<s>
Optical	O
holography	B-Algorithm
is	O
a	O
technique	O
which	O
enables	O
an	O
optical	O
wavefront	O
to	O
be	O
recorded	O
and	O
later	O
re-constructed	O
.	O
</s>
<s>
Holography	B-Algorithm
is	O
best	O
known	O
as	O
a	O
method	O
of	O
generating	O
three-dimensional	O
images	O
but	O
it	O
also	O
has	O
a	O
wide	O
range	O
of	O
other	O
applications	O
.	O
</s>
<s>
A	O
hologram	B-Algorithm
is	O
made	O
by	O
superimposing	O
a	O
second	O
wavefront	O
(	O
normally	O
called	O
the	O
reference	O
beam	O
)	O
on	O
the	O
wavefront	O
of	O
interest	O
,	O
thereby	O
generating	O
an	O
interference	O
pattern	O
which	O
is	O
recorded	O
on	O
a	O
physical	O
medium	O
.	O
</s>
<s>
Holograms	B-Algorithm
can	O
also	O
be	O
computer-generated	B-Algorithm
by	O
modelling	O
the	O
two	O
wavefronts	O
and	O
adding	O
them	O
together	O
digitally	O
.	O
</s>
<s>
The	O
process	O
of	O
producing	O
a	O
holographic	B-Algorithm
reconstruction	O
is	O
explained	O
below	O
purely	O
in	O
terms	O
of	O
interference	O
and	O
diffraction	O
.	O
</s>
<s>
It	O
is	O
somewhat	O
simplified	O
but	O
is	O
accurate	O
enough	O
to	O
give	O
an	O
understanding	O
of	O
how	O
the	O
holographic	B-Algorithm
process	O
works	O
.	O
</s>
<s>
A	O
simple	O
hologram	B-Algorithm
can	O
be	O
made	O
by	O
superimposing	O
two	O
plane	O
waves	O
from	O
the	O
same	O
light	O
source	O
on	O
a	O
light	O
recording	O
medium	O
such	O
as	O
a	O
photographic	O
emulsion	O
.	O
</s>
<s>
When	O
a	O
plane	O
wave	O
is	O
added	O
to	O
a	O
point	O
source	O
and	O
the	O
resulting	O
interference	O
pattern	O
recorded	O
,	O
a	O
point	O
source	O
hologram	B-Algorithm
is	O
produced	O
.	O
</s>
<s>
This	O
is	O
known	O
as	O
an	O
in-line	O
hologram	B-Algorithm
.	O
</s>
<s>
This	O
is	O
known	O
as	O
an	O
off-axis	O
hologram	B-Algorithm
.	O
</s>
<s>
It	O
was	O
first	O
developed	O
by	O
Leith	O
and	O
Upatnieks	O
and	O
was	O
a	O
vital	O
step	O
in	O
enabling	O
3-d	O
images	O
to	O
be	O
produced	O
with	O
holography	B-Algorithm
.	O
</s>
<s>
where	O
A	O
represents	O
the	O
amplitude	B-Application
of	O
the	O
vector	O
,	O
and	O
its	O
phase	O
.	O
</s>
<s>
The	O
intensity	O
of	O
the	O
combined	O
beams	O
is	O
the	O
average	O
value	O
of	O
the	O
complex	O
amplitude	B-Application
times	O
its	O
complex	O
conjugate	O
:	O
</s>
<s>
Assume	O
that	O
the	O
amplitude	B-Application
transmittance	O
,	O
of	O
the	O
developed	O
photographic	O
plate	O
is	O
linearly	O
related	O
to	O
the	O
intensity	O
of	O
the	O
interference	O
pattern	O
.	O
</s>
<s>
The	O
first	O
term	O
is	O
a	O
reduced	O
amplitude	B-Application
version	O
,	O
the	O
second	O
is	O
also	O
a	O
reduced	O
amplitude	B-Application
version	O
if	O
the	O
