Chapter 7

Rainbow Hologram

-If white light is used in reconstruction of a hologram, the spectral color images will be projected out at different vertical angles -the observer can see different color images by moving their head up and down

Most Basic Hologram

-a hologram of a point object -called a Gabor Zone Plate

How does one get an image from a hologram?

-actual hologram looks nothing like the point object -if placed in a parallel beam, it will give both real and virtual foci and images

How did Leith and Upatneiks improve holograms?

-brought laser and its superior coherence -off-axis technique allowed 3D objects and visual separation of real and virtual images -done by splitting beam between reflection and photographic plate

How do Fresnel Zone Plates focus?

-each zone is 1/2 wavelength further away from the focal point, but because every other zone is blackened, the transparent zones are at one wavelength intervals -as a result, the light passing through arrives at the focal point in phase and constructively interfere to create a bright spot

Fresnel Zone Plate

-has imaging properties like a lens, but uses diffraction and interference rather than refraction -concentric circles get closer together as they get larger -every other circle blackened

White Light Reflection Hologram

-if enough reflecting surfaces are present, then white light can be used in reconstruction -reduces cost

Problems with Early Holograms

-lack of good, coherent source of light (fixed by laser) -used filtered light which was incoherent and caused "noise" in image (fixed by laser) -limited to 2D transparencies -viewer saw both real and virtual image superimposed on each other

Holography

-method of storing images on film -essentially 3D, lensless photography

What is a hologram an interference pattern between?

-the Object Beam and the Reference Beam

Multiplex Hologram

-whole scene first recorded on ordinary motion picture film -device converts developed frame of movie to strip holograms -repeat for each frame until all frames of scene are recorded in vertical strips on one long, holographic film -displays limited to 45 seconds

2 Solutions to Mechanical Vibration

1. supporting systems on air or sand that limit movement 2. pulsed laser that gives a short exposure that nothing has time to move

White Light Transmission Hologram

1968: Stephen Benton of Polaroid -places horizontal slit in front of object -places real image of object near plane of hologram -horizontal slit restricts angle in vertical direction from which final image can be viewed -there's not vertical parallax, but this won't affect final image because we see with our eyes separated in horizontal direction

Who invented the holographic process?

Dennis Gabor, 1948

Gabor Zone Plate vs Fresnel Zone Plate

In the hologram, the change from a light to dark zone is gradual, while it is abrupt in Fresnel Zone Plates

What do photos and holograms store and record respectively?

PHOTOS: wave amplitude at plane of film HOLOGRAMS: Amplitude and Phase info from object **one hologram is like many photos at different angles

What was holographic process originally called?

Wavefront Reconstruction

Hologram

detailed, three dimensional image that is made of a complex interference pattern

Reference Beam

light directly from source

Object Beam

light reflected from object

Why do holograms require isolation from mechanical vibration?

movement can destroy interference pattern

Spatial Filtering

process in which laser beam is focused down to pass through a pinhole to produce a larger, spatially coherent beam