Abstract
A passively Q-switched mode-locked (QML) operation in Tm, Ho: CaYAlO4 bulk laser was demonstrated experimentally by employing double wall carbon nanotube (DWCNTs) as a saturable absorber. The laser is pumped by a self-made wavelength tunable Ti: sapphire laser, and the pump threshold of Tm, Ho: CaYAlO4 laser was measured as 677 mW by using transmittance of 1.5% output coupler. A stable Q-switched mode-locked operation state was achieved when the absorption pumping power reached 1958 mW. And when the pumping power reached 2.6 W, a maximum output power was 64 mw with central wavelength of 2085 nm, the corresponding repetition frequency of mode-locked pulse was 98.04 MHz, and the modulation depth in Q-switching envelopes is close to 100%.
Highlights
Thanks to the rapid development of laser technology, a variety of lasers, including medium infrared ultrafast lasers [1, 2], ultrafast fiber lasers [3, 4] are playing an important role in more and more fields [5, 6]
It can be seen that the absorption efficiency of laser crystal to the pump light at 798 nm is 89.7% due to a large amount of pump light that is absorbed by the crystal when there is no laser running in the cavity
When continuous wave (CW) operation in the cavity is realized, the absorption efficiency of the laser crystal increases to about 91.6% due to the large number of upper-level particles returning to the lower level under stimulated radiation
Summary
Thanks to the rapid development of laser technology, a variety of lasers, including medium infrared ultrafast lasers [1, 2], ultrafast fiber lasers [3, 4] are playing an important role in more and more fields [5, 6]. The passive mode-locking technique with saturable absorber (SA) [11,12,13] is the most widely convenient and low-cost method to obtain ultrafast lasers at 2-μm wavelength. The reports on mode-locked DWCNT-SAs are mainly focused on the solid-state and fiber lasers at 1-μm band [32, 33], while the reports on modelocked DWCNT-SAs at 2-μm band are few, and the output power is lower than 200 mW [34,35,36]. In 2018, our group realized the Q-switched and modelocked simultaneous operation with low threshold based on the DWCNTs in the Tm,Ho:LLF laser, and the maximum output power was 234 mW [39]. A stable simultaneously Q-switched modelocking (QML) operation was experimentally demonstrated for the first time in Tm,Ho:CaYAlO4 crystal by using DWCNTs-SA. Is calculated using the laser cavity mode ABCD propagation matrix theory
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