Researchers at Université Laval in Canada have developed what they say is the first fibre laser capable of producing bright femtosecond pulses in visible wavelengths.
Described in Optics Letters, such lasers could have applications in materials processing and a variety of biomedical applications.
According to the scientists, it hasn’t yet been possible to produce visible pulses with durations in the femtosecond (10-15s) range directly using fibre lasers, with complex and inherently inefficient setups usually being required.
Their new laser combines a lanthanide-doped fluoride fibre with a commercially available blue diode pump laser to emit red light at 635nm, achieving compressed pulses with a duration of 168fs, a peak power of 0.73kW and a repetition rate of 137MHz. The use of a commercial blue laser diode as the pump source helped make the overall design rugged, compact and cost-efficient.
“Our demonstration of a femtosecond fibre laser operating in the visible spectrum paves the way for a new class of reliable, efficient and compact ultrafast lasers,” remarked research team leader Réal Vallée.
The recent advent of semiconductor-based laser sources operating in the blue spectrum was key to the development of efficient visible fibre lasers, according to the researchers. They also noted that the refinement of fluoride fibre fabrication processes has also been crucial to them obtaining lanthanide-doped fibres with the properties required to develop efficient visible fibre lasers.
“Provided higher energies and powers can be achieved in the near future, many applications could benefit from this type of laser,” said Marie-Pier Lord, a doctoral student involved in the project. “Potential applications include high-precision, high-quality ablation of biological tissues and two-photon excitation microscopy. Femtosecond laser pulses also allow cold ablation during material processing, a process that can make much cleaner cuts [than longer pulses] because it doesn’t produce thermal effects.”
Next, the researchers would like to improve the technology by making the setup completely monolithic, meaning that the individual fibre-pigtailed optical components would all be directly bonded to each other. This would reduce the setup’s optical losses, improve efficiency and make the laser more reliable, compact and robust. They are also investigating different avenues to improve the laser’s pulse energy, pulse duration and average power.
Image: Jérôme Lapointe