Laser beam amplification device

Abstract

The present invention relates to a device (10) for amplifying a multi-wavelength laser beam, comprising: a. a first amplifying medium (M1) having a front face (20) and a reflecting rear face (22), which faces are tilted relative to each other by a first non-zero tilt, and b. a second amplifying medium (M2) having a front face (20) capable of receiving the beam (FR1) reflected by the rear face (22) and refracted by the front face (20) of the first amplifying medium (M1), and a reflecting rear face (22), which faces are tilted relative to each other by a second non-zero tilt, the first tilt, the second tilt and the orientation of the second amplifying medium (M2) being such that the sub-beams of each wavelength, which form the output beam (FR2) of the second amplifying medium (M2), are parallel to each other at the output of the second amplifying medium (M2).

Description

[0001] DESCRIPTION

[0002] TITLE: Device for amplifying a laser beam

[0003] The present invention relates to a device for amplifying a multi-wavelength laser beam.

[0004] The field of the invention is that of solid-state laser sources for scientific, industrial, medical and military applications. More specifically, it is advantageously used for amplifying medium materials (such as a crystal) which have a relatively small thickness compared to their aperture along the propagation axis of the laser beam, typically less than 1:3.

[0005] Pumping laser technology has evolved significantly in recent years and it is now possible to have a pulsed laser source that provides an average pumping power of at least a hundred Watts.

[0006] However, a number of configurations are not compatible with next-generation pump lasers for which high energy and high average power (higher repetition rate) are sought.

[0007] In the current state of the art, different solutions are used for the extraction of thermal power in an amplifying medium by working on the form factor of this medium, typically amplifying fibers, very thin disks, slabs and so-called thick disks.

[0008] The thick disk solution is well suited to certain amplifying media such as amorphous materials (like glasses), transparent ceramics, or crystals like Ti:Sa (short for Titanium:Sapphire). It allows access to high energy levels, high average powers, and short pulse durations thanks to the material's broad amplification spectrum.

[0009] In thick disk technology, the amplifying medium is cooled from its rear face. Cooling is then achieved by means of a fluid, liquid or gas, or a solid. Such rear-face cooling increases the heat exchange surface. It also generates a thermal gradient in the laser propagation direction in the amplifying medium, and also achieves high thermal extraction. The index variations related to temperature variations in the amplifying medium are then gradients predominantly oriented in the same direction as the laser beam propagation direction. However, rear-face-cooled laser amplification devices induce geometric folding of the beam due to the reflective rear face of the amplifying medium (e.g., a crystal).The output face of the amplifying medium is then the same as the input face, which implies that the parasitic pulses (due to parasitic reflections on the front face) are found before the main pulse, consequently degrading the temporal contrast of the pulse. The temporal contrast is defined by the ratio between the intensity of the main pulse and the foot of the pulse and / or any parasitic pulses.

[0010] To avoid this degradation, it is known from patent EP 2 915 226 B to modify the air / crystal interface to separate the main pulse and the parasitic pulses. To do this, the front face of the amplifying medium is inclined relative to its rear face by a non-zero angle. Thus, after propagation in the amplifying medium, the parasitic reflections are spatially separated from the main pulse and the temporal contrast is no longer degraded by the parasitic reflections.

[0011] For short pulses (with broad spectrum), this angle produces a prismatic effect which is compensated by a compensating prism positioned on the beam path, as described in EP 2 915 226 B. Thus, when several passes through the amplification medium are made, this involves the implementation of several prisms in the amplification system.

[0012] Beyond the financial impact, the implementation of numerous optics in transmission is a source of optical loss and a potential source of failure (damage leading to unavailability of the laser and a cost of repairing the part and labor for realignment).

[0013] There is therefore a need for an amplification device that can minimize optical losses while remaining satisfactory in terms of cooling and temporal contrast.

[0014] To this end, the invention relates to a device for amplifying a multi-wavelength laser beam, the device comprising: a. a first solid amplifying medium having a first refractive index, the first amplifying medium having at least two flat faces among a front face suitable for receiving the beam to be amplified, called the incident beam, and a reflective rear face, the front face being inclined relative to the rear face by a first non-zero inclination, the rear face (being suitable for being cooled, and b.a second solid amplifying medium having a second refractive index, the second amplifying medium having at least two planar faces among a front face suitable for receiving the beam reflected by the rear face and refracted by the front face of the first amplifying medium, and a reflective rear face, the front face being inclined relative to the rear face by a second non-zero inclination, the rear face being suitable for being cooled, the second amplifying medium being arranged on the path of the beam reflected by the rear face and refracted by the front face of the first amplifying medium, the first inclination, the second inclination and the orientation of the second amplifying medium being such that the sub-beams of each wavelength, forming the output beam of the second amplifying medium, are parallel to each other at the output of the second amplifying medium.

