[Joint Analyses of Na2SO4 Solution by Laser Induced Breakdown Spectroscopy and Raman Spectroscopy].

Spectroscopic sensor is becoming an important issue for the deep-sea exploration due to the advantages of multi-specie, multi-phases and stand-off detection. Different approach have been developing in recent years based on LIBS (Laser Induced Breakdown Spectroscopy) and Raman spectroscopy since Raman-LIBS are complementary techniques with the similar components and the capability of molecular and elementary analysis. In this work, we built a LIBS-Raman system and detected Na2SO4 in aqueous solution to evaluate the potential ocean application. With the same laser, spectrometer and detector, a hybrid of Raman and LIBS system was developed to realize the detection of anions and cations in the seawater. The optics was composed by two parts. Raman channel and LIBS channel, and the signal was collected by a Y type optical fiber bundle. The signal from two channels was separated by imaging on different arrays of the CCD detector. The Raman spectra of SO4(2-) and LIBS spectra of Na was successfully detected simultaneously when the pulse energy was above 3.6 mJ. However, due to the strong bremsstrahlung radiation of LIBS, the signal to noise ratio of Raman was significantly decreased as the laser energy increasing. The results manifested the great potential of Raman-LIBS combination for the underwater detection.

[Study on the Spatial Distribution of Laser Induced Plasma Emission Underwater with Different Laser Energies].

Laser-induced breakdown spectroscopy (LIBS), as a promising in-situ underwater detection technology, has received extensive attention in the field of ocean exploration. Improving the remote sensing ability of LIBS is crucial in bringing this technology into practical applications, hence higher laser energies, i.e. over threshold, are required. To characterize the plasma induced with super threshold energies and have a better understanding of resulted moving breakdown process, some extensive investigations into KCl water solution have been carried out with spectra-image jointed analysis. The spatial span and the brightest spot position of plasma radiation, with different laser energies from 1 to 20 mJ, were determined from the recorded plasma images. It was found that the plasma stretched from 0.49 to1.83 mm, as the laser pulse energy increased from 1 to 20 mJ, with a center position shift of 0.79 mm towards the incident laser beam. The obvious power dependence has also been observed from the obtained spatial resolved atomic spectra. Although the axial distributions at different energies were similar, both the position and the intensity of potassium atomic emission maximum varied. The optimal laser energy was determined to be 5 mJ with the emission intensity maximum higher than that at any other investigated energies. The obtained results suggested that the power dependence of atomic emission should be taken into account on increasing laser energy to meet the needs of stand-off LIBS applications. The FWHM and signal to background ratio of K Ⅰ 769.90 nm under different laser energies have also been investigated.

[Discrimination of Crude Oil Samples Using Laser-Induced Time-Resolved Fluorescence Spectroscopy].

The Laser-induced fluorescence spectra combined with pattern recognition method has been widely applied in discrimination of different spilled oil, such as diesel, gasoline, and crude oil. However, traditional three-dimension fluorescence analysis method, which is not adapted to requirement of field detection, is limited to laboratory investigatio ns. The development of oil identification method for field detection is significant to quick response and operation of oil spill. In this paper, a new method based on laser-induced time-resolved fluorescence combined with support vector machine (SVM) model was introduced to discriminate crude oil samples. In this method, time-resolved spectra data was descended into two dimensions with selecting appropriate range in time and wavelength domains respectively to form a SVM data base. It is found that the classification accurate rate increased with an appropriate selection. With a selected range from 54 to 74 ns in time domain, the classification accurate rate has been increased from 83.3% (without selection) to 88.1%. With a selected wavelength range of 387.00~608.87 nm, the classification accurate rate of suspect oil was improved from 84% (without selection) to 100%. Since the detection delay of fluorescence lidar fluctuates due to wave and platform swing, the identification method with optimizing in both time and wavelength domains could offer a better flexibility for field applications. It is hoped that the developed method could provide some useful reference with data reduction for classification of suspect crude oil in the future development.

[Automatic Recognition of Overlapped Spectral Peaks by Combined Symmetric Zero-Area Conversion and L-M Fitting].

