Optical fiber silica drying

For practical measurements, special equipment is necessary to cool the substances to low temperatures [2-4]. A small Dewar vessel can be fitted with two plan-parallel silica disks. A stream of dry and cool nitrogen will prevent clouding of the optical windows. Another effective precaution is to use fiber optics, and set the space between the optical windows and the fiber cables under vacuum [3]. Mainly liquid nitrogen and liquid helium are used as cooling agents, or solvents that form a glasslike solid (e.g., ethanol, propanol, methylpentane [4]). 

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