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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]

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]

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]

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]

Stimulated Raman scattering (SRS) of liquid water and heavy water have been investigated using Nd:YAG laser. The SRS spectra of liquid heavy water indicate that ice–VII and ice–VIII structures are formed by shock-induced compression (SIC) in forward and backward directions, respectively. Simultaneously, the SRS spectra reveal of liquid water that only ice-VII structure is formed in the backward direction. The difference in ice structures formed by SIC in liquid water and heavy water could be attributed to the effect of the hydrogen bond quantum nature with H + . SRS spectra of 2 M NaOH water solution with ice–VII and ice-VIII structures have been successfully obtained in forward and backward, respectively, as OH − greatly reduce the quantum nature of hydrogen bonds by neutralizing H + in water. The hydrogen bond quantum nature is important for understanding isotope calibration test structure and isotopic effect. [ABSTRACT FROM AUTHOR]

Stimulated Raman scattering (SRS) of water molecules excited by 532 nm laser is greatly enhanced by the application of CW (continuous-wave) seeding laser with 650 nm. When the CW laser power is 1 mW, the normalized SRS intensity of O–H stretching vibration at 3405 cm−1 is increased by ten orders of magnitude. Two new lower frequency shoulder peaks are also observed after adding CW seeding laser, which shift to the low-wavenumber due to the pulse heating of water molecules in the laser focused volume. The CW seeding laser not only lowers the threshold of SRS, but also increases the intensity of SRS. The mechanism of enhancement is attributed to the frequency difference between pump laser (532 nm) and CW seeding laser (650 nm) matching the O–H stretching vibrational frequency of water molecule, which provides the possibility of using resonance methods to enhance weak Raman vibration modes. • CW seeding laser lowers the threshold of SRS, but increases the intensity of SRS. • Frequency difference of two lasers matches O–H stretching vibrational frequency. • Resonance effect enhances Raman vibration modes in water. [ABSTRACT FROM AUTHOR]