The peaks' overlapping often exists in Raman spectroscopy analysis, because of the low spectral resolution of the spectrograph and the complex sample components. The overlapped peaks lead to the errors in peak parameters extraction easily, and at last lead to the analysis error of sample components, which increases the difficulty in automatic analysis of field spectra. The identification of overlapped peaks is the key difficulty of in-situ spectra analysis. To solve this problem, an automatic method of identifying the overlapped peaks was established basing on an analysis model with multiple Gaussian shape peaks. The peak number and the initial parameters(the peak position, peak height, and width) were obtained by symmetric zero-area transformation firstly, and then the parameters were optimized by Levenberg-Marquardt fitting method eventually. Some algorithm experiments were executed to test the method respectively by simulated data and Raman spectra data, and the former showed that the symmetric zero-area transformation method can extract the initial peak parameters with high accuracy, and then converges fast, and is adaptive to signal with wide dynamic range of SNR, but has false and omissive peaks to low SNR signal. The research results show that the automatic method of identifying the overlapped peaks with symmetric zero-area transformation combined with L-M fitting has a certain practical value.

[Characterization of Time-Resolved Laser-Induced Fluorescence from Crude Oil Samples].

To evaluate the feasibility of laser induced time-resolved fluorescence technique for in-situ detection of underwater suspended oil spill, extensive investigations have been carried out with different densities of crude oil samples from six different wells of Shengli Oilfield in this work. It was found that the fluorescence emission durations of these crude oil samples were almost the same, the Gate Pulse Delay of DDG (Digital Delay Generator) in the ICCD started at 52ns and ended at 82ns with a width (FWHM) of 10 ns. It appears that the peak location and lifetime of fluorescence for different crude oil samples varied with their densities, and those with similar densities shared a similar lifespan with the closer peak locations of fluorescence. It is also observed that the peak of fluorescence remained the same location before reaching the maximum intensity, subsequently shift to longer wavelength as fluorescence attenuated from maximum intensity with a red shift among 17-30 nm varied with samples. This demonstrated that the decay rate of fluorescent components in the crude oils was different, and energy transfer between these components might exist. It is hoped that those obtained results and characteristics could be the useful information for identification of suspended spilled-oil underwater.

[Raman Signal Enhancement for Gas Detection Using a Near Concentric Cavity].

The detection of dissolved gases in seawater plays an important role in ocean observation and exploration. Raman spectroscopy has a great advantage in simultaneous multiple species detection and is thus regarded as a favorable choice for ocean application. However, its sensitivity remains insufficient, and a demand in enhancements is called! for before putting Raman spectroscopy to actual use in marine studies In this work, we developed a near-concentric cavity, in which laser beam could be trapped and reflected back and forth, for the purpose of intensifying Raman signals. The factors that would influence Raman signals were taken into account. The result show that the smaller angle between collection direction and optical axis of reflection mirror, the stronger the signal and signal to noise ratio (SNR) is. With a collection angle of 30 degrees, our Near-concentric Cavity System managed to raise the SNR to a figure about 16 times larger than that of common methods applying 90 degrees. Moreover, the alignment pattern in our system made it possible to excel concentric cavity with a 3 times larger SNR. Compared with the single-pass Raman signal, the signal intensity of our near-concentric cavity was up to 70 times enhanced. According to the obtained results of CO2 measurement, it can be seen that the new system provides a limit of detection(LOD) for CO2 about 0.19 mg x L(-1) using 3-σ criterion standard, and the LOD of 11.5 µg x L(-1) for CH4 was evaluated with the theoretical cross section values of CO2 and CH4.

[Comparative investigation of underwater-LIBS using 532 and 1 064 nm lasers].

With the hope of applying laser induced breakdown spectroscopy (LIBS) to the ocean applications, the laser energy at 532 and 1 064 nm wavelength with 3 and 40 mj respectively was used, which was near their breakdown threshold. Extensive experimental investigations of LIBS from CaCl2 water solution were carried out in this paper using different laser wavelengths of 532 and 1 064 nm. The obtained results show that compared with the 532 nm laser, the 1 064 nm laser can induce the plasma in water with higher emission intensity and longer lifetime, while the reproducibility of LIBS signal under 1 064 nm laser is poorer. On the other hand, due to the different attenuation ratios of 532 and 1 064 nm laser energies in water, the LIBS signal of 1 064 nm laser decreases a lot within the transmission distance range 2-5 cm, while LIBS signal of 532 nm remains the same, because that the wavelength of 532 nm lies in the "transmission window" of the water solution. This study will provide valuable design considerations for the development of LIBS-sea system in near future.

