Showing papers on "Light scattering published in 1996"

An introduction to dynamics of colloids

Abstract: Brownian motion of non-interacting particles light scattering fundamental equations of motion hydrodynamics diffusion sedimentation critical phenomena phase separation kinetics. (part contents)

T-Matrix Computations of Light Scattering by Nonspherical Particles: A Review

Abstract: We review the current status of Waterman's T-matrix approach which is one of the most powerful and widely used tools for accurately computing light scattering by nonspherical particles, both single and composite, based on directly solving Maxwell's equations. Specifically, we discuss the analytical method for computing orientationally-averaged light-scattering characteristics for ensembles of nonspherical particles, the methods for overcoming the numerical instability in calculating the T matrix for single nonspherical particles with large size parameters and/or extreme geometries, and the superposition approach for computing light scattering by composite/aggregated particles. Our discussion is accompanied by multiple numerical examples demonstrating the capabilities of the T-matrix approach and showing effects of nonsphericity of simple convex particles (spheroids) on light scattering.

Spatially resolved absolute diffuse reflectance measurements for noninvasive determination of the optical scattering and absorption coefficients of biological tissue.

Abstract: The absorption and transport scattering coefficients of biological tissues determine the radial dependence of the diffuse reflectance that is due to a point source. A system is described for making remote measurements of spatially resolved absolute diffuse reflectance and hence noninvasive, noncontact estimates of the tissue optical properties. The system incorporated a laser source and a CCD camera. Deflection of the incident beam into the camera allowed characterization of the source for absolute reflectance measurements. It is shown that an often used solution of the diffusion equation cannot be applied for these measurements. Instead, a neural network, trained on the results of Monte Carlo simulations, was used to estimate the absorption and scattering coefficients from the reflectance data. Tests on tissue-simulating phantoms with transport scattering coefficients between 0.5 and 2.0 mm21 and absorption coefficients between 0.002 and 0.1 mm21 showed the rms errors of this technique to be 2.6% for the transport scattering coefficient and 14% for the absorption coefficients. The optical properties of bovine muscle, adipose, and liver tissue, as well as chicken muscle 1breast2, were also measured ex vivo at 633 and 751 nm. For muscle tissue it was found that the Monte Carlo simulation did not agree with experimental measurements of reflectance at distances less than 2 mm from the incident beam.

Chemical and size effects of hygroscopic aerosols on light scattering coefficients

Abstract: The extensive thermodynamic and optical properties recently reported [Tang and Munkelwitz, 1994a] for sulfate and nitrate solution droplets are incorporated into a visibility model for computing light scattering by hygroscopic aerosols. The following aerosol systems are considered : NH 4 HSO 4 , (NH 4 ) 2 SO 4 , (NH 4 ) 3 H(SO 4 ), NaHSO 4 , Na 2 SO 4 , NH 4 NO 3 , and NaNO 3 . In addition, H 2 SO 4 and NaCl are included to represent freshly formed sulfate and background sea-salt aerosols, respectively. Scattering coefficients, based on 1 μg dry salt per cubic meter of air, are calculated as a function of relative humidity for aerosols of various chemical compositions and lognormal size distributions. For a given size distribution the light scattered by aerosol particles per unit dry-salt mass concentration is only weakly dependent on chemical constituents of the hygroscopic sulfate and nitrate aerosols. Sulfuric acid and sodium chloride aerosols, however, are exceptions and scatter light more efficiently than all other inorganic salt aerosols considered in this study. Both internal and external mixtures exhibit similar light-scattering properties. Thus for common sulfate and nitrate aerosols, since the chemical effect is outweighed by the size effect, it follows that observed light scattering by the ambient aerosol can be approximated, within practical measurement uncertainties, by assuming the aerosol being an external mixture. This has a definite advantage for either visibility degradation or climatic impact modeling calculations, because relevant data are now available for external mixtures but only very scarce for internal mixtures.

Single Scattering Properties of Atmospheric Ice Crystals

Abstract: Simulations of scattering and polarization properties for randomly oriented polyhedral ice crystals are presented based on the geometric optics and the far-field diffraction approximation. Particle shapes range from various hexagonal symmetric particles to highly complex shaped deterministic and random fractals. All calculations are performed at a wavelength of 0.55 µm. Hexagonal symmetric particles show several narrow scattering peaks besides the well known 22° and 46° halos. Column-like ice crystals provide neutral points (NP) at larger scattering angles than plate-like ice crystals. The ranges of NPs for column-like and plate-like crystals are separated at a scattering angle of about 156°, which may allow a polarimetric distinction between these two crystal types. The effects of particle size are studied by applying observationally derived aspect-ratio parameterizations to the individual particle types. Differences in the asymmetry parameter versus size relations for column-like particle types...

