Research On Intracavity THz Parametric Oscillator

THz wave is a kind of electromagnetic wave, whose wavelength ranges between microwave and infrared wave. Because of its position in the spectrum and its own unique properties that make it has a wide range of applications in communication （broadband communication）, electronic warfare, radar, electromagnetic weapons, astronomy, medical imaging （unmarked genetic testing, cellular level imaging）, non-destructive testing, environmental monitoring and safety inspections （biological material inspection） and other areas. Therefore, how to get stable, tunable THz radiation becomes a key content of the study of THz wave. Currently, the methods of generating THz wave are mainly electronics and photonics approach, the latter could obtain high-frequency THz waves, system miniaturization and other advantages compared with former. In photonics approach, the intracavity THz parametric oscillator （TPO） radiation technology which is based on scattering of electromagnetic coupling has high efficiency, low oscillation threshold, small size, easy tuning, room temperature operation and other advantages, which make intracavity TPO technology become an important research content of current THz source technology. This paper is based on the intracavity TPO technology, the innovation and main contents are as follows:1. Theoretically analyzing the dynamic process of intracavity THz parametric oscillator （TPO）, and systematically analyzing the inverse particles, the intensity of pump light, and the intensity of stokes light with time changes in the relationship in the process of TPO. Thus it clearly shows the building process of the pump light and Stokes light in the cavity. In theory, the energy pump threshold of intracavity TPO is derived, and we calculate the energy pump threshold of the intracavity TPO in different conditions.2. Utilizing the method of THz wave output perpendicular to the crystal surface, a set of the intracavity tunable THz parametric oscillator is built. In the experiment we obtain the maximum average power of THz wave is 3.3 W, THz-wave energy conversion efficiency is 2.8×10^-6 with tuning range of 0.9-2.5 THz. the threshold is about 5.4mJ, which basically consistents with the theoretical calculations. Also the fourth order Stokes spectral line is observed.3. In order to compare the results with the intracavity TPO. We utilize the method of outputting perpendicular to the surface of crystal, and we design a compact external cavity THz parametric oscillator, making full use of the characteristics of small size of TPO technology. The maximum average power of THz wave of 10.8 W is obtained in the experiment, corresponding to the THz-wave energy conversion efficiency of 8.43×10^-6. Average power and conversion efficiency of intracavity TPO are smaller than that of external cavity TPO. The reasons are analyzed theoretically.4. As non-collinear phase-matching method is utilized in MgO:LiNbO3 crystal in the THz parametric oscillation, the interaction of three-waves is small. In order to improve the efficiency, an experimental system of intracavity TPO based on quasi-phase matching technique in the MgO:PPLN crystal is designed. We theoretically calculate the required polarization period and the polarization angle in the crystal. Then, we theoretically calculate the tunable ability of THz wave with the method of changing polarization period of the crystal.