Jean-Claude Vareille

Ferroelectric domain inversion by electron beam on LiNbO3 and Ti:LiNbO3

Periodically poled titanium in-diffused lithium niobate (Ti:LiNbO3) seems to be an attractive candidate for applications in the field of integrated optics for wavelength division multiplexed networks it could allow building of polarization-independent devices. In this study, we present the fabrication of reversed ferroelectric domain gratings by direct electron beam writing on both clear LiNbO3 and Ti:LiNbO3. First, a preliminary study was carried out on clear lithium niobate in order to determine the irradiation parameters (voltage, probe current, scanning speed) needed to create inverted ferroelectric domains, and then the same irradiation parameters were used for Ti:LiNbO3. The irradiated patterns were observed after chemical etching using a scanning electron microscope and optical microscopy. HeNe laser diffraction through the samples shows that the irradiation induces a variation of the linear optical refractive index in Ti:LiNbO3 but not in LiNbO3. Moreover, no topographical modification was observe...

Optical modifications of polymers by ion beam irradiation

Abstract Polymers subjected to ion beam or γ irradiation undergo structural modifications, which lead to an increase in refractive index for some materials, such as poly(diethylene glycol bis(allyl carbonate)) (CR39) and polycarbonate. The refractive index variation achieved with ion beam irradiation is sufficient to produce optical waveguides in CR39. The waveguide losses have been systematically studied in order to apply this technique to integrated optics (microstructure fabrication). A fundamental study using various spectroscopic methods (i.r. and u.v.-visible) has also been carried out, with the aim of gaining a better understanding of the structural modifications of polymeric materials caused by irradiation.

Thin reactive LiF films for nuclear sensors

Abstract Lithium fluoride (LiF) films are deposited by thermal evaporation on silicon substrates. The substrate temperature and deposition rates influence on the morphology and structure of the films are investigated. It is shown that it is necessary to work with a low deposition rate to have crack-free layers. Also, the substrate temperature has a great influence on coating morphology: the grain size increases with temperature. At the same time, the crystallization state increases up to 300°C. For higher temperatures, recrystallization seems to appear. The grain size increases as well as the grain boundary size.

CR-39 (poly(diethylene glycol bis(allyl carbonate))) under γ-rays and proton beams

Abstract The polymer poly(diethylene glycol bis(allyl carbonate)) (CR-39) subjected to γ-rays or ion beams (H, He, Li…) undergoes structural, physical and chemical modifications. The optical modifications of CR-39 irradiated by γ-rays or proton beams, and also the results of an EPR study of CR-39 under γ-rays are presented here. The latter showed that the increase of the refractive index observed in the irradiated polymer cannot be directly attributed to the presence of the free radicals in the material. The optical waveguides obtained by irradiation with proton beams present minimal losses of 2 dB/cm. They are exposed to thermal treatments in order to check their behaviour at temperatures around the glass transition temperature (Tg) of the unirradiated CR-39 polymer. This study showed that, on the range Tg − 10°C, Tg + 10°C, the obtained attenuation after the annealing treatment remains equal to its original value. Moreover, it pointed out the thermal stability of the refractive index. The first characterization results about microguides which were achieved using metallic masks and proton beams are also presented.

Optical waveguide fabrication by ion beams in the PADC-polymer

Abstract Ion beams and γ rays are used to modify refractive index of polyallyldiglycol carbonate (PADC). Ion irradiations (H, Li, B) lead to optical waveguides the properties of which depend on the kind of ions, ion fluences and energy. Radiation damage consistently increases the refractive index. Measured variations of refractive index are given as function of deposited energy density (by ions or γ rays). It appears that index variations are principally linked to structural modification due to deposited energy.

Damage around the ion path in cellulose triacetate. I. Total evaluation

Using the ‘‘scavenger technique’’ linked to visible spectroscopy, we evaluate the total number of radicals produced by one ion around its trajectory. This evaluation is achieved by the intermediary of a fictitious cylindrical volume containing all the various radicals likely to be produced whose radius a is determined by means of statistical calculation applied to the spectroscopical results. Then we compare the values of a calculated for various ions with different energies.

Etude des traces d'ions lourds dans des films de triacetate de cellulose preirradies ou non en photons γ

Abstract Cellulose triacetate produced by a method developed in our laboratory is studied as a solid-state track detector. It is bombarded by Ar ions, alpha particles and fission fragments of californium. it is shown that the detector response is affected by the concentration of the plasticizer. The effects of γ preirradiation on v g are correlated with our results from infrared investigations. In the dosage range of 1.9 × 106−11.4 × 106 rads, the ion tracks are not significantly changed, which is explained by a comparison between the energy provided by the bombarding ions and the energy deposited by the γ rays.

Study of free radicals in poly(diethylene glycol bis(allyl carbonate)) irradiated by γ rays

Abstract Free radicals in poly(diethylene glycol bis(allyl carbonate)), commercially known as CR-39 resin, cured by radical mechanism with various amounts of diisopropyl peroxydicarbonate were studied by electron paramagnetic resonance (e.p.r.) spectroscopy. It was found that the radicals can survive in the unirradiated polymer network for at least 6 months after polymerization. The dependence of the amplitude of the e.p.r. signal on the dose for CR-39 polymer irradiated by 60 Co γ rays was found to show a maximum which increased in magnitude and shifted in position to higher doses for samples cured with lower initiator concentration. This behaviour is explained by examining the role of residual allyl groups present in the cured polymer and the scission of the network at the carbonate group. It was found that the refractive index increase observed in the irradiated polymer cannot be directly attributed to the presence of free radicals in the network.

Damage around the ion path in cellulose triacetate. II. A track model

In this paper, a model of an ion track is proposed. It is justified by experimental results obtained by electron microscopy. These results show that a track is composed of two parts: (i) a core in which the material is totally destroyed, and (ii) a ‘‘halo’’ in which the damage decreases when the distance from the ion path increases. The overall results given in paper I and the calculation of deposited energy density of Fain [J. Fain, M. Monnin, and M. Montret, Proceedings of the 8th International Conference on Nuclear Photo., S.S.N.T.D., Bucarest (1972), p. 34, and J. Fain, M. Monnin, and M. Montret, Radiat. Res. 57, 379 (1974)] led us to the volume density of free radicals at every point inside the latent track. The core radius is established for ions of Z≤18 and E≤10 MeV/amu. A great density of damage close to the ion path is shown, and the influence of this phenomenon on track etching is studied.

Optical Guides In CR 39 Irradiated By Ion Beams

The paper deals with the increase of refractive index of polyallyl diethylenglycol carbonate (CR 39) when irradiated by proton beams at 300 keV, with th the fluence range (5 10 13 - 5 10 15 protons cm -2). Such irradiations lead to refractive indexincreases which can reach 8%, depending on the fluence of the beam, the initial value being close to 1.493. As the irradiated samples become optical waveguides, integrated optic methods enable us to study the index variations; the effective index values were obtained by means of the m-lines method. These values were then used to calculate the index profil2 by inverse WKB method. An attenuation of about 2 db cm 14 was measured for an irradiation of 10 protons cm . It was also noted that the attenuation increases with the ion beam fluence. On the other hand, the number of guide modes depends on the beam fluence and the variation of effective index versus fluence is given. Many considerations lead to consider that the index variation is mainly due to energy transfer all along the proton path. This is in good agreement with the comparison of the stopping power curve as a function of depth penetration and that of the index profile.