Coagulation Rate Measurements of Colloidal Particles by Simultaneous Static and Dynamic Light Scattering

Abstract: In this work we study the kinetics of coagulation of monodisperse spherical colloids in aqueous suspension at the early stage of coagulation. We have performed the measurements on a multiangle static and dynamic light scattering instrument using a fiber-optics-based detection system which permits simultaneous time-resolved measurements at different angles. The absolute coagulation rate constants are determined from the change of the scattering light intensity as well as from the increase of the hydrodynamic radius at different angles. The combined evaluation of static and dynamic light scattering results permits the determination of coagulation rate constants without the explicit use of light scattering form factors for the aggregates. For different electrolytes fast coagulation rate constants were estimated. Stability curves were measured as a function of ionic strength using different particle concentrations.

Determination of the Quantum Yield for the Photochemical Generation of Hydroxyl Radicals in TiO2 Suspensions

Abstract: The generation of hydroxyl (•OH) radicals plays a key role in the heterogeneous photocatalytic degradation of organic pollutants in aqueous suspensions of TiO2. The quantum yield of this process is thus an important parameter; however, it is not easy to measure in a particulate system arising from problems caused by light scattering from the particles. In this work, a reliable method for the determination of the quantum yield of hydroxyl radical production in heterogeneous systems has been developed, based on measurements of •OH radical generation rates and the photon flux absorbed by TiO2 suspensions. In this procedure, a modified integrating sphere method was used to determine the true fraction of light absorbed by TiO2 suspensions. A ferrioxalate chemical actinometer was used to measure the incident photon flux. As a check on the quantum yield method, good agreement with known literature values was obtained for quantum yield measurements of the photochemical generation of the p-benzosemiquinone (BQ•-) ...

Finite-difference time domain method for light scattering by small ice crystals in three-dimensional space

Abstract: The finite-difference time domain (FDTD) method for the solution of light scattering by nonspherical particles has been developed for small ice crystals of hexagonal shapes including solid and hollow columns, plates, and bullet rosettes commonly occurring in cirrus clouds. To account for absorption, we have introduced the effective permittivity and conductivity to circumvent the required complex calculations in the direct discretization of the basic Maxwell equations. In the construction of the finite-difference scheme for the time-marching iteration for the near field the mean values of dielectric constants are defined and evaluated by the Maxwell–Garnett rule. In computing the scattered field in the radiation zone (far field) and the absorption cross section, we have applied a new algorithm involving the integration of the electric field over the volume inside the scatterer on the basis of electromagnetic principles. This algorithm removes the high-angular-resolution requirement in integrating the scattered energy for the computation of the scattering cross section. The applicability and the accuracy of the FDTD technique in three-dimensional space are validated by comparison with Mie scattering results for a number of size parameters and wavelengths. We demonstrate that neither the conventional geometric optics method nor the Mie theory can be used to approximate the scattering, absorption, and polarization features for hexagonal ice crystals with size parameters from approximately 5 to 20.

Radiation dose distributions in three dimensions from tomographic optical density scanning of polymer gels: I. Development of an optical scanner

Abstract: A new method of dosimetry of ionizing radiations has been developed that makes use of tissue-equivalent polymer gels which are capable of recording three-dimensional dose distributions. The dosimetric data stored within the gels are measured using optical tomographic densitometry. The dose-response mechanism relies on the production of light scattering micro-particles which result from the polymerization of acrylic comonomers dispersed in the gel. The attenuation of a collimated light beam caused by scattering in the irradiated optically turbid medium is directly related to the radiation dose over the range 0 - 10 Gy. An optical scanner has been developed which incorporates an He - Ne laser, photodiode detectors, and a rotating gel platform. Using mirrors mounted on a translating stage, the laser beam scans across the gel between each incremental rotation of the platform. Using the set of optical density projections obtained, a cross sectional image of the radiation field is then reconstructed. Doses in the range 0 - 10 Gy can be measured to better than 5% accuracy with a spatial resolution of approximately 2 mm using the current prototype scanner. This method can be used for the determination of three-dimensional dose distributions in irradiated gels, including measurements of the complex distributions produced by multi-leaf collimators, dynamic wedge and stereotactic treatments, and for quality assurance procedures.

