Observation of stimulated Raman scattering in Y3Al5O12 single crystals and nanocrystalline ceramics and in these materials activated with laser ions Nd3+ and Yb3+

High-order Raman parametric generation was excited in the visible and near-IR regions on the Stokes and anti-Stokes lines of Y₃Al₅O₁₂ single crystals and nanocrystalline ceramics. All generation components, as well as the χ⁽³⁾-active vibrational modes of these materials, were identified. In connection with the extensive use of the Nd³⁺-and Yb³⁺-doped Y₃Al₅O₁₂ crystals and, in recent years, nanocrystalline Y₃Al₅O₁₂: Nd³⁺ ceramics in laser physics and quantum electronics, the applied aspect of the observed nonlinear properties of these materials is outlined.     

In situ Raman spectroscopy of annealed diamondlike carbon-metal composite films

Diamondlike carbon films and diamondlike carbon-metal composite films may provide increased component reliability, decreased fuel consumption, decreased noise/vibration/harshness (NVH), and decreased lubricant use in next generation automotive components. Raman spectra were obtained for diamondlike carbon, diamondlike carbon-platinum composite films, and diamondlike carbon-gold composite films, which were annealed to a temperature of 523 °C. The Raman spectra for these films were fitted using a two-Gaussian function. The variation of the G-peak position, the D-peak position, and the I_D/I_G ratio was examined as a function of temperature. The unalloyed diamondlike carbon film demonstrated greater thermal stability than the diamondlike carbon-noble metal composite films. These results suggest that the operating temperatures of the diamondlike carbon-coated automotive components must be kept under careful consideration.     

Evaluation of cavitation/corrosion synergy of the Cr3C2-25NiCr coating deposited by HVOF process

Wear processes are always present in components exposed to different work situations. Hydraulic turbines in electric power generation and ship propellers are good examples of components subject to wear and corrosion. One way to protect these components, for example, is the deposition of coatings by thermal spray processes. Indeed, there are several wear or corrosion mechanisms acting simultaneously, and the validation of the mechanisms separately, is not the best way to select the better material. When materials have passivation as protective mechanism against corrosion, the mass loss due erosion can affect the materials selection. This paper study the combined effect of the corrosion on the cavitation mass loss, as well as, the cavitation mass loss influence on the corrosion properties of a chromium carbide Cr₃C₂-25NiCr coating. Despite of the modification of the erosion mechanism on the cavitated samples under 3,5% NaCl solution, the volume loss did not show any significant alteration. Cavitation mass loss increase the corrosion process, reducing significantly the corrosion potential and raising the corrosion current. It was observed that the cavitation of the Cr₃C₂-25NiCr HVOF coating influences much more the corrosion kinetics, than the corrosion affects the cavitation resistance.     

A generalized Ginzburg-Landau approach to second harmonic generation

We develop a generalized Ginzburg-Landau theory for second harmonic generation (SHG) in magnets by expanding the free energy in terms of the order parameter in the magnetic phase and the susceptibility tensor in the corresponding high-temperature phase. The non-zero components of the SHG susceptibility in the ordered phase are derived from the symmetries of the susceptibility tensor in the high-temperature phase and the symmetry of the order parameter. In this derivation, the dependence of the SHG susceptibility on the order parameter follows naturally, and therefore its nonreciprocal optical properties. We examine this phenomenology for the magnetoelectric compound Cr₂O₃ as well as for the ferroelectromagnet YMnO₃. Received 27 August 1999     

The Effect of Flow Ratio between Elements of Groups III and V on the Structure and Properties of InGaAs Layers Grown by Low-Temperature Molecular-Beam Epitaxy

InGaAs layers grown by low-temperature molecular-beam epitaxy on InP substrates at variable flow ratios between elements of groups III and V are investigated. Layers with a defect structure and low electrophysical parameters are shown to grow with an excess of the components of group III. Growth with high As flows gives rise to trapping of excess arsenic and generation of point defects (As_III antistructural defects and V_III vacancies). High-quality InGaAs layers at low growth temperatures are produced under near-stoichiometric conditions (V/III = 1–4).     

