Quantum control of photoion circular dichroism using orthogonal laser beams.

The First World Congress on Industrial Process Tomography was held at the Palace Hotel, Buxton, Derbyshire from 14-17 April 1999. Over the four days, 130 delegates registered, of which about half were from the UK, one-third from continental Europe and the remainder from countries as diverse as China, Australia, USA, Canada, Brazil and Japan. Approximately one-quarter of the delegates were non-academic. Although this event was the first `World Congress', it followed on from two earlier series of conferences. These started in 1992 with the European Concerted Action on Process Tomography (ECAPT), which hosted four events across Europe. This was followed by the Engineering Foundation, which organized two conferences in the `Frontiers in Industrial Process Tomography' series, one in the US. Each meeting has seen a steady growth in interest in the subject, with more delegates from a wider range of countries and a greater participation by industry, reflecting the growing importance in the use of tomographic techniques to address industrial applications and solve industrial problems.

Universal Particle Detector Experiment

It is well known that arc welding of thin metallic sheets in difficult due to their easier distortion and deformation. On the other hand, in laser welding, such distortion and deformation is greatly reduced due to a smaller spot size and smaller heat input than in arc welding. Even in laser welding, thinner metallic sheets become more difficult to weld due to the loss of materials and the difficulty in supporting a shallow molten pool against evaporation and recoil pressure, leading to the formation of cut or drilled welds. In this study, therefore, lap welding characteristics of thin metallic sheets were investigated by utilizing combined beams or respective single beam of normal pulsed YAG laser and Q-switched SHG YAG laser. It was consequently found that the formation conditions for good lap welds in thin stainless steel sheets were broadened by using combined laser beams. Especially, lap welding of pure copper sheets was very difficult with single pulsed YAG laser; however, it was confirmed to be possible to weld them with combined laser beams of two different wavelengths in the air environment.

Developments of the amplified stimulated emission technique for spatially resolved species detection in flames

Stable zinc oxide nanoparticles were prepared by chemical process. Zinc oxide nanoparticles were synthesized using a modified method with zinc nitrate and sodium hydroxide at 60° C. The synthesized nanopowders were characterized in terms of chemical composition (EDS), structure FTIR and XRD, particle size and morphology by TEM. The XRD results confirm that ZnO nanoparticles were obtained with hexagonal arrangement (Wurtzite). The nanoparticles showed sizes between 10 to 30 nm and semispherical forms. The luminescent properties of the synthesized nanoparticles were measured in a photoluminescence assay on a Raman instrument. The samples were irradiated with two laser beams of different wavelengths. The application of the fingerprints on different surfaces was done using deferments surfaces.

A method for planar measurement of temperature in a compressible flow by means of two-line laser-induced iodine fluorescence is proposed. Temperature is determined from the ratio of the intensities of fluorescence, which are obtained by irradiation of two laser beams of different wavelength. Use of a high-sensitivity vidicon camera permits multiple-point measurements of temperature in the flow field. This method is applied to a supersonic free jet. It is found that the results obtained by P(16)/R(18) (514.720 nm) and P(26)/R(28) (514.942 nm) absorption lines in the transition of B(3)II(ou)+ (nu' = 43) ? X(1)sigma(g)+ (nu'' = 0) can predict temperature below 300 K with an accuracy of +/-5K.

The advent of free-electron laser (FEL) sources delivering two synchronized pulses of different wavelengths (or colours) has made available a whole range of novel pump–probe experiments. This communication describes a major step forward using a new configuration of the FERMI FEL-seeded source to deliver two pulses with different wavelengths, each tunable independently over a broad spectral range with adjustable time delay. The FEL scheme makes use of two seed laser beams of different wavelengths and of a split radiator section to generate two extreme ultraviolet pulses from distinct portions of the same electron bunch. The tunability range of this new two-colour source meets the requirements of double-resonant FEL pump/FEL probe time-resolved studies. We demonstrate its performance in a proof-of-principle magnetic scattering experiment in Fe–Ni compounds, by tuning the FEL wavelengths to the Fe and Ni 3p resonances.

We have developed the theory for using the deflection of laser beams of various wavelengths to determine molecular and thermal diffusion coefficients in multicomponent mixtures. In the past, simultaneous determination of molecular and thermal diffusion coefficients have only been achieved for binaries. Our procedure is faster and more accurate than the current techniques to determine molecular diffusion coefficients. The analysis for an N-component mixture requires deflections from (N - 1) beams of different wavelengths. We show in an example that the molecular and thermal diffusion coefficients can be determined reliably in a ternary mixture.

