Adventures in Holography in the 1960's
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Goodman, Joseph W.
In the 1960’s, I was fortunate to participate in the renaissance in holography that was launched in the U.S. by Emmett Leith and Juris Upatnieks. In this paper, I discuss some of our early activities in holography at Stanford. My discussion will cover the following subjects: Long distance holography (1966-69) – holography over a 12 km path; Digital reconstruction of holographic images (1967) – detection of a hologram on a vidicon and reconstruction of the image by computer; and Photon-limited holography (1968) – experiments verifying Gabor’s prediction tha,t under the right conditions, holography can be a more sensitive detection image method than conventional direct detection. These might be considered esoteric subjects, far from display holography. In at least one case, the work turned out to be important.
 Good afternoon, ladies and gentlemen. Let me begin by adding my personal welcome to this eighth international symposium on display holography, and to give you my sincere regrets that I am not in Shenzhen with you. I would like to express my deepest thanks to TJ and Frank for honoring me with the title Honorary Chairman of the Meeting. My talk today will be mostly about my personal involvement with holography in the 1960s, a time that was certainly one of the most exciting periods in the development of holography. I'll focus on research carried out at Stanford for its this work that I know best. Let me begin my talk by recognizing the founders of our field, Dennis Gabor, who received the Nobel Prize for his invention of holography Emmett Leith and Eurus Upatinix, who modified Gabor's ideas to vastly improve holography. Leith received the US Medal of Science and Upatinix the Grand Medal of the Latvian Academy of Sciences, and finally Yuri Denysyak, the inventor of reflection holography, who received the Lenin Prize for this work. The work I'll talk about today is certainly not of the same caliber as their work, but nonetheless I hope you'll find it interesting. Let me also pay tribute to the giants of the field of display holography, Lloyd Cross, the inventor of the multiplex hologram, and Stephen Benton, the inventor of the rainbow hologram. Examples of images from their holograms are also shown here. They've both had an enormous impact on the field of display holography. Next I'd like to show you a photo taken at a Stanford display holography meeting in the late 1960s. Albert Baez, an outstanding scientist and scientific diplomat shown in the center of this image, was asked by Encyclopedia Britannica to organize a small meeting at Stanford of people interested in holographic display to talk about the possibility of publishing a hologram in the Encyclopedia. At the left of this picture is Art Shallow, co-inventor of the laser and Nobel Prize winner. Next to him is his assistant who set up experiments for him. Unfortunately I've forgotten his name. Moving to the right you find my colleague, Matt Layman, who was responsible for much of the experimental holography work at Stanford in this time frame. To the right of Albert Baez is a much younger me. To the right of me is Hussain El-Sum, who made holograms as a graduate student in physics at Stanford in the 1950s. To the right of him is Ralph Worker, a co-inventor of pulsed holographic interferometry who worked at TRW in Los Angeles. Finally on the far right is Professor Paul Kirk Patrick of the physics department at Stanford, the co-inventor of the X-ray microscope together with Baez and the PhD supervisor of Baez, El-Sum and Worker. After our discussions we retired to Professor Kirk Patrick's home where we were served coffee and cookies by Joan Baez, the famous folk singer, the daughter of Albert Baez. After this general history I'd like to move on to describing some of our work in holography at Stanford in the 1960s. I'll first talk about the work we did in long distance holography. Then I'll turn to digital reconstruction of images from electronically detected holograms. And finally I'll speak about experiments in photon limited holography. First I consider long distance holography. The 1960s were in the midst of the Cold War and the US and the Soviet Union were each very nervous about the purposes of some of the satellites the other side was launching into space. It was highly desirable to obtain high resolution images of the others orbiting satellites and from those images determine what one could about the purpose of the spacecrafts. Unfortunately the resolution of images obtained from ground-based telescopes, the resolution was extremely poor due to distortions introduced by atmospheric turbulence near the ground. New methods for imaging through turbulence were of great interest. Here you see a picture of a Soviet Phobos satellite on the left and a typical image of a Soviet satellite obtained with a ground-based telescope shown on the right. In 1966 my colleagues and I realized that holography had a distinct advantage over conventional imaging when imaging through turbulence that is close to the entrance pupil of the imaging system. When a coherent reference beam and object beam suffer the same phase distortions on passing through a distorting medium such as atmospheric turbulence the fringe pattern recorded by a hologram is unaffected by the presence of distortions provided the reference and object are not too far apart. In retrospect we realized that this is simply a case of common path interferometry. The question then arose as to whether holography could be used to obtain high-resolution images of the unknown orbiting satellites. Many questions about applying this phenomenon to imaging