Silica–silica polyimide buffered optical fibre irradiation and strength experiment at cryogenic temperatures for 355nm pulsed lasers

Abstract

A controlled UV-light delivery system is envisioned to be built in order to study the stability properties of superconducting strands. The application requires a wave guide from room temperature to cryogenic temperatures.Hydrogen loaded and unloaded polyimide buffered silica-silica 100 m core fibres were tested at cryogenic temperatures. A thermal stress test was done at 1.9 K and at 4.2 K which shows that the minimal mechanical bending radius for the fibre can be 10 mm for testing (transmission was not measured). The cryogenic transmission loss was measured for one fibre to assess the magnitude of the transmission decrease due to microbending that takes place during cooldown. UV-irradiation degradation measurements were done for bent fibres at 4.2 K with a deuterium lamp and 355 nm pulsed lasers. The irradiation tests show that the fibres have transmission degradation only for wavelengths smaller than 330 nm due to the two photon absorption. The test demonstrates that the fibres are suitable for the cryogenic UV applications with 355 nm and 70 J pulsed lasers. (2012) Published in Cryogenics 52 b s t r a c tA controlled UV-light delivery system is envisioned to be built in order to study the stability properties of superconducting strands. The application requires a wave guide from room temperature to cryogenic temperatures. Hydrogen loaded and unloaded polyimide buffered silica-silica 100 lm core fibres were tested at cryogenic temperatures. A thermal stress test was done at 1.9 K and at 4.2 K which shows that the minimal mechanical bending radius for the fibre can be 10 mm for testing (transmission was not measured). The cryogenic transmission loss was measured for one fibre to assess the magnitude of the transmission decrease due to microbending that takes place during cooldown. UV-irradiation degradation measurements were done for bent fibres at 4.2 K with a deuterium lamp and 355 nm pulsed lasers. The irradiation tests show that the fibres have transmission degradation only for wavelengths smaller than 330 nm due to the two photon absorption. The test demonstrates that the fibres are suitable for the cryogenic UV applications with 355 nm and 70 lJ pulsed lasers.

An Experimental Setup to Measure the Minimum Trigger Energy for Magnetothermal Instability in $\hbox{Nb}_{3}\hbox{Sn}$ Strands

“…For 532 nm the cryogenic loss is calculated to be ≈1.8%. The cryogenic losses have been measured to be 25% at 355 nm for this type of fibre in another experiment [9]. The cryogenic conditions were similar, however the fibre was more than two times longer and had four 30 mm diameter loops in liquid helium.…”

“…In the station, it is possible to supply 2000 A into a superconducting strand which is mounted on a VAMAS barrel and in a 12 T external magnetic field. The barrel is located in a cryostat which can be cooled down to 4.3 K or 1.9 K. An all-silica optical fibre with 100 µm diameter [9] is installed in the cryostat to guide laserpulses from room temperature to the strand. Outside of the cryostat, the fibre is coupled to a UV laser which is able to send pulsed light at 355 nm or 532 nm wavelengths with 100 Hz repetition rate, pulse width in the order of 1 ns.…”