Fused silica ablation by double ultrashort laser pulses with dual wavelength and variable delays

Today, glass and other similar dielectric materials are widely used in modern manufacturing. However, glass is a brittle and a heat sensitive material. Laser technology is used to process glass but quality and throughput are still a key issue. In the present paper, we investigate dual-wavelength double ultrashort laser pulses in order to control free electrons dynamics and subsequent ablation for fused silica processing, and further improve the understanding of this laser-material interaction. We used a high average power Yb-doped femtosecond laser source (100 W) with two optical lines exhibiting different pulse durations and wavelengths (500 fs at 515 nm; and 1 or 10 ps at 1030 nm) with various fluences and delays. The best configuration in terms of ablation efficiency is expected to take place when the green pulse first induces free electrons, followed by their heating by the red pulse. The obtained results are discussed in terms of optical transmission as well as ablated volume, and are compared with single pulse ablation. Our experimental results are supported by absorbed energy density calculations based on a model considering the two-color laser induced electron dynamics, including photoionization, laser heating of free electrons, and their recombination. We demonstrate that there is an optimal cooperating effect between the two sub-pulses for a 1-ps delay, nevertheless there is no beneficial effect in splitting the beam for optimizing fused silica ablation compared with the single-pulse green configuration.

Improved modeling of the solid-to-plasma transition of polystyrene ablator for laser direct-drive inertial confinement fusion hydrocodes

The target performance of laser direct-drive inertial confinement fusion (ICF) can be limited by the development of hydrodynamic instabilities resulting from the nonhomegeneous laser absorption at the target surface, i.e., the laser imprint on the ablator. To understand and describe the formation of these instabilities, the early ablator evolution during the laser irradiation should be considered. In this work, an improved modeling of the solid-to-plasma transition of a polystyrene ablator for laser direct-drive ICF is proposed. This model is devoted to be implemented in hydrocodes dedicated to ICF which generally assume an initial plasma state. The present approach consists of the two-temperature model coupled to the electron, ion and neutral dynamics including the chemical fragmentation of polystyrene. The solid-to-plasma transition is shown to significantly influence the temporal evolution of both free electron density and temperatures, which can lead to different shock formation and propagation compared with an initial plasma state. The influence of the solid-to-plasma transition on the shock dynamics is evidenced by considering the scaling law of the pressure with respect to the laser intensity. The ablator transition is shown to modify the scaling law exponent compared with an initial plasma state.

Implementing a microphysics model in hydrodynamic simulations to study the initial plasma formation in dielectric ablator materials for direct-drive implosions

A microphysics model to describe the photoionization and impact ionization processes in dielectric ablator materials like plastic has been implemented into the one-dimensional hydrodynamic code LILAC for planar and spherical targets. At present, the initial plasma formation during the early stages of a laser drive are modeled in an ad hoc manner, until the formation of a critical surface. Implementation of the physics-based models predict higher values of electron temperature and pressure than the ad hoc model. Moreover, the numerical predictions are consistent with previous experimental observations of the shinethrough mechanism in plastic ablators. For planar targets, a decompression of the rear end of the target was observed that is similar to recent experiments. An application of this model is to understand the laser-imprint mechanism that is caused by nonuniform laser irradiation due to single beam speckle.

Optical Bloch modeling of femtosecond-laser-induced electron dynamics in dielectrics

A model based on optical Bloch equations is developed to describe the interaction of femtosecond laser pulses with dielectric solids, accounting for optical-cycle-resolved electron dynamics. It includes the main physical processes at play: photoionization, impact ionization, direct and collisional laser heating, and recombination. By using an electron band structure, this approach also accounts for material optical properties as nonlinear polarization response. Various studies are performed, shedding light on the contribution of various processes to the full electron dynamics depending on laser intensity and wavelength. In particular, the standard influence of the impact ionization process is retrieved.

