Researchers unveil the first visible wavelength femtosecond fiber laser

Researchers have developed the first fiber laser that can generate femtosecond pulses in the visible range of the electromagnetic spectrum. Fiber lasers that produce ultra-short, bright visible wavelength pulses can be used in a variety of biomedical applications as well as other fields such as material processing.

Femtosecond pulses are often obtained using complex and inherently inefficient setups. Although fiber lasers are a very promising alternative due to their robustness/reliability, small footprint, high efficiency, low cost, and high brightness, until now it has not been possible to produce visible pulses with femtosecond (10-15 s) durations.) Such lasers are used directly for ranging.

"We demonstrated femtosecond fiber lasers operating in the visible spectrum, paving the way for new types of reliable, efficient and compact ultrafast lasers," said Real Vallee, leader of the research team at Laval University in Canada.

In Optica Publishing Group's journal Optics Letters, the researchers describe their new laser, which is based on rare earth-doped fluoride fibers. The laser emits 635 nm red light and can achieve a compression pulse with a duration of 168 fs, a peak power of 0.73 kW and a repetition rate of 137 MHz. Using a commercial blue laser diode as a light source or pump source helps make the overall design robust, compact and cost-effective.

"If higher energy and power 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 biological tissue ablation and two-photon excitation microscopy. The femtosecond laser pulse also allows for cold ablation during material processing, a process that allows for a cleaner cut [than a long pulse] because it doesn't 'have a thermal effect."

Obtain visible light from a fiber laser

In fiber lasers, the fiber doped with rare earth elements acts as the laser medium. Although fiber lasers are one of the simplest, robust, and reliable high-brightness laser systems, the use of quartz fibers tends to limit them to the near-infrared spectral region. Vallee's team has been working to extend the spectral range of these laser sources by using fibers made of fluoride instead of silica.

"We previously focused on developing mid-infrared fiber lasers, but have recently become interested in visible fiber lasers," Lord said. "While the lack of a compact and efficient pumping source for such lasers has long hindered their development, the recent emergence of blue-spectrum semiconductor laser sources provides a key technology for the development of highly efficient visible fiber lasers."

After demonstrating fiber lasers that continuously emit visible wavelengths, the researchers hope to extend this progress to ultrafast pulse sources. Thanks to improvements in the manufacturing process of fluoride fibers, lanthanide doped fibers are now available, and their properties are critical for the development of highly efficient visible fiber lasers.

The new pulsed fiber laser developed by Vallee's team combines lanthanide doped fluoride fibers with a commercial blue diode-pumped laser. To generate and maintain the pulse output, the researchers also had to figure out how to carefully manage the polarization of light in the fiber.

"Developing lasers of new wavelengths, in which the material properties of the optical elements are different from those used previously, can sometimes be tricky," said co-author Michel Olivier. "However, our experiments show that the performance of our laser matches very well with our simulations." This confirms that the system performs well and is easy to understand, and that the important parameters of the system are properly characterized and well suited to the characteristics of pulsed lasers, especially the fiber we use."

Next, the researchers hope to improve the technology by making the device fully integrated, meaning that individual fiber pigtail optics will be bonded directly to each other. This will reduce the optical loss of the device, increase efficiency, and make the laser more reliable, compact, and robust. They are also investigating different ways to increase laser pulse energy, pulse duration and average power.

Source: Laser Network