WO1992022110A1 - Laser transmitter particularly for generating ultrasonic waves, and use thereof in a contactless nondestructive testing device - Google Patents

Laser transmitter particularly for generating ultrasonic waves, and use thereof in a contactless nondestructive testing device Download PDF

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Publication number
WO1992022110A1
WO1992022110A1 PCT/FR1992/000474 FR9200474W WO9222110A1 WO 1992022110 A1 WO1992022110 A1 WO 1992022110A1 FR 9200474 W FR9200474 W FR 9200474W WO 9222110 A1 WO9222110 A1 WO 9222110A1
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WO
WIPO (PCT)
Prior art keywords
plates
transmitter according
mirrors
generator
laser
Prior art date
Application number
PCT/FR1992/000474
Other languages
French (fr)
Inventor
Jean-Loup Lesne
Original Assignee
Electricite De France - Service National
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 Electricite De France - Service National filed Critical Electricite De France - Service National
Publication of WO1992022110A1 publication Critical patent/WO1992022110A1/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/0602—Crystal lasers or glass lasers
    • H01S3/0606—Crystal lasers or glass lasers with polygonal cross-section, e.g. slab, prism
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/02—Constructional details
    • H01S3/04—Arrangements for thermal management
    • H01S3/042—Arrangements for thermal management for solid state lasers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H01S3/0941—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/11—Mode locking; Q-switching; Other giant-pulse techniques, e.g. cavity dumping
    • H01S3/1123—Q-switching
    • H01S3/127—Plural Q-switches
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/23—Arrangements of two or more lasers not provided for in groups H01S3/02 - H01S3/22, e.g. tandem arrangements of separate active media
    • H01S3/2383—Parallel arrangements

Definitions

  • Laser emitter in particular for the generation of ultrasonic waves and its application to a non-destructive contactless control device.
  • the present invention relates to laser transmitters and, more particularly, to a laser transmitter especially for the generation of ultrasonic waves with controlled di ⁇ rectivity and the application of such a transmitter. non-destructive testing devices.
  • non-destructive testing of materials and products is no longer to be demonstrated. Many technical sectors use non-destructive testing, for example using ultrasound, to check the quality and / or condition of basic materials or manufactured products.
  • One of the main difficulties is due to the relatively low acoustic power of the ultrasonic waves induced by laser radiation which must be used if the operating regime must ensure that the behavior of the product to be checked remains ultrasonic. preferably in the thermoelastic limit so as not to alter the surface state. Since, moreover, the surface condition of the product to be checked is rarely comparable to that resulting from an optical polish, additional difficulties appear for detection which even f fine optical techniques using heterodyne interferometry do not easily allow. to solve for sure. Indeed, the not perfectly smooth surface state causes a modulation of the amplitude of the signal detected by speckle effect.
  • MACH-ZEHNDER equipped with an acousto-optic modulator allowing to operate in heterodyne mode.
  • the object of the invention is to remedy most of the drawbacks listed previously with the aid of a solution which does not require scanning techniques.
  • the subject of the invention is a laser emitter in particular for the generation of ultrasound waves with controlled directivity consisting, inter alia, of a resonant optical cavity made of two parallel plane mirrors, one of which is completely reflecting and the other partially reflecting and a laser generator placed between these mirrors to emit radiation normal to the mirrors and emerge through the partially reflecting mirror.
  • This transmitter is particularly characterized in that this generator is composed of plates of active material which are oriented in such a way that their longitudinal axes are perpendicular to these mirrors and which are attached to one another, and in that it com ⁇ takes a multiple synchronization switch interposed between the generator and the fully reflecting mirror to cause the sequential emission of the plates.
  • the subject of the invention is also the application of such an emitter to a device for the non-destructive testing of a sample so as to irradiate the latter and preferably to generate in particular expansions by thermoelastic effect in order to be able to know it. contactless behavior.
  • the embodiment schematically drawn of a laser transmitter for the generation of ultrasonic waves with controlled directivity consists, inter alia, of an optical cavity reso ⁇ nante 10 made of two mirrors 11 and 12. These mirrors are parallel planes and such that one, the mirror 11 is fully reflective and the other the mirror 12 is partially reflective.
  • a laser generator 20 is placed between the mirrors 11 and 12 to emit laser radiation R 0 which is normal to the mirrors 11 and 12 and which emerges through the partially reflecting mirror 12.
  • This generator 20 is composed of plates, bars, bars or the like 200, of active material, which are oriented so that their particular longitudinal axes are perpendicular to the mirrors 11 and 12, and which are placed side by side as shown in the examination of the drawing.
  • the plates or the like 200 are preferably parallelepipeds with a rectangular base 201 and which are oriented obliquely at the angle of BRE STER, with respect to the optical axis defined by the mirrors 11 and 12. As can be observe it, the plates are joined to each other by their lateral faces 202.
  • the coplanar free faces 203 of the plates 200 are equipped with laser diodes 21 to ensure the optical pumping of the plates 200. can also use conventional flash lamps.
  • the other coplanar free faces 204 of the plates 200 are provided, if necessary, with a radiator 22 for removing heat produced during operation. For example, a water or PEL-TIER effect radiator is used.
  • the laser transmitter according to the invention also comprises a multiple synchronization switch 30 interposed between the generator 20 and the fully reflecting mirror 11 to cause the sequential emission of each of the bars 200.
  • this multiple synchronization switch 30 consists of cells 300 from P0CKELS each of which is associated with one of the plates 200 as illustrated.
  • a polarizer 40 is interposed between the generator 20 and the optical switch 30, as shown.
  • a supply circuit 50 controls the operation of the generator 20 and of the switch 30. To do this, this circuit is connected to each of the cells POCKELS 300 and to each of the laser diodes 21 which are used for the optical pumping of the active plates.
  • the switch 30 fixes the order, the duration and the power of the sequential emission of each of the plates.
  • the transmitter according to the invention i n comprises for example at least sixteen plates. These plates are constituted by the active material YAG composed of a matrix ⁇ 3 A ls0i2 doped with the Nd ⁇ + ion emitting at 1064 nm. One can also use for active maté ⁇ riau plates of other matrices doped by • 15 trivalent ions.
  • the operation of the transmitter is such that the sequential emission of the plates is manifested in the form of a train of pulses of adjustable frequency each of which, preferably, has a duration of less than 0 ns and a repetition frequency of the order from 30 to 50 Hz or even some 100 Hz.
  • the minimum total energy used is of the order of 200 mJ.
  • Each plate emits a beam whose diameter is of the order of 4 mm and whose divergence is of the order of 5 of 1 mrad. In this way, a total spatial extension of the sources of about 3 cm is obtained and an emission with a well defined d gram of directivity, with marked asymmetry and without secondary lobe.
  • an anamorphosor In order to ensure the distribution of the light energy 0 in this "acoustic pupil" composed of a set of thermoelastic sources whose lateral dimension is variable, an anamorphosor is used.
  • This anamorphoser which acts on the elementary, cylindrical and parallel beams, includes preferably cylindrical focusing lenses and a variable focal length lens which transforms beams into equidistant lines.
  • each pulse has a uniphase spatial distribution.
  • the peak value of the power is adjustable between a few kilowatts and a few megawatts.
  • this laser emitter according to the invention can be used to emit a significantly higher incident energy in order to operate in ablation regime with surface vaporization of the material and no longer dilation as in thermo ⁇ regime elastic. 5
  • Such a laser transmitter according to the invention is particularly suitable for a device for non-destructive testing, in particular in hos ⁇ tile environments or for online manufacturing processes.

