Infrared laser addressing of media for recording and displaying of high-resolution graphic information

Abstract

Projection display systems which use a scanned infra-red laser beam to thermally record graphic information on different media may offer a useful alternative to CRT and other display systems. Three different types of thermal-recording projection display systems are reviewed. Laser micromachining of thin bismuth film has proved to be a very simple and efficient way to obtain instant high-quality images which are also permanent. Variable amplitude light pulses produced by an intracavity modulated laser beam were used to write these images. With an average laser power of 20 mW, 8×10 mm2facsimile type continuous-tone images, with a resolution of 1300×2000 resolvable elements, were recorded in 4 s. Thermal writing on liquid crystals offers a unique and simple way to record and display high-quality high-resolution graphic images with the capabilities of fast total or local erase. A CW Nd:YA1G laser was used to write graphic and alphanumeric-type information on cholesteric and smectic-type liquid-crystal light valves. High quality black and white images with a resolution of 2000×2000 picture elements were recorded within 30×30 mm2of liquid-crystal cell frames. With 4 mW of laser power, images were recorded at a rate of 104resolvable elements per second. A contrast ratio of 7:1 was obtained with the cholesteric-type liquid-crystal light valve. The stored image was electrically erased in about 0.1 s. In smectic-type light valves, the contrast ratio was better than 10:1 and local erase was achieved by the application of an electric field while the laser beam locally heated the erased area.