LED innovations boost laser fibres, human-safe UV-C
Researchers in Germany are developing directly tunable laser sources from 532 nm to 561 nm to 590 nm with up to 2W output power in continuous wave operation.
The compact laser sources being developed by the Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik (FBH) have the potential to replace significantly larger dye and copper bromide lasers.
The researchers increased the peak output power of its diode laser bars in quasi-continuous operation by up to four times while maintaining excellent efficiency. This reduces the cost in euros per watt – a key parameter for industry.
FBH has also built optimized diode lasers into stack modules, with improvements in packaging and optics. For example, a fibre-coupled pulsed pump laser source with 1 kW output power at 780 nm wavelength was demonstrated for the first time in a 1 mm core fibre (previously 1.9 mm). The passively cooled module was able to increase the duty cycle from 20 percent to up to 50 percent
Researchers at the institute have also developed a high power, human-safe UV-C LED for irraditation applications. This is being tested at the Charité, Universitätsmedizin Berlin and at the Greifswald University Hospital. In the future, this irradiation concept will be used to inactivate multidrug-resistant pathogens such as MRSA and coronaviruses including SARS-CoV-2 directly on humans in a way that does not harm the skin.
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Each system is equipped with 120 LEDs that emit at 233 nm wavelength, developed jointly with TU Berlin. The LED uses an optimised semiconductor epitaxy and chip process technology to deliver twice the current of 3 mW output power at 200 mA.
FBH has also developed new silicon-based LED packages in collaboration with the CiS Forschungsinstitut für Mikrosensorik. In addition to efficient heat dissipation, aluminum reflectors and a plano-convex lens ensure a beam angle of only 60 degrees. This, in turn, increases the transmission.
The systems can irradiate an area of 70 mm diameter with a homogeneity of more than 90 %. The UVC light is free of skin-damaging wavelengths above 240 nm and has an irradiance of 0.4 mW/cm2 – ten times more than that achieved by previous systems.
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