Abstract

A laser transmitter particularly intended for generating controlled-directivity ultrasonic waves, and comprising, inter alia, an optical cavity resonator (10) made up of two plane and parallel mirrors (11, 12) of which one (11) is completely reflective while the other (12) is partially reflective, as well as a laser generator (20) placed between said mirrors for transmitting radiation (R) perpendicularly thereto and exiting through mirror (12), wherein said generator (20) consists of plates (200) made of an active material and directed in such a way that the longitudinal axes thereof are perpendicular to said mirrors, said plates being attached to one another, and wherein a multiple-contact synchronising switch (30) is arranged between the generator (20) and the completely reflective mirror (11) to cause sequential plate emission (200). The laser transmitter may be used in nondestructive tests, in particular those using thermoelasticity or ablation.

Description

Emetteur laser notamment pour la génération d'ondes ultrasonores et son application à un dispositif de contrôle non destructif sans contact. Laser emitter in particular for the generation of ultrasonic waves and its application to a non-destructive contactless control device.
La présente invention concerne les émetteurs laser et, plus particulièrement, un émetteur laser no¬ tamment pour la génération d'ondes ultrasonores à di¬ rectivité contrôlée et 1'application d'un tel émetteur < . aux dispositifs de contrôle non destructif.The present invention relates to laser transmitters and, more particularly, to a laser transmitter especially for the generation of ultrasonic waves with controlled di¬ rectivity and the application of such a transmitter. non-destructive testing devices.
L'intérêt des contrôles non destructifs des matériaux et produits n'est plus à démontrer. De nom¬ breux secteurs techniques utilisent les contrôles non destructifs par exemple à l'aide d'ultra-sons pour vé- 0 rifier la qualité et/ou l'état de matériaux de base ou de produits ouvrés.The value of non-destructive testing of materials and products is no longer to be demonstrated. Many technical sectors use non-destructive testing, for example using ultrasound, to check the quality and / or condition of basic materials or manufactured products.
Tel est par exemple le cas de 1 ' industrie sidérurgique pour la vérification des produits longs et/ou plats et aussi le cas de l'industrie aéronauti- 5 que pour s'assurer de la qualité de pièces complexes en cours de fabrication ou ultérieurement, après usage, pour s'assurer que leur vieillissement ne ris¬ que pas de nuire à la sécurité.This is for instance the case of one steel industry for the verification of long products and / or food and also the case of the 5 aéronauti- industry to ensure that the quality of current manufacturing complex parts or later after use, to ensure that their aging does not risk compromising safety.
Toutefois, l'utilisation des ultra-sons pour 0 les essais non destructifs pose des problèmes qui, parfois, en limitent sérieusement les applications pratiques puisqu'il est très souvent nécessaire d'as¬ surer un couplage physique, par exemple à l'aide d'un liquide, pour maintenir la continuité acoustique entre = les émetteurs ou les récepteurs, d'une part, et le produit vérifié, d'autre part.However, the use of ultrasound for non-destructive testing 0 poses problems which sometimes seriously limit practical applications since it is very often necessary to provide physical coupling, for example using of a liquid, to maintain the acoustic continuity between = the transmitters or the receivers, on the one hand, and the verified product, on the other hand.
Des tentatives ont été faites pour s'affran¬ chir de cette obligation de 1'utilisation d'un tel couplage et ainsi réussir à faire des contrôles non 0 destructifs à l'aide d'ultra-sons sans contact physi¬ que en se servant de sources de rayonnement impul¬ sionnel tels que des lasers pour générer des ultra¬ sons. Non seulement une telle émission d'ultra-sons pose des problèmes mais aussi leur détection ulté- rieure, après réception par le produit à contrôler.Attempts have been made to overcome this obligation of the use of such a coupling and thus succeed in making non-destructive checks using ultrasound without physical contact only by using sources of pulse radiation such as lasers to generate ultrasound. Not only does such an emission of ultrasound pose problems but also their subsequent detection. after receiving the product to be checked.
Une des principales difficultés est due à la relativement faible puissance acoustique des ondes ul¬ tra-sonores induites par un rayonnement laser qu'il faut utiliser si le régime de fonctionnement doit faire en sorte que le comportement aux ultra-sons du produit à vérifier reste de préférence dans la limite thermo-élastique afin de ne pas en altérer 1'état de surface. Comme de plus, l'état de surface du produit à vérifier est rarement comparable à celui résultant d'un poli optique, des difficultés supplémentaires apparaissent pour la détection que même des techniques optiques f nes faisant appel à 1'interférométrie hétérodyne ne permettent pas facilement de résoudre à coup sûr. En effet, l'état de surface non parfaitement lisse provoque une modulation de l'amplitude du signal détecté par effet speckle.One of the main difficulties is due to the relatively low acoustic power of the ultrasonic waves induced by laser radiation which must be used if the operating regime must ensure that the behavior of the product to be checked remains ultrasonic. preferably in the thermoelastic limit so as not to alter the surface state. Since, moreover, the surface condition of the product to be checked is rarely comparable to that resulting from an optical polish, additional difficulties appear for detection which even f fine optical techniques using heterodyne interferometry do not easily allow. to solve for sure. Indeed, the not perfectly smooth surface state causes a modulation of the amplitude of the signal detected by speckle effect.
