Polaroid's SUNSPOT is a novel imaging system comprising a thermal imaging medium designed to produce a full-color, high-resolution transparent image in a single sheet, addressed by a set of three diode lasers, each emitting at a different wavelength between 750 and 950 nm.The medium contains three active layers, each of which can provide an image in one of the three subtractive primary colors. A digitized image is written onto the Sunspot medium by the lasers, one for each color. Absorption of the radiation leads to local heating of an imaging layer to an extremely high temperature, causing an irreversible thermal reaction in which a colored material is formed.Innovations in two types of dyes make the system practical: infrared-absorbing squaraine dyes exhibiting high specific absorbance in a narrow waveband as well as very low visible absorption, and thermal color-forming materials which are extremely stable at room temperature for many years, but undergo a rapid unimolecular thermal conversion to stable dyes under imaging conditions.The medium is conveniently imaged using diode lasers rated at 100 to 500 milliwatts and provides full-color images with very high color saturation (density >3.0) and resolution (as small as three microns). Imaging requires no pre- or post-processing, the medium can be handled in ambient light before and after imaging, and no by-products or waste are produced.In a typical application, the medium may be coated onto a plastic “blank” which comprises the image area and the mount of a conventional 35 mm slide. This “blank” may be inserted into a printer, imaged, and then used immediately in a slide projector with no further steps involved.
John L. Marshall, "Single-Sheet High-Definition Trichrome Laser Thermal Imaging" in Proc. IS&T Int'l Conf. on Digital Printing Technologies (NIP14), 1998, pp 176 - 179, https://doi.org/10.2352/ISSN.2169-4451.1998.14.1.art00043_1