Analysis of the stimulated Raman effects in an anisotropic crystal KDP.
Stimulated Raman effects in anisotropic crystal potassium dihydrogen phosphate with Stokes generations
ANISOTROPIC MATERIAL↗
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Results for “RAMAN EFFECT”
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First-principles study of the magneto-Raman effect in van der Waals layered magnets
Magneto-Raman spectroscopy has been used to study spin-phonon coupling in two-dimensional (2D) magnets. Raman spectra of CrI 3 show a strong dependence on the magnetic order within a layer and between the layers. Here we carry out the first systematic theoretical investigation of the magneto-Raman effect in 2D magnets by performing density functional theory calculations and developing a generalized polarizability model. Our first-principles simulations well reproduce experimental Raman spectra of CrI 3 with different magnetic states. The model reveals how the change of spin orientation in each layer is coupled to the layer’s vibration to induce or eliminate the spin-dependent anti-symmetric off-diagonal terms in the Raman tensor for altering the selection rules. We also uncover that the correlation between phonon modes and magnetic orders is a universal phenomenon, which should exist in other phonon modes and 2D magnets. Our predictive simulations and modeling are expected to guide the research in 2D magnets.
36 MATERIALS SCIENCE↗
Giant magneto-optical Raman effect in a layered transition metal compound
Significance Raman scattering is a powerful technique to probe optical phonons in solids. It usually involves an electron-mediated three-step process, involving photon–electron, electron–phonon, and electron–photon interactions. In principle, manipulating electrons, for instance by applying a magnetic field, should affect Raman phonon intensity, yet there is no direct experimental measurement to demonstrate this. In this work we report the first realization to our knowledge of the idea in a prototype material, MoS 2 . From monolayer and bilayer to bulk MoS 2 we observe a dramatic modification of Raman phonon intensity induced by magnetic field. Such a giant magneto-optical effect appearing at a monoatomic layer level and its technological implications for magnetic-optical devices should inspire a new branch of inelastic light scattering.
36 MATERIALS SCIENCE↗
Raman effect, structural and dielectric properties of sol-gel synthesized polycrystalline GaFe{sub 1-x}Zr{sub x}O{sub 3} (0≤x≤0.15)
Polycrystalline ceramic samples of Zirconium (Zr)-doped GaFeO{sub 3} (GaFe{sub 1-x}Zr{sub x}O{sub 3}) were studied using powder X-ray diffraction, complex impedance spectroscopy and Raman spectroscopic measurements to understand the effect of Zr doping on the structural and dielectric properties. The samples with varying Zr content were prepared by Sol-Gel method. X-ray data analysis confirmed the formation of single phase material without formation of any secondary phases and all are crystallized in Pc2{sub 1}n orthorhombic symmetry. Rietveld refinement of the X-ray data suggested an increase in the lattice constants due to size effect and decreases on x = 0.15 due to the effect of change in interplanner spacing. Impedance studies on the samples showed that the dielectric constant increases while loss tangent decrease as the Zr content increases. Raman scattering on GaFe{sub 1-x}Zr{sub x}O{sub 3} (x = 0, 0.05, 0.10, & 0.15) used to understand the composition dependence on phonon modes at room temperature. On Zr doping, Raman modes frequencies shifts to lower energies consistent with the X-ray data.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
On probing the outer planets with the Raman effect
The paper examines the feasibility of using the H2 rotational Raman spectrum to study the physical structure of the atmospheres of the outer planets. Computations of the strengths of the S(0) and S(1) lines are made for a wide range of physical conditions on the basis of a semi-infinite homogeneous pure H2 atmospheric model. Initial applications of the Raman probe technique to Jupiter and Uranus are reported.
