Leith and Upatnieks needed a laser to reconstruct their 1962 hologram

What you see

By the University of Michigan's own account of this work, Emmett Leith (1927-2005), the object recorded in this specific 1962 result was a photographic transparency, not yet an arbitrary solid object. Illuminating the developed plate with a beam matching the original reference beam reconstructed a virtual image that, in Leith's own recollection quoted by the university, was "indistinguishable from the original object itself." Full-parallax holograms of ordinary three-dimensional objects, the kind now most associated with the word, came from the same pair about a year later.

How it works

The paper itself, "Reconstructed Wavefronts and Communication Theory," published in the October 1962 issue of the Journal of the Optical Society of America, frames hologram-making as three linked operations: a modulation, a frequency dispersion, and a square-law detection, with reconstruction as the inverse. In practice this is the off-axis, or carrier-frequency, method: coherent laser light is split into an object beam and a reference beam angled obliquely onto the recording plate rather than head-on as in Gabor's original arrangement. Separating the beams by angle also separates the reconstructed image from its distracting mirror-image twin, since the two now travel in different directions. Michigan's account adds that Leith recalled the coherence needed was, if anything, about 15 percent less demanding than Gabor's original method, despite the cleaner result.

Viewing conditions and limits

Reconstruction at this stage required illumination by a beam closely matching the original reference beam's direction and wavelength, ordinarily a laser rather than daylight or an incandescent bulb. A hologram made by this 1962 method could not yet be viewed under ordinary room light, and it existed only as a laboratory transparency-hologram method rather than a display technology for physical objects.

What it is not

This is not yet a diffuse hologram of a solid object with the parallax most people now picture when they hear the word "hologram"; that step followed in fall 1963, once adequately coherent lasers were available. It is also not the first proposal to notice Gabor's twin-image problem, which Gabor himself had already identified without solving; it is the specific engineering fix, an obliquely angled reference beam, that made the fix work.

• Does a claimed "1962 hologram" describe a photographic transparency or an arbitrary solid object?
• Could the described hologram be viewed under ordinary light, or did it require laser illumination to reconstruct?
• Is the twin-image problem this paper solved named, or is the paper credited with holography's invention outright?

Solving the twin-image problem with an oblique reference beam is a specific, dateable engineering step, distinct from either Gabor's original 1948 proposal or the laser-illuminated three-dimensional holograms Leith and Upatnieks would show the following year. Each of the three deserves its own credit.