Pour tenter de résoudre certaines de ces difficultés, on a proposé de déposer l'énergie rayon- né par un émetteur laser sur le produit à contrôler sous forme d'une succession d'impacts obtenus à 1'aide d'un déflecteur acousto-optique. Mais il est apparu que cette technique est peu fiable du fait de son manque de fidélité, de la longévité relativement courte des sources lasers utilisées ainsi que des faibles cadences de mises en oeuvre. Pour ce qui est de la détection, on a aussi proposé d'utiliser un récepteur comprenant un interféromètre de typeIn an attempt to resolve some of these difficulties, it has been proposed to deposit the energy radiated by a laser emitter on the product to be checked in the form of a succession of impacts obtained using an acousto-optical deflector. . But it appeared that this technique is not very reliable due to its lack of fidelity, the relatively short longevity of the laser sources used as well as the low rates of implementation. With regard to detection, it has also been proposed to use a receiver comprising an interferometer of the type
MACH-ZEHNDER équipé d'un modulateur acousto-optique permettant de fonctionner en mode hétérodyne.MACH-ZEHNDER equipped with an acousto-optic modulator allowing to operate in heterodyne mode.
Aucune de ces tentatives faites ne donne entière satisfaction du fait de son coût de mise en oeuvre et de ses difficultés pratiques d'utilisation qui en limitent l'usage au laboratoire, ce qui en in- terdit pratiquement tout usage industriel pour des contrôles en routine.None of these attempts is entirely satisfactory because of its cost of implementation and its practical difficulties of use which limit its use in the laboratory, which in turn almost all industrial use is prohibited for routine checks.
Le but de 1'invention est de remédier à la plupart des inconvénients énu érés précédemment à l'aide d'une solution qui ne fait pas appel à des techniques de balayage.The object of the invention is to remedy most of the drawbacks listed previously with the aid of a solution which does not require scanning techniques.
L'invention a pour objet un émetteur laser notamment pour la génération d'ondes ultra-sonores à directivité contrôlée constitué, entre autres, d'une cavité optique résonante faite de deux miroirs plans parallèles dont l'un est totalement réfléchissant et 1'autre partiellement réfléchissant et d'un générateur laser placé entre ces miroirs pour émettre un rayonnement normal aux miroirs et émergent par le miroir partiellement réfléchissant. Cet émetteur est notamment caractérisé en ce que ce générateur est composé de plaques en matériau actif qui sont orientées de telle manière que leurs axes lon¬ gitudinaux sont perpendiculaires à ces miroirs et qui sont accolées les unes aux autres, et en ce qu'il com¬ prend un interrupteur multiple de synchronisation in¬ terposé entre le générateur et le miroir totalement réfléchissant pour provoquer l'émission séquentielle des plaques. L'invention a aussi pour objet l'application d'un tel émetteur à un dispositif pour le contrôle non destructif d'un échantillon de manière à irradier ce dernier et de préférence à y engendrer notamment des dilatations par effet thermoélastique afin de pouvoir en connaître le comportement sans contact.The subject of the invention is a laser emitter in particular for the generation of ultrasound waves with controlled directivity consisting, inter alia, of a resonant optical cavity made of two parallel plane mirrors, one of which is completely reflecting and the other partially reflecting and a laser generator placed between these mirrors to emit radiation normal to the mirrors and emerge through the partially reflecting mirror. This transmitter is particularly characterized in that this generator is composed of plates of active material which are oriented in such a way that their longitudinal axes are perpendicular to these mirrors and which are attached to one another, and in that it com ¬ takes a multiple synchronization switch interposed between the generator and the fully reflecting mirror to cause the sequential emission of the plates. The subject of the invention is also the application of such an emitter to a device for the non-destructive testing of a sample so as to irradiate the latter and preferably to generate in particular expansions by thermoelastic effect in order to be able to know it. contactless behavior.
D'autres caractéristiques de 1'invention ressortiront de la lecture de la description et des revendications qui suivent ainsi que de 1'examen du dessin annexé donné seulement à titre d'exemple où la figure unique illustre schématiquement en perspective un mode de réalisation d'un émetteur selon 1'inven¬ tion.Other characteristics of the invention will emerge from reading the description and the claims which follow, as well as from examining the appended drawing given only by way of example where the single figure illustrates diagrammatically in perspective. an embodiment of a transmitter according to the invention.
Les techniques relatives aux émetteurs laser et plus particulièrement relatives à ceux d'entre eux utilisés pour la génération d'ondes ultra-sonores étant bien connues dans la technique, on ne décrira par la suite que ce qui concerne directement ou indi¬ rectement l'invention. Pour le surplus, le spécialiste de la technique considérée puisera dans les solutionsThe techniques relating to laser transmitters and more particularly relating to those of them used for the generation of ultrasonic waves being well known in the art, we will only describe below what relates directly or indirectly to invention. For the rest, the specialist in the technique considered will draw on the solutions
