Low-temperature, low-cost growth of robust ATR GeO2 hollow fibers based on copper capillary tubes for transmission of CO2 laser light

Attenuated total reflectance (ATR) infrared hollow waveguide attracts particular interest since it has both advantages of a hollow fiber and a light guiding mechanism similar to that of solid-core fibers. Presently, ATR hollow waveguides are mainly structured with single-crystal sapphire or glassy materials. These waveguides are somewhat brittle. More robust ATR hollow fibers are required in many military and domestic applications. In this work, ATR GeO2 hollow waveguides were prepared based on a copper capillary tube for transmitting CO2 laser light. The inner wall of the copper structural tube was polished using a high-pressure pulsed nanofluid technique. A hexagonal crystalline GeO2 reflective layer with sufficient thickness (>4 μm) was grown on the inner tube wall via a simple liquid phase deposition process at room temperature. The GeO2 coated copper hollow fiber exhibits a low-loss band within 10-11.5 μm. It can still be bent since the hollow-core size (1.4 mm) and the wall thickness (50 μm) are not too large. The transmissions of CO2 laser light are 91% and 43% under a straight condition and a 90° bend with a 30-cm radius condition, respectively. The waveguide displays high heat-resisting properties due to high thermal conductivity of the copper substrate tube and a high melting point (1115°C) of the GeO2 reflective layer. This work opens a door for low-temperature, low-cost growth of long ATR GeO2 infrared hollow fibers based on various substrate tubes, even including plastic capillary tubes.