Thulium-doped fiber amplifiers have been limited to average output powers of around 1 kW for over a decade. To achieve multi-kW powers around 2 μm wavelength, we propose using dual-grating Spectral Beam Combining (SBC). Three customized kW-class Tm-doped fiber amplifiers operating in the 2030-2050 nm range were developed. The amplifiers consist of three stages and are pumped with non-stabilized, fiber-coupled diode lasers at 790 - 795 nm. Singlemode, TMI-free output powers exceeding 800 W, with narrow linewidths of FWHM ⪅115 pm, were achieved and subsequently combined using highly efficient in-house fabricated reflection gratings. With an overall combining efficiency of 90 % and a thermal slope of the combining grating measured as 6.8 K/kW, scalability to kW-level powers is enabled. The combined output power achieved a record-breaking 1.91 kW with good beam quality (M2 ⪅2) and potential for further optimization. Finally, the potential power scalability of this non-coherent combining approach to power levels exceeding 20 kW is discussed.
Wavelength-tunable femtosecond light sources are essential in various research fields and technologies, including medical diagnostics, biophotonics, and metrology. Although fiber lasers have emerged as leaders in the development of such sources, achieving wide spectral tunability for femtosecond pulses remains a significant challenge. To address this challenge, dispersive wave generation offers a powerful solution. In this study, we exploit the concept of quasi-phase matching to enable multi-order dispersive wave formation with unprecedented spectral tunability and femtosecond durations. Here, liquid-core fibers (LCFs) with periodically controlled dispersion of a higher-order mode along the fiber are applied, achieved by axial modulation of the liquid core diameter, relying on the strong dependence of dispersion on the core diameter. Nonlinear optical experiments and simulations, as well as phase-mismatching considerations based on an effective dispersion, confirm the conversion process and reveal unique emission features This resonance-empowered approach provides a versatile photonic platform with unique dispersion control capabilities for efficient, coherent femtosecond multi-frequency conversion.
Similar to ytterbium doped laser materials laser operation with thulium doped media is possible within a quasi-three level scheme, which especially for pulse pumped lasers is a drawback for efficient laser operation, as a significant amount of energy is required to bleach out the laser medium. Since this energy cannot be extracted, it is lost for the amplification process. Hence, operation of such lasers at cryogenic temperatures seems to be an appropriate solution. For further modeling and derivation of design rules for future laser systems based on such a scheme reliable spectral data is needed. We will present absorption and emission measurements on Tm:YAG as a function of temperature in the range from 80 K to 300 K covering both the absorption bands around 800 nm and the emission bands up to 2.1 μm. The spectral measurements were carried out on two samples of Tm:YAG with doping levels of 2 at.% and 8 at.%. Precautions for reabsorption effects were taken to allow for accurate results over the whole measurement range. From these measurements we have derived absorption and emission cross sections and radiative lifetimes. By comparing the latter values to values obtained by highly accurate measurements of the lifetime using the pinhole method we could also estimate the quantum efficiency.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.