Cover Page

The Hologram

Principles and Techniques

 

Martin J. Richardson

De Montfort University, Leicester, UK

 

John D. Wiltshire

Independent Consultant, UK

 

 

 

 

 

 

 

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Dedications and Acknowledgements

Martin J. Richardson

Dedicated to my daughters Elizabeth and Florence, who are inspirational, and my partner Nicky, for persevering more than thirty years of holographic mayhem, thank you!

John D. Wiltshire

For Carol, Jonathan and Darren.

Many thanks to Martin for the invitation to join him in the creation of this book. After 45 years working in the production, transport and recording of light, I hope my experience in practical issues will be useful to readers.

My uncle, Harold Swannell, an electrician at the Royal Small Arms Factory, Enfield, inspired and nurtured my lifelong interest in electricity, light and chemistry over sixty years ago.

Later, Joyce and Stanley Wiltshire, my late mother and father, coped patiently with explosions, fires and evil odours in our home throughout my trying youth. Thank you.

My Mum had ten siblings – her legacy: “The Turner Heritage.”

Thanks to everyone who lived the “Holography Dream” together at Applied Holographics from 1983, during my 14 years at Braxted Park, and especially to Paul Dunn and Andrew Rowe for their recent help as I sought to remember and record those halcyon days.

My earliest inspiration for holography came from the late Graham Saxby, Nick Phillips and Steve Benton.

For the inspiring technical discussions I’ve had over the years with Peter Howard, Howard Buttery, Dave Oliff, Simon Brown, Jeff Blyth, Craig Newswanger, Peter Miller, David Winterbottom, Nigel Abraham, Mike Medora, Brian Holmes, Gideon Raeburn, Hans Bjelkhagen, Patrick Flynn, Satyamoorthy “Kabi” Kabilan, Jonathan Wiltshire and many other great scientists and engineers.

For my friends who didn’t make it this far: Rob Rattray, Hamish Shearer, Micky Finlay and my soulmate Barney, I’m carrying the baton.

Thanks for irreplaceable contributions to this book and 20 years of friendship with Alexandre Cabral.

My sincere gratitude to project editor Samanaa Srinivas at John Wiley & Sons for invaluable help and advice in the realisation of a working manuscript.

To my friends throughout Europe – still love you – back soon!

Thank you.

Foreword

It was a great honour to receive the invitation to write this foreword. Holography has been part of my life both at the research level, applied to security of documents and products, and at the academic level, as a powerful tool to teach many of the complex aspects of optics.

The idea behind this book clearly detaches it from existing holography books that focus on the physics of the technique, requiring some considerable background in optics and mathematics, on the exquisite chemistry around the recording of the hologram, or on the artistic concept that surrounds this fabulous creative tool. In this book it is possible to navigate the interfaces between various types of knowledge involved and, when essential, the required physical/optical/chemical concepts are explained in a simple and pragmatic way, allowing the content to be easily explored by someone not entirely familiar with the subject, or to be appreciated by a specialist due to the simplified and abridged approach.

Reading this book reminded me of an anecdote (that I adapted to holography) about a complex holography camera that was having problems of consistency for several months. After using all the expertise available from scientists of all possible areas, the institution decided to call an old holographer who had worked in holography all his life. After a detailed analysis, the holographer fastened one screw with the proper torque and the holographic camera immediately started to give wonderful results. The institution was profoundly thankful to the holographer but considered the cost to be unexpectedly high for the activity performed. As a reply, the invoice from the holographer detailed: 1% of the cost – fastening the screw, 99% of the cost – knowing which screw to fasten!

This simple joke applies perfectly to the challenging complexity behind holography and makes us aware of something that is (apparently more than in other fields) fundamental and, above all the academic/scientific knowledge, required to make good holograms: Experience. This book also conveys to the reader know‐how gathered from several decades of experience, and this is undoubtedly a fundamental instrument if someone wants to take holography to the next level.

In conclusion, whether a researcher in a science institute, a teacher or a student in an optics class, or an artist in a holography studio, this book is a highly valuable tool for those starting to take the first steps on the difficult journey that is holography, and an excellent complement to the physics and chemistry books for those more advanced in the subject. Joyce Carol Oates, an American writer, once wrote that, “Beauty is a question of optics. All sight is illusion.” If holography is an optical illusion, it is undoubtedly the most beautiful one.

Dr Alexandre Cabral

Preface

Hologram - The Thinking Picture

With the legacy of the inventions of Lippmann, Gabor et al., we are lucky enough to have been the generation who have experienced the dawn of the Age of Holography first hand. Still, when we think of holograms, we think of the future, a place full of wondrous inventions. A place where driverless cars defy gravity, civilisation is established on Mars or cities are built under Earth’s oceans. And then, of course, holographic images that materialise in thin air and communicate with each other using artificial intelligence, indistinguishable from human consciousness.