Coherent optical harmonic generation in rat-tail tendon

Measurements of the angular divergence of optical second harmonic generation in rat-tail tendon reveal a very narrow forward peak. This implies the existence of coherent order and, together with the demonstration of nonlinear susceptibility components d₃₃ and d₃₂, confirms prior indications that the tendon is polar. Some biological consequences of this polarity are considered.     

Temporal and spatial TaO emission generated from UV laser ablation of Ta and Ta2O5 in oxygen ambient

2 O₅ targets in oxygen ambient are presented. Line assignments indicate the presence of the excited Ta(I), Ta(II), and TaO in the plume. At higher oxygen pressure, a single peak appears in the TaO emission spectrum from the laser ablation of Ta while two peaks corresponding to a fast and a slow component of TaO emission are observed from the laser ablation of the Ta₂O₅ target by time-resolved emission spectroscopy. The delay times after laser pulse corresponding to two components of TaO emission from the laser ablation of Ta₂O₅ have been investigated as a function of oxygen pressure, laser fluence, and observation distance from the target surface. The two components of TaO emission could be attributed to different pathways for the generation of excited TaO molecules. A blast wave model is proposed to describe the behavior of the excited TaO in the plume of laser ablation of Ta₂O₅. Received: 1 February 1997/Accepted: 12 March 1997     

Reconstruction of the coordinate dependences of quadratic susceptibility tensor \hat \chi ^{(2)} (z, ω1 ± ω2; ω1, ±ω2) components for the one-dimensionally inhomogeneous absorbing medium

A method for the unambiguous reconstruction of the spatial profiles of all components (except for ?? _zzz ) of the quadratic susceptibility complex tensor {ie165-2} (z, ??₁ + ??₂; ??₁, ??₂), which is responsible for the sumfrequency generation in a one-dimensionally inhomogeneous plate is proposed and proven for the first time. Such reconstruction is possible if the symmetry of the medium provides the diagonal character of the linear permittivity tensor {ie165-3} (z, ??). The procedure involves the measurement of the complex amplitude of the new wave with the frequency ??₁ + ??₂ that is reflected from the plate for a certain interval of the angles of incidence of the wave with the frequency ??₂. The reflected wave results from the nonlinear interaction of the wave with frequency ??₂ and the wave with frequency ??₁ that exhibits the normal incidence. A similar approach can be used to determine the profiles of the components of the quadratic susceptibility tensor {ie165-4}(z, ??₁ ? ??₂; ??₁, ? ??₂), which is responsible for the difference-frequency generation.     

Origin of salt mixtures and mixed salts in atmospheric particulate matter

The atmospheric particulate matter contains components of natural and anthropogenic origin, some of them are sulphates and nitrates. Considering the usual occurrence of many ions in the atmosphere and the presence of water, the generation of salt mixtures and mixed salts is possible as a consequence of dissolution–precipitation processes within water droplets, e.g., in fog or haze. This contribution presents the Raman spectroscopic study of the sodium–potassium nitrate system, which generates a salt mixture of both compounds. A phase transition of a KNO₃ crystal within a single solution droplet was observed. Additionally, we postulate the atmospheric generation of the mixed salt Na₃(NO₃)(SO₄)·H₂O (darapskite) by dissolution–precipitation processes, because Na⁺, SO₄^2–, and NO₃^– can be usually found in the atmosphere. The polarized Raman spectra of synthetic darapskite are reported. Copyright © 2011 John Wiley & Sons, Ltd.     

Generation of a wide discrete visible spectrum in a frequency-doubling optical fiber

We describe some special features of frequency doubling in a Ge-doped SiO₂ optical fiber. The generation of a multi-frequency visible spectrum in a single short fiber pumped with 1.06 µm radiation is demonstrated. This effect is the result of an interplay between the processes of frequency doubling and third-order nonlinear frequency mixing. Most of the new components coincide with the characteristic stimulated four-wave-mixing spectrum of the fiber, although the power of the internally generated 0.532 µm pump was more than an order of magnitude below the respective thresholds.     

