The process of Thomson scattering of an ultra-intense laser pulse by a relativistic electron bunch has been proposed as a way to obtain a bright source of short, tunable and quasi-monochromatic X-ray pulses. The real applicability of such a method depends crucially on the electron-beam quality, the angular and energetic distributions playing a relevant role. In this paper we present the computation of the Thomson-scattered radiation generated by a plane-wave, linearly polarized and flat-top laser pulse, incident on a counterpropagating electron bunch having a sizable angular divergence and a generic energy distribution. Both linear and nonlinear Thomson-scattering regimes are considered and the impact of the rising front of the pulse on the scattered-radiation distribution has been taken into account. Simplified relations valid for long laser pulses and small values of both scattering angle and bunch divergence are also reported. Finally, we apply the results to the cases of backscattering with electron bunches typically produced with both standard radio-frequency-based accelerators and laser-plasma accelerators

A gamma-ray source with an intense component around the giant dipole resonance for photonuclear absorption has been obtained via bremsstrahlung of electron bunches driven by a 10-TW tabletop laser. 3D particle-in-cell simulation proves the achievement of a nonlinear regime leading to efficient acceleration of several sequential electron bunches per each laser pulse. The rate of the gamma-ray yield in the giant dipole resonance region (8

We use a one-shot measurement technique to study effects of laser prepulses on the electron laser wakefield acceleration driven by relativistically intense laser pulses (lambda=790 nm, 11 TW, 37 fs) in dense helium gas jets. A quasimonoenergetic electron bunch with an energy peak approximately 11.5 MeV[DeltaE/E approximately 10% (FWHM)] and with a narrow-cone angle (0.04pi mm mrad) of ejection is detected at a plasma density of 8 x 10(19) cm(-3). A strong correlation between the generation of monoenergetic electrons and optical guiding of the pulse in a thin channel produced by picosecond laser prepulses is observed. This generation mechanism is well corroborated by two-dimensional particle-in-cell simulations.

International audienceThe interaction of 150 fs laser pulses with very thin plastic targets at an intensity of 5×1017 W/cm2 was investigated experimentally. Second-harmonic (SH) radiation was found to be emitted only in the specular direction. Both SH intensity and hard x-ray yield were found to be strongly dependent upon the laser polarization. The main features of SH emission are in agreement with a theoretical model which assumes resonance absorption as the source mechanism of electron plasma waves. Measurements suggest that, in conditions of maximum energy absorption, wave breaking of resonantly excited electron plasma waves takes place

Såo Paulo t9B8 /<- .-ll ! I il ll "0n üous a dit aussí que La uie est obecunítá" et dans ootre f,atígue ttous nápátez ce que disent Les Las. Et je Ðous dis que La oie est ráeLlement obscuyítá sauf, Lã où +L y a éLan, Et tout áLan est aueugle sauf Là où iL y a sauoiz,, Eþ tout saÐo¿y est uain sauf Là où iL g a tnauail, Et tout tyaÐa¿L est uíde sauf Là où it, y a amourj Et Lorsque tous tvaÐaiLLez azlec amour Ðous 1)ous Líez à uous-nâne, et Ltun ã Ltautz.e" et à Díeu.tl KhaLiL Gib z,an Ã, Gíana, fíLhínha da razão e do poz,que, que soube corajosamente eupo?t.a,? ausàncias e a pyesença maL dis-tz,ibuída, durante as ÐãT¿as etapas de realização desse tz,ab aLh o. Aos neus país e ã minha famíLía,pelo sacrífício da ausàncía imposta, pana a neaLização de um ídeal, ttf n Memotiamtl Ao neu írnão e amígo Una tese de doutorado, dificilmente é fruto de i déia isolada ou conquista individual , sendo, en geral, decorrên cia de u¡na linha de pesquisas, so¡nat6ria de esforços e de múfti-plas colaborações. Co¡no conseqtlência, desejamos registrar nesta página nossa homenagen e a nossa gratidão: Ao Professor Doutor José Vicente Valarelli, pela orientação cientÍfica e pelos preciosos conselhos, e dedicação que tornara¡n esse trabalho uma realidade' Ao Doutor François Delbove, a guen devenos todo a poio e incansáve1 colab.oração técnica-científica, durante a rea-lização dos trabalhos experinentais no "Centre d.e Recherche sur la synthèse et chinie des ¡ninéraux" do CNRS de orléans, França. Ao Professor Doutor Rainer A. Schultz-GUtt1er, pe los valiosos auxílios e sugestões durante a execução deste estu-do. Ao Professor Luiz Fernando de Carvalho, a quem di reta e indiretamente devemos nossa iniciação ã GeoquÍmica e ¡'line ralogia Experimental. Mestre, anigo e incentivador, cujo apoio, nos nonentos difÍceis, não pode ser esquecido. ttO amoz, ensina a não fícar do Lado bon de uma bz'iga podpe, Ensina d, enconþr'ay a briga b.oa: a briga peLa constz,ução de una noïq, ordem de ¿ntegyq.ção entz'e sub-jetíuo e objeþ¿Ðô, cíãncia e f,á, oriente e ocidente, politica e eaeíetãncía, justiça e Líbendade, na quaL há, maís d,?tè e menos conpetíção, naís uida e nenos morte. IJma peseoa prepaxada para o amo! é muíto maís pez,i goea paya, quaLquer LtaÍuA quo yep?essioo do que uma pessoa prepanada pa,ya a ódío, a guer.Ta. ou o combate, Esta é mais f,ã.cíL conbater. Anav á trans foz'mar a intenção en gesto moral, ou seia, em ato que possâ. eez. un¿Ðersc¿Lizado aen dano, perda ou sofz.imento.tl Artuy. da Iã.to La AGRADEC IMENTOS É con prazer que agradece¡nos a todos que nos ajuda ran a realizar esse trabalho, Ao Doutor Z.Johan, diretor do I'Centre de Recherche sur la synthèse et chinie des minéraux'r do CNRS-Orléans, França, por nos acolher naquele centro de pesquísa durante a realização dos trabalhos experinentais.

