Characterization Of Nonlinear Optical Properties Of Deep-ultraviolet Transparent BaMgF₄Crystal

Since the90s of last century, with the fast development of laser lithography,laser micro-machining, laser spectroscopy and laser photochemical synthesis,there is a large demand on deep-ultra-violet （DUV） coherent light source below200nm. In particular, the all-solid-state laser （ASSL） which works at thesewavelengths attracts much attention from the scientists in the whole worldbecause of its advantages of compact size, narrow bandwidth, high-quality beamand so on. As the key technique, the DUV nonlinear crystals which can beutilized to generate DUV harmonics are the focus of attention. At present,BaMgF₄crystal is considered as one of the most potential candidate because ofits very short cut-off wavelength （125nm） and the ability of frequencyconversion in the whole transparent area by the quasi-phase-matching （QPM）technique.In this thesis, the frequency-doubling coefficients of BaMgF₄crystal aremeasured by Maker fringe method. Using LiNbO3crystal as stand sample, d31,d32and d33of BaMgF₄crystal are determined. The results are0.15pm/V,0.32pm/V and0.12pm/V respectively. Moreover, the experiments of frequencydoubling and sum-frequency generation in BaMgF₄crystal are performed usingTi: Sapphire laser and Nb: YAG laser as the pumps. The harmonic with thewavelength of355nm is obtained which is the reported harmonic with theshortest wavelength in BaMgF₄crystal so far. The third-order nonlinear optical coefficients of BaMgF4crystal are measured by Z-scan method. Using Ti:Sapphire femtosecond laser as the light source, the three third-order nonlinear refractive indices along three crystallographic axes are determined for the first time. The results are n2.a=2.90×10-19m2/W, n3.b=6.38×10-19m2/W and n2.c=2.35×10-18m2/W respectivly. The large measured values show the potential applications of BaMgF4crystal in DUV nonlinear process and all-optical switch. In addition, by focusing femtosecond laser into BaMgF4crystal, the supercontinuum phenomenon resulting from self-phase modulation effect is investigated and correlated to the third-order nonlinear coefficients of BaMgF4crystal.The QPM parameters are calculated and the poling of BaMgF4crystal is performed to observe the reversed ferroelectric domains. By programming, the QPM grating period, period bandwidth, wavelength bandwidth and angular bandwidth are calculated for preparation of QPM experiment. Using electrical-poling process in room temperature, the reversed ferroelectric domains of BaMgF4crystal are observed in the microscopy.At last this thesis generalizes the QPM theory. The three-dimensional （3D） QPM is put forward. The three typical structures of3D nonlinear photonic crystals are designed and the novel nonlinear processes which may generated in these structures are envisaged.