WO2003100928A1 - High power laser amplification system - Google Patents

High power laser amplification system Download PDF

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Publication number
WO2003100928A1
WO2003100928A1 PCT/FR2003/001600 FR0301600W WO03100928A1 WO 2003100928 A1 WO2003100928 A1 WO 2003100928A1 FR 0301600 W FR0301600 W FR 0301600W WO 03100928 A1 WO03100928 A1 WO 03100928A1
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WO
WIPO (PCT)
Prior art keywords
gain medium
amplifier system
mirrors
beams
pump
Prior art date
Application number
PCT/FR2003/001600
Other languages
French (fr)
Inventor
Vincent Moro
Franck Falcoz
Thierry Fayette
Original Assignee
Thales
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
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Publication of WO2003100928A1 publication Critical patent/WO2003100928A1/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
    • H01S3/23—Arrangements of two or more lasers not provided for in groups H01S3/02 - H01S3/22, e.g. tandem arrangements of separate active media
    • H01S3/2308—Amplifier arrangements, e.g. MOPA
    • H01S3/2325—Multi-pass amplifiers, e.g. regenerative amplifiers
    • 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

Definitions

  • the present invention relates to a high power laser amplification system, for example for an amplification chain of a femtosecond laser pulse.
  • a system for amplifying an incident laser beam called a “signal” beam generally comprises, in a known manner, a gain medium, for example a crystal serving as gain medium, reflection means allowing the multiple passage of the signal beam in the gain medium in order to increase the power of the amplified signal, and a device for pumping the gain medium.
  • the reflection means comprise for example reflecting mirrors of the signal beam, arranged on either side of the gain medium and forming what is known as the "butterfly" (or “bow tie” according to the expression Anglo-Saxon).
  • the pumping device generally comprises one or two laser beams called pump beams, incident in the gain medium.
  • the invention proposes a high power amplification system with a pumping device with at least four pump beams, thus making it possible to increase the energy on the gain medium, the beams being arranged so that they have reduced angles between them and with the signal beam.
  • the invention proposes a high power amplification system of an incident signal laser beam comprising a gain medium, first reflection means allowing the multiple passage of the signal beam in said gain medium so that the beam incident signal and the reflected beams are contained in the same plane, and a device for pumping the gain medium, characterized in that the pumping device comprises at least four pump beams incident in the gain medium in directions not contained in said plane of the signal beam.
  • the pumping device comprises second reflection means with at least one frame on which are positioned at least four mirrors for deflecting said pump beams in the gain medium.
  • FIG. 1A represents an exemplary embodiment of a high power amplification system of an incident signal beam Is according to a top view. It includes a gain medium 10, first reflection means 11 a to 11 f allowing the multiple passage of the signal beam in said gain medium in order to form an amplified beam IA-
  • These reflection means formed in this example of 3 mirrors arranged on each side of the gain medium, are conventionally called the "butterfly" because of the bow tie shape of the arrangement of the mirrors.
  • the incident signal beam Is and the beams reflected by the various mirrors are contained in the same plane rie, which is here the plane of FIG. 1A. It is interesting to have all the butterfly mirrors in one plane because the system is thus simpler to make and align.
  • the amplification system according to the invention also comprises a device for pumping the gain medium 10 comprising at least four pump beams (in this example eight Ipi beams at Ips symbolized by double arrows), these beams being incident in the medium gain in directions not contained in said plane of the signal beam.
  • FIG. 1A represents the amplification system according to a top view, which explains why a single line materializes two pump bundles. Actually Ipi and Ip2, IP3 and Ip 4 , etc.
  • the pump beams are not in the same plane with respect to ⁇ B, as it appears on the side view of FIG. 1 B. Thanks to this arrangement of the pump beams, it is possible to have more than two pump beams, and therefore to increase the amplification power, while not requiring an increase in the angles of incidence in the gain medium of the signal beam and of the reflected beams, which would be inevitable with a conventional arrangement in which the pump beams are contained in the butterfly plane. Indeed, in this case, it is necessary to separate the mirrors of the butterfly to allow the passage of the pump beams.
  • the pump bundles Ip-j, Ip3. Ip 5 are not in the same plane with respect to ⁇ B, as it appears on the side view of FIG. 1 B. Thanks to this arrangement of the pump beams, it is possible to have more than two pump beams, and therefore to increase the amplification power, while not requiring an increase in the angles of incidence in the gain medium of the signal beam and of the reflected beams, which would be inevitable with a conventional arrangement in which the pump beam
  • Ip 7 are incident with a given angle ⁇ with respect to the plane ⁇ B of the butterfly and the pump beams Ip 2 , Ip 4 , Ip ⁇ .
  • Ip ⁇ are incident with an angle - ⁇ for example with respect to the plane of the butterfly.
  • Figure 1B shows a side view of the arrangement of Figure 1A.