orbiting objects occurred immediately. I should note that the US and the Soviet Union had signed a treaty pledging that neither side would illuminate the other satellites with lasers so these ideas would be relevant only if this treaty broke down. How would one obtain a reference wave? Could specular reflections from the object itself serve this purpose? Specular reflections were common in conventional images of such objects. Could holograms really be recorded over long distances? Were pulse ruby lasers sufficiently coherent? Could sufficient signal-to-noise ratio be achieved? How would the holograms be detected and the images reconstructed? These questions stimulated a series of research projects that we undertook. In 1968 and 1969 we performed a series of long-distance holography experiments at an observatory in Cloudcroft, New Mexico. The telescope had a primary mirror of 1.2 meter diameter and we attempted to image objects over a 12 kilometer horizontal path. Note that this is not the ideal path for holography for it works best when the atmospheric turbulence is primarily near the telescope. A Q-switched ruby laser located at the telescope was used for illumination of the distant objects. In these experiments the reference was supplied by a corner cube reflector next to the object so lensless Fourier transform holograms were recorded. In this slide a profile of the 12 kilometer path is shown and a diagram of the telescope optics. Note that the camera recording the hologram is focused on the primary mirror of the telescope. On the bottom left a scotch light bar target used as the object is shown and on the bottom right a typical hologram is shown. The interference fringes are quite clear. These images are of a different target in this case two corner cubes. The holographic image on the left is from a night of low atmospheric turbulence and the image on the right from a night of high atmospheric turbulence. On the night of good atmospheric seeing the two corner cubes are clearly resolved. Note the twin images which one expects in holography. You may not see much in this image but I see a lot. In this case the object was a uniform scotch light board used as background. In front of this board is my colleague Matt Lehmann 12 kilometers away with a pipe in his mouth. To help you see what I see I've sketched his head and pipe on the right. This particular experiment was performed over a shorter 1.9 kilometer path using a scotch light bar chart. On the left is the hologram. In the middle a reconstructed image from that hologram and on the right a conventional image of the same object. Object detail can be seen in the holographic image but not in the conventional image showing that under the right conditions there is an advantage to holographic imaging. Next I would like to turn to digital reconstruction of images from holograms work that we published in 1967. By way of background in 1966 Brown and Lehmann had published their first paper on computer generated holograms. In their work a mathematical object is assumed and a hologram of that object is computed and then plotted. The image of the mathematical object is then reconstructed optically. Our problem was in some sense the opposite. We wish to record a hologram optically on an electronic detector and then digitally reconstruct an image. Also in 1966 Enlo Murphy and Rubenstein of Bell Labs had electronically detected a hologram on a viticon then photographed a display of the hologram and reconstructed an image optically. We wish to dispense with optics in the reconstruction. We performed an experiment in which we detected an optical lensless Fourier transform hologram on a viticon as shown on the left of this slide and digitally reconstructed the image shown in the middle. An optically reconstructed image of the same object is shown on the right in the case of a hologram detected on film. Some comments on the experiment that I just described. The detector was a low quality viticon with the lens assembly removed. The coarse fringes seen arise due to second reflections from the glass plate cover on the viticon. As mentioned the hologram was of the lensless Fourier transform type. The object was a transparency of the letter P illuminated through a diffuser. The hologram was sampled in a 256 by 256 array which was twice the Nyquist rate. Now some comments on the calculated image. The FFT algorithm, the fast Fourier transform algorithm was first published by Kulian Tuki in 1965 and was used in these experiments. A PDP6 computer was used. The computation time for the image you see was 5 minutes and would have been 3 hours without the FFT algorithm. You see twin images as expected and you see speckle in the image as you might expect for a diffuse object. The two spots that are close to the optical axis arise from the second reflection fringe pattern mentioned earlier. It's interesting to compare our work in 1967 to what can be and is being done today. What took 5 minutes on a PDP6 computer in 1967 now takes less than 10 milliseconds on a desktop home computer. That's a gain of 30,000 from technology over just more than 40 years. In some current applications such as holographic and speckle interferometry, digital image formation is now the method of choice due to the fact that the data is electronic at the start. Digital reconstruction has also been used in soft X-ray holographic imaging as described in the reference shown. Here's an example of a commercial application of digital reconstruction from holograms. The microscope made by Linse Tech detects a hologram on a CCD array and reconstructs the image digitally, focusing digitally by changing the parameters of the reconstruction algorithm. Lastly, I'd like to discuss