reference	O
wave	O
amplitude	B-Application
is	O
uniform	O
.	O
</s>
<s>
is	O
the	O
reconstructed	O
object	O
wave	O
which	O
is	O
identical	O
to	O
the	O
original	O
wave	O
except	O
that	O
its	O
amplitude	B-Application
is	O
reduced	O
.	O
</s>
<s>
When	O
the	O
object	O
wave	O
is	O
generated	O
by	O
light	O
scattered	O
from	O
an	O
object	O
or	O
a	O
series	O
of	O
objects	O
,	O
a	O
real	O
image	O
is	O
formed	O
on	O
the	O
opposite	O
side	O
of	O
the	O
hologram	B-Algorithm
plate	O
to	O
where	O
the	O
object	O
was	O
located	O
and	O
is	O
deflected	O
from	O
the	O
normal	O
axis	O
by	O
twice	O
the	O
angle	O
between	O
the	O
reference	O
wave	O
and	O
the	O
normal	O
direction	O
.	O
</s>
<s>
from	O
which	O
it	O
can	O
be	O
seen	O
that	O
the	O
transmission	O
of	O
the	O
holographic	B-Algorithm
recording	O
varies	O
sinusoidally	O
,	O
i.e.it	O
is	O
a	O
diffraction	O
grating	O
,	O
where	O
spacing	O
of	O
the	O
fringes	O
depends	O
on	O
the	O
angle	O
between	O
the	O
two	O
waves	O
and	O
the	O
orientation	O
of	O
the	O
holographic	B-Algorithm
plate	O
.	O
</s>
<s>
it	O
is	O
the	O
reconstructed	O
object	O
wave	O
with	O
a	O
modified	O
amplitude	B-Application
.	O
</s>
<s>
If	O
one	O
of	O
the	O
waves	O
is	O
normally	O
incident	O
to	O
the	O
hologram	B-Algorithm
plate	O
,	O
and	O
the	O
other	O
is	O
incident	O
at	O
an	O
angle	O
,	O
the	O
spacing	O
of	O
the	O
fringes	O
is	O
and	O
the	O
first	O
order	O
diffracted	O
waves	O
will	O
be	O
at	O
angles	O
given	O
by	O
.	O
</s>
<s>
where	O
both	O
the	O
phase	O
and	O
the	O
amplitude	B-Application
vary	O
with	O
.	O
</s>
<s>
To	O
make	O
a	O
hologram	B-Algorithm
,	O
the	O
following	O
are	O
required	O
:	O
</s>
<s>
a	O
recording	O
medium	O
which	O
converts	O
this	O
interference	O
pattern	O
into	O
an	O
optical	O
element	O
which	O
modifies	O
either	O
the	O
amplitude	B-Application
or	O
the	O
phase	O
of	O
an	O
incident	O
light	O
beam	O
according	O
to	O
the	O
intensity	O
of	O
the	O
interference	O
pattern	O
.	O
</s>
<s>
Since	O
the	O
wavelength	O
of	O
light	O
is	O
of	O
the	O
order	O
of	O
0.5μm	O
,	O
it	O
can	O
be	O
seen	O
that	O
very	O
small	O
changes	O
in	O
the	O
optical	O
paths	O
travelled	O
by	O
either	O
of	O
the	O
beams	O
in	O
the	O
holographic	B-Algorithm
recording	O
system	O
lead	O
to	O
movement	O
of	O
the	O
interference	O
pattern	O
which	O
is	O
the	O
holographic	B-Algorithm
recording	O
.	O
</s>
<s>
The	O
exposure	O
time	O
required	O
to	O
record	O
the	O
hologram	B-Algorithm
depends	O
on	O
the	O
laser	O
power	O
available	O
,	O
on	O
the	O
particular	O
medium	O
used	O
and	O
on	O
the	O
size	O
and	O
nature	O
of	O
the	O
object(s )	O
to	O
be	O
recorded	O
,	O
just	O
as	O