[The symmetric zero-area conversion adptive peak-seeking method research for LIBS/Raman spectra].

Automatic peak seeking is an indispensable link for in situ and real-time spectral detection and analysis, and has important significance for application of spectral technology to such fields as long-term marine monitoring and oil mud logging. Based on some typical LIBS/Raman spectrum data obtained from lab, three kinds of symmetric zero-area transformation functions respectively constructed from Gaussian, Lorentz and Voigt function were compared, and the results show that there exists an optimal symmetrical zero-area transformation function for peak seeking, but all the transformation functions obtain the same peak position and peak width under their optimal parameters. The proposed method is free from spectrum background and baseline trend influence, adaptive to the wide range of SNR, close to or even better than artificial recognition for weak peak, and could be used in future automatic in-situ analysis of LIBS and Raman.

[The measurement of methane dissolved in water using raman spectroscopy assisted with CCl4 extraction].

While under laboratory conditions, the concentration of methane dissolved in water is too low to be detected because of the low solubility of methane using Raman spectroscopy. In the present paper, a novel approach based on CCl4 extraction was introduced, and used in the measurement of methane dissolved in water using Raman spectroscopy under laboratory conditions. Saturated aqueous solution of CH4, CCl4 solution after extraction of CH4 from the saturated aqueous solution and the saturated CCl4 solution of CH4 were prepared, and the Raman spectra of three samples were obtained. The obtained results show that the CH4 dissolved in saturated aqueous solution(the concentration of CH4 is about 1.14 mmol x L(-1)) can't been detected using Raman spectroscopy under laboratory conditions, but the CH4 Raman peak can be clearly seen in the spectra obtained for CCl4 solution after extraction. All the results demonstrate that the proposed approach can improve the Raman spectroscopy sensitivity of methane detection dissolved in water, and this approach has significant potential to be developed as an effective method for detection of methane dissolved in water.

[Detection and analysis of polycyclic aromatic hydrocarbons using surface-enhanced Raman spectroscopy].

In the present paper, the gold colloid with parameters optimized was used as surface-enhanced Raman scattering (SERS) active substrate to realize the trace detection of polycyclic aromatic hydrocarbons (PAHs) in water for the first time. Gold colloids with different size were prepared using chemical reduction method, and the optimum size selected at 632.8 nm excitation wavelength by experiment is (32 +/- 3) nm. The influence of pH value on the enhancement of PAHs was researched, and the optimal pH value is 13. Spectral intensity increased by approximately 20-fold compared with pH 6. The SERS spectra of naphthalene, phenanthrene and pyrene aqueous solutions were detected by the optimum gold colloid, and the minimum concentrations obtained were 20, 4 and 4 nmol x L(-1), respectively. There was a linear relationship between peak intensity and concentration, and the linear regression correlation coefficients were all above 0.985. For the mixture, the authors could distinguish each PAH easily for their own characteristic peaks. The experimental results show that such active substrate has a very high sensitivity as well as good application prospect.

[Effects of laser wavelength on detection of metal elements in water solution by laser induced breakdown spectroscopy].

In the present paper, aiming at the problem of laser induced breakdown spectroscopy (LIBS) applyication in ocean detection, the effects of laser wavelength on the detection of Ca in water solution were investigated. The evolvement characteriza tion of electron density was studied by analyzing the time resolved spectra of the plasma. The experimental results show that the lifetime of plasma is about 1 200 and 600 ns respectively induced by 1 064 and 532 nm laser. Based on the optical transmission characteristic and the LIBS experimental results, the dependence of needed laser energy before incidence into water E(iopt)(r) for optimal detection effect on the detection distance in water was found, and the dependence was simulated by applying to the in situ detection in water solution. The simulated results suggest that the needed laser energy of 1 064 nm laser before incidence into water is about 100 mJ when the detection distance is no larger than 5 cm. When the detection distance increases to 10 cm, the needed laser energy of 532 nm before incidence into water is only about 30 mJ. So it should be considered to choose 532 nm laser as the ablation source with the increase in the in situ detection distance.

[Study of cuttings identification using laser-induced breakdown spectroscopy].

