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Driven by applications in chemical sensing, biological imaging and material characterisation, Raman spectroscopies are attracting growing interest from a variety of scientific disciplines. The Raman effect originates from the inelastic scattering of light, and it can directly probe vibration/rotational-vibration states in molecules and materials. Despite numerous advantages over infrared spectroscopy, spontaneous Raman scattering is very weak, and consequently, a variety of enhanced Raman spectroscopic techniques have emerged. These techniques include stimulated Raman scattering and coherent anti-Stokes Raman scattering, as well as surface- and tip-enhanced Raman scattering spectroscopies. The present review provides the reader with an understanding of the fundamental physics that govern the Raman effect and its advantages, limitations and applications. The review also highlights the key experimental considerations for implementing the main experimental Raman spectroscopic techniques. The relevant data analysis methods and some of the most recent advances related to the Raman effect are finally presented. This review constitutes a practical introduction to the science of Raman spectroscopy; it also highlights recent and promising directions of future research developments.

The coherent Patterson function, derived from the coherent scattering intensities from N atoms, can be described as an auto-holographic image, i.e., the superposition of N -holographic images in which each atom serves as the source of a different reference wave, and as a mathematical graph of the unknown structure. These insights indicate that the unknown structure is significantly over-determined by the inherent information content in a Patterson function by a factor of ( N − 1)/2 (for non-degenerate structures), independent of dimensionality. However, we also show that the ability to resolve the distinct features in the Patterson function depends strongly on details of the experimental design (data range, sampling frequency, and dimensionality). This re-interpretation suggests that the coherent Patterson function provides a natural context for describing the information content in coherent scattering, reveals that there is no inherent phase problem for coherently illuminated pointwise structures, and enables the design of an algorithm which retrieves the structure directly from the Patterson function, without using error metric minimization.

1.4418 hardened stainless steel (SS) is widely used in mechanical engineering because of its high functional properties. They can also be enhanced by procuring improvements in the state of the surface layer (SL) and, above all, in the factors of its strengthening, among others the average size of coherent scattering regions (ASCSR), dislocation density (DD), residual stresses (RS) of first and second orders, and relative micro-deformations of the crystal lattice (RMCL). This study investigates the effect of cutting speed ( v c ) ranging from 100 to 250 m/min and feed rate ( f ) ranging from 0.005 to 0.25 mm/rev on the indicators of SL condition after finish turning the steel tested. A reduction in ASCSR values below 8 nm was obtained for v c  = 100–135 m/min, while an increase of ~ 20% was obtained for 180–250 m/min and with the f ranging from 0.2 to 0.25 mm/rev. An increase in RMCL of ~ 90% was registered for v c  = 170–230 m/min and f  = 0.2–0.25 mm/rev. A decrease in DD below 10 9  cm −2 was obtained for v c  = 180–250 m/min and its ~ 25% increase for v c  = 100–135 m/min. A high correlation between ASCSR and DD was shown. In the deformed material, the dislocation’s resistance to motion increases in proportion to the increase in its density. A high linear correlation coefficient in the range of 0.8–0.9 is found between ASCSR, DD, and first-order RS on the one hand, and Sa and Sz surface texture parameters, which are used in the industry to assess product quality, on the other. Additionally, the effect of plastic side flow (PSF) was observed and described. When machining with v c  = 119 m/min and f  = 0.22 mm/rev, the intense plastic deformation of the material causes outflow and shearing of the surface micro-hills. Favorable compressive stresses (below − 100 MPa) were registered in the range of v c  = 225–250 m/min at f  = 0.005–0.05 m/rev and 0.2–0.25 mm/rev, as well as v c  = 115–180 m/min and f  = 0.05–0.17 mm/rev. The study proved the existence of a relationship between the cutting parameters and indicators of the thin crystalline structure of SL. This means that by proper controlling of these parameters, it is possible to obtain such a state of the SL workpiece, which will ensure its long-term use.

Neutron–antineutron oscillation (nnbar-osc) is a baryon number-violating process and a sensitive probe for physics beyond the standard model. Ultra-cold neutrons (UCNs) are attractive for nnbar-osc searches because of their long storage time, but earlier analyses indicated that phase shifts on wall reflection differ for neutrons and antineutrons, leading to severe decoherence and a loss of sensitivity. Herein, we revisit this problem by numerically solving the time-dependent Schrödinger equation for the two-component n/nbar wave function, explicitly including wall interactions. We show that decoherence can be strongly suppressed by selecting a wall material whose neutron and antineutron optical potentials are nearly equal. Using coherent scattering length data and estimates for antineutrons, we identify a Ni–Al alloy composition that matches the potentials within a few percent while providing a high absolute value, enabling long UCN storage. With such a bottle and an improved UCN source, the sensitivity could reach an oscillation period τnnbar of the order 1010 s, covering most of the range predicted with certain grand unified models. This approach revives the feasibility of high-sensitivity nnbar-osc searches using stored UCNs and offers a clear path to probe baryon number violation far beyond existing limits.