in	O
conventional	O
photography	O
.	O
</s>
<s>
It	O
is	O
possible	O
to	O
make	O
holograms	B-Algorithm
of	O
much	O
less	O
stable	O
objects	O
by	O
using	O
a	O
pulsed	O
laser	O
which	O
produces	O
a	O
large	O
amount	O
of	O
energy	O
in	O
a	O
very	O
short	O
time	O
( μs	O
or	O
less	O
)	O
.	O
</s>
<s>
These	O
systems	O
have	O
been	O
used	O
to	O
produce	O
holograms	B-Algorithm
of	O
live	O
people	O
.	O
</s>
<s>
A	O
holographic	B-Algorithm
portrait	O
of	O
Dennis	O
Gabor	O
was	O
produced	O
in	O
1971	O
using	O
a	O
pulsed	O
ruby	O
laser	O
.	O
</s>
<s>
Generally	O
,	O
the	O
smaller	O
the	O
object	O
,	O
the	O
more	O
compact	O
the	O
optical	O
layout	O
,	O
so	O
that	O
the	O
stability	O
requirements	O
are	O
significantly	O
less	O
than	O
when	O
making	O
holograms	B-Algorithm
of	O
large	O
objects	O
.	O
</s>
<s>
A	O
good	O
holography	B-Algorithm
laser	O
will	O
typically	O
have	O
a	O
coherence	O
length	O
of	O
several	O
meters	O
,	O
ample	O
for	O
a	O
deep	O
hologram	B-Algorithm
.	O
</s>
<s>
A	O
hologram	B-Algorithm
of	O
a	O
shiny	O
object	O
can	O
be	O
made	O
by	O
locating	O
it	O
very	O
close	O
to	O
the	O
recording	O
plate	O
.	O
</s>
<s>
There	O
are	O
three	O
important	O
properties	O
of	O
a	O
hologram	B-Algorithm
which	O
are	O
defined	O
in	O
this	O
section	O
.	O
</s>
<s>
A	O
given	O
hologram	B-Algorithm
will	O
have	O
one	O
or	O
other	O
of	O
each	O
of	O
these	O
three	O
properties	O
,	O
e.g.	O
</s>
<s>
an	O
amplitude	B-Application
modulated	O
,	O
thin	O
,	O
transmission	O
hologram	B-Algorithm
,	O
or	O
a	O
phase	O
modulated	O
,	O
volume	O
,	O
reflection	O
hologram	B-Algorithm
.	O
</s>
<s>
An	O
amplitude	B-Application
modulation	O
hologram	B-Algorithm
is	O
one	O
where	O
the	O
amplitude	B-Application
of	O
light	O
diffracted	O
by	O
the	O
hologram	B-Algorithm
is	O
proportional	O
to	O
the	O
intensity	O
of	O
the	O
recorded	O
light	O
.	O
</s>
<s>
A	O
phase	O
hologram	B-Algorithm
is	O
made	O
by	O
changing	O
either	O
the	O
thickness	O
or	O
the	O
refractive	O
index	O
of	O
the	O
material	O
in	O
proportion	O
to	O
the	O
intensity	O
of	O
the	O
holographic	B-Algorithm
interference	O
pattern	O
.	O
</s>
<s>
The	O
efficiency	O
(	O
i.e.	O
,	O
the	O
fraction	O
of	O
the	O
illuminated	O
object	O
beam	O
which	O
is	O
converted	O
into	O
the	O
reconstructed	O
object	O
beam	O
)	O
is	O
greater	O
for	O
phase	O
than	O
for	O
amplitude	B-Application
modulated	O
holograms	B-Algorithm
.	O
</s>
<s>
A	O
thin	O
hologram	B-Algorithm
is	O
one	O
where	O
the	O
thickness	O
of	O
the	O
recording	O
medium	O
is	O
much	O
less	O
than	O
the	O
spacing	O
of	O
the	O
interference	O
fringes	O
which	O
make	O
up	O
the	O
