Femtosecond Third-Order Optical Nonlinearity of Au：Bi203 Nanocomposite Films

Ultrafast third-order optical nonlinearities of the as-deposited and annealed Au：Bi2O3 nanocomposite films deposited by magnetron cosputtering are investigated by using femtosecond time-resolved optical Kerr effect （OKE） and pump probe techniques. The third-order optical nonlinear susceptibility is estimated to be 2.6Ф×10^- 10 esu and 1.8 × 10.9 esu at wavelength of 800nm, for the as-deposited and the annealed film, respectively. The OKE signal of the as-deposited film is nearly temporally symmetrical with a peak centred at zero delay time, which indicates the dominant contribution from intraband transition of conduction electrons. For the annealed film, the existence of a decay process in OKE signal implies the important contribution of hot electrons. These characteristics are in agreement with the hot electron dynamics observed in pump probe measurement.     

An Artificially Garnet Crystal Materials Using In Terahertz Waveguide

A hypothesis is brought forward that the materials with low propagation loss in both optical and microwave band may exhibit good performance in terahertz （THz） band because THz wave band interspaces those two wave bands. For the purpose-of exploring a kind of low-loss material for THz waveguide, Lu2.1Bi0.9Fe5O12（LuBiIG） garnet films are prepared by liquid phase epitaxy （LPE） method on a gadolinium gallium garnet （GGG） substrate from lead-free flux because of the good properties in both optical and microwave bands. In microwave band, the ferromagnetic resonance （FMR） linewidth of the film 2△H = 2.8-5.1Oe; in optical band, the optical absorption coefficient is 600cm^-1 at visible range and about 100-170cm^-1 when the wavelength is longer than 800nm. In THz range, our hypothesis is well confirmed by a THz-TDS measurement which shows that the absorbance of the film for THz wave is 0.05-0.3 cm 1 and the minimum value appears at 2.3 THz. This artificial ferromagnetic material holds a great promise for magnetic field tunable THz devices such as waveguide, modulator or switch.     

Formation Mechanisms of Electrical Conductivity and Optical Properties of ZnO:N Film Produced by Annealing Treatment

The effects of annealing on the chemical states of N dopant, electrical, and optical properties of N-doped ZnO film grown by molecular beam epitaxy (MBE) are investigated. Both the as-grown ZnO:N film and the film annealed in N₂ are of n-type conductivity, whereas the conductivity converts into p-type conductivity for the film annealed in O₂. We suggest that the transformation of conductivity is ascribed to the change in ratio of the N molecular number on O site (N₂)_O to the N atom number on O site (N_O) in ZnO:N films under the various annealed atmosphere. For the ZnO:N film annealed in N₂, the percentage content of (N₂)_O is larger than that of N_O, i.e.the ratio >1, resulting in the n-type conductivity. However, in the case of the ZnO:N film annealed in O₂, the percentage content of (N₂)_O is fewer than that of N_O, i.e., the ratio <1, giving rise to the p-type conductivity. There is an obvious difference between low-temperature (80K) PL spectra of ZnO:N film annealed in N₂ and that of ZnO:N film annealed in O₂. An emission band located at 3.358eV is observed in the spectra of the ZnO:N film after annealed in N₂, this emission band is due to donor-bound exciton (D⁰X). After annealed in O₂, the PL of the donor-bound exciton disappeared, an emission band located at 3.348eV is observed, this emission band is assigned to acceptor-bound exciton (A⁰X).     

Vacuum Ultraviolet Excited Photoluminescence Properties of Novel Na3Y9O3（BO3）8：Tb^3＋ Phosphor

The novel vacuum ultraviolet （VUV） excited Na3 Y9O3 （BO3）8：Tb^3＋ （NYOB：Tb^3＋） green phosphor is prepared. Strong VUV photoluminescence and high quenching concentration of Tb^3＋ （20 wt%） are observed in NYOB： Tb^3＋ and the strong emission are correlated with the unique layer-type structure of NYOB. All the characteristic 4 f - 5d transitions of Tb^3＋ and the host absorption band in VUV region are identified in the excitation spectrum. Based on the results, the energy levels scheme of Tb^3＋ in NYOB：Tb^3＋ is first established. This newly developed NYOB：Tb^3＋ phosphor shows excellent optical properties when compared with the commercial Zn2SiO4：Mn^2＋ and would be a potential VUV-excited green phosphor.     