Frequency conversion in novel materials and its application to high resolution gas sensing

We have constructed a compact room-temperature mid-infrared spectrometer and gas sensor, based on quasi-phase matched difference-frequency generation in periodically poled ferroelectric crystals of the KTiOPO₄ family, namely: KTiOPO₄, KTiOAsO₄ and RbTiOAsO₄. The wide tunabilty of the spectrometer (3.1–3.75 μm) enables us to cover an entire vibrational band of gases such as methane and nitrous oxide. The high spectral resolution (1 MHz) is used to investigate the spectral profile of the hyperfine components of a single rotational transition. The sensitivity of the described spectrometer is 75 parts per million. Applications of this technology include the detection of polluting or toxic gases, biomedical sensing, atmospheric research, volcanic monitoring and industrial process control.     

Quasi-phase matching in LiNbO3 using nonlinear coefficients in the XY plane

We report quasi-phase-matched second-harmonic generation in periodically poled lithium niobate (PPLN), where both fundamental and second-harmonic waves are ordinary waves. It provides a lower-limit value for d₂₂ of 1.1 pm/V. The measured temperature and wavelength bandwidth of the second-harmonic signal are in good agreement with the theoretical predictions. Since the d₂₂=d_YYY nonlinear coefficient of LiNbO₃ changes its sign as a result of electric field periodic poling along the Z direction, we deduce that all tensor components of the second-order susceptibility χ⁽²⁾ of trigonal 3m crystals are reversed, thereby expanding the quasi-phase-matching possibilities in these crystals. Furthermore, it enables the realization of all-optical processes based on the nonlinear coefficients in the XY plane, such as all-optical polarization rotation in PPLN, as well as multipartite entanglement experiments based on simultaneous phase matching using different elements of χ⁽²⁾ in a single LiNbO₃ crystal. PACS 42.65.-k; 42.65.Ky; 42.65.Lm     

Dibaryon Concept for Short-Range 2N and 3N Forces: Consequences for Hadronic and Nuclear Physics

The short-range aspects of 2N and 3N nuclear interactions are considered in light of numerous novel experimental data obtained in JLab, BNL, Mainz, etc. Many of these new experimental results contradict strongly to the traditional models for short-range (or high-momentum) components of nuclear forces and therefore require a novel understanding within new models alternative to the traditional (one-boson-exchange) ones. At the NN distances r _{N N} < 1 fm the nucleon quark cores get overlapped with each other and thus the generation of the common six-quark bag is very likely. So, the dibaryon concept considers the generation of the intermediate six-quark bag dressed with meson (predominantly the scalar-isoscalar σ-meson) clouds as a driving mechanism for short-range nuclear force. Numerous predictions of the above dibaryon model are considered in the paper.     

Nonlinear optical microscopy for drug delivery monitoring and cancer tissue imaging

A multimodal nonlinear optical microscope that combines coherent anti‐Stokes Raman scattering (CARS), two‐photon excitation fluorescence (TPEF), second‐harmonic generation (SHG) and sum‐frequency generation (SFG) was developed and applied to image breast cancer tissue and MCF‐7 cells as well as monitoring anticancer drug delivery in live cells. TPEF imaging showed that drugs are preferentially localized in the cytoplasm and the nuclear envelope in resistant cells. Moreover, the extracellular matrix was observed by TPEF signals arising from elastin's autofluorescence and SHG signals from collagen fibrils in breast tissue sections. Additionally, CARS signals arising from proteins and (PO₂)⁻ allowed identification of tumors. Label‐free imaging with chemical contrast of significant components of cancer cells and tissue suggests the potential of multimodal nonlinear optical microscopy for early detection and diagnosis of cancer. Copyright © 2010 John Wiley & Sons, Ltd.     

Theory of a waveguide laser

The role of diffusion of the components of the gas mixture is the generation mechanism of a waveguide CO₂ laser is analyzed. A method is proposed for reducing the multicomponent problem of linear diffusion with dissipation to a one-component problem. The superposition of relaxation modes for a cylindrical waveguide is considered. The diffusion contribution to the loss of electromagnetic energy is estimated for the case of the field hybrid mode EH₁₁ of a dielectric waveguide. The rapid increase in the loss for a SiO₂ waveguide tube and the observation of the filtration properties of the laser in conditions when the diffusion is taken into account are noted.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 17–21, July, 1975.     

