EP0916236A1 - Device for generating ultra-short x-ray pulses - Google Patents

Device for generating ultra-short x-ray pulses

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Publication number
EP0916236A1
EP0916236A1 EP97935647A EP97935647A EP0916236A1 EP 0916236 A1 EP0916236 A1 EP 0916236A1 EP 97935647 A EP97935647 A EP 97935647A EP 97935647 A EP97935647 A EP 97935647A EP 0916236 A1 EP0916236 A1 EP 0916236A1
Authority
EP
European Patent Office
Prior art keywords
ray
pulses
rays
focusing
radiation
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP97935647A
Other languages
German (de)
French (fr)
Inventor
Jean-François A. Résidence Rosiers ELOY
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Original Assignee
Commissariat a lEnergie Atomique CEA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Commissariat a lEnergie Atomique CEA filed Critical Commissariat a lEnergie Atomique CEA
Publication of EP0916236A1 publication Critical patent/EP0916236A1/en
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21K—TECHNIQUES FOR HANDLING PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
    • G21K1/00—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating
    • G21K1/06—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating using diffraction, refraction or reflection, e.g. monochromators
    • G21K1/062—Devices having a multilayer structure
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y10/00—Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21K—TECHNIQUES FOR HANDLING PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
    • G21K1/00—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating
    • G21K1/06—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating using diffraction, refraction or reflection, e.g. monochromators

Definitions

  • the present invention relates to a device for generating ultra-short pulses of electromagnetic radiation of the X-ray type. It allows in particular:
  • the device which is the subject of the invention makes it possible to diagnose the physical state of a condensed medium, ionized (of the plasma type) or not, at each moment of its evolution. This device makes it possible to detect the appearance of this micro-instabilities which disturb the thermodynamic equilibrium.
  • the present invention finds applications in particular in studies:
  • electromagnetic radiation short wavelength, X-ray type
  • Such a source is sometimes called an auxiliary source.
  • This technique requires the use of a source of intense electromagnetic radiation, capable of illuminating the medium that one wants to study during its transient evolutionary phase.
  • the characteristics of the radiation from this source are chosen in such a way that the measurements, either of the reflected part, or of the transmitted part of this auxiliary electromagnetic radiation, can reveal, after interference and detection, the spatial and physical characteristics. temporal specific of the medium which was illuminated by this source.
  • This known method consists in illuminating this plasma or this medium with an ultra-short pulse of X-ray radiation, induced by the impact of a beam to be lasered. of ultra-short duration (a few femtoseconds) on a metal target.
  • a method of diagnosing a condensed medium, ionized or not, molecular or atomic, is also known.
  • This method consists in illuminating this medium by partially coherent electromagnetic radiation, of the svnchrotron radiation type, emitted during the interaction of a beam of relativistic electrons with a magnetic structure of the inverter type ("wiggler").
  • a pulsed radiation source either coherent (laser radiation), or partially coherent (synchrotron radiation of interaction of relativistic electrons-magnetic structure of inverter type) or inconsistent
  • X-ray In the case of the study of a plasma-laser, it is known that this radiation can originate from the source of laser radiation which generates the plasma-laser to be studied. In this case, the diagnostic means is called X-ray X-ray.
  • the radiation is reflected or transmitted can be focused diffractively in order to provide an image of the condensed medium via a camera.
  • a material made up of a multilayer lamellar network diffracts an X-ray beam of given energy band as a function of the angle of incidence, on the one hand by dispersing the radiation in reflected multibeams of specific wavelengths (according to the different corresponding orders) and on the other hand by reducing the bandwidth.
  • a metallic surface or a crystal for example a rubidium phthalate crystal, or RBAP, a potassium phthalate crystal, or KAP, or a lead stearate crystal
  • a metallic surface or a crystal for example a rubidium phthalate crystal, or RBAP, a potassium phthalate crystal, or KAP, or a lead stearate crystal
  • the devices of the prior art have a repeating optical source producing a sufficient number of pulses of electromagnetic radiation to illuminate the medium with a high repetition rate, during a shortest possible time.
  • the devices fulfilling this function temporally modulate the radiation beam in a free pulse dispersing means of the type
  • the principles of generating ultra-short pulses and using the modulator-sequencer forming part of these devices remain limited to the spectral domains of use of the optical components, ranging from the domain visible in the infrared and submillimetric domains. This does not apply to pulses of X-laser or synchrotron radiation.
  • the pulse X serving as a probe cannot be considered to be of ultra-short duration compared to the lifetime of the atomic and molecular states to be studied,
  • the object of the present invention is to remedy the above drawbacks by proposing a device for generating ultra-short pulses of X-rays which uses two multilayer lamellar networks for X-rays which occupy conjugate positions.
  • the subject of the present invention is a device for generating pulses: on X-ray radiation, this device: f etar.t characterized in that l comprises:
  • first and second multilayer lamellar networks for X-ray radiation occupying positions which are optically conjugate with each other, and - first and second X-ray focusing means, having a common focus and forming an optical assembly which is placed on the path of the X-ray, between the first and second networks, the X-ray thus passing from the intermediate optical means to the first network then to the second network via the first focusing means and then the second focusing means, the second network supplying ultra-short pulses of X-ray radiation.
  • this device further comprises a mterferential filter which is arranged at the level of the focal plane common to the first and second focusing means.
  • this device further comprises an adjustable collimation means which is arranged at the focal plane common to the first and second focusing means.
  • this device further comprises an adjustable collimation means and a mterferential filter which are arranged at the level of the focal plane common to the first and second focusing means.
  • Each of the first and second focusing means may comprise a cylindrical mirror for X-rays or a sphe ⁇ que mirror for X-rays or a curved crystal capable of focusing the X-rays.
  • the intermediate optical means can also comprise a cylindrical mirror for X-ray radiation or a spherical mirror for X-rays or a curved crystal capable of focusing X-rays.
  • This crystal can be a rubidium phthalate crystal or a potassium phthalate crystal.
  • the means for generating the X-ray drawn beam include:
  • FIG. 1 represents a block diagram of an example of the device described in document (1)
  • FIGS. 2A to 2C represent the time evolution of various signals or beams used in the context of a method described in this document (1)
  • FIG. 3 is a block diagram of an autocorrelator with optoelectronic sampling usable with the device of FIG. 1,
  • FIG. 4 is a schematic view of a particular embodiment of the device which is the subject of the invention, using a mterferential filter, and
  • FIG. 5 is a schematic view of another particular embodiment of the device object of the invention, using a collimation means. Detailed description of specific embodiments
  • FIG. 1 represents a block diagram of an example of the device described in this document (1).
  • a laser not shown in FIG. 1, emits pulses of radiation referenced 2 in this FIG. 1.
  • the pulses emitted by the laser are preferably pulses of the femtosecond type, with a temporal width of the order of 10 " to 10 " 13 s.
  • Target 6 is composed of a metallic material of the titanium, nickel, zinc or tungsten type. Under the effect of the focused laser beam 2, a radiative emission from the surface of this target takes place, which results in the emission of intense radiation 8 of X-ray radiation, the energy and spectral characteristics of which depend on the target material selected. .
  • the radiation beam thus obtained is reflected by a mirror 12, for X-rays, in the direction of a multilayer mirror 14.
  • This mirror essentially comprises a series of alternating layers 16, 18 20, 22.
  • these layers may for example be alternately layers of carbon and tungsten, or tungsten and molybdenum.
  • This multilayer mirror makes it possible to transform a single incident X-ray pulse into a plurality of pulses constituting a tra of pulses. In fact, a single X-ray pulse will undergo successive propagation and reflections on the stacked layers.
  • n is the index of the material constituting a layer of the mirror, at the average wavelength of the X-rays, and knowing that a delay of nxlOO additional femtoseconds corresponds to a layer thickness of 30 ⁇ m (for directions of orthogonal incidence and reflection), it is possible to select the time difference between the X pulses of the pulse tram.
  • the multilayer mirror 14 allows
  • the angle solid of the reflected X-ray beam is sufficient to separate (by collimation) this beam into two distinct branches in two different directions.
  • the temporal evolution of the intensity of the pulsed laser beam is shown schematically in solid lines in FIG. 2A, while the curve in dashed lines schematically represents the temporal evolution of the X-ray pulse obtained after breakdown on the surface of the target 16.
  • This second pulse is wider than the first: for a laser pulse of the order of 10 " " s, the X-ray pulse has a time width of approximately 10 '* - s.
  • FIG. 2B represents the time evolution of the pulse tra obtained after reflection of a single X-ray pulse on the multilayer mirror 14.
  • the pulse tram has as many peaks or elementary pulses as there are reflections on the mirror 1.
  • Each of the two beams, the beam emitted towards the medium 24 to be studied and the reference beam 30 emitted towards the detector 26, have the same time distribution as that shown in FIG. 2B.
  • Temporal evolution signal 32 is schematically shown in Figure 2C.
  • the detector is therefore subjected to two beams • the reference beam 30 coming directly from the mirror multilayer 14, and the signal beam 32 re-emitted by the medium 2.
  • the field to be taken into account for the triggering of the latter is the electric field
  • E E 0 + E 2 , where E 0 is the contribution of the beam 30 to the electric field, at the detector 26, and E., is the contribution of the beam 32 to the electric field, at the level of the detector 26. Consequently, if the fields E 0 and E- are, at a certain time t, in phase, the detector is sensitive to the total field and is triggered.
  • This principle makes it possible to "mark" the signal beam 32 with a known time reference (the beam 30).
  • the fast or ultra-fast detector 26 is sensitive in the range of radiation to be studied.
  • this may for example be a detector based on an ultra-fast photoconductive material, the lifetime of the carriers being less than 1 ps.
  • Such a material can be CdTe, GaAs, silicon doped with oxygen on sapphire or diamond.
  • Diamond is the best performing material because it is the most resistant to radiation.
  • This detector 26 can be coupled to an optoelectronic autocorrelator device 34, with sliding contact.
  • This sampler is a microsystem capable of analyzing pulses up to 50 gigahertz.