the noise performance of holographic detection as compared with conventional image detection. The work was done in 1968 with two graduate students, Richard Miles and Ralph Kimball. In unpublished work in the early 1950s, Gabor concluded that holography could be a more sensitive method of image detection than conventional focused image detection. He estimated that the advantage could be a factor of 10 in sensitivity. This advantage comes for very weak objects and requires the use of a very strong reference wave. When a strong reference wave interferes with a weak object wave, the detected information is in effect amplified by the reference wave, a phenomenon known as conversion gain in conventional heterodyne detection. As with heterodyne detection, holographic detection can approach the quantum limit of sensitivity for the detector used, whether it's film or an electronic detector. Experiments we performed in 1968 confirmed at least a tenfold advantage of holography in terms of the number of object photons required per object resolution cell. Our experiments were carried out on plus x film and the results were compared with conventional imaging. This slide shows experimental results for conventional focused images in the top row. Results for 9,000 photons, 4,500 photons, and 3,000 photons per object resolution cell are shown. It was found that 900 photons per resolution cell created an observable effect on the film negative, but the effect was too weak to reproduce in the journal publication. At the bottom we show a holographic image obtained with only 90 photons per object resolution cell copolarized with a reference wave. The coarsest bars can be seen quite easily. Hence, a tenfold improvement in sensitivity is a slightly conservative estimate of the gain. Finally, I want to mention that I have had the privilege during my career of working with 49 talented PhD students, about 20 of whom worked on problems related to holography and optical information processing. I've listed those 20 here, and I only want to point out a few that some of you might recognize. Jack Gaskell, University of Arizona, Alexander Saatchat, USC, James Fianna, University of Rochester, Raymond Kostak, University of Arizona. The two students who have received perhaps the highest positions are both women, indicated by the arrows and the photos. Ellen Ochoa on the bottom, Deputy Director of NASA's Johnson Space Flight Center, and a veteran of four space shuttle flights, approximately 1,000 hours in space. And Christina Johnson at the top, Dean of Engineering at Duke University, then Provost of Johns Hopkins University, and now Undersecretary of Energy in the Obama Administration. I'm very proud of all of my former students. By way of conclusions, the 1960s were without doubt the most exciting years of my career, due mainly to the advent of modern holography. Fundamental research problems in holography were to be found everywhere. At Stanford, we attacked a small subset of those problems, having a great deal of fun in the process. In closing, let me thank you all for listening to these historical reminiscences, which I hope you found interesting, even though they have little to do with display holography. Thank you.
 Good afternoon, ladies and gentlemen. Let me begin by adding my personal welcome to  this eighth international symposium on display holography, and to give you my sincere regrets  that I am not in Shenzhen with you. I would like to express my deepest thanks to TJ and  Frank for honoring me with the title Honorary Chairman of the Meeting. My talk today will  be mostly about my personal involvement with holography in the 1960s, a time that was certainly  one of the most exciting periods in the development of holography. I'll focus on research carried  out at Stanford for its this work that I know best. Let me begin my talk by recognizing the  founders of our field, Dennis Gabor, who received the Nobel Prize for his invention of holography  Emmett Leith and Eurus Upatinix, who modified Gabor's ideas to vastly improve holography. Leith  received the US Medal of Science and Upatinix the Grand Medal of the Latvian Academy of Sciences,  and finally Yuri Denysyak, the inventor of reflection holography, who received the Lenin Prize  for this work. The work I'll talk about today is certainly not of the same caliber as their work,  but nonetheless I hope you'll find it interesting. Let me also pay tribute to the giants of the  field of display holography, Lloyd Cross, the inventor of the multiplex hologram, and Stephen  Benton, the inventor of the rainbow hologram. Examples of images from their holograms are  also shown here. They've both had an enormous impact on the field of display holography. Next  I'd like to show you a photo taken at a Stanford display holography meeting in the late 1960s.  Albert Baez, an outstanding scientist and scientific diplomat shown in the center of this image,  was asked by Encyclopedia Britannica to organize a small meeting at Stanford of people interested  in holographic display to talk about the possibility of publishing a hologram in the Encyclopedia.  