Digital Holography for 3D Printing - A Proposal

In the absence of a CAD model for an object, a 3D printer cannot produce a part.  One approach has been to use specialized video recorders to capture images of the object and then extract a 3D CAD model from those images.  There could be issues with the tolerances of the generated 3D CAD model with such devices.

Solution

In lieu of a CAD model of the object, a digital hologram of that object may be used.  In digital holography the numerical reconstruction of object data is from the recorded measurement data, in distinction to an optical reconstruction which reproduces an aspect of the object. Digital holography typically delivers three-dimensional surface or optical thickness data. There are different techniques available in practice, depending on the intended purpose.  See, for example, http://en.wikipedia.org/wiki/Digital_holography .

By recording the phase as well as intensity of light wave, holography allows reconstruction of the images of three-dimensional objects since the hologram contains all the information needed to reconstruct an image (real or virtual) of these objects in 3 dimensions. The conventional process of holography uses photographic plates. Note that in this approach to holography, real-time process is not feasible unless one uses photo-refractive and other nonlinear optical materials. 

The first ingredient of this disclosure is the construction of a 360-degree digital hologram of an object.  There are multiple known ways of creating a 360-degree hologram using a single reference beam such as Conical Denisyuk Holograms, Cylindrical Denisyuk Holograms, 360-degree Flat Holograms, 360-degree Transmission Holograms. 

The key requirement for this disclosure is that the holographic interference pattern is digitally sampled by CCD/CMOS camera and the image is numerically reconstructed by applying the results from the diffraction theory.  This is pre-existing art and various research teams have accomplished this task.  Please see the http://www.springer.com/physics/optics+%26+lasers/book/978-0-387-31340-5 and the references therein.

There is another method, called Computer Generated Holography (CGH), for generating holographic interference patterns.  In this method a holographic image can be generated; i.e. by digitally computing a holographic interference pattern from digitally captured images.  This computed pattern can then be printed onto a mask or film for subsequent illumination by suitable coherent light source.

Both of these methods lead to the same outcome, the creation of a digital hologram.

These approaches to the construction of a digital hologram offers a number of significant advantages such as the ability to acquire the images rapidly, the availability of both the amplitude and the phase information of the optical field and the versatility of the processing techniques that can be applied to the complex field data.

Note that because in digital holography, the phase of the optical field, as well as the amplitude, results directly from the numerical diffraction of the optically recorded holographic interference pattern, one can have images of optical thickness profile with a precision of a fraction of a wavelength.

Now, the next step.

After the construction of the digital hologram, it can be made to numerically interact with a numeric coherent reference beam of using computer software and the theory of Wave Optics.  That is, a 3D digital image of the object can thus be created in the computer memory that contains both phase and intensity information.  This reconstructed digital image can then be fed, via a suitable control mechanism, to the laser printer heads of the 3D printer and guide the construction of the 3D part.

Possible Modifications

A different approach for using holograms in 3D printing is to forego the digitalization step all together and to capture 360-degree hologram of the object on holographic film.

Yet another approach is to record the digital hologram on holographic film and use the holographic film to create an image.

Either way, the next, using the reference beam and a converging lens, one can create a real image of the object in space within the 3D printer chamber.  This is called a pseudoscopic 3D image; please see https://www.youtube.com/watch?x-yt-ts=1422327029&v=_Y9rmizlrg8&x-yt-cl=84838260  

Printer heads, in this embodiment, like an ink-jet printer head, would spew out a suitable polymeric material.  The jets would be directed at the location of the real pseudoscopic image that is created via the interaction of the laser reference beam and the hologram.  The real image would then sinter the polymer material.  Depending on the geometry of the 3D image, the printer-heads could move up-down or down-up.

Yet another approach is to record the digital hologram on holographic film.