  • the ⁇ TB plane of the butterfly is materialized by a dotted line.
  • the pump beams are incident in the gain medium with a non-zero angle relative to the plane ⁇ TB.
  • the pumping device comprises second reflection means formed by deflection mirrors for sending the pump beams into the gain medium.
  • these are the mirrors Mi to Ms respectively for the pump beams h to ⁇ Q.
  • the applicant has developed a particularly advantageous mount for the amplification system according to the invention on which at least four mirrors for deflecting said pump beams can be positioned in the gain medium, which makes it possible to reduce the bulk and therefore to decrease the angles of incidence in the gain medium and facilitate adjustment.
  • the mount 20 comprises a single support 21 intended to be fixed on the mounting table of the amplification device (not shown ) by two fixing points on either side of the frame.
  • the term “single support” is understood to mean any support formed from one or more parts integral in a translational movement.
  • the frame is adjustable in translation thanks to two oblong holes 22 a and 22 located on either side.
  • On the support are fixed plates 23 a to 23 ⁇ j movable along two axes, each plate supporting a deflection mirror. In this way, it minimizes the size of the frame while allowing easy adjustment of the mirrors thanks to the means of translation of the single support and the movable plates.
  • the example in FIG. 2 represents a mount adapted to the example in FIG. 1A with 4 mirrors M 5 , M ⁇ , M 7 , Me for deflecting the four pump beams IP5 to IP ⁇ -
  • the deflection mirrors are in this example arranged in the form of a square whose plane I1B of the incident signal forms a plane of symmetry.
  • two mounts identical to those shown in FIG. 2 are arranged on either side of the gain medium to send the eight pump bundles.
  • the mirrors are oriented so as to send the pump beams from external sources (not shown) to the medium gain.
  • the mirrors M5 and M 7 are oriented at 45 °.
  • the external sources can be made up of as many independent lasers as there are pump beams or one or two more powerful lasers emitting beams which are then divided to form the pump beams.
  • part of the return mirrors are recycling mirrors intended to return one of the pump beams to the gain medium for a second pass through the gain medium.
  • Each recycling mirror is located in a symmetrical position of a return mirror with respect to the gain medium and is oriented so as to return the pump beam to the gain medium for a second passage.
  • the amplification system comprises two mounts of the type of that of FIG.
  • each mount comprising four deflection mirrors, the two upper mirrors making it possible to return the pump harnesses coming from external sources and the two lower mirrors being recycling mirrors, which are intended to return a pump beam for a second passage in the gain medium.
  • the mirrors MQ and Ms are oriented to allow recycling.
  • the return mirrors can also be arranged differently on the support 21 of the frame 20. For example, they can be arranged in the form of a crown, while preferably keeping the plane IB of the incident signal as plane of symmetry in order to optimize the angles of incidence of the pump beams in the gain medium.
  • FIGS. 3A and 3B represent top and side views of an amplification system according to the invention according to a variant.
  • the gain medium 10 has two faces 10 a and 10 and the first reflection means notably comprise a mirror 11 positioned near one of the faces (10 a ) of the gain medium and allowing two passages of the laser beam signal Is in the gain medium.
  • the signal beam Is and the reflected beam forming the amplified signal IA are in the same plane ⁇ B as in the previous example (plane of FIG. 3A).
  • the pumping device then comprises at least four pump beams incident in the gain medium in directions not contained in the plane ⁇ B, as illustrated in FIG. 3B.
  • the pumping device comprises a mount such as that described in FIG. 2, with four deflection mirrors oriented to allow four pump beams from four external sources to be sent to the gain medium.
  • the high power amplification system according to the invention can be integrated for example in an amplification chain of a femtosecond laser pulse.
  • the gain medium is a Sapphire-Titanium crystal suitable for amplifying a signal in the near infrared, the wavelength of the pump beams possibly being 532 nm for example.
  • the amplification system according to the invention the applicant was able to produce low-rate femtosecond amplification chains (less than 20 Hz) with peak power greater than 15 TW, thanks to a pumping device with four pump beams ( two incident pump bundles on each side of the gain medium) and a recycling function as described above.
  • the pump laser is for example an Nd: YAG laser doubled in frequency.
  • an Nd: glass type laser (neodymium doped glass) is used for the pump.
  • the applicant also implemented a high rate amplification system (greater than 1 kHz), using a pumping device with four pump beams and the recycling function.
  • the pump laser is for example an Nd: YLF type laser (Ytterbium Lithium Fluor doped Neodymium) emitting at 527 nm or 523.5 nm.
  • the gain medium is advantageously a Sapphire-Titanium crystal.

