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Buffalo State PHY 690 - Holography and Its Application

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Spr09 PHY 518 Dr. MacIsaacHolography and Its Application in the Physics ClassroomTimothy R. CoughlinThe study and measurement of the interference of waves is one that is essential to any classroom discussing the nature of light. The invention and application of the interferometer changed our very perception of physics and our place in the universe in the twentieth century. However, interference of light waves and interferometry is not always obvious in its application to real world use for students beyond the laboratory. According to Arons, “concrete experience isstill an essential factor in cultivating understanding of the phenomena and grasp of the extensive vocabulary that is generated” (Arons, 1997, 234). One extension of interferometry that has real world application to provide that concrete experience for students is holography. The process of making a hologram is illustrated below (see Figure 1). Essentially, a hologram is made by dividing a beam of light into two waves, one used as illuminating beam thatscatters from some object, and a reference beam that reflects directly toward a film. “The scattered light and the reference beam meet at the film and interfere” (Knight, p.690). This interference pattern from the object wave and reference wave is called a hologram. By later passing only the reference beam through the film, it is diffracted through the parts of the hologram that are transparent. The process of reconstructing the hologram can be seen below in Figure 2. The diffraction pattern of the reference beam is identical to the scattered wave from the object. “The diffracted reference beam reconstructs the original scattered wave. As you look at this diffracted wave, from the far side of the hologram, you “see” the object exactly as if it were there” (Knight, p.691).Coughlin 1Spr09 PHY 518 Dr. MacIsaacFigure 1. Optical arrangement for constructing a hologram (Holography, 2009). Figure 2. Optical arrangement for reconstructing a hologram (Holography, 2009).Some argue that the development of holograms occurred, but was not quite fully understood, long before holograms and holography were defined. For example, “…already as early as 1934 the inventor and artist Hans Weil patented a method to produce simple pictures thatappeared floating in space, by scratching a transparent or metallic surface in certain direction” (Abramson). However, most scientists, researchers, and historians will point to 1947 as the birth of holography. During this year, Dennis Gabor produced the “first” hologram. Using a source ofmonochromatic light and a nearly transparent object, Gabor was able to “store” the image of an object on an emulsified film. This first hologram, referred to as an “in-line” hologram as all the Coughlin 2Spr09 PHY 518 Dr. MacIsaacstructural components were “in-line” with each other, used light from a mercury vapor lamp that passed through a lens to both reflect off (object wave) and transmit through (reference wave) the object and interfere at the emulsifying film. His work later won the Nobel Prize in Physics in 1971 (Holography, 2009). These first holograms had many limitations in both resolution and the types of objects that could be captured on film. Holography did not come to be as it is known today until after the invention of the laser as a source of monochromatic light. From this development, a variety of different types, refinements, and subsequent applications of holograms arose.The first major development in holography that followed the laser can be credited to Emmett Leith and Jaris Upatnieks in 1962 in creating the transmission hologram (Leith, Upatnieks, 1962). Using the laser as the source of light, they successfully used a beam splitter, as described above, and then mirrors to change the coherence length of the phases of the two waves to produce clearer images of 3D objects. By changing the coherence length, different depth objects could be captured. However, these transmission holograms still needed to be illuminated later by the laser or another monochromatic light source to be viewed.In 1968, Robert Benton further refined the transmission hologram to be viewed under white light. These are called “rainbow-transmission holograms.” “The object is illuminated withlaser light, and an image is formed in the plane of the hologram plate used to record the hologram. A narrow horizontal slit is placed between the object and the lens. The hologram plate is also illuminated with a reference beam derived from the same laser, and the interference pattern between object and reference beams is recorded” (Rainbow Holograms, 2009). By viewing this type of hologram under white light, the observer can see the image from every anglethat various monochromatic sources would produce the image. Just as a rainbow is produced in Coughlin 3Spr09 PHY 518 Dr. MacIsaaca definite order based on the wavelengths of light, a rainbow hologram would produce an image at different angles through the slit, depending on the wavelength of light it was illuminated by. However, when illuminated by white light, all of the angles are accounted for and the full image can be seen from any point. “Rainbow holograms are commonly seen today on credit cards as a security feature and on product packaging” (Holography, 2009).Yuri Denisyuk then developed another type of hologram that could be viewed under white light. This was called a reflection hologram as the captured image reflected the white lightthat illuminated it (Holography, 2009). He did this by exposing the emulsion film with the reference beam on the opposite side of the beam scattered from the object. These reflection holograms are “type of hologram normally seen in holographic displays. They are also capable ofmulticolour-image reproduction” (Holography, 2009).Another type of hologram that is still being researched is that which is produced by viewing images through scratches like the one that Hans Weil patented in 1934. In this, bundles of light rays are manipulated instead of interfering wave fronts. William Beaty is credited with first publishing the method for producing these scratch holograms (Beaty, 1995). This was a phenomena Beaty chanced upon while walking through a parking lot and noticing a three-dimensional hand floating in the hood of a car left “by a polishing mitt ‘that had traced out millions of nearly parallel scratches in the black


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Buffalo State PHY 690 - Holography and Its Application

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