[0015] According to other advantageous aspects of the invention, the device comprises one or more of the following characteristics, taken in isolation or in all technically possible combinations:

[0016] - the front face of the first amplifying medium is perpendicular to an axis Oz, the first inclination forming an angle p? on a plane xOz and Pi” on a plane yOz, the second inclination forming an angle P2' on a plane xOz and P2” on a plane yOz, the following condition being verified:

[0017] - the second amplifying medium is arranged relative to the first amplifying medium so that: a. the front face of the second amplifying medium is parallel to the front face of the first amplifying medium, and b. the rear face of the second amplifying medium is parallel to the rear face of the first amplifying medium;

[0018] - the beam at the output of the second amplifying medium has an enlarged diameter (relative to the diameter of the incident beam, the amplification device comprising an optical compensation assembly capable of compensating for the enlargement of the beam at the output of the second amplifying medium so that the beam at the output of the amplification device has a diameter substantially equal to the diameter of the incident beam;

[0019] - the optical compensation assembly comprises: a. a third solid amplifying medium having a third refractive index, the third amplifying medium having at least two planar faces among a front face suitable for receiving the beam at the output of the second amplifying medium and a reflective rear face, the front face (being inclined relative to the rear face by a third non-zero inclination, the rear face being suitable for being cooled, b. a fourth solid amplifying medium having a fourth refractive index, the fourth amplifying medium having at least two planar faces among a front face suitable for receiving the beam reflected by the rear face and refracted by the front face of the third amplifying medium, and a reflective rear face, the front face being inclined relative to the rear face by a fourth non-zero inclination, the rear face being suitable for being cooled,the fourth amplifying medium being arranged on the path of the beam reflected by the rear face and refracted by the front face of the third amplifying medium, the third inclination, the fourth inclination, the orientation of the third amplifying medium and the orientation of the fourth amplifying medium being such that the output beam of the fourth amplifying medium has a diameter substantially equal to the diameter of the incident beam and that the sub-beams of each wavelength, forming said output beam, are parallel to each other at the output of the fourth amplifying medium;,

[0020] - the front face of the third amplifying medium is perpendicular to an axis Oz, the third inclination forming an angle P3' on a plane xOz and P3” on a plane yOz, the third inclination forming an angle P3' on a plane xOz and P3” on a plane yOz, the following condition being verified:

[0021] - the third amplifying medium is arranged relative to the fourth amplifying medium so that: a. the front face of the third amplifying medium is parallel to the front face of the fourth amplifying medium, and b. the rear face of the third amplifying medium is parallel to the rear face of the fourth amplifying medium;

[0022] - the first amplifying medium, the second amplifying medium, the third amplifying medium and the fourth amplifying medium are identical;

[0023] - the first medium, the second medium, the third medium and the fourth medium form an amplification unit, called a reference amplification unit, the beam reflected by the rear face and refracted by the front face of the fourth medium forming the output beam of the reference amplification unit, the amplification device comprising one or more successive amplification units, identical to the reference amplification unit, each amplification unit being arranged so as to receive, as an input beam, the output beam of the previous amplification unit;

[0024] - the optical compensation assembly comprises at least one mirror arranged so that the output beam of the amplification device is superimposed on the incident beam;

[0025] - the front face of the first amplifying medium is suitable for receiving the incident beam and for reflecting a beam, called the first parasitic beam, from the incident beam, the second amplifying medium being arranged outside the path of the first parasitic beam.

[0026] - the front face of the second amplifying medium is suitable for receiving the beam at the output of the first amplifying medium and for reflecting a beam, called the second parasitic beam, from the received beam, the third amplifying medium being arranged outside the path of the second parasitic beam, and

[0027] - the front face of the third amplifying medium is suitable for receiving the beam at the output of the second amplifying medium and for reflecting a beam, called the third parasitic beam, from the received beam, the fourth amplifying medium being arranged outside the path of the third parasitic beam.

[0028] Other features and advantages of the invention will become apparent upon reading the following description of embodiments of the invention, given by way of example only, and with reference to the drawings which are:

[0029] - [Fig 1] figure 1, a schematic representation seen from above of an amplification device according to a first embodiment,

[0030] - [Fig 2] figure 2, a schematic representation seen from above of an amplification device according to an exemplary implementation of a second embodiment,

[0031] - [Fig 3] figure 3, a schematic representation seen from above of an amplification device according to another example of implementation of a second embodiment, and

[0032] - [Fig 4] figure 4, a schematic representation seen from above of an amplification device according to a third embodiment.

[0033] In the remainder of the description, a propagation direction z is defined, represented in the figures by a z axis and corresponding to the propagation direction of the laser beam. A first transverse direction is further defined, perpendicular to the propagation direction, and represented in the figures by an x ​​axis, such that the plane (xOz) corresponds to a top view of the amplification device 10. A second transverse direction y is also defined, perpendicular to the propagation direction z and to the first transverse direction x. The second transverse direction y is represented in the figures by a y axis and is such that the plane (yOz) corresponds to a side view of the amplification device 10.