  • FIG. 3 Schematically, such a device is shown in Figure 3. It is an integrated component, made in a microelectronic type technology.
  • It comprises a main propagation line 36 on which the single signal S (t) to be sampled is sent, as well as n sampling lines 38-1, 38-2, 38-3, ..., 38-n.
  • sampling lines 38- ⁇ (l £ ⁇ ⁇ n) are arranged in a "comb" along the main line.
  • each of the sampling lines 38- ⁇ and the main line 36 is a pad 40- ⁇ (l i ⁇ n) of photoconductive material.
  • Each sampling line is also also connected to a storage capacity 42-1, 42-2, ..., 42-n as well as to an acquisition electronics not shown in FIG. 3.
  • Each photoconductive element 40 -1, 40-2, ..., 40-n is triggered by an ultra-fast laser pulse.
  • a convenient means of obtaining such a pulse for each photoconductive element consists, as shown in FIG. 1, of taking a secondary beam 44-1 from the beam 2 of the femtosecond laser, using a mirror 46.
  • This secondary beam 44-1 can itself be divided into several into several sub-beams 44-2, ..., 44-n, using partially transparent mirrors 43-2, ..., 43-n , interposed on its route.
  • the main sub-beam 44-1 triggers the photoconductive element 40-1.
  • a first secondary sub-beam 44-2 obtained using the mirror 43-2 triggers the photoconductive element 40-2 at an instant determined by the length of the delay line defined by the beam path between the mirror 43 -2 and the photoconductive element 40-2.
  • the third photoconductive element 40-3 is triggered by a second secondary sub-beam 44-3, at an instant itself defined by the length of a second delay line.
  • each photoconductive element 40- ⁇ (l £ i ⁇ n), the latter being triggered at an instant t i. defined by the length of the ith delay line.
  • the ultrafast laser pulse incident on a photoconductor 40- ⁇ closes the switch formed by this photoconductor.
  • a signal is then taken, signal which corresponds to the intensity of the signal S opposite the line i at time t. closing the photoconductor.
  • each photoconductive material may for example be cadmium telluride Pass temperature
  • the main and secondary transmission lines can be made of aluminum.
  • An electronic circuit for measuring for example of the charge amplifier type, and for recording the signals delivered by each sampling line
  • the time step for sampling the signal delivered by the photodetector 26 is defined by the spatial distance between two neighboring lines 38-i, as explained in the publication mentioned above.
  • 40-1 is closed, determines when the sampling will start.
  • this triggering instant will define the portion of the plasma or of the medium 24 being studied, from which the analyzed signals will be retransmitted. This means that it is possible to choose to sample signals coming from a peripheral zone 50 of the studied medium 24 or from a zone 52 lying deep in the studied medium 24.
  • the device according to the invention which is schematically shown in Figure 4, is intended to generate ultrashort X-ray pulses.
  • these ultra-short X-ray pulses are intended for the characterization of a medium 53.
  • the device of FIG. 4 comprises: means 54 for generating a pulsed beam 55 of X-ray radiation,
  • an intermediate optical means 56 which transforms this beam 55 into a pulsed beam 58 substantially parallel to X-ray radiation (that is to say that the rays of this beam 58 are substantially parallel to each other),
  • first multi-layer lamellar network 60 for X-ray radiation as well as a second multi-layer lamellar network 62 for X-ray radiation, these networks 60 and 62 occupying positions which are optically conjugate with each other, and
  • first means 6-4 for focusing X-rays as well as a second means 66 for focusing X-rays which have a common focal plane and therefore a common focal point and form an optical assembly placed on the path of the X-ray between the reeds 60 and 62.
  • the X-ray interacts successively with the optical means 56, the network 60, the focusing means 64, the location means 66 and the network 62.
  • Ultra-short pulses 67 of X-ray radiation are consequently supplied by the network 62 and sent to the medium 53 via a mirror 68 for X-ray radiation, this mirror 68 being, for example, plane.
  • the means 54 for generating the drawn beam 55 of X-ray radiation include:
  • an intense laser source 70 capable of emitting ultra-short laser pulses 71
  • a target 72 which is made of a solid material and which is capable of producing the intense beam 55 when it receives the laser pulses.
  • the ultra-short pulses supplied by the laser 70 are focused on the target 72 by an appropriate lens 74.
  • ultra-short pulses pulses of duration less than 10 " s, for example lying in the range from 10 " 1 "to 10 " 1 "s, or in any case of much longer duration short as the lifespan of the medium that we want to study.
  • the target 72 is made of a metallic material such as T, Ni, Zn or W.
  • the energetic and spectral characteristics of the intense beam 55 depend on this material.
  • the X-radiation, reference 76 which is retransmitted by the medium 53 after interaction thereof with the radiation 69 reflected by the mirror 68, is measured by a suitable sensor 78 which is associated with an optoelectronic autocorrelating device 80.
  • This device 80 is controlled by ultra-short laser pulses 81 which are taken from the palse beam from the laser 70 using a. n beam beam splitter 82 which is placed in the beam supplied by the laser 70 as seen in FIG. 4.
  • the device of FIG. 4 also comprises a mterferential filter 84 which is arranged at the level of the focal plane P common to the focusing means 64 and 66.
  • the networks 60 and 62 comprise reflective metallic layers regularly stacked.
  • Each of the focusing means 64 and 66 can be a cylindrical or spherical mirror for X-rays or a curved crystal, capable of focusing X-rays.
  • a rubidium phthalate crystal or a potassium phthalate crystal can be used.
  • the intermediate optical means 56 can be a cylindrical or spherical mirror for X-ray radiation or a curved crystal, for example made of rubidium phthalate or potassium phthalate, of a suitable shape for focusing X-ray radiation.
  • the device according to the invention differs from that of FIG. 4 by the fact that it includes, instead of the mterferential filter 84, a collimation means 86 which is arranged at the level from the focal plane P common to the focusing means 64 and 66.
  • the filter 84 and the collimation means 86 are used in the fo ⁇ .s and these are placed at the focal plane P.
  • the collimating means 86 can be a collimator or an openwork absorbent screen.
  • this collimation means 86 is adjustable in the sense that it is displaceable parallel to the focal plane P in order to be able to select such and such a line of the radiation coming from the focusing means 64.
  • X-ray radiation from a synchrotron can be used as 55 radiation.
  • control the device 80 it is possible to use pulses produced by a triggering system itself controlled by synchrotron radiation.
  • the intermediate optical means 56 makes it possible not only to significantly reduce the divergence of the beam 55 but also to filter the high frequencies and bass of this beam 55.
  • the networks 60 and 62 which occupy conjugate positions and are associated with the focusing means 64 and 66, make it possible to remedy the drawbacks of the prior art.
  • Each source point of the surface of the network 60 has an image point on the network 62 located at the same optical distance for all the equivalent frequency space.
  • the beam resulting from the processing by the optical system composed of the grids 60 and 62 and the focusing means 64 and 66 has the same spectral distribution.
  • the multiplicity of X-rays which are reflected at the same angle (and therefore have the same frequency) and which originate from the different source points of the surface of the network 60 will traverse optical trajectories that are shorter as the frequency of the considered radius will be higher due to the spectral dispersion property of the networks 60 and 62.
  • the optical paths of the probing beams X (which come from the network 60 and are references FI, ..., FN, with N> 2, only the beams FI and FN being represented) appear, according to the mterferential structure of the filter 84 and / or the position of the collimator 86, at reflection angles (due to the properties of the grating 60) which differ according to the mean useful frequency of the X-ray.
  • the respective positions considered of the source points and of the image points on the networks occupying conjugate positions, according to the characteristics of emission from the laser source (or synchrotron).
  • the orientations of the two networks in conjugate positions offer a new possibility of temporal modulation of the single pulse original following a train of X pulses (which can reach 5 to 15 successive pulses) with a repetition rate which can be high and reach a few terahertz according to the principle of a sequencing system of the Michelson type applied to X-ray beams .
  • the collimation reduces the bandwidth of the probing beams X and limits the duration of the resulting pulse.
  • the choice of distribution and arrangement of the assembly formed by the networks 60, 62, the focusing means 64, 66, the filter 84 and / or the collimation means 86 depends on the temporal dispersion characteristics sought for the beam X.
  • the choice of the position of the colli ation means 86 essentially allows the processing and selection of a preferential part of the X-ray spectrum.
  • the assembly consisting of networks 60, 62, focusing means 64, 66, and the filter 84 and / or the collimation means 86 provides an X-ray beam composed of a train of X pulses which are regularly spaced apart. '' the same time interval and which are then directed towards the medium 53 to be characterized, by means of the mirror 68 for X-rays provided for this purpose.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Chemical & Material Sciences (AREA)
  • Nanotechnology (AREA)
  • Mathematical Physics (AREA)
  • Theoretical Computer Science (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Analysing Materials By The Use Of Radiation (AREA)
  • X-Ray Techniques (AREA)

Abstract

A device for generating ultra-short X-ray pulses is disclosed. The device includes means (54) for generating a pulsed X-ray beam, means (56) for converting said beam into a substantially parallel beam, first and second multilayer lamellar X-ray arrays (60, 62) in mutually optically conjugated positions, and X-ray focusing means (64, 66) having a common focus and arranged between the arrays. The second array provides the ultra-short pulses. The device is useful for characterising media.

Description

DISPOSITIF DE GENERATION D'IMPULSIONS ULTRA-COURTES DEVICE FOR GENERATING ULTRA-SHORT PULSES
DE RAYONNEMENT XRADIATION X
DESCRIPTIONDESCRIPTION
Domaine techniqueTechnical area
La présente invention concerne un dispositif de génération d'impulsions ultra-courtes de rayonnement électromagnétique du type rayons X. Elle permet notamment :The present invention relates to a device for generating ultra-short pulses of electromagnetic radiation of the X-ray type. It allows in particular:
• de disposer d'une source de rayonnement électromagnétique de durée d'émission suffisamment courte et répétitive pour permettre d'acquérir une connaissance précise et résolue en temps (historique des processus) de l'évolution spatio-temporelle des caractéristiques physiques des mil] eux condensés ou gazeux, moléculaires ou atomiques, ionises ou non, a durée de vie transitoire et a caractère évolutif dans un état hors équilibre thermodynamique,• to have a source of electromagnetic radiation of sufficiently short and repetitive duration of emission to allow to acquire a precise and resolved knowledge in time (process history) of the spatio-temporal evolution of the physical characteristics of millet] them condensed or gaseous molecular or atomic, ionized or not a duration of transient life and evolving nature da n s a non-equilibrium state,
• de déterminer les propriétés physiques transitoires, de durée ultra-courte, des milieux ionisés et condenses a instabilités localisées.• to determine the transient physical properties, of ultra-short duration, of the ionized and condensed media with localized instabilities.
