BRIGHT: Blue- and violet-emitting rare-earth-doped innovative gain media for high laser efficiencies at thermoelectric cooling

• Applicant: Dr. Christian Kränkel
• Subject Area: Synthesis and Properties of Functional Materials ; Experimental Condensed Matter Physics ; Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 575273641

Laser sources operating in the wavelength range between 400 nm and 500 nm are of high relevance for a broad spectrum of scientific and technological applications, including spectroscopy, fluorescence microscopy, quantum technologies, and high-resolution lithography. While InGaN-based laser diodes are commercially available in this spectral region, directly emitting violet-blue solid-state lasers offer several advantages, such as improved beam quality, better energy storage capacity for pulsed operation, and the possibility of integrating additional functionalities like single-frequency operation or intracavity frequency-doubling to the UV range. To date, solid-state lasers in the violet-blue region mostly rely on nonlinear frequency conversion schemes. These are typically associated with increased complexity, limited efficiency, and higher system costs. Only a few solid-state lasers with direct emission in this spectral range have been demonstrated so far, and these typically require cryogenic operating conditions, achieved through cooling with liquid nitrogen or even helium. Even under such conditions, output powers and efficiencies remained comparably low. Cryogenic operation in general offers advantages, including increased absorption and emission cross sections, reduced spectral linewidths, and improved thermal conductivity. The narrowed linewidths may help to reduce spectral overlap with parasitic transitions and suppress detrimental energy transfer processes. However, liquid nitrogen cooling is impractical for many applications. The BRIGHT project aims to identify and investigate innovative solid-state laser materials that enable direct emission in the violet-blue spectral range and allow for efficient operation at moderate temperatures, ideally under thermoelectric cooling or even at room temperature. This approach takes into account that many modern laser systems already operate in sealed enclosures filled with dry nitrogen, which is well suited for thermoelectric cooling. The focus of the project lies on the spectroscopic and laser characterization of innovative fluoride and oxide crystals doped with the trivalent rare-earth ions thulium (Tm), terbium (Tb), or praseodymium (Pr). These gain materials will be grown as single crystals with tailored composition and studied across a temperature range from 77 K to room temperature. Temperature-dependent measurements of relevant spectroscopic as well as laser properties will be used to investigate the mechanisms that limit performance at elevated temperatures. Based on these findings, suitable host materials and operating conditions will be identified to enable efficient direct violet-blue solid-state laser emission under thermoelectric cooling or even at room temperature.

• DFG Programme: Research Grants