Modeling the solid-to-plasma transition for laser imprinting in direct-drive inertial confinement fusion

Laser imprinting possesses a potential danger for low-adiabat and high-convergence implosions in direct-drive inertial confinement fusion (ICF). Within certain direct-drive ICF schemes, a laser picket (prepulse) is used to condition the target to increase the interaction efficiency with the main pulse. Whereas initially the target is in a solid state (of ablators such as polystyrene) with specific electronic and optical properties, the current state-of-the-art hydrocodes assume an initial plasma state, which ignores the detailed plasma formation process. To overcome this strong assumption, a model describing the solid-to-plasma transition, eventually aiming at being implemented in hydrocodes, is developed. It describes the evolution of main physical quantities of interest, including the free electron density, collision frequency, absorbed laser energy, temperatures, and pressure, during the first stage of the laser-matter interaction. The results show that a time about 100 ps is required for the matter to undergo the phase transition, the initial solid state thus having a notable impact on the subsequent plasma dynamics. The nonlinear absorption processes (associated to the solid state) are also shown to have an influence on the thermodynamic quantities after the phase transition, leading to target deformations depending on the initial solid state. The negative consequences for the ICF schemes consist in shearing of the ablator and possibly preliminary heating of the deuterium-tritium fuel.

Novel natural and synthetic inhibitors of solute carriers SGLT1 and SGLT2

Selective analogs of the natural glycoside phloridzin are marketed drugs that reduce hyperglycemia in diabetes by inhibiting the active sodium glucose cotransporter SGLT2 in the kidneys. In addition, intestinal SGLT1 is now recognized as a target for glycemic control. To expand available type 2 diabetes remedies, we aimed to find novel SGLT1 inhibitors beyond the chemical space of glycosides. We screened a bioactive compound library for SGLT1 inhibitors and tested primary hits and additional structurally similar molecules on SGLT1 and SGLT2 (SGLT1/2). Novel SGLT1/2 inhibitors were discovered in separate chemical clusters of natural and synthetic compounds. These have IC50-values in the 10-100 μmol/L range. The most potent identified novel inhibitors from different chemical clusters are (SGLT1-IC50 Mean ± SD, SGLT2-IC50 Mean ± SD): (+)-pteryxin (12 ± 2 μmol/L, 9 ± 4 μmol/L), (+)-ε-viniferin (58 ± 18 μmol/L, 110 μmol/L), quinidine (62 μmol/L, 56 μmol/L), cloperastine (9 ± 3 μmol/L, 9 ± 7 μmol/L), bepridil (10 ± 5 μmol/L, 14 ± 12 μmol/L), trihexyphenidyl (12 ± 1 μmol/L, 20 ± 13 μmol/L) and bupivacaine (23 ± 14 μmol/L, 43 ± 29 μmol/L). The discovered natural inhibitors may be further investigated as new potential (prophylactic) agents for controlling dietary glucose uptake. The new diverse structure activity data can provide a starting point for the optimization of novel SGLT1/2 inhibitors and support the development of virtual SGLT1/2 inhibitor screening models.

Direct-drive measurements of laser-imprint-induced shock velocity nonuniformities

Perturbations in the velocity profile of a laser-ablation-driven shock wave seeded by speckle in the spatial beam intensity (i.e., laser imprint) have been measured. Direct measurements of these velocity perturbations were recorded using a two-dimensional high-resolution velocimeter probing plastic material shocked by a 100-ps picket laser pulse from the OMEGA laser system. The measured results for experiments with one, two, and five overlapping beams incident on the target clearly demonstrate a reduction in long-wavelength (>25-μm) perturbations with an increasing number of overlapping laser beams, consistent with theoretical expectations. These experimental measurements are crucial to validate radiation-hydrodynamics simulations of laser imprint for laser direct drive inertial confinement fusion research since they highlight the significant (factor of 3) underestimation of the level of seeded perturbation when the microphysics processes for initial plasma formation, such as multiphoton ionization are neglected.

