Study On The Technology Of Actively Mode-locked Tm:YAG Laser

2μm laser is in the band of eye safe, so it can be used for medicine, environmental monitoring, material processing, communication and so on. Ultrashort pulses have the extensive application in many fields such as micro machining of biological tissues because of its very narrow pulse width, high peak power. The laser that we researched combines the advantages of the above two aspects, so it has more important research value and application value. The main purpose of this article is to obtain the ultrashort pulse of Tm:YAG laser using active mode locking technology.Firstly, we introduced the current research situation of Tm:YAG laser and 2μm mode-locked laser. At the same time, we introduced optical and spectroscopic properties, physical and chemical properties of Tm:YAG crystal. According to the absorption spectrum, we chosed semiconductor laser as the pumping source which has the center wavelength of 785 nm. According to the energy level structure of Tm3+, we obtained the rate equation of Tm:YAG solid state laser. We analysed the threshold of Tm:YAG solid state laser according to the rate equation. At the same time,we analysed the thermal field theory of Tm:YAG crystal. Then we measured the thermal focal length of Tm:YAG crystal by building a simple resonant cavity. On the other hand, we verified the measuring results using the method of beam quality backstepping.Secondly, we explained the principle of active mode locking, including the analysis of time domain and frequency domain, the principle of phase modulation and amplitude modulation, the analysis of pulse width without mismatch. We also introduced the design principle of mode locking resonator cavity. We obtained theoretical value of each parameter by the analysis of the influence of various parameters on the resonant cavity. Then we determined the specific structure of the resonant cavity.Finally, according to the designed resonant cavity, we builded a final experimental device. The relaxation oscillation phenomenon is verified and measured. We matched the cavity length and the driven frequency by adjusting the cavity and the mode locking drive, then we obtained the continuous mode locking pulse. We also introduced the output characteristics of the continuous operation and the mode locking operation, including output power, output wavelength, time domain waveform, frequency spectrum and light spot diagram. The maximam output power is 0.95 W, the center wavelength is 2012.5 nm, the repetition rate is 84.066 MHz, the pulse width is 458.3 ps and the beam quality is 1.37.