A technique to produce mirrors for the Auger Observatory

The Fluorescence Detector of the Pierre Auger Cosmic Ray Observatory will provide a measurement of the parameters of Extensive Air Showers with energy >10/sup 19/ eV. The mirror of the Fluorescence Detector prototype has dimension /spl sim/3.6/spl times/3.6 m/sup 2/ and is composed of 49 trapezoidal segments of approximately 50/spl times/50 cm/sup 2/. Each segment is curved using a steel mold in which the glass sags in a controlled environment. The glass is then aluminized under vacuum and coated with oxide (Al/sub 2/O/sub 3/). The oxide thickness is chosen to maximize the reflectivity in the wavelength range of fluorescence light (300 nm