holographic	B-Algorithm
recording	O
.	O
</s>
<s>
The	O
thickness	O
of	O
a	O
thin	O
hologram	B-Algorithm
can	O
be	O
down	O
to	O
60nm	O
by	O
using	O
a	O
topological	O
insulator	O
material	O
Sb2Te3	O
thin	O
film	O
.	O
</s>
<s>
Ultrathin	O
holograms	B-Algorithm
hold	O
the	O
potential	O
to	O
be	O
integrated	O
with	O
everyday	O
consumer	O
electronics	O
like	O
smartphones	O
.	O
</s>
<s>
A	O
thick	O
or	O
volume	B-Algorithm
hologram	I-Algorithm
is	O
one	O
where	O
the	O
thickness	O
of	O
the	O
recording	O
medium	O
is	O
greater	O
than	O
the	O
spacing	O
of	O
the	O
interference	O
pattern	O
.	O
</s>
<s>
The	O
recorded	O
hologram	B-Algorithm
is	O
now	O
a	O
three	O
dimensional	O
structure	O
,	O
and	O
it	O
can	O
be	O
shown	O
that	O
incident	O
light	O
is	O
diffracted	O
by	O
the	O
grating	O
only	O
at	O
a	O
particular	O
angle	O
,	O
known	O
as	O
the	O
Bragg	O
angle	O
.	O
</s>
<s>
If	O
the	O
hologram	B-Algorithm
is	O
illuminated	O
with	O
a	O
light	O
source	O
incident	O
at	O
the	O
original	O
reference	O
beam	O
angle	O
but	O
a	O
broad	O
spectrum	O
of	O
wavelengths	O
;	O
reconstruction	O
occurs	O
only	O
at	O
the	O
wavelength	O
of	O
the	O
original	O
laser	O
used	O
.	O
</s>
<s>
A	O
volume	B-Algorithm
hologram	I-Algorithm
effectively	O
acts	O
as	O
a	O
colour	O
filter	O
.	O
</s>
<s>
A	O
transmission	O
hologram	B-Algorithm
is	O
one	O
where	O
the	O
object	O
and	O
reference	O
beams	O
are	O
incident	O
on	O
the	O
recording	O
medium	O
from	O
the	O
same	O
side	O
.	O
</s>
<s>
Normally	O
,	O
transmission	O
holograms	B-Algorithm
can	O
only	O
be	O
reconstructed	O
using	O
a	O
laser	O
or	O
a	O
quasi-monochromatic	O
source	O
,	O
but	O
a	O
particular	O
type	O
of	O
transmission	O
hologram	B-Algorithm
,	O
known	O
as	O
a	O
rainbow	O
hologram	B-Algorithm
,	O
can	O
be	O
viewed	O
with	O
white	O
light	O
.	O
</s>
<s>
In	O
a	O
reflection	O
hologram	B-Algorithm
,	O
the	O
object	O
and	O
reference	O
beams	O
are	O
incident	O
on	O
the	O
plate	O
from	O
opposite	O
sides	O
of	O
the	O
plate	O
.	O
</s>
<s>
Only	O
volume	B-Algorithm
holograms	I-Algorithm
can	O
be	O
used	O
to	O
make	O
reflection	O
holograms	B-Algorithm
,	O
as	O
only	O
a	O
very	O
low	O
intensity	O
diffracted	O
beam	O
would	O
be	O
reflected	O
by	O
a	O
thin	O
hologram	B-Algorithm
.	O
</s>
<s>
Examples	O
of	O
full-color	O
reflection	O
holograms	B-Algorithm
of	O
mineral	O
specimens	O
:	O
</s>
<s>
The	O
recording	O
medium	O
has	O
to	O
convert	O
the	O
original	O
interference	O
pattern	O
into	O
an	O
optical	O
element	O
that	O
modifies	O
either	O
the	O
amplitude	B-Application
or	O
the	O
phase	O
of	O
an	O
incident	O
light	O
beam	O
in	O
proportion	O
to	O
the	O
intensity	O
