Experimental Research On LD End-pumped All-solid-state Passively Continuous-wave Mode-locked Lasers

Diode end-pumped all-solid-state passively mode-locked lasers have many advantages, such as compactness, high efficiency, robustness and long lifetime et al. As the development of laser technology, they have been widely used in the fields of industry machining, nonlinear frequency conversion, optical biology, laser spectroscopy and medical diagnostic purposes et al.The main contents and key creation points of this dissertation are as follows:1. Double output beams mode-locked lasers with semiconductor saturable absorber mirror (SESAM). The continuous-wave mode-locked (CWML) Nd:YVO₄ used a surface-state SESAM as the self-starting device. The average output power was 5.3W and the pulses repetition rate was 83MHz. In Brewster-cut Nd:GdVO₄ laser, Experiment validated that the smaller the modulation depth of the SESAM, the broader the pulse width. Adding a Brewster plate to the Nd:YLF mode-locked lasers, the CWML pulses of 1047nm and 1053nm were obtained. And the average output power was 1.1W and 900mW, respectively.2. Output power >5W of single output beam CWML lasers with SESAM. Inserting a KTP crystal decreased the mode-locked incident pump power threshold. The double pulse splitting of the CWML pulses has been observed for the first time in the above laser. In addition, another laser by combining quadratic polarization switching and a SESAM was presented. The pump threshold was also decreased and the pulses trains stability was improved.3. The output transmission of the single beam SESAM laser could be adjusted by combining a quarter wave plate (QWP) and a thin-film polarizer (TFP). When the gain medium was Nd:YVO₄, the output power was 4.8W, optical-optical conversion efficiency 34.3%, and the optimum output transmission was about 16.5%. Using the degraded polarization losses as useful output, the CWML Nd:YAG laser has an average output power of 2.3W.4. Demonstrated a bi-directional picosecnd pulsed ring Nd:YVO₄ laser for the first time in China. The six mirrors ring laser cavity has a low threshold of <0.3-W of pump power, due to the low intra-cavity losses. The bi-directional pulse train has a repetition rate of 117.5-MHz and a pulse width 81-ps (23-ps). At the incident pump power of 3W, the output power was 2×200-mW and could be increased by increasing the transmission of the output mirror.5. By placing the SESAM in a special location in the laser cavity, we successfully demonstrated a mode-locking technique for multiplying the pulse repetition rate of a picosecond passively mode-locking Nd:YVO₄ laser for the first time. Optical pulses up to 250-MHz with average power 5-W were experimentally obtained with multiplying the fundamental mode-locking frequency, which is 3-times the fundamental mode-locked frequency determined by the master cavity length. The optical-optical conversion efficiency and the slope efficiency of the laser were 40% and 41%, respectively.6. Presented a short cavity and a long cavity CWML nonlinear mirror mode-locked laser. To the best of our knowledge, this is the first time that we observed double pulses splitting, multi-pulses and four pulses harmonic mode-locking in the nonlinear mirror mode-locked Nd:YVO₄ laser. At the incident pump power of 9.3W, the CWML laser average output power was 4W. The optical-optical conversion efficiency and the slope efficiency of the laser were 43% and 52%, respectively. So far, this is the highest conversion efficiency in the Nd doped NLM lasers to our knowledge. We researched the NLM laser operated in different polarization incident angles for the first time. When the polarization incident angle in the range of18 72 , the laser can be continuous-wave mode-locked.7. Presented a compact and high output power diode end-pumped Nd:YAG laser which operated at the wavelength of 1123nm. Continuous wave laser output power of 2.6W was achieved at the incident pump power of 15.9W. Intra-cavity doubled frequency by KTP, the output power of yellow laser at 561nm was 22.2mW.