Magneto-Optical Trapping of Ytterbium Atoms with a 398.9nm Laser

We report the realization of ytterbium magneto-optical trap （MOT） operating on the dipole-allowed ^1S0 - ^1P1 transition at 398.9nm. The MOT is loaded by a slowed atomic beam produced by a Zeeman slower. All seven stable isotopes of Yb atoms could be trapped separately at different laser detuning values. Over 10^7 174 Yb atoms are collected in the MOT, whereas the atom number of fermionic isotope ^171Yb is roughly 2.3 × 10^6 due to a lower abundance. Without the Zeeman slower the trapped atom numbers are one order of magnitude lower. Both the even and odd isotopes are recognized as excellent candidates of optical clock transition, so the cooling and trapping of ytterbium atoms by the blue MOT is an important step for building an optical clock.     

Sensitive birefringence measurement in a high-finesse resonator using diode laser optical self-locking

We demonstrate a new method to measure weak birefringence of dielectric mirrors with excellent spatial resolution and sensitivity (<10^-7 radians). We exploit a well-known optical feedback scheme for line-width narrowing and frequency locking of a diode laser to a high-finesse cavity. Feedback comes from the intracavity field which builds up at resonance, selected by its change in polarization with respect to the incident field. This change, due to the residual birefringence of the cavity mirror coatings, was already exploited for birefringence measurements using an active laser-locking scheme. Here we measure the optical feedback rate as a function of rotation angle of one of the cavity mirrors (around the cavity axis). A stable feedback signal is obtained since the laser, as soon as it locks to a cavity resonance, effectively behaves as a monochromatic source. By fitting the data with a theoretical expression, we determine quantitatively the local birefringence vectors of both mirrors, which are around 10^-6 radians. Our scheme is simple, works with cavities of very high finesse (F∼10⁵), and is promising for measuring birefringence in gases induced by external fields. Received: 18 July 2001 / Final version: 14 March 2002 / Published online: 8 May 2002     

Surface Emitting THz Wave Parametrical Oscillator Using MgO：LiNbO3

Room-temperature operation terahertz （THz） wave source is demonstrated using three MgO：LiNbO3 crystals which have a noncollinear arrangement. The experimental results show that the THz wave can be tunable from 0.8 THz to 3.0 THz, and the peak energy output is 103 pJ/pulse at 1.5 THz. The noncoilinear cavity configuration makes the THz beam have Gaussian-like spatial distribution, small divergence angle, perpendicularly eradiated from the crystal surface. The beam quality factor M2 is measured to be Mx^2 = 1.15, Mx^2 = 1.25 for characterizing the THz wave beam. Experiments also show that the THz beam can be focused by using a polyethylene lens, and the focal spot size is close to the diffraction limit.     

Research on Intracavity Laser Cooling of Solid

A theoretical study of intra-cavity laser cooling by anti-Stokes luminescence in a rare-earth doped glass is performed. Compared with cooling in an external cavity by multipassing the radiation, intra-cavity cooling has the advantage of high pumping power and high-absorbed power. However, one must ensure that the cavity can still form a laser by locating the material in the cavity. A model is developed to evaluate the enhancement factor and the absorbed power. The results show that for a low optical density, especially when the sample length is less than 2ram, the intracavity configuration is a very efficient method for laser cooling. The diode laser, which may become the best candidate for our model, is briefly discussed.     

Electroluminescence from Multilayered Diamond/CeF3/SiO2 Films

We report a thin film electroluminescent device with a three-layer structure （diamond/CeF3/SiO2 films）, which has a luminance of 1.5 cd/m^2 at dc voltage 215 V. The electroluminescence spectrum at room temperature shows that the main peaks locate at 527 and 593nm, which are attributed to isolated emission centers of Ce^3＋ ions.     

吡咯俘精酸酐的光致各向异性研究

将有机光致变色化合物—吡咯取代俘精酸酐掺杂于PMMA中形成薄膜.在紫外光照射下,薄膜由无色态转换为呈色态.用650 nm线偏振激光照射薄膜,在由呈色态转变为无色态时产生光致各向异性.对633 nm的探测光具有正单轴晶体特性,光轴方向平行于激发光振动方向,光致二向色性率(D_⊥-D_∥)可达0.2,光致双折射率(n_∥-n_⊥)可达2×10^-3.实验还测量了光致各向异性与曝光量的特性曲线,发现最佳曝光量为13～20 J/cm²;理论分析了其原因.这些结果为俘精酸酐材料在光信息处理方面的应用提供了实验数据.     

