We report on highly efficient and power-scalable laser operation in a thulium-doped high-phonon-energy crystal [monoclinic double tungstate, ${\rm KLu}{({{\rm WO}_4})_2}$] on the ${^3{{\rm H}}_4} \to {^3{{\rm H}}_5}\;{{\rm Tm}^{3 +}}$ transition giving rise to the short-wave infrared emission at ${\sim}{2.3}\;\unicode{x00B5}{\rm m}$. A 3 at. % Tm-doped crystal generated a maximum continuous-wave output power of 1.12 W at ${\sim}{2.22}$ and 2.29 µm with a record-high slope efficiency of 69.2% (versus the absorbed pump power), a slightly multimode beam (${\rm M}_{x,y}^2 = {2.2}$ and 2.6), and a linear laser polarization. The ${\sim}{2.3}\;\unicode{x00B5}{\rm m}$ laser outperformed the one operating on the conventional ${^3{{\rm F}}_4} \to {^3{{\rm H}}_6}$ transition (at ${\sim}{1.95}\;\unicode{x00B5}{\rm m}$). The effect of the Tm concentration on the ${\sim}{2.3}\;\unicode{x00B5}{\rm m}$ laser performance indicates a gradually increasing pump quantum efficiency for the ${^3{{\rm H}}_4}$ upper laser level with the Tm doping. For the 3 at. % Tm-doped crystal, it reached ${1.8} {\pm} {0.1}$ (almost two-for-one pump process), which is attributed to efficient energy-transfer upconversion. We discuss the physical nature of the laser emissions occurring at intermediate wavelengths between the electronic ${^3{{\rm H}}_4} \to {^3{{\rm H}}_5}$ and ${^3{{\rm F}}_4} \to {^3{{\rm H}}_6}$ transitions and highlight the role of electron-phonon coupling (vibronic processes) in the appearance of such laser lines. This allowed us to better understand the near- and mid-infrared emission from thulium ions, which can be used in broadly tunable and fs mode-locked 2–2.3 µm lasers.

中文翻译：

---

基于高声子能量晶体的高效2.3 µm ul激光器：振动辅助发射的证据

我们报告了在the掺杂高声子能量晶体[单斜双钨酸盐$ {\ rm KLu} {（{{\ rm WO} _4}）_ 2} $ ]上的高效且可缩放功率的激光操作。$ {^ 3 {{\ rm H}} _ 4} \到{^ 3 {{\ rm H}} _ 5} \; {{\ rm Tm} ^ {3 +}} $过渡产生短波$ {\ sim} {2.3} \; \ unicode {x00B5} {\ rm m} $的红外发射。3点 ％Tm掺杂的晶体在$ {\ sim} {2.22} $和2.29 µm时产生的最大连续波输出功率为1.12 W，斜率效率达到创纪录的69.2％（相对于吸收的泵浦功率），略有多模光束（$ {\ rm M} _ {x，y} ^ 2 = {2.2} $和2.6）和线性激光偏振。的$ {\ SIM} {2.3} \; \ {的unicode x00B5} {\ RM米} $激光的性能优于传统$ {^ 3 {{\ rm F}} _ 4} \到{^ 3 {{\ rm H}} _ 6} $过渡（在$ {\ sim} {1.95} \; \\ unicode {x00B5} {\ rm m} $）。Tm浓度对$ {\ sim} {2.3} \; \ unicode {x00B5} {\ rm m} $激光性能的影响表明，对于$ {^ 3 {{rm H} } _4} $带有Tm掺杂的较高激光能级。对于3 at。掺有Tm的晶体百分比达到$ {1.8} {\ pm} {0.1} $（几乎是两对一的泵浦过程），这归因于有效的能量传输上转换。我们讨论了在电子$ {^ 3 {{\ rm H}} _ 4}至{^ 3 {{\ rm H}} _ 5} $和$ {^ 3 {{\ rm F}} _ 4} \到{^ 3 {{\ rm H}} _ 6} $跃迁，突显了电子-声子耦合（振动过程）在此类激光线出现中的作用。这使我们可以更好地了解from离子的近红外和中红外发射，可将其用于广泛可调且fs锁模的2–2.3 µm激光器中。