Le dispositif objet de l'invention permet de diagnostiquer l'état physique d'un milieu condense, ionise (de type plasma) ou non, a chaque moment de son évolution. Ce dispositif permet de détecter l'apparition ce micro-instabilités qui perturbent l'equ liore thermodynamique . La présente invention trouve des applications notamment dans les études :The device which is the subject of the invention makes it possible to diagnose the physical state of a condensed medium, ionized (of the plasma type) or not, at each moment of its evolution. This device makes it possible to detect the appearance of this micro-instabilities which disturb the thermodynamic equilibrium. The present invention finds applications in particular in studies:
• de la matière condensée par radiographie- éclair (dans le domaine de la détonique) , • des gaz ionisés,• matter condensed by flash x-ray (in the field of detonics), • ionized gases,
• des claquages dans les gaz (en particulier dans le domaine des bougies, des éclateurs et de la foudre) ,• breakdowns in the gases (in particular in the field of candles, spark gaps and lightning),
• de la combustion dans les tuyères de réacteurs (en aéronaut: que ) ,• combustion in reactor nozzles (in aeronautics: that),
• de réacteurs photochimiques,• photochemical reactors,
• des plasmas de souαure par laser ou de soudure à l'arc,• laser welding or arc welding plasmas,
• des plasmas de fusion magnétique, • des plasmas de fusion par confinement mertiel,• magnetic fusion plasmas, • mertial confinement fusion plasmas,
• de l'ionosphère et de la magnétosphère (en physique spatiale).• the ionosphere and the magnetosphere (in spatial physics).
Etat de la technique antérieureState of the art
Pour mesurer et connaître les propriétés thermodynamiques, électroniques et physico-chimiques des milieux condensés ou gazeux, moléculaires ou atomiques, ionisés ou non, à durée de vie transitoire et à caractère évolutif, tels que les plasmas laser, les plasmas de combustion dans les tuyères, les plasmas de souαure à l'arc ou de soudure par laser, les milieux que l'en rencontre dans les chambres de combustion ou les c.-.ambres de réaction photochimique, il est généralement rais en oeuvre des moyens de diagnostic et de spertroscopie faisant appel à 1 ' éclairement de ces milieux par une source de rayonnement électromagnétique (de courte longueur d'onde, du type rayonnement X) constituant un rayonnement externe.To measure and know the thermodynamic, electronic and physicochemical properties of condensed or gaseous, molecular or atomic media, ionized or not, with transient lifetime and of evolving nature, such as laser plasmas, combustion plasmas in nozzles , arc welding or laser welding plasmas, the media encountered in combustion chambers or photochemical reaction chambers, it is generally used diagnostic and spertroscopy using the illumination of these media by a source of electromagnetic radiation (short wavelength, X-ray type) constituting external radiation.
Une telle source est parfois appelée source auxiliaire . Cette technique nécessite la mise en oeuvre d'une source de rayonnement électromagnétique intense, capable d'illuminer le milieu que l'on veut étudier pendant sa phase évolutive transitoire.Such a source is sometimes called an auxiliary source. This technique requires the use of a source of intense electromagnetic radiation, capable of illuminating the medium that one wants to study during its transient evolutionary phase.
De plus, les caractéristiques du rayonnement issu de cette source sont choisies de telle manière que les mesures, soit de la partie réfléchie, soit de la partie transmise de ce rayonnement électromagnétique auxiliaire, puisse révéler, après interférence et détection, les caractéristiques physiques spatio- temporelles spécifiques du milieu qui a ete illuminé par cette source.In addition, the characteristics of the radiation from this source are chosen in such a way that the measurements, either of the reflected part, or of the transmitted part of this auxiliary electromagnetic radiation, can reveal, after interference and detection, the spatial and physical characteristics. temporal specific of the medium which was illuminated by this source.
A ce sujet, on consultera le document suivant et notamment la description αe sa figure 1 :On this subject, one will consult the following document and in particular the description in its figure 1:
(ι) Demande de brevet français n°9515393 du(ι) French patent application n ° 9515393 of
22 décembre 1995, intitulée "Procède et dispositif inte'-ferometriques de caracterisation d'un milieu", invention de Jean-François ELOY.December 22, 1995, entitled "Process and inter-ferometric device for characterizing a medium", invention of Jean-François ELOY.
On connaît aussi une méthode de diagnostic au rayonnement électromagnétique ems par un plasma ionise ou non, ou par un milieu condense.There is also known a method of diagnosis with electromagnetic radiation ems by an ionized plasma or not, or by a condensed medium.
Cette méthode connue consiste a illuminer ce p__asma ou ce milieu par une impulsions ultra-courte de rayonnement X, induite par l'impact d'un faisceau ιaser de durée ultra-courte (quelques femtosecondes) sur une cible métallique.This known method consists in illuminating this plasma or this medium with an ultra-short pulse of X-ray radiation, induced by the impact of a beam to be lasered. of ultra-short duration (a few femtoseconds) on a metal target.
A ce sujet, on consultera le document suivant :On this subject, consult the following document:
(2) Demande de brevet français n°9515390 du 22 décembre 1995, intitulée "Procédé et dispositif de caractérisation d'un milieu ionisé mettant en oeuvre une source de rayonnement électromagnétique à durée ultracourte", invention de Jean-François ELOY et Hans WILHELMSSON.(2) French patent application No. 9515390 of December 22, 1995, entitled "Method and device for characterizing an ionized medium using an electromagnetic radiation source with an ultra-short duration", invention of Jean-François ELOY and Hans WILHELMSSON.
On connaît par ailleurs une méthode de diagnostic de milieu condensé, ionise ou non, moléculaire ou atomique .A method of diagnosing a condensed medium, ionized or not, molecular or atomic, is also known.
Cette méthode consiste a illuminer ce milieu par un rayonnement électromagnétique partiellement cohérent, du type rayonnement svnchrotron, émis lors de l'interaction d'un faisceau d'eiectrons relativistes avec une structure magnétique αe type onduleur ("wiggler") .This method consists in illuminating this medium by partially coherent electromagnetic radiation, of the svnchrotron radiation type, emitted during the interaction of a beam of relativistic electrons with a magnetic structure of the inverter type ("wiggler").
A cet effet, il est connu d'utiliser une source de rayonnement puisé, soit cohérent (rayonnement laser), soit partiellement cohérent (rayonnement synchrotron d'interaction électrons relativistes-structure magnétique de type onduleur) soit incohérentFor this purpose, it is known to use a pulsed radiation source, either coherent (laser radiation), or partially coherent (synchrotron radiation of interaction of relativistic electrons-magnetic structure of inverter type) or inconsistent
( rayonnement X) . Dans le cas de l'étude d'un plasma-laser, on sait que ce rayonnement peut avoir pour origine la source de rayonnement laser qui engendre le plasma-laser a étudier . Dans ce cas, le moyen de diagnostic est dénommé radiographie par flash X.(X-ray). In the case of the study of a plasma-laser, it is known that this radiation can originate from the source of laser radiation which generates the plasma-laser to be studied. In this case, the diagnostic means is called X-ray X-ray.
On sait aussi que le rayonnement soit réfléchi soit transmis peut être focalisé de manière diffractive afin de fournir une image du milieu condensé par l'intermédiaire d'une caméra.It is also known that the radiation is reflected or transmitted can be focused diffractively in order to provide an image of the condensed medium via a camera.
Il est connu par ailleurs qu'un matériau constitue en reseau lamellaire ulticouche (par exemple des couches de tungstène-carbone) diffracte un faisceau de rayonnement X de bande d'énergie donnée en fonction de l'angle d'incidence, d'une part en dispersant le rayonnement en multifaisceaux réfléchis de longueurs d'ondes spécifiques (suivant les différents ordres correspondants) et d'autre part en réduisant la bande passante.It is also known that a material made up of a multilayer lamellar network (for example tungsten-carbon layers) diffracts an X-ray beam of given energy band as a function of the angle of incidence, on the one hand by dispersing the radiation in reflected multibeams of specific wavelengths (according to the different corresponding orders) and on the other hand by reducing the bandwidth.
A ce sujet, on consultera le document suivant :On this subject, consult the following document:
(3) S. BAC, Journal of X Ray Science and Technology, vol. 5, p. 161 a 180, 1995.(3) S. BAC, Journal of X Ray Science and Technology, vol. 5, p. 161-180, 1995.
On sait aussi qu'une surface métallique ou un cristal (par exemple un cristal de phtalate de rubidium, ou RBAP, un cristal de phtalate de potassium, ou KAP, ou un cristal de stéarate de plomb) , de forme convexe ou concave, peut faire diverger ou converger un faisceau de rayonnement X en superposant a cet effet de lentille X un effet de filtrage en fréquence du rayonnement réfléchi.It is also known that a metallic surface or a crystal (for example a rubidium phthalate crystal, or RBAP, a potassium phthalate crystal, or KAP, or a lead stearate crystal), of convex or concave shape, can causing an X-ray beam to diverge or converge by superimposing on this X-ray lens effect a frequency filtering effect of the reflected radiation.