Ultrashort laser induced spatial redistribution of silver species and nano-patterning of etching selectivity in silver-containing glasses

Femtosecond laser-induced spatial redistribution of silver species (ions, clusters, and hole centers) in a silver-containing phosphate glass is investigated by correlative means of near-field scanning optical microscopy (NSOM) images, numerical simulations, chemical micro-probe analysis, and nanoscale spatial profiles after soft etching. In particular, we found that the chemical etching selectivity for nanoscale patterning is strongly dependent upon the irradiation of femtosecond laser due to the spatial redistribution of silver species within the affected area. These results strongly indicate that controlling the distribution of silver species by femtosecond laser irradiation may open new routes for surface nanoscale chemical and/or spatial patterning for the fabrication of 2D surface photonic crystals.

Laser writing of nonlinear optical properties in silver-doped phosphate glass

The formation of both local second- and third-harmonic generations (SHG and THG) induced by a train of femtosecond laser pulses in silver-doped phosphate glasses is addressed. Based on modeling calculations, including various diffusion and kinetic processes, THG is shown to result from the formation of silver clusters. The latter organize into a ring-shape structure, leading to the emergence of a static electric field. By breaking the glass centro-symmetry, this field gives rise to a local effective second-order susceptibility, inducing SHG. Both theoretically predicted SHG and THG evolutions with respect to the number of pulses in the train are in good agreement with experimental observations. In particular, the observed reaching of a maximum in the nonlinear optical responses after a few thousands of pulses is explained by the competition of various physical processes. A cooling of the glass is shown to improve the process efficiency of the laser writing of second-order nonlinearity.

Experimental Investigation of the Collective Raman Scattering of Multiple Laser Beams in Inhomogeneous Plasmas

Experiments have been performed evidencing significant stimulated Raman sidescattering (SRS) at large angles from the density gradient. This was achieved in long scale-length high-temperature plasmas in which two beams couple to the same scattered electromagnetic wave further demonstrating for the first time this multiple-beam collective SRS interaction. The collective nature of the coupling and the amplification at large angles from the density gradient increase the global SRS losses and produce light scattered in novel directions out of the planes of incidence of the beams. These findings obtained in plasmas conditions relevant of inertial confinement fusion experiments similarly apply to the more complex geometry of these experiments where anomalously large levels of SRS were measured.

Enhanced photoemission from laser-excited plasmonic nano-objects in periodic arrays

The process of photoelectron emission from gold surfaces covered with nano-objects that are organized in the form of a periodic array is addressed in the short laser pulse regime ([Formula: see text] fs) at moderate intensities [Formula: see text] W cm(-2) and for various laser wavelengths. The emission spectrum from a gold single crystal measured under the same conditions is used for reference. The comparison of the photo-emission yield and the energy of the ejected electrons with their counterparts from the (more simple) reference system shows that the periodic conditions imposed on the target surface drastically enhance both quantities. In addition to the standard mechanism of Coulomb explosion, a second mechanism comes into play, driven by surface plasmon excitation. This can be clearly demonstrated by varying the laser wavelength. This interpretation of the experimental data is supported by predictions from model calculations that account both for the primary quantum electron emission and for the subsequent surface-plasmon-driven acceleration in the vacuum. Despite the fact that the incident laser intensity is as low as [Formula: see text] W cm(-2), such a structured target permits generating electrons with energies as high as 300 eV. Experiments with two incident laser beams of different wavelengths with an adjustable delay, have also been carried out. The results show that there exist various channels for the decay of the photo-emission signal, depending on the target type. These observations are shedding light on the various relaxation mechanisms that take place on different timescales.

Coupled hydrodynamic model for laser-plasma interaction and hot electron generation

We present a formulation of the model of laser-plasma interaction (LPI) at hydrodynamical scales that couples the plasma dynamics with linear and nonlinear LPI processes, including the creation and propagation of high-energy electrons excited by parametric instabilities and collective effects. This formulation accounts for laser beam refraction and diffraction, energy absorption due to collisional and resonant processes, and hot electron generation due to the stimulated Raman scattering, two-plasmon decay, and resonant absorption processes. Hot electron (HE) transport and absorption are described within the multigroup angular scattering approximation, adapted for transversally Gaussian electron beams. This multiscale inline LPI-HE model is used to interpret several shock ignition experiments, highlighting the importance of target preheating by HEs and the shortcomings of standard geometrical optics when modeling the propagation and absorption of intense laser pulses. It is found that HEs from parametric instabilities significantly increase the shock pressure and velocity in the target, while decreasing its strength and the overall ablation pressure.