[0034] In the remainder of the description, the term "chromatic spatial dispersion" is understood to mean the angular dispersion of a beam due to variations in the deflection angle as a function of the wavelengths in a diopter. The term "chromatic lateral dispersion" is understood to mean the broadening of the diameter of a beam as a function of the wavelengths (pupil shift) following passage through two diopters whose interfaces are parallel (plates with parallel faces).

[0035] A first embodiment of an amplification device 10 is illustrated in FIG. 1.

[0036] The amplification device 10 is configured to amplify a laser beam, in particular a multi-wavelength pulsed laser beam. The beam to be amplified is, for example, an infrared beam.

[0037] The beam to be amplified has, for example, an average power greater than 10 Watts (W).

[0038] The amplification device 10 according to the first embodiment comprises at least one first amplifying medium M1 and at least one second amplifying medium M2.

[0039] The first medium M1 is a solid medium. The first medium M1 is, for example, a crystal such as Titanium-doped sapphire, or Yb:YAG, Yb:CaF2 or a polymer, a ceramic or a glass or any other material in the solid state.

[0040] The first medium M1 has a first refractive index n1.

[0041] Preferably, the following relationship holds:

[0042] Where vl is the constringency of the first amplifying medium M1. This aims to preserve the multi-wavelength character of the beam F s at the output of the amplification device 10.

[0043] The first medium M1 has at least two flat faces including a front face 20 suitable for receiving the beam to be amplified, called incident beam Fi, and a reflective rear face 22.

[0044] The front face 20 is inclined relative to the rear face 22 by a non-zero inclination Pi (angle). The first medium M1 thus has a disc shape whose front and rear faces are inscribed in a prism with a trapezoidal base (figure 1) or triangular base. In the following, p? denotes the projection of the inclination Pi onto the plane (xOz) and Pi” the projection of the inclination Pi onto the plane (yOz). In the particular example of figure 1, the angle p? is equal to the inclination Pi and the angle Pi” is zero. The base of the first medium M1 is thus contained in a plane parallel to the plane (xOz). As will be described in the following, this makes it possible to eject the parasitic pulses in the plane (xOz). Such a configuration is however given as an example, the angles P'i and Pi” can also both be non-nuisance.

[0045] The front face 20 of the first medium M1 is suitable for receiving the incident beam Fi and, on the one hand, reflecting a parasitic beam, called the first parasitic beam FPI and, on the other hand, refracting a beam, called the first useful beam FRI after such a beam has been reflected by the rear face 22.

[0046] Advantageously, the front face 20 is anti-reflective treated.

[0047] The rear face 22 of the first medium M1 is capable of reflecting the incident beam Fi, after its passage through the front face 20 of the first medium M1, to form the first useful beam FRI.

[0048] The rear face 22 is suitable for being cooled by a cooling device, which is, for example, included in the amplification device 10. The cooling is represented in FIG. 1 by an arrow attached to the rear face 22.

[0049] The second amplifying medium M2 is a solid medium. The second medium M2 is, for example, a crystal such as Titanium-doped sapphire, or Yb:YAG, Yb:CaF2 or a polymer, a ceramic or a glass or any other solid-state material.

[0050] The second medium M2 has a second refractive index n2.

[0051] Preferably, the following relationship holds:

[0052] Where v2 is the constringency of the second amplifying medium M2. This aims to preserve the multi-wavelength character of the beam F s at the output of the amplification device 10.

[0053] The second medium M2 has at least two flat faces including a front face 20 suitable for receiving the beam to be amplified, called incident beam Fi, and a reflective rear face 22.

[0054] The front face 20 of the second medium M2 is inclined relative to the rear face 22 by a non-zero inclination P2 (angle). The second medium M2 thus has the shape of a disc whose front and rear faces are inscribed in a prism with a trapezoidal base (figure 1) or triangular base. In the following, P2' designates the projection of the inclination P2 onto the plane (xOz) and P2” the projection of the inclination P2 onto the plane (yOz).

[0055] In the particular example of Figure 1, the angle P2' is equal to the inclination P2 and the angle P2” is zero. The base of the second medium M2 is, thus, contained in a plane parallel to the plane (xOz). As will be described in the following, this makes it possible to eject the parasitic pulses in the plane (xOz). Such a configuration is however given as an example, the angles P'2 and P2” can also both be uninterrupted.

[0056] In a preferred implementation example, the second medium M2 is identical to the first medium M1. Thus, n1 = n2 and Pi = P2. Advantageously, the first medium M1 and the second medium M2 were manufactured during the same manufacturing process.

[0057] Advantageously, the front face 20 is anti-reflective treated.

[0058] The rear face 22 is suitable for being cooled by a cooling device, which is, for example, included in the amplification device 10. The cooling is represented in FIG. 1 by an arrow attached to the rear face 22.