Pour améliorer la resolution spatio-temporelle de ces moyens de caractérisation et, du même coup, la compréhension des phénomènes physiques transitoires dans les milieux condensés ou les milieux gazeux ionisés à propriétés évolutives, les dispositifs de l'art antérieur disposent d'une source optique répétitive produisant un nombre suffisant d'impulsions de rayonnement électromagnétique pour illuminer le milieu avec un taux de répétition élevé, durant un temps le plus bref possible.To improve the spatio-temporal resolution of these characterization means and, at the same time, the understanding of transient physical phenomena in condensed media or ionized gaseous media with evolving properties, the devices of the prior art have a repeating optical source producing a sufficient number of pulses of electromagnetic radiation to illuminate the medium with a high repetition rate, during a shortest possible time.
Les dispositifs remplissant cette fonction modulent temporellement le faisceau de rayonnement dans un moyen de dispersion d'impulsion libre de typeThe devices fulfilling this function temporally modulate the radiation beam in a free pulse dispersing means of the type
Michelson (voir le document (1)).Michelson (see document (1)).
Il existe une première limitation importante d'application de ces dispositifs de l'art antérieur pour atteindre des résolutions spatio-temporelles élevées : la durée des impulsions de rayonnement X ou de rayonnement synchrotron est trop longue, car nettement supérieure à une picoseconde.There is a first important limitation in the application of these devices of the prior art for achieving high space-time resolutions: the duration of the X-ray or synchrotron radiation pulses is too long, since it is clearly greater than a picosecond.
Il existe aussi une seconde limitation importante d'application de ces dispositifs de l'art antérieur pour atteindre des résolutions spatio-temporelles élevées : l'impossibilité technique d'obtenir des sources X à haut taux de répétition.There is also a second important limitation in the application of these devices of the prior art to achieve high spatio-temporal resolutions: the technical impossibility of obtaining X sources with a high repetition rate.
En effet, en raison de propriétés spécifiques des matériaux utilisés, les principes de génération d'impulsions ultra-courtes et d'utilisation du modulateur-séquenceur faisant partie de ces dispositifs restent limités aux domaines spectraux d'utilisation des composants optiques, allant du domaine visible au domaine infrarouge et au domaine submillimétrique . Cela n'est pas applicable aux impulsions de rayonnement X-laser ou synchrotron.Indeed, due to the specific properties of the materials used, the principles of generating ultra-short pulses and using the modulator-sequencer forming part of these devices remain limited to the spectral domains of use of the optical components, ranging from the domain visible in the infrared and submillimetric domains. This does not apply to pulses of X-laser or synchrotron radiation.
Dans une méthode de diagnostic de milieux condenses et/ou ionisés évolutifs temporellement, le fait que les impulsions de rayonnement X ne soient pas de durée suffisamment brève présente des inconvénients :In a method of diagnosing condensed and / or ionized media that are temporally evolving, the the fact that the X-ray pulses are not of sufficiently short duration has drawbacks:
• l'impulsion X servant de sonde ne peut pas être considérée de durée ultracourte par rapport à la durée de vie des états atomiques et moléculaires à étudier,• the pulse X serving as a probe cannot be considered to be of ultra-short duration compared to the lifetime of the atomic and molecular states to be studied,
• cette impulsion perd ses propriétés particulières de propagation dans ces milieux à la limite des valeurs de fréquence-plasma de coupure .• this pulse loses its particular propagation properties in these media at the limit of the cutoff frequency-plasma values.
Exposé de l'inventionStatement of the invention
La présente invention a pour but de remédier aux inconvénients précédents en proposant un dispositif de génération d'impulsions ultra-courtes de rayonnement X qui utilise deux réseaux lamellaires multicouches pour rayonnement X qui occupent des positions conjuguées.The object of the present invention is to remedy the above drawbacks by proposing a device for generating ultra-short pulses of X-rays which uses two multilayer lamellar networks for X-rays which occupy conjugate positions.
De façon précise, la présente invention a pour objet un dispositif de génération d ' impuls: ons αe rayonnement X, ce disposit: f etar.t caractérisé en ce qu' l comprend :Specifically, the subject of the present invention is a device for generating pulses: on X-ray radiation, this device: f etar.t characterized in that l comprises:
- des moyens de génération d'un faisceau puise de rayonnement X, - un moyen optique intermédiaire apte a transformer ce faisceau en un faisceau puise sensiblement parallèle de rayonnement X,means for generating a beam drawn from X-ray radiation, an intermediate optical means capable of transforming this beam into a beam drawn from substantially parallel X-ray radiation,
- des premier et deuxième réseaux lamellaires multicouches pour rayonnement X, occupant des positions optiquement conjuguées l'une de l'autre, et - des premier et deuxième moyens de focalisation de rayonnement X, ayant un foyer commun et formant un ensemble optique qui est placé sur le trajet du rayonnement X, entre les premier et deuxième réseaux, le rayonnement X passant ainsi du moyen optique intermédiaire au premier réseau puis au deuxième réseau par l'intermédiaire du premier moyen de focalisation puis du deuxième moyen de focalisation, le deuxième reseau fournissant des impulsions ultra-courtes de rayonnement X.first and second multilayer lamellar networks for X-ray radiation, occupying positions which are optically conjugate with each other, and - first and second X-ray focusing means, having a common focus and forming an optical assembly which is placed on the path of the X-ray, between the first and second networks, the X-ray thus passing from the intermediate optical means to the first network then to the second network via the first focusing means and then the second focusing means, the second network supplying ultra-short pulses of X-ray radiation.
Selon un premier mode de réalisation particulier du dispositif objet de l'invention, ce dispositif comprend en outre un filtre mterferentiel qui est disposé au niveau du plan focal commun aux premier et deuxième moyens de focalisation. Selon un deuxième mode de réalisation particulier, ce dispositif comprend en outre un moyen de collimation réglable qui est disposé au niveau du plan focal commun aux premier et deuxième moyens de focalisation.According to a first particular embodiment of the device which is the subject of the invention, this device further comprises a mterferential filter which is arranged at the level of the focal plane common to the first and second focusing means. According to a second particular embodiment, this device further comprises an adjustable collimation means which is arranged at the focal plane common to the first and second focusing means.
Selon un troisième mode de réalisation particulier, ce dispositif comprend en outre un moyen de collimation réglable et un filtre mterferentiel qui sont disposés au niveau du plan focal commun aux premier et deuxième moyens de focalisation.According to a third particular embodiment, this device further comprises an adjustable collimation means and a mterferential filter which are arranged at the level of the focal plane common to the first and second focusing means.
Chacun des premier et deuxième moyens de focalisation peut comprendre un miroir cylindrique pour rayonnement X ou un miroir spheπque pour rayonnement X ou un cristal couroe apte à focaliser le rayonnement X.Each of the first and second focusing means may comprise a cylindrical mirror for X-rays or a spheπque mirror for X-rays or a curved crystal capable of focusing the X-rays.
Le moyen optique intermédiaire peut aussi comprendre un miroir cylindrique pour rayonnement X ou un miroir spherique pour rayonnement X ou un cristal courbe apte a focaliser le rayonnement X.The intermediate optical means can also comprise a cylindrical mirror for X-ray radiation or a spherical mirror for X-rays or a curved crystal capable of focusing X-rays.
Ce cristal peut être un cristal de phtalate de rubidium ou un cristal de phtalate de potassium. Selon un mode de réalisation particulier de l'invention, les moyens de génération du faisceau puise de rayonnement X comprennent :This crystal can be a rubidium phthalate crystal or a potassium phthalate crystal. According to a particular embodiment of the invention, the means for generating the X-ray drawn beam include:
- un laser apte a émettre des impulsions laser, et - une cible qui est faite d'un matériau solide et qui est apte a produire le faisceau puise de rayonnement X lorsqu'elle reçoit les impulsions laser.- a laser capable of emitting laser pulses, and - a target which is made of a solid material and which is capable of producing the beam drawn from X-ray radiation when it receives the laser pulses.
Le dispositif objet de l'invention présente les avantages suivants :The device which is the subject of the invention has the following advantages:
- il permet de multiplier la somme des données que l'on peut collecter sur un milieu a caractériser, par unité de temps et par expérience, au moyen d'un faisceau de rayonnement X, a haut taux c^ r pétition,- it makes it possible to multiply the sum of the data that can be collected on a medium to be characterized, per unit of time and by experience, by means of an X-ray beam, at a high rate of petition,
- il permet de réduire a αuree des impulsions X permettant de sonder le milieu en dispersant spectralement et en comprimant temporellement ces impulsions au moyen de deux reseaux lamellaires multicouches,- it makes it possible to reduce X-ray pulses at a rapid rate, making it possible to probe the medium by spectrally dispersing and temporally compressing these pulses by means of two multilayer lamellar networks,
- il permet de réduire, si nécessaire, la largeur spectrale des impulsions X en sélectionnant la fréquence moyenne utile du rayonnement au moyen d'une fente collimafrice positionnée a cet effet entre les deux reseaux lamellaires multicouches, d'où un avantage supplémentaire du dispositif qui permet alors d'améliorer la résolution temporelle d'un diagnostic effectué au moyen de ce dispositif.- it makes it possible to reduce, if necessary, the spectral width of the X pulses by selecting the useful average frequency of the radiation by means of a collimafrice slot positioned for this purpose between the two multilayer lamellar networks, hence an additional advantage of the device which then lets to improve the temporal resolution of a diagnosis carried out using this device.
