EP0868835B1 - Method and device for characterising an ionised medium using an electromagnetic radiation source having an ultrashort duration - Google Patents

Method and device for characterising an ionised medium using an electromagnetic radiation source having an ultrashort duration Download PDF

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EP0868835B1
EP0868835B1 EP96943163A EP96943163A EP0868835B1 EP 0868835 B1 EP0868835 B1 EP 0868835B1 EP 96943163 A EP96943163 A EP 96943163A EP 96943163 A EP96943163 A EP 96943163A EP 0868835 B1 EP0868835 B1 EP 0868835B1
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ray
radiation
laser
photoconducting
ionized medium
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EP0868835A1 (en
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Jean-François Eloy
Hans Wilhelmsson
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Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05G—X-RAY TECHNIQUE
    • H05G2/00—Apparatus or processes specially adapted for producing X-rays, not involving X-ray tubes, e.g. involving generation of a plasma
    • H05G2/001—X-ray radiation generated from plasma
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H1/00—Generating plasma; Handling plasma
    • H05H1/0006—Investigating plasma, e.g. measuring the degree of ionisation or the electron temperature
    • H05H1/0012—Investigating plasma, e.g. measuring the degree of ionisation or the electron temperature using electromagnetic or particle radiation, e.g. interferometry
    • H05H1/0043—Investigating plasma, e.g. measuring the degree of ionisation or the electron temperature using electromagnetic or particle radiation, e.g. interferometry by using infrared or ultraviolet radiation

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  • the present invention relates to a method and a device for characterizing an ionized medium using a radiation source ultra short duration electromagnetic.
  • thermodynamics electronics and physico-chemicals of an ionized medium with a transient lifetime and at evolutionary character, such as laser plasma, plasma nozzle combustion, or a welding plasma arc or laser
  • diagnostic and spectroscopic means using to the illumination of this environment by a source of short electromagnetic radiation wave, X-ray type or external radiation, sometimes called an auxiliary source.
  • a source of short electromagnetic radiation wave X-ray type or external radiation
  • auxiliary source sometimes called an auxiliary source.
  • Such a process requires the use of a radiation source intense electromagnetic capable of illuminating the medium ionized, or plasma, to know during its phase evolutionary transient.
  • the characteristics of this radiation-source are chosen in such a way that the measurements, either of the reflected part, or of the transmitted part of this electromagnetic radiation, may reveal, after interpretation, the specific temporal physical characteristics of the medium, condensed or gaseous, ionized which has been illuminated.
  • a source of pulsed radiation is coherent, of the type laser radiation, either incoherent, radiation type X. This radiation can originate from the source even laser radiation that generates the plasma at to study.
  • the diagnostic means is a X-ray flash X-ray.
  • the radiation is reflected, either transmitted, can be focused so diffractive in order to deliver an image of the ionized medium through a camera.
  • the source radiation is coherent laser radiation
  • characterization of the radiation transmitted by the ionized plasma medium allows to implement a magnetic rotational polarization measurement for calculate the spatial gradients of density and temperature of this medium, as described in the document referenced [3].
  • type electromagnetic radiation X radiation issued transiently but repetitive, can be detected, discriminated against temporally (sampled) and recorded.
  • These three operations can then be performed by a single autocorrelation sampling device optoelectronics.
  • laser method pump-probe we temporally modulate the phenomenon generated by a laser pump beam by means of a opto-mechanical, or opto-acoustic modulation device, according to a fixed repetition frequency, and in parallel by means of the laser probe beam generating the switching phenomenon.
  • plasma laser single shot a solved measurement method in time, pump-probe type, is not applicable by principle. So far, a measurement method time resolved rather uses a device sampling. Plus the measurement, well only temporally sampled, concerns only one global radiation pulse measurement spatio-temporally averaged electromagnetic and emitted directly by the constituent particles, transiently, the whole medium, condensed or gaseous, ionized to study. For there to be measurement, it is necessary that there be emission. Now a very localized medium or ionized gas does not emit systematically electromagnetic radiation detectable, which can be absorbed by the surrounding ionized medium. Even if this device allows to discriminate advantageously, and with a resolution high temporal, direct radiation pulse issued, the information collected by this single element only restore average vision of the physical state of the environment, although the signal be resolved in time.
  • this prior art system has an important limitation: The signal to detected by the sampling device cannot not be time modulated. Indeed, a level of significant system noise affects the sensitivity of the measurement by sampling and limits the application of this system to detect and measure signals of high amplitude, which stand out clearly above noise from the associated electronic system.
  • the document referenced [5] studies the formation and consistency of fringes due to a wave X-ray laser illuminating a Mach-Zehnder interferometer.
  • This document describes in particular a device and an interferometric method for assessing the temporal and spatial coherence properties of the laser wave, this device can be used to electronic density measurements in plasmas.
  • the document referenced [6] describes a single short pulse measurement device, comprising at least one measuring assembly comprising a conductive line to which a set of photoconductors, the line and the photoconductors being placed between two dielectrics forming a single support in which the length of the line separating the photoconductors two by two is equal to the product of the propagation speed over the line by the ratio of the duration of the pulse on the number of measuring points, the service life of majority carriers constituting the photoconductors being chosen equal to or less than 10% of the duration of the impulse, the device thus allowing to obtain a time analysis or the autocorrelation function of the impulse which can be an impulse of electromagnetic, or ionizing radiation or a electrical impulse.
  • the document referenced [7] describes imaging systems to analyze high plasmas density in the soft X-ray regime.
  • the system experiment includes a spherical mirror multilayer which reflects a narrow band of soft x-ray radiation in the energy region 50 to 200 ev.
  • This mirror image is the own emission of a plasma produced by laser and / or the shadow of the laser in expansion generated by an X-ray source produced by a separate laser with approximately one amplification of 50 in the image plane and a submicron resolution in the target plane.
  • resolution time of around 150 ps is obtained either with a grid microchannel plate intensifier in as a detector, be a “backlighter” device short pulse X-rays.
  • the document referenced [8] describes the use of the backlighting technique of soft X-rays to measure the density of dense plasma produced in a capillary discharge.
  • Plasma tellurium produced by laser is used as a source of x-rays and a two-dimensional flash image with a 140 ⁇ m resolution is obtained.
  • the document referenced [9] describes a device for evaluating an X-ray optical element. improves efficiency of use of shelves X from an X-ray generator in converting x-rays from the means of projection in parallel X-rays or by condensing these at one point.
  • the document referenced [10] describes a X-ray interferometer to test a plasma produced by laser with micron spatial resolutions.
  • a soft X-ray laser operating at 155 Angstroms is combined with a multilayer Mach-Zehnder interferometer to get electron density profiles in a plasma produced by laser irradiation of a target.
  • two beams are used primary and secondary laser derived from the same ultra-short duration laser beam.
  • the interaction means is a metallic target material included among the following materials: titanium, nickel, zinc or tungsten which, under the effect of the main beam focused by a lens, generates an X-ray beam.
  • a spherical mirror, reflector of the X-ray is located between the interaction medium and the X-ray beam sequencing means.
  • the X-ray beam sequencing means is a mirror composed of metallic layers reflectors stacked regularly and oriented way to deliver a compound X-ray beam of a train of temporally spaced X pulses regularly.
  • Several reflecting optical means are disposed between the beam separation means and the detection means for modifying the path of the secondary beam.
  • the radiation detection means is a microelectronic technology optoelectronic component autocorrelating type, combining a insulating substrate, a photoconductive material under a fast type laser impact on which is deposited a metallic electrical signal transmission line emitted by the detector under the impact of X-rays secondary re-emitted by the ionized medium.
  • the insulating substrate is a sapphire or gallium arsenide or telluride material cadmium (CdTe); the photoconductive material is a gallium arsenide or cadmium telluride material low temperature ; the transmission line is in aluminum.
  • the present invention therefore relates to a device for characterizing an ionized medium transient, resolved in time.
  • the optoelectronic device 31 of microelectronic technology combines a substrate insulator, for example in a material such as sapphire, gallium arsenide, cadmium telluride, a photoconductive material (under laser impact) of type fast, for example in low gallium arsenide temperature, on which is deposited the line of metallic transmission 34, the material used being for example aluminum, of the electrical signal emitted by the detector 30 under the impact of secondary X-rays 35 re-emitted by the ionized medium 21.
  • a substrate insulator for example in a material such as sapphire, gallium arsenide, cadmium telluride
  • a photoconductive material (under laser impact) of type fast for example in low gallium arsenide temperature, on which is deposited the line of metallic transmission 34, the material used being for example aluminum
  • the electrical signal emitted by the detector 30 under the impact of secondary X-rays 35 re-emitted by the ionized medium 21 for example in
  • these photoconductive elements 33 are each formed by a discontinuity between each sampling line 32 and the line of transmission 34.
  • the optoelectronic device 31 is a microsystem capable of analyzing impulses up to 50 Ghz.
  • This device is an integrated component, realized in a microelectronic type technology, and comprising photoconductive elements and lines microstrips. It consists of a line of main propagation 34 where the signal is sent unique to sample, and n lines 32 arranged in a "comb" along this line. Between each of these lines sampling line and the main line, there is a pad or layer of photoconductive material 33.
  • the principle of this device is relatively simple and reminds a little of photography: right now propagation where the signal is "delayed" by the lines sampling, an ultra-fast laser pulse lights and closes the n switches that constitute photoconductive elements. The signals as well samples are then stored in a capacity and read by dedicated electronics.
  • each line 32 can be connected to a connected CCD 40 element to a drawer responsible for storing information in a register.
  • Detector 30 is a sensitive detector x-ray, very fast. It includes material photoconductor whose carriers have a lifetime less than picosecond; it can be, by example, CdTe, GaAs, Si doped oxygen on sapphire or diamond.
  • the optoelectronic device 31 can, also, be a sliding contact device whose the operating principle is described in the document referenced [4].
  • the second laser pulse train of few femtoseconds results not only from the spatial distribution of the photoswitches 33 but can also result from a temporal distribution of the attenuated laser beam delivered by the mirror 22, obtained by passing the laser radiation from start in a sequencing device 37, for example Michelson type possibly followed by an amplifier beam.
  • the method of the invention which is a new method of applying the pump-probe method, has the advantage of eliminating imprecision space-time of the prior art because it allows discriminatingly probe the ionized medium of spatio-temporal way.

