Photodetecting apparatus having cryo- genic cooling and flushing means

Claim 1

APPARATUS FOR MAINTAINING A LIGHT SENSITIVE ELEMENT AT EXTREMELY LOW TEMPERATURES AND FREE FROM GASEOUS CONTAMINATION, COMPRISING: SENSING MEANS FOR ABSORBING ELECTROMAGNETIC RADIATION, SAID SENSING MEANS ENCLOSED WITHIN AN ULTRA HIGH VACUUM CELL HAVING A FIRST WINDOW THEREIN FOR ALLOWING ELECTROMAGNETIC RADIATION TO PASS THERETHROUGH TO SAID SENSING MEANS, HEAT SINK MEANS INCLUDING LIQUID NITROGEN ASSOCIATED WITH SAID VACUUM CELL FOR COOLING SAID CELL AND SAID ENCLOSED SENSING MEANS, A CHAMBER SURROUNDING SAID ULTRA HIGH VACUUM CELL AND HAVING A SECOND TRANSPARENT WINDOW THEREIN FOR ALLOWING ELECTROMAGNETIC RADIATION TO PASS THERETHROUGH TO SAID FIRST WINDOW, SAID SECOND WINDOW BEING OF THIN, POROUS AND PLASTIC MATERIAL HVING A LIGHT TRANSMISSION SPECTRUM FROM 2250 ANGSTROMS IN THE ULTRAVIOLET TO 15,000 ANGSTROMS IN THE INFRARED, MEANS INTERCONNECTING SAID HEAT SINK MEANS AND SAID CHAMBER, NITROGEN GAS PASSING FROM SAID HEAT SINK MEANS TO SAID CHAMBER THROUGH SAID INTERCONNECTING MEANS AND PASSING OUTWARDLY THROUGH SAID POROUS WINDOW FOR CONTINUOUSLY FLUSHING THE AREA SURROUNDING SAID ULTRA HIGH VACUUM CELL, A VACUUM ENCLOSURE MEANS ENVELOPING SAID CELL AND A PORTION OF SAID CHAMBER FOR PREVENTING CONDUCTION OF HEAT, AND ELECTRICAL CIRCUIT MEANS CONNECTED TO SAID SENSING MEANS MEASURING THE VARIATION OF THE CONDUCTIVITY OF THE SAME.