Brève description des dessinsBrief description of the drawings
La présente invention sera mieux comprise à la lecture de la description d'exemples de réalisation donnés ci-après, à titre purement indicatif et nullement limitatif, en faisant référence aux dessins annexés sur lesquels :The present invention will be better understood on reading the description of exemplary embodiments given below, by way of purely indicative and in no way limiting, with reference to the appended drawings in which:
- la figure 1 représente un schéma de principe d'un exemple du dispositif décrit dans le document ( 1 ) ,FIG. 1 represents a block diagram of an example of the device described in document (1),
- les figures 2A a 2C représentent l'évolution temporelle de divers signaux ou faisceaux mis en oeuvre dans le cadre d'un procédé décrit dans ce document (1),FIGS. 2A to 2C represent the time evolution of various signals or beams used in the context of a method described in this document (1),
- la figure 3 est un schéma de principe d'un autocorrélateur a échantillonnage optoélectronique utilisable avec le dispositif de la figure 1,FIG. 3 is a block diagram of an autocorrelator with optoelectronic sampling usable with the device of FIG. 1,
- la figure 4 est une vue schématique d'un mode de réalisation particulier du dispositif objet de l'invention, utilisant un filtre mterferentiel, etFIG. 4 is a schematic view of a particular embodiment of the device which is the subject of the invention, using a mterferential filter, and
- la figure 5 est une vue schématique d'un autre mode de réalisation particulier du dispositif objet de l'invention, utilisant un moyen de collimation. Exposé détaillé de modes de réalisation particuliers- Figure 5 is a schematic view of another particular embodiment of the device object of the invention, using a collimation means. Detailed description of specific embodiments
On commence par revenir sur le document (1) . La figure 1 représente un schéma de principe d'un exemple du dispositif décrit dans ce document (1) . Un laser, non représenté sur la figure 1, émet des impulsions d'un rayonnement référencé 2 sur cette figure 1.We start by going back to document (1). FIG. 1 represents a block diagram of an example of the device described in this document (1). A laser, not shown in FIG. 1, emits pulses of radiation referenced 2 in this FIG. 1.
Ce rayonnement est focalisé par une lentille 4 à la surface d'une cible solide 6. Les impulsions émises par le laser sont de préférence des impulsions de type femtoseconde, avec une largeur temporelle de l'ordre de 10" a 10"13 s.This radiation is focused by a lens 4 on the surface of a solid target 6. The pulses emitted by the laser are preferably pulses of the femtosecond type, with a temporal width of the order of 10 " to 10 " 13 s.
La cible 6 est composée d'un matériau métallique de type titane, nickel, zinc ou tungstène. Sous l'effet du faisceau laser focalisé 2, une émission radiative de la surface de cette cible a lieu, et il en resuite l'émission d'un rayonnement intense 8 de rayonnement X, dont les caractéristiques énergétiques et spectrales dépendent du matériau cible sélectionné.Target 6 is composed of a metallic material of the titanium, nickel, zinc or tungsten type. Under the effect of the focused laser beam 2, a radiative emission from the surface of this target takes place, which results in the emission of intense radiation 8 of X-ray radiation, the energy and spectral characteristics of which depend on the target material selected. .
Le faisceau de rayonnement ainsi obtenu est réfléchi par un miroir 12, pour rayons X, en direction d'un miroir multicouche 14.The radiation beam thus obtained is reflected by a mirror 12, for X-rays, in the direction of a multilayer mirror 14.
Ce miroir comporte essentiellement une série de couches alternées 16, 18 20, 22.This mirror essentially comprises a series of alternating layers 16, 18 20, 22.
Pour l'application au domaine de rayonnement X, ces couches peuvent être par exemple alternativement des couches de carbone et de tungstène, ou de tungstène et de molybdène. Ce miroir multicouche permet de transformer une impulsion de rayonnement X unique, incidente, en une pluralité d'impulsions constituant un tra d ' impulsions . En effet, une impulsion unique de rayonnement X va subir une propagation et des reflexions successives sur les couches empilées.For application to the X-ray domain, these layers may for example be alternately layers of carbon and tungsten, or tungsten and molybdenum. This multilayer mirror makes it possible to transform a single incident X-ray pulse into a plurality of pulses constituting a tra of pulses. In fact, a single X-ray pulse will undergo successive propagation and reflections on the stacked layers.
A partir des coefficients d'absorption et de réflexion des couches du miroir 14, il est possible de choisir l'espacement et le nombre des couches reflectπces du miroir en fonction de la plage temporelle sur laquelle le tram d'impulsion doit être étale . Si n est 1 ' indice du matériau constitutif d'une couche du miroir, a la longueur d'onde moyenne des rayons X, et sachant qu'un retard de nxlOO femtosecondes supplémentaires correspond a une épaisseur de couche de 30 μm (pour des directions d'incidence et de reflexion orthogonales), il est possible de sélectionner l'écart temporel entre les impulsions X du tram d'impulsions.From the absorption and reflection coefficients of the layers of the mirror 14, it is possible to choose the spacing and the number of the reflective layers of the mirror as a function of the time range over which the pulse tram must be spread. If n is the index of the material constituting a layer of the mirror, at the average wavelength of the X-rays, and knowing that a delay of nxlOO additional femtoseconds corresponds to a layer thickness of 30 μm (for directions of orthogonal incidence and reflection), it is possible to select the time difference between the X pulses of the pulse tram.
En fait, le miroir multicouche 14 permetIn fact, the multilayer mirror 14 allows
- d'une part de diriger deux faisceaux réfléchis, comportant chacun un train d'impulsions X ayant les mêmes caractéristiques temporelles, l'un des faisceaux étant émis vers le milieu a étudier 24 et l'autre (faisceau sonde 30 ou faisceau de référence) étant émis en direction d'un détecteur 26,on the one hand to direct two reflected beams, each comprising a train of pulses X having the same temporal characteristics, one of the beams being emitted towards the medium to be studied 24 and the other (probe beam 30 or reference beam ) being emitted towards a detector 26,
- de moduler et de distribuer temporellement une impulsion unique de rayonnement X primaire pour former une pluralité, ou tram, d'impulsions X retardées régulièrement dans le temps, remplaçant ainsi ou jouant ainsi le rôle d'une pluralit de sources X décalées dans le temps.- to modulate and distribute in time a single pulse of primary X-ray to form a plurality, or tram, of X pulses delayed regularly in time, thus replacing or thus playing the role of a plurality of X sources shifted in time .
Du fait de l'ouverture angulaire du faisceau de rayonnement X sur le miroir multicouches, l'angle solide du faisceau X réfléchi est suffisant pour séparer (par collimation) ce faisceau en deux branches distinctes selon deux directions différentes.Due to the angular opening of the X-ray beam on the multilayer mirror, the angle solid of the reflected X-ray beam is sufficient to separate (by collimation) this beam into two distinct branches in two different directions.
L'évolution temporelle de l'intensité du faisceau laser impulsionnel est représentée schématiquement en trait plein sur la figure 2A, tandis que la courbe en traits interrompus représente schématiquement l'évolution temporelle de l'impulsion de rayonnement X obtenue après claquage en surface de la cible 16. Cette deuxième impulsion est plus large que la première : pour une impulsion laser de l'ordre de 10" " s, l'impulsion de rayonnement X a une largeur temporelle d'environ 10'*- s.The temporal evolution of the intensity of the pulsed laser beam is shown schematically in solid lines in FIG. 2A, while the curve in dashed lines schematically represents the temporal evolution of the X-ray pulse obtained after breakdown on the surface of the target 16. This second pulse is wider than the first: for a laser pulse of the order of 10 " " s, the X-ray pulse has a time width of approximately 10 '* - s.
La figure 2B représente l'évolution temporelle du tra d'impulsions obtenu après reflexion d'une impulsion unique de rayonnement X sur le miroir multicouche 14.FIG. 2B represents the time evolution of the pulse tra obtained after reflection of a single X-ray pulse on the multilayer mirror 14.
Le tram d'impulsions comporte autant de pics ou d'impulsions élémentaire qu'il y a de reflexions sur le miroir 1 .The pulse tram has as many peaks or elementary pulses as there are reflections on the mirror 1.
Chacun des deux faisceaux, le faisceau émis en direction au milieu 24 a étudier et le laisceεu de référence 30 émis en direction du détecteur 26, ont la même distribution temporelle que celle représentée sur la figure 2B.Each of the two beams, the beam emitted towards the medium 24 to be studied and the reference beam 30 emitted towards the detector 26, have the same time distribution as that shown in FIG. 2B.
L'interaction du train d'impulsions, c'est-a-dire du faisceau 28, avec le milieu 24, provoque la reemission, par ce dernier, d'un faisceau-signal 32 en direction du détecteur 26. L'évolution temporelle du signal 32 est schématiquement représentée sur la figure 2C .The interaction of the train of pulses, that is to say of the beam 28, with the medium 24, causes the re-transmission, by the latter, of a signal beam 32 in the direction of the detector 26. Temporal evolution signal 32 is schematically shown in Figure 2C.
Le détecteur est donc soumis a deux faisceaux • le faisceau de référence 30 issu directement du m±roir multicouche 14, et le faisceau-signal 32 réémis par le milieu 2 .The detector is therefore subjected to two beams • the reference beam 30 coming directly from the mirror multilayer 14, and the signal beam 32 re-emitted by the medium 2.
Ces deux faisceaux interfèrent au niveau du détecteur 26 : le champ à prendre en compte pour le déclenchement de ce dernier est le champ électriqueThese two beams interfere at the level of the detector 26: the field to be taken into account for the triggering of the latter is the electric field
E = E0 + E2 , où E0 est la contribution du faisceau 30 au champ électrique, au niveau du détecteur 26 , et E., est la contribution du faisceau 32 au champ électrique, au niveau du détecteur 26. Par conséquent, si les champs E0 et E-, sont, à un certain instant t, en phase, le détecteur est sensible au champ total et est déclenche.E = E 0 + E 2 , where E 0 is the contribution of the beam 30 to the electric field, at the detector 26, and E., is the contribution of the beam 32 to the electric field, at the level of the detector 26. Consequently, if the fields E 0 and E- are, at a certain time t, in phase, the detector is sensitive to the total field and is triggered.
Par contre, si, à un instant t', les composantesOn the other hand, if, at an instant t ', the components
E.., et E sont en opposition de phase, le champ résultant est nul au niveau du détecteur 26 et ce dernier n'est pas déclenché.E .., and E are in phase opposition, the resulting field is zero at the detector 26 and the latter is not triggered.
Ce principe permet de "marquer" le aisceau-signal 32 avec une référence temporelle connue (le faisceau 30) . Le détecteur rapide ou ultrarapide 26 est sensible dans la gamme des rayonnements a étudier.This principle makes it possible to "mark" the signal beam 32 with a known time reference (the beam 30). The fast or ultra-fast detector 26 is sensitive in the range of radiation to be studied.