Direct, nondestructive observation of a Bose condensate

Abstract: The spatial observation of a Bose condensate is reported. Dispersive light scattering was used to observe the separation between the condensed and normal components of the Bose gas inside a magnetic trap. This technique is nondestructive, and about a hundred images of the same condensate can be taken. The width of the angular distribution of scattered light increased suddenly at the phase transition.

Three-dimensional computation of light scattering from cells

Abstract: Using the finite-difference time-domain method, three-dimensional scattering patterns are computed for cells containing multiple organelles. The scattering cross section and average cosine of the scattering angle are computed for cells as a function of volume fraction of melanin granules and mitochondria. Results show that small organelles play a significant role in light scattering from cells, and the volume fraction of organelles affects both the total amount of scattered light and the angular distribution of scattered light.

Quantum Phase Diffusion of a Bose-Einstein Condensate.

Abstract: We discuss the quantum properties of the Bose-Einstein condensate of a dilute gas of atoms in a trap. We show that the phase of the condensate undergoes quantum diffusion which can be detected in far off-resonant light scattering experiments.

Light Scattering: Principles and development

Abstract: 1. Theoretical developments in static light scattering from polymers 2. Static scattering properties of colloidal suspensions 3. Theory of light scattering from rod-like polyelectrolytes 4. Polyelectrolytes in solution 5. Light scattering in concentrated polymer solutions 6. Applications of light scattering to large particle systems 7. Polymer-polymer interactions in dilute solutions 8. Scattering properties of ternary polymer systems 9. Light scattering in complex micellar systems 10. Scattering from block copolymer micellar systems 11. Light scattering by block copolymer liquids in the ordered and disordered states 12. Low angle light scattering and its applications 13. Combined static and dynamic light scattering 14. Size distributions from static light scattering 15. Light scattering and chromatography in combination

Dependence of tissue optical properties on solute-induced changes in refractive index and osmolarity.

Abstract: Additions of a solute/carbohydrate in tissue affect the size of tissue cells and the refractive indexes of the extra- and intracellular fluids, and thus the overall tissue scattering properties. We use both the Rayleigh- Gans and Mie theory approximation in calculating effects of the osmolarity and refractive indexes on the reduced scattering coefficient of tissue, and employ photon diffusion theory to associate the reduced scattering coefficient to the mean optical path length. The calculations show that changes of scattering in tissue depend not only on the change in extracellular refractive index but also on the change in osmolarity, and thus on the change in cell size and volume fraction. Experimentally, we have utilized time-domain and frequencydomain NIR techniques to measure the changes of optical properties caused by an addition of a solute in tissue models and in perfused rat livers. The temperature-dependent path length measurement of the perfused liver confirms the dependence of tissue scattering on the tissue cell size. The results obtained from the liver with three kinds of carbohydrate perfusion display different scattering aspects and can be well explained by changes in cell size and in extracellular as well as intracellular refractive indexes. The consistency between the theoretical and experimental results confirms the dependence of optical properties in (liver) tissue on both tissue osmolarity and relative refractive indexes between the extracellular and intracellular compartments. This study suggests that the NIR technique is a novel and useful tool for noninvasive, physiological monitoring.

An investigation of light transport through scattering bodies with non-scattering regions

Abstract: Near-infra-red (NIR) spectroscopy is increasingly being used for monitoring cerebral oxygenation and haemodynamics. One current concern is the effect of the clear cerebrospinal fluid upon the distribution of light in the head. There are difficulties in modelling clear layers in scattering systems. The Monte Carlo model should handle clear regions accurately, but is too slow to be used for realistic geometries. The diffusion equation can be solved quickly for realistic geometries, but is only valid in scattering regions. In this paper we describe experiments carried out on a solid slab phantom to investigate the effect of clear regions. The experimental results were compared with the different models of light propagation. We found that the presence of a clear layer had a significant effect upon the light distribution, which was modelled correctly by Monte Carlo techniques, but not by diffusion theory. A novel approach to calculating the light transport was developed, using diffusion theory to analyse the scattering regions combined with a radiosity approach to analyse the propagation through the clear region. Results from this approach were found to agree with both the Monte Carlo and experimental data.

