Study of underwater laser propulsion using different target materials.

In order to investigate the influence of target materials, including aluminum (Al), titanium (Ti) and copper (Cu), on underwater laser propulsion, the analytical formula of the target momentum IT is deduced from the enhanced coupling theory of laser propulsion in atmosphere with transparent overlay metal target. The high-speed photography method and numerical simulation are employed to verify the IT model. It is shown that the enhanced coupling theory, which was developed originally for laser propulsion in atmosphere, is also applicable to underwater laser propulsion with metal targets.

[The influence of temperature on the orientation of pigments in PS II].

The effect of temperature on the orientation of pigment in PSII was studied by the fluorescence excitation spectra and polarization fluorescence spectra of spinach thylakoid solution. The experimental results showed that in the temperature range of 15-45 degrees C the absorption band of chl a at 436 nm at room temperature red-shifted with increasing temperature. The excitation spectra intensity reached the maximum at the temperature of 35 degrees C, but greatly reduced with temperature at 65 and 78 degrees C. In the polarization fluorescence spectra the fluorescence peak of PSII didn't change with temperature from 15 to 45 degrees C. It was also found that the calculated fluorescence polarization degree increased with the temperature in the entire temperature range. The analysis indicated that temperature would affect the orientation of the pigments in PSII and the coupling strength between pigments so to change photosynthetic efficiency. The results will give a certain reference for the study of the energy absorption and transmission, regulation mechanism and also on solar cell materials.

Formation and dynamics of a toroidal bubble during laser propelling a cavity object in water.

We captured stable self-oscillations of a toroidal bubble moving away from a laser propelled cavity object in water using a high-speed imaging system. The entire laser propelling process generates a hemispherical bubble, two toroidal bubbles, and a microbubble cluster. The hemispherical bubble is formed by laser breakdown in water. The toroidal bubbles are formed by the variation of the pressure field as a result of the propagation, reflection, and convergence of the laser plasma shockwave in the cavity.

Evaluation of third-order elastic constants using laser-generated multi-type ultrasound for isotropic materials.

Within the linear elasticity approximation the speed of a small-amplitude sound in conventional linear elasticity is determined only by the second order elastic (SOE) constants and the density of the medium. Subjecting the conveying solid to a static strain of a sufficient magnitude introduces the third-order elastic (TOE) constants in the equation of the sound speed. In this work we applied a homogeneous isotropic deformation caused by a thermal expansion of an aluminum alloy sample. Velocities of three acoustic modes: longitudinal, shear and Rayleigh waves were measured as functions of temperature within a range of 25-100 °C. Two TOE constants C111 and C112 were evaluated in an assumption that the third independent module C144 is far smaller than the former two.

[Effects of experimental parameters on elemental analysis of aluminum alloy by laser-induced breakdown spectroscopy].

Laser-induced breakdown spectroscopy (LIBS) has been used to detect the elements of 2519A aluminum alloy by Nd : YAG laser in the present paper. The atomic spectral lines of Al and Cu were observed using a portable spectrometer. The impacts of lens-to-sample distance, probe angle, laser pulse energy, observation height and ambient pressure on the line intensities were studied. The results show that all these experimental parameters have great influence on the precision of LIBS such as line intensity, signal to background ratio and repeatability. Finally, the best results can be observed by using the optimum experimental conditions.

[Hydration of liquid ethanol probed by Raman spectra].

In order to study the concentration dependence of the molecular interactions in ethanol-water hydrogen bonded system, Raman spectra of ethanol-water mixtures with different water contents were obtained at room temperature. It was found that the positions of the 3 C-H stretching vibration bands of ethanol molecule located in the range of 2 800-3 050 cm(-1) would generally present blue shifts when more water was added into the mixture; at the same time, however, the C-O stretching vibration band located at around 1 048 cm(-1) showed an opposite behavior. The different hydration, which is induced by hydrogen bonding, which happened in different concentration mixtures, was thought to be responsible for this situation, the hydration process of liquid ethanol was thus deduced: when adding a small amount of water into pure ethanol, and clusters containing one water molecule and several ethanol molecules were formed instead of ethanol self-association short chain clusters existing in pure ethanol; the clusters would combine more water molecules to form ringlike clusters through hydrogen bond association when adding more water into the mixture, then a temporary saturation would be seen when the volume percent of water reached 50%, and this saturation state would last until the water content reached 70 vol%; after that, the large number of water molecules would dissociate the ringlike clusters to smaller clusters and then associate to the ends of these dissociated clusters through hydrogen bonding; in addition, the improper hydrogen bonding between oxygen atom of water molecule and C-H bond of ethanol molecule is considered to be formed after the content of water reached a high value.