Cutting identification is one of the most important links in the course of cutting logging which is very significant in the process of oil drilling. In the present paper, LIBS was used for identification of four kinds of cutting samples coming from logging field, and then multivariate analysis was used in data processing. The whole spectra model and the feature model were built for cuttings identification using PLS-DA method. The accuracy of the whole spectra model was 88.3%, a little more than the feature model with an accuracy of 86.7%. While in the aspect of data size, the variables were decreased from 24,041 to 27 by feature extraction, which increased the efficiency of data processing observably. The obtained results demonstrate that LIBS combined with chemometrics method could be developed as a rapid and valid approach to cutting identification and has great potential to be used in logging field.

[Identification of spill oil species based on low concentration synchronous fluorescence spectra and RBF neural network].

In this paper, a new method was developed to differentiate the spill oil samples. The synchronous fluorescence spectra in the lower nonlinear concentration range of 10(-2) - 10(-1) g x L(-1) were collected to get training data base. Radial basis function artificial neural network (RBF-ANN) was used to identify the samples sets, along with principal component analysis (PCA) as the feature extraction method. The recognition rate of the closely-related oil source samples is 92%. All the results demonstrated that the proposed method could identify the crude oil samples effectively by just one synchronous spectrum of the spill oil sample. The method was supposed to be very suitable to the real-time spill oil identification, and can also be easily applied to the oil logging and the analysis of other multi-PAHs or multi-fluorescent mixtures.

[Time-resolved evaluation of self-absorption in laser induced plasma from nickel sample].

Laser induced breakdown spectroscopy (LIBS) has been shown to be a promising technique for element analysis. However, self-absorption effect deeply influences the LIBS measurements. In the present paper, a Q-switched Nd:YAG laser operated at 1 064 nm was used to generate nickel plasmas in air. Four atomic lines Ni I 341.476/351.034/351.505/352.454 nm which belong to the same electronic configuration (3d9 (2D)4p-3d9 (2D)4s) of Ni were chosen for self-absorption investigation. Self-absorption of Ni I 351. 034 nm corresponding to the highest energy level 3D1 of 3d(9) (2D)4s was not observed in the plasma emission investigated. While for the other three lines, a strong self-absorption appeared at the prophase of the plasma and tended to weaken. The self-absorption at Ni I 352.454 nm was the most serious and still visible at the delay of 1100 ns, compared with the lines of Ni I 341.476/351.505 nm whose self-absorption duration is 900 and 500 ns respectively. It was also found that the self-absorption effect had power dependence and decreased with the increase in laser pulse energy. The obtained results suggest that the self-absorption effect could be alleviated by suitable atomic line selection, operating at a higher pulse energy and detecting with a longer delay. The possible reasons for the self-absorption duration difference for different lines were also discussed.

[Ultrasonic nebulizer assisted LIBS for detection of trace metal elements dissolved in water].

Because of the complex factors in bulk water, the effect of LIBS on the analysis of liquid sample is limited in liquid sample. Under this circumstances, a new method of LIBS assisted by ultrasonic nebulizing technology has been introduced. According to this method, the liquid sample is transformed into dense droplets by ultrasonic nebulizing technology, and these dense droplets are subjected to the analysis of LIBS later. Based on this thought, a detection experimental system was established, composing of ultrasonic system, 1 064 nm ND: YAG laser, and ICCD system. A series of experiments and analysis were carried out to detect the magnesium element dissolved in pure water using the detection experimental system mentioned above. The results showed that even with a very low laser pulse energy (30 mJ), the signals of LIBS still have a long lifetime and a high signal to background ratio. The limit of detection for magnesium element could reach as low as 0.242 ppm. At the same time, the electron density of plasma was calculated utilizing the Halpha line to give the evolution features of plasma induced by this new method.

[Experimental investigation of quantitatively analysing trace Mo in complex metallic alloys by laser induced breakdown spectroscopy].

The quantitative analysis using laser induced breakdown spectroscopy (LIBS), lack of appropriate interior label element, is described and applied to trace element molybdenum (Mo) detection in complex metallic alloys. A Q-switched Nd : YAG laser operating at 532 nm was utilized to generate plasma and the emission was recorded by a grating spectrometer equipped with CCD, boxcar and PMT. The three peak heights of Mo I , 550.649, 553.305 and 557.045 nm, changing with Mo mass fraction in metallic alloys were measured to produce calibration curves respectively, and double blind method was used to analyse a test sample. Based on Mo I 550.649 nm line, the Mo mass fraction in the test sample was determined to be 2.229% with relative error of 5.57% in comparison with the given value of 2.111%. On using Mo I 557.045 nm line, the relative error was found to be doubled due to the overlap with Fe emission lines. While taking the total height of three atomic lines into account in analysis, the resulted error dropped to 7.58%, even better than the average of predicted concentrations based on the above three lines. The obtained results demonstrate that satisfactory precision could be obtained under a consistent experiment condition with the above scheme, even without appropriate interior label element. The methods of maintaining stable laser ablation efficiency on sample are also discussed.

