has been continued by Michael Katz of
Johns Hopkins University up to the present day. The research
with which Dr Nebrensky was concerned is, however, a European
venture. The main project, called the Holomar System, is in the
joint care of Brunel, Aberdeen and Southampton Universities,
with inputs from Germany and Italy. It is aimed at unravelling
some of the mysteries of small-scale marine biology, about which
even now little is known. Photography is unsatisfactory owing to
the restricted depth of field, but pulse holography as carried
out by Holomar effectively ‘freezes’ a volume of up to 50
litres, enabling microscopy to be carried out throughout the
depth of the sample.
The Holomar pod itself is about 2.4
m long and 1 m in diameter. It weighs some 2.3 tonnes in air,
but has approximately neutral buoyancy in seawater. The light
source is a 0.7 joule pulse frequency-doubled Nd/YAG laser
operating at 532 nm in the green, with pulse duration of about
10 nanoseconds. Owing to the withdrawal of Agfa film the film
holder had to be redesigned to accommodate Millimask plates
(these are manufactured by Agfa for microlithography, and the
emulsion is in fact the same as 8E56). The optical system can be
remotely switched between two configurations, giving either
in-line or off-axis images. The in-line system gives silhouette
images recording through a volume of about 3.5 litres of water,
and the off-axis system records about 50 litres. The former has
great depth but little parallax, whereas the latter has full
parallax but suffers from optical aberrations caused by the
mismatch in refractive index between seawater for taking and air
for replaying. (This can be largely overcome by reconstructing
the image using a CW laser of approximately 30% shorter
wavelength.)
The analysis of the imagery presents
the biggest headache. Each dive produces 45 separate holograms,
and each hologram contains some 30 terabytes of information.
Although much of the image is empty water, the analysis still
presents a formidable challenge. At present the information is
recorded from the holographic image by a video camera on a
translation stage, and digitised via a frame grabber. Work is in
progress to use shape recognition by a neural network, but there
are still technical problems. There is also a project to use
digital recording rather than silver halide, but this is at
present limited to in-line imagery, as the resolution of current
digital sensors is too low for off-axis recording.
Dr Nebrensky illustrated his lecture
with a great many slides, both still and animated, and left us
all a good deal better informed about copepods, dinoflagellates,
asterionella and volvox than before. This was a very interesting
presentation on a field of research few of us would have
expected to be enlightened by holography.
Graham Saxby
Clearing up a misconception
When I used to teach photography and
optics, I often had to sort out what might be described as
scientific old wives’ tales about the subject: for example, that
the colours in a white light spectrum include indigo (find it!);
that diffuse reflection is caused by the roughness of a surface
(it isn’t); that both perspective rendition and depth of focus
in a photograph depend on focal length (neither does); that heat
can be radiated (this is nonsense); that the ocular image is
focused by the eye lens (it is in fact focused by the cornea),
and so on. There are also, I am sorry to say, some muddled ideas
around concerning holograms. At present there is a discussion
going on at one of the holography websites that assumes that a
hologram is a Fourier transform, or perhaps an inverse Fourier
transform, whatever that may be. Of course it is no such thing.
It is a record of the energy distribution of an electromagnetic
disturbance in space, coded to retain phase information by the
presence of a reference beam.
A Fourier transform (FT) is a
mathematical device. To obtain the FT of a mathematical
expression you multiply it by a related exponential function and
integrate the whole lot between plus and minus infinity. If you
repeat this operation on the result you get back to the original
expression, give or take the odd constant. This means that an FT
is its own inverse, so that the idea of an inverse FT is a
nonsense. The origin of the connection between optics and the FT
is that in the 1950s it was realised that a two-dimensional FT
provided a very good model for the way a lens forms an image. It
can be shown that, with an ideal lens, the electromagnetic field
in the rear focal plane is the FT of the field in the front
focal plane. A further lens, positioned so that the rear focal
plane of the first lens is at the front focal plane of the
second lens, produces an FT of this field in its own rear focal
plane, and this, of course, is identical to the original field.
In simple terms, it forms an image of the object that is at the
front focal plane of the first lens (which fits the simple
geometrical model).
With the advent of the laser and its
well-behaved light beam, it became possible to record the FT
field by introducing a second (reference) beam to produce a
stationary interference pattern. If this is done in the FT
plane, then and only then is the hologram a record of the
FT of the object field.
