Liangbi Su

We report on continuous-wave and Kerr-lens mode-locked operation of an ytterbium-doped mixed sesquioxide ceramic laser. Pumped by a 976 nm Yb-fiber laser, the Yb:(Lu,Sc) ₂ O ₃ ceramic laser delivered a maximum continuous-wave output power of 1.05 W near 1039 nm for an absorbed pump power of 1.78 W, corresponding to a slope efficiency of 64.9%. By inserting a Lyot filter into the cavity, continuous wavelength tuning over 80 nm was achieved. In the mode-locked regime, soliton pulses as short as 44 fs were generated at 1083.3 nm via soft-aperture Kerr-lens mode-locking. The mode-locked laser generated a maximum average output power of 420 mW at a pulse repetition rate of ∼61.5 MHz, corresponding to a peak power of ∼137 kW. To the best of our knowledge, these are the shortest pulses ever generated from any ytterbium-doped sesquioxide ceramic laser, demonstrating the potential of Yb:(Lu,Sc) ₂ O ₃ ceramic as a broadband gain medium for few-optical-cycle solid-state lasers.

We report on an Yb:YAB laser pumped by a spatially single-mode, low-power, fiber-coupled InGaAs laser diode at 976 nm, delivering soliton pulses as short as 36 fs at 1059.7 nm via soft-aperture Kerr-lens mode-locking. The average output power amounts to 156 mW at a pulse repetition rate of ∼66.7 MHz. To the best of our knowledge, this represents the first demonstration of Kerr-lens mode-locked operation with the Yb:YAB crystal, and the shortest pulses ever achieved from an Yb:YAB laser.

Power scaling of a continuous-wave (CW) bulk laser in the mid-infrared (Mid-IR) spectral region has been demonstrated employing a 2.5 at.% Er:CaF ₂ crystal slab with double-end-pumping configuration and tailored pump beam profile for better geometry matching. A maximum output power of 22.5 W is achieved at 2.8 μm, corresponding to a slope efficiency of 29.4%. The M ² -factor is 1.27 in the y -direction, compared to 10.29 in the x -direction. To the best of our knowledge, this presents the record power for end-pumped solid-state CW lasers in the 3-μm spectral range at room temperature. This work indicates that Er:CaF ₂ crystals with a low doping level are promising candidates for high-power laser emission in the Mid-IR region.

The degradation of calcium fluoride (CaF ₂ ) crystals in deep ultraviolet (DUV) lithography systems poses a critical challenge to the safe and stable operation of such systems. Understanding the degradation dynamics and underlying physical mechanisms induced by high-energy photon irradiation is essential for improving the radiation resistance of CaF ₂ crystals. This work proposes a rapid assessment method for evaluating the radiation-resistant lifetime of CaF ₂ crystals based on X-ray exposure. By characterizing the dynamic degradation behavior of CaF ₂ crystals under various X-ray doses and integrating multidimensional defect characterization techniques, the physical mechanism of X-ray-induced degradation was systematically elucidated, with dislocation density identified as the dominant factor governing the radiation resistance of CaF ₂ crystals. This study not only elucidates the dynamic evolution and critical factors of degradation processes in CaF ₂ crystals under X-ray irradiation but also lays a solid foundation for the future optimization of their radiation-resistant properties in high-energy radiation environments.

We report on the passively mode-locked operation of an Yb:SrF ₂ laser generating sub-40 fs pulses at ∼1 μm. By using a high-brightness Yb-fiber laser as the pump source, the Yb:SrF ₂ laser delivered soliton pulses as short as 37 fs at 1066.4 nm via soft-aperture Kerr-lens mode-locking, with an average output power of 85 mW at a pulse repetition rate of ∼71.8 MHz. To the best of our knowledge, this is the first demonstration of Kerr-lens mode-locking using the Yb:SrF ₂ crystal.

We report on continuous-wave and passively mode-locked operation of a diode-pumped Yb:Ca ₃ TaGa ₃ Si ₂ O ₁₄ laser. In the continuous-wave regime, the laser delivered a maximum output power of 408 mW at 1045.5 nm, corresponding to a slope efficiency of 58.1% and a laser efficiency of 53.4%. By incorporating a quartz-based Lyot filter, a continuous wavelength tuning range of 82 nm, spanning from 1007 to 1089 nm, was achieved. In the mode-locked regime, a commercial semiconductor saturable absorber mirror was employed to initiate and sustain soliton-like pulse shaping, and pulses as short as 50 fs were generated at a central wavelength of 1052.4 nm, with an average output power of 40 mW at a pulse repetition rate of 73.9 MHz. To the best of our knowledge, this is the first demonstration of a mode-locked laser based on the Yb:Ca ₃ TaGa ₃ Si ₂ O ₁₄ langasite-type non-centrosymmetric crystal, highlighting its significant potential as a gain medium for sub-100 fs solid-state lasers.

Mid-infrared (MIR) vortex laser sources, particularly in the 3-5 µm region, have important potential applications in space communications and molecular spectroscopy, etc. However, the generated vortex beams in the 3 µm region were limited to first-order. Here, we demonstrate the direct generation of MIR order-tunable Laguerre-Gaussian (LG) beams from an Er:CaF ₂ laser with a spot-defect mirror. By selecting the defect size, the order of chirality-degenerate LG beams can be tuned from 1 to 8. To the best of our knowledge, this represents the highest-order LG beams directly generated from a laser in the 3 µm region. Single-chirality vortices with the orders of 1–5 are also generated by inserting a tilted YAG plate in the cavity. This work offers flexible and compact MIR LG beam sources with tunable orders towards various applications.

Mode-locked lasers operating in the 2 μm region are of great value for various spectroscopic applications and investigations of laser-matter interactions. However, ultrafast lasers that exhibit both a short pulse duration and a wide emission spectrum below 1.9 μm remain challenging. In this work, a passively mode-locked Tm:CaF ₂ laser was demonstrated at approximately 1886.2 nm with a pulse duration of 3.7 ps and a maximum average output power of 171 mW, by using Gires-Tournois interferometer mirrors for intracavity dispersion compensation. In contrast, the introduction of Gd ³⁺ co-doping enabled the first realization of a mode-locked Tm,Gd:CaF ₂ laser, which generated significantly shorter pulses of 1.7 ps. Moreover, the Tm,Gd:CaF ₂ laser exhibited a broadened tuning range of 142.2 nm compared to 127.6 nm obtained in the Tm:CaF ₂ laser. These results confirm that co-doping Gd ³⁺ ions enhances the performance of Tm-based CaF ₂ lasers, making Tm,Gd:CaF ₂ crystals a promising gain medium for a broadband mode-locked laser around 1.9 μm.