E-BEAM PUMPED LASER PROJECTORS

A CRT with a high-voltage (e.g., 65 kV) electron beam bombarding a single crystal target, causing it to act as a laser, is called a "quantoscope" (Figure 4.8). Because of their high light output (3,000 lm), these devices are being evaluated for large screen projection systems. Three monochrome tubes (e.g., CdS Green, CdSe + CdS Red, and Cd:ZnSe Blue) are optically converged to create a full-color image.


Figure 4.8. Cross section diagram of the EBSL tube (#1).

Platan has invested heavily in R&D for these devices and demonstrated impressive RGB pictures, up to 5 m x 12 m in size, to the WTEC visitors. Recent developments include a high resolution (>2,500 lines) red tube that was shorter by one- half (approx. 0.5 m in length) compared to previous designs, and the elimination of the gettering pump by inclusion of internal getters. Various targets have allowed demonstration of wavelengths from the ultraviolet (330 nm) to as long as 8 microns.

Rosich has developed an improved version of the quantoscope (Figure 4.9), [Several other organizations, including Platan and the Lebedev Institute] have also claimed ownership of this design. that projects the light out the rear of the device (the e-beam bombarded side) rather than through the adhesive material and the liquid cooled faceplate. The screen temperature can be maintained at -120 degrees centigrade to -130 degrees centigrade by a very quiet and compact refrigeration unit that can remove up to 60 W at these temperatures. The life of the screen was quoted as 300-500 hrs at present, and will be at least 2,000 hrs ultimately.


Figure 4.9. Cross section diagram of the EBSL tube (#2).

The life is limited by the mirror coating, not the single crystal material. (Lifetime is defined as the time required for the output to drop to 70% of its initial value.) Resolution of 2,500 scanning lines should be achieved with improved electronics, and 4,000-5,000-line resolution is ultimately possible.

Rosich and Chromatron (a manufacturer of shadow mask CRTs) have formed an alliance under which Chromatron will manufacture quantoscopes and components for light valve projectors.

The panel did not visit the P.N. Lebedev Physical Institute, Moscow, which is also involved in the development of laser CRTs. Principia Optics of Los Angeles, California has exclusive rights to develop, manufacturer, sublicense, and market Lebedev's technology outside the FSU, and has been issued seven U.S. patents. Principia has a joint development program with Stanford University and the Jet Propulsion Laboratory (JPL), and expects to have a demonstration at JPL in late 1994. The long-term goals of this program are (1) 15-20,000 lm; (2) room temperature operation; and (3) 10,000 hrs life. Additional details may be obtained from Michael Tiberi, President of Principia Optics, at 818-309-4336.


Published: December 1994; WTEC Hyper-Librarian