Price, M. J.↗
Calculating the true line contour of the Raman effect based on the observable line contour
Calculation method for true profile of Raman lines
SPECTRAL LINE↗
Preventing Raman Lasing in High-Q WGM Resonators
A generic design has been conceived to suppress the Raman effect in whispering- gallery-mode (WGM) optical resonators that have high values of the resonance quality factor (Q). Although it is possible to exploit the Raman effect (even striving to maximize the Raman gain to obtain Raman lasing), the present innovation is intended to satisfy a need that arises in applications in which the Raman effect inhibits the realization of the full potential of WGM resonators as frequency-selection components. Heretofore, in such applications, it has been necessary to operate high-Q WGM resonators at unattractively low power levels to prevent Raman lasing. (The Raman-lasing thresholds of WGM optical resonators are very low and are approximately proportional to Q(sup -2)). Heretofore, two ways of preventing Raman lasting at high power levels have been known, but both entail significant disadvantages: A resonator can be designed so that the optical field is spread over a relatively large mode volume to bring the power density below the threshold. For any given combination of Q and power level, there is certain mode volume wherein Raman lasing does not start. Unfortunately, a resonator that has a large mode volume also has a high spectral density, which is undesirable in a typical photonic application. A resonator can be cooled to the temperature of liquid helium, where the Raman spectrum is narrower and, therefore, the Raman gain is lower. However, liquid-helium cooling is inconvenient. The present design overcomes these disadvantages, making it possible to operate a low-spectral-density (even a single-mode) WGM resonator at a relatively high power level at room temperature, without risk of Raman lasing.
Savchenkov, Anatoliy↗
Raman thermometry: Effective temperature of the nonuniform temperature field induced by a Gaussian laser
Raman spectroscopy is a widely applied analytical technique with numerous applications that is based on inelastic scattering of monochromatic light, which is typically provided by a laser. Irradiation of a sample by a laser beam is always accompanied by an increase in the sample temperature, which may be unwanted or may be beneficial for studying temperature-related effects and determining thermal parameters. This work reports analyses of the temperature field induced by a Gaussian laser to calculate the Raman scattered intensity related to each temperature value of the nonuniform field present on the sample. The effective temperature of the probed field, calculated as an average weighted by the laser intensity, is demonstrated to be about 70% of the maximum temperature irrespective of the absorption coefficient or the laser focus. Finally, using crystalline silicon as a model material, it is shown that this effective value closely approximates the temperature value identified from the thermally related peak shift.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
Electron and solid state physics
Electron and solid state physics - reflected light, Raman effects, solid and liquid optical properties, spectroscopy, Brillouin effects, and carbon dioxide laser
BRILLOUIN EFFECT↗
Effects of Raman scattering on the water-leaving radiance
The contribution of Raman scattering to the water-leaving radiance is examined using Monte Carlo simulations. Exit angle information is retained, allowing a comparison of different satellite viewing directions. Chlorophyll values of 0.0, 0.01, 0.1, and 1.0 mg Chl/cu m are simulated. Little directional variability is found, with the exception of the direct solar backscatter direction. The wavelength variability is greatest for low chlorophyll concentrations and is negligible for 1.0 mg Chl/cu m. At 550 nm the Raman contribution ranges from approximately 18% of the total water-leaving radiance for pure water to 3% for 1.0 mg Chl/cu m. At 440 nm the range is from 6% to 2%, indicating that Raman scattering will impact radiance ratios for ocean color satellite algorithms.