[Study on the elements of the fluorescence spectra emitted from ethanol-water mixture].

The 236 nm UV-light was adopted to excite the 10 ethanol-water mixture samples in which the volume percent of ethanol ranges from 10% to 95%, and the Gaussian decomposition method was used to decompose the fluorescence spectra obtained above to Gaussian curves, where every Gaussian curve can be attributed to the fluorescence emission of a certain kind of luminescent ethanol-water cluster, which is formed by the association between water molecules and ethanol molecules. It was found that every spectrum of the certain binary mixture contains 8 Gaussian elements, and the emission density and peak wavelength of each element were also obtained. The authors studied the mechanism of the fluorescence emission of the mixtures based on the structural characters of fluorescence substances and concluded that the water molecules play an important role in the fluorescence emission: they enlarge the conjugate system as the electron donors; they bridge the ethanol molecules to form 8 kinds of new clusters at the same time, and the conformation of the clusters is rings and chains composed by several rings. Through the peak wavelengths of the Gaussian elements decomposed from the certain concentration spectrum the authors got the information about the relative size of the new clusters, i.e. the clusters are bigger or show chain structures when the peak wavelength of the Gaussian curves is located at the longer positions. The emission transition energies of the 8 kinds of new clusters were also calculated. In addition, it was found that there was a certain relation between the half-width and the association situation. The research contributes to the study of ethanol-water cluster structures and their physical and chemical characteristics.

[Identification of protoporphyrin IX fluorescence spectrum in human blood serum by biorthogonal spline wavelet].

For the low content and weak fluorescence intensity, usually presenting shoulder peaks, it is often hard to locate protoporphyrin IX and identify its fluorescence intensity in human blood serum. Biorthogonal spline wavelet may work for the identification of its weak signal Superimposing protoporphyrin IX fluorescence signal on the background of blood serum spectrum, a series of varied fluorescence spectra of them can be obtained. The protoporphyrin IX fluorescence signal from blood serum background is separated and the fluorescence spectrum can be divided into corresponding discrete approximate signals (a1-a7) and discrete details signals (d1-d7) by biorthogonal spline wavelet bior 5.5 seven levels decomposition. The signal frequency shows a gradual decrease with increasing decomposition. Protoporphyrin IX fluorescence peak emerges when it comes to the 7th decomposition. The signal peak shifts about 2.5 mm downwards as the signal intensity decreases, whereas the signal peak from wavelet filter remains where it was. As the synchronization disappears between signal intensity and signal peak, usually it is hard to assure the fluorescence intensity and peak location. However, signal from wavelet filter may ignore the affect and identify the protoporphyrin IX in human blood serum with the help of biorthogonal spline wavelet. As the linear alternation of wavelet and discrete details signals maintain their inborn linear relations, the authors can carry out the qualitative and quantitative analysis for the precise content and quantity of protoporphyrin IX in blood serum, which provides a feasible method for the application of blood serum fluorescence spectrum to tumor early diagnosis.

[Fluorescence spectrum analysis system for protoporphyrin IX in serum based on wavelet transform].

Protoporphyrin IX is an important kind of organic compound for vital movement, and can be used as the sign of tumour blood. Human protoporphyrin IX content in serum is very low, and affected by various factors. The serum fluorescence spectrum analysis system based on wavelet transform was used to discriminated the protoporphyrin IX weak signals. The protoporphyrin IX fluorescence spectrum was obtained by a multi-function spectrum measuring system, and decomposed several times by wavelet transform to distinguish the noise and spectrum signals. The fluorescence spectrum can be divided into corresponding discrete approximations signals (a1-a6) and discrete details signals (d1-d6) by six times of decomposition, showing the signal frequency decreasing with decomposition times increasing and the protoporphyrin IX fluorescence character peak appears here. The weak signals were discriminated and the exactly component and quantity can be acquired for further analysis. So it can be analysed quantitatively. The researches in the present paper provide the potential application in the diagnosis of incipient tumous using the serum fluorescence spectrum

[Experiment study of alcohol-water mixtures absorption and fluorescence spectra induced by UV-light].