Metrabase: a cheminformatics and bioinformatics database for small molecule transporter data analysis and (Q)SAR modeling

ABSTRACT

Both metabolism and transport are key elements defining the bioavailability and biological activity of molecules, i.e. their adverse and therapeutic effects. Structured and high quality experimental data stored in a suitable container, such as a relational database, facilitates easy computational processing and thus allows for high quality information/knowledge to be efficiently inferred by computational analyses. Our aim was to create a freely accessible database that would provide easy access to data describing interactions between proteins involved in transport and xenobiotic metabolism and their small molecule substrates and modulators. We present Metrabase, an integrated cheminformatics and bioinformatics resource containing curated data related to human transport and metabolism of chemical compounds. Its primary content includes over 11,500 interaction records involving nearly 3,500 small molecule substrates and modulators of transport proteins and, currently to a much smaller extent, cytochrome P450 enzymes. Data was manually extracted from the published literature and supplemented with data integrated from other available resources. Metrabase version 1.0 is freely available under a CC BY-SA 4.0 license at http://www-metrabase.ch.cam.ac.uk.

Modeling of the cross-beam energy transfer with realistic inertial-confinement-fusion beams in a large-scale hydrocode

A method for modeling realistic laser beams smoothed by kinoform phase plates is presented. The ray-based paraxial complex geometrical optics (PCGO) model with Gaussian thick rays allows one to create intensity variations, or pseudospeckles, that reproduce the beam envelope, contrast, and high-intensity statistics predicted by paraxial laser propagation codes. A steady-state cross-beam energy-transfer (CBET) model is implemented in a large-scale radiative hydrocode based on the PCGO model. It is used in conjunction with the realistic beam modeling technique to study the effects of CBET between coplanar laser beams on the target implosion. The pseudospeckle pattern imposed by PCGO produces modulations in the irradiation field and the shell implosion pressure. Cross-beam energy transfer between beams at 20(∘) and 40(∘) significantly degrades the irradiation symmetry by amplifying low-frequency modes and reducing the laser-capsule coupling efficiency, ultimately leading to large modulations of the shell areal density and lower convergence ratios. These results highlight the role of laser-plasma interaction and its influence on the implosion dynamics.

Towards modeling of nonlinear laser-plasma interactions with hydrocodes: the thick-ray approach

This paper deals with the computation of laser beam intensity in large-scale radiative hydrocodes applied to the modeling of nonlinear laser-plasma interactions (LPIs) in inertial confinement fusion (ICF). The paraxial complex geometrical optics (PCGO) is adapted for light waves in an inhomogeneous medium and modified to include the inverse bremsstrahlung absorption and the ponderomotive force. This thick-ray model is compared to the standard ray-tracing (RT) approach, both in the chic code. The PCGO model leads to different power deposition patterns and better diffraction modeling compared to standard RT codes. The intensity-reconstruction technique used in RT codes to model nonlinear LPI leads to artificial filamentation and fails to reproduce realistic ponderomotive self-focusing distances, intensity amplifications, and density channel depletions, whereas PCGO succeeds. Bundles of Gaussian thick rays can be used to model realistic non-Gaussian ICF beams. The PCGO approach is expected to improve the accuracy of ICF simulations and serve as a basis to implement diverse LPI effects in large-scale hydrocodes.

Capsule shell material impacts the in vitro disintegration and dissolution behaviour of a green tea extract

Purpose

In vitro disintegration and dissolution are routine methods used to assess the performance and quality of oral dosage forms. The purpose of the current work was to determine the potential for interaction between capsule shell material and a green tea extract and the impact it can have on the release.

