| This thesis consists of two parts of research contents. One part is the experimental research on the surface-emitted terahertz-wave parametric oscillator (TPO). The other one is the measurement of the stimulated emission cross sections of five Nd-doped crystals in4F3/2â†'4I11/2transition (at1.06μm wavelength).Terahertz (THz) wave means the electromagnetic wave whose frequency is in the range from0.1THz to10THz. Its position in the spectrum lies between the microwave and the infrared. With its special characteristics, THz wave have wide applications in material testing, medical imaging, safety inspection, terahertz spectrum signature analysis, ultra-high speed space communication and ultra-high resolution weapon guidance. Many countries regard THz technology as strategic objectives, and call it one of the top ten technologies to change the future of the world. There are two kinds of methods for terahertz-wave generation:electronic methods and optical methods. Among the optical methods, terahertz-wave parametric oscillators (TPOs) based on stimulated polariton scattering are outstanding with their compact structure, narrow linewidth, tunability and room temperature operation.Stimulated emission cross section of a laser gain medium is a crucial parameter which determines the maximum gain, saturation power, and optimum output mirror reflectivity, etc. It is very important for laser designing and optimizing. There are many experimental methods to measure the stimulated emission cross sections of gain media. The method based on spectroscopic technique is widely used, and it can be used for all materials no matter whether their laser operations have been realized. But it is difficult to obtain the fluorescent quantum efficiency and the fluorescent branching ratios of the F3/2level. For materials that have shown laser actions already, the method based on laser characteristics is convenient and effective.The main contents and innovations of this thesis are as follows:1. Experimental research on an extracavity pumped surface-emitted terahertz-wave parametric oscillator (TPO) is conducted. The nonlinear crystal is a bulk specially designed MgO:LiNbO3. The pump laser is a1064nm electro-optical Q-switched Nd:YAG laser with a pulse repetition period of800ms. The nonlinear crystal is put on a rotating platform, which can tune the phase matching angle between the pump light and the Stokes light. We study the dependences of the terahertz wave pulse energy on the phase matching angle and the pump light intensity. The obtained terahertz wave can be tuned from1THz to2.3THz. The maximum single pulse amplitude detected by Golay Cell is2.49V, and the output energy is1.06μJ. It is the highest energy from the terahertz-wave parametric oscillators.2. An improved method for measuring the stimulated emission cross section is put forward. Unlike the previous measurement method, in which the input-output relation of the laser is fitted linearly, we get a revised formula for calculating the stimulated emission cross section. By taking the ratio of the pump beam radius to and laser beam radius into consideration, and introducing a κ factor, the revised formula is more accurate. With this formula, the stimulated emission cross section can be calculated in better accuracy by measuring the input-output relation of the laser.3. The stimulated emission cross sections of five crystals are measured. The measures to minimize the errors are analyzed. The thermal lens effects are taken into consideration. The setup is designed and five crystals (Nd:YAG, Nd:YVO4, Nd:LuVO4, LGT and NGAB) are put into the setup respectively. Then the input-output relations of five lasers are measured. The stimulated emission cross sections of five crystals are obtained as2.58X10-19cm2,10.76X10-19cm2,1.15×10-19cm2,12.3X10-19cm2,3.52X10-19cm2. Because an identical setup is used, the error will be almost the same. Even if the absolute values of the five stimulated emission cross sections have some errors, their relative values should have more accuracy. |
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