Application of Blue Diode Lasers to Printing
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ABSTRACT The availability of blue diode lasers would have a significant impact on several printing
applications. The laser printing market is moving towards higher resolutions and higher print speeds. The optical systems for polygon scanner laser printers are diffraction limited and therefore to improve the optical resolution it is very advantageous to reduce the wavelength of the scanning laser beam from that of the IR or red lasers currently being used. The other printing application of blue lasers is exposure of film, an area where argon ion lasers are currently being used. Replacement of these by diode lasers would potentially lower system costs. In this paper, the applications of blue lasers to printing will be outlined and the technical requirements that the lasers will need to satisfy will be discussed. INTRODUCTION The recent development of continuous wave (cw) diode lasers based on the AIGaInN alloy system with wavelengths in the blue region of the spectrum• has attracted the attention of groups interested in applying these devices to optical systems. In the case of optical data storage, wavelengths shorter than those in the red and infr'ared enable higher packing densities. In this paper the use of these blue lasers for printing will be discussed. The first application that will be considered, laser printing based on the electrophotography process, is likely to require lasers in larger numbers. The advantage of AIGaInN diode lasers for laser printing is analogous to the optical storage situation: the shorter wavelengths enable higher resolution printing. The second application that will be discussed is the more specialized usage of these lasers in writing on film. In this case the new technology represents an opportunity to replace the existing air-cooled argon ion lasers. The key advantages of blue diode lasers in this case are the reduction of size, cost and power requirements. To avoid confusion, in the remainder of the paper we will use the term "laser writing" to refer to this second application and "laser printing" to refer to the electrophotography case where a laser is used to expose a photoconductor. LASER PRINTING In this section, the processes used for laser printing will be described, and the advantages of laser diodes with wavelengths in the blue region of the spectrum will be outlined. This will be followed by a summary of the type of specifications that are necessary for a laser component to be successful. The Process of Laser Printing Electrophotography is the underlying technology for both photocopying and for laser printing. The process makes prints on paper by exposing a pattern on to an initially uniformly charged photoreceptor layer. The charged areas attract dry ink particles which are then transferred to paper. This sequence is shown schematically in Figure 1. 1203 Mat. Res. Soc. Symp. Proc. Vol. 482 © 1998 Materials Research Society
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Qoner
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Image Laser
Polygon
ChargecE Erase 0 Paper 0
Transfer Fuser
Figure : (a) Schematic of a laser printer in which a laser be
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