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Description

Domaine de l'inventionField of the invention

La présente invention concerne un procédé et un dispositif de caractérisation d'un milieu ionisé mettant en oeuvre une source de rayonnement électromagnétique à durée ultracourte.The present invention relates to a method and a device for characterizing an ionized medium using a radiation source ultra short duration electromagnetic.

Etat de la technique antérieureState of the art

Pour mesurer et connaítre les propriétés thermodynamiques, électroniques et physico-chimiques d'un milieu ionisé à durée de vie transitoire et à caractère évolutif, tel qu'un plasma laser, un plasma de combustion de tuyère, ou un plasma de soudure à l'arc ou à laser, on met généralement en oeuvre des moyens de diagnostic et de spectroscopie faisant appel à l'éclairement de ce milieu par une source de rayonnement électromagnétique de courte longueur d'onde, de type radiation X ou de radiation externe, appelée parfois source auxiliaire. Un tel procédé nécessite la mise en oeuvre d'une source de rayonnement électromagnétique intense capable d'illuminer le milieu ionisé, ou plasma, à connaítre pendant sa phase évolutive transitoire. Les caractéristiques de ce rayonnement-source sont choisies de telle manière que les mesures, soit de la partie réfléchie, soit de la partie transmise de ce rayonnement électromagnétique, puissent révéler, après interprétation, les caractéristiques physiques temporelles spécifiques du milieu, condensé ou gazeux, ionisé qui a été illuminé.To measure and know the properties thermodynamics, electronics and physico-chemicals of an ionized medium with a transient lifetime and at evolutionary character, such as laser plasma, plasma nozzle combustion, or a welding plasma arc or laser, we generally use diagnostic and spectroscopic means using to the illumination of this environment by a source of short electromagnetic radiation wave, X-ray type or external radiation, sometimes called an auxiliary source. Such a process requires the use of a radiation source intense electromagnetic capable of illuminating the medium ionized, or plasma, to know during its phase evolutionary transient. The characteristics of this radiation-source are chosen in such a way that the measurements, either of the reflected part, or of the transmitted part of this electromagnetic radiation, may reveal, after interpretation, the specific temporal physical characteristics of the medium, condensed or gaseous, ionized which has been illuminated.

Comme décrit dans le document référencé [1] en fin de description, on peut utiliser à cet effet une source de rayonnement pulsé soit cohérent, de type rayonnement laser, soit incohérent, de type rayonnement X. Ce rayonnement peut avoir pour origine la source même de rayonnement laser qui génère le plasma à étudier.As described in the document referenced [1] at the end of the description, one can use a source of pulsed radiation is coherent, of the type laser radiation, either incoherent, radiation type X. This radiation can originate from the source even laser radiation that generates the plasma at to study.

Dans le cas d'une source à rayonnement laser, le moyen de diagnostic est un dispositif de radiographie par flash X. Le rayonnement soit réfléchi, soit transmis, peut être focalisé de manière diffractive afin de délivrer une image du milieu ionisé par l'intermédiaire d'une caméra. Dans le cas où le rayonnement-source est un rayonnement laser cohérent, la caractérisation du rayonnement transmis par le milieu de plasma ionisé permet de mettre en oeuvre une mesure de polarisation rotatoire magnétique pour calculer les gradients spatiaux de densité et de température de ce milieu, comme décrit dans le document référencé [3].In the case of a radiation source laser, the diagnostic means is a X-ray flash X-ray. The radiation is reflected, either transmitted, can be focused so diffractive in order to deliver an image of the ionized medium through a camera. In case the source radiation is coherent laser radiation, characterization of the radiation transmitted by the ionized plasma medium allows to implement a magnetic rotational polarization measurement for calculate the spatial gradients of density and temperature of this medium, as described in the document referenced [3].

Par ailleurs, comme décrit dans le document référencé [2], un rayonnement électromagnétique de type radiation X, émis de manière transitoire mais répétitive, peut être détecté, discriminé temporellement (échantillonné) et enregistré. Ces trois opérations peuvent alors être réalisées par un seul dispositif d'échantillonnage à autocorrélation optoélectronique. Dans la méthode de mesure, résolue en temps, couramment employée pour l'étude des phénomènes physico-chimiques transitoires, dénommée "méthode laser pompe-sonde", on module temporellement le phénomène généré par un faisceau-pompe laser au moyen d'un dispositif de modulation opto-mécanique, ou opto-acoustique, selon une fréquence de répétition fixe, et en parallèle au moyen du faisceau-sonde laser générant le phénomène de commutation. On extrait alors du signal délivré par le dispositif détecteur à échantillonnage la composante spectrale correspondant à cette fréquence.Furthermore, as described in the document referenced [2], type electromagnetic radiation X radiation, issued transiently but repetitive, can be detected, discriminated against temporally (sampled) and recorded. These three operations can then be performed by a single autocorrelation sampling device optoelectronics. In the measurement method, resolved in time, commonly used for the study of phenomena transient physico-chemical, called "laser method pump-probe ", we temporally modulate the phenomenon generated by a laser pump beam by means of a opto-mechanical, or opto-acoustic modulation device, according to a fixed repetition frequency, and in parallel by means of the laser probe beam generating the switching phenomenon. We then extract from the signal delivered by the sampling detector device the spectral component corresponding to this frequency.

