A groundbreaking development in laser technology has led to the creation of the world’s first fiber laser capable of producing femtosecond pulses in the visible range of the electromagnetic spectrum. This significant achievement opens up a multitude of possibilities for various fields, including biomedical applications and material processing.
Traditionally, obtaining visible femtosecond pulses involved intricate and inefficient setups. However, fiber lasers offer a promising alternative due to their reliability, compact size, efficiency, affordability, and high brightness. Until now, directly generating visible femtosecond pulses with fiber lasers has remained a challenge.
The research team, led by Réal Vallée from Canada’s Université Laval, has successfully demonstrated a femtosecond fiber laser operating in the visible spectrum. Their laser is based on a lanthanide-doped fluoride fiber and emits red light at a wavelength of 635 nm. The compressed pulses achieved by this laser have a duration of 168 fs, a peak power of 0.73 kW, and a repetition rate of 137 MHz. The overall design of the laser is rugged, compact, and cost-efficient, utilizing a commercial blue laser diode as the optical pump source.
According to Marie-Pier Lord, a doctoral student involved in the project, the potential applications of this laser technology are extensive. With the possibility of achieving higher energies and powers in the future, numerous fields can benefit from this advancement. For instance, high-precision and high-quality ablation of biological tissues, as well as two-photon excitation microscopy, could be significantly enhanced. Furthermore, femtosecond laser pulses enable cold ablation during material processing, resulting in cleaner cuts due to the absence of thermal effects.
Getting visible light from fiber lasers
Fiber lasers, which utilize optical fibers doped with rare-earth elements, serve as the lasing medium. These lasers are known for their simplicity, durability, reliability, and high brightness. However, their use of silica fibers limits their operation to the near-infrared range of the electromagnetic spectrum. To overcome this limitation, Vallée’s team has been investigating the use of fluoride fibers instead of silica to extend the spectral range of fiber lasers.
“While our previous focus was on developing mid-infrared fiber lasers, we have recently become interested in visible fiber lasers,” explained Lord. She further mentioned that the development of such lasers was hindered for a long time due to the lack of compact and efficient pump sources. However, the emergence of semiconductor-based laser sources operating in the blue spectrum has provided a crucial technology for the advancement of efficient visible fiber lasers.
Having already demonstrated fiber lasers that emit visible wavelengths continuously, the researchers aimed to expand their breakthrough to ultrafast pulsed sources. By refining the fabrication process of fluoride fibers, they have now achieved lanthanide-doped fibers with the necessary properties for the development of efficient visible fiber lasers.
Integrating technologies into a new laser
The newly developed pulsed fiber laser by Vallée’s team utilizes a lanthanide-doped fluoride fiber and a commercially available blue diode pump laser. To achieve pulsed output, the researchers had to carefully manage the light polarization within the fiber.
According to co-author Michel Olivier, developing a laser at a new wavelength, where the material properties of the optical components differ from previous setups, can present challenges. However, their experiments demonstrated that the laser’s performance aligned excellently with their simulations. This confirmation indicated that the system was well-behaved and understood, with the relevant parameters properly characterized, especially those of the optical fiber used for pulsed lasers.
Moving forward, the researchers aim to enhance the technology by achieving a fully monolithic setup. This involves directly bonding the individual fiber-pigtailed optical components together. By doing so, they expect to reduce optical losses, improve efficiency, and enhance the laser’s reliability, compactness, and robustness. Additionally, they are exploring various approaches to enhance the laser’s pulse energy, pulse duration, and average power.