Heat and vibration are no problem for an ultrafast laser with a cavity made entirely of polarization-maintaining optical fiber. The design emits 220-fs pulses with energies up to 3.5 nJ. Its 1030-nm output wavelength can be multiplied by generating higher-order harmonics. The device could be useful for materials processing, as well as sensing and imaging, according to its developers at the University of Warsaw. "In our laser, the ultrashort pulses are generated directly in the fiber optic cable," said Dr. Yuriy Stepanenko. "The design is so simple that there is nothing that might break down." Doctoral student Jan Szczepanek works on a fiber optic femtosecond laser. Courtesy of Grzegorz Krzyzewski, UW Physics. The flexible fiber also allows laser pulses to be delivered into places inaccessible to traditional laser techniques. Regardless of how the fiber is positioned, the beam's cross section maintains an optimal Gaussian distribution. "Optical fibers have for years been known as a source of laser radiation, including laser pulses," said doctoral student Jan Szczepanek. "We have taken things a step further: We have carefully selected the right combination of laser pump diode and fiber optic cable, and developed a way to stabilize the whole system so that it is most energy efficient for it to work in the pulse regime we wanted." The simplicity of the design will make the fiber laser a relatively inexpensive instrument, the researchers said. Built using a commercially available pump semiconductor diode and its driver, the system would cost just a few thousand euros. Companies interested in commercializing the device could also seek additional ways to cut the cost, for instance by using a custom-designed driver. Its simplicity also makes the system resilient: The researchers said it continued operating even when a segment of the optical fiber was heated to more than 120 °C and when it experienced accelerations of more than 7 g. The laser is likely best suited to microscale surface finishing, where ultrashort pulses can be used to create micro-holes with smooth, precision-profiled edges, the researchers said. Other potential applications lie in cutting semiconducting solar panels and marking hard materials such as diamond. In materials processing, femtosecond lasers have an advantage over instruments that generate longer pulses because they minimize thermal stress in the material, which can lead to discoloration and cracking. The laser could also be used in devices generating terahertz radiation, such as airport scanners, as well as medical imaging devices, according to the researchers. The work was published in Optics Letters (doi: 10.1364/OL.40.003500).