Methods

A green tea extract was formulated into simple powder-in-capsule formulations of which the capsule shell material was either of gelatin or HPMC origin. The disintegration times were determined together with the dissolution profiles in compendial and biorelevant media.

Results

All formulations disintegrated within 30 min, meeting the USP criteria for botanical formulations. An immediate release dissolution profile was achieved for gelatin capsules in all media but not for the specified HPMC formulations. Dissolution release was especially impaired for HPMC_gell at pH 1.2 and for both HPMC formulations in FeSSIF media suggesting the potential for food interactions.

Conclusions

The delayed release from studied HPMC capsule materials is likely attributed to an interaction between the catechins, the major constituents of the green tea extract, and the capsule shell material. An assessment of in vitro dissolution is recommended prior to the release of a dietary supplement or clinical trial investigational product to ensure efficacy.

Phytosterol ester processing in the small intestine: impact on cholesterol availability for absorption and chylomicron cholesterol incorporation in healthy humans

Phytosterols (plant sterols and stanols) can lower intestinal cholesterol absorption, but the complex dynamics of the lipid digestion process in the presence of phytosterol esters (PEs) are not fully understood. We performed a clinical experiment in intubated healthy subjects to study the time course of changes in the distribution of all lipid moieties present in duodenal phases during 4 h of digestion of meals with 3.2 g PE (PE meal) or without (control meal) PE. In vitro experiments under simulated gastrointestinal conditions were also performed. The addition of PE did not alter triglyceride (TG) hydrolysis in the duodenum or subsequent chylomicron TG occurrence in the circulation. In contrast, cholesterol accumulation in the duodenum aqueous phase was markedly reduced in the presence of PE (-32%, P < 0.10). In vitro experiments confirmed that PE reduces cholesterol transfer into the aqueous phase. The addition of PE resulted in a markedly reduced presence of meal-derived hepta-deuterated cholesterol in the circulation, i.e., in chylomicrons (-43%, PE meal vs. control; P < 0.0001) and plasma (-54%, PE meal vs. control; P < 0.0001). The present data show that addition of PE to a meal does not alter TG hydrolysis but displaces cholesterol from the intestinal aqueous phase and lowers chylomicron cholesterol occurrence in humans.

Delivery of Functionality in Complex Food Systems: Physically Inspired Approaches from Nanoscale to Microscale, Wageningen 18-21 October 2009

The Wageningen Delivery of Functionality symposium covered all aspects involved with food structural design to arrive at high-quality foods which meet demanding customer expectations and regulatory requirements. The symposium integrated aspects from the structural organization of foods at molecular and supramolecular scales to dedicated techniques required to describe and visualize such structures, the gastro-intestinal events and how to model these in a laboratory setting, and finally the impact those food structures and ingredients have on the consumer's physiology and on the human perception. As an interdisciplinary platform, bringing together more than 160 researchers from academia and industry, the symposium meanwhile fulfills an important role in the food science community.

Food-dependent disintegration of immediate release fosamprenavir tablets: in vitro evaluation using magnetic resonance imaging and a dynamic gastrointestinal system

In the present study, we demonstrated the value of two advanced tools, the TNO gastric and small Intestinal Model (TIM-1) and magnetic resonance imaging (MRI), for the in vitro evaluation of food-dependent disintegration of immediate release fosamprenavir tablets. Upon introduction of a tablet with the nutritional drink Scandishake Mix® in the stomach compartment of TIM-1, simulating the fed state, disintegration and fosamprenavir dissolution were significantly postponed compared to the fasted state (lag time 80 ± 23 min). This resulted in a lag in the appearance of bioaccessible fosamprenavir (<5% during the first 2h), even though the nutritional state did not significantly alter the cumulative bioaccessibility after 5h. These results were in agreement with the previously observed postprandial delay in gastric fosamprenavir tablet disintegration and subsequent amprenavir absorption in healthy volunteers. Therefore, TIM-1 can be used in tablet development to identify food-induced disintegration issues causing unexpected clinical behavior. From a mechanistic perspective, we applied MRI to illustrate impaired water ingress in fosamprenavir tablets immersed in the nutritional drink compared to simulated gastric fluid. This effect may be attributed to both competition between nutritional components and the tablet for the available water (indicated by reduced rotational and translational diffusion) as well as the possible formation of a food-dependent precipitation layer on the HPMC-coated tablet.