[0059] The second amplifying medium M2 is arranged relative to the first medium M1 so as to be on the path of the first useful beam FRI. Such a first useful beam FRI is thus received on the front face 20 of the second medium M2. Thus, the front face 20 of the second medium M2 is capable of, on the one hand, reflecting a parasitic beam, called the second parasitic beam F P2 (not shown in figure 1 so as not to overload the figure) and, on the other hand, to refract a useful beam, called the second useful beam F R2 , after such a beam has been reflected by the rear face 22 of the second medium M2.

[0060] The first inclination Pi, the second inclination P2 and the orientation of the second amplifying medium M2 are chosen so that the sub-beams of each wavelength, forming the second useful beam FR2 output from the second amplifying medium M2, are parallel to each other at the output of the second amplifying medium M2. In Figure 1, only two sub-beams are shown so as not to overload the figure. The second medium M2 thus makes it possible to compensate for the chromatic spatial dispersion induced by the prismatic effect resulting from the inclination Pi between the front face 20 and the rear face 22 of the first medium M1.

[0061] Advantageously, the following condition is verified:

[0062] Advantageously, the second amplifying medium M2 is arranged relative to the first amplifying medium M1 so that:

[0063] - the front face 20 of the second amplifier medium M2 is parallel to the front face 20 of the first amplifier medium M1, and

[0064] - the rear face 22 of the second amplifying medium M2 is parallel to the rear face 22 of the first amplifying medium M1. Thus, if the two media M1 and M2 were joined together without modifying their respective orientations, a diopter with parallel faces would be obtained.

[0065] Advantageously, the second amplifying medium M2 is arranged outside the path of the first parasitic beam F P i.

[0066] Preferably, the second medium M2 is arranged at a distance L from the first medium M1 so that the amplified beams (output beam F S =F R2 in Figure 1), parasites F Pi and incidents Fi are spatially separated. This separation is obtained for L such that:

[0067] OR :

[0068] • <P est le diamètre du faisceau incident Fi,

[0069] • 6i is the angle of incidence in the plane (xOz) of the incident beam on the front face 20 of the first medium M1,

[0070] • <pi est l’angle d’incidence dans le plan (yOz) du faisceau incident sur la face avant 20 du premier milieu M1 ,

[0071] • fa is the angle resulting from the projection of the inclination Pi in the plane (xOz),

[0072] • p" is the angle resulting from the projection of the inclination Pi in the plane (yOz), and

[0073] • n ± is the optical index of the first medium M1.

[0074] The operation of the amplification device 10 according to the first embodiment will now be described.

[0075] Initially, the beam (pulse) to be amplified Fi of diameter arrives on the front face 20 of the first amplifying medium M1 with an angle of incidence 0i in the plane (xOz) and an angle of incidence <pL in the plane (yOz).

[0076] The useful beam is reflected by the rear face 22, the parasitic beam F Pi by the front face 20. The parasitic beam, also called parasitic pulses, is deflected on this front face 20 by an angle 20i in the plane (xOz) and 2 <pt dans le plan (yOz). Le faisceau amplifié FRI dans le milieu amplificateur M1 aussi désigné impulsion principale, est défléchi en sortie d'un angle 2(0i + Pi'.(n1 -1 )) dans le plan (xOz) et d’un angle 2(<p ( + Pi".(n1 -1 )) in the plane (yOz).

[0077] As it is a multi-wavelength laser source, the angle p / formed by the faces 20 and 22 in the plane (xOz) and the angle pr formed by the faces 20 and 22 in the plane (yOz), produce a prismatic effect. Thus, after passing through the first amplifying medium M1, the wavelengths of the beam F™ refracted by the front face 20 and reflected by the rear face 22 of the first medium M1 (useful beam) are angularly separated.

[0078] The second medium M2 arranged after the separation of the useful beam FRI and the parasitic beam F P i, on the path of the useful beam FRI makes it possible to correct this chromatic spatial dispersion according to the wavelengths.

[0079] In particular, in the particular example of Figure 1, <p L = 0, (3i'= Ps' = P and Pi”= P2”=0, which means that all propagation takes place in the plane (xOz).

[0080] It should be noted that at the output of the second amplifying medium M2, the spectral components of the amplified beam FR2 form a spot of diameter <t> + A <t>. Note that A <t>includes the increase in diameter introduced by the divergence of the beam during the double crossing of the first amplifying medium M1, then that introduced by the divergence of the beam on the path between the output face (front face 20) of the first medium M1 and the second medium M2. We find the same diameter <t> + A <t>at the output of the second amplifying medium M2. To preserve the multi-wavelength character of the output beam, the broadening A <t>of the diameter of the amplified beam F R2 must be small in front <t>. This is the case when n ±

[0081] Indeed, or, which implies that

[0082] Thus, the amplification device 10 according to the first embodiment makes it possible to compensate for the chromatic spatial dispersion induced by the inclination of the first amplifying medium M1 without, however, introducing additional losses. The compensation is, in fact, carried out by another amplifying medium which does not introduce losses, but on the contrary more gain than a single thick disc.