Abstract

The invention relates to a high power laser amplification system, for a femtosecond laser pulse amplification system, for example. According to the invention, the amplification system comprises a gain medium (10), first reflection means (11a to 11f), which allow a multiple passage of signal beams into said gain medium such that the incident signal beam and the reflected beams are disposed on the same plane (?B) and a pumping device in the gain medium. According to the invention, the pumping device comprises at least four incident pump beams (IP1 to IP8) within the gain medium in directions not contained within said plane (?B) of the signal beam.

Description

Système d'amplification laser à haute puissance High power laser amplification system
La présente invention concerne un système d'amplification laser à haute puissance, par exemple pour une chaîne d'amplification d'une impulsion laser femtoseconde.The present invention relates to a high power laser amplification system, for example for an amplification chain of a femtosecond laser pulse.
Un système d'amplification d'un faisceau laser incident, appelé faisceau « signal » comprend généralement et de façon connue un milieu à gain, par exemple un cristal servant de milieu à gain, des moyens de réflexion permettant le passage multiple du faisceau signal dans le milieu à gain afin d'augmenter la puissance du signal amplifié, et un dispositif de pompage du milieu à gain. Les moyens de réflexion comprennent par exemple des miroirs réfléchissants du faisceau signal, disposés de part et d'autre du milieu à gain et formant ce qu'il est connu d'appeler le « papillon » (ou « bow tie » suivant l'expression anglo-saxonne). Le dispositif de pompage comprend généralement un ou deux faisceaux laser dits faisceaux de pompe, incidents dans le milieu à gain. Pour augmenter la puissance du signal amplifié, il est connu d'augmenter la puissance des faisceaux de pompe, et/ou d'augmenter le nombre de passages du faisceau signal dans le milieu à gain. Mais la présence des faisceaux de pompe entraîne des contraintes angulaires sur le positionnement des miroirs réfléchissants du papillon, qui se trouvent éloignés les uns des autres et parfois dans des plans différents, entraînant des angles importants du faisceau signal dans le milieu à gain, ce qui se traduit par des effets d'aberration sur le signal amplifié. L'invention propose un système d'amplification haute puissance avec un dispositif de pompage à quatre faisceaux de pompe au moins, permettant ainsi d'augmenter l'énergie sur le milieu à gain, les faisceaux étant agencés de telle sorte qu'ils présentent des angles réduits entre eux et avec le faisceau signal. Plus précisément, l'invention propose un système d'amplification haute puissance d'un faisceau laser signal incident comprenant un milieu à gain, des premiers moyens de réflexion permettant le passage multiple du faisceau signal dans ledit milieu à gain de telle sorte que le faisceau signal incident et les faisceaux réfléchis soient contenus dans un même plan, et un dispositif de pompage du milieu à gain, caractérisé en ce que le dispositif de pompage comprend au moins quatre faisceaux de pompe incidents dans le milieu à gain selon des directions non contenues dans ledit plan du faisceau signal.A system for amplifying an incident laser beam, called a “signal” beam generally comprises, in a known manner, a gain medium, for example a crystal serving as gain medium, reflection means allowing the multiple passage of the signal beam in the gain medium in order to increase the power of the amplified signal, and a device for pumping the gain medium. The reflection means comprise for example reflecting mirrors of the signal beam, arranged on either side of the gain medium and forming what is known as the "butterfly" (or "bow tie" according to the expression Anglo-Saxon). The pumping device generally comprises one or two laser beams called pump beams, incident in the gain medium. To increase the power of the amplified signal, it is known to increase the power of the pump beams, and / or to increase the number of passages of the signal beam in the gain medium. However, the presence of the pump beams causes angular constraints on the positioning of the butterfly's reflecting mirrors, which are distant from each other and sometimes in different planes, causing large angles of the signal beam in the gain medium, which results in aberration effects on the amplified signal. The invention proposes a high power amplification system with a pumping device with at least four pump beams, thus making it possible to increase the energy on the gain medium, the beams being arranged so that they have reduced angles between them and with the signal beam. More specifically, the invention proposes a high power amplification system of an incident signal laser beam comprising a gain medium, first reflection means allowing the multiple passage of the signal beam in said gain medium so that the beam incident signal and the reflected beams are contained in the same plane, and a device for pumping the gain medium, characterized in that the pumping device comprises at least four pump beams incident in the gain medium in directions not contained in said plane of the signal beam.
Avantageusement, le dispositif de pompage comprend des seconds moyens de réflexion avec au moins une monture sur laquelle sont positionnés au moins quatre miroirs de renvoi desdits faisceaux de pompe dans le milieu à gain.Advantageously, the pumping device comprises second reflection means with at least one frame on which are positioned at least four mirrors for deflecting said pump beams in the gain medium.