of	O
the	O
original	O
light	O
field	O
.	O
</s>
<s>
Photographic	O
film	O
has	O
a	O
very	O
low	O
or	O
even	O
zero	O
response	O
at	O
the	O
frequencies	O
involved	O
and	O
cannot	O
be	O
used	O
to	O
make	O
a	O
hologram	B-Algorithm
–	O
for	O
example	O
,	O
the	O
resolution	O
of	O
Kodak	O
's	O
professional	O
black	O
and	O
white	O
film	O
starts	O
falling	O
off	O
at	O
20	O
lines/mm	O
–	O
it	O
is	O
unlikely	O
that	O
any	O
reconstructed	O
beam	O
could	O
be	O
obtained	O
using	O
this	O
film	O
.	O
</s>
<s>
The	O
table	O
below	O
shows	O
the	O
principal	O
materials	O
used	O
for	O
holographic	B-Algorithm
recording	O
.	O
</s>
<s>
Note	O
that	O
these	O
do	O
not	O
include	O
the	O
materials	O
used	O
in	O
the	O
mass	O
replication	O
of	O
an	O
existing	O
hologram	B-Algorithm
,	O
which	O
are	O
discussed	O
in	O
the	O
next	O
section	O
.	O
</s>
<s>
+	O
General	O
properties	O
of	O
recording	O
materials	O
for	O
holography	B-Algorithm
,	O
Material	O
Reusable	O
Processing	O
Type	O
Theoretical	O
max	O
.	O
</s>
<s>
An	O
existing	O
hologram	B-Algorithm
can	O
be	O
copied	O
by	O
embossing	O
or	O
optically	O
.	O
</s>
<s>
Most	O
holographic	B-Algorithm
recordings	O
(	O
e.g.	O
</s>
<s>
When	O
the	O
nickel	O
layer	O
is	O
thick	O
enough	O
,	O
it	O
is	O
separated	O
from	O
the	O
master	O
hologram	B-Algorithm
and	O
mounted	O
on	O
a	O
metal	O
backing	O
plate	O
.	O
</s>
<s>
The	O
material	O
used	O
to	O
make	O
embossed	O
copies	O
consists	O
of	O
a	O
polyester	O
base	O
film	O
,	O
a	O
resin	O
separation	O
layer	O
and	O
a	O
thermoplastic	O
film	O
constituting	O
the	O
holographic	B-Algorithm
layer	O
.	O
</s>
<s>
In	O
order	O
to	O
permit	O
the	O
viewing	O
of	O
embossed	O
holograms	B-Algorithm
in	O
reflection	O
,	O
an	O
additional	O
reflecting	O
layer	O
of	O
aluminum	O
is	O
usually	O
added	O
on	O
the	O
hologram	B-Algorithm
recording	O
layer	O
.	O
</s>
<s>
The	O
first	O
book	O
to	O
feature	O
a	O
hologram	B-Algorithm
on	O
the	O
front	O
cover	O
was	O
The	O
Skook	O
(	O
Warner	O
Books	O
,	O
1984	O
)	O
by	O
JP	O
Miller	O
,	O
featuring	O
an	O
illustration	O
by	O
Miller	O
.	O
</s>
<s>
The	O
first	O
record	O
album	O
cover	O
to	O
have	O
a	O
hologram	B-Algorithm
was	O
"	O
UB44	O
"	O
,	O
produced	O
in	O
1982	O
for	O
the	O
British	O
group	O
UB40	O
by	O
Advanced	O
Holographics	B-Algorithm
in	O
Loughborough	O
.	O
</s>
<s>
This	O
featured	O
a	O
5.75	O
inch	O
square	O
embossed	O
hologram	B-Algorithm
showing	O
a	O
3D	O
image	O
of	O
the	O
letters	O
UB	O
carved	O
out	O
of	O
polystyrene	O
to	O
look	O
like	O
stone	O
and	O
the	O
numbers	O
44	O
hovering	O
in	O
space	O
on	O
the	O
picture	O
plane	O
.	O
</s>
<s>
On	O
the	O
inner	O
