Qiuqun Chen

Enhanced 2.0 μm emission and gain coefficient of transparent glass ceramic containing BaF 2 : Ho 3+ ,Tm 3+ nanocrystals

Transparent glass ceramic containing BaF(2):Ho(3+),Tm(3+) nanocrystals has been prepared by melt quenching and subsequent thermal treatment. The precipitation of BaF(2) nanocrystals was confirmed by X-ray diffraction and high-resolution transmission electron microscopy. Intense 2.0 microm fluorescence originating from Ho(3+): (5)I(7) --> (5)I(8) transition was achieved upon excitation with 808 nm laser diode. A large ratio of forward Tm(3+) --> Ho(3+) energy transfer constant to that of backward process indicated high efficient energy transfer from Tm(3+)((3)F(4)) to Ho(3+)((5)I(7)), benefited from the reduced ionic distances of Tm(3+)-Tm(3+) and Tm(3+)-Ho(3+) pairs and low phonon energy environment with the incorporation of rare-earth ions into the precipitated BaF(2) nanocrystals. The results indicate that glass ceramic is a promising candidate material for 2.0 microm laser.

Spectroscopic investigation of 2.02 μm emission in Ho3+/Tm3+ codoped transparent glass ceramic containing CaF2 nanocrystals

Tm3+ and Ho3+ codoped transparent glass ceramic (GC) containing CaF2 nanocrystals were fabricated by melt-quenching and subsequent thermal treatment. X-ray diffraction and transmission electron microscopy analysis confirmed the precipitation of CaF2 nanocrystals among the glass matrix. Energy-dispersive x-ray spectroscopy results evidenced the incorporation of Tm3+ and Ho3+ into the CaF2 nanocrystals. Judd–Ofelt parameters were calculated based on the absorption spectra, the smaller Ω2 and larger Ω6 imply that Tm3+ and Ho3+ ions has entered into a symmetrical ionic crystal field. 2.02 μm emission spectral of the GC samples were recorded at room temperature with an excitation of 808 nm laser diode. The enhancement of the emission at 2.02 μm in the GC samples could be attributed to more efficient cross relaxation process of Tm3+:H34+Tm3+:H36→2Tm3+:H34, and energy transfer from Tm3+ to Ho3+ benefited from the incorporation of rare earth ions into CaF2 nanocrystals.

Vertically standing layered MoS 2 nanosheets on TiO 2 nanofibers for enhanced nonlinear optical property

Vertical layered MoS₂ nanosheets rooting into TiO₂ nanofibers were successfully prepared by a facile two-step method: prefabrication of porous TiO₂ nanofibers based on an electrospinning technique, and assembly of MoS₂ ultrathin nanosheets through a simple hydrothermal reaction. Significant enhancement of nonlinear optical response of the MoS₂/TiO₂ nanocomposite was confirmed by an open-aperture z-scan measurement. The nanocomposite displayed strong optical limiting (OL) effects to ultrafast laser pulses with a low OL threshold of ~22.3 mJ/cm², which is lower than that of pristine TiO₂ nanofibers and MoS₂ nanosheets. In addition to the contribution of the strong nonlinear absorption of MoS₂ nanosheets and TiO₂ nanofibers, such phenomenon is also attributed to the unique structure of vertically standing layered MoS₂ nanosheets on TiO₂ nanofibers with a large amount of exposed edge states, large surface areas and fast electron transfer between TiO₂ and MoS₂. This work broadens our vision to engineering novel hierarchical MoS₂-based nanocomposite for efficiently enhanced nonlinear light-matter interaction.

New insight into two-step near-infrared quantum cutting in Pr 3+ singly doped oxyfluoride glass-ceramics

Efficient near-infrared (NIR) quantum cutting (QC) in RE3+/Yb3+ requires the UV-blue photon excited RE3+ donor has intermediate energy level to separate the energy gaps (~10000 cm−1) resonant to Yb3+absorption. Thus the unique Pr3+/Yb3+ resonant QC at low Yb3+content (room temperature) essentially requires Pr3+-doping features distinctive NIR radiative transitions: in our prepared Pr3+-doped oxyfluoride glass-ceramics containing CaF2 nanocrystals, a two-photon NIR-QC from blue-photon excited 3Pj (j = 0, 1, 2) states takes place efficiently with 1G4 acting as an intermediate level. The underlying energy transfer mechanisms involving the two-step sequential transitions of 3P0→1G4 ~915 nm and 1G4→3H4 ~990 nm (crucial resonant routes for the further 1Pr3+→2Yb3+), as well as the 1D2→3F2 ~873 nm and 1D2→3F3,4 ~1040 nm, are rationally distinguished by means of photoemission, excitation, and time-resolved fluorescence spectra.

Evolution of polarization dependent microstructures induced by high repetition rate femtosecond laser irradiation in glass

We report the observation of an anomalous polarization dependent process in an isotropic glass induced by long time stationary irradiation of a high repetition rate near-infrared femtosecond laser. Two distinctive types of polarization dependent microstructures were induced at different irradiation stages. At early stage (a few seconds), a dumbbell-shaped structure elongated perpendicularly to the laser polarization formed at the top of the modified region, which was later erased by further irradiation. At later stage (above 30 s), bubbles filled with O2 formed by the irradiation, which were distributed along the laser polarization at a distance far beyond the radius of the laser beam. Based on a simple modeling of light reflection on boundaries, a thermal accumulation process was proposed to explain the formation and evolution of the dumbbell-shaped microstructure. The possible factors responsible for polarization dependent distribution of bubbles are discussed, which needs further systematic investigations. The results may be helpful in the development of femtosecond laser microprocessing for various applications.

Enhanced nonlinear optical response of Se-doped MoS2 nanosheets for passively Q-switched fiber laser application

An enhanced nonlinear optical (NLO) performance was observed in Se-doped MoS2 nanosheets synthesized through a facile annealing process. Se-doped MoS2 nanosheets with a large saturable intensity and high modulation depth generated stable passively Q-switched fiber laser pulses at 1559 nm. In comparison with the Q-switched fiber laser utilizing the pristine MoS2 nanosheets as a saturable absorber, the passive Q-switching operation based on Se-doped MoS2 nanosheets could be conducted at a lower threshold power of 50 mW, a wider range of repetition rates from 28.97 to 130 kHz, and a higher SNR of 56 dB. More importantly, the shortest pulse duration of 1.502 μs was realized and the output power and pulse energy reached 17.2 mW and 133.07 nJ, respectively. These results indicate that tailoring the chemical composition of optical nanomaterials by introducing a dopant is a feasible method of improving the NLO response of the MoS2 nanosheets and realizing excellent ultrafast pulse generation.