Electron mobility in two-dimensional electron gas in AlGaN/GaN heterostructures and in bulk GaN

Abstract: We report on temperature dependencies of the electron mobility in the two-dimensional electron gas (2DEG) in AIGaN/GaN heterostructures and in doped bulk GaN. Calculations and experimental data show that the polar optical scattering and ionized impurity scattering are the two dominant scattering mechanisms in bulk GaN for temperatures between 77 and 500K. In the 2DEG in AIGaN/GaN heterostructures, the piezoelectric scattering also plays an important role. Even for doped GaN, with a significant concentration of ionized impurities, a large volume electron concentration in the 2DEG significantly enhances the electron mobility, and the mobility values close to 1700 cm2/Vs may be obtained in the GaN 2DEG at room temperature. The maximum measured Hall mobility at 80K is nearly 5000 cm2/Vs compared to approximately 1200 cm2/Vs in a bulk GaN layer. With a change in temperature from 300 to 80K, the 2DEG in our samples changes from nondegenerate and weakly degenerate to degenerate. Therefore, in order to interpret the experimental data, we propose a new interpolation formula for low field mobility limited by the ionized impurity scattering. This formula is valid for an arbitrary degree of the electron gas degeneracy. Based on our theory, we show that the mobility enhancement in the 2DEG is related to a much higher volume electron concentration in the 2DEG, and, hence, to a more effective screening.

Light scattering by gaussian random particles: ray optics approximation

Abstract: We model the shapes of irregular small particles using multivariate lognormal statistics (Gaussian random shape), and compute absorption and scattering cross sections, asymmetry parameters, and scattering phase matrices in the ray optics approximation. The random shape is fully described by the autocovariance function, which can be conveniently modeled by two statistical parameters: the standard deviation of radius and the correlation length of angular variations. We present an efficient spherical harmonics method for generating sample Gaussian random particles, and outline a ray tracing algorithm that can be adapted to almost arbitrary, mathematically star-like particles. We study the scattering and absorption properties of Gaussian random particles much larger than the wavelength by systematically varying their statistical parameters and complex refractive indices. The results help us understand, in part, light scattering by solar system dust particles, and thereby constrain the physical properties of, for example, asteroid regoliths and cometary comae.

Display of clouds taking into account multiple anisotropic scattering and sky light

Abstract: Methods to display realistic clouds are proposed To display realistic images, a precise shading model is required: two components should be considered One is multiple scattering due to particles in clouds, and the other factor to be considered is sky light For the former, the calculation of cloud intensities has been assumed to be complex due to strong forward scattering However, this paper proposes an efficient calculation method using these scattering characteristics in a positive way The latter is a very significant factor when sky light is rather stronger than direct sunlight, such as at sunset/sunrise, even though sky light has been ignored in previous methods This paper describes an efficient calculation method for light scattering due to clouds taking into account both multiple scattering and sky light, and the modeling of clouds CR Categories and Subject Descriptors:

Light propagation in tissues with controlled optical properties

Abstract: Theoretical and computer modeling approaches, such as Mie theory, radiative transfer theory, diffusion wave correlation spectroscopy, Monte Carlo simulation method were applied for tissue optics analysis in a process of its clearance. CW collimated transmittance and forward scattering measurements as well as intensity correlation experiments were used for tissue structure and optical properties monitoring. Conrolled tissue samples of the human sclera were taken. A chemical applicator-conrollers Trazograph, glucose and polyethileneglycol solutions were used. On the base of sclera samples clearance investigation the general principles of tissue optical and structural parameters controlling were established.

Dynamic light scattering studies on the sol-gel transition of a suspension of anisotropic colloidal particles

Abstract: Structural relaxation in amorphous systems is an area of much current interest. Many studies have been devoted to the sol-gel transition in systems based on polymers @1‐3#, natural gelatine @4#, and gels based on spherical colloids @5‐7#. Here we report on the sol-gel transition in a system of charged disks with an aspect ratio of 25, suspended in water. In such systems the orientational degrees of freedom play a crucial role not only in the dynamics but also in the static structure of the gel. Molecular dynamics simulations on hard disk systems reveal a rich phase diagram with nematic and cubatic liquid crystalline phases @8#. However, before these liquid crystalline phases can be formed the system enters a glassy phase or gel. Current opinion favors the ‘‘house of cards’’ structure for the gel @9#, which implies a random structure with short range orientational order. On the average the disks are oriented with their positively charged rim towards the negatively charged base of their neighbor. Within this view the orientational degrees of freedom will play a crucial role in the formation of the gel. Structure and dynamics in the neighborhood of the transition can be studied best by using the noninvasive technique of light scattering, dynamic ~DLS! and static. DLS probes the density correlation function describing the time evolution of the density fluctuations. The striking feature, largely emerging from DLS measurements around the gel point @4‐6#, is the marked similarity of the behavior of the correlation function with the scenarios given by the mode cou