Using of sonochemically prepared components for vapor phase growing of SbI3·3S8

The using of sonochemically prepared components for growth of SbI₃·3S₈ single crystals from the vapor phase is presented for the first time. The good optical quality of the obtained crystals is important because this material is valuable for optoelectronics due to its non-linear optical properties. The products were characterized by using techniques such as X-ray crystallography, powder X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, high-resolution transmission electron microscopy, selected area electron diffraction, optical diffuse reflection spectroscopy and optical transmittance spectroscopy. The direct and indirect forbidden energy gaps of SbI₃·3S₈ illuminated with plane polarized light with electric field parallel and perpendicular to the c-axis of the crystal have been determined. The second harmonic generation of light in the grown crystals was observed.     

Interface trap-induced negative differential resistance in nMOSFET with floating source

Interface trap can act as the generation center in device to induce a very weak generation current. We observed the negative differential resistance NDR of this generation current I_D in nMOSFET with the floating source. It originates from that the generation function of interface trap is enabled and then is shut down in turn as increasing the drain voltage. This change relies on the interaction among the interface trap energy-level and the electron's Fermi-levels of drain and source under the floating source condition. It is found that the peak-to-valley ratio of I_D is beyond 30.     

Beryllium Silicate,Be2SiO4 (phenakite) – a Novel Trigonal SRS‐Active Crystal

In single crystals of the beryllium silicate Be₂SiO₄ with trigonal symmetry , known also as the mineral phenakite, χ⁽³⁾‐nonlinear lasing by stimulated Raman scattering (SRS) is investigated. All observed Stokes and anti‐Stokes lasing components are identified and ascribed to a single SRS‐promoting vibration mode with ω_SRS ≈876 cm⁻¹. With picosecond single‐wavelength pumping at one micrometer the generation of an octave‐spanning Stokes and anti‐Stokes comb is observed.     

Ultrafast processes of photoinduced charge and energy transfer in nanostructural fullerene-metal films

The primary stages of photoinduced processes in tin-doped C₆₀ fullerene films have been studied using a femtosecond pump-probe technique with 150-fs laser excitation pulses (λ = 400 nm) and differential transmission and reflection probing in the 1100–1700 nm range. The relaxation dynamics strongly depends both on the metal-to-fullerene ratio in the film and on the mutual distribution (packing) of components in the nanocomposite material. The observed response signal dynamics is related to features in the charge carrier generation, energy transfer between fullerene molecules, and charge transport between metal and fullerene.     

Determination of the spatial dependence of the complex components of the tensor \hat \chi ^{(2)} (z, ω 1 + ω 2; ω 1, ω 2) of a medium with one-dimensional inhomogeneity using a biharmonic wave

It is proven that the spatial profiles of different components of the complex quadratic susceptibility tensor $\hat \chi ^{(2)}$ (z,?? ₁+?? ₂; ?? ₁, ?? ₂), which is responsible for the generation of sum-frequency wave in a plate with one-dimensional inhomogeneity, can be reconstructed unambiguously. A reconstruction technique is proposed. To implement it, one has to direct a plane biharmonic wave with monochromatic components at frequencies ?? ₁ and ?? ₂ onto a plate and measure (in some range of the angles of incidence) the complex amplitude of the sum-frequency wave reflected from the plate. Changing the plane of incidence of the initial wave and (or) the polarization of its monochromatic components, one can determine the coordinate dependences for more than half of the components of $\hat \chi ^{(2)}$ (z,?? ₁+?? ₂; ?? ₁, ?? ₂). This reconstruction can be performed if the symmetry of the plate medium provides a diagonal form for its linear permittivity tensor. The technique proposed implies measurement of the intensities of the sum-frequency waves generated under special conditions using an auxiliary reference plate; this approach allows one to do without complex phase measurements.