Silica Fresnel Lens for Laser Communications

INCLUDED IN THE ADVANCEMENT OF LASER COMMINICATIONS SYSTEMS IS DEVELOPMENT OF THE NECESSARY OPTICS, AND ONE OF THE MOST DESIRABLE CANDICATES FOR SUCH OPTICS IS A LOW DIFFRACTION FRESNEL LENSES ARE MOST COMMONLY MANUFACTURED IN PLASTICS, WHICH ARE NOT SUITABLE FOR SPACE APPLICATIONS DUE TO THE EFFECTS OF RADIATION AND OUTGASSING OF THE MATERIAL. A GLASS FRESNEL LENS WOULD BE A PRACTICAL SOLUTION TO THIS PROBLEMS, BUT THESE ARE NOT AVAILABLE BY CONVENTIONAL METHODS. IN RECENT YEARS DEVELOPMENT WORK AT GELTECH USING THE SOL-GEL PROCESS HAS MADE IT POSSIBLE TO REPLICATE SURFACES IN HIGH PURITY SILICA GLASS BY A ROOM TEMPERATURE MOLDING TECHNIQUE. BASED ON THIS SOL-GEL TECHNOLOGY, GELTECH IS PROPOSING IN PHASE I TO DEMONSTRATE THE FEASIBILITY OF MANUFACTURING A 1.5" PROTOTYPE SILICA FRESNEL LENS WHICH WOULD SATISFY, IN A COST-EFFECTIVE WAY, THE OPTICS REQUIREMENTS OF LASER COMMUNICATIONS SYSTEMS. SUCCESS IN THIS DEVELOPMENT IS EXPECTED TO OPEN THE DOOR TO MANY OTHER APPLICATIONS, BOTH TERRESTRIAL AND SPACE, WHERE SILICA GLASS FRESNEL LENSES WOULD BE FAR SUPERIOR TO PLASTICS, AND IN SOME CASES, ABSOLUTELY NECESSARY. 277 AN INNOVATIVE REGENERATOR USEABLE IN STIRLING, PULSE TUBE, GIFFORD-MCMAHON AND SIBLING CYCLE CRYOCOOLERS IS PROPOSED. IT WILL OFFER IMPROVED PERFORMANCE IN TERMS OF RELIABILITY, UNIFORMITY, COST AND EFFICIENCY. THE REGENERATOR WILL BE FABRICATED WITH AVAILABLE MATERIALS AND TECHNIQUES USED IN AN ENTIRELY NEW WAY. THE MATERIAL IS STAINLESS STEEL FOIL. THE TECHNIQUE CREATES PRECISE PATTERNS OF CHANNELS ON ITS SURFACE AND PATTERNS OF SLOTS THAT PENETRATE THE WHOLE DEPTH OF THE FOIL. THE PROCESSED FOIL IS THEN WOUND IN JELLY-ROLL FASHION AND INSERTED INTO THE REGENERATOR HOUSING. WITH FLOW CHANNELS AND SLOTS PROPERLY SHAPED AND SPACED, REGENERATOR INEFFECTIVENESS IS EXPECTED TO BE LESS THAN HALF OF THAT EXPERIENCED IN WOVEN SCREEN REGENERATORS. THE FLOW PASSAGES THROUGH THE PROPOSED REGENERATOR ARE UNIFORM, REDUCING DEGRADATION OF PERFORMANCE DUE TO CONTAMINATION. THE OBJECTIVE OF PHASE I IS TO DEVELOP THE COMPUTATIONAL TOOLS NEEDED TO DETERMINE THE OPTIMAL PATTERN OF CHANNELS AND SLOTS. THE COMPUTATIONAL TOOLS WILL BE CREATED BY MODIFYING AND COMBINING SEVERAL EXISTING COMPUTER MODELS TO