Passively Q-Switched Wavelength-Tunable Bulk Laser Using Topological Insulator at $1~\mu \text{m}$

The multi-wavelength and tunable Yb 3+ :Ca 3 Y 2 (BO 3 ) 4 solid-state lasers using topological insulator Bi 2 Te 3 nanosheets as saturable absorber have been reported for the first time. A maximum output power of 161 mW with single pulse energy up to $1.09~\mu \text{J}$ was achieved for the multi-wavelength condition. The corresponding shortest pulse duration and the largest repetition rate were 416 ns and 147.7 kHz, respectively. By further inserting an etalon to modulate the laser spectra, the $Q$ -switched laser could be continuously tuned from 1027.9 to 1040.3 nm with a tuning range of 12.4 nm. At a fixed pump power of 5.09 W, it got a maximum output power and shortest pulse width at 1035 nm. This letter suggests that a topological insulator exhibits outstanding wideband saturable absorption properties because of its unique band structure of narrow bulk state and gapless surface state.