[0083] The amplification device 10 according to the first embodiment therefore makes it possible to minimize optical losses while remaining satisfactory in terms of cooling and temporal contrast.

[0084] Such an amplification device 10 further allows the gain to be shared across multiple disks, which has advantages for thermal loading per disk and for transverse lasing.

[0085] According to a second embodiment as visible in figures 2 and 3, the elements identical to the amplification device 10 according to the first embodiment described with reference to figure 1, are not repeated. Only the differences are highlighted.

[0086] In the second embodiment, in addition to the elements of the first amplification device 10, the amplification device 10 comprises an optical compensation assembly 30 capable of compensating for the broadening AT> of the beam FR2 at the output of the second amplifying medium M2 (beam reflected by the rear face 22 and refracted by the front face 20) so that the beam Fs at the output of the amplification device 10 has a diameter substantially equal to the diameter of the incident beam Fi. The compensation device 30 is thus capable of compensating for lateral chromatic dispersion.

[0087] As illustrated in Figures 2 and 3, the optical compensation assembly 30 comprises a third amplifying medium M3 and a fourth amplifying medium M4.

[0088] The third medium M3 is a solid medium. The third medium M3 is, for example, a crystal such as Titanium-doped sapphire, or Yb:YAG, Yb:CaF2 or a polymer, a ceramic or a glass or any other material in the solid state.

[0089] The third medium M3 has a third refractive index n3.

[0090] Preferably, the following relationship holds:

[0091] Where v3 is the constringency of the third amplifying medium M3. This aims to preserve the multi-wavelength character of the beam F s at the output of the amplification device 10.

[0092] The third medium M3 has at least two flat faces among a front face 20 suitable for receiving the second useful beam F R2 at the output of the second amplifier medium M2, and a reflective rear face 22.

[0093] The front face 20 of the third medium M3 is inclined relative to the rear face 22 of the third medium M3 by a non-zero inclination p3. The third medium M3 thus has the shape of a disc whose front and rear faces are inscribed in a prism with a trapezoidal base (figures 2 and 3) or triangular base. In the following, p3' denotes the projection of the inclination p3 onto the plane (xOz) and p3” the projection of the inclination p3 onto the plane (yOz).

[0094] In the particular example of Figures 2 and 3, the angle p3' is equal to the inclination p3 and the angle p3” is zero. The base of the third medium M3 is, thus, contained in a plane parallel to the plane (xOz). As will be described in the following, this makes it possible to eject the parasitic pulses in the plane (xOz). Such a configuration is however given as an example, the angles P'3 and p3” can also both be uninterrupted.

[0095] Advantageously, the following condition is verified: In a preferred implementation example, the third medium M3 is identical to the second medium M2 and the first medium M1. Thus, n1 = n2 = n3 and 01 = 02= 03. Advantageously, the first medium M1, the second medium M2 and the third medium M3 were manufactured during the same manufacturing process.

[0096] The front face 20 of the third medium M3 is suitable for receiving the beam F R2 at the output of the second amplifier medium M2 and, on the one hand, reflect a parasitic beam, called the third parasitic beam F P3 (not shown in figures 2 and 3 so as not to overload the figures) and, on the other hand, to refract a beam, called third useful beam FRS, after such a beam has been reflected by the rear face 22 of the third medium M3.

[0097] The rear face 22 of the third medium M3 is suitable for reflecting the beam F R2 at the output of the second amplifier medium M2, after passing through the front face 20 of the third medium M3, to form the useful beam F R3 .

[0098] The rear face 22 of the third medium M3 is suitable for being cooled by a cooling device, which is, for example, included in the amplification device 10. The cooling is represented in Figures 2 and 3 by an arrow attached to the rear face 22 of the third medium M3.

[0099] Advantageously, the front face 20 third middle M3 is anti-reflective treated.

[0100] The fourth amplifying medium M4 is a solid medium. The fourth medium M4 is, for example, a crystal such as titanium-doped sapphire, or Yb:YAG, Yb:CaF2 or a polymer, a ceramic or a glass or any other solid-state material.

[0101] The fourth medium M4 has a fourth refractive index n4.

[0102] Preferably, the following relationship holds:

[0103] Where v4 is the constringency of the fourth amplifying medium M4. This aims to preserve the multi-wavelength character of the beam F s at the output of the amplification device 10.

[0104] The fourth medium M4 has at least two flat faces including a front face 20 suitable for receiving the beam to be amplified, called incident beam Fi, and a reflective rear face 22.

[0105] The front face 20 of the fourth medium M4 is inclined relative to the rear face 22 by a fourth inclination 04 (angle) which is not zero. The fourth medium M4 thus has a disc shape whose front and rear faces are inscribed in a prism with a trapezoidal base (figures 2 and 3) or a triangular base. In the following, 04' designates the projection of the inclination 04 onto the plane (xOz) and 04” the projection of the inclination 04 onto the plane (yOz). In the particular example of figures 2 and 3, the angle p4' is equal to the inclination p4 and the angle p4” is zero. The base of the fourth medium M4 is thus contained in a plane parallel to the plane (xOz). As will be described in the following, this makes it possible to eject the parasitic pulses in the plane (xOz). Such a configuration is however given as an example, the angles P'4 and p4” can also both be unnuanced.