sleeve	O
was	O
an	O
explanation	O
of	O
the	O
holographic	B-Algorithm
process	O
and	O
instructions	O
on	O
how	O
to	O
light	O
the	O
hologram	B-Algorithm
.	O
</s>
<s>
National	O
Geographic	O
published	O
the	O
first	O
magazine	O
with	O
a	O
hologram	B-Algorithm
cover	O
in	O
March	O
1984	O
.	O
</s>
<s>
Embossed	O
holograms	B-Algorithm
are	O
used	O
widely	O
on	O
credit	O
cards	O
,	O
banknotes	O
,	O
and	O
high	O
value	O
products	O
for	O
authentication	O
purposes	O
.	O
</s>
<s>
It	O
is	O
possible	O
to	O
print	O
holograms	B-Algorithm
directly	O
into	O
steel	O
using	O
a	O
sheet	O
explosive	O
charge	O
to	O
create	O
the	O
required	O
surface	O
relief	O
.	O
</s>
<s>
The	O
Royal	O
Canadian	O
Mint	O
produces	O
holographic	B-Algorithm
gold	O
and	O
silver	O
coinage	O
through	O
a	O
complex	O
stamping	O
process	O
.	O
</s>
<s>
A	O
hologram	B-Algorithm
can	O
be	O
copied	O
optically	O
by	O
illuminating	O
it	O
with	O
a	O
laser	O
beam	O
,	O
and	O
locating	O
a	O
second	O
hologram	B-Algorithm
plate	O
so	O
that	O
it	O
is	O
illuminated	O
both	O
by	O
the	O
reconstructed	O
object	O
beam	O
,	O
and	O
the	O
illuminating	O
beam	O
.	O
</s>
<s>
When	O
the	O
hologram	B-Algorithm
plate	O
is	O
illuminated	O
by	O
a	O
laser	O
beam	O
identical	O
to	O
the	O
reference	O
beam	O
which	O
was	O
used	O
to	O
record	O
the	O
hologram	B-Algorithm
,	O
an	O
exact	O
reconstruction	O
of	O
the	O
original	O
object	O
wavefront	O
is	O
obtained	O
.	O
</s>
<s>
If	O
several	O
objects	O
were	O
present	O
when	O
the	O
hologram	B-Algorithm
was	O
recorded	O
,	O
the	O
reconstructed	O
objects	O
move	O
relative	O
to	O
one	O
another	O
,	O
i.e.	O
</s>
<s>
exhibit	O
parallax	B-Device
,	O
in	O
the	O
same	O
way	O
as	O
the	O
original	O
objects	O
would	O
have	O
done	O
.	O
</s>
<s>
It	O
was	O
very	O
common	O
in	O
the	O
early	O
days	O
of	O
holography	B-Algorithm
to	O
use	O
a	O
chess	O
board	O
as	O
the	O
object	O
and	O
then	O
take	O
photographs	O
at	O
several	O
different	O
angles	O
using	O
the	O
reconstructed	O
light	O
to	O
show	O
how	O
the	O
relative	O
positions	O
of	O
the	O
chess	O
pieces	O
appeared	O
to	O
change	O
.	O
</s>
<s>
A	O
holographic	B-Algorithm
image	I-Algorithm
can	O
also	O
be	O
obtained	O
using	O
a	O
different	O
laser	O
beam	O
configuration	O
to	O
the	O
original	O
recording	O
object	O
beam	O
,	O
but	O
the	O
reconstructed	O
image	O
will	O
not	O
match	O
the	O
original	O
exactly	O
.	O
</s>
<s>
When	O
a	O
laser	O
is	O
used	O
to	O
reconstruct	O
the	O
hologram	B-Algorithm
,	O
the	O
image	O
is	O
speckled	O
just	O
as	O
the	O
original	O
image	O
will	O
have	O
been	O
.	O
</s>
<s>
This	O
can	O
be	O
a	O
major	O
drawback	O
in	O