10 classiques courantes à sa disposition pour faire face aux problèmes particuliers auxquels il est confronté.10 common classics at his disposal to face the particular problems with which he is confronted.
Dans ce qui suit, un même numéro de référen¬ ce identifie toujours un élément homologue, quel que soit le mode de réalisation, ou sa variante d'exécu- ι<= tion, de l'invention.In what follows, the same reference number always identifies a homologous element, whatever the embodiment, or its variant of execution, of the invention.
Pour la commodité de l'exposé, on décrira successivement chacun des constituants de 1'invention avant d'en exposer le fonctionnement.For the convenience of the description, each of the constituents of the invention will be described successively before explaining its operation.
Comme on le voit en examinant la figure, le mode de réalisation dessiné schématiquement d'un émetteur laser pour la génération d'ondes ultra-sono¬ res à directivité contrôlée selon l'invention, est constitué, entre autres, d'une cavité optique réso¬ nante 10 faite de deux miroirs 11 et 12. Ces miroirs sont plans parallèles et tels que l'un, le miroir 11 est totalement réfléchissant et que 1'autre le miroir 12 est partiellement réfléchissant.As can be seen by examining the figure, the embodiment schematically drawn of a laser transmitter for the generation of ultrasonic waves with controlled directivity according to the invention, consists, inter alia, of an optical cavity reso¬ nante 10 made of two mirrors 11 and 12. These mirrors are parallel planes and such that one, the mirror 11 is fully reflective and the other the mirror 12 is partially reflective.
Un générateur laser 20 est placé entre les miroirs 11 et 12 pour émettre un rayonnement laser R 0 qui est normal aux miroirs 11 et 12 et qui émerge par le miroir 12 partiellement réfléchissant. Ce généra¬ teur 20 est composé de plaques, barrettes, barreaux ou simlaires 200, en matériau actif, qui sont orientés de manière que leurs axes longitudinaux particuliers sont perpendiculaires aux miroirs 11 et 12, et qui sont accolés les uns aux autres comme cela ressort de l'examen du dessin. Les plaques ou similaires 200 sont, de préférence, des parallélépipèdes à base 201 rectangulaire et qui sont orientés obliquement à l'angle de BRE STER, vis-à-vis de l'axe optique défini par les miroirs 11 et 12. Comme on peut l'observer, les plaques sont accolées les unes aux autres par leurs faces latérales 202. Comme on peut 1'observer aussi, les faces 203 libres coplanaires des plaques 200 sont équipées de diodes lasers 21 pour assurer le pompage optique des plaques 200. On peut aussi utili¬ ser des lampes à éclairs classiques. Les autres faces 204 libres coplanaires des plaques 200 sont munies, s'il y a lieu, d'un radiateur 22 pour évacuer de la chaleur produite au cours du fonctionnement. On uti¬ lise par exemple un radiateur à eau ou à effet PEL- TIER.A laser generator 20 is placed between the mirrors 11 and 12 to emit laser radiation R 0 which is normal to the mirrors 11 and 12 and which emerges through the partially reflecting mirror 12. This generator 20 is composed of plates, bars, bars or the like 200, of active material, which are oriented so that their particular longitudinal axes are perpendicular to the mirrors 11 and 12, and which are placed side by side as shown in the examination of the drawing. The plates or the like 200 are preferably parallelepipeds with a rectangular base 201 and which are oriented obliquely at the angle of BRE STER, with respect to the optical axis defined by the mirrors 11 and 12. As can be observe it, the plates are joined to each other by their lateral faces 202. As can also be observed, the coplanar free faces 203 of the plates 200 are equipped with laser diodes 21 to ensure the optical pumping of the plates 200. can also use conventional flash lamps. The other coplanar free faces 204 of the plates 200 are provided, if necessary, with a radiator 22 for removing heat produced during operation. For example, a water or PEL-TIER effect radiator is used.
L'émetteur laser selon 1'invention comprend aussi un interrupteur 30 multiple de synchronisation interposé entre le générateur 20 et le miroir 11 totalement réfléchissant pour provoquer 1'émission séquentielle de chacun des barreaux 200. De préfé¬ rence, cet interrupteur multiple de synchronisation 30 est constitué de cellules 300 de P0CKELS dont chacune est associée à l'une des plaques 200 comme illustré.The laser transmitter according to the invention also comprises a multiple synchronization switch 30 interposed between the generator 20 and the fully reflecting mirror 11 to cause the sequential emission of each of the bars 200. Preferably, this multiple synchronization switch 30 consists of cells 300 from P0CKELS each of which is associated with one of the plates 200 as illustrated.
En outre, comme il est classique pour ce type d'émetteur, un polariseur 40 est intercalé entre le générateur 20 et l'interrupteur optique 30, comme dessiné.In addition, as is conventional for this type of transmitter, a polarizer 40 is interposed between the generator 20 and the optical switch 30, as shown.
Un circuit 50 d'alimentation, seulement illustré schématiquement, pilote le fonctionnement du générateur 20 et de l'interrupteur 30. Pour ce faire, ce circuit est connecté à chacune des cellules de POCKELS 300 et à chacune des diodes lasers 21 qui sont utilisées pour le pompage optique des plaques actives. Ce type de circuit est classique et pour cela non il¬ lustré en détail. Ce circuit est, par exemple, sous la •= dépendance d'un micro-calculateur programmable.A supply circuit 50, only illustrated diagrammatically, controls the operation of the generator 20 and of the switch 30. To do this, this circuit is connected to each of the cells POCKELS 300 and to each of the laser diodes 21 which are used for the optical pumping of the active plates. This type of circuit is conventional and therefore not il¬ glossy in detail. This circuit is, for example, under the • = dependence of a programmable microcomputer.
