Research Of Synthesis And Second Harmonic Generation Of BaMgF₄

With the fast development of laser lithography,laser micro-machining,laser spectroscopy,laser photochemical synthesis and photonic devices manufacturing,there is a large demand on deep-ultra-violet?DUV?coherent light source below 200nm.In particular,solid state laser with good stability,easy to carry,the beam quality and high characteristic,has become an important research direction in the development of deep ultraviolet laser.BaMgF₄ crystal has a high transparency at ultraviolet wavelengths,and its UV cut-off wavelength is 125 nm,so it is the ideal crystal materials of deep UV solid-state laser.In previous study,some researches have shown that nonlinear random materials can also be used for frequency conversion.Therefore,the nonlinear optical properties of BaMgF₄ crystal and microcrystal are investigated in this thesis.Firstly,we have studied the growth and basic properties of BaMgF₄ crystal.In the thesis,we compared three crystal techniques,including Czochralski method,Bridgman method and temperature gradient technique.After adjust suitable parameters,like temperature and time,dislocations and cracks of crystal are effectively decreased.Then,the BaMgF₄ single crystal with diameter of 75 mm and length of 50 mm was successfully grown.The BaMgF₄ crystal sample has been characterized by density measurement,UV transmission spectroscopy,X-ray energy spectrum,differential thermal analysis,Raman spectroscopy and so on.Secondly,we have investigated the second harmonic generation of BaMgF₄ microcrystal.The BaMgF₄ microcrystal was compounded by hydrothermal method.Then,the morphology of the BaMgF₄ microcrystal was characterized by SEM.The X-ray diffraction spectrum of BaMgF₄ microcrystal was measured and it fits well with the standard data.BaMgF₄microcrystal powders were deposited on an ITO glass by chemical electrophoresis.The 532nm second harmonic light was observed when the film was radiated by 1064 nm laser.Using the feedback wave-front shaping method based on the genetic algorithm,the SH signal was focused to a bright point.The enhancement factor at the focused location was approximately30 after 300 generations.Moreover,we studied the phenomenon that the SH intensity was enhanced by nearly 100 times when the FW was illuminated onto the scratch of the film.Additionally,by using the feedback wavefront shaping method,the conversion efficiency of second harmonic generation in weakly scattering BaMgF₄ crystal was recovered.At last,this thesis put forward the BaMgF₄ microcrystal powders capillary,and this new structure may enhance the intensity of second harmonic generation.