# Types of Hologram and their Formation

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Summary:  The purpose of this document is to provide an example of how authors must format the report for submission for the Report assessment in PHY3304 – Photonics. The Summary should be a self-contained and explicit overview of the report with a clear statement of the conclusions reached. It should be at least 100 words, but should not exceed 150 words. It must be single spaced, justified across the width of the page, and start two single line spaces down from the author affiliation list.

An analogue hologram is a generally a flat film made of a material that is able to record the interference pattern produced by a reference light wave and an object light wave.  The resultant image preserved on the film is three-dimensional and preserves the original parallaxes and depths of the subject matter.  There are several types of holograms, differentiated by their physical properties and the techniques employed in recording them.  The first part of this report will examine two specific holographic methodologies, reflection and transmission holograms.  Included in this investigation is a discussion of the main processes involved in recording and reconstructing both types of hologram, and a comparative summary of both types of hologram.  The second part of this document is to provide a methodology for constructing a transmission hologram in a laboratory environment, utilising a hologram kit and laboratory equipment. (126 words).

Keywords:  list up to eight words or groups of words in order of priority, separated by commas – do not use general terms like “photonics”.

1 Introduction

Holograms differ significantly from a standard photograph by the extent of information the final

image is encoded with. The key difference between a photograph and a hologram is that photograph is encoded with information about the amount of intensity of the light reflecting of the surface of the object and is devoid of any information regarding the phase of the wave (Hecht 2017).  What this means is that there is no depth information, and the image created is a two-dimensional projection of a three-dimensional object or scene.  The final can be viewed under any type of light source.

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In contrast, a hologram is encoded with both the amplitude (irradiance) and phase information, and because phase is a relative property, the construction of a hologram requires a “reference wave” in addition to the light that is reflected from the surface of the object, or “object wave”.  This combination of reference wave and object wave, creates an interference pattern and when captured together on a recording material, will produce a three-dimensional (3D) image which then preserves the original parallaxes and depths of the object (Hecht 2017).   What this means is, that for the observer, the image can be viewed from different angles, the observer will also see different relative positions of the object in the image, and the observer will perceive the different distances of the object relative to the observer.  The final image of a hologram generally requires the original or similar light source that created the hologram.

The ability to capture the superposition of both amplitude and phase wave information on a recording material has had a punctuated history due to the fact that creating a holographic image was not necessarily the prime motivation for this important achievement (Hecht 2017).  It is Dennis Gabor (1900 – 1979), who is often credited in much of the historical literature for creating the “first” holographic image, by utilizing, a two-step process of recording and reconstructing an image (Hecht 2017).  More recent literature proposes that it is was the work of Ernst Abbe (1840 – 1905), that provided the earliest known theory and stimulus for holographic development by describing a formation of an image using a two-step diffraction process, involving the use of a plane wave illuminating a “grating like” object, and when imaged by a lens forms a set of regularly spaced bright spots or fringes at the back focal plane of the lens (Kostuk 2019)…..(expand)

With the advent of laser technology in the 1960’s, holographic techniques evolved significantly in terms of the recording geometry, the type of modulation imposed on the object beam, thickness of the recording material and the method of image formation.  There are several fundamental differences between the two types of holograms referenced in literature, that place an emphasis on the geometry of the reference wave, the object beam and the subject matter.  If the object and reference beams traverse the recording material from the same side, the resulting hologram is known as a transmission hologram.  Where the reference wave and the object wave are incident on the recording material from opposite sides, the resulting image is known a reflection hologram (Hecht 2017), (Kostuk 2019).

Within this broad categorization, there are several variations of each type of hologram.  For this project and subsequent experiment, discussion will be limited to the geometric arrangements of the transmission and reflection hologram and a brief outline on the impact this arrangement has on the recording material in each case.