Waters, Kirk J.↗
Size effects in near-ultraviolet Raman spectra of few-nanometer-thick silicon-on-insulator nanofilms
We have fabricated Si-on-insulator (SOI) layers with a thickness h{sub 1} of a few nanometers and examined them by Raman spectroscopy with 363.8 nm excitation. We have found that phonon and electron confinement play important roles in SOI with h{sub 1} < 10 nm. We have confirmed that the first-order longitudinal optical phonon Raman band displays size-induced major homogeneous broadening due to phonon lifetime reduction as well as minor inhomogeneous broadening due to wave vector relaxation (WVR), both kinds of broadening being independent of temperature. Due to WVR, transverse acoustic (TA) phonons become Raman-active and give rise to a broad band in the range of 100–200 cm{sup −1}. Another broad band appeared at 200–400 cm{sup −1} in the spectrum of SOI is attributed to the superposition of 1st order Raman scattering on longitudinal acoustic phonons and 2nd order scattering on TA phonons. Suppression of resonance-assisted 2-nd order Raman bands in SOI spectra is explained by the electron-confinement-induced direct band gap enlargement compared to bulk Si, which is confirmed by SOI reflection spectra.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Near-octave lithium niobate soliton microcomb
Thin film lithium niobate (LN) is bringing renewed potential to the realm of integrated photonics. Its strong quadratic and cubic nonlinearities as well as wide transparency window are ideal for realizing on-chip self-referenced soliton microcombs. However, broadband Kerr cavity soliton generation in LN thin films remains challenging due to limited dispersion control and competition from strong stimulated Raman scattering (SRS). Here, we demonstrate the generation of soliton microcombs in LN thin films featuring broad spectral spans up to 4/5 octaves with the emission of dual dispersion waves (2/3 octaves apart) and sub-terahertz repetition rates (down to 335 GHz) by suppressing strong SRS. Numerical simulations based on coupled-mode equations that incorporate Raman effects further elucidate the soliton dynamics in this highly Raman-active material system.
Gong, Zheng (ORCID:0000000301704870)↗
A combined Raman lidar for low tropospheric studies
One of the main goals of laser sensing of the atmosphere was the development of techniques and facilities for remote determination of atmospheric meteorological and optical parameters. Of lidar techniques known at present the Raman-lidar technique occupies a specific place. On the one hand Raman lidar returns due to scattering on different molecular species are very simple for interpretation and for extracting the information on the atmospheric parameters sought, but, on the other hand, the performance of these techniques in a lidar facility is overburdened with some serious technical difficulties due to extremely low cross sections of Raman effect. Some results of investigations into this problem is presented which enables the construction of a combined Raman lidar capable of acquiring simultaneously the profiles of atmospheric temperature, humidity, and some optical characteristics in the ground atmospheric layer up to 1 km height. The operation of this system is briefly discussed.
Arshinov, Y. F.↗
Iterative Method to Obtain Raman Spectra of Organic Dyes by Their Chaotic Generation in Multiple-Scattering Media
An iterative method is developed to obtain vibrational spectra of laser organic dyes from their secondary radiation spectra in multiple-scattering media, which manifests as a result of coupled process of chaotic generation (CG) and stimulated Raman scattering (SRS). The developed method increases significantly the capability to detect weak Raman lines by using batch processing of a set of experimental SRS-CG spectra, which makes it possible to optimize the deconvolution of these spectra and to average vibrational spectra obtained from the set of experimental SRS-CG spectra. The method is tested on spectra of the SRS-CG laser dye pyrromethene 597 in a vesicular film. The obtained results agree well with Raman spectra calculated by the Hartree–Fock method.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Control of Charge Transfer in C60–ZnO Composite Under the Influence of UV Laser Radiation by the Methods of Raman Spectroscopy and Photoluminescence
Raman and photoluminescence spectra of nanostructured ZnO films with adsorbed C60 molecules were studied. The possibility of intensive C60–ZnO electronic coupling forming in this composite was investigated. It is shown that such an electron coupling can be significantly enhanced by irradiating the composite with high intensity UV laser radiation (λ = 325 nm).
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Fluorescence and Raman Spectroscopy of Doped Nanodiamonds
Raman and fluorescence spectroscopic techniques were used to study doped nanodiamonds synthesized at high pressure and high temperature (HPHT technique) and by chemical vapor deposition from the gas phase (CVD technique). For the CVD diamonds, a hundred-fold increase in fluorescence intensity of the silicon-vacancy centers normalized to the volume of the probe material was observed with an increase in synthesized diamond particle diameter from 150 to 300 nm. Graphitization temperature upon heating in the air significantly lower than for detonation nanodiamonds was found for the boron-doped HPHT nanodiamonds.
77 NANOSCIENCE AND NANOTECHNOLOGY↗