Pour des rayons X, ce peut être par exemple un détecteur a base d'un matériau photoconducteur ultrarapide, la durée de vie des porteurs étant inférieure à 1 ps .For X-rays, this may for example be a detector based on an ultra-fast photoconductive material, the lifetime of the carriers being less than 1 ps.
Un tel matériau peut être du CdTe, du GaAs, du silicium dope à l'oxygène sur du saphir ou du diamant.Such a material can be CdTe, GaAs, silicon doped with oxygen on sapphire or diamond.
Le diamant est le matériau le plus performant car le plus résistant aux rayonnements. Ce détecteur 26 peut être couplé a un dispositif autocorrélateur optoélectronique 34, a contact glissant . Cet échantillonneur est un microsystème capable d'analyser les impulsions jusqu'à 50 gigahertz.Diamond is the best performing material because it is the most resistant to radiation. This detector 26 can be coupled to an optoelectronic autocorrelator device 34, with sliding contact. This sampler is a microsystem capable of analyzing pulses up to 50 gigahertz.
Schématiquement, un tel dispositif est représenté sur la figure 3. C'est un composant intégré, réalisé dans une technologie de type microélectronique.Schematically, such a device is shown in Figure 3. It is an integrated component, made in a microelectronic type technology.
Il comporte une ligne de propagation principale 36 sur laquelle est envoyé le signal unique S(t) à échantillonner, ainsi que n lignes d'échantillonnage 38-1, 38-2, 38-3, ..., 38-n.It comprises a main propagation line 36 on which the single signal S (t) to be sampled is sent, as well as n sampling lines 38-1, 38-2, 38-3, ..., 38-n.
Ces lignes d'échantillonnage 38-ι (l£ι<n) sont disposées en "peigne" le long de la ligne principale.These sampling lines 38-ι (l £ ι <n) are arranged in a "comb" along the main line.
Entre chacune des lignes d ' échantillonnage 38-ι et la ligne principale 36 se trouve un plot 40-ι (l i<n) de matériau photoconducteur.Between each of the sampling lines 38-ι and the main line 36 is a pad 40-ι (l i <n) of photoconductive material.
Chaque ligne d'échantillonnage est par ailleurs également reliée à une capacité de stockage 42-1, 42-2, ..., 42-n ainsi qu'à une électronique d'acquisition non représentée sur la figure 3. Chaque élément photoconducteur 40-1, 40-2, ..., 40-n est déclenche par une impulsion laser ultrarapide.Each sampling line is also also connected to a storage capacity 42-1, 42-2, ..., 42-n as well as to an acquisition electronics not shown in FIG. 3. Each photoconductive element 40 -1, 40-2, ..., 40-n is triggered by an ultra-fast laser pulse.
Un moyen commode d'obtenir une telle impulsion pour chaque élément photoconducteur consiste, comme le montre la figure 1, à prélever dans le faisceau 2 du laser femtoseconde un faisceau secondaire 44-1, a l'aide d'un miroir 46.A convenient means of obtaining such a pulse for each photoconductive element consists, as shown in FIG. 1, of taking a secondary beam 44-1 from the beam 2 of the femtosecond laser, using a mirror 46.
Ce faisceau secondaire 44-1 peut être lui-même divise en plusieurs en plusieurs sous-faisceaux 44-2, ..., 44-n, à l'aide de miroirs 43-2, ..., 43-n partiellement transparents, interposes sur son trajet.This secondary beam 44-1 can itself be divided into several into several sub-beams 44-2, ..., 44-n, using partially transparent mirrors 43-2, ..., 43-n , interposed on its route.
Le sous-faisceau principal 44-1 vient déclencher l'élément photoconducteur 40-1. Un premier sous-faisceau secondaire 44-2 obtenu à l'aide du miroir 43-2 vient déclencher l'élément photoconducteur 40-2 à un instant déterminé par la longueur de la ligne à retard définie par le trajet du faisceau entre le miroir 43-2 et l'élément photoconducteur 40-2.The main sub-beam 44-1 triggers the photoconductive element 40-1. A first secondary sub-beam 44-2 obtained using the mirror 43-2 triggers the photoconductive element 40-2 at an instant determined by the length of the delay line defined by the beam path between the mirror 43 -2 and the photoconductive element 40-2.
De même, le troisième élément photoconducteur 40-3 est déclenché par un second sous-faisceau secondaire 44-3, à un instant lui-même défini par la longueur d'une seconde ligne à retard.Likewise, the third photoconductive element 40-3 is triggered by a second secondary sub-beam 44-3, at an instant itself defined by the length of a second delay line.
Ce principe de déclenchement est appliqué à cnaque élément photoconducteur 40-ι (l£i<n), celui-ci étant déclenché à un instant t,. défini par la longueur de la îème ligne à retard. L'impulsion laser ultrarapide incidente sur un photoconducteur 40-ι ferme l'interrupteur constitué par ce photoconducteur.This triggering principle is applied to each photoconductive element 40-ι (l £ i <n), the latter being triggered at an instant t i. defined by the length of the ith delay line. The ultrafast laser pulse incident on a photoconductor 40-ι closes the switch formed by this photoconductor.
Un signal est alors prélevé, signal qui correspond à l'intensité du signal S en regard de la ligne i a l'instant t. de fermeture du photoconducteur.A signal is then taken, signal which corresponds to the intensity of the signal S opposite the line i at time t. closing the photoconductor.
D'autres détails concernant la réalisation de 1 ' échantillonneur optoélectronique ainsi que le procède de mesure correspondant peuvent être trouves dans la publication de la demande européenne EP-327 420. En particulier, chaque matériau photoconducteur peut être par exemple du tellurure de cadmium Passe température, tandis que les lignes de transmission principale et secondaire peuvent être en aluminium.Other details concerning the production of the optoelectronic sampler as well as the corresponding measurement method can be found in the publication of European application EP-327 420. In particular, each photoconductive material may for example be cadmium telluride Pass temperature , while the main and secondary transmission lines can be made of aluminum.
Un circuit électronique de mesure, par exemple de type amplificateur de charge, et d'enregistrement des signaux délivrés par chaque ligne d'échantillonnageAn electronic circuit for measuring, for example of the charge amplifier type, and for recording the signals delivered by each sampling line
38-ι est ' également prévu mais n'est pas représente sur la figure 3. Avec ce dispositif, le pas temporel d'échantillonnage du signal délivré par le photodétecteur 26 est défini par la distance spatiale entre deux lignes 38-i voisines, comme cela est expliqué dans la publication mentionnée ci-dessus.38-ι is' also provided but is not shown in Figure 3. With this device, the time step for sampling the signal delivered by the photodetector 26 is defined by the spatial distance between two neighboring lines 38-i, as explained in the publication mentioned above.
De même, le faisceau principal de déclenchementLikewise, the main trigger beam
44-1, prélevé dans le faisceau laser femtoseconde 2, déterminant l'instant auquel le premier photoconducteur44-1, taken from the femtosecond laser beam 2, determining the instant at which the first photoconductor
40-1 est fermé, détermine l'instant auquel l'échantillonnage va commencer.40-1 is closed, determines when the sampling will start.
Suivant la longueur du trajet parcouru par ce faisceau 44-1, cet instant de déclenchement définira la portion du plasma ou du milieu 24 étudie en provenance de laquelle les signaux analysés seront réémis. Ceci signifie qu'il est possible de choisir d'échantillonner des signaux provenant d'une zone 50 périphérique du milieu étudié 24 ou d'une zone 52 se trouvant en profondeur dans le milieu étudié 24.Depending on the length of the path traveled by this beam 44-1, this triggering instant will define the portion of the plasma or of the medium 24 being studied, from which the analyzed signals will be retransmitted. This means that it is possible to choose to sample signals coming from a peripheral zone 50 of the studied medium 24 or from a zone 52 lying deep in the studied medium 24.
Ainsi, en faisant varier l'instant de déclenchement du dispositif d'échantillonnage, on obtient une image d'une "tranche", ou d'une zone, plus ou moins profonde du milieu étudie 24.Thus, by varying the instant of triggering of the sampling device, one obtains an image of a "slice", or of a more or less deep zone of the medium studied 24.
En fait d'image, il s'agit plutôt de l'analyse temporelle du signal réémis par ladite zone ou ladite tranche.In terms of image, it is rather a temporal analysis of the signal retransmitted by said zone or said slice.
Par conséquent, on obtient une résolution à la fois temporelle et spatiale du comportement du plasma.Consequently, a resolution is obtained, both temporally and spatially, of the behavior of the plasma.
Le dispositif conforme à l'invention, qui est schématiquement représenté sur la figure 4, est destine à engendrer des impulsions de rayonnement X ultracourtes . Dans l'exemple représenté, ces impulsions ultracourtes de rayonnement X sont destinées à la caractérisation d'un milieu 53.The device according to the invention, which is schematically shown in Figure 4, is intended to generate ultrashort X-ray pulses. In the example shown, these ultra-short X-ray pulses are intended for the characterization of a medium 53.
Le dispositif de la figure 4 comprend : - des moyens 54 de génération d'un faisceau puisé 55 de rayonnement X,The device of FIG. 4 comprises: means 54 for generating a pulsed beam 55 of X-ray radiation,
- un moyen optique intermédiaire 56 qui transforme ce faisceau 55 en un faisceau puisé 58 sensiblement parallèle de rayonnement X (c'est-à-dire que les rayons de ce faisceau 58 sont sensiblement parallèles les uns aux autres) ,an intermediate optical means 56 which transforms this beam 55 into a pulsed beam 58 substantially parallel to X-ray radiation (that is to say that the rays of this beam 58 are substantially parallel to each other),
- un premier réseau lamellaire multicouche 60 pour rayonnement X ainsi qu'un deuxième réseau lamellaire multicouche 62 pour rayonnement X, ces réseaux 60 et 62 occupant des positions optiquement conjuguées l'une de l'autre, eta first multi-layer lamellar network 60 for X-ray radiation as well as a second multi-layer lamellar network 62 for X-ray radiation, these networks 60 and 62 occupying positions which are optically conjugate with each other, and
- un premier moyen 6-4 de focalisation de rayonnement X ainsi qu'un deuxième moyen 66 de focalisation de rayonnement X qui ont un plan focal commun et donc un foyer commun et forment un ensemble optique placé sur le trajet du rayonnement X entre les roseaux 60 et 62.a first means 6-4 for focusing X-rays as well as a second means 66 for focusing X-rays which have a common focal plane and therefore a common focal point and form an optical assembly placed on the path of the X-ray between the reeds 60 and 62.
