Time of Flight Measurements for Neutrons Produced in Reactions Driven by Laser-Target Interactions at Petawatt level

Abstract Short intense pulses of fast neutrons were produced in a two stage laser-driven experiment. Protons were accelerated by means of the Target Normal Sheath Acceleration (TNSA) method using the TITAN facility at the Lawrence Livermore National Laboratory. Neutrons were obtained following interactions of the protons with a secondary lithium fluoride (LiF) target. The properties of the neutron flux were studied using BC-400 plastic scintillation detectors and the neutron time of flight (nTOF) technique. The detector setup and the experimental conditions were simulated with the Geant4 toolkit. The effects of different components of the experimental setup on the nTOF were studied. Preliminary results from a comparison between experimental and simulated nTOF distributions are presented.

Measurement of electromagnetic pulses generated during interactions of high power lasers with solid targets

A target irradiated with a high power laser pulse, blows off a large amount of charge and as a consequence the target itself becomes a generator of electromagnetic pulses (EMP) owing to high return current flowing to the ground through the target holder. The first measurement of the magnetic field induced by the neutralizing current reaching a value of a few kA was performed with the use of an inductive target probe at the PALS Laser Facility (Cikhardt et al. Rev. Sci. Instrum. 85 (2014) 103507). A full description of EMP generation should contain information on the spatial distribution and temporal variation of the electromagnetic field inside and outside of the interaction chamber. For this reason, we consider the interaction chamber as a resonant cavity in which different modes of EMP oscillate for hundreds of nanoseconds, until the EMP is transmitted outside through the glass windows and EM waves are attenuated. Since the experimental determination of the electromagnetic field distribution is limited by the number of employed antennas, a mapping of the electromagnetic field has to be integrated with numerical simulations. Thus, this work reports on a detailed numerical mapping of the electromagnetic field inside the interaction chamber at the PALS Laser Facility (covering a frequency spectrum from 100 MHz to 3 GHz) using the commercial code COMSOL Multiphysics 5.2. Moreover we carried out a comparison of the EMP generated in the parallelepiped-like interaction chamber used in the Vulcan Petawatt Laser Facility at the Rutherford Appleton Laboratory, against that produced in the spherical interaction chamber of PALS.

Laser IInduced Liinear and Nonlliinear Optiicall Studiies on Certaiin Metall Halliides and Tartrate Crystalls ffor Photoniic Applliicatiions

Nonlinear optics is a broad field of research and technology that encompasses subject matter in the field of Physics, Chemistry, and Engineering. It is the branch of Optics that describes the behavior of light in nonlinear media, that is, media in which the dielectric polarization P responds nonlinearly to the electric field E of the light. This nonlinearity is typically only observed at very high light intensities. This area has applications in all optical and electro optical devices used for communication, optical storage and optical computing. Many nonlinear optical effects have proved to be versatile probes for understanding basic and applied problems. Nonlinear optical devices use nonlinear dependence of refractive index or absorption coefficient on the applied field. These nonlinear optical devices are passive devices and are referred to as intelligent or smart materials owing to the fact that the sensing, processing and activating functions required for optical processes are inherent to them which are otherwise separate in dynamic devices.The large interest in nonlinear optical crystalline materials has been motivated by their potential use in the fabrication of all-optical photonic devices. Transparent crystalline materials can exhibit different kinds of optical nonlinearities which are associated with a nonlinear polarization. The choice of the most suitable crystal material for a given application is often far from trivial; it should involve the consideration of many aspects. A high nonlinearity for frequency conversion of ultra-short pulses does not help if the interaction length is strongly limited by a large group velocity mismatch and the low damage threshold limits the applicable optical intensities. Also, it can be highly desirable to use a crystal material which can be critically phasematched at room temperature. Among the different types of nonlinear crystals, metal halides and tartrates have attracted due to their importance in photonics. Metal halides like lead halides have drawn attention because they exhibit interesting features from the stand point of the electron-lattice interaction .These materials are important for their luminescent properties. Tartrate single crystals show many interesting physical properties such as ferroelectric, piezoelectric, dielectric and optical characteristics. They are used for nonlinear optical devices based on their optical transmission characteristics. Among the several tartrate compounds, Strontium tartrate, Calcium tartrate and Cadmium tartrate have received greater attention on account of their ferroelectric, nonlinear optical and spectral characteristics. The present thesis reports the linear and nonlinear aspects of these crystals and their potential applications in the field of photonics.

Multi-kilowatt peak power nanosecond Er-doped fiber laser

We report a two-stage diode-pumped Er-doped fiber amplifier operating at the wavelength of 1550 nm at the repetition rate of 10-100 kHz with an average output power of up to 10 W. The first stage comprising Er-doped fiber was core-pumped at the wavelength of 1480 nm, whereas the second stage comprising double-clad Er/Yb-doped fiber was clad-pumped at the wavelength of 975 nm. The estimated peak power for the 0.4-nm full-width at half-maximum laser emission at the wavelength of 1550 nm exceeded 4-kW level. The initial 100-ns seed diode laser pulse was compressed to 3.5 ns as a result of the 34-dB total amplification. The observed 30-fold efficient pulse compression reveals a promising new nonlinear optical technique for the generation of high power short pulses for applications in eye-safe ranging and micromachining.