High concentrating photovoltaic (HCPV) technology plays a more and more important role in solar power generation due to its extremely high efficiency. However, the efficiency of the HCPV module can be reduced by many factors. Especially, there are not enough researches and knowledge on the light intensity distribution and non-uniform illumination of different wavelengths of light concentrated by Fresnel lens. It is generally considered that the maximum power of multi-junction solar cell is achieved when the cell is placed on the focal plane of Fresnel lens. But it is proved to be incorrect by our research. When light beams of different wavelengths go through the Fresnel lens, their light spot distributions on the optical axis are not the same as those when they have different refractive indexes in Fresnel lens. At the same time, the triple-junction solar cell consists of three sub-cells which absorb light beams of different wavelengths respectively. Therefore, the performance of triple-junction cells would be influenced by the light distribution along the optical axis, this is exactly what we want to study in this work. The method of simulating the light tracing is used to calculate and analyze the light intensity distribution and non-uniform characteristics of different wavelengths of light concentrated by Fresnel lens. Combined with them from the circuit network model of a triple-junction solar cell, the electrical performances of triple-junction solar cell at different positions along the optical axis are studied. It is found from the simulation that the performance of cell does not reach the best state when cell is placed on the focal plane. The power of cell on the focal plane reaches only 0.41 W while the maximum point arrives at 0.69 W. The high non-uniformity of light on cell surface when cell is placed on the focal plane causes the decline of power. And an outdoor HCPV testing system with the ability to change the distance between Fresnel lens and the cell is conducted. The experimental results and the simulation results match well, therefore our simulation approach is verified. It shows that the module achieves the maximum power on either side of the focal plane, and the output power can increase more than 20% after optimization. It is a result after equilibrium between light intensity and uniformity on cell surface.

In mass spectrometry enantiomers can be distinguished by multiphoton ionization employing circular polarized laser pulses. The circular dichroism (CD) is detected from the normalized difference in the ion yield after excitation with light of opposite handedness. While there are cases in which fragment and parent ions exhibit the same sign of the CD in the ion yield, several experiments show that they might also differ in sign and magnitude. Supported by experimental observations it has been proposed that the parent ion, once it has been formed, is further excited by the laser, which may result in a change of the CD in the ion yield of the formed fragments compared to the parent ion. To gain a deeper insight in possible excitation pathways we calculated and compared the electronic CD absorption spectra of neutral and cationic (R)-3-methylcyclopentanone, applying density functional theory. In addition, electron wavepacket dynamics were used to compare the CD of one- and two-photon transitions. Our results support the proposed subsequent excitation of the parent ion as a possible origin of the difference of the CD in the ion yield between parent ion and fragments.

The authors report simultaneous measurements of both Na+ and Na2+ ion yields when Na vapour in the 1012-1013 cm-3 density range is irradiated by a pulsed laser tuned to one of the 3S1/2-3P1/2,3/2 resonances with intensities in the 103-106 W cm-2 range. In the studied vapour density and laser intensity ranges, electron impact ionisation and multiphoton ionisation processes are negligible; the ion yields are hence interpreted in terms of atom-atom collisions. The influence of associative ionisation on the Na2+ yield is analysed on the basis of the experimental data and a calculated potential curve for the 1 Sigma g molecular state correlated to Na(3p)-Na(3p). A critical discussion of possible laser-induced (laser-assisted and/or laser-modified) ionising processes is given. A good account of the data is obtained only if laser-induced associative ionisation and laser-induced Penning ionisation (as the most probably processes) are assumed to take place in the vapour. The distribution over the vibrational levels of the Na2+ ions thus formed and the photodissociation of these levels are discussed as well as the existence of independent Na+ ion formation.

Turbidity in a titration solution or dilution upon sample introduction causes systematic errors in automatic Spectrophotometric set-point titrations. The reduction of these errors with a factor of about 10 is realized by subtracting the signals of two light beams of different wave length which pass the same titration solution. The signal values both depend on the absorption of coloured substances (indicator) and on turbidity or dilution effects. Assuming that these effects are independent of the wave length and selecting wave lengths at which indicator absorbance differs greatly, subtraction of the signals leads to the elimination of said effects. As an illustration nMole amounts of sulphate were titrated in 80–90% aceton with a lead(II)-titrant using dithizone as indicator. The standard deviation was about 2%. A titration took 1–2 min.

Circular dichroism in ion yield has promising new potentials for chiral analysis. Our progress of its development is described here. Circular dichroism in ion yield is achieved by resonance-enhanced multiphoton ionization. The feasibility of circular dichroism spectroscopy and quantitative determination of circular dichroism by this method is demonstrated. Several excitation schemes have been applied using different types of lasers, which vary in wavelength and repetition rate. Progress to improve the statistical error and thus the lower limit of measurable circular dichroism is described. This is achieved by adding achiral compounds or racemic mixtures of chiral compounds to the sample gas as reference substances and ionizing them by the same laser pulse. Therefore, in the mass spectrum of every single laser pulse, ion signals of sample and reference species appear both being subject to the same kind of instrumental fluctuations (in particular of laser pulse energy). In another approach, a laser repetition rate of 200 Hz allowed averaging of large numbers of laser pulses.

Mechanical and thermal properties of h-BN based composite containing dual glass phases at elevated temperatures

The feasibility of measuring circular dichroism (CD) in ion yields is demonstrated in multiphoton ionization employing femtosecond laser radiation for the first time. CD values for (R)-propylene oxide are reported at 738 nm, 810 nm and 878 nm. The data suggest the possibility of resonance contributions at 810 nm. At the other wavelengths the CD appears to originate from non-resonant multiphoton ionization. Possible implications of measuring non-resonant CD are discussed.