Le rayonnement X interagit successivement avec le moyen optique 56, le reseau 60, le moyen de focalisation 64, le moyen de localisation 66 et le réseau 62.The X-ray interacts successively with the optical means 56, the network 60, the focusing means 64, the location means 66 and the network 62.
Des impulsions ultra-courtes 67 de rayonnement X sent en conséquence fournies par le réseau 62 et envoyées vers le milieu 53 par l'intermédiaire d'un miroir 68 pour rayonnement X, ce miroir 68 étant par exemple plan. Dans l'exemple représente sur la figure 4, les moyens 54 de génération du faisceau puise 55 de rayonnement X comprennent :Ultra-short pulses 67 of X-ray radiation are consequently supplied by the network 62 and sent to the medium 53 via a mirror 68 for X-ray radiation, this mirror 68 being, for example, plane. In the example shown in FIG. 4, the means 54 for generating the drawn beam 55 of X-ray radiation include:
- une source laser intense 70 apte à émettre des impulsions laser 71 ultra-courtes, etan intense laser source 70 capable of emitting ultra-short laser pulses 71, and
- une cible 72 qui est faite d'un matériau solide et qui est apte a produire le faisceau intense 55 lorsqu'elle reçoit les impulsions laser. Les impulsions ultra-courtes fournies par le laser 70 sont focalisées sur la cible 72 par une lentille appropriée 74.- A target 72 which is made of a solid material and which is capable of producing the intense beam 55 when it receives the laser pulses. The ultra-short pulses supplied by the laser 70 are focused on the target 72 by an appropriate lens 74.
Par "impulsions ultra-courtes", on entend des impulsions de durée inférieure a 10" s, par exemple comprise dans l'intervalle allant de ÎO"1"" s a 10"1'' s, ou en tout cas de durée beaucoup olus brève que la durée de vie du milieu que l'on veut étudier.By "ultra-short pulses" is meant pulses of duration less than 10 " s, for example lying in the range from 10 " 1 "to 10 " 1 "s, or in any case of much longer duration short as the lifespan of the medium that we want to study.
Dans l'exemple 1 représente, la cible 72 est faite d'un matériau métallique tel que T , Ni, Zn ou W. Les caractéristiques énergétiques et spectrales du faisceau puise intense 55 dépendent de ce matériau.In example 1 represents, the target 72 is made of a metallic material such as T, Ni, Zn or W. The energetic and spectral characteristics of the intense beam 55 depend on this material.
Dans l'exemple représente sjr la figure 4, le rayonnement X, référence 76, qui est reemis par le milieu 53 après interaction de celui-ci avec le rayonnement 69 réfléchi par le miroir 68, est mesure par un détecteur approprie 78 qui est associe a un dispositif autocorrelateur optoélectronique 80.In the example represents sj r Figure 4, the X-radiation, reference 76, which is retransmitted by the medium 53 after interaction thereof with the radiation 69 reflected by the mirror 68, is measured by a suitable sensor 78 which is associated with an optoelectronic autocorrelating device 80.
Ce dispositif 80 est commande par des impulsions laser ultra-courtes 81 qui sont prélevées au faisceau palse issu du laser 70 grâce a. n séparateur αe faisceau 82 ("beam splitter") qui est place dans le faisceau fourni par le laser 70 comme on le voit sur la figure 4. Le dispositif de la figure 4 comprend aussi un filtre mterferentiel 84 qui est disposé au niveau du plan focal P commun aux moyens de focalisation 64 et 66. Les réseaux 60 et 62 comprennent des couches métalliques réflectrices régulièrement empilées.This device 80 is controlled by ultra-short laser pulses 81 which are taken from the palse beam from the laser 70 using a. n beam beam splitter 82 which is placed in the beam supplied by the laser 70 as seen in FIG. 4. The device of FIG. 4 also comprises a mterferential filter 84 which is arranged at the level of the focal plane P common to the focusing means 64 and 66. The networks 60 and 62 comprise reflective metallic layers regularly stacked.
Chacun des moyens de focalisation 64 et 66 peut être un miroir cylindrique ou spherique pour rayonnement X ou un cristal courbe, apte à focaliser un rayonnement X.Each of the focusing means 64 and 66 can be a cylindrical or spherical mirror for X-rays or a curved crystal, capable of focusing X-rays.
On peut utiliser un cristal de phtalate de rubidium ou encore un cristal de phtalate de potassium.A rubidium phthalate crystal or a potassium phthalate crystal can be used.
De même, le moyen optique intermédiaire 56 peut être un miroir cylindrique ou spherique pour rayonnement X ou un cristal courbe, par exemple en phtalate de rubidium ou en phtalate de potassium, de forme appropriée pour focaliser un rayonnement X.Likewise, the intermediate optical means 56 can be a cylindrical or spherical mirror for X-ray radiation or a curved crystal, for example made of rubidium phthalate or potassium phthalate, of a suitable shape for focusing X-ray radiation.
Le dispositif conforme a l'invention, qu est schématiquement représente sur la figure 5, diffère de celui de la figure 4 par le fa t qu'il comprenc, au lieu du filtre mterferentiel 84, un moyen de collimation 86 qui est dispose au niveau du plan focal P commun aux moyens de focalisation 64 et 66.The device according to the invention, which is schematically represented in FIG. 5, differs from that of FIG. 4 by the fact that it includes, instead of the mterferential filter 84, a collimation means 86 which is arranged at the level from the focal plane P common to the focusing means 64 and 66.
Dans un autre dispositif conforme à l'invention non représenté, on utilise a la foι.s le filtre 84 et le moyen de collimation 86 et l'on dispose ceux-ci au niveau du plan focal P.In another device according to the invention not shown, the filter 84 and the collimation means 86 are used in the foι.s and these are placed at the focal plane P.
On précise que le moyen de collimat on 86 peut être un collimateur ou un écran absorbant ajouré. De plus, ce moyen de collimation 86 est réglable en ce sens qu'il est deplacable parallèlement au pian focal P pour pouvoir sélectionner telle ou telle raie du rayonnement issu du moyen de focalisation 64. On peut utiliser le rayonnement X provenant d'un synchrotron en tant que rayonnement 55.It is specified that the collimating means 86 can be a collimator or an openwork absorbent screen. In addition, this collimation means 86 is adjustable in the sense that it is displaceable parallel to the focal plane P in order to be able to select such and such a line of the radiation coming from the focusing means 64. X-ray radiation from a synchrotron can be used as 55 radiation.
Alors, pour commander le dispositif 80, on peut utiliser des impulsions produites par un système de déclenchement lui-même commandé par le rayonnement synchrotron.Then, to control the device 80, it is possible to use pulses produced by a triggering system itself controlled by synchrotron radiation.
On revient maintenant au dispositif de la figure 4 ainsi qu'à sa variante qui est représentée sur la figure 5. On précise que le moyen optique intermédiaire 56 permet non seulement de réduire notablement la divergence du faisceau 55 mais encore de filtrer les fréquences hautes et basses de ce faisceau 55.We now come back to the device of FIG. 4 as well as to its variant which is represented in FIG. 5. It is specified that the intermediate optical means 56 makes it possible not only to significantly reduce the divergence of the beam 55 but also to filter the high frequencies and bass of this beam 55.
Les réseaux 60 et 62, qui occupent des positions conjuguées et sont associés aux moyens de focalisation 64 et 66, permettent de remédier aux inconvénients de 1 ' art antérieur .The networks 60 and 62, which occupy conjugate positions and are associated with the focusing means 64 and 66, make it possible to remedy the drawbacks of the prior art.
Chaque point-source de la surface du réseau 60 a un point-image sur le reseau 62 situé à la même distance optique pour tout l'espace fréquentiel équivalent .Each source point of the surface of the network 60 has an image point on the network 62 located at the same optical distance for all the equivalent frequency space.
Donc, à chaque instant, le faisceau résultant du traitement par le système optique composé des réseaux 60 et 62 et des moyens de focalisation 64 et 66 a la même distribution spectrale.Therefore, at each instant, the beam resulting from the processing by the optical system composed of the grids 60 and 62 and the focusing means 64 and 66 has the same spectral distribution.
Cependant, la multiplicité des rayons X qui sont réfléchis selon le même angle (et ont donc la même fréquence) et qui sont issus des différents points- sources de la surface du réseau 60 va parcourir des trajectoires optiques d'autant plus courtes que la fréquence du rayon considéré sera plus élevée du fait de la propriété de dispersion spectrale des réseaux 60 et 62. Les trajectoires optiques des faisceaux X de sondage (qui sont issus du reseau 60 et sont références FI, ..., FN, avec N>2, seuls les faisceaux FI et FN étant représentés) apparaissent, suivant la structure mterférentielle du filtre 84 et/ou la position du collimateur 86, à des angles de réflexion (du fait des propriétés du réseau 60) qui différent selon la fréquence moyenne utile du rayonnement X.However, the multiplicity of X-rays which are reflected at the same angle (and therefore have the same frequency) and which originate from the different source points of the surface of the network 60 will traverse optical trajectories that are shorter as the frequency of the considered radius will be higher due to the spectral dispersion property of the networks 60 and 62. The optical paths of the probing beams X (which come from the network 60 and are references FI, ..., FN, with N> 2, only the beams FI and FN being represented) appear, according to the mterferential structure of the filter 84 and / or the position of the collimator 86, at reflection angles (due to the properties of the grating 60) which differ according to the mean useful frequency of the X-ray.
