Dysprosium-doped silica fiber as saturable absorber for mid-infrared pulsed all-fiber lasers

High-efficiency mode-locked erbium-doped ZBLAN fiber laser around 2.8 µm by directly depositing Bi2S3 particles onto a cavity mirror

Mid-infrared (MIR) pulsed lasers near a 3 µm waveband show great potential for the high absorption of water molecules and many important gas molecules. A passively Q-switched mode-locked (QSML) E r ³⁺-doped fluoride fiber laser with a low laser threshold and high slope efficiency around a 2.8 µm waveband is reported. The improvement is achieved by depositing bismuth sulfide (B i ₂ S ₃) particles onto the cavity mirror directly as a saturable absorber and using the cleaved end of the fluoride fiber as output directly. -QSML pulses begin to appear with the pump power of 280 mW. The repetition rate of the QSML pulses reaches a maximum of 33.59 kHz with the pump power of 540 mW. When the pump power is further increased, the output of the fiber laser switches from the QSML to the continuous-wave mode-locked operation with the repetition rate of 28.64 MHz and the slope efficiency of 12.2%. The results indicate that B i ₂ S ₃ is a promising modulator for the pulsed lasers near a 3 µm waveband, which paves the way for further development of various applications in MIR wavebands, including material processing, MIR frequency combs, and modern healthcare.

Laser cooling experiments to measure the quantum efficiency of Yb-doped silica fibers

A detailed investigation into the wavelength-dependent cooling efficiencies of two ultra-pure large core diameter ytterbium-doped silica fibers is carried out by means of the laser-induced thermal modulation spectroscopy (LITMoS) method. From these measurements, an external quantum efficiency of 0.99 is obtained for both fibers. Optimal cooling is seen for pump wavelengths between 1032 and 1035 nm. The crossover wavelength from heating to cooling is identified to be between 1018 and 1021 nm. The fiber with higher Yb³⁺ ion density exhibits better cooling, seen by the input power normalized temperature differential.