De la sorte, l'interrupteur 30 fixe l'ordre, la durée et la puissance de l'émission séquentielle de chacune des plaques.In this way, the switch 30 fixes the order, the duration and the power of the sequential emission of each of the plates.
De préférence, l'émetteur selon l'invention in comprend par exemple au moins seize plaques. Ces pla¬ ques sont constituées par le matériau actif YAG com¬ posé d'une matrice γ3Als0i2 dopée par l'ion Nd^+ émettant à 1064 nm. On peut aussi utiliser pour maté¬ riau actif des plaques d'autres matrices dopées par •15 des ions trivalents.Preferably, the transmitter according to the invention i n comprises for example at least sixteen plates. These plates are constituted by the active material YAG composed of a matrix γ 3 A ls0i2 doped with the Nd ^ + ion emitting at 1064 nm. One can also use for active maté¬ riau plates of other matrices doped by • 15 trivalent ions.
Le fonctionnement de 1'émetteur est tel que l'émission séquentielle des plaques se manifeste sous la forme d'un train d'impulsions de fréquence ajusta¬ ble dont chacune, de préférence, a une durée infé- 0 rieure à 15 ns et une fréquence de répétition de 1'or¬ dre de 30 à 50 Hz voire quelques 100 Hz. L'énergie to¬ tale minimale utilisée est de l'ordre de 200 mJ. Chaque plaque émet un faisceau dont le diamètre est de 1'ordre de 4 mm et dont la divergence est de 1'ordre 5 de 1 mrad. On obtient de la sorte une extension spa- ciale totale des sources de 3 cm environ et une émis¬ sion avec un d gramme de directivité bien défini, à asymétrie marquée et sans lobe secondaire.The operation of the transmitter is such that the sequential emission of the plates is manifested in the form of a train of pulses of adjustable frequency each of which, preferably, has a duration of less than 0 ns and a repetition frequency of the order from 30 to 50 Hz or even some 100 Hz. The minimum total energy used is of the order of 200 mJ. Each plate emits a beam whose diameter is of the order of 4 mm and whose divergence is of the order of 5 of 1 mrad. In this way, a total spatial extension of the sources of about 3 cm is obtained and an emission with a well defined d gram of directivity, with marked asymmetry and without secondary lobe.
Afin d'assurer la distribution de 1'énergie 0 lumineuse dans cette "pupille acoustique" composée d'un ensemble de sources thermoélastiques dont la dimension latérale est variable, on utilise un anamor- phoseur. Cet anamorphoseur, qui agit sur les faisceaux élémentaires, cylindriques et parallèles, comprend de préférence des lentilles cylindriques de focalisation et un objectif à focale variable qui transforme des faisceaux en traits équidistants.In order to ensure the distribution of the light energy 0 in this "acoustic pupil" composed of a set of thermoelastic sources whose lateral dimension is variable, an anamorphosor is used. This anamorphoser, which acts on the elementary, cylindrical and parallel beams, includes preferably cylindrical focusing lenses and a variable focal length lens which transforms beams into equidistant lines.
On s'assure que chaque impulsion a une dis¬ tribution spatiale uniphase. La valeur de crête de la puissance est ajustable entre quelques kilowatts et quelques mégawatts.We make sure that each pulse has a uniphase spatial distribution. The peak value of the power is adjustable between a few kilowatts and a few megawatts.
On fait en sorte, si nécessaire que la puissance d'émission de chaque plaque est ajustable 0 séparément.We make sure, if necessary, that the emission power of each plate is adjustable 0 separately.
On voit donc que grâce à l'invention, il est possible de réaliser un émetteur laser pour la généra¬ tion d'ondes ultra-sonores à directivité contrôlée qui fonctionne entièrement à distance et sans contact *=^ grâce à des faiseaux lasers judicieusement pilotés qui permettent d'opérer notamment en régime thermoélasti¬ que du produit irradié avec des ultra-sons de puissan¬ ce suffisante.It can therefore be seen that, thanks to the invention, it is possible to produce a laser transmitter for the generation of ultrasonic waves with controlled directivity which operates entirely remotely and without contact * = ^ thanks to judiciously controlled laser beams which allow to operate in particular in thermoelastic regime as the irradiated product with ultrasound of sufficient power.
Il va de soi que cet émetteur laser selon n 'invention peut être utilisé pour émettre une énergie incidente notablement plus forte afin d'opérer en ré¬ gime d'ablation avec vaporisation superficielle du ma¬ tériau et non plus dilation comme en régime thermo¬ élastique. 5 Un tel émetteur laser selon 1'invention con¬ vient particulièrement bien à un dispositif pour le contrôle non destructif en particulier en milieu hos¬ tile ou pour des processus de fabrication en ligne.It goes without saying that this laser emitter according to the invention can be used to emit a significantly higher incident energy in order to operate in ablation regime with surface vaporization of the material and no longer dilation as in thermo¬ regime elastic. 5 Such a laser transmitter according to the invention is particularly suitable for a device for non-destructive testing, in particular in hos¬ tile environments or for online manufacturing processes.
Ce qui précède met bien en lumière les par- 0 ticularités et les avantages apportés par l'invention. The above clearly highlights the par- 0 peculiarities and advantages provided by the invention.

