Transmitting characteristics of polarization information under seawater.

We have presented the performance evaluation for light communication under water based on polarization information. In particular, we focused on the transmitting characteristics of the polarized lights under different conditions of water types and link distances. The trajectories of transmitted photons propagating in a water channel can be simulated based on the Monte Carlo (MC) algorithm. The simulated results demonstrate that the intensity of the polarized light after being transmitted underwater decreases sharply as the transmission distance increases, but the degree of polarization (DoP) of the transmitted lights remains above 0.75. The polarization retrieve (PR) method is used for reducing the scattering impact on the DoP of the light, and the maximal enhancement of the linear degree of polarization (LDoP) can be obtained as about 16%. Meanwhile, the modified PR method with a different retrieval Mueller matrix (RMM) derived from different distances (l) of the transmission channel has also been investigated, which shows that the retrieval accuracy will be enhanced with the increase of transmission distance of the RMM.

Plasmonics metalens independent from the incident polarizations.

An ultra-thin, planar, broadband metalens composed of L-shaped gap antennas on a thin gold film has been designed, which is suitable for both circular and X/Y linear polarizations focusing simultaneously. The phase discontinuity of the cross-polarized transmisson light can be manipulated by the length and width of the L-shaped gap antenna accurately. The designed planar metalens posses a strong focusing ability over a large wavelength range, and the size of the focus spot is in sub-wavelength scale. The focal lengths change from 13 to 7 um with incident wavelength from 750 to 1300 nm, and the cause of dispersion is explained and analyzed in detail. The designed metalens can work very well at a wide incident angles of 0~45°. Most importantly, its unique focusing ability that is independent of the incident polarizations will greatly promotes the practical applications and developments of the metasurfaces.

Ice phase as an important factor on the seasonal variation of polycyclic aromatic hydrocarbons in the Tumen River, Northeastern of China.

BACKGROUND, AIM AND SCOPE: The climatic characteristic is a major parameter affecting on the distribution variation of organic pollutants such as polycyclic aromatic hydrocarbons (PAHs). The Tumen River is located in Northeastern of China. The winter era lasts for more than 5 months in a year, and the river water was frozen and covered by ice phase. Coal combustion is an essential heating source in the Tumen River Basin. The objective of this research is to study ice phase effect on the seasonal variation of PAHs in the Tumen River environment. MATERIALS AND METHODS: Samples were collected from 13 sites along the River in March, July, October, and December of 2008. In addition, the ice sample, under ice water and air particulate were also collected in winter. The samples were analyzed for 16 PAHs (naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, beazo[a]anthene, chrysene, beazo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, indeno(1,2,3-cd)pyrene, dibenz(a,h)anthracene, and benzo(ghi)perylene). The compounds were extracted from the water samples and solid samples using LLE and Soxhlet extraction technique, respectively, and it is determined by gas chromatography-mass spectrometry. RESULTS AND DISCUSSION: Among 16 PAHs, fluorene, phenanthrene, and pyrene were found to be present in high concentrations and at high detection frequencies. The total concentration of PAHs in the water, particulate, sediment and ice phase ranged from 35.1-1.05 x 10(3) ng L(-1), 25.4-817 ng L(-1), 117-562 ng g(-1)and 62.8-136 ng g(-1), respectively. The levels of PAHs were generally higher in spring than other seasons. The ice phase in winter acts like a major reservoir of the pollutants and it is major contributor on the seasonal variation of PAHs in Tumen River. The PAHs found in water, particulate, and sediment in the Tumen River were possibly derived from similar pollution sources a proposition based on the compositions and isomer ratios of PAHs. CONCLUSIONS: The distribution of PAHs was showed clear seasonal variation in the Tumen River environment, the ice phase and air pollution look like an important factor affecting on the seasonal variation. RECOMMENDATIONS AND PERSPECTIVES: The ice phase as an important factor affecting on the seasonal variation of PAHs in Tumen River environment. Further studies regarding the effects of air pollution on the river and the mechanisms of migration and transformation of them in the environment are currently being conducted in our laboratory.

[Laser-induced isotopic discrimination effect in laser resonance ionization process of lead atom].

Isotope ratio measurements have been increasingly used in geochemistry, geochronology, cosmos chemistry and environmental science. Precise and accurate isotope ratio measurements are an important task in many applications such as the determination of isotope variations in geological and cosmic samples. Due to its high sensitivity, high ionization efficiency and high element selectivity, laser resonance ionization spectroscopy has nowadays become one of the key techniques, including isotope ratio measurements and trace amount analyses. Because of the isotope shifts and hyperfine structure, there is laser-induced isotopic discrimination effect in the process of laser resonance ionization. The different isotope ionization efficiency can affect precise and accurate measurement of isotope ratios. In the present paper, the dependences of the laser-induced isotopic discrimination effect on some of the laser parameters were studied by theoretical methods. Based on the numerical simulation of the population rate equations, laser-induced isotopic discrimination effect of lead isotopes was studied, by calculating laser resonance ionization transition "6s2 6p23 P0-6s2 6p7 s3 P1(0) --> ionization". The population rate equations was approximated considering some factors which affect the probability of laser resonance transition such as spectral lines width of laser and atom, isotope shifts and hyperfine structure. According to the approximated population rate equations, "1+1" laser resonant ionization process was employed to calculate the ionization probability of lead isotopes by means of computer simulation. The dependences of laser-induced isotopic discrimination effect on the laser parameters, such as laser central wavelength, bandwidth and intensity were investigated. The calculated results show that the laser-induced isotopic discrimination effect of lead isotopes could be almost eliminated by operating at optimized wavelength and could be lessened by using wide band laser. Saturated ionization of lead isotopes was achieved by using a high intensity laser, consequently the laser-induced isotopic discrimination effect of lead isotopes could be eliminated.

