A brief introduction on holography and holograms

2. Dr. RENJU R KRISHNAN
ASSISTANT PROFESSOR AND HEAD
PG DEPARTMENT OF PHYSICS
ST. XAVIER’S COLLEGE, THUMBA
THIRUVANANTHAPURAM
HOLOGRAPHY

3. Holography is a two-step, lensless process of optical imagery, in
which 3 dimensional image of a 2 dimensional object is obtained.
The term holography is derived from greek words ‘holos’
meaning whole and ‘gram’ meaning writing or viewing.
Holography is "lensless photography" in which an image is
captured not as an image focused on film, but as an interference
pattern at the film.

4. A hologram is a recording in a two- or three-dimensional medium of the
interference
pattern formed when a point source of light (the reference beam) of fixed
wavelength
encounters light of the same fixed wavelength arriving from an object
(the object beam). When the hologram is illuminated by the reference beam
alone,
the interference pattern recreates the wave fronts of light from the original
object

5. These three images of the same hologram were taken by positioning the camera
at three positions, moving the camera from left to right. Note that the pawn
appears on the right side of the king in the left photo, but transitions to the left
of the king as you move the viewing position across the hologram so that you
are viewing it from further to the right. This is real parallax, which tells you
that the image is truly 3-dimensional

6. THEORY OF HOLOGRAPHY
 RECORDING OF A HOLOGRAM
 RECONSTRUCTION OF THE IMAGE

7. Step 1: Recording of a hologram

8. Step 2: Reconstruction of the image

9. HOW DOES THE IMAGE ON A HOLOGRAM LOOK
LIKE?
 The image on the film for a transmission hologram is formed by the
interference of the light from the object and the reference beam. This
interference pattern looks something like the ripples on a pond when a
bunch of small pebbles is thrown in. The interference pattern on this
hologram is extraordinarily well defined
 Viewing a transmission hologram involves illuminating it with a
coherent source like a laser and looking through the film at the
image in space behind the film. The image shown is associated with
the interference pattern shown

10. DIFFERENCE BETWEEN HOLOGRAM AND
PHOTOGRAPH (1/2)
 A photograph is a 2D representation of an object, whereas a hologram is a 3D
representation of the object
 A photograph can be recorded using normal light sources (sunlight or electric
lighting) whereas a laser is required to record a hologram
 In a photograph, only the intensity variations of light is recorded. Whereas, in a
hologram, the phase variations of the light is also recorded
 A lens is required in photography to record the image, whereas in holography,
the light from the object is scattered directly onto the recording medium

11.  When a photograph is cut in half, each piece shows half of the
scene. When a hologram is cut in half, the whole scene can still be
seen in each piece. This is because, whereas each point in a
photograph only represents light scattered from a single point in the
scene, each point on a holographic recording includes information
about light scattered from every point in the scene
Difference between hologram and photograph
(2/2)