Measurements of relativistic self-phase-modulation in plasma

We report the first systematic observations of relativistic self-phase-modulation (RSPM) due to the interaction of a high intensity laser pulse with plasma. The plasma was produced in front of a solid target by the prepulse of a 100 TW laser beam. RSPM was observed by monitoring the spectrum of the harmonics generated by the intense laser pulse during the interaction. The multipeaked broadened spectral structure produced by RSPM was studied in plasmas with different density scale lengths for laser interactions at intensities up to 3.0x1019 W cm(-2) (a=p(osc)/m(e)c=4.7). The results are compared with calculated spectra and agreement is obtained.

Measurements of negative ion densities by absorption spectroscopy

A novel diagnostic technique for the measurement of negative ions is presented. The absorption of a cw-laser beam with a wavelength close to the maximum of the photodetachment cross section is measured. The laser beam undergoes multiple reflections through the discharge volume using a multipass cell there a Herriott arrangement). Proof-of-principle measurements of negative hydrogen ions in a hybrid volume source are presented. The measured H- density is in agreement with results of conventional, Langmuir probe-based photodetachment measurements. (C) 1998 American Institute of Physics. [S0003-6951(98)02119-6].

Comparison of plasma transport theory with measurements in a H- discharge

This paper and its companion paper describe the comparison between a one-dimensional theoretical model of a hydrogen discharge in a magnetic multipole plasma source and experimental measurements of the plasma parameters. The discharge chamber, described here, has been designed to produce significant densities of H- ions by incorporating a weak transverse field through the discharge to obtain electron cooling so as to maximize H- production. Langmuir probes are used to monitor the plasma, determining the ion density, the electron density and temperature and the plasma potential. The negative density is measured by photo-detachment of the extra electron using an intense laser beam. The model, described in the companion paper, uses the presented source geometry to calculate these plasma quantities as a function of the major are parameters; namely the are current and voltage and gas pressure. Good agreement is obtained between theory and experiment as a function of position and arc parameters.

Optical Cooling of Atoms in Microtraps by Time-Delayed Reflection

We present a theoretical analysis of a novel scheme for optical cooling of particles that does not in principle require a closed optical transition. A tightly confined laser beam interacting with a trapped particle experiences a phase shift, which upon reflection from a mirror or resonant microstructure produces a time-delayed optical potential for the particle. This leads to a nonconservative force and friction. A quantum model of the system is presented and analyzed in the semiclassical limit.

IMAGING OF SURFACE-PLASMON LAUNCH AND PROPAGATION USING A PHOTON SCANNING TUNNELING MICROSCOPE

The spectroscopic capability of the photon scanning tunneling microscope is exploited to study directly the launch and propagation of surface plasmons on thin silver films. Two input beams, of different wavelength, are incident through the prism in a prism-Ag film-air-fibre tip system. Both excite surface plasmons at the Ag-air interface and light of both wavelengths is coupled into the fibre probe via the respective surface plasmon evanescent fields. One laser beam is used for instrument control. The second, or probe beam is tightly focused on the sample, within the area of the unfocused or control beam, giving a well-defined and symmetrical, confined surface plasmon launch site. However, the image at the probe wavelength is highly asymmetrical in section with an exponential tail extending beyond one side of the launch site. This demonstrates in a very direct fashion;the propagation of surface plasmons; a propagation length of similar to 11.7 mu m is measured at a probe wavelength of 543.5 nm. On rough Ag films the excitation of localised scattering centres is also observed in addition to the launch of delocalised surface plasmons.

INTERPLAY OF CAF2 SUBSTRATE ROUGHENING AND FILM DEPOSITION RATE ON RADIATIVE SCATTERING OF SURFACE-PLASMON POLARITONS FROM AG FILMS

The radiative decay of surface plasmon polaritons has been investigated in an attempt to characterize the surface roughness of Ag films prepared under different conditions. The polaritons were excited by the method of attenuated total reflection of light. The films were deposited on the face of a 60-degrees BK-7 glass prism at a rate that was deliberately fixed in two different ranges (centred on 0.1 and 10 nm s-1) and in some cases a CaF2 underlayer was used to roughen the film surfaces. The intensity of the scattered light emitted from the opposite face of the films was measured as a function of direction for each using the same sensitivity scale and was correlated with the preparation of the film. It was found that on nominally smooth substrates fast-deposited thinner films give out more light and are deduced to have greater short wavelength (300-600 nm) roughness amplitude. There is also evidence for long wavelenth (7 mum) periodic roughness due to the prism substrate itself. On CaF2 roughened surfaces the light output from the films is further increased and the peak intensity is backward directed with respect to the exciting laser beam direction. Here roughness on a lateral scale of 350 nm is responsible. Also, elastic scattering of surface plasmon polaritons at grain boundaries reduces the light output from fast deposited, small grain, films on CaF2 roughened surfaces. Overall, a consistent picture of roughness induced radiative polariton decay emerges for all cases studied.

Scaling of Ion Spectral Peaks in the Hybrid RPA-TNSA Region

The role of the radiation pressure of an intense laser beam in the formation of proton and carbon spectra from thin foils is discussed. The data presented suggests that, in competition with the Target Normal Sheath Acceleration mechanism, the onset of the Light Sail (LS) region of Radiation Pressure Acceleration can be obtained for suitably thin targets at currently available laser intensities,. The spectral features and their scaling with the laser and target parameters are consistent with the scenario of Light Sail (LS) acceleration.

Kitchen robot prod. line development. Proj. of Bowden cables cutting and thermal forming machine.

