Low-threshold lasing at 1975  nm in thulium-doped tellurite glass microspheres

Abstract

Thulium-doped (Tm-doped) tellurite glass microspheres are used as laser media. Emission lines at wavelengths near 1975 nm are observed. The onset of laser emission is achieved with 8.6 and 30 μW of coupled pump power and injected pump power, respectively, at a wavelength of 1554 nm. To the authors' knowledge, these are the lowest laser threshold values recorded for a Tm-doped tellurite glass microcavity. Intrinsic Q-factors above 10(6) for the undoped tellurite glass microspheres assert the quality of the fabrication processes. An optical intrinsic Q-factor comparison between Tm-doped tellurite and undoped tellurite microspheres shows that ion absorption is the dominant loss source at pump wavelengths. Lower lasing threshold powers and higher power conversion are observed at longer pump wavelengths in agreement with theoretical models.

Spectral and Modal Properties of a Mid-IR Spherical Microlaser

“…Nearly all near-IR WGMLs demonstrated before used expensive tunable pump lasers and precisely controlled coupling gaps to optimize the laser [1,18,31]. As such, in spite of small size of the microsphere, the laser became a large desktop system.…”

Dual-band Tm3+-doped tellurite fiber amplifier and laser at 1.9 μm and 2.3 μm

“…The rate equations for the population densities n 1 , n 2 , n 3 , n 4 (normalized to the concentration of Tm 3+ ions in the core N Tm  = 5·10 19  cm −3 ) are given by 29 :where τ 4 , τ 4 R and τ 4 NR are the total, radiative and non-radiative lifetimes of level 4, respectively ( τ 4  = 0.3 ms 20,34 , τ 4 R  = 0.4 ms 29 , τ 4 NR  = (1/ τ 4  − 1/ τ 4 R ) −1  = 1.2 ms); τ 3 is the total (non-radiative) lifetime of level 3 ( τ 3  = 0.13 μs 20,34 ); τ 2 is the total lifetime of level 2 ( τ 2  = 3 ms 20,24,29 ); β 4y is the branching ratio from level 4 to level y  = 1, 2, 3 ( β 41  = 0.9, β 42  = 0.07, β 43  = 0.03 29 ); K CR is the coefficient of cross-relaxation ( K CR  = 1000 s –1   29 ), W xy are the stimulated rates. Stimulated rates by hydroxyl groups were neglected due to their extremely low concentration in the produced sample.…”

“…Laser generation at 2.3 μm in a bulk Tm-doped tellurite glass sample was recently demonstrated by Denker et al 20,21 . It was the first experimental confirmation that a tellurite glass matrix is suitable for lasing at the 3 H 4  →  3 H 5 transition whereas laser generation near 2 μm at the 3 F 4  →  3 H 6 transition was previously obtained for different tellurite gain elements such as bulk samples 22 , microspheres 23,24 , and fibers: solid step-index 22,25–27 and microstructured ones 28 .…”

Power scaling of narrow-linewidth mid-IR spherical microlasers

“…Moreover, since the circulating optical power is not easily accessible in ICLs and QCLs, these lasers are not easily adaptable for ultrahigh-sensitivity intracavity molecular detection. In addition, the 2.7 -2.8 µm MIR spectral range for high-sensitivity molecular detection application of several important molecular species (such as H 2 O, CO 2 , HF, HOCL) is not easily achievable by narrow linewidth ICLs or QCLs [3,4].Glass-based whispering gallery mode lasers (WGMLs) are alternative compact sources of narrow linewidth NIR [5,6] and MIR radiation [7,8,9] that are not only highly amenable for intracavity sensing applications (because of the extension of the evanescent tail into the surrounding analyte-bearing medium), but also readily lend themselves to much simpler fabrication processes [5-10], largely because high quality factor ("high-Q") glass WGML microspheres of variable dimensions are relatively easy to fabricate individually, and the doped-glass gain medium also serves as the laser cavity without the need for any external mirror or feedback…”