Chemistry Reference
In-Depth Information
latent image (an invisible image before development) produced by the standing
waves that are characterised by a series of interference maxima and minima. After
the recording medium was developed,
fixed and dried through the traditional pho-
tographic methods, planes of reduced silver particles had reciprocal distances as a
function of the wavelength of the light used during recording. Upon illumination
with white light, the silver planes diffracted a coloured projection of the recorded
image [
53
]. In the 1910s, X-ray microscopy for recreating the image from the
diffraction pattern of a crystal lattice structure were studied by Bragg, Broersch and
Zernike [
42
,
54
]. In the 1920s, Wolfke reported that if an X-ray diffraction pattern is
illuminated with a monochromatic light, a new diffraction pattern, which is identical
with the image of the object is formed [
55
]. In the late 1940s, Gabor, while trying to
improve the resolution of the electron microscope by overcoming the spherical
aberration of the lenses, found that adding a coherent background as a phase ref-
erence, the original object wave was contained in an interferogram, which he called a
hologram [
56
,
57
]. The term hologram was coined from the Greek words holos,
meaning
. He received the Nobel Prize in
physics in 1971 for establishing the principle of holography. However, the stability
of the interference required
(i) mechanical and thermal stability of the interferometer used in the holographic
recording, and (ii) a coherent light source.
The foundations of the laser (Light Amplification by Stimulated Emission of
Radiation) theory were established in the early years of the 20th century by Einstein
[
58
]. In the 1960s, lasers (optical oscillators) were developed to produce mono-
chromatic light [
59
,
60
]. After the development of the laser, Denisyuk of the former
Soviet Union, and Leith and Upatnieks in the US recorded independently the
“
whole,
”
and gramma, meaning
“
message
”
rst
holograms in 1962 [
61
,
62
]. These early holograms were based on silver halide
chemistry. Transmission holograms, originally created by Leith and Upatnieks,
require monochromatic light (usually a laser) to view the image, otherwise viewing
in white light causes severe chromatic aberrations; whereas holograms produced by
Denisyuk
s method, can be viewed in light of a broad spectral range [
43
]. Denisyuk
was originally inspired by the method of colour photography constructed by
Lippmann. In particular, Denisyuk holograms have generated considerable interest
in artistic displays, optical devices, data storage and analytical instruments.
Holographic gratings can be generated using various geometries, which involves
the use of multiple collimated laser beams. The
'
first step in recording transmission
holograms involves passing a single laser beam through a beam splitter, which
divides the beam into two beams. The
first beam is expanded by a lens, and
deviated by mirrors (front surface) onto an object. The light that is scattered back
falls onto a recording medium. Meanwhile the second beam, expanded by a lens,
travels directly onto the recording medium. The interference of the two mutually
coherent beams forms constructive (antinodes) and destructive (nodes) interfer-
ences, at regions of the recording medium dictated by the Fourier transform of the
object, which implies that all optical information about the object is coded in the