Amplification d’impulsions brèves de haute énergie par effet Raman stimulé dans les fibres optiques

Le développement au cours des dernières décennies de lasers à fibre à verrouillage de modes permet aujourd’hui d’avoir accès à des sources fiables d’impulsions femtosecondes qui sont utilisées autant dans les laboratoires de recherche que pour des applications commerciales. Grâce à leur large bande passante ainsi qu’à leur excellente dissipation de chaleur, les fibres dopées avec des ions de terres rares ont permis l’amplification et la génération d’impulsions brèves de haute énergie avec une forte cadence. Cependant, les effets non linéaires causés par la faible taille du faisceau dans la fibre ainsi que la saturation de l’inversion de population du milieu compliquent l’utilisation d’amplificateurs fibrés pour l’obtention d’impulsions brèves dont l’énergie dépasse le millijoule. Diverses stratégies comme l’étirement des impulsions à des durées de l’ordre de la nanoseconde, l’utilisation de fibres à cristaux photoniques ayant un coeur plus large et l’amplification en parallèle ont permis de contourner ces limitations pour obtenir des impulsions de quelques millijoules ayant une durée inférieure à la picoseconde. Ce mémoire de maîtrise présente une nouvelle approche pour l’amplification d’impulsions brèves utilisant la diffusion Raman des verres de silice comme milieu de gain. Il est connu que cet effet non linéaire permet l’amplification avec une large bande passante et ce dernier est d’ailleurs couramment utilisé aujourd’hui dans les réseaux de télécommunications par fibre optique. Puisque l’adaptation des schémas d’amplification Raman existants aux impulsions brèves de haute énergie n’est pas directe, on propose plutôt un schéma consistant à transférer l’énergie d’une impulsion pompe quasi monochromatique à une impulsion signal brève étirée avec une dérive en fréquence. Afin d’évaluer le potentiel du gain Raman pour l’amplification d’impulsions brèves, ce mémoire présente un modèle analytique permettant de prédire les caractéristiques de l’impulsion amplifiée selon celles de la pompe et le milieu dans lequel elles se propagent. On trouve alors que la bande passante élevée du gain Raman des verres de silice ainsi que sa saturation inhomogène permettent l’amplification d’impulsions signal à une énergie comparable à celle de la pompe tout en conservant une largeur spectrale élevée supportant la compression à des durées très brèves. Quelques variantes du schéma d’amplification sont proposées, et leur potentiel est évalué par l’utilisation du modèle analytique ou de simulations numériques. On prédit analytiquement et numériquement l’amplification Raman d’impulsions à des énergies de quelques millijoules, dont la durée est inférieure à 150 fs et dont la puissance crête avoisine 20 GW.

Identification Of Corynebacterium Spp. Isolated From Bovine Intramammary Infections By Matrix-assisted Laser Desorption Ionization-time Of Flight Mass Spectrometry.

Corynebacterium species (spp.) are among the most frequently isolated pathogens associated with subclinical mastitis in dairy cows. However, simple, fast, and reliable methods for the identification of species of the genus Corynebacterium are not currently available. This study aimed to evaluate the usefulness of matrix-assisted laser desorption ionization/mass spectrometry (MALDI-TOF MS) for identifying Corynebacterium spp. isolated from the mammary glands of dairy cows. Corynebacterium spp. were isolated from milk samples via microbiological culture (n=180) and were analyzed by MALDI-TOF MS and 16S rRNA gene sequencing. Using MALDI-TOF MS methodology, 161 Corynebacterium spp. isolates (89.4%) were correctly identified at the species level, whereas 12 isolates (6.7%) were identified at the genus level. Most isolates that were identified at the species level with 16 S rRNA gene sequencing were identified as Corynebacterium bovis (n=156; 86.7%) were also identified as C. bovis with MALDI-TOF MS. Five Corynebacterium spp. isolates (2.8%) were not correctly identified at the species level with MALDI-TOF MS and 2 isolates (1.1%) were considered unidentified because despite having MALDI-TOF MS scores >2, only the genus level was correctly identified. Therefore, MALDI-TOF MS could serve as an alternative method for species-level diagnoses of bovine intramammary infections caused by Corynebacterium spp.

Morphological Aspects And Cox-2 Expression After Exposure To 780-nm Laser Therapy In Injured Skeletal Muscle: An In Vivo Study.

