Tm:CYA Q-switched mode-locked laser realized by tandem-pumping

Passively Q-switched mode-locked operation was realized for the first time by inserting a semiconductor saturable absorption mirror (SESAM) as a mode-locking element into a Tm:CaYALO(4)(Tm:CYA) laser using tandem-pumping technology. The laser cavity adopted an X-type four-mirror cavity structure, and the pumping source was an Er:Y3Al5O12 (Er:YAG) solid-state laser with a central wavelength of 1 650 nm. Output coupling mirrors with transmittances of 0.5%, 1.5%, 3%, and 5% were used to study the laser's continuous wave (CW) output and mode-locking output characteristics. The experimental results show that the laser has the best output characteristics when an output coupling mirror with a transmittance of 5% is used. The maximum power of 894 mW and the maximum slope efficiency of 16% were obtained when the laser operated in the CW regime. After the CW power was optimized to the highest, the mode-locked element SESAM was added to the optical path. When the absorbed pump power became greater than 1.86 W, the laser operation entered an unstable Q-switched state; when the absorbed pump power increased to 5.7 W, a stable passively Q-switched mode-locked operation was achieved; when the absorbed pump power reached 6.99 W, a mode-locked pulse laser with a maximum output power of 399 mW was obtained by using the output coupling mirror with transmittance of 5%. At that time, the repetition frequency under the Q-switched envelope was 98.11 MHz, the pulse width was 619.4 ps, and the corresponding maximum single pulse energy was 4.07 nJ. The mode-locked pulse modulation depth in a Q-switched envelope was observed to be close to 100%. The above results show that tandem-pumping technology can be used in lasers to generate Q-switched mode-locked pulses, which provides a new pumping method for generating ultrashort pulse lasers.