A research team at the Hefei Institutes of Physical Science of the Chinese Academy of Sciences has advanced mid-infrared laser technology by developing a new Er³⁺-doped SGGG (Er:SGGG) laser gain medium operating at 2.8 μm.
"The new crystal can produce the mid-infrared laser at 2.8 μm," explained Prof. SUN Dunlu, who led the team, "it could help make future medical treatments and environmental sensing tools more precise and efficient."
The related studies were published in Optics and Laser Technology, Infrared Physics and Technology, and Optics Express.
The 2.8 μm wavelength, strongly absorbed by water, makes these lasers useful for biomedical, remote sensing, and nonlinear optics applications. Er³⁺ ions can be efficiently pumped by ~970 nm laser diodes, and the mixed-crystal SGGG structure broadens absorption and fluorescence, improving laser performance.
Using the Czochralski technique, the team successfully grew a high-concentration (30 at.%) Er:SGGG crystal, which exhibited a broadened absorption band near the 970 nm pump wavelength. Initial pulsed-laser tests confirmed stable 2.8 μm output and favorable energy conversion characteristics.
To improve continuous-wave (CW) laser operation, the team designed a dual end-pumping configuration that enhanced output stability and output power compared with single end-pumping. The researchers further explored thermal and optical optimization by fabricating bonded SGGG/Er:SGGG and SGGG/Er:SGGG/SGGG structures. These bonded crystals demonstrated better beam characteristics, and the dual pumping geometry helped reduce thermal stress during CW laser operation.
The results indicate that bonded end-caps can effectively improve mid-infrared beam quality, while optimized pumping strategies contribute to more efficient and thermally stable operation.
These developments highlight the potential of Er:SGGG as a promising gain medium for compact and efficient 2.8 μm lasers, with possible applications in medical treatment, environmental monitoring, and advanced photonic systems, according to the team.
Dual end-pumping laser structure for Er: SGGG laser crystal (Image by LI Hongyuan)
Laser performance of SGGG/Er:SGGG and SGGG/Er:SGGG/SGGG (Image by LI Hongyuan)