A des fins plus spécifiques de diagnostic monocoup de plasma laser une méthode de mesure résolue en temps, de type pompe-sonde, n'est pas applicable par principe. Jusqu'à présent, une méthode de mesure résolue en temps utilise plutôt un dispositif d'échantillonnage. De plus la mesure, bien qu'échantillonnée temporellement, ne concerne qu'une mesure d'impulsion globale de rayonnement électromagnétique moyennée spatio-temporellement et émise directement par les particules constituant, transitoirement, tout le milieu, condensé ou gazeux, ionisé à étudier. Pour qu'il y ait mesure, il est nécessaire qu'il y ait émission. Or une zone très localisée du milieu ou gaz ionisé n'émet pas systématiquement de rayonnement électromagnétique détectable, celui-ci pouvant être absorbée par le milieu ionisé environnant. Même si ce dispositif permet de discriminer avantageusement, et avec une résolution temporelle élevée, l'impulsion de rayonnement direct émise, les informations recueillies par ce seul élément de diagnostic ne restituent qu'une vision moyenne d'ensemble de l'état physique du milieu, bien que le signal soit résolu en temps.For more specific diagnostic purposes plasma laser single shot a solved measurement method in time, pump-probe type, is not applicable by principle. So far, a measurement method time resolved rather uses a device sampling. Plus the measurement, well only temporally sampled, concerns only one global radiation pulse measurement spatio-temporally averaged electromagnetic and emitted directly by the constituent particles, transiently, the whole medium, condensed or gaseous, ionized to study. For there to be measurement, it is necessary that there be emission. Now a very localized medium or ionized gas does not emit systematically electromagnetic radiation detectable, which can be absorbed by the surrounding ionized medium. Even if this device allows to discriminate advantageously, and with a resolution high temporal, direct radiation pulse issued, the information collected by this single element only restore average vision of the physical state of the environment, although the signal be resolved in time.

Pour améliorer la compréhension des phénomènes physiques des milieux, condensés ou à gaz, ionisés, un tel système monocoup nécessite un élément de diagnostic complémentaire capable de restituer séparément l'aspect cartographique de l'émission de rayonnement. To improve understanding of physical phenomena of the media, condensed or gas, ionized, such a single shot system requires an element of complementary diagnosis capable of restoring separately the cartographic aspect of the emission of radiation.

De plus, ce système de l'art antérieur présente une limitation importante : Le signal à détecter par le dispositif à échantillonnage ne peut pas être modulé temporellement. En effet, un niveau de bruit important du système affecte la sensibilité de la mesure par échantillonnage et limite l'application de ce système à la détection et à la mesure de signaux d'amplitude élevée, qui ressortent nettement au-dessus du bruit du système électronique associé.In addition, this prior art system has an important limitation: The signal to detected by the sampling device cannot not be time modulated. Indeed, a level of significant system noise affects the sensitivity of the measurement by sampling and limits the application of this system to detect and measure signals of high amplitude, which stand out clearly above noise from the associated electronic system.

Le document référencé [5] étudie la formation et la cohérence de franges dues à une onde laser rayons X illuminant un interféromètre Mach-Zehnder. Ce document décrit notamment un dispositif et un procédé interférométrique permettant d'évaluer les propriétés de cohérence temporelle et spatiale de l'onde laser, ce dispositif pouvant être utilisé pour des mesures de densité électronique dans des plasmas.The document referenced [5] studies the formation and consistency of fringes due to a wave X-ray laser illuminating a Mach-Zehnder interferometer. This document describes in particular a device and an interferometric method for assessing the temporal and spatial coherence properties of the laser wave, this device can be used to electronic density measurements in plasmas.

Le document référencé [6] décrit un dispositif de mesure d'une impulsion brève, unique, comprenant au moins un ensemble de mesure comportant une ligne conductrice à laquelle sont reliés un ensemble de photoconducteurs, la ligne et les photoconducteurs étant placés entre deux diélectriques formant un unique support dans lequel la longueur de la ligne séparant les photoconducteurs deux à deux est égale au produit de la vitesse de propagation sur la ligne par le rapport de la durée de l'impulsion sur le nombre de points de mesure, la durée de vie des porteurs majoritaires constituant les photoconducteurs étant choisie égale ou inférieure à 10 % de la durée de l'impulsion, le dispositif permettant ainsi d'obtenir une analyse temporelle ou la fonction d'autocorrélation de l'impulsion qui peut être une impulsion de rayonnement électromagnétique, ou ionisant ou une impulsion électrique. The document referenced [6] describes a single short pulse measurement device, comprising at least one measuring assembly comprising a conductive line to which a set of photoconductors, the line and the photoconductors being placed between two dielectrics forming a single support in which the length of the line separating the photoconductors two by two is equal to the product of the propagation speed over the line by the ratio of the duration of the pulse on the number of measuring points, the service life of majority carriers constituting the photoconductors being chosen equal to or less than 10% of the duration of the impulse, the device thus allowing to obtain a time analysis or the autocorrelation function of the impulse which can be an impulse of electromagnetic, or ionizing radiation or a electrical impulse.

Le document référencé [7] décrit des systèmes d'imagerie pour analyser des plasmas haute densité dans le régime rayons X mous. Le système d'expérimentation comprend un miroir sphérique multicouches qui réfléchit une bande étroite de rayonnement de rayons X mous dans la région d'énergie 50 à 200 ev. Ce miroir image soit l'émission propre d'un plasma produit par laser et/ou l'ombre du laser en expansion généré par une source de rayons X produite par un laser séparé avec approximativement une amplification de 50 dans le plan image et une résolution submicronique dans le plan de la cible. let temps de résolution d'environ 150 ps est obtenu soit avec un intensifieur de plaque microcanal à grille en tant que détecteur, soit un dispositif « backlighter » rayons X courtes impulsions.The document referenced [7] describes imaging systems to analyze high plasmas density in the soft X-ray regime. The system experiment includes a spherical mirror multilayer which reflects a narrow band of soft x-ray radiation in the energy region 50 to 200 ev. This mirror image is the own emission of a plasma produced by laser and / or the shadow of the laser in expansion generated by an X-ray source produced by a separate laser with approximately one amplification of 50 in the image plane and a submicron resolution in the target plane. let resolution time of around 150 ps is obtained either with a grid microchannel plate intensifier in as a detector, be a “backlighter” device short pulse X-rays.

Le document référencé [8] décrit l'utilisation de la technique de « backlighting» de rayons X mous pour mesurer la densité d'un plasma dense produit dans une décharge capillaire. Un plasma tellurium produit par laser est utilisé comme source de rayons X et une image flash à deux dimensions avec une résolution de 140 µm est obtenue.The document referenced [8] describes the use of the backlighting technique of soft X-rays to measure the density of dense plasma produced in a capillary discharge. Plasma tellurium produced by laser is used as a source of x-rays and a two-dimensional flash image with a 140 µm resolution is obtained.

Le document référencé [9] décrit un dispositif pour évaluer un élément optique rayons X. Il permet d'améliorer l'efficacité d'utilisation de rayons X provenant d'un générateur de rayons X en convertissant les rayons X provenant des moyens de projection en rayons X parallèles ou en condensant ceux-ci en un point.The document referenced [9] describes a device for evaluating an X-ray optical element. improves efficiency of use of shelves X from an X-ray generator in converting x-rays from the means of projection in parallel X-rays or by condensing these at one point.

Le document référencé [10] décrit un interféromètre à rayons X pour tester un plasma produit par laser avec des résolutions spatiales microniques. Un laser rayons X mous fonctionnant à 155 Angstrôm est combiné avec un interféromètre Mach-Zehnder multicouche pour obtenir des profils de densité électronique dans un plasma produit par l'irradiation laser d'une cible. The document referenced [10] describes a X-ray interferometer to test a plasma produced by laser with micron spatial resolutions. A soft X-ray laser operating at 155 Angstroms is combined with a multilayer Mach-Zehnder interferometer to get electron density profiles in a plasma produced by laser irradiation of a target.

L'invention a pour objet un procédé et un dispositif de caractérisation d'un milieu ionisé dans lequel on puisse :

  • acquérir une connaissance précise et résolue en temps (historique des processus) de l'évolution spatio-temporelle des caractéristiques physiques de ce milieu à durée de vie transitoire et à caractère évolutif dans un état hors-équilibre thermodynamique ;
  • déterminer des paramètres transitoires de durée ultracourte ; tout en palliant les inconvénients des dispositifs de l'art antérieur, définis ci-dessus.
The subject of the invention is a method and a device for characterizing an ionized medium in which it is possible:
  • acquire a precise and time-resolved knowledge (process history) of the spatio-temporal evolution of the physical characteristics of this medium with a transitory lifespan and of an evolving nature in a thermodynamic out-of-equilibrium state;
  • determine transient parameters of ultrashort duration; while overcoming the drawbacks of the devices of the prior art, defined above.

