The Hologram

Principles and Techniques

Martin J. Richardson, John D. Wiltshire

• Publisher: Wiley-IEEE Press
• Year: 2017
• Print ISBN:
  9781119088905
• Edition: 1
• eBook ISBN:
  9781119088936
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

The practical and comprehensive guide to the creation and application of holograms

Written by Martin Richardson (an acclaimed leader and pioneer in the field) and John Wiltshire, The Hologram: Principles and Techniques is an important book that explores the various types of hologram in their multiple forms and explains how to create and apply the technology. The authors offer an insightful overview of the currently available recording materials, chemical formulas, and laser technology that includes the history of phase imaging and laser science. Accessible and comprehensive, the text contains a step-by-step guide to the production of holograms. In addition, The Hologram outlines the most common problems encountered in producing satisfactory images in the laboratory, as well as dealing with the wide range of optical and chemical techniques used in commercial holography.

The Hologram is a well-designed instructive tool, involving three distinct disciplines: physics, chemistry, and graphic arts. This vital resource offers a guide to the development and understanding of the recording of materials, optics and processing chemistry in holography and:

•    Discusses the pros and cons of the currently available recording materials

•    Provides tutorials on the types of lasers required and optical systems, as well as diffraction theory and wave front reconstruction

•    Details the chemical formulations for processing techniques

Researchers and technicians working in academia and those employed in commercial laboratories on the production of holograms as well as students of the sciences will find The Hologram to be a comprehensive and effective resource.

1
What is a Hologram?

1.1 Introduction

First, we should define in technical terms what precisely is meant by the term “hologram” and discuss some of the important milestones in the development of the technique.

Some years ago, holography was tauntingly dubbed “the solution looking for a problem” and it has taken some time to establish the true nature of the technology and disperse some of the urban myths which it seemed to attract so readily in earlier years.

We shall mention some of the important types of hologram recording which are possible, and end this chapter with a view of the public perception of holography; explaining a number of 3D systems which are frequently labelled “holograms” by the public, but which do not realistically meet the criteria for inclusion in this category.

Before embarking on a career in holography, remember that the holographer has to be prepared for the frequent request to re‐create R2‐D2’s projection of Princess Leia, and also patiently to stand fast through the knowing wink accompanying the statement “Oh yes that’s the method where the broken hologram still contains all of the image!”

1.2 Gabor's Invention of Holography

The word “hologram”, coined by Denis Gabor from Greek roots, seems to be difficult to define precisely, so the authors prefer to assume the most appropriate English meaning to be “the entire message”.

Of course, in an era where the Hellenic Institute of Holography plays a prominent role in development of new techniques for ultra‐real representation of museum artefacts, the word has now ironically become “anglicised” to the extent that it now translates directly back into modern Greek as “ολόγραμμα”!

Gabor’s intention was to refer, in the name, to the unique ability of this technique to record an incoming wave of light from an object in terms of both its phase and amplitude. Gabor was working in electron microscopy when he observed that interference recording was a way to achieve recordings of ultra‐high resolution without the difficulties introduced in optical systems by the limitations of recording materials, lenses and conventional optics.

The hologram differs greatly from the simple photographic recording of an image based solely on the amplitude of light arriving from the field of view of the optical system, because when we look at a black and white film exposed in an everyday camera, after applying developer, we see a perfectly recognisable “negative” image of the subject beyond the lens. In comparison, in its simplest form, the hologram recording itself, in the appropriate high‐resolution silver halide film or plate, tends to be something that, at first sight, is a meaningless jumble of lines or zones in varying tones.

So, what is the “hologram”? In the etymological sense, in the early years there was a move to call the recording itself, the “holograph” and the reconstructed image, the “hologram”. This seemed a logical and useful division, as it is often confusing during discussion in the workplace, as to whether we are referring to the glass plate in the laboratory or to the image which springs forth from it when the laser is switched on.

However, this terminology appears to have fallen by the wayside, and today’s dictionary does not generally acknowledge the word “holograph” except in a separate sense with reference to the special legal value of handwritten documents.

