Trivalent Terbium: A new active ion for green and yellow emitting solid-state lasers (TiTAN)

• Applicant: Dr. Christian Kränkel
• Subject Area: Synthesis and Properties of Functional Materials
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 458056764

This projects targets the investigation of trivalent terbium as a laser ion with visible emission in the green and yellow spectral range. Even after 60 years of laser research, in particular the generation of yellow laser light is still a challenge. Applications of yellow laser radiation in dermatology and ophthalmology are still based on inefficient, expensive, toxic, or complex approaches such as dye lasers, copper vapor lasers or non-linear frequency conversion. Our preliminary work has proven that trivalent terbium is generally suitable as an active ion for simple and efficient diode-pumped solid-state lasers (DPSSL) that emit directly in the yellow spectral range. However, not all energy transfer processes involved in the laser action are understood, yet, and the proposed research will help to fully exploit the potential of trivalent terbium as a laser ion. Within this research project, we want to solve the open questions. For this purpose, we will grow novel highly terbium-doped fluoride and oxide crystals, conduct systematic spectroscopic investigations and reveal their potential as laser material. The experiments will focus on intra- and interionic energy transfer processes, which will be studied using highly doped fluoride crystals. We aim to understand nature and ion-concentration dependence of the energy transfer processes in trivalent terbium allowing to define optimal doping concentrations for terbium-based laser gain media based on different host crystals.Understanding all energy transfer processes will also enable to define suitable host crystal properties for efficient visible lasing. In particular, the influence of the crystal field of the host material on the excited state absorption of trivalent terbium seems to be crucial. To study this correlation, we will grow terbium-doped oxide crystals exhibiting different host crystal field strengths. We plan to perform temperature- and time-dependent fluorescence measurements, UV/VIS absorption spectroscopy and pump-probe spectroscopy. A characterization of the laser performance of suitable samples will confirm the spectroscopic results.The knowledge gained during this project will allow to define guidelines and suitable host crystal properties for optimized performance of terbium-based diode-pumped solid-state lasers with emission in the green and in particular the yellow spectral range and, by that, to further improve output power and efficiency. These are important steps toward commercialization of Tb-based visible lasers. The results and developed methods can be also applied to other laser ions used for the generation of visible laser radiation and will be of great relevance for lasers based on trivalent praseodymium, samarium or dysprosium.

• DFG Programme: Research Grants