Multilayer Au/TiO2Composite Films with Ultrafast Third-Order Nonlinear Optical Properties

We report on the ultrafast third-order optical nonlinearity in multilayer Au/TiO2 composite films fabricated on quartz substrates by pulsed laser deposition technique. The linear optical properties of the films are determined and optical absorption peaks due to surface plasmon resonance of Au particles are observed at about 590hm. The third-order optical nonlinearities of the films are investigated by z-scan method using a femtosecond laser （50 fs） at the wavelength of 800 nm. The sample showed fast nonlinear optical responses with nonlinear absorption coefficient and nonlinear refractive index being -3.66 × 10^-10 m/W and -2.95 × 10^-17 m^2/W, respectively. The results also show that the nonlinear optical effects increase with the increasing Au concentration in the composite films.     

Artificial Modulation of Ferroelectric Thin Films into Antiferroelectric through H+ Implantation for High-Density Charge Storage

Hydrogen ions are implanted into Pb（Zro.3Tio.7）03 1014 ions/cm^2. Pseudo-antiferroelectric behaviour in thin films at the energy of 40keV with a flux of 5 x the implanted thin films is observed, as confirmed by the measurements of polarization versus electric hysteresis loops and capacitance versus voltage curves. X-ray diffrac- tion patterns show the film structures before and after H＋ implantation both to be perovskite of a tetragonal symmetry. These findings indicate that hydrogen ions exist as stable dopants within the films. It is believed that the dopants change domain-switching behaviour via the boundary charge compensation. Meanwhile, time dependence of leakage current density after time longer than lOs indicates the enhancement of the leakage cur- rent nearly in one order for the implanted film, but the current at time shorter than i s is mostly the same as that of the original film without the ionic implantation. The artificial tailoring of the antiferroelectric behaviour through H＋ implantation in ferroelectric thin films is finally proven to be achievable for the device application of high-density charge storage.     

Evolution of Structural Defects in SiOx Films Fabricated by Electron Cyclotron Resonance Plasma Chemical Vapour Deposition upon Annealing Treatment

We study the structural defects in the SiO, film prepared by electron cyclotron resonance plasma chemical vapour deposition and annealing recovery evolution. The photoluminescence property is observed in the as-deposited and annealed samples. [-SiO3]^2- defects are the luminescence centres of the ultraviolet photoluminescence （PL） from the Fourier transform infrared spectroscopy and PL measurements. [-SiO3]^2- is observed by positron annihilation spectroscopy, and this defect can make the S parameters increase. After 1000℃ annealing, [-SiO3]^2- defects still exist in the films.     

Fine-Structure Splittings of Nitrogen Isoelectronic Sequence： Competitions among Spin-Orbit Interactions, Breit Interactions and Electron Correlations

Using the multi-configuration Dirac-Fock self-consistent field method and the relativistic configuration interaction method with quantum-electrodynamics corrections performed by the GRASP code, we calculate the fine-structure energy levels of the ground-state configuration （1s^22s^22p^3） of the nitrogen isoelectronic sequence, according to the L-S coupling scheme with atomic number Z up to 22. Based on the calculated results, we elucidate the mechanism of the orderings of fine-structure energy levels of 2^ D3/2,5/2 and 2^P1/2,3/2 respectively, i.e. for 2^D3/2,5/2 orderings, the competition between the spin-orbit interactions and the Breit interactions; for 2^P1/2,3/2 orderings, the electron correlations, especially the electron correlations owing to the 2p^5 configuration interactions.     

Spectral Hole-Burning of Eu^3＋：Y2SiO5 Crystal at 16 K

By using an Ar^＋ ion laser, a tunable Rh 6G dye laser （linewidth 0.5cm^-1） pumped by the second harmonic of a YAG：Nd laser and a Coherent 899-21 dye laser as light sources and using a monochromator, a phase-locking amplifier and a computer as the data detecting system, we detect the optical properties of Eu^3＋-doped Y2SiO5 crystal. Persistent ,spectral hole burning （PSHB） are observed in the Eu^3＋ ions spectral lines （^5 Do-T Fo transition） in the crystal at the temperature of 16K. For 15mW dye laser burning the crystal for 0.1 s spectral holes with hole width about 80 MHz both at 579.62nm and at 579.82nm are detected and the holes can remain for a long time, more than 10h.     