Claims

REVENDICATIONS 1 - Emetteur laser notamment pour la génération d'ondes ultrasonores à directivité contrôlée constitué, entre autres, d'une cavité opti- que résonante (10) faite de deux miroirs (11, 12) plans parallèles dont l'un (11) est totalement réfléchissant, et l'autre (12) partiellement réfléchissant et d'un générateur (20) laser placé entre ces miroirs pour émettre un rayonnement (R) nor- mal aux miroirs et émergent par le miroir (12) partiellement réfléchissant, caractérisé en ce que ce générateur (20) est composé de plaques (200) en maté¬ riau actif qui sont orientées de telle manière que leurs axes longitudinaux sont perpendiculaires à ces miroirs et qui sont accolées les unes aux autres, et en ce qu'il comprend un interrupteur (30) multiple de synchronisation interposé entre le générateur (20) et le miroir (11) totalement réfléchissant pour provoquer 1'émission séquentielle des plaques (200). 2 - Emetteur selon la revendication 1, ca¬ ractérisé en ce que l'interrupteur multiple (30) est un interrupteur optique (30) à cellules (300) de POCKELS. CLAIMS 1 - Laser emitter in particular for the generation of ultrasonic waves with controlled directivity consisting, inter alia, of a resonant optical cavity (10) made of two mirrors (11, 12) parallel planes of which one (11) is fully reflecting, and the other (12) partially reflecting and of a laser generator (20) placed between these mirrors to emit radiation (R) normal to mirrors and emerge through the partially reflecting mirror (12), characterized in that this generator (20) is composed of plates (200) of active material which are oriented in such a way that their longitudinal axes are perpendicular to these mirrors and which are joined to one another, and in that it comprises a multiple synchronization switch (30) interposed between the generator (20) and the fully reflecting mirror (11) to cause the sequential emission of the plates (200). 2 - Transmitter according to claim 1, ca¬ characterized in that the multiple switch (30) is an optical switch (30) with cells (300) from POCKELS.
3 - Emetteur selon l'une des revendications 1 et 2, caractérisé en ce que les plaques (200) sont des parallélépipèdes à bases (201) rectangulaires et en ce que chacune de ces faces taillées à 1'angle de Brewster (201) fait face obliquement à l'un de ces miroirs (11, 12). 4 - Emetteur selon l'une quelconque des re¬ vendications 1 à 3, caractérisé en ce que l'interrup¬ teur multiple (30) fixe d'une manière programmable l'ordre, la durée et la puissance de l'émission sé¬ quentielle de chacune des plaques (200). 5 - Emetteur selon 1'une quelconque des re¬ vendications 1 à 4, caractérisé en ce que chaque pla¬ que (200) est munie.d'une diode laser (21) pour son pompage optique et en ce que ces diodes sont montées sur les faces (203) libres coplanaires des plaques (200).3 - Transmitter according to one of claims 1 and 2, characterized in that the plates (200) are parallelepipeds with rectangular bases (201) and in that each of these faces cut at the Brewster angle (201) makes facing obliquely to one of these mirrors (11, 12). 4 - Transmitter according to any one of the re¬ vendications 1 to 3, characterized in that the multiple interrup¬ tor (30) fixes in a programmable manner the order, the duration and the power of the broadcast sé¬ of each of the plates (200). 5 - Transmitter according to any one of the claims 1 to 4, characterized in that each plate (200) is fitted with a laser diode (21) for its optical pumping and in that these diodes are mounted on the coplanar free faces (203) of the plates (200).
6 - Emetteur selon 1'une quelconque des re¬ vendications 1 à 5, caractérisé en ce que les faces libres (204) coplanaires des plaques (200) sont munies d'un radiateur (22) pour évacuer la chaleur produite en fonctionnement.6 - Transmitter according to any one of re¬ vendications 1 to 5, characterized in that the free faces (204) coplanar plates (200) are provided with a radiator (22) to remove the heat produced in operation.
