The Study On An All-solid-state Quasi-continuous Dual-wavelength Tunable Ti³⁺: Sapphire Laser And THz Radiation Via Optical Difference Frequency Generation

Dual-wavelength tunable laser is regarded for its important applications such as differential absorption lidar(DIAL), atmospheric pollution monitoring, non-linear frequency conversion, and so on. In 1970s dual-wavelength laser had already been reported. In the end of 1980s, a novel dual-wavelength laser appeared, which was Ti:sapphire dual-wavelength laser, with large stimulated emission cross sections and broad tuning ranges. Many researches have been developed into it abroad and home, which has been one of the most active projects in laser technology fields.The paper has deeply studied the theory of the operation of the all-solid-state quasi-continuous dual-wavelength tunable Ti:sapphire laser. Tunable methods and THz radiation via dual-wavelength difference frequency and many experiments have been also developed. The main content and key innovative points of this dissertation are concluded in four aspects as follows:1. The rate equation of all-solid-state qusi-continuous-wave dual-wavelength tunable Ti:sapphire laser is provided based on the rate equation of the four-level system. We come to a conclusion that in order to realize simultaneous dual wavelength laser. The thresholds of both lasers with different wavelengths are required to satisfy an inequality. Moreover and expression of the least pump power for a simultaneous dual wavelength laser is also given.2. Two kinds of laser-tuning and line width-narrowing components which are the birefringence filter (BF) and the prisms are studied based on the principle of interference and dispersion. The BF and the prism are used to realize the operation of the all-solid-state qusi-continuous-wave dual-wavelength tunable Ti:sapphire laser. Three chips of the quartz birefringence were employed in our experiment with the proportion of the thickness h 1:2:4. In terms of the dispersion equations for quartz crystal, the transmission curve of the assembled BF in the Ti:sapphire waveband was plotted. The point angles of two pieces of dense flit glass prisms are both 60o.3. In the design of the laser, we adopted a frequency-doubled Nd:YAG as the pumping source, the birefringence filter and the prisms as the tuning element. Tunable dual-wavelength outputs with one wavelength range from 750nm to 795nm, another from 800nm to 850mn have been demonstrated. With a pump power of 23W at 532nm, the maximum output power is 5.6W. At last, we sum up merits and drawbacks of the two tuning methods.4. The model of surface-emitted THz wave by difference frequency generation in slant-strip-type PPLN is introduced in theory for the first time and THz radiation system via dual-wavelength tunable Ti:sapphire laser PPLN intracavity difference frequency is promoted for the first time. With the dual-wavelength range from 781.2~805.4nm, the temperature of PPLN 140°C, grating period 10μm or so, wide-band THz radiation 4~6THz can be obtain via the technology of intra-cavity difference frequency.