$\sim 2$ - $\mu \text{m}$ Single-Mode Laser Output in Tm3+-Doped Tellurium Germanate Double-Cladding Fiber

A single-mode laser output of 0.75 W near 2 μm was obtained with a slope efficiency of 28.7% with respect to the absorbed pump power when a self-developed double-cladding Tm
³⁺
-doped tellurium germanate glass fiber laser was pumped using a 793-nm diode laser. The core glass possesses an infrared cutoff edge reaching ~5 μm. The calculated peak emission cross section of Tm
³⁺
at 1.9 μm was 6.8 × 10
^-21
cm
²
. The measured fluorescence lifetime of
³
F
₄
energy level was 2.96 ms. A single-mode double-cladding tellurium germanate glass fiber was fabricated in house using the rod-in-tube drawing technique. The lasing threshold was 0.56 W and the lasing wavelength was centered at 1968 nm. Spatial beam quality of the fiber was measured and a value of M
²
= 1.36 was obtained.