As (Hecht 2017) explains, the early holograms utilized transmission methodologies, and in addition endured a number of disadvantages, primarily due to the lack of a coherent light source, on-axis (or inline) geometry and limitations of the recording material.  Gabor’s inline holograms, prior to laser technology, were blemished by the presence of a twin image in the final reconstructed hologram.  This ghosting effect would later be resolved by William Bragg (1862-1942) and (Gordon Rogers), by taking a second holographic image at twice the distance of the first, utilizing a method of wave subtraction to overcome this problem (Hennelly et al. 2009).

With the invention of the laser in the early 1960’s, and the introduction of an “off-axis” geometry developed by Emmett Leith (1927 – 2005) and Juris Upatnieks (1936 – ), which placed the reference wave incident on the hologram plane at an angle relative to the normal, eliminated the ghosting effects created by the in-line geometry, and it would also eliminate the need for wave subtraction (Hennelly et al. 2009).  The compromise to the off-axis configuration, was the need for additional optical elements, such as beam splitters and mirrors (Figure 1), which still allowed for the reference and object wave to create an interference pattern in front of the recording material (Hennelly et al. 2009).

Fig 1: Beam Splitter/Mirror schematic of Transmission hologram

Simplified even further, the transmission hologram illustrated in Figure 2, demonstrates how this type hologram outlined above can be constructed negating the complexity of the instrumentation used by Leith and Upatnieks.  The laser light generated by a diode laser, is similar to a spherical wave with the object placed in one part of the laser light.  Interference fringes are produced by the light that reaches the recording film unobstructed (reference wave) and the light that has been scattered from the object (object wave).

Fig 2: Simplified schematic of Transmission hologram

The impact on the recording film, means that the fringes lie in planes perpendicular to the plane of the recording film, a similar manner to grooves in a record.  This will also impact on how the transmission hologram is reconstructed.  As a consequence, any frequency of light can pass through the recording material.  What this means is that if this hologram was reconstructed using a source other than what was originally used to record it, the image itself would be indistinguishable.

In contrast to the work of Gabor, Leith and Upatneiks, Yuri Denisyuk (1927-2006), who worked in parallel to, and unaware of Gabor’s work, developed a holographic technique that could construct of 3D images by reflection in white light (Johnson).  Commonly known as reflection holograms, the geometry differs slightly from the transmission hologram in that the reference wave and the object wave are incident on the holographic film from opposite sides.  With reference to Figure XX, the reference wave is again similar

In the reflection hologram, the fringes lie in planes that are parallel to the holographic plate.

The specific aims of the project are twofold.  First, to replicate the work of Leith and Upatneiks, by confirming the off-axis method of recording and reconstruction of transmission holograms.

Second, albeit without the sophistication of the original experiment, demonstrate in a laboratory environment, how an off-axis transmission hologram can be constructed that not only supports the above literature, also mimics the same hologram achieved as the white light reflection hologram created in the USQ residential school (USQ reference – Experiment 8).  The simplified reproduction of both transmission and reflection holograms share a similar methodology with a slightly different geometry, in terms of how holographic plate is positioned relative to the object and the laser.  Furthermore, using a diode laser, both methods of hologram can be constructed without the use of beam splitters and mirrors to direct the reference beam and object beam towards the recording material.

The following section outlines a methodology for the constructing and viewing a transmission hologram, and has been prepared in a similar format to an experiment manual, including safety information.  Due to the similarities in equipment and procedure outlined in the white light reflection hologram experiment, sections of this experiment have been reproduced in part

Safety aspects outlined at the beginning of this experiment, have also been reproduced based on the information included in the University of Southern Queensland PHY 3304 Experiment Manual – Semester 2, 2019.

Due to the uncertainty of the exposure time associated with the recording medium, it is recommended that a number of test exposures be conducted to establish a suitable time frame that will produce a clearly defined holographic image.  The length of time associated with conducting test exposures and subsequent analysis of the final images, assuming five test exposures, and initial set-up time, it is anticipated that the entire experiment could take approximately two hours to conduct from initial set-up to completion.