Efficiency Enhancement of Dye-Sensitized Solar Cells： Using Salt CuI as an Additive in an Ionic Liquid

Energy conversion efficiency of the dye-sensitized solar cell is improved from 3.5% to 4.5% by adding a small amount of CuI into an ionic liquid electrolyte. It is found that other copper-I salts, for example, CuBr, have the same effect for the dye-sensitized solar cell. Experimental results show that no Cu^2＋ ions exist in this electrolyte. It is suggested that this improvement is caused by the adsorption of Cu^＋ onto the TiO2 porous film.     

Luminescent Characteristics of LiSrBO3：Eu3＋ Phosphor for White Light Emitting Diode

LiSrBO3 ：Eu3＋ phosphor is synthesized by a high solid-state reaction method, and its luminescent characteristics are investigated. The emission and excitation spectra of LiSrBO3：Eu3＋ phosphors exhibit that the phosphors can be effectively excited by near ultraviolet （401 nm） and blue （471 nm） light, and emit 615nm red light. The effect of Eua＋ concentration on the emission spectrum of LiSrBO3：Eu3＋ phosphor is studied; the results show that the emission intensity increases with increasing Eu3＋ concentration, and then decreases because of concentration quenching. It reaches the maximum at 3mol%, and the concentration self-quenching mechanism is the dipoledipole interaction according to the Dexter theory. Under the conditions of charge compensation Li＋, Na＋ or K＋ incorporated in LiSrBO3, the luminescent intensities of LiSrBO3 ：Eua＋ phosphor are enhanced.     

Effects of Helium and Oxygen Common Implantation in Silicon Wafer

Defect engineering for SiO2 precipitation is investigated using He-ion implantation as the first stage of separation by implanted oxygen （SIMOX）. Cavities axe created in Si by implantation with helium ions. After thermal annealing at different temperatures, the sample is implanted with 120 keV 8.0 ×1016 cm 2 0 ions. The Q ion energy is chosen such that the peak of the concentration distribution is centred at the cavity band. For comparison, another sample is implanted with O ions alone. Cross-sectionM transmission electron microscopy （XTEM）, Fourier transform infrared absorbance spectrometry （FTIR） and atomic force microscopy （AFM） measurements are used to investigate the samples. The results show that a narrow nano-cavity layer is found to be excellent nucleation sites that effectively assisted SiO2 formation and released crystal lattice strain associated with silicon oxidation.     

MICROSCOPIC OPTICAL POTENTIAL CALCULATION BY THE MODIFIED SKYRME FORCES WITH THE t3ρα TERM

The real part and the imaginary part of the optical potential and their volume integrals per nucleon for ⁴⁰Ca and ²⁰⁸Pb are calculated on the basis of the modified Skyrme-forces with the t₃ρ^α term (α<1) which was developed recently. The calculated results and their comparison with the phenomenological optical potential and empirical values show that the nuclear force parameters of SKa and SKb are the best, SGI is the next and the others are rather bad.     

Influence of Vacuum Organic Contaminations on Laser-Induced Damage of 1064 nm Anti-Reflective Coatings

We investigate the influence of vacuum organic contaminations on laser-induced damage threshold （LIDT） of optical coatings. Anti-reflective （AIR） coatings at 1064 nm made by Ta2 O5/SiO2 are deposited by the ion beam sputtering method. The LIDTs of AR coatings are measured in vacuum and in atmosphere, respectively. It is exhibited that contaminations in vacuum are easily to be absorbed onto optical surface because of lower pressure, and they become origins of damage, resulting in the decrease of LIDT from 24.5J/cm^2 in air to 15.TJ/cm^2 in vacuum. The LIDT of coatings in vacuum has is slightly changed compared with the value in atmosphere after the organic contaminations are wiped off. These results indicate that organic contaminations are the main reason of the LIDT decrease in vacuum. Additionally, damage morphologies have distinct changes from vacuum to atmosphere because of the differences between the residual stress and thermal decomposability of filmy materials.