Temporal gating in highly scattering media by the degree of optical polarization

Abstract: The temporal profiles of polarized laser pulses propagating through a scattering medium differ for scattered light parallel and perpendicular to the incident polarization. The degree of polarization is conserved over 100 ps after the arrival of the ballistic component. This observation can be used as a time gate for the early portion of the scattered light, reducing the diffusive component.

Theory of lasing in a multiple-scattering medium

Abstract: In several recent experiments, isotropic lasing action was observed in paints that contain rhodamine 640 dye molecules in methanol solution as gain media and titania particles as optical scatterers. These so-called paint-on laser systems are extraordinary because they are highly disordered systems. The microscopic mechanism for laser activity and the coherence properties of light emission in this multiple-light-scattering medium have not yet been elucidated. In this paper we derive the emission intensity properties of a model dye system with excited singlet and triplet electronic energy levels, which is immersed in a multiple-scattering medium with transport mean free path l * . Using physically reasonable estimates for the absorption and emission cross section for the singlet and triplet manifolds, and the singlet-triplet intersystem crossing rate, we solve the nonlinear laser rate equations for the dye molecules. This leads to a diffusion equation for the light intensity in the medium with a nonlinear intensity-dependent gain coefficient. Using this model we are able to account for nearly all of the experimentally observed properties of laser paint reported so far when l *@l0, the emission wavelength. This includes the dependence of the peak intensity of amplified emission on the mean free path l * , the dye concentrationr, and the pump intensity characteristics. Our model recaptures the collapse of the emission linewidth at a specific threshold pump intensity and describes how this threshold intensity varies with l * . In addition, our model predicts a dramatic increase in the peak intensity and a further lowering of the lasing threshold for the strong scattering limit l *→l0. This suggests a striking enhancement of the characteristics of laser paint near the photon localization threshold in a disordered medium. @S1050-2947 ~96!07510-5#

Dynamic structure factor of semiflexible macromolecules in dilute solution

Abstract: The dynamic structure factor for molecular chains with variable stiffness in a dilute solution is investigated. In the limit of small scattering vectors q only the overall translational motion of the macromolecules contributes to the dynamic structure factor. The translational diffusion coefficient D exhibits a chain length dependence D∼1/√L for flexible chains and D∼ln L/L+const/L for rodlike chains. For flexible chains there is an intermediate scattering vector regime in which the decay rate or spectral linewidth of the dynamic structure factor is proportional to q3 indicating that stretching modes are dominant. Such an intermediate scattering vector regime cannot be observed for semiflexible or rodlike chains. At large scattering vectors q/2p≳1.5, where 1/2p is the persistence length of the macromolecules, the chain stiffness becomes important for any kind of molecules, i.e., even for very flexible ones. The dynamic structure factor and the decay rate are compared with experimental results of quasielastic neutron and light scattering experiments on different natural and synthetic macromolecules. These experimental results are in good agreement with the theoretical predictions. Furthermore, we determine the persistence length of F‐actin from a dynamic light scattering experiment.

Polarized hyper-rayleigh light scattering measurements of nonlinear optical chromophores

Abstract: Hyper‐Rayleigh light scattering measurements at incident wavelengths of 1064 and 1319 nm are reported for several organic nonlinear optical chromophores in solution with approximately 5%–10% uncertainty in the relative first hyperpolarizabilities. The measured chromophores include representatives from C1, Cs, C2V, and D3 molecular point groups and include both neutral and ionic compounds. The measurements were made with 2–5 cm−1 spectral resolution and include polarization analysis of the incident and scattered light. Polarization ratios were measured with 2%–3% uncertainty for each molecule, and relative magnitudes of the hyperpolarizability components were deduced. Two‐photon induced fluorescence from several chromophores was observed to overlap with the scattered second harmonic light spectrum. The use of a scanning monochromator, however, generally allows the separation of these two sources of photons. The measured first hyperpolarizabilities are consistent with previous electric field induced second ...