D'autres avantages et caractéristiques apparaîtront plus clairement à la lecture de la description qui suit, illustrée par les figures annexées qui représentent : - Les figures 1A et 1 B, les schémas selon deux vues d'un système d'amplification haute puissance selon l'invention ;Other advantages and characteristics will appear more clearly on reading the following description, illustrated by the appended figures which represent: - Figures 1A and 1B, the diagrams according to two views of a high power amplification system according to the invention;
- La figure 2, un exemple de réalisation d'une monture pour le support des miroirs du dispositif de pompage ;- Figure 2, an embodiment of a mount for supporting the mirrors of the pumping device;
- Les figures 3A et 3B, des schémas selon deux vues d'un exemple de réalisation du système d'amplification selon l'invention selon une autre variante. La figure 1A représente un exemple de réalisation d'un système d'amplification haute puissance d'un faisceau signal incident Is selon une vue de dessus. Il comprend un milieu à gain 10, des premiers moyens de réflexion 11a à 11f permettant le passage multiple du faisceau signal dans ledit milieu à gain afin de former un faisceau amplifié IA- Ces moyens de réflexion, formés dans cet exemple de 3 miroirs disposés de chaque côté du milieu à gain, sont appelés classiquement le « papillon » à cause de la forme en nœud papillon de l'agencement des miroirs. Selon l'invention, le faisceau signal incident Is et les faisceaux réfléchis par les différents miroirs sont contenus dans un même plan rie, qui est ici le plan de la figure 1A. Il est intéressant d'avoir tous les miroirs du papillon dans un même plan car le système est ainsi plus simple à réaliser et à aligner. Le système d'amplification selon l'invention comprend également un dispositif de pompage du milieu à gain 10 comprenant au moins quatre faisceaux de pompe (dans cet exemple huit faisceaux Ipi à Ips symbolisés par des flèches doubles), ces faisceaux étant incidents dans le milieu à gain selon des directions non contenues dans ledit plan rie du faisceau signal. La figure 1A représente le système d'amplification selon une vue de dessus ce qui explique qu'une seule ligne matérialise deux faisceaux de pompe. En fait Ipi et Ip2, IP3 et Ip4, etc. ne sont pas dans le même plan par rapport à ΠB, comme cela apparaît sur la vue de côté de la figure 1 B. Grâce à cet agencement des faisceaux de pompe, il est possible d'avoir plus de deux faisceaux de pompe, et donc d'augmenter la puissance d'amplification, tout en ne nécessitant pas d'augmenter les angles d'incidence dans le milieu à gain du faisceau signal et des faisceaux réfléchis, ce qui serait inévitable avec un agencement classique dans lequel les faisceaux de pompe sont contenus dans le plan du papillon. En effet, dans ce cas, il est nécessaire d'écarter les miroirs du papillon pour permettre le passage des faisceaux de pompe. Ainsi, dans l'exemple de la figure 1A, les faisceaux de pompe Ip-j, Ip3. Ip5. Ip7 sont incidents avec un angle θ donné par rapport au plan ΠB du papillon et les faisceaux de pompe Ip2, Ip4, Ipβ. Ipβ sont incidents avec un angle -θ par exemple par rapport au plan du papillon.- Figures 3A and 3B, diagrams according to two views of an exemplary embodiment of the amplification system according to the invention according to another variant. FIG. 1A represents an exemplary embodiment of a high power amplification system of an incident signal beam Is according to a top view. It includes a gain medium 10, first reflection means 11 a to 11 f allowing the multiple passage of the signal beam in said gain medium in order to form an amplified beam IA- These reflection means, formed in this example of 3 mirrors arranged on each side of the gain medium, are conventionally called the "butterfly" because of the bow tie shape of the arrangement of the mirrors. According to the invention, the incident signal beam Is and the beams reflected by the various mirrors are contained in the same plane rie, which is here the plane of FIG. 1A. It is interesting to have all the butterfly mirrors in one plane because the system is thus simpler to make and align. The amplification system according to the invention also comprises a device for pumping the gain medium 10 comprising at least four pump beams (in this example eight Ipi beams at Ips symbolized by double arrows), these beams being incident in the medium gain in directions not contained in said plane of the signal beam. FIG. 1A represents the amplification system according to a top view, which explains why a single line materializes two pump bundles. Actually Ipi and Ip2, IP3 and Ip 4 , etc. are not in the same plane with respect to ΠB, as it appears on the side view of FIG. 1 B. Thanks to this arrangement of the pump beams, it is possible to have more than two pump beams, and therefore to increase the amplification power, while not requiring an increase in the angles of incidence in the gain medium of the signal beam and of the reflected beams, which would be inevitable with a conventional arrangement in which the pump beams are contained in the butterfly plane. Indeed, in this case, it is necessary to separate the mirrors of the butterfly to allow the passage of the pump beams. Thus, in the example of FIG. 1A, the pump bundles Ip-j, Ip3. Ip 5 . Ip 7 are incident with a given angle θ with respect to the plane ΠB of the butterfly and the pump beams Ip 2 , Ip 4 , Ipβ. Ipβ are incident with an angle -θ for example with respect to the plane of the butterfly.
