Appendix C
Holography
Until now, man has been up against Earth’s nature. From now
on he will be up against his Own nature.
— Dennis Gabor
C.1 Introduction to Holography
Holography was invented by Dennis Gabor in 1947 through his work on improving
images produced in electron microscopes. He wanted to use the whole of the
information in the electron waves which formed an image, i.e. not just the intensity
but also the phase information. (The Greek word for whole is óλoζ , pronounced
holos.) For electromagnetic wave holography, he used a highly-filtered mercury
lamp ‘point’ source to get a reference wave that was close to one frequency and
spatially coherent. The later development of lasers in 1960 made optical holography
practical.
Holography is the technique of recording and displaying a three-dimensional
image using a two-dimensional interference pattern. A hologram is made by splitting coherent waves, with one split beam illuminating an object and the other made
to interfere with waves reflected from the object. (See Fig. C.1. The interference
pattern is recorded on a two-dimensional surface, such as a photographic film.
Holograms are usually produced optically using lasers because laser light can be
intense and coherent. However, the principle works for any coherent or partially
coherent wave, including sound waves.
One can show that the three-dimensional information determining the surface of
bodies is stored on the two-dimensional hologram surface as a Fourier transform of
the object. The positions of the object’s surface is recovered by a second Fourier
transform.
For imaging of surfaces and volumes, holograms require storage of both the
intensity and the phase of the wave components. Ordinary photography records
only intensity of light onto a two-dimensional surface. Color information is, in
effect, recorded separately, one image for each of at least three distinct colors.
A single photographic image does not contain information about the distance
from the image surface to each of the object points where light was emitted, so
© Springer Nature Switzerland AG 2020
W. C. Parke, Biophysics, https://doi.org/10.1007/978-3-030-44146-3
635
Holography
Until now, man has been up against Earth’s nature. From now
on he will be up against his Own nature.
— Dennis Gabor
C.1 Introduction to Holography
Holography was invented by Dennis Gabor in 1947 through his work on improving
images produced in electron microscopes. He wanted to use the whole of the
information in the electron waves which formed an image, i.e. not just the intensity
but also the phase information. (The Greek word for whole is óλoζ , pronounced
holos.) For electromagnetic wave holography, he used a highly-filtered mercury
lamp ‘point’ source to get a reference wave that was close to one frequency and
spatially coherent. The later development of lasers in 1960 made optical holography
practical.
Holography is the technique of recording and displaying a three-dimensional
image using a two-dimensional interference pattern. A hologram is made by splitting coherent waves, with one split beam illuminating an object and the other made
to interfere with waves reflected from the object. (See Fig. C.1. The interference
pattern is recorded on a two-dimensional surface, such as a photographic film.
Holograms are usually produced optically using lasers because laser light can be
intense and coherent. However, the principle works for any coherent or partially
coherent wave, including sound waves.
One can show that the three-dimensional information determining the surface of
bodies is stored on the two-dimensional hologram surface as a Fourier transform of
the object. The positions of the object’s surface is recovered by a second Fourier
transform.
For imaging of surfaces and volumes, holograms require storage of both the
intensity and the phase of the wave components. Ordinary photography records
only intensity of light onto a two-dimensional surface. Color information is, in
effect, recorded separately, one image for each of at least three distinct colors.
A single photographic image does not contain information about the distance
from the image surface to each of the object points where light was emitted, so
© Springer Nature Switzerland AG 2020
W. C. Parke, Biophysics, https://doi.org/10.1007/978-3-030-44146-3
635