Spectral analyses of Dy/Sr: LaF and Dy/Ca: LaF mixed crystals for laser applications.

Mixed crystals of Dy/Sr: LaF and Dy/Ca: LaF were grown by Bridgman technique and their spectral properties were investigated. Spectra broadening and peak shifts were observed, indicating the co-doping of Sr/Ca brings about a more disordered local symmetry of Dy, 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 Dy in crystals.

Ultrasensitive nonlinear absorption response of large-size topological insulator and application in low-threshold bulk pulsed lasers.

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.