La figure 1 B représente une vue de côté de l'agencement de la figure 1A. Le plan ΓTB du papillon est matérialisé par une ligne en pointillé. Les faisceaux de pompe sont incidents dans le milieu à gain avec un angle non nul par rapport au plan ΓTB.Figure 1B shows a side view of the arrangement of Figure 1A. The ΓTB plane of the butterfly is materialized by a dotted line. The pump beams are incident in the gain medium with a non-zero angle relative to the plane ΓTB.
De façon connue, le dispositif de pompage comprend des seconds moyens de réflexion formés de miroirs de renvoi pour envoyer les faisceaux de pompe dans le milieu à gain. Dans l'exemple des figures 1A et 1 B, il s'agit des miroirs Mi à Ms respectivement pour les faisceaux de pompe h à \Q. La déposante a développé pour le système d'amplification selon l'invention une monture particulièrement avantageuse sur laquelle peuvent être positionnés au moins quatre miroirs de renvoi desdits faisceaux de pompe dans le milieu à gain, ce qui permet de réduire l'encombrement et donc de diminuer les angles d'incidence dans le milieu à gain et de faciliter le réglage.In known manner, the pumping device comprises second reflection means formed by deflection mirrors for sending the pump beams into the gain medium. In the example of FIGS. 1A and 1B, these are the mirrors Mi to Ms respectively for the pump beams h to \ Q. The applicant has developed a particularly advantageous mount for the amplification system according to the invention on which at least four mirrors for deflecting said pump beams can be positioned in the gain medium, which makes it possible to reduce the bulk and therefore to decrease the angles of incidence in the gain medium and facilitate adjustment.
La figure 2 représente une telle monture adaptée à l'exemple de réalisation des figures 1A et 1 B. La monture 20 comprend selon l'invention un support unique 21 destiné à être fixé sur la table de montage du dispositif d'amplification (non représentée) par deux points de fixation de part et d'autre de la monture. Par support unique, on comprend tout support formé d'une ou plusieurs pièces solidaires dans un mouvement en translation. Avantageusement, la monture est réglable en translation grâce à deux trous oblongs 22a et 22 situés de part et d'autre. Sur le support sont fixés des platines 23a à 23<j mobiles selon deux axes, chaque platine supportant un miroir de renvoi. De cette manière, on rend minimal l'encombrement de la monture tout en permettant un réglage aisé des miroirs grâce aux moyens de translation du support unique et aux platines mobiles. L'exemple de la figure 2 représente une monture adaptée à l'exemple de la figure 1A avec 4 miroirs M5, MΘ, M7, Me de renvoi des quatre faisceaux de pompe IP5 à IPβ- Les miroirs de renvoi sont dans cet exemple agencés sous forme d'un carré dont le plan I1B du signal incident forme un plan de symétrie. Dans l'exemple de la figure 1A, deux montures identiques à celles représentées sur la figure 2 sont disposées de part et d'autre du milieu à gain pour envoyer les huit faisceaux de pompe.2 shows such a mount adapted to the embodiment of Figures 1A and 1 B. The mount 20 according to the invention comprises a single support 21 intended to be fixed on the mounting table of the amplification device (not shown ) by two fixing points on either side of the frame. The term “single support” is understood to mean any support formed from one or more parts integral in a translational movement. Advantageously, the frame is adjustable in translation thanks to two oblong holes 22 a and 22 located on either side. On the support are fixed plates 23 a to 23 < j movable along two axes, each plate supporting a deflection mirror. In this way, it minimizes the size of the frame while allowing easy adjustment of the mirrors thanks to the means of translation of the single support and the movable plates. The example in FIG. 2 represents a mount adapted to the example in FIG. 1A with 4 mirrors M 5 , MΘ, M 7 , Me for deflecting the four pump beams IP5 to IPβ- The deflection mirrors are in this example arranged in the form of a square whose plane I1B of the incident signal forms a plane of symmetry. In the example of FIG. 1A, two mounts identical to those shown in FIG. 2 are arranged on either side of the gain medium to send the eight pump bundles.
Lorsque l'on veut envoyer dans le milieu à gain huit faisceaux de pompe, comme dans l'exemple de la figure 1A, les miroirs sont orientés de telle sorte à envoyer les faisceaux de pompe issus des sources extérieures (non représentées) vers le milieu à gain. Ainsi, dans l'exemple de la figure 2, les miroirs M5 et M7 sont orientés à 45°. Les sources extérieures peuvent être constituées d'autant de lasers indépendants qu'il y a de faisceaux de pompe ou d'un ou deux lasers plus puissants émettant des faisceaux qui sont ensuite divisés pour former les faisceaux de pompe.When we want to send eight gain pump beams to the gain medium, as in the example in FIG. 1A, the mirrors are oriented so as to send the pump beams from external sources (not shown) to the medium gain. Thus, in the example of FIG. 2, the mirrors M5 and M 7 are oriented at 45 °. The external sources can be made up of as many independent lasers as there are pump beams or one or two more powerful lasers emitting beams which are then divided to form the pump beams.