[0106] In a preferred embodiment, the fourth medium M4 is identical to the third medium M3. Thus, n3 = n4 and p3 = p4. Advantageously, the third medium M3 and the fourth medium M4 were manufactured during the same manufacturing process.

[0107] Advantageously, the front face 20 is anti-reflective treated.

[0108] The rear face 22 is suitable for being cooled by a cooling device, which is, for example, included in the amplification device 10. The cooling is represented in Figures 2 and 3 by an arrow attached to the rear face 22.

[0109] The fourth amplifying medium M4 is arranged on the path of the beam F R3 reflected by the rear face 22 and refracted by the front face 20 of the third amplifying medium M3. Such a beam F R3 is thus received by the front face 20 of the fourth medium M4. Thus, the front face 20 of the fourth medium M4 is capable of, on the one hand, reflecting a parasitic beam, called the fourth parasitic beam F P4 and, on the other hand, to refract a useful beam F R4 after such a beam has been reflected by the rear face 22 of the fourth medium M4.

[0110] The third inclination p3, the fourth inclination p4, the orientation of the third amplifying medium M3 and the orientation of the fourth amplifying medium M4 are chosen so that the beam F R4 output of the fourth amplifying medium M4 (corresponding to the output beam Fs of the amplification device 10 in figures 2 and 3) has a diameter substantially equal to the diameter of the incident beam Fi and that the sub-beams of each wavelength, forming said output beam F R4 , are parallel to each other at the output of the fourth amplifier medium M4. Thus, the third medium M3 and the fourth medium M4 make it possible to compensate for the lateral chromatic dispersion of the beam.

[0111] Advantageously, the following condition is verified:

[0112] Advantageously, the fourth amplifier medium M4 is arranged relative to the third amplifier medium M3 so that:

[0113] - the front face 20 of the third amplifier medium M3 is parallel to the front face 20 of the fourth amplifier medium M4, and - the rear face 22 of the third amplifier medium M3 is parallel to the rear face 22 of the fourth amplifier medium M4.

[0114] Thus, if the two media M3 and M4 were joined without modifying their respective orientations, we would obtain a diopter with parallel faces.

[0115] Advantageously, the third amplifying medium M3 is arranged outside the path of the second parasitic beam F P2 .

[0116] Advantageously, the fourth amplifying medium M4 is arranged outside the path of the third parasitic beam F P3 .

[0117] Preferably, the first medium M1, the second medium M2, the third medium M3 and the fourth medium M4 are identical (same materials, same angles), and have for example been manufactured during the same manufacturing cycle or process. This particular case is illustrated in Figure 2. In this particular case, there is an axis of symmetry As between the first and second medium, on the one hand, and the third and fourth medium, on the other hand. The fourth medium M4 is, thus, the symmetrical of the first medium M1 by the axis of symmetry As; and the third medium M3 is the symmetrical of the second medium M2 by the axis of symmetry As.

[0118] Figure 3 illustrates another example of implementation of the second embodiment in which the first medium M1 and the second medium M2 are identical and the third medium M3 and the fourth medium M4 are identical, but different from the first medium M1 and the second medium M2. In this case, there is no axis of symmetry between the first and second medium, on the one hand, and the third and fourth medium, on the other hand.

[0119] During operation of the amplification device 10 according to the second embodiment, in addition to the operation described for the first embodiment, the useful beam F R2 at the output of the second medium M2 is received on the front face 20 of the third medium M3, which gives a third parasitic reflection F P3 and a third useful beam F R3 (reflected on the rear face 22 and refracted on the front face 20 of the third medium M3). The third useful beam F R3 is received on the front face 20 of the fourth medium M4, which gives a fourth parasitic reflection F P4 and a fourth useful beam F R4 (reflected on the rear face 22 and refracted on the front face 20 of the fourth medium M4). It will be noted that in Figures 2 and 3, for the sake of clarity, the parasitic reflections F P3 were not represented.

[0120] The configuration of the third medium M3 and the fourth medium M4 relative to the first medium M1 and the second medium M2 thus makes it possible to compensate for the chromatic lateral dispersion of the amplified output beam of the amplification device 10. Thus, the amplification device 10 according to the second embodiment makes it possible, in addition to the advantages of the first embodiment, to compensate for the chromatic lateral dispersion induced by the divergence of the beam when passing through the first medium M1, and this without introducing additional losses. On the contrary, the compensation is carried out by other amplifying media which introduce an amplification gain.