At the left of this picture is Art Shallow, co-inventor of the laser and Nobel Prize winner. Next  to him is his assistant who set up experiments for him. Unfortunately I've forgotten his name. Moving  to the right you find my colleague, Matt Layman, who was responsible for much of the experimental  holography work at Stanford in this time frame. To the right of Albert Baez is a much younger  me. To the right of me is Hussain El-Sum, who made holograms as a graduate student in physics  at Stanford in the 1950s. To the right of him is Ralph Worker, a co-inventor of pulsed holographic  interferometry who worked at TRW in Los Angeles. Finally on the far right is Professor Paul Kirk  Patrick of the physics department at Stanford, the co-inventor of the X-ray microscope together  with Baez and the PhD supervisor of Baez, El-Sum and Worker. After our discussions we retired  to Professor Kirk Patrick's home where we were served coffee and cookies by Joan Baez, the famous  folk singer, the daughter of Albert Baez. After this general history I'd like to move on to  describing some of our work in holography at Stanford in the 1960s. I'll first talk about  the work we did in long distance holography. Then I'll turn to digital reconstruction of  images from electronically detected holograms. And finally I'll speak about experiments in  photon limited holography. First I consider long distance holography. The 1960s were in the midst  of the Cold War and the US and the Soviet Union were each very nervous about the purposes of some  of the satellites the other side was launching into space. It was highly desirable to obtain  high resolution images of the others orbiting satellites and from those images determine what  one could about the purpose of the spacecrafts. Unfortunately the resolution of images obtained  from ground-based telescopes, the resolution was extremely poor due to distortions introduced by  atmospheric turbulence near the ground. New methods for imaging through turbulence were of great  interest. Here you see a picture of a Soviet Phobos satellite on the left and a typical image of a  Soviet satellite obtained with a ground-based telescope shown on the right. In 1966 my colleagues  and I realized that holography had a distinct advantage over conventional imaging when imaging  through turbulence that is close to the entrance pupil of the imaging system. When a coherent  reference beam and object beam suffer the same phase distortions on passing through a distorting  medium such as atmospheric turbulence the fringe pattern recorded by a hologram is unaffected  by the presence of distortions provided the reference and object are not too far apart. In  retrospect we realized that this is simply a case of common path interferometry. The question  then arose as to whether holography could be used to obtain high-resolution images of the unknown  orbiting satellites. Many questions about applying this phenomenon to imaging orbiting objects  occurred immediately. I should note that the US and the Soviet Union had signed a treaty pledging  that neither side would illuminate the other satellites with lasers so these ideas would be  relevant only if this treaty broke down. How would one obtain a reference wave? Could specular  reflections from the object itself serve this purpose? Specular reflections were common in  conventional images of such objects. Could holograms really be recorded over long distances? Were  pulse ruby lasers sufficiently coherent? Could sufficient signal-to-noise ratio be achieved?  How would the holograms be detected and the images reconstructed? These questions stimulated a  series of research projects that we undertook. In 1968 and 1969 we performed a series of long-distance  holography experiments at an observatory in Cloudcroft, New Mexico. The telescope had a primary  mirror of 1.2 meter diameter and we attempted to image objects over a 12 kilometer horizontal path.  Note that this is not the ideal path for holography for it works best when the atmospheric  turbulence is primarily near the telescope. A Q-switched ruby laser located at the telescope  was used for illumination of the distant objects. In these experiments the reference was supplied  by a corner cube reflector next to the object so lensless Fourier transform holograms were recorded.  In this slide a profile of the 12 kilometer path is shown and a diagram of the telescope optics.  Note that the camera recording the hologram is focused on the primary mirror of the telescope.  On the bottom left a scotch light bar target used as the object is shown and on the bottom  right a typical hologram is shown. The interference fringes are quite clear.  These images are of a different target in this case two corner cubes. The holographic image  on the left is from a night of low atmospheric turbulence and the image on the right from  a night of high atmospheric turbulence. On the night of good atmospheric seeing the two  corner cubes are clearly resolved. Note the twin images which one expects in holography.  You may not see much in this image but I see a lot. In this case the object was a uniform  scotch light board used as background. In front of this board is my colleague Matt Lehmann  12 kilometers away with a pipe in his mouth. To help you see what I see I've sketched his  head and pipe on the right. This particular experiment was performed over a shorter 1.9  kilometer path using a scotch light bar chart. On the left is the hologram. In the middle  a reconstructed image from that hologram and on the right a conventional image of the same  object. Object detail can be seen in the holographic image but not in the conventional image showing  that under the right conditions there is an advantage to holographic imaging. Next I would  like to turn to digital reconstruction of images from holograms work that we published  in 1967. By way of background in 1966 Brown and Lehmann had published their first paper  on computer generated holograms. In their work a mathematical object is assumed and  a hologram of that object is computed and then plotted. The image of the mathematical  object is then reconstructed optically. Our problem was in some sense the opposite. We  wish to record a hologram optically on an electronic detector and then digitally reconstruct  an image. Also in 1966 Enlo Murphy and Rubenstein of Bell Labs had electronically detected a  hologram on a viticon then photographed a display of the hologram and reconstructed an  image optically. We wish to dispense with optics in the reconstruction. We performed  an experiment in which we detected an optical lensless Fourier transform hologram on a viticon  as shown on the left of this slide and digitally reconstructed the image shown in the middle.  