7 - Emetteur selon 1'une quelconque des re¬ vendications 1 à 6, caractérisé en ce que les plaques (200) sont faites du matériau actif YAG composé d'une matrice γ3^^-ζ^±2 dopée par l'ion Nd3+.7 - Transmitter according to any one of claims 1 to 6, characterized in that the plates (200) are made of the active material YAG composed of a matrix γ 3 ^^ - ζ ^ ± 2 doped by the ion Nd 3+ .
8 - Emetteur selon 1'une quelconque des re¬ vendications 1 à 6, caractérisé en ce que les plaques (200) sont faites d'une matrice dopée par des ions trivalents. 9 - Emetteur selon 1'une quelconque des re¬ vendications 1 à 8, caractérisé en ce que le nombre des plaques (200) est au moins égal à seize.8 - Transmitter according to any one of claims 1 to 6, characterized in that the plates (200) are made of a matrix doped with trivalent ions. 9 - Transmitter according to any one of claims 1 to 8, characterized in that the number of plates (200) is at least equal to sixteen.
10 - Emetteur selon l'une quelconque des re¬ vendications 1 à 9, caractérisé en ce que l'émission séquentielle des plaques (200) est faite d'un train d'impulsions de fréquence ajustable dont chacune a une durée inférieure à 15 ns, une fréquence de répétition de l'ordre de 30 à 50 Hz et une énergie totale minima¬ le de 200 mJ. 11 - Emetteur selon l'une quelconque des re¬ vendications 1 à 10, caractérisé en ce que l'émission séquentielle à une puissance de crête comprise entre 100 kW environ et 100 MW environ.10 - Transmitter according to any one of the re¬ vendications 1 to 9, characterized in that the sequential emission of the plates (200) is made of a train of pulses of adjustable frequency each of which has a duration of less than 15 ns , a repetition frequency of the order of 30 to 50 Hz and a minimum total energy of 200 mJ. 11 - Transmitter according to any one of the re¬ vendications 1 to 10, characterized in that the sequential emission at a peak power of between approximately 100 kW and approximately 100 MW.
12 - Emetteur selon la revendication 10 et/ou 12, caractérisé en ce que chaque impulsion a une distribution spatiale uniphase.12 - Transmitter according to claim 10 and / or 12, characterized in that each pulse has a uniphase spatial distribution.
13 - Emetteur selon l'une quelconque des re¬ vendications 1 à 12, caractérisé en ce que la puissan- ce d'émission de chaque plaque (200) est ajustable sé¬ parément.13 - Transmitter according to any one of claims 1 to 12, characterized in that the emission power of each plate (200) is adjustable separately.
14 - Emetteur selon 1'une quelconque des revendications 1 à 13, caractérisé en ce qu'il com¬ prend un anamorphoseur pour assurer la distribution de l'énergie lumineuse dans une pupille acoustique.14 - Transmitter according to any one of claims 1 to 13, characterized in that it takes an anamorphic agent to ensure the distribution of light energy in an acoustic pupil.
15 - Application d'un émetteur selon l'une quelconque des revendications 1 à 14 à un dispositif pour irradier un échantillon afin d'y engendrer des dilatations par effet thermoélastique de manière à pouvoir en connaître le comportement sans contact, par un essai non destructif. 15 - Application of a transmitter according to any one of claims 1 to 14 to a device for irradiating a sample in order to generate expansions by thermoelastic effect so as to be able to know its behavior without contact, by a non-destructive test .
PCT/FR1992/000474 1991-05-30 1992-05-27 Laser transmitter particularly for generating ultrasonic waves, and use thereof in a contactless nondestructive testing device WO1992022110A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR9106540A FR2677185B1 (en) 1991-05-30 1991-05-30 LASER TRANSMITTER IN PARTICULAR FOR THE GENERATION OF ULTRASONIC WAVES AND ITS APPLICATION TO A NON-DESTRUCTIVE NON-CONTACT CONTROL DEVICE.
FR91/06540 1991-05-30