[0121] The person skilled in the art will understand that figures 2 and 3 illustrate only four amplifying media, however the advantages of the second embodiment are generalized to a larger number of successive amplifying media with the condition that this number is a multiple of four (a multiple of two but not of four would only amount to compensating for the chromatic spatial dispersion but not the chromatic lateral dispersion).

[0122] Thus, the second embodiment is generalized in the following manner. The first medium M1, the second medium M2, the third medium M3 and the fourth medium M4 form an amplification unit, called a reference unit. The beam FR4 reflected by the rear face 22 and refracted by the front face 20 of the fourth medium M4 forms the beam F s output of the reference amplification unit. The amplification device 10 comprises one or more successive amplification units, identical to the reference amplification unit, each amplification unit being arranged so as to receive, as input beam, the output beam of the previous amplification unit.

[0123] Thus, the number of amplification units (and therefore amplification media) is adjustable according to the desired amplification level.

[0124] Other additions are also conceivable for the second embodiment. For example, an afocal is suitable for being inserted in the path of the light beam between the second medium M2 and the third medium M3 to increase the size of the beam between the second medium M2 and the third medium M3. This makes it possible to optimize the amplification efficiency.

[0125] Also, in an implementation variant, a baffle is suitable for being inserted in the path of the light beam between the second medium M2 and the third medium M3. The baffle is for example formed of two plane mirrors inclined at 45° to each other. This makes it possible to implement a different geometric arrangement of the amplifying media (“in line”).

[0126] According to a third embodiment as seen in Figure 4, the elements identical to the amplification device 10 according to the first embodiment described with reference to Figure 1 are not repeated. Only the differences are highlighted.

[0127] In the third embodiment, in addition to the elements of the first amplification device 10, the amplification device 10 comprises an optical compensation assembly 30 capable of compensating of the beam FR2 at the output of the second amplifying medium M2 (beam reflected by the rear face 22 and refracted by the front face 20) so that the beam Fs at the output of the amplification device 10 has a diameter substantially equal to the diameter of the incident beam Fi.

[0128] As illustrated in Figure 4, the optical compensation assembly 30 comprises at least one mirror 40 (plane mirror) arranged so that the beam F s output of the amplification device 10 is superimposed on the incident beam Fi.

[0129] Thus, the mirror 40 is arranged so that the beam F R2 at the output of the last medium, in this case the second medium M2, makes a return journey superimposed on the outward journey by passing through the amplifying mediums.

[0130] According to the principle of reverse light return, this makes it possible to compensate for the chromatic lateral dispersion in the beam Fs at the output of the amplification device 10.

[0131] During operation of the amplification device 10 according to the third embodiment, in addition to the operation described for the first embodiment, the laser beam performs a reverse return so that it exits through the first medium M1 superimposed on the incident beam Fi.

[0132] Thus, the amplification device 10 according to the third embodiment makes it possible, in addition to the advantages of the first embodiment, to compensate for the chromatic lateral dispersion induced by the divergence of the beam when passing through the first medium M1, and this without introducing additional losses. On the contrary, the compensation is accompanied by an additional amplification since the laser beam passes through the first medium M1 and the second medium M2.

[0133] Those skilled in the art will understand that the embodiments described above are capable of being combined with each other when such a combination is compatible.

[0134] In particular, the second and third embodiments are fully compatible, regardless of the number of amplification units.

[0135] Furthermore, those skilled in the art will understand that the first and third embodiments generalize to a larger number of successive amplifying media, provided that this number is a multiple of two. For the first embodiment, when this number is a multiple of four, this reverts to the second embodiment, and when this number is a multiple of two but not four, only the advantages of the first embodiment are obtained. For the third embodiment, the advantages of the third embodiment are obtained regardless of the number of successive amplifying media, provided that this number is a multiple of two.

[0136] Finally, it will also be understood that Figures 1 to 4 are given as examples with an angle for the amplifying media inducing that the base of each amplifying medium is in a plane parallel to the propagation plane of the laser beam (plane (xOz)). Nevertheless, this angle is likely to take other values, and in particular to have a non-zero projection in each of the planes (xOz) and (yOz).< / t> < / t> < / t> < / t> < / t> < / t> < / t>

Claims

DEMANDS 1. A device (10) for amplifying a multi-wavelength laser beam, the device (10) comprising: a. a first solid amplifying medium (M1) having a first refractive index (n1), the first amplifying medium (M1) having at least two flat faces from among a front face (20) adapted to receive the beam to be amplified, called the incident beam (Fi), and a reflective rear face (22), the front face (20) being inclined relative to the rear face (22) at a first non-zero inclination (Pi), the rear face (22) being adapted to be cooled, and b. a second solid amplifying medium (M2) having a second refractive index (n2), the second amplifying medium (M2) having at least two flat faces from among a front face (20) adapted to receive the beam (F m) reflected by the rear face (22) and refracted by the front face (20) of the first amplifying medium (M1), and a reflective rear face (22), the front face (20) being inclined relative to the rear face (22) by a second non-zero inclination (p2), the rear face (22) being suitable for cooling, the second amplifying medium (M2) being arranged on the path of the beam (FRI) reflected by the rear face (22) and refracted by the front face (20) of the first amplifying medium (M1), the first inclination (Pi), the second inclination (P2) and the orientation of the second amplifying medium (M2) being such that the sub-beams of each wavelength, forming the output beam (FR2) of the second amplifying medium (M2), are parallel to each other at the output of the second amplifying medium (M2).

