Research On All-Solid-State Intracavity Optical Parametric Oscillator And Intracavity Frequency Doubling Technology

Intracavity optical parametric oscillator (IOPO) and intracavity frequency-doubled techniques are important components in nonlinear optical frequency conversion. They can take advantage of high fundamental power density within the oscillator to realize high-power, high-energy laser output, and have the characteristics of low threshold and high efficiency. Nowadays, IOPO is considered to be an efficient mean of obtaining 1.5xμm laser, which has attracted much attention in many potential applications such as in communications, laser range finder, laser radar, remote sensing, atmospheric sounding and medical application. Moreover, due to the merits of THz-wave, the generation of coherent THz-wave based on THz-wave parametric oscillator (TPO) is an area of growing interest. High-power LD pumped green laser has become the research focus because its important applications in material processing, laser color display, medical application and laser isolation of uranium isotopes, etc. Intracavity frequency-doubled technique is one more promising approach for high-power green laser.The main contents and key creation points of this dissertation are as follows:1. The threshold pump rate for passively Q-switched quasi-continuous-wave (QCW) diode-pumped laser was derived firstly based on its rate equations. The pump rate and pump power range can be estimated according to the number of output pulses. The effects of the pump rate, pump-pulse duration and output mirror reflectivity on the laser operation characteristics were studied theoretically. The passively Q-switched laser can be optimized through theoretical calculation.2. The dynamics equations that described the intracavity singly resonant and doubly resonant OPOs within actively Q-switched laser and passively Q-switched laser were investigated in theory. And numerical simulations were carried out. The effects of output mirror reflectivity, pump intensity and the initial transmission of saturable absorber on the signal wave operation were studied. The threshold pump intensity for a singly resonant IOPO was derived firstly. The results provide a theoretical basis for the IOPO experimental research.3. Based on the technique of IOPO, eye-safe 1.57μm lasers were investigated experimentally with different Q-switching operation. We have obtained 1.2W of 1.57μm at 3.5kHz from an intracavity KTP-OPO, pumped by a diode-side-pumped acoustic-optic Q-switched Nd:YAG laser. The pulse width was 4.9ns. This was the first time to realize watt-level 1.57μm laser based on diode-side-pumped Nd:YAG lasers with IOPO. Using a QCW diode-pumped electric-optical Q-switched Nd:YAG laser as pumping source, 31.5mJ energy at 1.57μm wavelength was achieved at 10Hz with pulse duration of 3.48ns. Moreover, an efficient, IOPO inside a passively Q-switched quasi-cw diode-pumped Nd:YAG was demonstrated. We achieved up to 2.3mJ energy at 1.57μm wavelength for 40Hz repetition rate. The pulse width was only 2.6ns. To our knowledge, the signal pulse energies in the last two experiments are the highest in the same type of laser. The results are ahead in the world.4. We summarized and analyzed the dispersion and absorption properties of MgO:LiNbO₃ crystal in the infrared, near-infrared and THz wavelength. The wavelength tunablility for THz-wave parametric oscillator was calculated under noncollinear phase matching condition. The theory of dual-wavelength coherent THz-wave generation is firstly deduced according to the principle of THz optical parametric oscillator. Based on a diode-laser-pumped electric-optical Q-switched Nd:YAG laser and employing an intracavity geometry, we have demonstrated the Stokes radiation is continuously tunable over the range 1069.4-1073.4nm and is of narrow spectral bandwidth, while the continuous tuning range of coherent THz radiation is 1.4-2.5THz according to calculation.5. The high-power green laser was studied experimentally and theoretically. The thermal distributions in laser gain medium (the single Nd:YAG crystal and composite ceramic Nd:YAG crystal) and nonlinear crystal were calculated in theory. Using a ray matrix method, the resonator stability conditions are analyzed graphically with the thermal birefringence effect for a plano-concave resonator. By use of CW diode laser stacked arrays, side-pumping Q-switched composite ceramic Nd:YAG rod laser based on a type II KTP crystal intracavity frequency-doubled, average output power of 104W was obtained at a repetition rate of 10.6kHz. The power fluctuation is 0.1% for the average output power of about 100W. To our knowledge, this is the highest green power with composite ceramic Nd:YAG rod. When the double acousto-optic Q-switches and high gray track resistance KTP cystal were employed, the green laser output power of 153W was obtained at 25kHz. The optical-optical conversion efficiency is up to 14.72%. The power fluctuation is 0.6% for the average output power of about 130W. The whole performance keeps ahead in the world.6. The single-frequency green laser was studied experimentally and theoretically. A birefringent filter formed by a Brewster plate (BP) and a birefringent KTP crystal is used to realized single-frequency choose. The calculation based on Jones calculus was proposed to predict the ability of frequency selectivity with different lengths of KTP crystal and Nd:YVO₄ crystal. Moreover, we analyzed the effect of temperature on frequency shift. In our experiment, by using the stationary wave cavity and the structure of single KTP/single BP, 0.37W single-frequency green output was obtained with 8W pump power.