Lasing effects in new Nd3+-doped TeO2–Nb2O5–WO3 bulk glasses

Abstract

This paper demonstrates for the first time continuous wave (cw) and pulsed lasing effects in a 75TeO2–20NbO2.5–5WO3 glass doped with 1mol.% in Nd3+. It is divided into two parts:–The first part treats all the aspects related to the elaboration and the characterization of the materials. Thus, glasses elaborated within the TeO2–Nb2O5–WO3 ternary system show a rather high glass transition temperature Tg∼375°C, with an excellent thermal stability of ∼160°C. Compared to glasses synthesized in either TeO2–Nb2O5 or TeO2–WO3 binary systems, glasses fabricated within such system show improved mechanical performances, with larger Young’s modulus values. The structural characteristics of the samples, studied by Raman spectroscopy, are also presented. Linear optical properties (refractive index and extinction coefficient) are accessed by spectroscopic ellipsometry. As well, the optical transmission of the various bulk glasses is measured, in the case of both uncoated and coated glasses. In particular, specific anti-reflective coatings at 808nm (laser diode pump wavelength) and 1064nm (laser emission wavelength) are respectively deposited on the two surfaces of the sample in order to minimize the losses due to Fresnel reflections at the two glass/air interfaces. In addition, another specific surface treatment (Rmax at 1064nm) was employed to serve as the back mirror of the laser cavity. The optical transmission data testified to the real efficiency of all these coatings. Finally, the photoluminescence properties (emission and excitation spectra, and luminescence decay curve) of the Nd3+-doped glasses, measured at room temperature for bulk samples, and as a function of temperature for powder glasses, are discussed.–The second part is focused on evidencing (cw) and pulsed lasing effects in such coated bulk lasers. Cylindric samples of only a few millimeters in height and in diameter were tested and led to a laser emission around 1064nm, characterized by a very low pump power threshold of ∼5mW, but with a limited slope efficiency (∼4.6%). The spectral characteristics were also measured and some anisotropic enlargement of the laser emission band toward longer wavelength was noticed with increasing the pump power. Finally, monomodal or multimodal laser emission was evidenced, depending again on the pump power.