An optically reconstructed image of the same object is shown on the right in the case of  a hologram detected on film. Some comments on the experiment that I just described. The  detector was a low quality viticon with the lens assembly removed. The coarse fringes  seen arise due to second reflections from the glass plate cover on the viticon. As mentioned  the hologram was of the lensless Fourier transform type. The object was a transparency  of the letter P illuminated through a diffuser. The hologram was sampled in a 256 by 256 array  which was twice the Nyquist rate. Now some comments on the calculated image. The FFT  algorithm, the fast Fourier transform algorithm was first published by Kulian Tuki in 1965  and was used in these experiments. A PDP6 computer was used. The computation time for  the image you see was 5 minutes and would have been 3 hours without the FFT algorithm.  You see twin images as expected and you see speckle in the image as you might expect for  a diffuse object. The two spots that are close to the optical axis arise from the second  reflection fringe pattern mentioned earlier. It's interesting to compare our work in 1967  to what can be and is being done today. What took 5 minutes on a PDP6 computer in 1967  now takes less than 10 milliseconds on a desktop home computer. That's a gain of 30,000 from  technology over just more than 40 years. In some current applications such as holographic  and speckle interferometry, digital image formation is now the method of choice due  to the fact that the data is electronic at the start. Digital reconstruction has also  been used in soft X-ray holographic imaging as described in the reference shown. Here's  an example of a commercial application of digital reconstruction from holograms. The  microscope made by Linse Tech detects a hologram on a CCD array and reconstructs the image digitally,  focusing digitally by changing the parameters of the reconstruction algorithm. Lastly, I'd  like to discuss the noise performance of holographic detection as compared with conventional image  detection. The work was done in 1968 with two graduate students, Richard Miles and Ralph Kimball.  In unpublished work in the early 1950s, Gabor concluded that holography could be a more  sensitive method of image detection than conventional focused image detection. He estimated that  the advantage could be a factor of 10 in sensitivity. This advantage comes for very weak objects  and requires the use of a very strong reference wave. When a strong reference wave interferes  with a weak object wave, the detected information is in effect amplified by the reference wave,  a phenomenon known as conversion gain in conventional heterodyne detection. As with heterodyne detection,  holographic detection can approach the quantum limit of sensitivity for the detector used,  whether it's film or an electronic detector. Experiments we performed in 1968 confirmed  at least a tenfold advantage of holography in terms of the number of object photons required  per object resolution cell. Our experiments were carried out on plus x film and the results  were compared with conventional imaging. This slide shows experimental results for conventional  focused images in the top row. Results for 9,000 photons, 4,500 photons, and 3,000 photons  per object resolution cell are shown. It was found that 900 photons per resolution cell  created an observable effect on the film negative, but the effect was too weak to reproduce in  the journal publication. At the bottom we show a holographic image obtained with only  90 photons per object resolution cell copolarized with a reference wave. The coarsest bars can  be seen quite easily. Hence, a tenfold improvement in sensitivity is a slightly conservative  estimate of the gain. Finally, I want to mention that I have had the privilege during my career  of working with 49 talented PhD students, about 20 of whom worked on problems related  to holography and optical information processing. I've listed those 20 here, and I only want  to point out a few that some of you might recognize. Jack Gaskell, University of Arizona, Alexander  Saatchat, USC, James Fianna, University of Rochester, Raymond Kostak, University of Arizona.  The two students who have received perhaps the highest positions are both women, indicated  by the arrows and the photos. Ellen Ochoa on the bottom, Deputy Director of NASA's Johnson  Space Flight Center, and a veteran of four space shuttle flights, approximately 1,000  hours in space. And Christina Johnson at the top, Dean of Engineering at Duke University,  then Provost of Johns Hopkins University, and now Undersecretary of Energy in the Obama  Administration. I'm very proud of all of my former students.  By way of conclusions, the 1960s were without doubt the most exciting years of my career,  due mainly to the advent of modern holography. Fundamental research problems in holography  were to be found everywhere. At Stanford, we attacked a small subset of those problems,  having a great deal of fun in the process. In closing, let me thank you all for listening  to these historical reminiscences, which I hope you found interesting, even though they  have little to do with display holography. Thank you.
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