Reprint from the SPIE PROCEEDINGS Series, Volume 2652, Practical Holography X, 1996, pgs. 204-212

ã 1996 SPIE. All Rights Reserved.

 

Using HOEs in the Holographic Image Making Process

by Rudie Berkhout

ABSTRACT

In this paper, the artist outlines several of his image-making techniques in holography. Using the work "Event Horizon" as an example, he describes the master set-up as well as the white light transmission set-up that was used in the making of this artwork. Specifically, the design and use of Holographic Optical Elements (HOEs) and imperfect collimating lenses in the mastering steps are discussed.

INTRODUCTION AND BACKGROUND

"Event Horizon" was made in 1980. It is a pivotal piece for me as, for the first time, it incorporated an image element that was created with light itself. Since 1975, I have been producing artwork that explores new and unconventional ways of making holographic images and, as an artist, I felt that the finished work would be the "published paper". Rather than publishing the details of the techniques, I presented the art work itself in a limited edition of nine, with two artist's proofs. My reason for avoiding a technical explanation was to keep the mystery intact. As the viewer's imagination takes flight it produces all kinds of solutions and techniques in trying to figure out how it was done. I was also concerned, at that time, about commercial appropriations of technology that I had developed but had not patented. Now, sixteen years later, that is no longer a fear, and I would like to share the drawings and diagrams of each optical set-up that was used to make "Event Horizon". Only the HOE#3 is not included because it is a collimator and can be replaced by a lens or mirror. The drawings are made to read easily and to communicate all the relevant information of each set-up visually.

HOE #1

In my notebooks I recorded this hologram as SLP#40. SLP, my designation, stands for Spatial Location Program, which describes the use of the plate. This one in particular is a linear image multiplier. It is a two beam recording with a small angle in between, resulting in a simple holographic grating. The angle determines how many orders of diffraction can be expected around the zero order. Depending on the exposure and the development of the holographic plate, different orders of diffraction can dominate or can be balanced in relative brightness. When used in subsequent set-ups it results in a set of images displaced linearly. Care needs to be taken to keep the optical noise level of the developed holograms as low as possible.

HOE #2

This is a diagonal image extender made on March 3, 1980 as SLP#47. The two important distances in this set-up are the 45" between the spatial filter and the plate holder, and the 40" between the plate holder and the diagonal line. This almost makes it a lensless Fourier-Transform hologram with a large angle. It was an intuitive approach to create the desired transformation from a point of light into a line of light.

The angle in between the two beams is determined by the requirements of the set-up it has to fit into. In this case the element is used to make Master #3.

The width of the diagonal line is about 2 mm and it makes a 45-degree angle with the table. This angle is suggested by the design of the image and the nature of the white light transmission technique. A horizontal line would not show any perspective when viewed from side to side.

MASTER #1, THE SPHERE

The masters for making a white light transmission (WLT) hologram are made from two inch glass strips cut from 8" x 10" or 12" x 16" plates. A two inch wide master allows for a tight set-up and more flexibility.

HOE #3 provides the collimated reference beam to record Master #1. It can be replaced by a large cylindrical lens or mirror as long as it collimates the beam.

The sphere is a large clear plastic ball attached with hot glue to its support. The object beam is directed into the hotglue, which acts as a scatterer and makes the sphere radiate from the inside out.

MASTER #2, THE FIELD

With the help of a spatial filter and a cylindrical lens the object beam is shaped into a (1"- 2" wide) strip of light. This strip is multiplied by HOE #1 and illuminates the field that is constructed from foam core, glued to 3/4 plywood and standing on edge. All my set-ups used to be sideways, but today I make masters right-side-up, using the HOE #3 collimator positioned horizontal and overhead.

The skimming light, illuminating the field from the back, circumvents the coherence length limitation of most HeNe lasers. At the same time it provides excellent object depth as well as an interesting illusion of perspective.

MASTER #3, MOVING ENERGY

Recorded on March 6, 1980 as M #54, this hologram makes use of the abberations of a large glass lens (16" diameter) that was salvaged from an old projector. Its real focal "point" is "smeared" in 3-D space. HOE #1 multiplies this focus and HOE #2 turns this set of moving foci into a sequence of bending and moving diagonals, visually expressing the optical characteristics of the glass lens and the two HOEs as well.

The animated nature of this set-up requires a balance between the amount of image movement, image size, and the perception of space. Moving the real focal point of the glass lens along its optical axis and/or changing the distance HOE #2 - M #3, can adjust for the most comfortable binary vision. This optical transform together with the collimated reference beam from HOE #3 is recorded as Master #3.

THE TRANSFER SET-UP

"EVENT HORIZON"

The geometry of this set-up determines the important angles and distances of the previous optical configuration. In particular the angle between the the object and reference beam and the distance between the object and master are crucial as they determine the colors and the composition of the final work.

HOE #3 provides the collimated play-back light for the three masters. They are placed in line, using the zero order light of the previous master. This makes efficient use of the space and light that is available in the set-up. However, the playback beam is attenuated with the optical noise from the previous master and this can show up as noise in the final image.

A 2-D diagram of the transfer set-up is included in the way I would record the relevant date today. The three real images from the masters are recorded simultaneously, together with the reference beam, as a white light transmission hologram. This recording is ideally accomplished with a collimated or converging reference beam. As all abberations and blemishes of a collimating lens will show up in the final image, I prefer instead to use a long throw on the reference beam. It does distort the holographic space, because the conjugate of the reference beam is used in the play-back. For me this is an acceptable compromise.

CONCLUSION

HOEs can be used very successfully in the creation of holographic artwork. Specifically, the image making possibilities are greatly enhanced. Since 1977, I have incorporated them in almost every finished piece. For instance, in the "12 mW Boogie", two different HOEs were used while making the transfer, resulting in image and color multiplication.

I also use HOEs in exhibits by themselves and as elements of a light installation. When illuminated with white light, they exhibit spectral lines or fields in a unique and pure optical space. I often refer to this space as hyperspace because an object, multiplied along the Z-axis, appears to get larger and larger the further it recedes from the emulsion. It is the opposite of what happens in our familiar space, and not an easy one to make visible due to the contrary clues about space. However, this property is one of many that makes this medium so fascinating and eye-opening.

Acknowledgements

I would like to thank H.J. Gerritsen (Brown University), Stephen A. Benton (MIT Media Lab.), Rosemary Jackson (Great Exuma, Bahama) and Hudson Talbott II (Cairo, NY) for their continuous encouragement and support since my early years in holography. A special thanks to Michael von Uchtrup and Peter van Riper for helping me prepare this paper.

General References

1. Stephen A. Benton, "Method for Making Reduced Bandwidth Holograms". U.S. Patent no 3,633,989, Jan. 11, 1972.

2. Stephen A. Benton, "The Mathematical Optics of White Light Transmission Holograms", International Symposium on Display Holography, Lake Forest, IL, Vol.1, 1982.

3. H.J. Caulfield, "Handbook of Optical Holography", Academic Press, New York, 1979.

4. H.I. Bjelkhagen, "Silver-Halide Recording Materials for Holography and their Processing", Springer-Verlag, Berlin, 1993.

5. Graham Saxby, "Practical Holography", Second Edition, Prentice Hall, New York, 1994.

ã 1996 Rudie Berkhout. All Rights Reserved.

email: rudieberkhout@mindspring.com

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