Kong Yongfa

Time-Resolved Femtosecond Degenerate Four-Wave Mixing in LiNbO3:Fe,Mg Crystal

Forward degenerate four-wave mixing (DFWM) processes are investigated with a femtosecond pulsed laser in lithium niobate crystal doubly-doped with magnesium and iron (LiNbO3:Fe,Mg). The pulse energy dependence reveals a pure third-order nonlinear response, and the third-order nonlinear susceptibility χ(3) in the material is evaluated to be 4.96×10−13 esu. The time-resolved DFWM process shows a response time of χ(3) shorter than 100 fs, which is due to the nonresonant electronic nonlinearities. Our results indicate that LiNbO3 crystals have potentials for ultrafast real-time optical processing systems, which require a large and fast χ(3) optical nonlinearity.

Photorefraction Resistance of Na2O-Doped Lithium Niobate Single Crystals

Na2O-doped (up to 3 mol% Na in the melt) LiNbO3 crystals have been grown by the Czochraski method. The experimental results show that Na2O dopants can increase the ability of LiNbO3 to resist light-induced optical damage, but the photorefraction of LiNbO3:Na(3 mol%) is larger than that of LiNbO3:Na (1 mol%) and the absorption edge of the former crystal has a longer wavelength compared with that of the latter. These two abnormal phenomena were interpreted as that some ilmenite structure (NaNbO3) regions are formed in doped LiNbO3 crystals with the increasing dopant concentration of Na2O.

Molecular dynamic simulations of surface morphology and pulsed laser deposition growth of lithium niobate thin films on silicon substrate

The molecular dynamic simulation of lithium niobate thin films deposited on silicon substrate is carried out by using the dissipative particle dynamics method. The simulation results show that the Si (111) surface is more suitable for the growth of smooth LiNbO3 thin films compared to the Si(100) surface, and the optimal deposition temperature is around 873 K, which is consistent with the atomic force microscope results. In addition, the calculation molecular number is increased to take the electron spins and other molecular details into account.

The two photorefractive centres in iron doped nearly stoichiometric lithium niobate crystals

This paper investigates the photorefractive properties of iron doped lithium niobate with different [Li]/[Nb] ratios. The experimental results show two photorefractive centres for iron doped near-stoichiometric lithium niobate crystal. Besides Fe2+ and Fe3+ ions, small polarons and bipolarons are considered as another photoactive centre.

Light-Induced Domain Inversion in Mg-Doped near Stoichiometric Lithium Niobate Crystals

We investigate the influence of visible light on domain inversion in Mg-doped near stoichiometric lithium niobate crystals and find that the switching electric field decreases about 70% above a threshold light intensity. This effect helps us optically control domain switching and produce bulk domain structures on the micrometre scale. Finally, we introduce a model of photo-induced carriers to explain the origin of the reduction of switching electric field.

Progress on electro-optic crystals for Q-switches

Electro-optic Q-switched laser systems with high peak power have been widely applied in medical, cosmetology, measurement, processing, military industry, and other fields, while the crystal for electro-optic Q-switch is the core optoelectronic material for outputting high peak power pulse laser. With the technological progress and the development of short pulse, high repeat frequency and high power laser system application, the performance of crystals for electro-optic Q-switch is constantly improved. The paper reviews the research progress on basic characteristics, crystal preparation technology and electro-optic Q-switch application technology of several important electro-optic crystals for Q-switches including lithium niobate (LN) crystal, deuterated potassium dihydrogen phosphate (DKDP) crystal, low temperature phase barium metaborate (BBO) crystal, rubidium oxygen titanium phosphate (RTP) crystal, langasite (LGS) crystal and potassium titanium oxide phosphate (KTP) crystal, and propose that the research on practical electro-optic crystals for Q-switches is urgent to make breakthroughs. For a long time to come, exploring the electro-optic crystal materials, with high electro-optic coefficient, high laser damage threshold, stable performance, high temperature applicability and low cost, will be still an important issue in the field of crystal materials research.

Photo-Induced Carriers in Near-Stoichiometric LiNbO3:Fe Crystal

We detect the photo-induced carriers in near-stoichiometric iron doped LiNbO3 crystal by the holographic technique. The results show that the dominant carriers are electrons in the sample with Li/Nb ratio of 0.9988. By analysis of the OH− absorption spectra of the crystal, we contribute the electron domination in near-stoichiometric Fe-doped LiNbO3 crystal to the existence of NbLi which provides the anti-site defect to Fe2+.

Light-Induced Absorption in Nominally Pure Bismuth Silicon Oxide

Light-induced absorption in the nominally pure bismuth silicon oxide is investigated experimentally and the result shows that it consists of transient and persistent parts. The experimental evidence is analysed based on the model of three groups of trap (donor) centres.