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A holography laser is part of a photography system that produces three-dimensional (3D) images of an object using laser light to illuminate and record its features, and special film to develop it in a form that gives the image depth and a different appearance when viewed from separate angles. Early forms of holography laser systems used just one laser and produced a monochromatic image, usually in bright green. New holographic technology developing into practical applications as of 2011, however, uses red, green, and blue lasers, as well as a white light source, to generate a 3D image that displays the natural color of the object that was scanned.
The film used in creating a basic hologram is usually a type of high-contrast black-and-white film with a silver halide coating. Advanced forms of materials that can record images, such as dichromated gelatin, photo sensitive plastics, or ferro-electric crystals, produce brighter images, but they may not have as much depth as the sharper effect silver halide film generates. Film-based holography laser systems create what are known as reflection holograms that can be viewed in ordinary light like a typical photograph, except that they have a 3D look to them.
The difference between using laser holography to record an image on film and a standard camera to do so is that the holographic process involves recording two overlapping light sources on one section of film. The laser is split into two beams as it targets the film, one which targets the film and one which illuminates the object being photographed. They then interact on the film and cause an interference pattern that creates a rudimentary 3D image.
One-half of the laser beam is channeled through a lens and reflected off of a mirror to directly impact on the film and not touch the object being photographed at all; this is called the reference beam. The other half of the laser beam is aimed directly at the object being recorded, known as the object beam. As this object beam hits the object, some of its light is naturally reflected back off of it and onto the film as well. These two beams of light then interact through constructive interference patterns on the film surface simultaneously, recording the image of the object from two different angles, since both beams originated from separate angles. This recorded image has an overlapping effect which lends it a sense of depth, and this is how all early holograms have been made.
The more advanced version of holography laser technology uses three laser colors — red, blue and green — and white light to generate a true-color image. This type of holography laser generates a transmission hologram, which, in some cases, can only be viewed by powering up the lasers themselves to recreate the image. All three colored lasers are aimed at the object to create interference patterns, as the object reflects back portions of this light. A white light is also shined on silver halide film to stimulate the reflected light from the lasers that has impacted it, generating a mixture of colors that resembles the true color of the object itself.
The science of laser holography has been in development since the 1960s, and still has a distance to go as of 2011 before it can generate large, 3D, true-color images of objects. Currently, generating full color 3D images of objects about the size of a small apple are the limits of the technology. A holography laser as of 2011 can only record still objects as well, as any movement immediately blurs the image beyond recognition.
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