Il en resuite que la dispersion spatiale du faisceau 58 (résultant de la source laser 70 ou d'un synchrotron) par le reseau 60 entraîne une variation du trajet optique suivant .It follows that the spatial dispersion of the beam 58 (resulting from the laser source 70 or from a synchrotron) by the network 60 results in a variation of the following optical path.
- d'une part l'angle de reflexion correspondant aux différents ordres de diffraction, et - d'autre part, les positions respectives considérées des points-sources et des points- images sur les reseaux occupant des positions conjuguées, suivant les caractéristiques d'émission de la source laser (ou du synchrotron) .- on the one hand the angle of reflection corresponding to the different orders of diffraction, and - on the other hand, the respective positions considered of the source points and of the image points on the networks occupying conjugate positions, according to the characteristics of emission from the laser source (or synchrotron).
L'adjonction du filtre 8^ ou du moyen de collimation 86 au niveau au foyer commun aux deux moyens de focalisation 64 et 6o, de manière a moduler spatialement (et éventuellement frequentiellement ) la transmission entre les deux moyens de focalisation 64 et 66, permet d'eliπuner la transmission pour certaines trajectoires et donc d'obtenir un faisceau de rayonnement X module temporellement a la sortie de l'ensemble forme par les reseaux 60, 62 et par les moyens de focalisation 64, 66The addition of the filter 8 ^ or of the collimation means 86 at the level of the focal point common to the two focusing means 64 and 6o, so as to spatially (and possibly frequency) modulate the transmission between the two focusing means 64 and 66, allows to lighten the transmission for certain trajectories and therefore to obtain an X-ray beam of time modulated radiation at the exit of the assembly formed by the networks 60, 62 and by the focusing means 64, 66
Les orientations des deux reseaux dans des positions conjuguées offrent une nouvelle possibilité de modulation temporelle de l'impulsion unique d'origine suivant un train d'impulsions X (qui peut atteindre 5 à 15 impulsions successives) avec un taux de répétition qui peut être élevé et atteindre quelques térahertz suivant le principe d'un système séquenceur de type Michelson appliqué aux faisceaux de rayonnement X.The orientations of the two networks in conjugate positions offer a new possibility of temporal modulation of the single pulse original following a train of X pulses (which can reach 5 to 15 successive pulses) with a repetition rate which can be high and reach a few terahertz according to the principle of a sequencing system of the Michelson type applied to X-ray beams .
C'est le filtre 84 ou le collimateur 86 qui fixe le nombre d'impulsions contenues dans le tram d'impulsions ainsi que le taux de répétition dans ce tram.It is the filter 84 or the collimator 86 which fixes the number of pulses contained in the pulse tram as well as the repetition rate in this tram.
Dans le cas de la figure 5, la collimation réduit la bande passante des faisceaux X de sondage et limite la durée de l'impulsion résultante.In the case of FIG. 5, the collimation reduces the bandwidth of the probing beams X and limits the duration of the resulting pulse.
Le choix de la répartition et de l'agencement de l'ensemble formé par les réseaux 60, 62, les moyens de focalisation 64, 66, le filtre 84 et/ou le moyen de collimation 86 dépend des caractéristiques de dispersion temporelle recherchées pour le faisceau X.The choice of distribution and arrangement of the assembly formed by the networks 60, 62, the focusing means 64, 66, the filter 84 and / or the collimation means 86 depends on the temporal dispersion characteristics sought for the beam X.
Dans le cas de la figure 5, le choix de la position du moyen de colli ation 86 permet essentiellement le traitement et la sélection d'une partie préférentielle du spectre de rayons X.In the case of FIG. 5, the choice of the position of the colli ation means 86 essentially allows the processing and selection of a preferential part of the X-ray spectrum.
La combinaison des variantes des figures 4 et 5The combination of variants of Figures 4 and 5
(utilisation du filtre 84 et du moyen de collimation 86 au niveau du plan focal commun P) permet à la fois de réduire la durée de chaque impulsion X fournie et d'obtenir un tram d'impulsions à taux de répétition élevé .(use of the filter 84 and the collimation means 86 at the level of the common focal plane P) makes it possible both to reduce the duration of each pulse X supplied and to obtain a tram of pulses with a high repetition rate.
L'ensemble constitué des réseaux 60, 62 , des moyens de focalisation 64, 66, et du filtre 84 et/ou du moyen de collimation 86 fournit un faisceau de rayons X composé d'un train d'impulsions X qui sont espacées régulièrement d'un même intervalle temporel et qui sont ensuite dirigées vers le milieu 53 a caractériser, par l'intermédiaire du miroir 68 pour rayons X prévu a cet effet. The assembly consisting of networks 60, 62, focusing means 64, 66, and the filter 84 and / or the collimation means 86 provides an X-ray beam composed of a train of X pulses which are regularly spaced apart. '' the same time interval and which are then directed towards the medium 53 to be characterized, by means of the mirror 68 for X-rays provided for this purpose.

Claims

REVENDICA IONS REVENDICA IONS
1. Dispositif de génération d'impulsions de rayonnement X, ce dispositif étant caractérisé en ce qu'il comprend :1. Device for generating X-ray pulses, this device being characterized in that it comprises:
- des moyens (54) de génération d'un faisceau puisé de rayonnement X,- means (54) for generating a pulsed beam of X-ray radiation,
- un moyen optique intermédiaire (56) apte à transformer ce faisceau en un faisceau puisé sensiblement parallèle de rayonnement X,an intermediate optical means (56) capable of transforming this beam into a substantially parallel pulsed beam of X-ray radiation,
- des premier et deuxième réseaux lamellaires multicouches (60, 62) pour rayonnement X, occupant des positions optiquement conjuguées l'une de l'autre, et - des premier et deuxième moyens (64, 66) de focalisation de rayonnement X, ayant un foyer commun et formant un ensemble optique qui est placé sur le trajet du rayonnement X, entre les premier et deuxième réseaux, le rayonnement X passant ainsi du moyen optique intermédiaire au premier réseau puis au deuxième réseau par l'intermédiaire du premier moyen de focalisation puis du deuxième moyen de focalisation, le deuxième réseau (62) fournissant des impulsions ultra-courtes de rayonnement X.- first and second multilayer lamellar networks (60, 62) for X-ray radiation, occupying optically conjugate positions of each other, and - first and second means (64, 66) for focusing X-ray radiation, having a common focal point and forming an optical assembly which is placed on the path of the X-ray, between the first and second networks, the X-ray thus passing from the intermediate optical means to the first network and then to the second network via the first focusing means then from the second focusing means, the second grating (62) providing ultra-short pulses of X-ray radiation.
2. Dispositif selon la revendication 1, caractérisé en ce qu'il comprend en outre un filtre mterferentiel (84) qui est disposé au niveau du plan focal commun aux premier (64) et deuxième (66) moyens de focalisation. 2. Device according to claim 1, characterized in that it further comprises a mterferential filter (84) which is arranged at the focal plane common to the first (64) and second (66) focusing means.
3. Dispositif selon la revendication 1, caractérisé en ce qu'il comprend en outre un moyen de collimation réglable (86) qui est disposé au niveau du plan focal commun aux premier (64) et deuxième (66) moyens de focalisation.3. Device according to claim 1, characterized in that it further comprises an adjustable collimation means (86) which is arranged at the focal plane common to the first (64) and second (66) focusing means.
4. Dispositif selon la revendication 1, caractérisé en ce qu'il comprend en outre un moyen de collimation réglable (86) et un filtre mterferentiel (84) qui sont disposés au niveau du plan focal commun aux premier (64) et deuxième (66) moyens de focalisation.4. Device according to claim 1, characterized in that it further comprises an adjustable collimation means (86) and a mterferential filter (84) which are arranged at the focal plane common to the first (64) and second (66 ) means of focusing.
5. Dispositif selon l'une quelconque des revendications 1 à 4, caractérisé en ce que chacun des premier (64) et deuxième (66) moyens de focalisation comprend un miroir cylindrique pour rayonnement X ou un miroir spherique pour rayonnement X ou un cristal courbe apte à focaliser le rayonnement X.5. Device according to any one of claims 1 to 4, characterized in that each of the first (64) and second (66) focusing means comprises a cylindrical mirror for X-rays or a spherical mirror for X-rays or a curved crystal able to focus X-rays.
6. Dispositif selon l'une quelconque des revendications 1 à 5, caractérise en ce que le moyen optique intermédiaire (56) comprend un miroir cylindrique pour rayonnement X ou un miroir spherique pour rayonnement X ou un cristal courbe apte a focaliser le rayonnement X.6. Device according to any one of claims 1 to 5, characterized in that the intermediate optical means (56) comprises a cylindrical mirror for X-rays or a spherical mirror for X-rays or a curved crystal capable of focusing the X-rays.
7. Dispositif selon l'une quelconque des revendications 5 et 6, caractérise en ce que le cristal est un cristal de phtalate de rubidium ou un cristal de phtalate de potassium. 7. Device according to any one of claims 5 and 6, characterized in that the crystal is a rubidium phthalate crystal or a potassium phthalate crystal.
8. Dispositif selon l'une quelconque des revendications 1 à 7, caractérisé en ce que les moyens (54) de génération du faisceau puisé de rayonnement X comprennent : - un laser (70) apte à émettre des impulsions laser, et8. Device according to any one of claims 1 to 7, characterized in that the means (54) for generating the pulsed beam of X-rays comprise: - a laser (70) capable of emitting laser pulses, and
- une cible (72) qui est faite d'un matériau solide et qui est apte à produire le faisceau puisé de rayonnement X lorsqu'elle reçoit les impulsions laser. - a target (72) which is made of a solid material and which is capable of producing the pulsed beam of X-ray radiation when it receives the laser pulses.
EP97935647A 1996-07-30 1997-07-29 Device for generating ultra-short x-ray pulses Withdrawn EP0916236A1 (en)

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FR9609577A FR2752101B1 (en) 1996-07-30 1996-07-30 DEVICE FOR GENERATING ULTRA-SHORT X-RAY PULSES
PCT/FR1997/001413 WO1998005189A1 (en) 1996-07-30 1997-07-29 Device for generating ultra-short x-ray pulses

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