Selon une variante de l'invention une partie des miroirs de renvoi sont des miroirs de recyclage destinés à renvoyer vers le milieu à gain un des faisceaux de pompe pour un deuxième passage dans le milieu à gain. Cela permet notamment dans le cas de milieux à gain à faible absorption de rendre maximale l'énergie stockée dans le milieu à gain et d'augmenter ainsi le rendement de l'amplificateur. Chaque miroir de recyclage est situé dans une position symétrique d'un miroir de renvoi par rapport au milieu à gain et est orienté de telle sorte à renvoyer vers le milieu à gain le faisceau de pompe pour un deuxième passage. Par exemple, le système d'amplification comprend deux montures du type de celle de la figure 2, chaque monture comprenant quatre miroirs de renvoi, les deux miroirs supérieurs permettant de renvoyer les faisceaux de pompe issus des sources extérieures et les deux miroirs inférieurs étant des miroirs de recyclage, qui sont destinés à renvoyer un faisceau de pompe pour un deuxième passage dans le milieu à gain. Dans l'exemple de la figure 2, les miroirs MQ et Ms sont orientés pour permettre le recyclage. Selon l'invention, les miroirs de renvoi peuvent également être agencés différemment sur le support 21 de la monture 20. Par exemple, ils peuvent être agencés sous forme d'une couronne, tout en gardant de façon préférentielle le plan I B du signal incident comme plan de symétrie afin d'optimiser les angles d'incidence des faisceaux de pompe dans le milieu à gain.According to a variant of the invention, part of the return mirrors are recycling mirrors intended to return one of the pump beams to the gain medium for a second pass through the gain medium. This makes it possible in particular in the case of gain media with low absorption to maximize the energy stored in the gain medium and thus increase the efficiency of the amplifier. Each recycling mirror is located in a symmetrical position of a return mirror with respect to the gain medium and is oriented so as to return the pump beam to the gain medium for a second passage. For example, the amplification system comprises two mounts of the type of that of FIG. 2, each mount comprising four deflection mirrors, the two upper mirrors making it possible to return the pump harnesses coming from external sources and the two lower mirrors being recycling mirrors, which are intended to return a pump beam for a second passage in the gain medium. In the example of Figure 2, the mirrors MQ and Ms are oriented to allow recycling. According to the invention, the return mirrors can also be arranged differently on the support 21 of the frame 20. For example, they can be arranged in the form of a crown, while preferably keeping the plane IB of the incident signal as plane of symmetry in order to optimize the angles of incidence of the pump beams in the gain medium.
Les figures 3A et 3B représentent des vues de dessus et de coté d'un système d'amplification selon l'invention selon une variante. Dans cet exemple, le milieu à gain 10 présente deux faces 10a et 10 et les premiers moyens de réflexion comprennent notamment un miroir 11 positionné à proximité d'une des faces (10a) du milieu à gain et permettant deux passages du faisceau laser signal Is dans le milieu à gain. Le faisceau signal Is et le faisceau réfléchi formant le signal amplifié IA sont dans un même plan ΠB comme dans l'exemple précédent (plan de la figure 3A). Selon l'invention, le dispositif de pompage comprend alors au moins quatre faisceaux de pompe incidents dans le milieu à gain selon des directions non contenues dans le plan ΠB, comme cela est illustré sur la figure 3B. Avantageusement, le dispositif de pompage comprend une monture telle que celle décrite sur la figure 2, avec quatre miroirs de renvoi orientés pour permettre d'envoyer vers le milieu à gain quatre faisceaux de pompe issus de quatre sources extérieures.FIGS. 3A and 3B represent top and side views of an amplification system according to the invention according to a variant. In this example, the gain medium 10 has two faces 10 a and 10 and the first reflection means notably comprise a mirror 11 positioned near one of the faces (10 a ) of the gain medium and allowing two passages of the laser beam signal Is in the gain medium. The signal beam Is and the reflected beam forming the amplified signal IA are in the same plane ΠB as in the previous example (plane of FIG. 3A). According to the invention, the pumping device then comprises at least four pump beams incident in the gain medium in directions not contained in the plane ΠB, as illustrated in FIG. 3B. Advantageously, the pumping device comprises a mount such as that described in FIG. 2, with four deflection mirrors oriented to allow four pump beams from four external sources to be sent to the gain medium.
