Growth and Holographic Storage Properties of Sc, Fe Co-Doped Lithium Niobate Crystals

The holographic storage properties of Fe （0.03% （mass fraction） Fe2O3）：LiNbO3 doped with Sc at different levels （0, 1%, 2%, 3%） were investigated. The Sc threshold concentration in Fe：LiNbO3 was implied to be about 3% （mole fraction） because O-H vibration absorption peak of Sc （3%）：Fe：LiNbO3 was at 3508 cm^-1, compared with 3484 cm^-1 of crystals with lower Sc doping level. Sc（3%）：Fe：LiNbO3 exhibited higher optical damage resistance ability. The threshold intensity （wavelength 488 nm） of Sc （3%）：Fe：LiNbO3 was 2.2 ×10^2 W ·cm^-2, two orders of masnitude higher than that of Fe：LiNbO3. Holographic storage properties of the crystals were determined in an extraordinary polarized laser of wavelength 632.8 nm by a two-wave coupling method. It was found that in terms of holographic storage properties, the optimal doping concentration of Sc was 2% （mole fraction） among this crystal series.

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 Fe^2＋ and Fe^3＋ ions, small polarons and bipolarons are considered as another photoactive centre.

Formation Enthalpy Calculation of Oxygen Vacancy Defect in Doped Lithium Niobate Crystals

The relationship between temperature and oxygen vacancy concentration is deduced in this paper. Based on the data of thermal weight-loss experiment, the formation enthalpies of congruent and several doped LN crystals have been calculated. It was found that the formation enthalpy of oxygen vacancies can be decreased evidently by doping valence-changeable ions. The experimental results were discussed and a new reduction process of the photorefractive LN crystal at a relatively low temperature was proposed, and the reduced crystals showed a good effect in practical use.

Potassium tantalate niobate crystals:Efficient quadratic electro-optic materials and their laser modulation technology

Electro-optic(EO)crystals are important material for all-solid-state laser technology,which can be used to fabricate various laser modulators,such as EO switches,laser deflectors,and optical waveguide.The improvements in new high-efficiency EO crystal materials have held great significance to the development of laser technology.Potassium tantalate niobate(KTN)is a popular multifunctional crystal because of its remarkable and excellent quadratic EO effect.KTN EO modulation technology offers numerous advantages,such as high efficiency,good stability,a quick response time,and inertia-free characteristics.In this paper,we summarize the research progress of KTN series crystals systemically,including the theoretical exploration on quadratic EO effect,solid-melt crystal growth technique,comprehensive physical characterization,new physical effect and mechanisms exploration,new EO devices development and design.The EO modulation technique based on the Kerr effect of KTN series crystal offers obvious advantages in reducing the drive voltage and device size,which could better meet the developmental needs of future lasers with a wide wavelength,miniaturization,and integration.This may provide theoretical guidance and an experimental basis for the design and development of new EO crystal devices and promote the development of laser technology.

Light-Induced Photorefractive Waveguides in Iron-Doped Lithium Niobate Crystals

Waveguides were fabricated in lithium niobate crystals solely by light irradiation using binary optical masks and SLM-prepared optical masks. Arrayed-waveguides were also obtained by once or twice irradiations of an interferogram of two plane waves.

Continuous-wave mid-infrared intracavity singly resonant optical parametric oscillator based on periodically poled lithium niobate

This paper reports a continuous-wave （CW） mid-infrared intracavity singly resonant optical parametric oscillator based on periodically poled lithium niobate （PPLN） pumped by a diode-end-pumped CW Nd：YVO4 laser. Considering the thermal lens effects, it adopted an optical ballast lens and the near-concentric cavity for better operation. At the PPLN＇s grating period of 28.5 μm and the temperature of 140℃, the maximum idler output power of 155 mW at 3.86 μm has been achieved when the 808 nm pump power is 8.5 W, leading to an optical-to-optical conversion efficiency of 1.82%.

High efficiency continuous-wave tunable signal output of an intracavity singly resonant optical parametric oscillator based on periodically poled lithium niobate

In this paper we report on a continuous-wave （CW） intracavity singly resonant optical parametric oscillator （ICSRO） based on periodically poled LiNbO3 （PPLN） pumped by a diode-end-pumped CW Nd：YVO4 laser. Considering the thermal lens effects and diffraction loss, an optical ballast lens and a near-concentric cavity are adopted for better operation. Through varying the grating period and the temperature, the tunable signal output from 1406 nm to 1513 nm is obtained. At a PPLN grating period of 29 pm and a temperature of 413 K, a maximum signal output power of 820 mW at 1500 nm is achieved when the 808 nm pump power is 10.9 W, leading to an optical-to-optical conversion efficiency of 7.51%.

