Optical fibres made with fused silica quartyz solid cores are able to transmit ultraviolet light over an extended period. Read more below.
The ability of hydrogen to change the performance of optical fibres used in transmitting laser beams has been known for years. The problem has been how to achieve it.
Optical fibres are essentially transparent fibres of fused silica glass about the thickness of a human hair. Light can be transmitted between both ends of the fibre. It can also conduct electricity. These fused silica fibres are more efficient than metal wires because their transmission losses are far lower, and they are also more resistant to electromagnetic interference.
The real problem with optical fibres has been their inability to transmit ultraviolet light. This short-wavelength light tends to react with various impurities that are present in the fibres, and this results in a severe cut in the laser beam’s intensity, a process called solarisation. The fibres effectively stop working.
Researchers at the United States National Institute of Standards Technology (NIST) have discovered a hydrogen therapy solution to this problem. They carried out tests on optical fibres made of fused silica cores that were surrounded by air holes, creating a lattice structure. The result was an elongated crystal structure that could contain the shape of a laser beam transmitted through them.
Hydrogen gas at 100 times atmospheric pressure was infused into the fibres over periods ranging between four and six days. The fibres were later cured by exposure to ultraviolet light. This second period took a further several days.
Tests conducted after the infusion and curing periods showed that the fibres did not display any solarisation effects when ultraviolet light was transmitted through them. There was no damage even at high laser wavelengths of 313 nanometres and output powers of 125 watts. This level of power and wavelength is several times greater than that needed by NIST researchers to conduct experiments using the lasers.
As a comparison, the researchers passed light at 100 watts power and 313 nanometres wavelengths through untreated optical fibres and found that the transmission through them was reduced to zero after only four hours. This confirmed the effectiveness of the hydrogen treatment.
Such treated optical fibres can be used in many applications. They can be used to reduce fluctuations in laser beams and to clean up misshapen laser beams.
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