Spr09 PHY 518 Dr MacIsaac Holography and Its Application in the Physics Classroom Timothy R Coughlin The 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 is still 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 that scatters 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 1 Spr09 PHY 518 Dr MacIsaac Figure 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 that appeared 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 of monochromatic 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 2 Spr09 PHY 518 Dr MacIsaac structural 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 with laser 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 angle that various monochromatic sources would produce the image Just as a rainbow is produced in Coughlin 3 Spr09 PHY 518 Dr MacIsaac a 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 light that 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 of multicolour 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 threedimensional 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 paint Jones Bey 2003 They can be easily recreated using merely a pair of dividers or classroom compass and a reflective surface like a piece of acrylic plastic used for a compact disc jewel case To construct a scratch hologram an image
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