Exposé de l'inventionStatement of the invention

L'invention concerne un procédé de caractérisation d'un milieu ionisé en mettant en oeuvre une source de rayonnement électromagnétique de quelques 10-15 secondes de durée, dans lequel :

  • on utilise deux faisceaux laser synchronisés de rayonnement : un faisceau principal et un faisceau secondaire ;
  • on génère un rayonnement intense de radiation X ;
  • on réfléchit le rayonnement X de manière à le diriger et à le focaliser sur le volume de l'espace où se trouve situé le milieu ionisé ;
  • on réfléchit le rayonnement X, selon un angle spécifique dépendant de l'angle d'incidence sous la forme d'un faisceau de photons X composé d'un premier train d'impulsions X espacées régulièrement, ce train d'impulsions étant dirigé vers le milieu ionisé à diagnostiquer ;
  • on délivre un second train d'impulsions de même distribution temporelle que le premier ;
caractérisé en ce que :
  • on génère le rayonnement intense de radiation X par impact du faisceau principal sur une cible métallique, les caractéristiques de ce rayonnement dépendant de la cible sélectionnée ;
  • on détecte le rayonnement X réémis par le milieu ionisé avec un dispositif comprenant une ligne de transmission et plusieurs lignes d'échantillonnage pouvant être reliées à celle-ci par des éléments photoconducteurs en activant ces éléments photoconducteurs par le second train d'impulsions ;
  • on mesure et on enregistre les signaux délivrés par chaque ligne d'échantillonnage connectée aux éléments photoconducteurs.
The invention relates to a method for characterizing an ionized medium by using a source of electromagnetic radiation of a duration of 10 -15 seconds, in which:
  • two synchronized laser beams of radiation are used: a main beam and a secondary beam;
  • intense X-ray radiation is generated;
  • the X-ray is reflected so as to direct it and focus it on the volume of the space where the ionized medium is located;
  • the X-ray is reflected at a specific angle depending on the angle of incidence in the form of a beam of X photons composed of a first train of X pulses regularly spaced, this train of pulses being directed towards the ionized medium to be diagnosed;
  • a second train of pulses with the same time distribution as the first is delivered;
characterized in that:
  • generating intense X-ray radiation by impact of the main beam on a metal target, the characteristics of this radiation depending on the selected target;
  • detecting the X-ray re-emitted by the ionized medium with a device comprising a transmission line and several sampling lines which can be connected to the latter by photoconductive elements by activating these photoconductive elements by the second pulse train;
  • the signals delivered by each sampling line connected to the photoconductive elements are measured and recorded.

Avantageusement on utilise deux faisceaux laser principal et secondaire dérivés d'un même faisceau laser de durée ultracourte.Advantageously, two beams are used primary and secondary laser derived from the same ultra-short duration laser beam.

L'invention concerne également un dispositif de caractérisation d'un milieu ionisé, comprenant :

  • une source délivrant un faisceau laser de rayonnement électromagnétique de quelques 10-15 secondes de durée ;
  • un moyen de séparation de ce faisceau en deux faisceaux laser synchronisés de rayonnement : un faisceau principal et un faisceau secondaire ;
  • un moyen d'interaction qui génère un rayonnement intense de radiation X ;
  • un miroir réflecteur du rayonnement X de manière à le diriger et à le focaliser sur le volume de l'espace où se trouve situé le milieu ionisé ;
  • un moyen séquenceur orienté de manière à réfléchir le rayonnement X, selon un angle spécifique dépendant de l'angle d'incidence sous la forme d'un faisceau de photons X composé d'un premier train d'impulsions X espacées régulièrement, ce train d'impulsions X étant dirigé vers le milieu ionisé ;
  • une série d'optiques de reprise du faisceau secondaire ;
  • un séquenceur de faisceau laser délivrant un second train d'impulsions de même distribution temporelle que le premier ;
caractérisé en ce que le moyen d'interaction génère le rayonnement intense de radiation X sous l'effet du faisceau principal, les caractéristiques de ce rayonnement X dépendant du moyen d'interaction considéré ; et en ce que ledit dispositif comprend en outre :
  • un dispositif optoélectronique à la fois détecteur du rayonnement X réémis par le milieu ionisé et autocorrélateur optoélectronique comprenant une ligne de transmission et plusieurs lignes d'échantillonnage pouvant être reliées à celle-ci par des photocommutateurs, une ligne à retard optique étant associée à chaque élément photoconducteur, ces éléments photoconducteurs étant activés par le second train d'impulsion ;
  • un système électronique de mesure et d'enregistrement des signaux délivrés par chaque ligne d'échantillonnage connectée aux éléments photoconducteurs.
The invention also relates to a device for characterizing an ionized medium, comprising:
  • a source delivering a laser beam of electromagnetic radiation of a duration of 10 -15 seconds;
  • means for separating this beam into two synchronized laser beams of radiation: a main beam and a secondary beam;
  • an interaction means which generates intense X-ray radiation;
  • an X-ray reflecting mirror so as to direct it and focus it on the volume of the space in which the ionized medium is located;
  • a sequencer means oriented so as to reflect the X-ray radiation, at a specific angle depending on the angle of incidence in the form of a beam of X photons composed of a first train of X pulses regularly spaced, this train d X pulses being directed towards the ionized medium;
  • a series of optics for taking up the secondary beam;
  • a laser beam sequencer delivering a second train of pulses with the same time distribution as the first;
characterized in that the interaction means generates intense X-ray radiation under the effect of the main beam, the characteristics of this X-radiation depending on the interaction means considered; and in that said device further comprises:
  • an optoelectronic device which is both a detector of X-rays re-emitted by the ionized medium and an optoelectronic autocorrelator comprising a transmission line and several sampling lines which can be connected to this by photocwitches, an optical delay line being associated with each element photoconductive, these photoconductive elements being activated by the second pulse train;
  • an electronic system for measuring and recording the signals delivered by each sampling line connected to the photoconductive elements.

Dans un exemple de réalisation avantageux du dispositif de l'invention, le moyen d'interaction est un matériau-cible métallique compris parmi les matériaux suivants : titane, nickel, zinc ou tungstène qui, sous l'effet du faisceau principal focalisé par une lentille, génère un faisceau de rayons X.In an advantageous exemplary embodiment of the device of the invention, the interaction means is a metallic target material included among the following materials: titanium, nickel, zinc or tungsten which, under the effect of the main beam focused by a lens, generates an X-ray beam.

Un miroir de forme sphérique, réflecteur du rayonnement X, est situé entre le moyen d'interaction et le moyen séquenceur du faisceau de rayons X.A spherical mirror, reflector of the X-ray, is located between the interaction medium and the X-ray beam sequencing means.

Le moyen séquenceur du faisceau de rayons X est un miroir composé de couches métalliques réflectrices empilées régulièrement et orientées de manière à délivrer un faisceau de photons X composé d'un train d'impulsions X espacées temporellement régulièrement.The X-ray beam sequencing means is a mirror composed of metallic layers reflectors stacked regularly and oriented way to deliver a compound X-ray beam of a train of temporally spaced X pulses regularly.

Plusieurs moyens optiques réflecteurs sont disposés entre le moyen de séparation de faisceaux et le moyen de détection pour modifier le trajet du faisceau secondaire.Several reflecting optical means are disposed between the beam separation means and the detection means for modifying the path of the secondary beam.

