Dongzhen Li

Non-radiative relaxation hinders the performance of erbium-based mid-infrared lasers. Here, we demonstrate that anion-engineering in fluorite crystal provides a solution to this challenge, facilitating efficient laser operation. The Er,Se-co-doped CaF ₂ crystal exhibits extended lifetimes at characteristic emission bands compared to Er:CaF ₂ . First-principles calculations reveal the spatial proximity of Se ²⁻ to Er ³⁺ clusters within CaF ₂ lattice, alongside the introduction of low-frequency phonon modes, underpinning the observed phenomena. Efficient 2.75 µm continuous-wave laser operation was demonstrated on this crystal, exhibiting high slope efficiencies of 34.4% and 12.2% under 976 nm resonant and 1532 nm upconversion pumping, respectively. Our results highlight the role of anion-engineering in designing advanced laser materials.

To the best of our knowledge, this is the first report on continuous and passively mode-locked operation of the multi-component fluoride CaSrBaF₆ crystal. A novel disorder laser material, Yb:CaSrBaF₆ (Ca_0.33Sr_0.33Ba_0.33F₂) of multi-component middle entropy crystal was designed and grown by temperature gradient technique (TGT) for the first time. X-ray diffraction (XRD) and X-ray fluorescence (XRF) analysis of Yb:CaSrBaF₆ crystal reveals that Ca²⁺, Sr²⁺, and Ba²⁺ of near equal atomic ratio (1:1:1) have formed a homogeneous single-phased fluorite solid solution. The first principle calculation further shows that Ca²⁺, Sr²⁺, Ba²⁺ ions tend to be evenly distributed in the matrix crystal. The total formation energy is the lowest -547.17 ev and the structure is also the most stable at this time. The spectral properties of the crystal are systematically characterized. The emission cross section of ²F_5/2→²F_7/2 transition at 1040 nm is 0.62 × 10⁻²⁰ cm² with the larger full width at half maximum (FWHM) of 60.5 nm. The evenly disordered distribution of various cations and lattice distortion effect leads to the more diverse local structure and the diversity of luminescence, which can cause non-uniform broadening of the spectrum. Meanwhile, the Yb:CaSrBaF₆ crystal generated a continuous wave (CW) output power of 1.128 W, corresponding to a slope efficiency of 32% and an optical-to-optical conversion efficiency of 28.7% at 1055.4 nm. By implementing a semiconductor saturable absorber mirror (SESAM) for stable mode-locked laser operation, when the absorbed pump power reached 3.79 W, the laser ran into continuous wave mode-locking (CWML) regime, the maximum average output power of 123 mW was generated and the pulse duration of 89 ps was achieved at a pulse repetition rate of 54.6 MHz, with a pulse energy of 2.25 nJ and a pulse peak power of 25 W. Better laser performance could be expected after optimizing pump core diameter and elimination of dispersion. All results show that Yb:CaSrBaF₆ crystal is regarded as a what we believe to be novel laser materials, which also provide a reference for the development of disordered material and other rare earth ions doping.

High quality 0.3 at.% Pr, 2.5 at.% Yb:BaF₂ and 0.6 at.% Pr, 3 at.% Yb:BaF₂ single crystals were grown by the temperature gradient technique (TGT). The absorption spectra, fluorescence spectra, fluorescence decay curves and energy transfer process are measured and analyzed at room temperature. By co-doping Yb³⁺ ions as a sensitizer of Pr³⁺ ions, the broad near-infrared band emission from ¹G₄ energy level at 1.3 µm is observed in the Pr³⁺/Yb³⁺: BaF₂ crystal with low maximum phonon energy for the first time. In addition, the visible fluorescence emission can be detected and the luminescence components are mainly blue-green transition. The emission cross sections of ¹G₄→³H₅ and ³P₀→³H₄ transitions are calculated to be 0.21 × 10⁻²⁰ cm² and 1.12 × 10⁻²⁰ cm² with the larger FWHM of 103.8 nm and 4.2 nm in 0.6 at.% Pr, 3 at.% Yb:BaF₂ crystal, respectively. The luminescence lifetime of ¹G₄ and ³P₀ energy levels are fitted to be 259.6 µs and 126.1 µs in 0.3 at.% Pr, 2.5 at.% Yb:BaF₂ crystal, which is much increased by Yb³⁺ ions co-doping. The energy transfer efficiency in BaF₂ crystal from Yb³⁺ to Pr³⁺ ions is calculated to be 60.3% and 70.5%, respectively. All results show that the Pr³⁺/Yb³⁺:BaF₂ crystal is a promising candidate of laser gain medium for near-IR laser at 1.3 µm and blue laser operation.

