In this Letter, to the best of our knowledge, we present the first thulium (Tm) single-crystal fiber (SCF) laser with free-space propagation of the laser beam only. The SCF is equipped with diffusion-bonded end caps of undoped YAG for better thermal management and enhancement of pump guiding. By utilizing mode matching and pump guiding in different SCF parts, an output power of 9.1 W is achieved at
∼
2.02
µ
m
with a slope efficiency of 49.4%. This straightforward approach, which is also simple to realize and is based on combining the advantages of fiber-geometry structure and crystalline properties of Tm:YAG, is expected to be useful for 2 µm amplification stages in different time formats as well.
Intense femtosecond optical vortices with spatially structured amplitude and spiral phase front give rise to novel phenomena in light-matter interactions and strong-field physics. However, current femtosecond vortex sources exhibit a poor power handling capability and amplification remains an open challenge due to a number of inherent technical difficulties. Here, it is demonstrated that a single-crystal fiber laser amplifier is particularly well-suited to directly amplify a femtosecond optical vortex without pulse stretching and compression in the time domain, while still maintaining the spatial properties associated with a clear central singularity and a spiral phase front, i.e., a well-defined amount of orbital angular momentum (OAM).The optical nonlinearity experienced by such twisted light is verified to be substantially weaker compared to a fundamental mode beam where supercontinuum generation and spatial distortion are observed. The simple design and straightforward power scaling capability pave the way toward ultrahigh-intensity femtosecond singular laser sources with an arbitrary topological charge. Such ultrafast OAM light sources are expected to help reveal complex physical phenomena in light-matter interactions and expand the applications to attoscience with X-ray vortices, laser plasma acceleration, and micromachining.
We present a high-power continuous-wave (CW) Tm:YAG single-crystal fiber (SCF) laser wing-pumped by laser diodes at 791 nm. A maximum output power of 63.3 W is achieved at ∼ 2.01 µm, corresponding to a slope efficiency of 34.2%. This is, to the best of our knowledge, the highest power obtained from the SCF laser in the 2 µm spectral range. In addition to the wing pumping scheme, the large surface-to-volume ratio of such fiber-geometry crystalline rod with diffusion-bonded undoped YAG end caps are benefited for the spatial uniform distribution of pump intensity and thermal load, and thus improving the power scalability.
Lutetium aluminum garnet single-crystal fiber (SCF, ∼ Φ 0.9 mm – 165 mm) doped with 0.5 at.% Ho3+ has been grown by the micro-pulling-down (µ-PD) technique. The room-temperature absorption and emission spectra exhibit similar features to the bulk crystal. Laser performances of the SCFs with two different pump configurations, i.e., pump guiding and free-space propagation, are studied by employing a 1.9-µm laser diode and a high-brightness fiber laser, respectively. Laser slope efficiencies obtained with both pump configurations can be higher than 50%, and a maximum output power of 6.01 W is achieved at ∼ 2.09 µm with the former pump. The comparable efficiency to the high-brightness pump is an indication of that high laser performance can also be expected through pump-guiding in the SCF even with a low pump beam quality.
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