The Photonics topics are associated with your project?

2 Methodologies

Experiment 9.1 Constructing a Transmission Hologram (off axis method)

Safety

Prior to undertaking any part of this experiment the participant (student) will need to read the online PowerPoint presentation titled ‘Student Safety Induction’ found via the following link:

In addition to the ‘Student Safety Induction’ PowerPoint, students should familiarize themselves with sections 1.1 General Safety, 1.2 Attire and Personal Protective Equipment (PPE) and 1.3 Equipment and Materials in the front of the Experiment Manual.

Warning!

During the course of this experiment the participant will be using a Laser.  Do not look directly at the laser, regardless of the output capacity permanent eye damage may occur.

Aim:

Using a hologram kit, and additional university laboratory equipment, gain a physical appreciation about holography by constructing a transmission hologram and observing its optical characteristics.

Introduction:

A hologram is a recording of the interference pattern formed when a point source of light (the reference wave) of fixed wavelength encounters light of the same fixed wavelength arriving from an object (the object beam).

Apparatus

The hologram kit ‘Standard

${{\mathrm{HOLOKIT}}}^{{\mathrm{TM}}}$

’ that contains:

• Integraf Holography Diode Laser (3 – 4 mW) – 650 nm when operated by a 3.0 v d.c. The advantage of this laser is that it does not need a separate spreader, as its collimating lens can be removed to obtain a naturally spread beam.
• Litiholo C-RT20 ‘Instant Hologram’ plates (no development required)

Requirements and other materials:

• A dark room* (it is preferable that this experiment is conducted inside to minimize the amount of light incident on the recording plates).
• A basic night light or green safelight.
• A stable table to serve as a work area.
• A bright, solid object (this object will act as the subject matter of the hologram i.e. coins or keys).
• Two

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size batteries (to power the laser).

• A stand for the laser.  (clothes peg or similar equipment to hold the laser).
• A piece of white card.
• A stand that will enable the holographic plate to stand vertically.
• A flat hardcover book to serve as a laser ‘shutter’ (preferable size 150mm x 200mm in size).
• A computer mouse pad or tray of sand (salt or sugar) to act as a vibration isolation system (preferable size 15cm x 20cm x 5cm).

Procedure:

Make the Transmission Hologram:

1. Unscrew the black collimating lens from the front of the laser. A small spring behind the lens will pop out (Figures 1 and 2).  Keep both the lens and the spring so that they can both be reattached to the laser.  Note:  To avoid touching the exposed circuit board, hold the laser by the brass cylinder.

Figure 1: Diode Laser with collimating lens

(Integraf LLC 2019)

Figure 2: Diode Laser with collimating removed lens ((Integraf LLC 2019)

1. Mount the laser in its holder (clothes peg or similar equipment), Figure 3.

Figure 3: Example of holding laser and stabilizing laser stand (Integraf LLC 2019)

1. Load the battery pack with two ‘D’ size batteries and then connect the wires together (red to red and black to black) to power the laser.
2. Before proceeding with the experiment allow five minutes for the laser to warm up.
3. Position the laser so that its beam spreads out horizontally in an elliptical shape, Figure 4.

Figure 4: Example of elliptical beam shape (Integraf LLC 2019)

.

1. Place the bright solid object on the computer mouse pad or other antivibration device in front of the holographic plate; a distance of 35 to 40cm from the laser and at a 90 degree angle from the plate, Figure 5.