Le moyen de détection de rayonnement est un composant optoélectronique de technologie micro-électronique type autocorrélateur, associant un substrat isolant, un matériau photoconducteur sous un impact laser de type rapide sur lequel est déposé une ligne de transmission métallique du signal électrique émis par le détecteur sous l'impact des rayons X secondaires réémis par le milieu ionisé.The radiation detection means is a microelectronic technology optoelectronic component autocorrelating type, combining a insulating substrate, a photoconductive material under a fast type laser impact on which is deposited a metallic electrical signal transmission line emitted by the detector under the impact of X-rays secondary re-emitted by the ionized medium.

Avantageusement le substrat isolant est un matériau saphir ou arséniure de gallium ou tellurure de cadmium (CdTe) ; le matériau photoconducteur est un matériau arséniure de gallium ou tellurure de cadmium basse température ; la ligne de transmission est en aluminium.Advantageously, the insulating substrate is a sapphire or gallium arsenide or telluride material cadmium (CdTe); the photoconductive material is a gallium arsenide or cadmium telluride material low temperature ; the transmission line is in aluminum.

La présente invention concerne donc un dispositif de caractérisation d'un milieu ionisé transitoire, résolue en temps.The present invention therefore relates to a device for characterizing an ionized medium transient, resolved in time.

Elle permet de diagnostiquer l'état physique d'un milieu ionisé de type plasma à chaque moment de son chauffage. Elle permet de détecter l'apparition de micro-instabilités qui perturbent ce chauffage.It helps diagnose the condition physics of an ionized plasma type medium at each time of its heating. It detects the appearance of micro-instabilities which disturb this heater.

L'invention s'applique notamment aux études :

  • de la matière condensée par radiographie éclair (domaine de la détonique) ;
  • des gaz ionisés ;
  • des claquages dans les gaz (bougies, éclateurs, foudre) ;
  • de la combustion dans les tuyères de réacteurs en aéronautique ;
  • du plasma de soudure laser ou à l'arc ;
  • du plasma de fusion magnétique ;
  • du plasma de fusion par confinement inertiel ;
  • en physique spatiale : étude de l'ionosphère et de la magnétosphère.
The invention is particularly applicable to studies:
  • matter condensed by flash radiography (field of detonics);
  • ionized gases;
  • breakdowns in the gases (candles, spark gaps, lightning);
  • combustion in the jet nozzles in aeronautics;
  • laser or arc welding plasma;
  • magnetic fusion plasma;
  • inertial confinement fusion plasma;
  • in spatial physics: study of the ionosphere and the magnetosphere.

Brève description des dessinsBrief description of the drawings

la figure illustre schématiquement le dispositif de l'invention.the figure schematically illustrates the device of the invention.

Exposé détaillé de modes de réalisationDetailed description of embodiments

Le dispositif de l'invention comporte les éléments suivants, représentés sur la figure 1 :

  • une source intense de lumière laser pulsée permettant de générer deux faisceaux laser synchronisés de rayonnement ; un faisceau principal 10 et un faisceau secondaire 12 ;
  • un matériau-cible 11 composé d'un matériau métallique, par exemple de type titane, nickel, zinc ou tungstène, qui sous l'effet du faisceau principal 10, focalisé par une lentille 13, génère un rayonnement intense de radiation X 15 dont les caractéristiques énergétiques (et spectrales) dépendent du matériau-cible sélectionné ;
  • un miroir 16, de forme sphérique par exemple, réflecteur du rayonnement X 15 de manière à le diriger et à la focaliser sur le volume de l'espace où se trouve situé le milieu ionisé ;
  • un miroir 18 composé de couches métalliques réflectrices 19 empilées régulièrement et orienté de manière à réfléchir le rayonnement X 15, selon un angle spécifique dépendant de l'angle d'incidence sous la forme d'un faisceau de photons X composé d'un premier train 20 d'impulsions X espacées régulièrement d'un délai temporel correspondant au temps de propagation aller et retour du faisceau incident dans chaque empilement de couches : ce faisceau de photons X 20 résultant de la réflexion sur le miroir multicouche 18 est dirigé vers le milieu ionisé 21 à diagnostiquer ;
  • un dispositif 22 permettant le dédoublement de la ligne optique du faisceau laser de durée ultracourte (soit dans le régime femtoseconde, quelques 10-15s, soit de durée beaucoup plus brève que la durée de vie du milieu ionisé à diagnostiquer) et d'obtenir ainsi le faisceau principal 10 et le faisceau secondaire 12 ;
  • une série d'optiques de reprise 23, 24, 25 et 26 de la deuxième ligne de transfert 12 du rayonnement laser ;
  • un séquenceur 37 de faisceau laser de type Michelson délivrant un second train d'impulsions de même distribution temporelle que le premier ;
  • un dispositif opto-électronique (30, 31) à la fois détecteur 30 du rayonnement X réémis par le milieu ionisé 21 et autocorrélateur optoélectronique 31 comprenant une ligne de transmission 34 et plusieurs lignes d'échantillonnage 32 pouvant être reliées à celle-ci par des photocommutateurs 33,
  • un ensemble de lignes à retard optique 38 associées chacune à un élément photoconducteur 33 ;
  • un système électronique de mesure 36 de type amplificateur de charge par exemple et d'enregistrement des signaux délivrés par chaque ligne d'échantillonnage 32 connectée aux photocommutateurs 33.
The device of the invention comprises the following elements, represented in FIG. 1:
  • an intense source of pulsed laser light making it possible to generate two synchronized laser beams of radiation; a main beam 10 and a secondary beam 12;
  • a target material 11 composed of a metallic material, for example of the titanium, nickel, zinc or tungsten type, which under the effect of the main beam 10, focused by a lens 13, generates an intense radiation of X-ray radiation 15 whose energy (and spectral) characteristics depend on the target material selected;
  • a mirror 16, of spherical shape for example, reflecting X-rays 15 so as to direct and focus it on the volume of the space in which the ionized medium is located;
  • a mirror 18 composed of reflective metal layers 19 regularly stacked and oriented so as to reflect the X-ray 15, at a specific angle depending on the angle of incidence in the form of a beam of X photons composed of a first train 20 of X pulses regularly spaced by a time delay corresponding to the outward and return propagation time of the incident beam in each stack of layers: this beam of X photons 20 resulting from the reflection on the multilayer mirror 18 is directed towards the ionized medium 21 to be diagnosed;
  • a device 22 enabling the optical line of the laser beam of ultrashort duration to be split (either in the femtosecond regime, some 10 -15 s, or of duration much shorter than the lifetime of the ionized medium to be diagnosed) and to obtain thus the main beam 10 and the secondary beam 12;
  • a series of optics 23, 24, 25 and 26 for recovering the second transfer line 12 of the laser radiation;
  • a Michelson type laser beam sequencer 37 delivering a second train of pulses with the same time distribution as the first;
  • an opto-electronic device (30, 31) both a detector 30 of the X-ray re-emitted by the ionized medium 21 and an opto-electronic autocorrelator 31 comprising a transmission line 34 and several sampling lines 32 which can be connected to the latter by means of photoswitches 33,
  • a set of optical delay lines 38 each associated with a photoconductive element 33;
  • an electronic measurement system 36 of the charge amplifier type, for example, and of recording the signals delivered by each sampling line 32 connected to the photoswitches 33.

Le dispositif optoélectronique 31 de technologie micro-électronique associe un substrat isolant, par exemple en un matériau tel que le saphir, l'arséniure de gallium, le tellurure de cadmium, un matériau photoconducteur (sous l'impact laser) de type rapide, par exemple en arséniure de gallium basse température, sur lequel est déposée la ligne de transmission métallique 34, le matériau utilisé étant par exemple l'aluminium, du signal électrique émis par le détecteur 30 sous l'impact des rayons X secondaires 35 réémis par le milieu ionisé 21.The optoelectronic device 31 of microelectronic technology combines a substrate insulator, for example in a material such as sapphire, gallium arsenide, cadmium telluride, a photoconductive material (under laser impact) of type fast, for example in low gallium arsenide temperature, on which is deposited the line of metallic transmission 34, the material used being for example aluminum, of the electrical signal emitted by the detector 30 under the impact of secondary X-rays 35 re-emitted by the ionized medium 21.