The mathematical explanation of the
formation of a conventional hologram owes nothing to FT theory.
No lens is involved, and the holographic plane is too close to
the object for the wavefronts to have sorted themselves out.
What you have at the hologram plane, if you want to be pedantic,
is a Fresnel transform, a much more complicated thing to
analyse. So sorry, a hologram isn’t a Fourier transform or even
the record of one. It is simply the record of a stationary
interference pattern.
Graham Saxby
Department of Partly-Baked Ideas
The technology of optics and
photography has mostly progressed steadily, through refinements
of technique; but there have been occasional conceptual leaps
that have revolutionised it. The pinhole camera obscura
principle was discovered around 2 AD; the first multi-element
lens was computed in 1834; in the 1950s the concept of the
optical transfer function revolutionised optical thinking; and
the invention of the laser in the 1960s heralded the birth of
coherent optics (not to mention making holography practicable).
Digital imaging, now coming of age in the new century, threatens
to make wet processing redundant and film cameras obsolete. But
nobody has questioned some of the most fundamental tenets of
optics and photonics. Until now. Two of these seem to have been
noticeably bent, if not altogether broken.
The first renegade idea is the
concept of negative refractive index (RF). This has been noted
by the DPBI in a previous Newsletter, but it is worth pursuing
further. James Clerk Maxwell discovered that the RF of a
material can be expressed in terms of just two electrical
characteristics, namely its permittivity and its permeability,
and these define the speed of light in the substance, which also
defines the angle of refraction for a given incident beam. Now
either or both of these constants can be negative under certain
circumstances. Even Snell’s law allows a negative RI, as the
sine of a negative angle is itself negative. So in an
appropriately chosen material the sine of the angle of
refraction could be negative, and light entering a flat plate of
material with an RI of –1 at an angle of (+x)º would emerge at
an angle of (–x)º. A parallel-sided plate as a perfect lens!
This has already been achieved for microwave radiation; now we
wait for a breakthrough to light wavelengths. This has in fact
been achieved in a fashion, using the properties of evanescent
waves, as noted in a previous Newsletter; but perhaps, as
happened when masers became lasers by substituting atomic
transitions for molecular vibrations, some research team will
find the practical answer. Usually, when something is wanted
badly enough, eventually a way will be found to achieve it.
The second is the concept of slow
light. This smacks of science fiction. The speed of light in an
optical medium is inversely proportional to its RI, and the
highest RI we have in the real world is just over 4, for
germanium (and that is only for infrared). This retardation is
the result of interaction between the photons and the medium:
the photons are absorbed and then re-emitted in the original
direction, and this effect is limited. But there is another
approach. The speed of light is usually defined in terms of the
phase velocity, i.e. the speed at which successive
wavecrests pass a given point, and this is the usual definition
of the speed of light. On the other hand, if a single pulse of
light travels through a wavelength-dispersive medium, all the
constituent wavefronts quickly become out of phase, and
coherence is lost. But at just one peak all the waves are in
phase, and this peak has its own speed of propagation, or
group velocity. This depends on the RI of the material and
its dispersion coefficient, as well as the bandwidth of the
initial pulse. By juggling these figures it is possible to
achieve group velocities of only metres per second, or even
less.
The DPBI is still boggling at the
possibilities. A perfect lens from a flat plate? A block of
glass you can look into and see an event that took place weeks
ago? Just think: you could put a second block of glass, silvered
on the back, and have your image shuttling back and forwards for
months, Better than a hologram, eh?
Another query floated on the Net
recently, is whether you can form a hologram from two beams if
one has twice the frequency of the other. Well, when both beams
have the same frequency, when they are added algebraically one
of the terms generated is independent of time, and thus
represents a stationary pattern: this is what forms the
hologram. If you do the same sums with one term having double
the frequency, there is no term independent of time, and thus no
stationary pattern. Point settled? Not quite. Apart from the
fact that you would have to derive both beams from the same
laser to obtain phase locking, and each beam would be to some
extent contaminated by the other, no recording medium
(especially silver halide) has a linear response, and thus a
second harmonic would always be generated by the recording
medium itself. So the DPBI’s guess is that there would be
a holographic image (though probably not a strong one). It would
be interesting to find out if anyone has actually tried this.