The effectiveness of low-level laser therapy in muscle regeneration is still not well known. To investigate the effects of laser irradiation during muscle healing. For this purpose, 63 rats were distributed to 3 groups: non-irradiated control group (CG); group irradiated at 10 J/cm(2) (G10); and group irradiated at 50 J/cm(2) (G50). Each group was divided into 3 different subgroups (n=7), and on days 7, 14 and 21 post-injury the rats were sacrificed. Seven days post-surgery, the CG showed destroyed zones and extensive myofibrillar degeneration. For both treated groups, the necrosis area was smaller compared to the CG. On day 14 post-injury, treated groups demonstrated better tissue organization, with newly formed muscle fibers compared to the CG. On the 21(st) day, the irradiated groups showed similar patterns of tissue repair, with improved muscle structure at the site of the injury, resembling uninjured muscle tissue organization. Regarding collagen deposition, the G10 showed an increase in collagen synthesis. In the last period evaluated, both treated groups showed statistically higher values in comparison with the CG. Furthermore, laser irradiation at 10 J/cm(2) produced a down-regulation of cyclooxygenase 2 (Cox-2) immunoexpression on day 7 post-injury. Moreover, Cox-2 immunoexpression was decreased in both treated groups on day 14. Laser therapy at both fluencies stimulated muscle repair through the formation of new muscle fiber, increase in collagen synthesis, and down-regulation of Cox-2 expression.

Evaluation Of Photodynamic Therapy Using A Diode Laser And Different Photosensitizers Against Enterococcus Faecalis.

Photodynamic therapy (PDT) has been proven to be effective in disinfecting root canals. The aim of this present study was to evaluate the effects of PDT on the viability of Enterococcus faecalis using methylene blue (MB) and malachite green (MG) as photosensitizers. Solutions containing E. faecalis (ATCC 29212) were prepared and harvested by centrifugation to obtain cell suspensions, which were mixed with MB and MG. Samples were individually irradiated by the diode laser at a distance of 1mm for 30, 60, or 120 seconds. Colonyforming units (CFU) were determined for each treatment. PDT for 60 and 120 seconds with MG reduced E. faecalis viability significantly. Similar results were obtained when MB was used as photosensitizer. PDT using MB and MG have antibacterial effect against E. faecalis, showing potential to be used as an adjunctive antimicrobial procedure in endodontic therapy.

Laser Printer Attribution: Exploring New Features And Beyond.

With a huge amount of printed documents nowadays, identifying their source is useful for criminal investigations and also to authenticate digital copies of a document. In this paper, we propose novel techniques for laser printer attribution. Our solutions do not need very high resolution scanning of the investigated document and explore the multidirectional, multiscale and low-level gradient texture patterns yielded by printing devices. The main contributions of this work are: (1) the description of printed areas using multidirectional and multiscale co-occurring texture patterns; (2) description of texture on low-level gradient areas by a convolution texture gradient filter that emphasizes textures in specific transition areas and (3) the analysis of printer patterns in segments of interest, which we call frames, instead of whole documents or only printed letters. We show by experiments in a well documented dataset that the proposed methods outperform techniques described in the literature and present near-perfect classification accuracy being very promising for deployment in real-world forensic investigations.

A Metabolomic Protocol For Plant Systematics By Matrix-assisted Laser-desorption/ionization Time-of Flight Mass Spectrometry.

Matrix-assisted laser desorption/ionization time-of flight mass spectrometry (MALDI-TOF MS) has been widely used for the identification and classification of microorganisms based on their proteomic fingerprints. However, the use of MALDI-TOF MS in plant research has been very limited. In the present study, a first protocol is proposed for metabolic fingerprinting by MALDI-TOF MS using three different MALDI matrices with subsequent multivariate data analysis by in-house algorithms implemented in the R environment for the taxonomic classification of plants from different genera, families and orders. By merging the data acquired with different matrices, different ionization modes and using careful algorithms and parameter selection, we demonstrate that a close taxonomic classification can be achieved based on plant metabolic fingerprints, with 92% similarity to the taxonomic classifications found in literature. The present work therefore highlights the great potential of applying MALDI-TOF MS for the taxonomic classification of plants and, furthermore, provides a preliminary foundation for future research.

Effect Of Low-level Laser Therapy (lllt) On Peripheral Nerve Regeneration Using Fibrin Glue Derived From Snake Venom.

The purpose of this study was to assess whether the adhesive permits the collateral repair of axons originating from a vagus nerve to the interior of a sural nerve graft, and whether low-level laser therapy (LLLT) assists in the regeneration process. Study sample consisted of 32 rats randomly separated into three groups: Control Group (CG; n=8), from which the intact sural nerve was collected; Experimental Group (EG; n=12), in which one of the ends of the sural nerve graft was coapted to the vagus nerve using the fibrin glue; and Experimental Group Laser (EGL; n=12), in which the animals underwent the same procedures as those in EG with the addition of LLLT. Ten weeks after surgery, the animals were euthanized. Morphological analysis by means of optical and electron microscopy, and morphometry of the regenerated fibers were employed to evaluate the results. Collateral regeneration of axons was observed from the vagus nerve to the interior of the autologous graft in EG and EGL, and in CG all dimensions measured were greater and presented a significant difference in relation to EG and EGL, except for the area and thickness of the myelin sheath, that showed significant difference only in relation to the EG. The present study demonstrated that the fibrin glue makes axonal regeneration feasible and is an efficient method to recover injured peripheral nerves, and the use of low-level laser therapy enhances nerve regeneration.