When we look though a microscope at a silver halide holographic recording plate which has been exposed to a suitable “standing wave” of interference, and processed in a suitable developer and either “fixed” or “stopped”, we see black and white lines in what appears to be a random pattern, or at least a pattern which does not appear to relate directly to the subject of the recording.

Its fringes might well, in some cases, be predominantly linear – leading to the concept of “surface‐relief holograms”. If the subject matter is relatively close to the plate, we may begin to recognise the shape of the object, but in a true “redundant” Fraunhofer hologram, it is quite impossible to relate the pattern to the subject matter (see Figure 1.1, which shows a magnified image of part of the recorded pattern in a holographic plate and, beside it, a black and white photograph of the recorded 3D image seen when the hologram was lit with helium–neon laser light).

Figure 1.1 (a) The amplitude fringe recording; (b) the image it produces in laser light.

So what is happening here?

The conditions for recording a hologram involve the use of a coherent light source. Lasers were not available in the era when Gabor invented holography, but nowadays we have a wide choice of laser types that can produce holograms, which will be detailed later.

Using a single laser, in the simplest format, we can arrange for one part of its emitted light to be incident upon a three‐dimensional object. The remainder of the beam travels towards a high‐resolution recording plate, and the light direct from the laser (“reference beam”) coincides near the plate with light reflected from the 3D object (“object beam”). The light reflected from the object contains information about the shape and tonality of the object and is “coherent” with the light arriving at the recording plate direct from the laser (Figure 1.2). In the vicinity of the plate these two beams “interfere” to produce a “standing wave of interference” which can be recorded in the photosensitive emulsion on the plate provided certain conditions of stability exist – by definition, this “standing wave” must not move or change during the recording process.

Figure 1.2 Making a transmission hologram with a single laser beam.

So what is the nature of this “standing wave”?

We are familiar with the classical experimental demonstration by Thomas Young early in the nineteenth century. By using sunlight issuing from a tiny hole in a window blind (which was a simplistic way to provide a beam of partially coherent light), he was thus able to demonstrate the wave nature of light. This was achieved by passing light from this single source through two adjacent narrow slits in such a way that the two waves issuing from slightly displaced sources continued towards a screen. His famous sketch in Figure 1.3 was made by the visualisation of waves on water.

Figure 1.3 Young’s slits visualisation [1].

Now that we are routinely able to utilise laser light, we can easily demonstrate the analogous wave effect in electromagnetic radiation. If the screen CDEF is stationary, the extended row of spots which results demonstrates the interference of light from the two separate sources A and B.

As shown in Figure 1.3, the “wave fronts” from the two sources provide an orderly sequence of high and low intensity in accordance with the distance between the slits, the wavelength of the light and the distance of the screen from the slits (i.e. the angle between the beams).

Of course, if we were to place a sheet of photosensitive film in the position of the line marked CDEF by Young, in an optical set‐up, we could record an interference pattern provided the “standing wave” was stationary.

Nowadays, we can very easily use a laser as a fully coherent light source and Figure 1.4 shows the effect of inter‐changing the laser wavelength between recordings with the same slit apertures, in this case a pair of thin (0.1 mm) lines spaced by 1.5 mm etched into a black‐developed photographic plate.

Figure 1.4 Twin‐slit diffraction of green and red lasers.

It is clear that increasing the distance betwee...

Table of contents

• Cover
• Title Page
• Table of Contents
• Foreword
• Preface
• Dedications and Acknowledgements
• About the Companion Website
• 1 What is a Hologram?
• 2 Important Optical Principles and their Occurrence in Nature
• 3 Conventional Holography and Lasers
• 4 Digital Image Holograms
• 5 Recording Materials for Holography
• 6 Processing Techniques
• 7 Infrastructure of a Holography Studio and its Principal Components
• 8 Making Conventional Denisyuk, Transmission and Reflection Holograms in the Studio
• 9 Sources of Holographic Imagery
• 10 A Personal View of the History of Holography
• Epilogue: An Overview of the Impact of Holography in the World of Imaging
• Index
• End User License Agreement