Direct AlGaAs LD pumped 2.1 μm Tm/Ho composite laser

We demonstrate a 2.1 μm Tm/Ho composite laser via diffusion-bonding the Tm-doped and Ho-doped YAG crystals into a single bulk structure, which facilitates the direct use of common AlGaAs diode lasers (LD) for an efficient and compact Ho laser source at room temperature. Locking the pump wavelength at absorption peak of 784.9 nm of the Tm-doped region of the composite gain medium, maximum output power of 6 W at 2122 nm was obtained with a slope efficiency (SE) of 40.1% and conversion efficiency (CE) of 33.6% from absorbed LD power to Ho laser, which is comparable in efficiency with the 1.9 μm LD resonantly pumped Ho lasers. Above 1.6 W Ho laser power at operation temperature range from 9 °C to 27 °C could also be realized by side-pumping absorption band of the Tm-doped region at 808 nm, which indicates a 40 nm broad pump wavelength range for the Ho laser at room temperatures. Via broad-band coating the output coupler with the same transmittance from 2000 nm to 2100 nm, synchronous Tm laser and Ho laser oscillation at both 2.1 μm and 2 μm was observed, where signal of the Tm laser was faded finally with the increased pump power. Furthermore, thermal lens and temperature distribution of the composite gain medium is analyzed basing on a proposed thermal model recently.