[Experimental study on Raman spectroscopy of alkane gases in simulated deep-sea extreme environments].

In the present work, Raman spectra of alkane gases aqueous solution under simulated deep-sea hydrothermal environment were acquired by high temperature and high pressure deep-sea simulation experiment system. The variation laws of the Raman spectral features with various temperature and pressure were analyzed and mathematical model between them were established. The results show that for all Raman peaks of these alkane gases in aqueous solution the frequency is lower than gaseous state because of hydrogen bond; the variations of their Raman spectrum were not obvious as the pressure increased (< or = 40 MPa) in room temperature; and all peak positions move to lower wave number and their full width at half maximum (FWHM) increased along with changing temperature in the range of room temperature to 350 degrees C at 40 MPa pressure. The results provide an experimental basis for the in-situ detection of deep sea by Raman laser spectroscopy system in hydrothermal environment.

PCE3 Plays a Role in the Reproduction of Male Nilaparvata lugens.

Nilaparvata lugens proclotting enzymes (NlPCEs) belong to the clip domain serine protease (clip-SP) family, which is a characteristic protease family in arthropods. NlPCE3 was previously reported to regulate egg production and development in female N. lugens, but its role in male N. lugens is unclear. In the present study, qPCR analysis showed that NlPCE3 was expressed in three different tissues (gut, testis and fat body). RNAi revealed that dsNlPCE3 injection made the male vas deferens thinner and reduced the oviposition level of the females that mated with dsNlPCE3-treated males, causing eggs not to hatch. Furthermore, immunofluorescence staining showed that NlPCE3 was widely expressed in the male internal genitalia. However, after dsNlPCE3 injection, expression of NlPCE3 was diffuse in the male internal genitalia, whose peripheral cells seemed degraded. Overall, these results indicate that NlPCE3 is important for reproduction in male N. lugens.

[Fingerprint discrimination technique of spill oil based on concentration auxiliary parameter fluorescence spectra].

In the present paper, concentration as an auxiliary parameter was introduced to the synchronous fluorescence to form concentration synchronous fluorescence matrix of the oil spill samples within the concentration range of 10(-1)-10 g x L(-1). Principal component analysis was used to classify the oil spill samples of 0# diesel, 93# gasoline and 5 crude oil simples from the Shengli oilfield. Experiments show that the introducing of concentration can reflect more composition information of the PAHs. This newly method has a better discrimination than the routine method of the synchronous fluorescence spectra obtained from spill oil samples in linear concentration range. It indicates that the spill oil samples of different type and source can be discriminated precisely, even from the same oilfield. The influence of the errors caused in the samples extraction procedure can be eliminated. All the results suggest that the technique may become a more convenient, rapid and accurate means in spill oil identification.

[Experimental investigation of Pb in soil slurries by laser induced breakdown spectroscopy].

Laser induced breakdown spectroscopy (LIBS) has been shown to be a promising technique for element analysis with many advantages including on-line, real time, standing off and multi-element detection capability. In the present paper, the LIBS experiments for Pb in slurry samples were carried out with the motivation of developing an in-situ sensor for monitoring heavy metal. A Q-switched Nd : YAG laser operating at 532 nm with repetition frequency of 10 Hz was utilized to generate plasma on the prepared slurry samples, which were doped with same weight manganese as reference and varied concentration of lead. The induced plasma emission was recorded by CCD. The LIBS signals at PbI 405.78 nm and MnI 403.07 nm from the slurry samples were investigated. It was found that the intensity ratio of I(Pb)/ I(Mn) increased as a linear function of the concentration of Pb with correlation coefficient R2 of 0.994 9. The obtained results show that LIBS with conjunction of referent element could be developed as a potential technique for contamination analysis of soil slurries. The main influence factors in LIBS signal detection were also discussed.