Presstek Inc., a manufacturer of high-tech digital imaging solutions for the graphic arts and laser imaging markets, has announced that its Lasertel division has formed an alliance to provide laser diode components and assemblies to Selex Sensors and Airborne Systems.    . . .    Del Global Technologies Corp., a manufacturer of products with industrial, medical and military applications, has announced that its subsidiary, Del Medical Imaging Corp., has entered into a two-year agreement with AFP Imaging Corp. under which AFP will exclusively sell, install and service the DMI-manufactured Universal and VetTek lines of veterinary x-ray systems worldwide. These systems produce and capture large format (up to 14-by-17 in.) images in either digital or x-ray film formats.