[en] In order to study the effect of defects on the laser-induced damage of different optical thin films, we carried out damage experiments on two kinds of thin films with a 1ms long-pulse laser. Surface-defect and subsurface-defect damage models were used to explain the damage morphology. The two-dimensional finite element method was applied to calculate the temperature and thermal-stress fields of these two films. The results show that damages of the two films are due to surface and subsurface defects, respectively. Furthermore, the different dominant defects for thin films of different structures are discussed.

[en] A rapid ultrasonic extraction method coupled with a heated-copper clean-up procedure for removing interfering constituents was developed for analyzing pyrethroid and phenylpyrazole pesticides in sediments. Incubation of the 60 mL extract with 12 g copper granules at 60 ^oC for 2 h was determined to be the optimal conditions for removing the interfering constituents. Eleven pyrethroid and phenylpyrazole pesticides were spiked into sediment samples to determine the effectiveness of the ultrasonic extraction method. The average recoveries of pyrethroids and phenylpyrazoles in sediment at 4 ^oC storage on day 0, 1, 7, 14, and 21 ranged from 98.6 to 120.0%, 79.2 to 116.0%, 85.0 to 119.7%, 93.6 to 118.7%, and 92.1 to 118.2%, respectively, with all percent relative standard deviations less than 10% (most < 6%). This illustrated the stability of pyrethroids and phenylpyrazoles in sediment during sediment aging at 4 ^oC. Recoveries of the pesticides ranged from 98.6% to 120.0% for lowest fortification level (2-16 μg kg^-1), from 97.8% to 117.9% for middle fortification level (10-80 μg kg^-1), and from 94.3% to 118.1% for highest fortification level (20-160 μg kg^-1). Relative standard deviations of pesticide recoveries were usually less than 7%. Method detection limits of target pesticides ranged from 0.22 μg kg^-1 to 3.72 μg kg^-1. Furthermore, field sediment samples collected from four residential lakes during a three-month monitoring period were analyzed to evaluate the effectiveness of this method. Bifenthrin was detected in all of sediment samples (highest concentration 260.33 ± 41.71 μg kg^-1, lowest concentration 5.68 ± 0.38 μg kg^-1), and fipronil sulfone was detected at least once in sediment samples collected from three sites with concentrations ranging from 1.73 ± 0.53 to 7.53 ± 0.01 μg kg^-1. - Highlights: → A rapid extraction and copper-based clean-up method was developed. → Recoveries after storage at 4 ^oC for 21 d ranged from 79.2 to 120.0%. → Percent relative standard deviations less than 10% (most < 6%). → Recoveries ranged from 94.3% to 120.0% at three fortification levels. → Method detection limits ranged from 0.22 μg kg^-1 to 3.72 μg kg^-1.

[en] Laser-induced breakdown spectroscopy has been performed to detect trace metal elements (Ca and Mg) in aqueous solution. In order to overcome the sensitivity drawbacks in liquid sample analysis, an absorbent paper was used as the sample support in this experiment. Calibration curves were constructed by using the standard solution with variable concentration and the limit of detection was estimated for each element. Finally this system was used to analyze three types of water samples collected from different locations in Nanjing, China and the results were compared with inductively coupled plasma atomic emission spectroscopy and showed good correlation.

[en] Two types of periodically modulated field for high voltage accelerating tubes are presented. The trajectories of secondary electrons emitted from electrodes have been computed. It is shown that the maximum energy obtained by the electrons decreases with the increasing field modulation. Therefore, it is possible to suppress the electron loading effect of high voltage accelerating tubes by these means

[en] To study the differences between the damaging of thin film components induced by long-pulse and short-pulse lasers, a model of single layer TiO₂ film components with platinum high-absorptance inclusions was established. The temperature rises of TiO₂ films with inclusions of different sizes and different depths induced by a 1 ms long-pulse and a 10 ns short-pulse lasers were analyzed based on temperature field theory. The results show that there is a radius range of inclusions that corresponds to high temperature rises. Short-pulse lasers are more sensitive to high-absorptance inclusions and long-pulse lasers are more easily damage the substrate. The first-damage decision method is drawn from calculations.

[en] A spatial axisymmetric finite element model of single-crystal silicon irradiated by a 1064 nm millisecond laser is used to investigate the thermal stress damage induced by a millisecond laser. The transient temperature field and the thermal stress field for 2 ms laser irradiation with a laser fluence of 254 J/cm² are obtained. The numerical simulation results indicate that the hoop stresses along the r axis on the front surface are compressive stress within the laser spot and convert to tensile stress outside the laser spot, while the radial stresses along the r axis on the front surface and on the z axis are compressive stress. The temperature of the irradiated center is the highest temperature obtained, yet the stress is not always highest during laser irradiation. At the end of the laser irradiation, the maximal hoop stress is located at r=0.5 mm and the maximal radial stress is located at r=0.76 mm. The temperature measurement experiments are performed by IR pyrometer. The numerical result of the temperature field is consistent with the experimental result. The damage morphologies of silicon under the action of a 254 J/cm² laser are inspected by optical microscope. The cracks are observed initiating at r=0.5 mm and extending along the radial direction.

[en] By using a Q-switched YAG laser and an optical path delay set-up, the author study the process in which a laser induces breakdown to produce plasma in air, and obtain time-resolved Mach-Zehnder interferograms and optical shadow grams of the initial stage of the plasma and the expansion wave produced in the process for the first time

[en] A zero-crossing dynamic speckle method is proposed to determine the velocities of nanoparticles in nanofluids. A Gaussian laser beam is used to illuminate nanofluids in a pipe, and the dynamic speckles are detected by a spatially integrating detector with an aperture. The integrated speckle intensity signal is processed by a computer and the zero-crossing rate is counted. The velocity of the nanoparticles can be determined from its relationship to zero-crossing rate. The results show that the nanoparticles exhibit features of flowing nanofluids, and when the average velocity of the nanofluids is 53.4 mm/s, the average velocity of the nanoparticles is 51.8 ± 5.1 mm/s. (authors)

[en] Micro-plasma and shock waves in the physiological saline produced by a Q-switched pulse YAG laser with nearby optical breakdown threshold energy are investigated by using optical shadowing exploring method, and a series of optical shadow graphs of micro-plasma and shock waves versus the incident laser energy and the delay time are obtained. Influence of mechanical action of shock waves for the high-power pulse laser on the ophthalmic treatment is discussed

[en] A Q-switched YAG laser is used to act repeatedly upon a charge-coupled devices (CCD) having metal-oxide-semiconductor structure, and plasmas in the process are investigated by a Mach-Zehnder interferometer. According to the production and development of the plasmas, the damage mechanism of the optoelectronic device is analyzed