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Forward stimulated Raman scattering and backward stimulated Raman scattering (BSRS) are measured when an intense 532 nm nanosecond pulsed laser is focused into water and heavy water. The investigation reveals a significant observation: the formation of the ice VII structure exclusively occurs in the backward direction when optical breakdown takes place, provided that the input energy falls below 90 mJ for liquid water or 75 mJ for heavy water. This phase transition is attributed to secondary shock compression, which comes from energy transfer and compression between the BSRS in plasmas with the pump laser. The optical breakdown experiment under pre-pressure reveals that the shock compression in the back direction is approximately 2.3 times that of the forward direction. This research is useful for shock compression and dynamics in plasmas. [ABSTRACT FROM AUTHOR]

Although shock experiments are traditionally performed in large facilities, tabletop experiments that provide convenient high-throughput shock testing have been growing in importance. Here, we describe tabletop experiments using a shock compression microscope that features a pulsed 0–6 km/s laser flyer plate launcher and a photon Doppler velocimeter. We also describe methods to mass-produce flyer plates and targets to achieve high throughput. We explain how to condition a laser beam to launch flyers that provide reproducible short-rise time impacts with minimal tilt, and we present a number of applications including measuring shock propagation in nanoporous media, a simple way to describe shock wave energy absorption, the use of photoemissive probes such as organic dyes or quantum dots to study shocked inhomogeneous media, the development of an apparatus to measure optical absorption in shocked media, methods to study and measure the temperature of shocked energetic materials in the form of plastic-bonded explosives and in a form that allows us to observe hot spots in real time, and studies of the shocked interface between a metal fuel and a ceramic oxidizer. Finally, a brief perspective is presented describing new possibilities for future research of a diverse set of applications including the chemistry of shocked water and biological systems, dense plasmas, and the use of laser-launched flyer plates as surrogates for hypersonic vehicles. [ABSTRACT FROM AUTHOR]

Stimulated Raman scattering (SRS) not only expands the spectral range of stimulated emission but also presents a way to delve into the intricate microscopic dynamics of matter. In this manuscript, SRS of O–O and O–H stretching vibrations in H2O–H2O2 solution is measured using 532 nm Nd:YAG laser. SRS peak intensities of O–O and O–H stretches are observed to engage in a competitive process, depending on the coupling direction of the excess electrons, which is determined by the recombination rate of H2O2 and H2O under laser-induced breakdown. Notably, a high-order (fifth order) SRS peak originating from H2O2 is detected, attributable to the Raman-active enhancement caused by surplus electrons and the amplification of vibration energy resulting from shockwaves. This experiment holds potential for advancing multi-wavelength selective regulation in terms of its contributions. [ABSTRACT FROM AUTHOR]

Stimulated Raman scattering (SRS) of OH stretching vibrations in pure water and dilute ethanol–water solutions under different pump laser energies has been investigated using Nd:YAG laser. Two characteristic peaks at about 3252 and 3390 cm−1 are observed in mixture solutions, indicating the formation of strong and weak hydrogen bonds in water. A new shoulder peak at 3350 cm−1 appears in the mixture solutions at high laser energy due to the enhancement of hydrogen bond structure of water molecules. Simultaneously, the normalized SRS intensity of mixture solutions is higher than that of pure water at the same laser energy. These results indicate that SRS of water molecules is enhanced in dilute ethanol–water solutions. We propose that the mechanism is the reduction of the laser breakdown threshold of liquid water via ethanol, resulting in a strong nanoshock wave, thereby enhancing the SRS of water. [ABSTRACT FROM AUTHOR]

Stimulated Raman scattering (SRS) and spontaneous Raman spectra are both used here to study the hydrogen bond (HB) structure and kinetics of methanol (MeOH)–water mixtures in different volume ratios. We have found that when the volume fraction of MeOH ranges from 0 to 0.27, the HB structure of water molecules is enhanced, originating from the cooperation of the hydroxyl-enhanced HBs in liquid water and the formation of an ice-like structure around the methyl groups. However, when the volume fraction of MeOH goes beyond 0.27, the main Raman peak of water becomes very weak and even disappeared, which reveals that the HB structure of liquid water is weakened. This weakening can be attributed to the H–H repulsion introduced by MeOH salvation derives. Furthermore, some HBs among water molecules are destroyed at a high MeOH volume fraction (0.7) based on the change of C–H vibrations. [ABSTRACT FROM AUTHOR]

