Researchers from Université Laval in Canada have made waves in the world of fiber laser technology with their groundbreaking achievement of developing the first-ever fiber laser capable of producing femtosecond pulses in the visible range of the electromagnetic spectrum. This remarkable milestone has the potential to completely revolutionize various fields, particularly biomedical applications and material processing.
Traditionally, obtaining visible femtosecond pulses has been a complex and inefficient process. However, fiber lasers offer a promising alternative due to their distinct advantages, including their ruggedness, reliability, small footprint, efficiency, lower cost, and high brightness. While fiber lasers have been widely used, producing visible pulses in the femtosecond range directly with these lasers has proven to be quite challenging.
Led by Réal Vallée, the research team recently published their groundbreaking findings in Optics Letters, where they unveiled their innovative laser based on a lanthanide-doped fluoride fiber. This particular fiber laser emits red light at 635 nm and achieves compressed pulses with a duration of 168 fs, a peak power of 0.73 kW, and a repetition rate of 137 MHz. Significantly, a commercial blue laser diode serves as the optical source of energy, or pump source, enabling the researchers to develop a rugged, compact, and cost-efficient design.
Expanding Application Possibilities
Marie-Pier Lord, a doctoral student involved in the project, emphasized the myriad potential applications that could benefit from this new type of laser. These include high-precision and high-quality ablation of biological tissues, two-photon excitation microscopy, and cold ablation during material processing. The use of femtosecond laser pulses allows for cleaner cuts compared to longer pulses because they do not generate thermal effects.
Revolutionizing Fiber Lasers
Fiber lasers rely on an optical fiber doped with rare-earth elements as the lasing medium. While fiber lasers are known for their simplicity, ruggedness, and reliability, their use of silica fibers has limited them to the near-infrared spectral region. Vallée’s group at Université Laval has been tirelessly working on expanding the spectral range of fiber lasers by utilizing fluoride fibers instead of silica.
While the research team previously focused on developing mid-infrared fiber lasers, they recently shifted their attention to visible fiber lasers due to the availability of compact and efficient pump sources operating in the blue spectrum. Building upon their previous work with fiber lasers emitting visible wavelengths continuously, the researchers aimed to extend the technology to ultrafast pulsed sources.
Through remarkable advancements in the fabrication process of fluoride fibers, the team successfully obtained lanthanide-doped fibers with properties crucial for the development of efficient visible fiber lasers. The new pulsed fiber laser combines a lanthanide-doped fluoride fiber with a commercially available blue diode pump laser. Additionally, the researchers meticulously controlled the light polarization in the fiber to create and maintain a pulsed output.
Co-author Michel Olivier acknowledged that developing a laser at a novel wavelength with different material properties can be quite challenging. However, the team’s experiments confirmed that their laser’s performance aligned precisely with their simulations, indicating a well-behaved and thoroughly understood system. They also ensured that the key parameters of the system, particularly the properties of the optical fiber, were properly characterized and suitable for pulsed lasers.
Looking ahead, the researchers have ambitious goals of improving the technology even further by creating a completely monolithic setup, where individual fiber-pigtailed optical components are directly bonded to each other. This advancement would greatly reduce optical losses, enhance efficiency, and make the laser more reliable, compact, and robust. Additionally, they are actively exploring various approaches to enhance the laser’s pulse energy, pulse duration, and average power.
New Possibilities Unleashed
The development of a femtosecond fiber laser operating in the visible spectrum undoubtedly opens up a world of new possibilities for reliable, efficient, and compact ultrafast lasers. The groundbreaking achievement by the dedicated research team at Université Laval holds immense promise for biomedical applications, material processing, and numerous other fields that can greatly benefit from the precision and capabilities offered by femtosecond pulses in the visible range.
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