Ultrafast high-BRightness Infrared laser sources at 2 µm – UBRIS2

UBRIS2 aims at developing innovative ways towards the realization of high-power ultrafast laser systems at the exotic wavelength of 2 µm. The project gathers researchers and engineers from XLIM, CORIA, IRCICA and LPN with proven expertise in design and fabrication of rare-earth-doped and dispersion-tailored optical fibers (XLIM and IRCICA), semi-conductor saturable absorber mirrors (LPN) and femtosecond oscillators and amplifiers (CORIA). Furthermore, the company NOVAE is in charge of the development of two products based on the project’s findings.

To build high-energy lasers at 2 µm, we propose two approaches. The first one is based on an innovative distributed chirped pulse oscillator, a concept patented by the CORIA and XLIM. This oscillator relies on Thulium-doped fibers with tailored high normal dispersion, providing large breathing in the oscillator leading to an increase in energy compared to conventional systems. A novel InP-based saturable absorber withstanding high optical fluences will be developed to initiate and stabilize sustained mode-locking in our innovative oscillators. This oscillator delivers highly stretched pulses, well suited for direct amplification to 10 µJ in Tm-doped singlemode large mode area fibers fabricated by the powder-sintering technique at XLIM.

In the second approach, the pulses from more conventional low power ultrafast oscillators will be amplified in parabolic amplifiers, a concept which remains largely unexploited due to the lack of properly designed fibers, especially at 2 µm. Based on realistic performances measured in passive fibers developed by XLIM and IRCICA, we have numerically showed that the 100-µJ milestone is at reach by using LMA Tm-doped high normal dispersion few-mode fibers.

In our two approaches we add a degree of freedom by controlling over the waveguide dispersion in the lasing fibers. From a basic viewpoint, tailoring the modal propagation constant in an amplifying fiber so as to reach high normal dispersion is attractive in many ways as the pulse dynamics within a cavity is strongly influenced by the dispersion. The first scientific outcome would be a much better understanding of pulse shaping in original cavity designs including strong waveguiding effects.

From a technical viewpoint, our concept is very flexible in terms of laser performance as the pulse duration and energy, and hence its peak power, can vary by orders of magnitude by adjusting the dispersion coefficient. The parabolic amplification relaxes the need for the localized stretcher in the usual chirped-pulse amplification technique as well as the need for perturbation-sensitive rod-type photonic crystal fibers.

The all-fiber architecture is expected to be stable against perturbations and likely to be used outside a lab environment. From an application viewpoint, extending the spectral coverage of ultrafast lasers towards the mid-IR, in a stable and compact architecture, is useful to increase the growth potential of the laser systems market. For instance, ultrafast high-power 2 µm lasers could be used for processing soft materials.

Our design strategy, based on Tm-doped few-mode fibers, has never been applied to ultrafast lasers. Our approaches therefore hold potential for patent pending. We will pay attention to patentability so as to transfer our findings to French and European industrialists. Industrial transfer is intrinsically taken into account in UBRIS2. Indeed the lasers developed will be fiabilized, integrated and packaged at NOVAE prior to their commercialization.