Electro-optic integration of embedded electrodes and waveguides in LiNbO3 using a femtosecond laser.

We describe the fabrication of a Mach-Zehnder optical modulator in LiNbO(3) by femtosecond laser micromachining, which is composed of optical waveguides inscripted by a femtosecond laser and embedded microelectrodes subsequently fabricated using femtosecond laser ablation and selective electroless plating. A half-wave voltage close to 19 V is achieved at a wavelength of 632.8 nm with an interaction length of 2.6 mm. This simple and cost-effective technique opens up new opportunities for fabricating integrated electro-optic devices.

Fabrication of two-dimensional periodic nanostructures by two-beam interference of femtosecond pulses.

Two-dimensional periodic nanostructures on ZnO crystal surface were fabricated by two-beam interference of 790 nm femtosecond laser. The long period is, as usually reported, determined by the interference pattern of two laser beams. Surprisingly, there is another short periodic nanostructures with periods of 220-270 nm embedding in the long periodic structures. We studied the periods, orientation, and the evolution of the short periodic nanostructures, and found them analogous to the self-organized nanostructures induced by single fs laser beam.

Multiphoton-excited upconversion luminescence of Nd:YVO(4).

Fluorescence spectra of Nd:YVO(4) under excitation of a continuous wave (CW) diode laser and a femtosecond laser at 800nm were investigated. It was found that Nd:YVO(4) shows different upconversion and downconversion luminescencent behaviors when excited by the diode laser and the femtosecond laser. The dependence of the upconversion luminescence intensity on the pump power of the femtosecond laser was discussed. The populations of the upper energy levels for upconversion and downconversion luminescence were calculated based on the Bloch equations. The calculations agree well with the experimental results.

Microstructures induced in the bulk of SrTiO3 crystal by a femtosecond laser.

Microstructures with the total length of hundreds of mu m were induced by fixing the focal point of the femtosecond laser at a certain depth in the bulk of SrTiO(3) crystal. By different combination of the focusing conditions with the laser parameters, different morphologies have been observed, such as void array, necklace-shaped structures, continuous/ segmental filaments and etc. The possible mechanism of the formation of those diversiform structures is discussed.

Selective metallization on insulator surfaces with femtosecond laser pulses.

We report selective metallization on surfaces of insulators (glass slides and lithium niobate crystal) based on femtosecond laser modification combined with electroless plating. The process is mainly composed of four steps: (1) formation of silver nitrate thin films on the surfaces of glass or crystal substrates; (2) generation of silver particles in the irradiated area by femtosecond laser direct writing; (3) removal of unirradiated silver nitrate films; and (4) selective electroless plating in the modified area. We discuss the mechanism of selective metallization on the insulators. Moreover, we investigate the electrical and adhesive properties of the copper microstructures patterned on the insulator surfaces, showing great potential of integrating electrical functions into lab-on-a-chip devices.

Orientation-controllable self-organized microgratings induced in the bulk SrTiO(3) crystal by a single femtosecond laser beam.

Self-organized microgratings were induced in the bulk SrTiO(3) crystal by readily scanning the laser focus in the direction perpendicular to the laser propagation axis. The groove orientations of those gratings could be controlled by changing the irradiation pulse number per unit scanning length, which could be implemented either through adjusting the scanning velocity at a fixed pulse repetition rate or through varying the pulse repetition rate at a fixed scanning velocity. This high-speed method for fabrication of microgratings will have many potential applications in the integration of micro-optical elements. The possible formation mechanism of the self-organized microgratings is also discussed.

[2+1, 1+1 and 1+1+1 multiphoton resonant ionization of manganese atom].

Resonance ionization spectroscopy (RIS) is an important technique for trace analyses. In the present paper, based on the population rate equations, "2+1", "1+1" and "1+1+1" multiphoton resonant ionization processes of Mn atom are studied by computer simulation. The phenomena and the threshold condition of saturated excitation and ionization processes are discussed. The threshold laser intensities for saturated ionization of Mn atom with different RIS schemes are calculated. With the typical Q-switched laser duration of 10 ns, the obtained saturation threshold laser intensity for the ionization steps in all the resonant ionization processes of Mn is about 10(8) W x cm(-2) with the exception of the "1+ 1" resonant ionization of Mn which is 3 orders of magnitude lower. The obtained threshold laser intensity for the saturated excitation steps is about 10(2)-10(3) W x cm(-2) in "1+1" and "1+1+1" ionization processes. It is also shown that the threshold laser intensity required for saturated excitation and ionization processes turns smaller with the laser duration prolonged.

[Fluorescence analysis of crude oil samples with different spectral approaches].

Fluorescence techniques based on emission spectrum, synchronous fluorescence spectrum (SFS), or three-dimensional (3D) fluorescence spectrum, have been widely used in medical, biological and chemical analyses. In the present paper, 25 crude oil samples from 15 different borefields in the concentration range from 10(-4) g x L(-1) to 10 g x L(-1) have been investigated with different spectral approaches. It was shown that, compared with conventional emission spectrum based technique used in oil logging, the 3D fluorescence technique can provide much more information in the analysis of crude oil samples but at the price of time consuming. While the SFS spectrum of a crude oil sample, taken under the emission and excitation wavelength synchronous scan with deltalambda=40 nm, can represent the main characteristic of the 3D spectrum provided, with even better spectral qualities. All the results suggest that SFS technique is a more suitable approach in crude oil sample analysis than the other two, and has a great potential to be developed as a new quantitative analysis method in petroleum logging.