viewing	O
a	O
hologram	B-Algorithm
.	O
</s>
<s>
Normally	O
,	O
if	O
a	O
hologram	B-Algorithm
is	O
illuminated	O
by	O
a	O
white	O
light	O
source	O
,	O
each	O
wavelength	O
can	O
be	O
considered	O
to	O
generate	O
its	O
own	O
holographic	B-Algorithm
reconstruction	O
,	O
and	O
these	O
will	O
vary	O
in	O
size	O
,	O
angle	O
,	O
and	O
distance	O
.	O
</s>
<s>
However	O
,	O
a	O
holographic	B-Algorithm
image	I-Algorithm
can	O
be	O
obtained	O
using	O
white	O
light	O
in	O
specific	O
circumstances	O
,	O
e.g.	O
</s>
<s>
with	O
volume	B-Algorithm
holograms	I-Algorithm
and	O
rainbow	O
holograms	B-Algorithm
.	O
</s>
<s>
The	O
white	O
light	O
source	O
used	O
to	O
view	O
these	O
holograms	B-Algorithm
should	O
always	O
approximate	O
to	O
a	O
point	O
source	O
,	O
i.e.	O
</s>
<s>
a	O
fluorescent	O
lamp	O
)	O
will	O
not	O
reconstruct	O
a	O
hologram	B-Algorithm
since	O
its	O
light	O
is	O
incident	O
at	O
each	O
point	O
at	O
a	O
wide	O
range	O
of	O
angles	O
,	O
giving	O
multiple	O
reconstructions	O
which	O
will	O
"	O
wipe	O
"	O
one	O
another	O
out	O
.	O
</s>
<s>
A	O
reflection-type	O
volume	B-Algorithm
hologram	I-Algorithm
can	O
give	O
an	O
acceptably	O
clear	O
reconstructed	O
image	O
using	O
a	O
white	O
light	O
source	O
,	O
as	O
the	O
hologram	B-Algorithm
structure	O
itself	O
effectively	O
filters	O
out	O
light	O
of	O
wavelengths	O
outside	O
a	O
relatively	O
narrow	O
range	O
.	O
</s>
<s>
In	O
theory	O
,	O
the	O
result	O
should	O
be	O
an	O
image	O
of	O
approximately	O
the	O
same	O
colour	O
as	O
the	O
laser	O
light	O
used	O
to	O
make	O
the	O
hologram	B-Algorithm
.	O
</s>
<s>
Such	O
a	O
hologram	B-Algorithm
recorded	O
in	O
a	O
silver	O
halide	O
gelatin	O
emulsion	O
by	O
red	O
laser	O
light	O
will	O
usually	O
display	O
a	O
green	O
image	O
.	O
</s>
<s>
In	O
this	O
method	O
,	O
parallax	B-Device
in	O
the	O
vertical	O
plane	O
is	O
sacrificed	O
to	O
allow	O
a	O
bright	O
,	O
well-defined	O
,	O
gradiently	O
colored	O
reconstructed	O
image	O
to	O
be	O
obtained	O
using	O
white	O
light	O
.	O
</s>
<s>
The	O
rainbow	O
holography	B-Algorithm
recording	O
process	O
usually	O
begins	O
with	O
a	O
standard	O
transmission	O
hologram	B-Algorithm
and	O
copies	O
it	O
using	O
a	O
horizontal	O
slit	O
to	O
eliminate	O
vertical	O
parallax	B-Device
in	O
the	O
output	O
image	O
.	O
</s>
<s>
The	O
viewer	O
is	O
therefore	O
effectively	O
viewing	O
the	O
holographic	B-Algorithm
image	I-Algorithm
through	O
a	O
narrow	O
horizontal	O
slit	O
,	O
but	O
the	O
slit	O
has	O
been	O
expanded	O
into	O
a	O
window	O
by	O
the	O
same	O
dispersion	O
that	O
would	O
otherwise	O
smear	O
the	O
entire	O
image	O
.	O
</s>
<s>
Horizontal	O