Stimulated Raman scattering (SRS) microscopy has gained popularity in recent years due to its linearity to molecule concentration and laser intensity, and to the lack of the nonresonant background that affects its analogous technique, coherent anti-Stokes Raman scattering. However, SRS is not a background-free technique. In fact, there are other optical processes - nonlinear transient scattering and nonlinear transient absorption - that can be detrimental to the contrast and sensitivity of SRS microscopy. In this review, we provide a description of these competing optical processes and present an up-to-date description of current solutions to minimize their effect on SRS measurements.

Coherent narrow resonances in a homogeneously broadened contour of selective reflection from the interface between a cell window and high-density atomic rubidium vapor, where the dipole broadening greatly exceeds the Doppler width of the unresolved components of rubidium D 2 line, are discussed. The formation of coherent resonances is caused by the coherent scattering of probe and pump optical fields from the oscillations of populations of the ground and excited states of atoms at the beat frequency. The width of each resonance depends on the population difference decay rate. Within a simple model conditions are found for observing resonances with a Lorentzian spectral profile. The experimentally recorded coherent resonances are described by a Lorentz function with fitting parameters in the form of amplitude, width, and spectral baseline. In the limit of zero optical saturation the measured half-width of a coherent resonance (HWHM) γ res /2π is about 52 MHz, which greatly exceeds the radiative decay rate of the rubidium excited state 5 P 3/2 .

Quantitative phase analysis is one of the major applications of X-ray powder diffraction. The essential principle of quantitative phase analysis is that the diffraction intensity of a component phase in a mixture is proportional to its abundance. Nevertheless, the diffraction intensities of the component phases cannot be compared with each other directly since the coherent scattering power per unit cell (or chemical formula) of each component phase is usually different. The coherent scattering power per unit cell of a crystal is well represented by the sum of the squared structure factors, which cannot be calculated directly when the crystal structure data is unavailable. Presented here is a way to approximate the coherent scattering power per unit cell based solely on the unit cell parameters and the chemical contents. This approximation is useful when the atomic coordinates for one or more of the phases in a sample are unavailable. An assessment of the accuracy of the approximation is presented. This assessment indicates that the approximation will likely be within 10% when X-ray powder diffraction data is collected over a sufficient portion of the measurable pattern.

Significance: Coherent Raman scattering (CRS) microscopy is an optical imaging technique with capabilities that could benefit a broad range of biomedical research studies. Aim: We reflect on the birth, rapid rise, and inescapable growing pains of the technique and look back on nearly four decades of developments to examine where the CRS imaging approach might be headed in the next decade to come. Approach: We provide a brief historical account of CRS microscopy, followed by a discussion of the challenges to disseminate the technique to a larger audience. We then highlight recent progress in expanding the capabilities of the CRS microscope and assess its current appeal as a practical imaging tool. Results: New developments in Raman tagging have improved the specificity and sensitivity of the CRS technique. In addition, technical advances have led to CRS microscopes that can capture hyperspectral data cubes at practical acquisition times. These improvements have broadened the application space of the technique. Conclusion: The technical performance of the CRS microscope has improved dramatically since its inception, but these advances have not yet translated into a substantial user base beyond a strong core of enthusiasts. Nonetheless, new developments are poised to move the unique capabilities of the technique into the hands of more users.

Understanding the non-equilibrium structure formation of thin films is a fundamental challenge with important implications also for technical applications. The interplay between adsorption, desorption, and surface diffusion may result in the formation of nontrivial surface morphologies. X-ray photon correlation spectroscopy opens up new possibilities for understanding these processes. In this work, we perform in situ x-ray experiments in grazing incidence geometry to follow the growth of diindenoperylene thin films in real time, revealing details of the dynamics during molecular island formation. Comparison with simulations allows to extract dynamic and kinetic time scales. We observe time scales in the range of a few hundred seconds which occur mainly due to kinetics, i.e. island growth. Importantly, we can relate the observed heterogeneous behavior in dynamics to the number of open layers, revealing information about the change in the roughness, and the growth speed of each layer.

Coherent Raman scattering (CRS) processes, including both the coherent anti-Stokes Raman scattering and stimulated Raman scattering, have been utilized in state-of-the-art microscopy platforms for chemical imaging of biological samples. The key advantage of CRS microscopy over fluorescence microscopy is label-free, which is an attractive characteristic for modern biological and medical sciences. Besides, CRS has other advantages such as higher selectivity to metabolites, no photobleaching, and narrow peak width. These features have brought fast-growing attention to CRS microscopy in biological research. In this review article, we will first briefly introduce the history of CRS microscopy, and then explain the theoretical background of the CRS processes in detail using the classical approach. Next, we will cover major instrumentation techniques of CRS microscopy. Finally, we will enumerate examples of recent applications of CRS imaging in biological and medical sciences.