The apparatus for sealing face plates (753) and cathodes (754) has three stations (701, 702, 703). The first (701) is a preheater, the second (702) is an alignment and
irradiation station and the third (703) is a controlled cooling
station. Beneath each
station, a
vacuum pump (710) capable of drawing ultralow pressures is provided. The preheater is equipped with upper and lower banks of radiant heaters and reflectors (712). The upper heaters are Provided above a
quartz: window (713) of a chamber (714) constituting the station. The pressure in the preheater is pumped down to that in the alignment and
irradiation station prior to opening of the
gate valve between them and transfer of the face plate and
cathode. At the alignment and
irradiation station, further heaters (716) are provided. Those above the face plate and
cathode, the face plate being uppermost, are mounted on frames (717) about hinges (718), whereby they can be swung up to clear this station's top
quartz window, exposing the face plate to the view of an optical
system (719) and a
laser (720). Manipulation controls (722) are provided for manipulating the position of the face plate to be pixel alignment, as measured by the optical
system (719), with the
cathode. The
laser is traversed around further. The cooling station (703) has meanwhile been pumped down and the sealed device is transferred to it. The temperature of the device is allowed to rise very slowly, in order to reduce the risk of thermal
cracking to as great an extent as possible. As the temperature slowly falls, air is slowly introduced, so that the finished device can be removed to the ambient surroundings.