ABSTRACT
Mixed crystals of Dy3+/Sr2+: LaF3 and Dy3+/Ca2+: LaF3 were grown by Bridgman technique and their spectral properties were investigated. Spectra broadening and peak shifts were observed, indicating the co-doping of Sr2+/Ca2+ brings about a more disordered local symmetry of Dy3+, which makes both crystals favorable for tunable lasing action. Low-temperature high resolution excitation and emission spectra were carried out for exploring the types of luminescent center of Dy3+ in crystals. Room-temperature absorption and emission spectra, together with the fluorescence decay curves were studied in both crystals for estimating their potentials for yellow and MIR lasers. Under 450 nm excitation, the largest emission cross-sections at 571 nm of 1.51 × 10-21 cm2 for Dy3+/Sr2+: LaF3 crystal and 1.56 × 10-21 cm2 for Dy3+/Ca2+: LaF3 crystal, along with the lifetimes of Dy3+: 4F9/2 level as 0.983 ms for Dy3+/Sr2+: LaF3 crystal, 1.143 ms for Dy3+/Ca2+: LaF3 crystal were obtained, respectively. Besides yellow emissions, MIR emissions approximately at 3 µm are more appealing. Under 1280 nm excitation, the largest emission cross-sections of 0.304 × 10-20 cm2 at 2885 nm in Dy3+/Sr2+: LaF3 crystal, and 0.319 × 10-20 cm2 at 2880 nm in Dy3+/Ca2+: LaF3 crystal, together with rather long lifetimes of Dy3+: 6H13/2 in the level of milliseconds were achieved, making them useful media for MIR lasers.
ABSTRACT
Dirac-like topological insulators have attracted strong interest in optoelectronic application because of their unusual and startling properties. Here we report for the first time that the pure topological insulator Bi2Te3 exhibited a naturally ultrasensitive nonlinear absorption response to photoexcitation. The Bi2Te3 sheets with lateral size up to a few micrometers showed extremely low saturation absorption intensities of only 1.1 W/cm(2) at 1.0 and 1.3 µm, respectively. Benefiting from this sensitive response, a Q-switching pulsed laser was achieved in a 1.0 µm Nd:YVO4 laser where the threshold absorbed pump power was only 31 mW. This is the lowest threshold in Q-switched solid-state bulk lasers to the best of our knowledge. A pulse duration of 97 ns was observed with an average power of 26.1 mW. A Q-switched laser at 1.3 µm was also realized with a pulse duration as short as 93 ns. Moreover, the mode locking operation was demonstrated. These results strongly exhibit that Bi2Te3 is a promising optical device for constructing broadband, miniature and integrated high-energy pulsed laser systems with low power consumption. Our work clearly points out a significantly potential avenue for the development of two-dimensional-material-based broadband ultrasensitive photodetector and other optoelectronic devices.