This document presents particular description of work done during student’s internship in PR Metal company realized as ERASMUS PROJECT at ISEP. All information including company’s description and its structure, overview of the problems and analyzed cases, all stages of projects from concept to conclusion can be found here. Description of work done during the internship is divided here into two pieces. First part concerns one activities of the company which is robotic chefs (kitchen robot) production line. Work, that was done for development of this line involved several tasks, among them: creating a single-worker montage station for screwing robots housing’s parts, improve security system for laser welding chamber, what particularly consists in designing automatically closing door system with special surface, that protects against destructive action of laser beam, test station for examination of durability of heating connectors, solving problem with rotors vibrations. Second part tells about main task, realized in second half of internship and stands a complete description of machine development and design. The machine is a part of car handle latch cable production line and its tasks are: cutting cable to required length and hot-forming plastic cover for further assembly needs.

Anisotropie de la photoluminescence dans des nanostructures organiques chirales autoassemblées

Nous investiguons dans ce travail la dynamique des excitons dans une couche mince d’agrégats H autoassemblés hélicoïdaux de molécules de sexithiophène. Le couplage intermoléculaire (J=100 meV) place ce matériau dans la catégorie des semi-conducteurs à couplage de type intermédiaire. Le désordre énergétique et la forte interaction électronsphonons causent une forte localisation des excitons. Les espèces initiales se ramifient en deux états distincts : un état d’excitons autopiégés (rendement de 95 %) et un état à transfert de charge (rendement de 5%). À température de la pièce (293K), les processus de sauts intermoléculaires sont activés et l’anisotropie de la fluorescence décroît rapidement à zéro en 5 ns. À basse température (14K), les processus de sauts sont gelés. Pour caractériser la dynamique de diffusion des espèces, une expérience d’anisotropie de fluorescence a été effectuée. Celle-ci consiste à mesurer la différence entre la photoluminescence polarisée parallèlement au laser excitateur et celle polarisée perpendiculairement, en fonction du temps. Cette mesure nous donne de l’information sur la dépolarisation des excitons, qui est directement reliée à leur diffusion dans la structure supramoléculaire. On mesure une anisotropie de 0,1 après 20 ns qui perdure jusqu’à 50ns. Les états à transfert de charge causent une remontée de l’anisotropie vers une valeur de 0,15 sur une plage temporelle allant de 50 ns jusqu’à 210 ns (période entre les impulsions laser). Ces résultats démontrent que la localisation des porteurs est très grande à 14K, et qu’elle est supérieure pour les espèces à transfert de charge. Un modèle numérique simple d’équations différentielles à temps de vie radiatif et de dépolarisation constants permet de reproduire les données expérimentales. Ce modèle a toutefois ses limitations, notamment en ce qui a trait aux mécanismes de dépolarisation des excitons.

Use of mirage effect for the detection of phase transitions in liquid crystals

he phenomenon of single beam mirage effect, otherwise known as photothermal deflection (PTD) effect using a He–Ne laser beam has been employed to detect phase transitions in some liquid crystals. It has been observed that anomalous changes in amplitude occur in the PTD signal level near the transition temperature. The experimental details and the results of measurements made in liquid crystals E8, M21 and M24 are given in this paper.

Investigation of nonlinear absorption and aggregation in aqueous solutions of rhodamine B using thermal lens technique

Thermal lensing effect was studied in aqueous solutions of rhodamine B using 532 nm, 9 ns pulses from a Nd:YAG laser. A low intensity He-Ne laser beam was used for probing the thermal lens. Results obtained show that it is appropriate to use this technique for studying nonlinear absorption processes like two photon absorption or excited state absorption and for analyzing dimerization equilibria.

Photoacoustic studies on multilayer dielectric coatings

Non-destructive testing d multilayer dielectric coatings (SiO2/TiO2 structure) has been carried out using the photoacoustic technique. This technique makes use d a 10 mW He-Ne laser, a photoacoustic cell and a lock-in amplifier. The chopped He-Ne laser beam is allowed to fall on the sample placed in a photoacoustic cell. The acoustic signals thus generated are detected using a microphone and the resulting output is processed by a lock-in amplifier. The amplitude and phase of the signals were measured as a function of the chopping frequency. Striking step-like variations are observed in me phase against frequency plot which dearly reveals the different layers present in the multilayer structure.

Fluorescence quantum yield of rhodamine 6G using pulsed photoacoustic technique

Experimental method for measuring photoacoustic(PA) signals generated by a pulsed laser beam in liquids is described. The pulsed PA technique is found to be a convenient and accurate method for determination of quantum yield in fluorescent dye solutions. Concentration dependence of quantum yield of rhodamine 6G in water is studied using the above method. The results indicate that the quantum yield decreases with increase in concentration in the quenching region in agreement with the existing reports based on radiometric measurements.

Use of mirage effect for the detection of phase transitions in solids

The phenomenon of mirage effect suffered by a He-Ne laser beam has been utilized to detect phase transitions in solids. It has been observed that anomalous fluctuations of large amplitude occur in the signal level near the transition temperature. The mean square value of the fluctuation is found to exhibit a well-defined peak at this point. Results of measurements made in the case of crystals of TGS ((NH2CH2COOH)3.H2SO4) and a ceramic sample (BaTiO3) are given to illustrate this technique.

Fluorescence Decay Characteristics of the Green Emission From CaF2:Ho3+

Variations in the decay times of the characteristic green emissions at 522.7, 551.3, 549.6, 547.6, 542.2, 540.2, 535.9 and 533.5nm from CaF2 :H03+ with concentration are studied at RT and LNT. A pulsed N2 laser beam of power density 1.5 MW cm-2 is used for the excitation. Temperature dependent concentration quenching of the decay times are observed for all the emission bands. But an increase in the decay time due to the reabsorption process is also observed for a few of the above bands.