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.

Pr³⁺-doped GdScO₃ single crystal was successfully grown by the Czochralski (Cz) method. Polarized absorption spectra, polarized fluorescence spectra, and fluorescence decay curves were measured at room temperature. The polarized spectroscopic property of Pr:GdScO₃ crystal for new-wavelength transition in the near infrared (NIR) region was discussed for the first time. The absorption cross-sections at 600 nm were calculated to be 0.39×10⁻²⁰ cm² (E∥a), 0.32×10⁻²⁰ cm² (E∥b) and 0.4×10⁻²⁰ cm² (E∥c). The emission cross sections at 1053 nm of ¹D₂ energy level were calculated to be 0.86×10⁻²⁰ cm² (E∥a), 0.79×10⁻²⁰ cm² (E∥b) and 0.78×10⁻²⁰ cm² (E∥c), with FWHM of 57.54 nm, 57.96 nm and 58.96 nm, respectively. The fluorescence lifetime and radiative lifetime of the ¹D₂ energy levels of Pr³⁺ ions were 45.46 µs and 393.94 µs, respectively. Those results show that the Pr:GdScO₃ crystal should be the potential near infrared laser gain medium originated from the ¹D₂ transition.

Single crystals fiber (SCF) of LuAG doped with 2.0 at.% thulium has been grown by using micro-pulling down (µ-PD) technique. A continuous-wave output power of 2.44 W was achieved with a slope efficiency of 11.7% using a 783-nm diode laser as pump source. The beam quality factors M² were 1.14 and 1.67 in the x and y directions, respectively. This is, to the best of our knowledge, the first report on the Tm:LuAG SCF laser. Using ray tracing analysis, the influence of laser performance by the pump intensity distribution in the SCF was also studied.

Odorant binding proteins (OBPs) play a key role in the olfactory recognition of insects, whose functions have been extensively studied in adult insects but rarely in larvae. In this study, one OBP (SlitOBP11) with high expression in larval antenna but low expression in adult antenna of Spodoptera litura was screened by RNA-seq and verified by quantitative real-time PCR. Furthermore, the function of SlitOBP11 was explored by analysis of the expression patterns and prokaryotic expression of proteins as well as assays of competitive binding. Competitive binding assay demonstrated that SlitOBP11 had high binding affinity to all four female sex pheromone components, but exhibited almost no binding affinity to plant volatiles except for a low affinity to Phenylacetaldehyde and Phenethyl acetate. Homology modeling and molecular docking implied that the shape of these four sex pheromones were linear, which were appropriate for the binding channel of SlitOBP11 and the amino acid residue Asn99 of SlitOBP11 might play an important role in binding. Taken together, our results indicate that SlitOBP11 may be involved in the perception of female sex pheromones by S. litura larvae, and OBPs in the larvae of S. litura play an important role in the olfactory perception process.

The polarized absorption spectra, polarized fluorescence spectra and fluorescence decay curve of Nd:Ca_0.7La_0.3Mg_0.3Al_11.7O₁₉ (CLnA) crystal were recorded at room temperature. The Judd-Ofelt parameters Ω₂, Ω₄ and Ω₆ were calculated to be 0.80×10⁻²⁰ cm², 3.83×10⁻²⁰ cm² and 2.71×10⁻²⁰ cm², respectively. The spontaneous transition rates, branching ratios and the radiative lifetime were calculated for the ⁴F_3/2 excited state. The emission cross section is 4.01×10⁻²⁰ cm² at 1052 nm for σ-polarization and 0.96×10⁻²⁰ cm² at 1052 nm for π-polarization, respectively. Continuous-wave (CW) laser operations of a-cut and c-cut Nd:Ca_0.7La_0.3Mg_0.3Al_11.7O₁₉ crystals have been demonstrated.