Reflection Holograms

Rainbow Holograms

Rainbow holograms are holograms which can be viewed in white light. They are made by a double holographic process where an ordinary hologram such as a transmission hologram is used as the object and a second hologram is made through a slit. A horizontal slit limits the vertical perspective of the first image so that there is no vertical parallax in the resultant rainbow hologram. This slit process removes the coherence requirement on the viewing light so that full advantage can be taken of the image brightness obtained from ordinary room light, while maintaining the three-dimensional character of the image as the viewers eye is moved horizontally. If the viewers eye is moved vertically, no parallax is seen and the image color sweeps through the rainbow spectrum from blue to red, hence "rainbow hologram".

Denisyuk Holograms

Denisyuk contributed to the development of the hologram by using Lippmann's photographic process to make reflection holograms which could be viewed in color if more than one coherent source was available. In his method the beam was passed through the photographic emulsion and back reflected from the object. The emulsion could then be mounted on a reflective backing for viewing by reflected light.

Hologram History

Historical notes:

Gabor was the discoverer of the hologram and received the Nobel Prize in Physics for it in 1971. This was pre-laser holography of course, and he made holograms only of transparencies where his reference beam was the unobstructed light which went through the clear parts of the transparency.

Leith and Upatnieks developed the off-axis reference beam method which is most often used today. It permitted the making of holograms of solid objects by reflected light.

Denisyuk contributed to the development by using Lippmann's photographic process to make reflection holograms which could be viewed in color if more than one coherent source was available. In his method the beam was passed through the photographic emulsion and back reflected from the object. The emulsion could then be mounted on a reflective backing for viewing by reflected light.

Benton is credited with the development of the rainbow hologram. Since it can be mass-copied and viewed with incoherent white light, it has become the most common type of hologram. Rainbow holograms have appeared on National Geographic's cover and on millions of credit cards as a deterrent to counterfeiting.

Composite holograms are made as multiple strips so that you get a different image from different angles. They can be viewed in white light.