Efficient directly emitting high-power Tb³⁺:LiLuF₄ laser operating at 5875  nm in the yellow range

Diode‐Pumped Laser Operation of Tb3+:LiLuF4 in the Green and Yellow Spectral Range

“…This spin–flip heavily reduces the probability for corresponding ESA transitions in the visible . However, detrimental 4f–4f ESA processes still prohibit laser operation in the orange and in the red in Tb 3+ :LLF . To further avoid ESA from the excited state 5 D 4 into higher and only singly spin‐forbidden, energy levels of the 5d configuration, it is still crucial to choose a host material with a large energy gap between the 4f energy ground state and the next higher levels of the 5d configuration 7 D .…”

“…[37] However, detrimental 4f-4f ESA processes still prohibit laser operation in the orange and in the red in Tb 3+ :LLF. [34,35,38] To further avoid ESA from the excited state 5 D 4 into higher and only singly spin-forbidden, energy levels of the 5d configuration, it is still crucial to choose a host material with a large energy gap between the 4f energy ground state and the next higher levels of the 5d configuration 7 D. [39] The low crystal field strength of fluorides compared to other laser host materials, [36] fulfills this requirement, and makes them suitable host materials for green and yellow Tb 3+ lasers.…”

“…[32] In contrast, yellow emitting Tb 3+ -doped laser materials exhibit an order of magnitude lower laser thresholds and slope efficiencies in excess of 25% under pumping with a 2 -OPSL at 486 nm. [34,35] Here, we present what we believe to be the simplest and most efficient direct yellow emitting solid-state laser up to now. The first diode-pumped Tb 3+ :LLF laser exhibits a slope efficiency of 22% at a wavelength of 587 nm in the yellow spectral range under pumping with a diode laser emitting up to 200 mW at 488 nm.…”

“…However, Pr 3+ ions do not allow for laser operation at wavelengths between 550 and 600 nm due to ground state absorption losses into the 1 D 2 ‐multiplet. Thus, trivalent dysprosium (Dy 3+ ), samarium (Sm 3+ ), and Tb 3+ are the only known laser active ions suitable for direct yellow emission. Among these, Sm 3+ and Tb 3+ were previously only pumped by complex frequency doubled optically pumped semiconductor lasers (2ω‐OPSL).…”

“…This insufficient performance is owed to the properties of the 6 H 13/2 terminal level of the respective Dy 3+ laser transition, which, even utilizing Tb 3+ ‐codoping for depopulation, exhibits too long a lifetime . In contrast, yellow emitting Tb 3+ ‐doped laser materials exhibit an order of magnitude lower laser thresholds and slope efficiencies in excess of 25% under pumping with a 2ω‐OPSL at 486 nm …”