By using equipment of UV-240 ultra-violet spectrophotometer and Sp-2558 multifunctional spectrometer system, the UV-light absorption spectra and the fluorescence spectra of propanol and isopropanol, as well as their comparison were studied. According to the results, propanol and isopropanol can be clearly distinguished with absorption spectra and fluorescence spectra. The reasons for difference spectra of the two liquids were also explained. Moreover, the fluorescence spectra of the four kinds of difference alcohol were compared and the results were discussed. The whole research outcomes will provide a new method for effective measurement of different alcohol, and also produce some valuable theoretical references to the calculation of quantum chemistry.

[Spectroscopy research on cholesterol in hypercholesterolemia serum].

The cholesterol with different concentration in hypercholesterolemia serum was studied by the method of spectroscopy technology. The absorption and fluorescence spectra of normal human serum and hypercholesterolemia serum were obtained respectively; the spectral characteristic of each sample and the difference between two kinds of samples were discussed too. The results indicate that the absorption and fluorescence spectra of hypercholesterolemia serum are different from those of normal human serum. The absorptivity and the fluorescence intensity of hypercholesterolemia serum are both higher than those of normal human serum. Besides, there are new absorptive peaks and new fluorescence peaks in the spectrogram. Thus, the abnormalism of cholesterol in serum can be judged by comparing the absorption and fluorescence spectra. The researches in the present paper provide an experimental foundation for the diagnosis of cholesterol in blood.

Attenuation of laser-generated shock waves in Plexiglas.

A simple analytic model is derived for describing the attenuation of a shock wave in a Plexiglas plate. At the same time, experimental measurements are presented with a well-designed optical-fiber sensor based on detection-beam deflection. The amplitude of the shock-wave pressure is measured experimentally and calculated numerically for analytic expressions at different distances from the region of the surface breakdown by the radiation of a single-pulse Nd:YAG laser. Good agreement between the experimental and the calculated values of the shock-wave pressure is established.

Investigation on utilizing laser speckle velocimetry to measure the velocities of nanoparticles in nanofluids.

Laser speckle velocimetry (LSV) is presented to measure the velocities of nanoparticles in nanofluids and its feasibility is verified in this paper. An optical scattering model of a single nanoparticle is developed and numerical computations are done to simulate the formation of the speckles by the addition of the complex amplitudes of the scattering lights from multiple nanoparticles. Then relative experiments are done to form speckles when nanofluids are illuminated by a laser beam. The results of the experiments are in agreement with the numerical results, which verify the feasibility of utilizing LSV to measure the velocities of nanoparticles in nanofluids.

[Influence of excitation light wavelength on the fluorescence spectra of ethanol solutions].

Ethanol solution can emit visible fluorescence when induced by UV light. With emission spectral profiles similar on the whole, the peaks are red-shifted distinctly when the excitation light alters from 200 to 250 nm. And the spectral profiles of ethanol solutions with different concentrations are also red-shifted when induced by the same wavelength of excitation light. A thorough analysis of the rule of spectrum peaks that are red-shifted is carried out and discussed in theory and in experiment. Investigation on the intrinsic fluorescence spectrum of ethanol solution and its characteristics will contribute to the study of the fluorescence spectra when ethanol serves as a solute and hydrolysis catalyst. Especially, this study will also help to offer a sensitive method of the determination of ethanol.

Shock-wave propagation and cavitation bubble oscillation by Nd:YAG laser ablation of a metal in water.

A highly sensitive fiber-optic sensor based on optical beam deflection is applied for investigating the propagation of a laser-induced plasma shock wave, the oscillation of a cavitation bubble diameter, and the development of a bubble-collapse-induced shock wave when a Nd:YAG laser pulse is focused upon an aluminum surface in water. By the sequence of experimental waveforms detected at different distances, the attenuation properties of the plasma shock wave and of the bubble-collapse-induced shock wave are obtained. Besides, based on characteristic signals, both the maximum and the minimum bubble radii at each oscillation cycle are determined, as are the corresponding oscillating periods.