Evidence of High Frequency Propagating Modes in Vitreous Silica.

Abstract: The detailed understanding of the dynamical properties of topologically disordered systems, like glasses, is still an open question. At low momentum transfer (Q) values, the existence of propagating collective excitations is demonstrated by the sharp Brillouin lines observable in light-scattering experiments. This is straightforward from an intuitive point of view since at low Q’s one samples particle-particle correlations on a long time and large space scales with respect to interatomic motions and distances. In the mesoscopic time-space domain the situation is more complicated, and the existence of collective dynamics is doubted. The evidence of modes in glasses in the mesoscopic region comes from incoherent neutron scattering and light scattering studies [1], where a broad band is found around 2 to 10 meV, almost independently from the material. This band has been named boson peak because its intensity scales with temperature approximately according to the Bose-Einstein statistics. The relaxational or vibrational character of the excitations giving rise to the boson peak is highly debated [1], especially in view of the fact that the extrapolation of the dispersion relation found at small Q to the mesoscopic Q region would give excitation energies similar to those of the boson peak. In this region, the experimental determination of the dynamical structure factor SsQ, Ed became only recently possible, thanks to the development of inelastic x-rays scattering (IXS) with meV energy resolution. It was shown for some “intermediate” [2] and “fragile” [3] glasses that propagating excitations exist up to energies comparable to that of the boson peak. Similar determinations have not been attempted yet on “strong” network-forming glasses. Among them, vitreous silica, y-SiO2, is probably the archetype [4]. In this Letter we present the measurement of the SsQ, Ed of y-SiO2 at T › 1050 K, in the 1 6 nm 21 momentum transfer range. We report the existence of collective modes in the whole investigated Q range. These modes are found to propagate with a velocity of sound y › 5800 6 200 my su p to Q ›3.5 nm 21 and E 13 meV. Hence, the energies spanned by these excitations cover the boson peak region [5], thus indicating that they must contribute to its origin. Moreover, the comparison of the present data with light-scattering data at T › 300 K shows that the linewidth of these excitations is temperature independent, suggesting that the peaks broadening is not associated with dynamical processes, but to the ill-definition of Q as a good quantum number. The experiment was carried out at the new very high energy resolution inelastic x-ray scattering beam line (BL21ID16) at the European Synchrotron Radiation Facility. This instrument is based on backscattering from high order reflections in perfect silicon crystals, and in this work we used the Si(999) reflection at 17.794 keV. The total instrumental resolution function was measured using a Plexiglas scatterer at the maximum of its static structure factor where the scattering is dominated by the elastic component; the energy resolution, full width at half maximum (FWHM), was 2.8 6 0.2 meV. The momentum transfer, Q › 2k0 sinsusy2d (where k0 and us are the wave vector of the incident photon and the scattering angle, respectively), was selected between 1 and 6 nm 21 . The Q resolution was set to 0.3 nm 21 by an aperture in front of the analyzer crystal. Energy scans were performed by varying the relative temperature between the monochromator and analyzer crystals. Each scan took about 120 min, and each Q point was obtained by typically averaging four scans. The data were normalized to the intensity of the incident beam. Further details on the beam line are reported elsewhere [2,6‐ 9]. The SiO2 suprasil sample, purchased from Goodfellow, was a 2 mm diameter rod. Its dimension was comparable to the x-ray photoabsorption length and gave negligible multiple scattering. A preliminary experiment performed at room temperature on y-SiO2 showed very weak IXS intensity, strongly merged into the tails of the central peak, thus not allowing a determination of the spectral shape with the necessary accuracy [10]. To increase the expected inelastic scattering signal we performed the measurements at about 1000 K. This gave an enhancement of the excitations with E 10 meV by a factor of 3.5. The y-SiO2 rod was placed inside a graphite tube ( 20 mm in length,

Energy transfer between crossing laser beams

Abstract: Induced scattering between crossing laser beams is considered, including the effects of long‐wavelength modulations in the plasma. This fundamental process can impact the choice of beam‐smoothing techniques for laser‐driven hohlraums. Study of this process is an ideal way to quantify stimulated scattering instabilities, since one can independently vary the intensity, polarization, and frequency separation of the crossing beams.