Postprandial evolution in composition and characteristics of human duodenal fluids in different nutritional states

The purpose of this study was to assess the changes in duodenal composition in three nutritional states: fasted, fed, and fat-enriched fed state. Two isocaloric meals were administered to healthy subjects on nonconsecutive days. Subsequently, duodenal samples were collected every 30 min after which they were characterized with respect to pH, lipolytic products, bile salts, phospholipids, osmolality, and surface tension. The resulting time profiles displayed fluctuating patterns, which reflect high inter- and intrasubject variability. Duodenal composition was not altered by the higher fat percentage of the fat-enriched liquid meal. Monoglycerides, amounting from 5% to 88% of total lipids, were the dominant lipolytic species, followed by free fatty acids. Within 30 min after meal administration, individual intraduodenal concentrations of lipid products were 0.0-5.5, 1.0-14.9, and 3.1-22.4 mg/mL in fasted, fed, and fat-enriched fed state, respectively. The corresponding values for bile salts were 2.0-9.0, 6.9-9.3, and 4.4-30.3 mM and for phospholipids 0.06-2.4, 2.6-5.7, and 1.4-9.3 mM, respectively. Specific trends though, were not detected. This study illustrates the variable intraluminal conditions that can result after food intake. As intraduodenal events (e.g., intraduodenal dissolution) affect absorption of poorly water soluble and/or highly lipophilic drugs, this variability may possibly contribute to the highly variable drug plasma-time profiles often observed.

Kinetics of biomarkers: biological and technical validity of isoprostanes in plasma

Isoprostanes, non-enzymatic peroxidation products of arachidonic acid, are attractive biomarkers of oxidative stress in research in biology, medicine and nutrition. For the appropriate use of biomarkers it is required that these are both biologically and technically valid. Whereas the biological validity of isoprostanes is well-established, it is technically quite complicated to measure isoprostanes and its metabolites in body fluids, and its rapid disappearance from plasma may hamper practical application. This paper shortly introduces isoprostanes as a biomarker for studies with humans, describes a novel fast and sensitive method for measuring isoprostanes in plasma by high-performance liquid chromatography and tandem mass spectrometry, and provides several examples of the use of the method in studies in humans. By taking care of the biological and technical validity of this biomarker it is possible to establish the antioxidant effects of some food ingredients in studies with human volunteers.

Assessment of the efficacy of functional food ingredients-introducing the concept "kinetics of biomarkers"

Functional foods are "foods and beverages with claimed health benefits based on scientific evidence". Health claims need to be substantiated scientifically. The future of functional foods will heavily rely on proven efficacy in well-controlled intervention studies with human volunteers. In order to have the maximum output of human trials, improvements are needed with respect to study design and optimization of study protocols. Efficacy at realistic intake levels needs to be established in studies with humans via the use of suitable biomarkers, unless the endpoint can be measured directly. The human body is able to deal with chemical entities irrespective of their origin, and the pharmaceutical terms "absorption, distribution, metabolism and excretion" have their equivalent when biomarkers are concerned. Whereas only "diurnal variation" or "circadian rhythm" is sometimes considered, little attention is paid to "kinetics of biomarkers". "Kinetics of biomarkers" comprises "formation, distribution, metabolism and excretion". However, this is at present neither an established science nor common practice in nutrition research on functional foods. As a consequence, sampling times and matrices, for example, are chosen on the basis of historical practice and convenience (for volunteers and scientists) but not on the basis of in depth insight. The concept of kinetics of biomarkers is illustrated by a variety of readily comprehensible examples, such as malaria, cholesterol, polyphenols, glutathione-S-transferase alpha, F2-isoprostanes, interleukin-6, and plasma triacylglycerides.