2. Amplification device (10) according to claim 1, wherein the front face (20) of the first amplifying medium (M1) is perpendicular to an Oz axis, the first inclination (Pi) forming an angle p? on an xOz plane and Pi” on a yOz plane, the second inclination (P2) forming an angle P2' on an xOz plane and P2” on a yOz plane, the following condition being satisfied:

3. Amplification device (10) according to claim 1 or 2, wherein the second amplifying medium (M2) is arranged relative to the first amplifying medium (M1) such that: a. the front face (20) of the second amplifying medium (M2) is parallel to the front face (20) of the first amplifying medium (M1), and b. the rear face (22) of the second amplifying medium (M2) is parallel to the rear face (22) of the first amplifying medium (M1).

4. Amplification device (10) according to any one of claims 1 to 3, wherein the beam (FR2 ) at the output of the second amplifying medium (M2) has an enlarged diameter ( <t> + A <t>) compared to the diameter ( <t>) of the incident beam (Fi), the amplification device (10) comprising an optical compensation assembly (30) suitable for compensating the broadening (A <t>) of the beam (F R2 ) at the output of the second amplifying medium (M2) so that the beam (Fs) at the output of the amplification device (10) has a diameter substantially equal to the diameter ( <t>) of the incident beam (Fi).

5. Amplification device (10) according to claim 4, wherein the optical compensation assembly (30) comprises: a. a third solid amplifying medium (M3) having a third refractive index (n3), the third amplifying medium (M3) having at least two flat faces among a front face (20) adapted to receive the beam (F R2 ) at the outlet of the second amplifying medium (M2) and a reflective rear face (22), the front face (20) being inclined relative to the rear face (22) at a third non-zero inclination (p3), the rear face (22) being suitable for cooling, b. a fourth solid amplifying medium (M4) having a fourth refractive index (n4), the fourth amplifying medium (M4) having at least two flat faces among a front face (20) suitable for receiving the beam (F R3 ) reflected by the rear face (22) and refracted by the front face (20) of the third amplifying medium (M3), and a reflective rear face (22), the front face (20) being inclined relative to the rear face (22) by a fourth non-zero inclination (p4), the rear face (22) being suitable for cooling, the fourth amplifying medium (M4) being arranged in the path of the beam (F R3 ) reflected by the rear face (22) and refracted by the front face (20) of the third amplifying medium (M3), the third inclination (P3), the fourth inclination (P4), the orientation of the third amplifying medium (M3) and the orientation of the fourth amplifying medium (M4) being such that the output beam (F s ) of the fourth amplifying medium (M4) has a diameter substantially equal to the diameter ( <t>) of the incident beam (Fi) and that the sub-beams of each wavelength, forming said output beam (F s ), are parallel to each other at the output of the fourth amplifying medium (M4).

6. Amplification device (10) according to claim 5, wherein the front face (20) of the third amplifying medium (M3) is perpendicular to an Oz axis, the third inclination (P3) forming an angle P3' on an xOz plane and P3” on a yOz plane, the third inclination (P3) forming an angle P3' on an xOz plane and P3” on a yOz plane, the following condition being satisfied:

7. Amplification device (10) according to claim 5 or 6, wherein the third amplifying medium (M3) is arranged with respect to the fourth amplifying medium (M4) such that: a. the front face (20) of the third amplifying medium (M3) is parallel to the front face (20) of the fourth amplifying medium (M4), and b. the rear face (22) of the third amplifying medium (M3) is parallel to the rear face (22) of the fourth amplifying medium (M4).

8. Amplification device (10) according to any one of claims 5 to 7, wherein the first amplifying medium (M1), the second amplifying medium (M2), the third amplifying medium (M3) and the fourth amplifying medium (M4) are identical.

9. Amplification device (10) according to any one of claims 5 to 8, wherein the first medium (M1), the second medium (M2), the third medium (M3) and the fourth medium (M4) form an amplification unit, referred to as the reference beam (F R4 ) reflected by the rear face (22) and refracted by the front face (20) of the fourth medium (M4) forming the output beam (F s ) of the reference amplification unit, the amplification device (10) comprising one or more successive amplification units, identical to the reference amplification unit, each amplification unit being arranged so as to receive, as an input beam, the output beam of the previous amplification unit.

10. Amplification device (10) according to any one of claims 4 to 9, wherein the optical compensation assembly (30) comprises at least one mirror arranged such that the output beam (F s ) of the amplification device (10) is superimposed on the incident beam (Fi).< / t> < / t> < / t> < / t> < / t> < / t>

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