Near total transmission of 30 fs laser pulses through 0.1 mm plastic foil targets has been observed for the first time at an intensity of 3 3 10 18 W͞cm 2 in absence of precursor plasma. This level of transmittivity is far above the level predicted by current theoretical models or numerical simulations. The transmittivity was found to drop by 40 times at an intensity of 4 3 10 17 W͞cm 2 and was within the experimental background level at 5 3 10 16 W͞cm 2 . Our measurements strongly suggest a new mechanism of propagation of electromagnetic waves through overdense plasmas.[S0031-9007 (97)04356-1] PACS numbers: 52.40.NkThe interaction of intense optical radiation with plasmas characterized by solid-density and ultrasteep gradients can now be studied by using short pulse lasers capable of delivering up to joules of energy in few tens of femtoseconds. In principle, such laser systems open the possibility of investigating phenomena produced by high intensity radiation in experimentally unexplored conditions, including propagation in plasmas whose density is orders of magnitudes higher than the critical density n c m e v 2 0 ͞4pe 2 , v 0 being the laser frequency. Recently, penetration of ultraintense, short laser pulses into overdense plasmas has been extensively investigated both theoretically and experimentally also in view of its relevance to the implementation of the fast ignitor concept [1]. Several effects have been considered that predict enhanced propagation, including anomalous skin effect [2], self-induced transparency [3], and hole boring [4,5]. Hole boring and self-induced transparency have been mostly investigated in the interaction of relativistic laser pulses with moderately overdense plasmas. In particular, hole boring has been proposed as a possible mechanism for deep energy deposition in overdense plasma regions due to ponderomotive forces at relativistic intensities. The importance of relativistic effects is given by the value of the normalized relativistic momentum, a 0 p os ͞m o c Х 0.85l 0 p I 0 where p os is the momentum of the electrons oscillating in the laser field, m o is the electron mass, c is the velocity of light, and I 0 and l 0 are the laser intensity in units of 10 18 W͞cm 2 and the wavelength in microns, respectively. For these effects to give a nonmarginal increase of transmittivity through plasma slabs, either the plasma must be weakly overdense or the intensity must be very high (a 0 ¿ 1).At nonrelativistic intensity the propagation of the electromagnetic (e.m.) wave into an overdense plasma is expected to be limited to the skin depth d 0 . A deeper penetration (anomalous skin effect) is possible in very hot plasmas, where the electron velocity becomes larger than v 0 d 0 [6]. Recently the anomalous skin effect in solid-density plasmas has been considered both analytically [7] and numerically [8], with attention to the case of interaction with thin foils.From an experimental point of view, a serious problem that can prevent interaction of short pulses with solid-density plasmas may...

Laser plasma interferograms are currently analyzed by extraction of the phase-shift map with fast Fourier transform (FFT) techniques [Appl. Opt. 18, 3101 (1985)]. This methodology works well when interferograms are only marginally affected by noise and reduction of fringe visibility, but it can fail to produce accurate phase-shift maps when low-quality images are dealt with. We present a novel procedure for a phase-shift map computation that makes extensive use of the ridge extraction in the continuous wavelet transform (CWT) framework. The CWT tool is flexible because of the wide adaptability of the analyzing basis, and it can be accurate because of the intrinsic noise reduction in the ridge extraction. A comparative analysis of the accuracy performances of the new tool and the FFT-based one shows that the CWT-based tool produces phase maps considerably less noisy and that it can better resolve local inhomogeneties.

Radiotherapy with very high energy electrons has been investigated for a couple of decades as an effective approach to improve dose distribution compared to conventional photon-based radiotherapy, with the recent intriguing potential of high dose-rate irradiation. Its practical application to treatment has been hindered by the lack of hospital-scale accelerators. High-gradient laser-plasma accelerators (LPA) have been proposed as a possible platform, but no experiments so far have explored the feasibility of a clinical use of this concept. We show the results of an experimental study aimed at assessing dose deposition for deep seated tumours using advanced irradiation schemes with an existing LPA source. Measurements show control of localized dose deposition and modulation, suitable to target a volume at depths in the range from 5 to 10 cm with mm resolution. The dose delivered to the target was up to 1.6 Gy, delivered with few hundreds of shots, limited by secondary components of the LPA accelerator. Measurements suggest that therapeutic doses within localized volumes can already be obtained with existing LPA technology, calling for dedicated pre-clinical studies.