Sur la figure ces éléments photoconducteurs 33 sont formés chacun par une discontinuité entre chaque ligne d'échantillonnage 32 et la ligne de transmission 34. Lorsque ces photoconducteurs sont frappés par un faisceau laser il y a création de conduction pendant une fraction de picoseconde pendant laquelle on peut détecter un signal.In the figure these photoconductive elements 33 are each formed by a discontinuity between each sampling line 32 and the line of transmission 34. When these photoconductors are struck by a laser beam there is creation of conduction during a fraction of a picosecond during which one can detect a signal.

Ainsi, le dispositif optoélectronique 31 est un microsystème capable d'analyser des impulsions jusqu'à 50 Ghz. Ce dispositif est un composant intégré, réalisé dans une technologie de type microélectronique, et comprenant éléments photoconducteurs et lignes microrubans. Il est constitué d'une ligne de propagation principale 34 où est envoyé le signal unique à échantillonner, et de n lignes d'échantillonnage 32 disposées en "peigne" le long de cette ligne. Entre chacune de ces lignes d'échantillonnage et la ligne principale, se trouve un plot ou une couche de matériau photoconducteur 33. Le principe de ce dispositif est relativement simple et rappelle un peu celui de la photographie : à l'instant de propagation où le signal est en "retard" des lignes d'échantillonnage, une impulsion laser ultra-rapide éclaire et ferme les n interrupteurs que constituent les éléments photoconducteurs. Les signaux ainsi prélevés sont ensuite stockés dans une capacité et lus par une électronique dédiée.Thus, the optoelectronic device 31 is a microsystem capable of analyzing impulses up to 50 Ghz. This device is an integrated component, realized in a microelectronic type technology, and comprising photoconductive elements and lines microstrips. It consists of a line of main propagation 34 where the signal is sent unique to sample, and n lines 32 arranged in a "comb" along this line. Between each of these lines sampling line and the main line, there is a pad or layer of photoconductive material 33. The principle of this device is relatively simple and reminds a little of photography: right now propagation where the signal is "delayed" by the lines sampling, an ultra-fast laser pulse lights and closes the n switches that constitute photoconductive elements. The signals as well samples are then stored in a capacity and read by dedicated electronics.

Comme représenté sur la figure, chaque ligne 32 peut être reliée à un élément CCD 40 connecté à un tiroir chargé de stocker les informations dans un registre.As shown in the figure, each line 32 can be connected to a connected CCD 40 element to a drawer responsible for storing information in a register.

Le détecteur 30 est un détecteur sensible aux rayons X, très rapide. Il comprend un matériau photoconducteur dont les porteurs ont une durée de vie inférieure à la picoseconde ; ce peut être, par exemple, du CdTe, GaAs,Si dopé oxygène sur saphir ou diamant.Detector 30 is a sensitive detector x-ray, very fast. It includes material photoconductor whose carriers have a lifetime less than picosecond; it can be, by example, CdTe, GaAs, Si doped oxygen on sapphire or diamond.

Le dispositif optoélectronique 31 peut, également, être un dispositif à contact glissant dont le principe de fonctionnement est décrit dans le document référencé [4].The optoelectronic device 31 can, also, be a sliding contact device whose the operating principle is described in the document referenced [4].

Le dispositif de l'invention comprend donc deux faisceaux laser 10, 12 synchronisés, car dérivés par dédoublement d'un même faisceau laser 10 de durée ultracourte (en femtoseconde, c'est-à-dire quelques 10- 15s), lui-même déclenché par le générateur principal du milieu ionisé 21 déclenchant :

  • d'une part l'illumination du milieu ionisé 21 par une série d'impulsions ultracourtes 20 réparties et distribuées dans le temps, de rayonnement électromagnétique pulsé auxiliaire à courte longueur d'onde de type radiations X ; et,
  • d'autre part l'activation d'une série d'éléments photoconducteurs 33 par le second train d'impulsions laser de quelques femtosecondes de même distribution temporelle, dans la gamme une picoseconde à une nanoseconde, que le train 20 d'impulsions de radiations X.
The device of the invention therefore comprises two laser beams 10, 12 synchronized, since they are derived by splitting of the same laser beam 10 of ultrashort duration (in femtosecond, that is to say some 10 - 15 s), itself even triggered by the main generator of the ionized medium 21 triggering:
  • on the one hand, the illumination of the ionized medium 21 by a series of ultrashort pulses 20 distributed and distributed over time, of auxiliary pulsed electromagnetic radiation at short wavelength of X-radiation type; and,
  • secondly, the activation of a series of photoconductive elements 33 by the second train of laser pulses of a few femtoseconds of the same time distribution, in the range from one picosecond to one nanosecond, as train 20 of radiation pulses X.

Ces caractéristiques permettent de pallier au caractère monocoup (une seule impulsion laser possible) de ce dispositif de caractérisation du milieu ionisé 21.These characteristics make it possible to overcome single shot character (single laser pulse possible) of this environment characterization device ionized 21.

Le second train d'impulsions laser de quelques femtosecondes résulte non seulement de la distribution spatiale des photocommutateurs 33 mais peut aussi résulter d'une distribution temporelle du faisceau laser atténué délivré par le miroir 22, obtenue en faisant transiter le rayonnement laser de départ dans un dispositif séquenceur 37, par exemple du type Michelson suivi éventuellement d'un amplificateur de faisceau.The second laser pulse train of few femtoseconds results not only from the spatial distribution of the photoswitches 33 but can also result from a temporal distribution of the attenuated laser beam delivered by the mirror 22, obtained by passing the laser radiation from start in a sequencing device 37, for example Michelson type possibly followed by an amplifier beam.

L'échantillonnage d'une part de la source X et d'autre part du train d'impulsions laser de quelques femtosecondes, activant la série d'éléments photoconducteurs 33, correspond à la mise en oeuvre d'une mesure de type pompe-sonde selon un nouveau procédé et avec une nouvelle technologie d'autocorrélation optoélectronique. En effet, la modulation du phénomène de pompe ou de sonde n'est plus de type actif mais passif grâce :

  • d'une part à l'adjonction d'un miroir réflecteur X multicouche 18 qui joue le rôle de séquenceur en délivrant un train d'impulsions X ultracourtes 20 à un taux de répétition supérieur à celui de tous les dispositifs modulateurs existants ;
  • d'autre pari par l'adjonction d'un séquenceur optique 37 de faisceau laser.
The sampling on the one hand of the source X and on the other hand of the train of laser pulses of a few femtoseconds, activating the series of photoconductive elements 33, corresponds to the implementation of a measurement of the pump-probe type. according to a new process and with a new optoelectronic autocorrelation technology. In fact, the modulation of the pump or probe phenomenon is no longer of the active but passive type thanks to:
  • on the one hand to the addition of a multilayer X reflective mirror 18 which plays the role of sequencer by delivering a train of ultrashort X pulses 20 at a repetition rate higher than that of all existing modulating devices;
  • other bet by the addition of an optical sequencer 37 of laser beam.

Le procédé de l'invention, qui est un nouveau procédé d'application de la méthode pompe-sonde, a pour avantage de supprimer l'imprécision spatio-temporelle de l'art antérieur car il permet de sonder de manière discriminante le milieu ionisé de manière spatio-temporelle.The method of the invention, which is a new method of applying the pump-probe method, has the advantage of eliminating imprecision space-time of the prior art because it allows discriminatingly probe the ionized medium of spatio-temporal way.