Such is the legacy of science fiction. In reality, this vision of the future may fall far beyond the laws of physics, but nevertheless there are some truly astounding developments taking place right now in the field of holography. I know, because as a research professor at De Montfort University, I’ve had the privilege of experiencing some of the world’s most incredible three‐dimensional holograms, and it’s a glimpse into a future I want to share with you.

It could be that the laws of physics, outlined in Chapter 2 of this book, will prevent holography from fulfilling the science fiction vision of Star Wars. Instead, the holographic medium serves another function, a function that underlines the very nature of technological advance, as science strives to catch up with science fiction. The spin‐offs are often more interesting than the original research intention! The fantasy of holography is a conceptual lubricant that facilitates the birth of other great ideas. Could it be, then, that the intrinsic, but unvoiced, value of holographic illusion points the way for next‐generation immersive augmented reality, promising to evolve into something other, something unpredictable?

When Microsoft recently announced its technical breakthrough toward interactivity with holograms, it was a jaw‐dropping moment for those within the holographic research community. The claim that Windows was about to enter our physical world through holographic technology owes much to the dream of science fiction and certainly adds another chapter to the history of three‐dimensional imaging.

It took me several days of thought regarding the implications this would have on the research community and, after going through my initial feeling of elation, thoughts slowly slipped into its darker meaning. Was Microsoft misleading the public into thinking they had found the Holy Grail of 3D? The thought of holograms populating our everyday lives also felt somehow unsettling. It simply didn’t align itself with current experience and, therefore, something seemed intrinsically wrong. Was the world on the brink of really merging with the digital Matrix? Was it a mirror rather than a window – a mirror reflecting another’s identity, thoughts, desires and, therefore, needs? The idea of the mirror seen through another’s eyes – someone else’s view of reality – seemed beyond our perception, because Microsoft’s HoloLens™ system threatens to invade the small amount of unencumbered reality we currently have, a space rapidly diminishing because of the ubiquitous screens on our walls, on our desks and in our pockets. Real space is an endangered, diminishing asset.

However, it quickly became clear that this interaction with our physical environment was through a head‐set that superimposes the Microsoft operating system on the actual world. The Microsoft HoloLens™ system may not be holographic in the purest sense (“What is Not a Hologram?” Section 1.11 of this book), but the fact that Gabor’s word “hologram”’ continues to inspire innovation in the twenty‐first century means our trip is far from over!

Perhaps The HoloLens™ could be said to be the modern‐day equivalent to “Pepper’s Ghost”, a historical device used to create spectacular visual illusions by the use of projection systems, explained in Chapter 1. By utilising an angled, partially reflective surface, of which the viewer is not aware, between the audience and the main subject of a display, it is possible to produce a ghostly or ethereal image which appears to the audience to be superimposed in the same space as the principal (“real”) display. Documentation of such a principle is recorded as far back as the sixteenth century in the writings of Giambattista della Porta. Later, such inventors as Rock [1] have attempted to improve the technique by suggesting improvements such as a method to hold a light, foil screen in position with a minimum of wrinkles in the film, which would normally be detrimental to the reflected image quality and thus to the illusion; ways to improve the brightness and contrast ratio of the projected images, and ways to eliminate extraneous light reflecting in the mirror screen, which tend to reduce the effectiveness of the illusion. Maas [2] also describes ways to improve the presentation of the basic principle. O’Connell [3] has shown ways of using this technique for video tele‐presence methods.

In 1987, Stephen Benton, one of the world’s great holographers and Professor at MIT, suggested that a stereographic three‐dimensional hologram display should be confined within a limited viewing space (the Benton Alcove Hologram [4]) so as to restrict the viewer from coming into contact with the angular viewing limitations of the holographic image, which we all agree tend to be the “Achilles Heel” of display holography.

Recent technological developments by Zebra Inc. and XYZ have improved horizontal viewing angles and also provided vertical parallax by digital ray‐tracing techniques, described in Chapter 8. The restriction of the ability to view the image from oblique angles is a severe disadvantage in comparison with Denisyuk holograms recently produced by Yves Gentet, Colour Holographic and Hans Bjelkhagen. But Denisyuk holograms of this type, whilst providing exceptionally realistic images (approaching facsimiles of reality), do not have the ability to represent computer‐generated animated images, such as may be realised by digital techniques.

In the 1980s, holographer Peter Miller produced a two‐colour reflection hologram with integrated sound system, featuring an image of a Barracuda Car Radio. Proximity switches behind the glass plate caused an audio effect to “change channel” when the viewer placed a finger in the real image of the channel selector button. This was a brilliant innovation which pre‐dated the modern iterations of interactivity with a hologram!

