Study Of The Growth Of Near Stoichiometric Lithium Niobate Crystaland Quasi-phase Matching Component

The quasi-phase-matched (QPM) technology is a phase-matched technology which can get high efficiency of non linear frequency change. In recent years, with the invention, maturation and mass application of the new nonlinear crystals, especially the invention of the periodically poled MgO-doped lithium niobate (MgO:PPLN) crystal, lots of important breakthroughs have been made in the field of Optical parametric oscillator (OPO) which based on the quasi-phase-matched technology. The OPO has been used in many fields, such as CARS, laser spectroscopy, environmental monitoring, remote sensing, material handling, laser ranging, infrared interference and countermeasure.Near-stoichiometric MgO-doped lithium niobate crystal has been grown by czochralski method. The author has done some theoretical and experimental research work on quasi-phase-matched continuous-tunable mid-infrared OPO which is based on MgO:PPSLN crystal. The main research works are summarized as follows:(1) The developing history of nonlinear transform technology based on quasi-phase-matched was introduced. The worldwide research status at present and the developing trend in the future of the continuous-tunable mid-infrared OPO have been studied and investigated, Therefore, the important points and the direction of our own research work are clear. The interrelated basic theories of the continuous-tunable mid-infrared OPO have been analyzed and discussed. Such as the three wave interaction in the OPO, QPM theory, and the basic theory of the OPO.(2) The MgO doped near stoichiometric LiNbO3 crystals were grown by the czochralski method, The IR absorption spectra of the single crystals, the absorption edge in the UV-Vis absorption spectra, curie temperature, coercivity were tested. The Li's content of SLN crystal were calculated through the Curie temperature measurements, and [Li] / [Nb] ratio in the the crystal were estimated, it was that the components in crystal was better consistency. According to Li vacancy model, the MgO doped Lithium Niobate crystal was characterized; the footprint of the ions was discussed, which indicated the quantity of doped MgO reached the threshold of resistance to the concentration of light damage. (3) The lithium niobate wafers.were polarized using the method of external electric field at room temperature. The domain changing of crystal were studied in the polarization experiment, we designed the periodical poled cycle and voltage. Polarized electric field method with a short pulse which suppress the thermal effect of the polarization current to eliminate the effects of uniformity were used. to obtaine Z-cut periodical poled wafer with 1.0mm thickness and 30μm period, The duty cycle of the inverted domain is closed to 50%.(5) The PPLN-OPO was studied using Z-cut periodical poled wafer of high MgO doped LiNbO3, the pump source is an acousto-optically Q-switched Nd:YAG laser of 1.064μm wavelength. The threshold of PPLN-OPO was 45mW(10kHz repetition frequency), Under the condition of 7.5W of input pump power and at 80℃,0.72W of output idle power was obtained ,and the conversion efficiency is 9.6%, and obtained 3.02μm～3.442μm of idle wave output by tuning crystal temperature(25～180℃).