5.1. Conclusion
We demonstrated two low threshold passive mode-locked Nd:GdVO4 lasers.
One is using SESAM and the other one is using nonlinear mirror with 1 cm KTP crystal. As increasing the pumping power, the laser output changes from CW, QML to CML in both lasers and two absorbers. Using SESAM, the CML threshold and pulse duration are 4.7 W and 15 ps. According to the Ref.15, we calculated the theoretical value of CML threshold to be 4.4 W, which is very close to our experiment value of 4.7 W and much lower than the result of the other group [5]. In using NLM, the CML threshold and pulse duration are 2.3 W and 38 ps. The CML threshold of NLM is also close to the theoretical value of 1.7 W in considering the reflection change as a function of pumping power.
Besides, we have for the first time observed the pulse splitting and harmonic mode locking by varying the distance between KTP and dichroic mirror in the NLM picosecod laser.
5.2. Future works
There are several works which are valuable to be studied in the future.
First of all, we will investigate the mechanisms of harmonic ML and pulse splitting in NLM. Second, we will convert the stable picosecond ML laser to generate the third and fourth harmonics as the excitation source for time-resolved PL measurement of the ZnO nanostructures. Finally, we plan to investigate the supercontinnum generation by launching the picosecond ML laser pulses into the photonic crystal fibers.
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