Le système d'amplification haute puissance selon l'invention peut être intégré par exemple dans une chaîne d'amplification d'une impulsion laser femtoseconde. Par exemple, le milieu à gain est un cristal de Saphir- Titane adapté pour l'amplification d'un signal dans le proche infrarouge, la longueur d'onde des faisceaux de pompe pouvant être de 532 nm par exemple. Grâce au système d'amplification selon l'invention, la déposante a pu réaliser des chaînes d'amplification femtoseconde basse cadence (inférieure à 20 Hz) de puissance crête supérieure à 15 TW, grâce à un dispositif de pompage à quatre faisceaux de pompe (deux faisceaux de pompe incidents de chaque côté du milieu à gain) et une fonction de recyclage telle qu'elle a été décrite précédemment. Le laser de pompe est par exemple un laser Nd :YAG doublé en fréquence.The high power amplification system according to the invention can be integrated for example in an amplification chain of a femtosecond laser pulse. For example, the gain medium is a Sapphire-Titanium crystal suitable for amplifying a signal in the near infrared, the wavelength of the pump beams possibly being 532 nm for example. Thanks to the amplification system according to the invention, the applicant was able to produce low-rate femtosecond amplification chains (less than 20 Hz) with peak power greater than 15 TW, thanks to a pumping device with four pump beams ( two incident pump bundles on each side of the gain medium) and a recycling function as described above. The pump laser is for example an Nd: YAG laser doubled in frequency.
Dans un autre exemple de réalisation, huit faisceaux de pompe sont utilisés, quatre de chaque côté, sans la fonction de recyclage. Avantageusement un laser de type Nd : verre (verre dopé Néodyme) est utilisé pour la pompe.In another exemplary embodiment, eight pump bundles are used, four on each side, without the recycling function. Advantageously, an Nd: glass type laser (neodymium doped glass) is used for the pump.
La déposante a également mis en œuvre un système d'amplification à cadence élevée (supérieure à 1 kHz), en utilisant un dispositif de pompage avec quatre faisceaux de pompe et la fonction de recyclage. Le laser de pompe est par exemple un laser de type Nd :YLF (Ytterbium Lithium Fluor dopé Néodyme) émettant à 527 nm ou 523,5 nm. Le milieu à gain est avantageusement un cristal de Saphir-Titane. The applicant also implemented a high rate amplification system (greater than 1 kHz), using a pumping device with four pump beams and the recycling function. The pump laser is for example an Nd: YLF type laser (Ytterbium Lithium Fluor doped Neodymium) emitting at 527 nm or 523.5 nm. The gain medium is advantageously a Sapphire-Titanium crystal.

Claims

REVENDICATIONS
1- Système d'amplification haute puissance d'un faisceau laser signal incident (Is) comprenant un milieu à gain (10), des premiers moyens de réflexion (11a à 11f) permettant le passage multiple du faisceau signal dans ledit milieu à gain de telle sorte que le faisceau signal incident et les faisceaux réfléchis soient contenus dans un même plan (I1B), et un dispositif de pompage du milieu à gain, caractérisé en ce que le dispositif de pompage comprend au moins quatre faisceaux de pompe incidents (IPi à IPβ) dans le milieu à gain selon des directions non contenues dans ledit plan (E1B) du faisceau signal.1- High power amplification system of an incident signal laser beam (Is) comprising a gain medium (10), first reflection means (11 a to 11f) allowing the multiple passage of the signal beam in said gain medium so that the incident signal beam and the reflected beams are contained in the same plane (I1B), and a device for pumping the gain medium, characterized in that the pumping device comprises at least four incident pump beams (IPi at IPβ) in the gain medium in directions not contained in said plane (E1B) of the signal beam.
2- Système amplificateur selon la revendication 1 , caractérisé en ce que le dispositif de pompage comprend des seconds moyens de réflexion (Mi à Me) avec au moins une monture (20) sur laquelle sont positionnés au moins quatre miroirs de renvoi desdits faisceaux de pompe dans le milieu à gain.2- Amplifier system according to claim 1, characterized in that the pumping device comprises second reflection means (Mi to Me) with at least one mount (20) on which are positioned at least four mirrors for deflecting said pump beams in the gain medium.
3- Système amplificateur selon la revendication 2, caractérisé en ce que sur chaque monture sont positionnés quatre miroirs de renvoi formant un carré dont le plan (ΠB) du signal incident forme un plan de symétrie. 4- Système amplificateur selon l'une des revendications 2 ou 3, caractérisé en ce que chaque monture comprend un support unique réglable en translation et des platines mobiles selon deux axes fixés sur ledit support, chaque platine supportant un miroir de renvoi.3- Amplifier system according to claim 2, characterized in that on each frame are positioned four deflection mirrors forming a square whose plane (ΠB) of the incident signal forms a plane of symmetry. 4- Amplifier system according to one of claims 2 or 3, characterized in that each mount comprises a single support adjustable in translation and movable plates on two axes fixed on said support, each plate supporting a deflection mirror.