Liquid water is a complex system consisting of ice‐like and quartz‐like structure based on the classic two‐state model. Although lots of theoretical work have been developed about this model, the experimental evidences are still needed. Herein, a 355‐nm pulse laser is employed to excite stimulated Raman scattering (SRS) of liquid water both in bulk and on surface, with the generation of shockwave‐induced dynamic high pressure. Two characteristic features Raman peaks of both spontaneous Raman and SRS indicate the coexistence of two structures in localized water area. The ice‐like structure corresponds to ice Ih phase under the presented conditions, because the pressure dependence behavior of Raman shift agree well with the anomaly of diffusion coefficient of ice Ih phase, when the shock wave‐induced dynamic high pressure forms. Two structures show different pressure‐dependent behaviors based on the SRS results; meanwhile, the distribution of two structures is different in bulk and on surface water. [ABSTRACT FROM AUTHOR]

Forward stimulated Raman scattering in pure water and H2O2–H2O mixture solutions are investigated under different pump laser energies. Three characteristic peaks are observed in mixture solutions due to the enhancement of hydrogen bonds (H‐bonds) structure of water molecules by H2O2. Simultaneously, stimulated Raman scattering lines indicate that high‐pressure ice‐phase is formed in mixture solutions, which is attributed to the reduction of the laser breakdown threshold of liquid water by H2O2, resulting in a strong dynamic high pressure. [ABSTRACT FROM AUTHOR]

Person re-identification is a challenging task due to its large variations on pedestrian pose, camera view, lighting and background. To solve pedestrian misalignment problem, most of the existing works assume that the pedestrian images are horizontally aligned so that the extracted features can be compared correspondingly. However, such assumption is not necessarily true in reality because the pedestrians may be misaligned vertically. To address the misalignment problem, we propose a dynamic locally connected (DLC) layer based on convolutional neural network (CNN). We use human parsing tool to get parsing results of pedestrian images, then map the results to the last feature map of our CNN. By doing this, proposed model is able to locate the human body parts dynamically within DLC layer, thus leads to a more accurate matching on local features. Furthermore, we adopt pre-training with two-step fine-tuning strategy on the small person re-identification datasets, which again boost the model performance. According to the experiments, proposed model achieves competitive results among the state-of-the-art models on four popular person re-identification datasets. [ABSTRACT FROM AUTHOR]

Stimulated Raman scattering (SRS) in H2O2–H2O mixture solutions are obtained in forward and backward directions. Characteristic features peaks related to OH stretching vibrations of water are the appearance of three enhancement peaks in both directions. Simultaneously, the low‐wavenumber SRS peaks in water at 840 and 1,700 cm−1 are enhanced. The mechanism of enhancement is attributed to excess electron‐enhanced Raman scattering. The electron‐enhanced process is also discussed. [ABSTRACT FROM AUTHOR]

Stimulated Raman scattering (SRS) spectra of the OH stretching vibrations of pure water and 2‐nm Si quantum dots (Si QDs) water solution have been investigated under different pump laser energies. Simultaneously, we have studied the spontaneous Raman spectra of pure water and Si QDs water solution at room temperature and atmospheric pressure. The results show that SRS intensity of Si QDs water solution is an order of magnitude higher than that of pure water at the same laser energy, which indicates that Si QDs enhance the SRS intensity of water molecules. The QDs enhancement SRS mechanism is attributed to the increase of third‐order nonlinear Raman susceptibility from the electric fields induced by the exciton effect of Si QDs. Stimulated Raman scattering (SRS) intensity of Si quantum dots (Si QDs) water solution is an order of magnitude higher than that of pure water.The increase of the third‐order nonlinear polarizability in water molecules is induced from the exciton effect of Si QDs.Due to Si QDs having a self‐absorption effect, the most obvious enhancement effect appears at laser energy of 110 mJ. [ABSTRACT FROM AUTHOR]