In common with so many modern optical systems, a key component of the Microsoft HoloLens™ technique is a holographic optical element (HOE). These optical devices have a similar effect to a conventional glass optic but take the form of a thin film that is optically clear and has unique abilities in the manipulation of light. Previous to the HOE, non‐holographic optical elements, made with a mechanical ruling device, were used in spectrophotometers, for example, as a dispersive grating to divide the spectrum from a white source into its separate colours, on an angular basis. An HOE is a convenient and relatively low‐cost component with a highly efficient grating made by laser imaging of a photosensitive material. It is possible, using holographic methods, however, to produce more complex optics such as diffusers which control the exact direction of scattered light, or volume holograms such as head‐up displays (HUDs) which direct reflected light of a narrow band of wavelengths in a specific (off‐axis) direction; for a holographic mirror, the angle of incidence is not necessarily equal to the angle of reflection! HOEs to assist the collection of solar power will inevitably follow. So, positive commercial statistics predicting the future of holography seem relatively clear‐cut.

In fact, modern holography offers many alternatives to light‐shaping devices in industry and may be compared with the role electronic circuits and microprocessors played at the beginning of the 1960s as an alternative to the valve. As mass‐produced holographic optical elements start replacing micro‐lens arrays, and holographic phase memory is poised ready to replace today’s standard magnetic hard drives, each has commercial potential previously thought impossible.

It remains to be seen if our ever‐increasing dependence on technology will impair our physical or mental faculties and our adaptability to nature, but we do know that the advantage modern holography gains over existing technology will be long term and, in some cases, life‐changing.

Creative computing will play a major role in the development of computer synthetic holograms within numerous applications including the arts, entertainment, games, mobile applications, multimedia, web design and other pervasive interactive systems. Due to the nature of these applications, computing technology needs to be developed specifically to tackle the conceptual complexity that does not exist in other applications. The challenges faced by creative computing come from the need to originate applications that involve knowledge in the disciplines of the Humanities and Arts more traditionally used to describe activities at human behaviour level. The main feature of these applications is that a creative system will directly serve people’s needs to improve quality of life. It is the rapid development of computing technology that will enable new creative industry and it is also this rapid development that requires serious academic discussion.

Creative computing supports the vision that computing technology will become an integral part of the design industry, where computing offers new design tools for artists and designers to extend the traditional products, and computing technology itself will be developed and enriched by reference to knowledge from the Humanities and the Arts.

Today, holograms are standard security issue on bank cards and banknotes, event tickets, postage stamps and passports – all aimed specifically at halting counterfeiting. They are a typical component in the validation of safety‐critical items – such as medicines and machine parts – and therefore save lives.

The list of applications of holography will increase in length as a growing number of five‐star research labs in universities and technical companies, including Microsoft, find new applications for these amazing devices. We are developing new types of holograms with the long‐term aim of progressing the medium beyond its ability simply to capture and replay three‐dimensional images, pursuing their general ability to diffract and manipulate light. Extensive technical documentation concerning holography has established it as an exciting, emerging medium. However, its potential still remains relatively untapped. So, how did we arrive at this juncture of technology? Why does holography have the potential power to change the way we see our world and, as we start our journey into the Age of Photonics, where did the holographic journey begin?

The word “hologram” means many things to many people. The word was used by Professor Stephen Hawking as a metaphor to describe concepts in quantum mechanics. Hawking related the holographic principle with that of the need to explain the anomalous behaviour at a black hole, comparing the way it flattens time and space with the way a two‐dimensional surface of a holographic recording carries a three‐dimensional image. Other theoretical scientists suggest that the universe has qualities resembling a hologram, in that information about the whole exists in every constituent part. I’m reminded of William Blake’s poem Auguries of Innocence:

To see a world in a grain of sand

And a Heaven in a wild flower

Hold infinity in the palm of your hand

And eternity in an hour

The word may also be used to describe the complete works of Shakespeare or a description of time, for example an organic life span from conception to death. Others tailor the word to promote idiosyncratic philosophy. The authors revert to the Greek roots of Gabor’s term “holo” (entire) and “graph” (message).

In the following chapters, the intention is to offer a stepping stone for those who have an interest in this fascinating area of holographic imaging. We hope to provide an entry point into the philosophical and practical aspects of hologram‐making; to understand how and why some of the holograms with which we are familiar today were made, and what the future holds for a relatively young technology as the related science develops.

Martin J. Richardson

Notes

  1. 1 James Rock. Patent application US20070201004A1: Projection apparatus and method for Pepper’s Ghost illusion.
  2. 2 Uwe Maas – Musion Eyeliner 3D Projection www.eyeliner3d.com
  3. 3 O’Connell, I. (2009) “Video Conferencing Technique”. New Scientist, 26 November.
  4. 4 Benton, S.A. (1987) “‘Alcove’ Holograms for Computer‐Aided Design,” Proceedings of SPIE, 0761, True Three‐Dimensional Imaging Techniques and Display Technologies, 53.

About the Companion Website

Don’t forget to visit the companion website for this book:

www.wiley.com/go/richardson/holograms img

There you will find valuable material designed to enhance your learning, including:

Video

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