KLN单晶的SHG特性

Tetragonal tungsten bronze structure potassium lithium niobate (KLN) crystals pr omise as a potentially useful material for nonlinear optical applications,especi ally,for blue laser radiation by second harmonic generation (SHG).We have grown KLN single crystals by TSSG method using different melt compositions and studied the properties of second harmonic generation (SHG).The crystals have the conten ts of Nb 2O 5 in the range of 51 54% and Li 2O in the range of 17.5 20% and a non critical SHG phase matching wavelength being a wide range from 843 and 9 67 nm. The dependence of temperature and SHG phase match wavelength and the temp erature acceptance were measured by a cw Ti∶Al 2O 3 laser(Spectra Physics M odel 3900S).The results show a linear relationship between phase match wavelengt h and temperature and a about 4℃ temperature acceptance.The homogeneity on a KL N crystal sample of 4×5×8mm was characterized where the SHG phase match wavele ngth changed within 887.8 and 887.5nm . With comparing the wavelength accepta nce being 0.5nm,the result suggests that the homogeneity is good. The dependence bet ween crystal composition,crystal lattice constants and SHG properties will be di scussed.

KLN晶体生长与蓝光SHG特性

In this paper,ferroelectric tetragonal tungsten bronze type potassium lithium niobate(KLN)crystal with a size of 20mm×8mm×43mm was grown from a melt with a composition of 32mol% K 2CO 3,24mol% Li 2CO 3 and 44mol% Nb 2O 5 by the top seeded solution growth (TSSG)method.The KLN crystal as grown along [110]axis has a perfect crystal melt interface dominated by {110} and {210} facets.Lattice constants were measured by X ray diffraction (XRD) analysis performed on {001}and {110}natural faces of single crystal samples.The anisotropic thermal expansion behavior of the crystal was also studied along [001] and [110] axes,respectively by using a Shimadzu TMA 50 thermomechnical analyzer.For the purpose of crystal poling,the dependence of crystal capacitance vs.temperature in both heating and cooling cycles was measured and the ferroelectric Curie temperature was determined to be 514℃.The crystal was poled at 506℃ with a dc field of about 250 V/cm along the c axis of the sample,for a time corresponding to about 1.5 h/cm.The blue second harmonic generation (SHG)characteristics of the KLN crystal were investigated by using a 3900s Ti∶sapphire CW tunable laser.Blue laser light at wavelength 432nm was obtained by the non critical phase matching (NCPM)SHG at room temperature.Based on the wavelength and temperature tuning curves for the NCPM SHG,the wavelength acceptance and temperature acceptance of this KLN crystal were measured.The crystal property homogeneity along the <110>growth axis was also studied by measuring the room temperature NCPM wavelength at different growth positions.

Compact 1×3 waveguide beam splitters with variable splitting ratios in LiNbO_(3) crystal fabricated by femtosecond laser direct writing

In this Letter,waveguide beam splitters(1×3)with type I modifications are fabricated in a LiNbO_(3) crystal by femtosecond laser direct writing.The influence of the relative positions of three sub-waveguides on power splitting ratios are investigated in detail and the corresponding output intensities as functions of the relative positions in the numerical simulation are plotted,which are in good accordance with the experimental results.In addition,the waveguide beam splitter with a 1:1:1 splitting ratio is fabricated by changing the relative widths of the three branch-waveguides.Guiding performances at 532 nm are measured and analyzed by a typical end-face coupling system.The simulation and experimental results demonstrate that the beam splitting ratio of the waveguide splitter can be precisely regulated by the positions and widths of the sub-waveguides.

Efficient idler broadening via oppositely dual-chirped difference frequency generation

Dual-chirped difference frequency generation(DFG)is an advantageous technique for generating the broadband midinfrared(IR)idler wave,which is inaccessible by a population-inversion-based laser system.In principle,the generated idler wave may even suffer a spectrum broadening compared with the driving pulsed lasers if the pump and signal waves are oppositely chirped.However,broadband phase-matching is always the determining factor for the resulting efficiency and the bandwidth of the generated idler wave.In this study,specific to an oppositely dual-chirped DFG scheme,we derive the precondition to realize broadband frequency conversion,wherein a negative(1/υp-1/υi)/(1/υs-1/υi),in terms of the correlation coefficient of the group velocity(σ),is necessary.However,most birefringence bulk crystals can only provide the required material dispersions in limited spectral regions.We show that the periodically poled lithium niobate crystal that satisfies an inactive Type-II(eo-o)quasi-phase-matching condition has a stable negativeσand exerts the expected broadband gain characteristic across an ultra-broad idler spectral region(1.7-4.0µm).Finally,we propose and numerically verify a promising DFG configuration to construct a tunable mid-IR spectrum broader based on the broadband phase-matched oppositely dual-chirped DFG scheme.