Publications (1)

Publication Number Publication Date
WO1992022110A1 true WO1992022110A1 (en) 1992-12-10

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Application Number Title Priority Date Filing Date
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WO (1) WO1992022110A1 (en)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6268956B1 (en) * 1998-07-07 2001-07-31 Trw Inc. End pumped zig-zag slab laser gain medium

Citations (5)

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Publication number Priority date Publication date Assignee Title
US4567769A (en) * 1984-03-08 1986-02-04 Rockwell International Corporation Contact-free ultrasonic transduction for flaw and acoustic discontinuity detection
GB2179198A (en) * 1985-07-31 1987-02-25 East China Inst Technology Sequence pulse laser
GB2185816A (en) * 1986-01-27 1987-07-29 Atomic Energy Authority Uk Ultrasonic weld monitoring
US4713822A (en) * 1985-05-24 1987-12-15 Amada Engineering & Service Co., Inc. Laser device
US4922502A (en) * 1987-06-30 1990-05-01 Hoya Corporation Solid-state laser device comprising a plurality of excitation units selectively energized

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4567769A (en) * 1984-03-08 1986-02-04 Rockwell International Corporation Contact-free ultrasonic transduction for flaw and acoustic discontinuity detection
US4713822A (en) * 1985-05-24 1987-12-15 Amada Engineering & Service Co., Inc. Laser device
GB2179198A (en) * 1985-07-31 1987-02-25 East China Inst Technology Sequence pulse laser
GB2185816A (en) * 1986-01-27 1987-07-29 Atomic Energy Authority Uk Ultrasonic weld monitoring
US4922502A (en) * 1987-06-30 1990-05-01 Hoya Corporation Solid-state laser device comprising a plurality of excitation units selectively energized

Also Published As

Publication number Publication date
FR2677185A1 (en) 1992-12-04
FR2677185B1 (en) 1993-09-24

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