5- Système amplificateur selon l'une des revendications 2 à 4, caractérisé en ce que lesdits moyens de réflexion comprennent deux montures situées de part et d'autre du milieu à gain, sur chaque monture étant positionnés au moins quatre miroirs de renvoi desdits faisceaux de pompe dans le milieu à gain.5- Amplifier system according to one of claims 2 to 4, characterized in that said reflection means comprise two frames located on either side of the gain medium, on each frame being positioned at least four mirrors for deflecting said beams pump in the gain medium.
6- Système amplificateur selon la revendication 5, caractérisé en ce qu'au moins un miroir de renvoi d'au moins une monture est un miroir de recyclage destiné à renvoyer vers le milieu à gain un faisceau de pompe pour un deuxième passage dans le milieu à gain.6- Amplifier system according to claim 5, characterized in that at least one return mirror of at least one frame is a recycling mirror intended to return to the gain medium a pump beam for a second passage in the medium gain.
7- Système amplificateur selon la revendication 6, caractérisé en ce que chaque monture comprend quatre miroirs de renvoi dont deux miroirs de recyclage, un miroir de recyclage d'une monture étant dans une position symétrique d'un miroir de renvoi de l'autre monture par rapport au milieu à gain.7- Amplifier system according to claim 6, characterized in that each frame comprises four deflection mirrors including two recycling mirrors, a mirror for recycling a frame being in a position symmetrical of a deflection mirror of the other mount with respect to the gain medium.
8- Système amplificateur selon l'une des revendications précédentes, caractérisé en ce que les premiers moyens de réflexion comprennent trois miroirs situés de chaque côté du milieu amplificateur, permettant trois passages du faisceau signal dans le milieu à gain.8- Amplifier system according to one of the preceding claims, characterized in that the first reflection means comprise three mirrors located on each side of the amplifying medium, allowing three passages of the signal beam in the gain medium.
9- Système amplificateur selon l'une des revendications 1 à 4, caractérisé en ce que le milieu à gain comprenant deux faces opposées, les premiers moyens de réflexion comprennent un miroir (11) positionné à proximité d'une desdites faces du milieu à gain, permettant deux passages du faisceau signal dans le milieu à gain, et en ce que les faisceaux de pompe sont incidents sur une face opposée à celle à proximité de laquelle se trouve ledit miroir des premiers moyens de réflexion.9- Amplifier system according to one of claims 1 to 4, characterized in that the gain medium comprising two opposite faces, the first reflection means comprise a mirror (11) positioned near one of said faces of the gain medium , allowing two passages of the signal beam in the gain medium, and in that the pump beams are incident on a face opposite to that close to which is located said mirror of the first reflection means.
10- Chaîne d'amplification d'une impulsion laser femtoseconde comprenant un système amplificateur haute puissance selon l'une des revendications précédentes.10- Amplification chain of a femtosecond laser pulse comprising a high power amplifier system according to one of the preceding claims.
11- Chaîne d'amplification selon la revendication 10, caractérisé en ce que le milieu à gain est un cristal de Saphir-Titane, la longueur d'onde des faisceaux de pompe est de 532 nm et la longueur d'onde du faisceau signal à amplifier est dans le proche infra rouge.11- Amplification chain according to claim 10, characterized in that the gain medium is a Sapphire-Titanium crystal, the wavelength of the pump beams is 532 nm and the wavelength of the signal beam to amplifier is in the near infrared.
12- Chaîne d'amplification basse cadence d'une impulsion laser femtoseconde comprenant un système amplificateur haute puissance selon la revendication 7, caractérisé en ce que le milieu à gain est un cristal de Saphir-Titane et les faisceaux de pompe sont obtenus à partir d'au moins un laser Nd :YAG doublé en fréquence fonctionnant à une cadence inférieure à 20 Hz.12- Low rate amplification chain of a femtosecond laser pulse comprising a high power amplifier system according to claim 7, characterized in that the gain medium is a Sapphire-Titanium crystal and the pump beams are obtained from '' at least one frequency-doubled Nd: YAG laser operating at a rate below 20 Hz.
13- Chaîne d'amplification haute cadence d'une impulsion laser femtoseconde comprenant un système amplificateur haute puissance selon la revendication 7, caractérisé en ce que le milieu à gain est un cristal de Saphir-Titane et les faisceaux de pompe sont obtenus à partir d'au moins un laser Nd :YLF fonctionnant à une cadence supérieure à 1 kHz. 13- High rate amplification chain of a femtosecond laser pulse comprising a high power amplifier system according to claim 7, characterized in that the gain medium is a Sapphire-Titanium crystal and the pump beams are obtained from '' at least one Nd: YLF laser operating at a rate higher than 1 kHz.
PCT/FR2003/001600 2002-05-28 2003-05-27 High power laser amplification system WO2003100928A1 (en)

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FR0206507A FR2840461B1 (en) 2002-05-28 2002-05-28 HIGH POWER LASER AMPLIFICATION SYSTEM

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