Si on analyse à présent le fonctionnement du procédé de l'invention : on dispose d'un milieu ionisé 21 de type plasma, ou gaz ionisé, par exemple d'un microplasma (cas du plasma laser à confinement inertiel). Au préalable une source laser émet un faisceau 10 dont la durée d'impulsion est inférieure à la durée de vie du plasma. Ce faisceau laser 10 frappe une cible métallique 11 et produit un flux 15 de radiations X intense et brève. Ce flux de radiations 15 est dirigé vers le milieu ionisé 21 à étudier et à diagnostiquer. Ce milieu 21 renvoie une partie de ce flux de radiations X vers un récepteur détecteur 30. Ce dernier analyse temporellement le signal reçu en fonction du faisceau laser qui génère le flux. De plus, l'invention consiste dans la mise en oeuvre simultanée :

  • d'un faisceau laser de puissance à durée ultracourte dont la plus grande partie de l'énergie, donc de la puissance, est destinée à générer, par impact sur une cible métallique 11, un faisceau 15 de rayons X et, dont l'autre faible partie 12 de l'énergie sert à piloter l'échantillonnage du dispositif optoélectronique 31 ;
  • d'un miroir multicouche 18 à radiations X destiné :
    • à diriger le faisceau réfléchi vers le milieu ionisé à illuminer,
    • à moduler et distribuer temporellement le flux de rayonnement X primaire 15 en une pluralité d'impulsions X 20 retardées régulièrement dans le temps. En effet, la propagation et les réflexions successives des impulsions X sur les couches régulièrement empilées a pour finalité de moduler temporellement en allongeant le temps d'illumination X du milieu ionisé par impulsions X discriminées. A partir des coefficients d'absorption et de réflexion des couches du miroir 18, un rapide calcul permet de choisir l'espacement et le nombre des couches réflectrices du miroir X en fonction de l'allongement de la plage temporelle recherchée. Sachant que n fois 100 femtosecondes supplémentaires correspondent à chaque couche espacée de 30 µ m (n étant l'indice du matériau à la longueur d'onde moyenne des radiations X), il est possible de sélectionner l'écart temporel entre les illuminations de chaque microsource X ;
  • d'un dispositif optoélectronique 30, 31 qui a pour fonction à la fois :
    • de détecter le rayonnement X réémis par le milieu ionisé, et
    • de discriminer le signal généré par ce même détecteur dans la ligne de transmission, par un autocorrélateur à échantillonnage temporel résultant de l'illumination successive des éléments photoconducteurs (distribués le long de la ligne de propagation) par le faisceau laser secondaire 12.
If we now analyze the operation of the process of the invention: there is an ionized medium 21 of the plasma type, or ionized gas, for example a microplasma (case of laser plasma with inertial confinement). Beforehand, a laser source emits a beam 10 whose pulse duration is less than the lifetime of the plasma. This laser beam 10 strikes a metal target 11 and produces a flow 15 of intense and brief X-rays. This radiation flow 15 is directed towards the ionized medium 21 to be studied and diagnosed. This medium 21 returns part of this X-ray radiation flow to a detector receiver 30. The latter temporally analyzes the signal received as a function of the laser beam which generates the flow. In addition, the invention consists in the simultaneous implementation:
  • an ultra-short duration power laser beam, most of whose energy, therefore power, is intended to generate, by impact on a metal target 11, a beam 15 of X-rays and, the other of which low part 12 of the energy is used to control the sampling of the optoelectronic device 31;
  • a X-ray multilayer mirror 18 intended for:
    • directing the reflected beam towards the ionized medium to be illuminated,
    • modulating and distributing the primary X-ray flux 15 temporally in a plurality of X-pulses 20 regularly delayed in time. The purpose of the propagation and the successive reflections of the X pulses on the regularly stacked layers is to temporally modulate by lengthening the illumination time X of the medium ionized by discriminated X pulses. From the absorption and reflection coefficients of the layers of the mirror 18, a rapid calculation makes it possible to choose the spacing and the number of the reflecting layers of the mirror X as a function of the lengthening of the sought time range. Knowing that n times 100 additional femtoseconds correspond to each layer spaced 30 µ m (n being the material index at the average wavelength of X-rays), it is possible to select the time difference between the illuminations of each microsource X;
  • an optoelectronic device 30, 31 which has the function of both:
    • detect X-rays re-emitted by the ionized medium, and
    • to discriminate the signal generated by this same detector in the transmission line, by a time-sampling autocorrelator resulting from the successive illumination of the photoconductive elements (distributed along the propagation line) by the secondary laser beam 12.

REFERENCESREFERENCES

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  • [3] "Faraday-Rotation Measurements of Megagauss Magnetic Fields in Laser-Produced Plasmas" de J.A. Stamper et B.H. Ripin (Physical Review Letters, volume 34, n° 3, pages 138-141, 20 janvier 1975)[3] "Faraday-Rotation Measurements of Megagauss Magnetic Fields in Laser-Produced Plasmas "by J.A. Stamper and B.H. Ripin (Physical Review Letters, volume 34, n ° 3, pages 138-141, 20 January 1975)
  • [4] "Mise au point d'un banc de test d'un générateur optoélectronique d'impulsions électromagnétiques ultracourtes" de Christophe Rivière (Projet de fin d'études, Ecole Nationale Supérieure de Physique de Grenoble ; Spécialité : Instrumentation physique effectué au service de physique expérimentale CEA/CESTA.- Département technique, du 1er mars au 15 Septembre 1994)[4] "Development of a generator test bench electromagnetic pulse optoelectronics ultracourtes "by Christophe Rivière (End project studies, National School of Physics of Grenoble; Specialty: Physical instrumentation performed in the experimental physics department CEA / CESTA.- Technical department, from March 1 to September 15, 1994)
  • [5] "Fringe Formation and Coherence Of a Soft-X-ray Laser Beam Illuminating a Mach-Zehnder Interferometer » de P. Celliers, F. Weber, L.B. Da Silva, T.W. Barbee, R. Cauble, A.S. Wan et J.C. Moreno (Optics Letters, 15 septembre, 1995, Volume 20, numéro 18, pages 1907 à 1909)[5] "Fringe Formation and Coherence Of a Soft-X-ray Laser Beam Illuminating a Mach-Zehnder Interferometer "by P. Celliers, F. Weber, L.B. Da Silva, T.W. Barbee, R. Cauble, A.S. Wan and J.C. Moreno (Optics Letters, September 15, 1995, Volume 20, number 18, pages 1907 to 1909)
  • [6] EP-A-0 327 420 [6] EP-A-0 327 420
  • [7] « Time Resolved Soft X-Ray Imaging With Submicron Spatial Resolution (Invited) » de O. Willi, T. Afshar-Rad, M. Desselberger, M. Dunne, J. Edwards, F. Khattak et R. Taylor (Review of Scientific instruments, volume 63, numéro 10, PCT II, octobre 1992, ISSN 0034-6748, pages 4818-4822, XP000321111)[7] "Time Resolved Soft X-Ray Imaging With Submicron Spatial Resolution (Invited) "by O. Willi, T. Afshar-Rad, M. Desselberger, M. Dunne, J. Edwards, F. Khattak and R. Taylor (Review of Scientific instruments, volume 63, number 10, PCT II, October 1992, ISSN 0034-6748, pages 4818-4822, XP000321111)
  • [8] « Density Measurement Of Dense Capillary Discharge Plasma using Soft X-Ray Backlighting » de B. Brill, B. Arad, M. Kishenevsky, A. Ludmisky et A. Zigler (Journal of Physics D,Applied Physics , volume 23, numéro 8, 14 août 1990, pages 1064-1068, XP 000150819)[8] "Density Measurement Of Dense Capillary Discharge Plasma using Soft X-Ray Backlighting "by B. Brill, B. Arad, M. Kishenevsky, A. Ludmisky and A. Zigler (Journal of Physics D, Applied Physics, volume 23, number 8, August 14, 1990, pages 1064-1068, XP 000150819)
  • [9] Patents Abstracts of Japan, volume 014, numéro 094 (P-1010), 21 février 1990, & JP-A-01301153, & Database WPI, Section ch, Week 9003, Derwent Publications Ltd, Londre, GP, Class K08, AN90-020040)[9] Patents Abstracts of Japan, volume 014, number 094 (P-1010), February 21, 1990, & JP-A-01301153, & Database WPI, Section ch, Week 9003, Derwent Publications Ltd, London, GP, Class K08, AN90-020040)
  • [10] « Electron Density Measurements Of High Density Plasmas Using Soft X-Ray laser Interferometry » de C.B Da Silva, T.W. Barbee, R. Cauble, P. Celliers, D. Ciarlo, S. Libby, R.A. London, D. Mattjews, S. Mrowka, J.C. Moreno, D. Ress, J.E. Trebes, A.S. Wan, et F. Weber (Physical Review Letters, volume 74, 1995, pages 3991-3994)[10] "Electron Density Measurements Of High Density Plasmas Using Soft X-Ray Laser Interferometry ”from C.B Da Silva, T.W. Barbee, R. Cauble, P. Celliers, D. Ciarlo, S. Libby, R.A. London, D. Mattjews, S. Mrowka, J.C. Moreno, D. Ress, J.E. Trebes, A.S. Wan, and F. Weber (Physical Review Letters, volume 74, 1995, pages 3991-3994)