Figure 5: Position of object relative to laser and plate (Integraf LLC 2019)

1. Place a white card directly behind the object and adjust the laser while looking at the shadow on the card.  Adjust the position of the laser until the object is illuminated sufficiently. Note: Ensure the beam is illuminating both the plate and the object with equal intensity.
2. Place the flat hardcover book (or shutter) in front of the laser, ensuring that the laser beam is blocked sufficiently from reaching the object.
3. In a less illuminated area of the room carefully remove a holographic plate from its container. Close the container.
4. Secure the holographic plate between the two clips and attach to the stand; ensure the plate is vertical and behind the object (refer Step 6)
5. Allow 10 seconds for the object to settle and ensure that external vibrations are eliminated.
6. Lift the hard cover book (or shutter) slightly – allow five seconds for the vibrations of this step to subside.
7. Lift the hard cover book completely away from the laser light to expose the holographic plate.  The exposure time of five minute is recommended by the manufacturer of the holographic plates.

Note: If the hologram was unsuccessful with the stated exposure time, experiment with different time frames and note which time frame produces the best results.

Viewing the Transmission Hologram:

After a suitable exposure time has been determined, the hologram can be viewed.  There are two different methods that can be used to view this type of hologram.

• Using the same diode laser that recorded the hologram, shine the light from the laser on to the holographic plate, a ‘virtual image’ of the object should be visible.  If a ‘virtual image” is not visible adjust the angle of the light shining on the recording material or the line of sight being used to see the image.
• An alternative method to view the virtual image is to return the holographic plate back to the location where is was recorded and allow the laser light to illuminate it from that position.  Block the light that lights up the plate from where the object was, and a see the image of the objects instead. Keep the lens off the laser, so the light is spread out.

References

• Reference for tips on exposure times regarding the type of film used in the experiment.
• http://www.litiholo.com/hologram-film.html
• University of Southern Queensland (2019). PHY3304 Photonics – Experiment Manual, Toowoomba, Australia: University of Southern Queensland.  viewed Day Month Year, <https://usqstudydesk.usq.edu.au/…………..>.
• Journal Article Author Year, ‘Article title’, Journal Title, volume, issue, viewed Day Month Year, <URL>.
• Integraf 2019, How to Make Transmission Holograms:
• The Body Shop Australia 2003, The Body Shop Australia, Mulgrave, Victoria, viewed 31 January 2003, <http://www.thebodyshop.com.au/>.
• Hecht, E 2017, Optics, 5th edn, Pearson, Boston.
• Hennelly, BM . Kelly DP, Pandey N, Monaghan D, Review of Twin Reduction and Twin Removal Techniques in Holography. In: CIICT 2009: proceedings of the China-Ireland information and communications technologies conference. National University of Ireland Maynooth, Ireland, pp. 241-245. ISBN 9780901519672
• https://pdfs.semanticscholar.org/0134/6acdb13a467d2ac22dd0de6b945acc4421c0.pdf
• Kenyon, IR 2011, The Light Fantastic: A Modern Introduction to Classical and Quantum Optics, 2nd edn, Oxford University Press, Oxford.
• Kostuk, RK 2019, Holography: Principals and Applications, CRC Press, Taylor & Francis Group, Boca Ranton, Florida.

Appendix

Body of the Report Formatting

Page Limit and File Format

Authors are encouraged to be concise and the maximum length of the Progress Report and the Final Report (including figures and tables, but NOT the reference list or Appendix) are 10 pages and 20 pages, respectively.

The report prepared using MS-Word is to be converted into PDF and must be submitted online using the prescribed Moodle Assessment submission area on the PHY3304 StudyDesk.

Page Format

Reports must be prepared on virtual “A4” (297 x 210 mm) paper, the top and side margins must be 25 mm and the bottom margin 18 mm.  The spacing between lines in the main body must be one 1.15 line space, except for before section titles where two 1.15 line spaces must be inserted.

Tables and Figures

Tables and figures must be integrated with the text and numbered consecutively with Arabic numerals in the order in which reference is made to them in the text of the reports. All captions must be italicised and centrally located above a table and below a figure.  The first table or figure caption would be referred to in the text as Table 1 or Fig. 1 and be presented as follows:

Table 1:  The first table in the paper

Table or Figure

Fig. 1:  The first figure in the paper

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