parallax	B-Device
information	O
is	O
preserved	O
but	O
movement	O
in	O
the	O
vertical	O
direction	O
results	O
in	O
a	O
color	O
shift	O
rather	O
than	O
altered	O
vertical	O
perspective	O
.	O
</s>
<s>
Because	O
perspective	O
effects	O
are	O
reproduced	O
along	O
one	O
axis	O
only	O
,	O
the	O
subject	O
will	O
appear	O
variously	O
stretched	O
or	O
squashed	O
when	O
the	O
hologram	B-Algorithm
is	O
not	O
viewed	O
at	O
an	O
optimum	O
distance	O
;	O
this	O
distortion	O
may	O
go	O
unnoticed	O
when	O
there	O
is	O
not	O
much	O
depth	O
,	O
but	O
can	O
be	O
severe	O
when	O
the	O
distance	O
of	O
the	O
subject	O
from	O
the	O
plane	O
of	O
the	O
hologram	B-Algorithm
is	O
very	O
substantial	O
.	O
</s>
<s>
Stereopsis	B-Algorithm
and	O
horizontal	O
motion	O
parallax	B-Device
,	O
two	O
relatively	O
powerful	O
cues	O
to	O
depth	O
,	O
are	O
preserved	O
.	O
</s>
<s>
The	O
holograms	B-Algorithm
found	O
on	O
credit	O
cards	O
are	O
examples	O
of	O
rainbow	O
holograms	B-Algorithm
.	O
</s>
<s>
These	O
are	O
technically	O
transmission	O
holograms	B-Algorithm
mounted	O
onto	O
a	O
reflective	O
surface	O
like	O
a	O
metalized	O
polyethylene	O
terephthalate	O
substrate	O
commonly	O
known	O
as	O
PET	O
.	O
</s>
<s>
Exact	O
reconstruction	O
is	O
required	O
in	O
holographic	B-Algorithm
interferometry	I-Algorithm
,	O
where	O
the	O
holographically	O
reconstructed	O
wavefront	O
interferes	O
with	O
the	O
wavefront	O
coming	O
from	O
the	O
actual	O
object	O
,	O
giving	O
a	O
null	O
fringe	O
if	O
there	O
has	O
been	O
no	O
movement	O
of	O
the	O
object	O
and	O
mapping	O
out	O
the	O
displacement	O
if	O
the	O
object	O
has	O
moved	O
.	O
</s>
<s>
This	O
requires	O
very	O
precise	O
relocation	O
of	O
the	O
developed	O
holographic	B-Algorithm
plate	O
.	O
</s>
<s>
For	O
instance	O
,	O
the	O
reconstructed	O
image	O
is	O
magnified	O
if	O
the	O
laser	O
used	O
to	O
reconstruct	O
the	O
hologram	B-Algorithm
has	O
a	O
longer	O
wavelength	O
than	O
the	O
original	O
laser	O
.	O
</s>
<s>
Since	O
each	O
point	O
in	O
the	O
object	O
illuminates	O
all	O
of	O
the	O
hologram	B-Algorithm
,	O
the	O
whole	O
object	O
can	O
be	O
reconstructed	O
from	O
a	O
small	O
part	O
of	O
the	O
hologram	B-Algorithm
.	O
</s>
<s>
Thus	O
,	O
a	O
hologram	B-Algorithm
can	O
be	O
broken	O
up	O
into	O
small	O
pieces	O
and	O
each	O
one	O
will	O
enable	O
the	O
whole	O
of	O
the	O
original	O
object	O
to	O
be	O
imaged	O
.	O
</s>
<s>
One	O
does	O
,	O
however	O
,	O
lose	O
information	O
and	O
the	O
spatial	O
resolution	O
gets	O
worse	O
as	O
the	O
size	O
of	O
the	O
hologram	B-Algorithm
is	O
decreased	O
–	O
the	O
image	O
becomes	O
"	O
fuzzier	O
"	O
.	O
</s>