    • Claims (17)

    1. Method of characterizing an ionized medium using an electromagnetic radiation source of some 10-15 seconds duration, in which:
      two synchronized laser beams are used: a primary beam (10) and a secondary beam (12);
      intense X-ray radiation (15) is generated;
      the X-ray radiation (15) is reflected such that it is directed and focused onto the volume of space where the ionized medium is located;
      the X-ray radiation (15) is reflected, at a specific angle depending on the angle of incidence, in the form of a beam of X-ray photons consisting of a first train (20) of regularly-spaced X-ray pulses, this pulse train (20) being directed towards the ionized medium (21);
      a second pulse train with the same temporal distribution as the first is delivered;
      characterized in that:
      the intense X-ray radiation (15) is generated by impact of the primary beam (10) on a metal target (11), the characteristics of this radiation depending on the target selected;
      the X-ray radiation re-emitted by the ionized medium (21) is detected (30) with a device (31) comprising a transmission line (34) and several sampling lines (32) able to be connected to the transmission line by photoconducting components (33) on activating these photoconducting components by the second pulse train;
      the signals delivered by each sampling line (32) connected to the photoconducting components (33) are measured (36) and recorded.
    2. Method according to Claim 1, characterized in that the operation of the laser beams is synchronized to that of the device generating the ionized medium to be characterized.
    3. Method according to Claim 1, characterized in that two laser beams (10, 12) are used, a primary beam and a secondary beam derived from the same laser beam of some 10-15 seconds duration.
    4. Device for characterizing an ionized medium, comprising:
      a source delivering a laser beam (10) of electromagnetic radiation of some 10-15 seconds duration;
      a means (22) for splitting this beam into two synchronized laser beams: a primary beam (10) and a secondary beam (12);
      an interaction means (11) which generates intense X-ray radiation (15);
      a mirror (16) for reflecting the X-ray radiation (15) such that it is directed and focused onto the volume of space where the ionized medium is located;
      a sequencing means (18) oriented so as to reflect the X-ray radiation (15), at a specific angle depending on the angle of incidence, in the form of a beam of X-ray photons consisting of a first train (20) of regularly-spaced X-ray pulses, this X-ray pulse train (20) being directed towards the ionized medium (21);
      a series of optical components (23, 24, 25 and 26) for returning the secondary beam;
      a laser beam sequencer (37) delivering a second pulse train with the same temporal distribution as the first;
      characterized in that the interaction means (11) generates the intense X-ray radiation under the effect of the primary beam (10), the characteristics of this radiation depending on the interaction means in question and in that the said device comprises, in addition:
      an optoelectronic device (30, 31) which acts both as a detector (30) of the X-ray radiation re-emitted by the ionized medium (21) and as an optoelectronic autocorrelator (31) comprising a transmission line (34) and several sampling lines (32) able to be connected to the transmission line by photoconducting components (33), an optical delay line (38) being combined with each photoconducting component (33), these photoconducting components being activated by the second pulse train;
      an electronic system for measuring (36) and recording signals delivered by each sampling line (32) connected to the photoconducting components (33).
    5. Device according to Claim 4, characterized in that the optoelectronic autocorrelating device (31) is a device for discriminating (31) the signal generated in a transmission line (34) by temporal sampling, resulting from the successive illumination of photoconducting components (33) distributed along this line (34) by the second pulse train.
    6. Device according to Claim 4, characterized in that the interaction means is a target material (11) which, under the effect of the primary beam (10) focused by a lens (13), generates an X-ray beam (15).
    7. Device according to Claim 6, characterized in that the target material (11) consists of a metal.
    8. Device according to Claim 7, characterized in that this metal is one of the following metals: titanium, nickel, zinc or tungsten.
    9. Device according to Claim 4, characterized in that this mirror (16) is a mirror of spherical shape.
    10. Device according to Claim 4, characterized in that the means for sequencing the X-ray beam is a mirror (18) consisting of regularly-stacked metallic reflecting layers and oriented so as to deliver a beam of X-ray photons consisting of a train (20) of regularly-spaced X-ray pulses.
    11. Device according to Claim 4, characterized in that several optical reflecting means (23, 24, 25, 26) are placed between the beam separation means (22) and the detection means (31) in order to modify the path of the secondary beam (12).
    12. Device according to Claim 4, characterized in that the detection means is an optoelectronic component made using microelectronics technology combining an insulating substrate and a photoconducting material under a fast laser impact, on which is deposited a metal line (34) for transmitting the electrical signal emitted by a detector (30) under the impact of the secondary X-rays (35) re-emitted by the ionized medium (21).
    13. Device according to Claim 12, characterized in that the insulating substrate is sapphire or gallium arsenide or cadmium telluride.
    14. Device according to Claim 12, characterized in that the photoconducting material is low-temperature cadmium telluride or gallium arsenide.
    15. Device according to Claim 12, characterized in that the transmission line is made of aluminium.
    16. Device according to Claim 4, characterized in that the means for sequencing the secondary beam (37) is a device of the Michelson type.
    17. Device according to Claim 16, characterized in that this sequencing means (37) is followed by a beam amplifier.
    EP96943163A 1995-12-22 1996-12-20 Method and device for characterising an ionised medium using an electromagnetic radiation source having an ultrashort duration Expired - Lifetime EP0868835B1 (en)

    Applications Claiming Priority (3)

    Application Number Priority Date Filing Date Title
    FR9515390 1995-12-22
    FR9515390A FR2742866B1 (en) 1995-12-22 1995-12-22 METHOD AND DEVICE FOR CHARACTERIZING AN IONIZED MEDIUM USING AN ULTRA-SHORT ELECTROMAGNETIC RADIATION SOURCE
    PCT/FR1996/002047 WO1997024020A1 (en) 1995-12-22 1996-12-20 Method and device for characterising an ionised medium using an electromagnetic radiation source having an ultrashort duration

    Publications (2)

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    EP0868835A1 EP0868835A1 (en) 1998-10-07
    EP0868835B1 true EP0868835B1 (en) 2001-07-25

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    EP96943163A Expired - Lifetime EP0868835B1 (en) 1995-12-22 1996-12-20 Method and device for characterising an ionised medium using an electromagnetic radiation source having an ultrashort duration

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    EP (1) EP0868835B1 (en)
    DE (1) DE69614143D1 (en)
    FR (1) FR2742866B1 (en)
    WO (1) WO1997024020A1 (en)

    Family Cites Families (2)

    * Cited by examiner, † Cited by third party
    Publication number Priority date Publication date Assignee Title
    FR2626376B1 (en) * 1988-01-22 1990-07-13 Commissariat Energie Atomique DEVICE AND METHOD FOR MEASURING A SHORT RADIATION PULSE OR A BRIEF ELECTRIC PULSE
    JPH01301153A (en) * 1988-05-30 1989-12-05 Toshiba Corp Device for evaluating x-ray optical element

    Non-Patent Citations (2)

    * Cited by examiner, † Cited by third party
    Title
    OPT. LETTERS, vol. 20, 1995, pages 1907-1909 *
    PHYSICAL REVIEW LETTERS, vol. 74, 1995, pages 3991-3994 *

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    DE69614143D1 (en) 2001-08-30
    FR2742866A1 (en) 1997-06-27
    WO1997024020A1 (en) 1997-07-03
    EP0868835A1 (en) 1998-10-07

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