In order to introduce Er:YAG lasers at 2.94 micrometers into medical applications such as minimally invasive surgery, appropriate infrared transmitting fibers are necessary. Because of their cheapness, variability in diameter, high flexibility, mechanical stability and regenerability, liquid core fibers have been taken into consideration as one type of conceivable lightguides. In this work IR absorption effects of water in the core and permeation of atmospheric water and of the solvent through the cladding are studied. The absorption of 2.94 micrometers which is due to the unresolved rotational structure of the stretching vibrations of dissolved water at 3617 and 3708 cm-1 increases when the water content rises. According to preliminary permeation measurements, keeping a liquid-filled plastic fiber under normal atmospheric conditions leads to an increasing water concentration in the core and, simultaneously, to a loss of the solvent. On the other hand the water content could be reduced when the lightguide was stored in a desiccator. These problems could be solved by using a liquid lightguide with an appropriate jacket. Compared to unjacketed counterparts it has a better long time transmission at 2.94 micrometers . Meanwhile the transmission could be improved to up to 55% (pathlength: 1 m). As these first results are thought to be further improvable they are well promising towards the realization of a liquid lightguide for medical purposes.
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