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    • 专利摘要:
    The present description relates in one aspect to a system (10) of generating pulses of high peak power laser comprising at least a first light source (101) for the emission of first laser pulses (IL), a fiber-optic device (110) for the transport of said first laser pulses, comprising at least a first multimode fiber with a single core arranged to receive said first laser pulses, and a module (102) for time shaping of said first laser pulses, arranged upstream of the fiber device, configured to decrease the power spectral density of said pulses by reducing time coherence.
    公开号:FR3081738A1
    申请号:FR1854860
    申请日:2018-06-05
    公开日:2019-12-06
    发明作者:Guillaume Gorju；Adam Ayeb；Xavier Levecq
    申请人:Imagine Optic；
    IPC主号:
    专利说明:

    METHODS AND SYSTEMS FOR THE GENERATION OF HIGH PEAK LASER PULSES
    STATE OF THE ART
    Technical field of the invention
    The present description relates to methods and systems for the generation of high peak power laser pulses intended for laser shock. The present description finds applications in particular in laser shot blasting, laser shock spectroscopy, the generation of ultrasound by laser or the laser cleaning of components.
    State of the art
    Laser shock surface treatment applications, that is to say with plasma formation, require pulses of very high peak power, typically around 10 megawatts (MW) or more, that is to say typically pulses whose duration is of the order of a few tens of nanoseconds or less and which have energies of more than a hundred millijoules. These pulses, focused on areas of a few mm 2 typically, make it possible to reach energy densities of the order of tens of Joule per square centimeter for the formation of laser shocks. These applications include, for example, laser shock spectroscopy, laser cleaning, generation of ultrasound by laser, for example for the analysis of the crystal structure of a material and "laser shot peening" according to the Anglo-Saxon expression) for the improvement of the service life and mechanical resistance of parts.
    Laser blasting is described, for example, in patents US 6002102 and EP 1 528 645. A first thin absorbent layer is deposited on the part to be treated. In operation, the laser peaks of high peak powers vaporize the absorbent layer which generates a hot plasma. The expansion of the plasma results in an intense compression wave which makes it possible to generate prestresses deep into the material of the part to be treated. A second layer, called the confinement layer, transparent to radiation, for example water or a material transparent to the length of the incident radiation, for example quartz, helps the shock probe to relax towards the inside of the surface to be treat. This process, called "laser peening" increases the mechanical resistance of the parts to cyclic fatigue. This process is generally carried out by transporting the beam in free space to the area to be treated.
    The transport of high-power laser beams in free space, however, creates security problems and makes accessibility to confined or hostile places (submerged environments for example) very complex.
    To access areas located in confined or hostile environments, optical fibers seem to be well suited tools, as described for example in patents US4937421 or US6818854. However, some of the previously described processes, such as laser shot blasting or laser surface cleaning, are generally carried out in dusty industrial environments and the damage thresholds of the fiber input and output surfaces are significantly reduced. Furthermore, apart from the aspects of cleanliness, for pulsed lasers with pulse duration less than 1 ps, the peak power level that can be injected into a fiber is limited by the dielectric damage threshold of the material constituting the core of the fiber. Thus, for pulses of 10 ns at 1064 nm the damage threshold of the air-silica interface is around 1 GW / cm 2
    To limit the risk of damage to injection and propagation, the use of waveguides with large core diameters is preferred. However, large hearts (typically greater than 1 mm) are not very flexible and excessive curvatures create losses by evanescent waves which can damage the fiber. A set of optical fibers (or “bundle”) can be used, as described for example in patent US6818854. However, to limit the injection and propagation losses in this type of component, it is preferable to inject the light energy into each fiber individually, which makes injection complex and expensive; moreover, it is necessary to provide at the output of the component an optical system for focusing with a large aperture, which makes the optical system complex, expensive and bulky.
    In particular for these reasons, the use of optical fibers for the transport of pulses is in practice limited to the transport of pulses of relatively low peak power (less than 10 MW) and to address easily accessible areas (non-tortuous path ).
    There is therefore a need for the generation of pulses of high peak power by means of a system with a fiber device, which makes it possible to push back the thresholds of damage to the fibers and improve the flexibility of the fiber device in order to avoid its optical deterioration by mechanical stress.
    An object of the present description is a method and a system for generating pulses of high peak power (typically around 10 MW or above), authorizing secure injection into a fiber device and ensuring secure propagation over long distances. while retaining great flexibility.
    SUMMARY OF THE INVENTION
    According to a first aspect, the present description relates to a system for generating laser pulses of high peak power, comprising:
    at least a first light source for the emission of first nanosecond laser pulses comprising one or more laser line (s);
    - a fiber-optic device for transporting said first laser pulses, comprising at least a first multimode fiber with a single core arranged to receive said first laser pulses;
    - a module for temporal shaping of said first laser pulses, arranged upstream of the fiber device, configured to reduce the power spectral density by reducing the temporal coherence of said first pulses.
    In the present description, the term “high peak power” is understood to mean laser pulses having a peak power of the order of, or greater than or equal to, 10 MW. Such pulses are suitable, after focusing on surfaces of a few mm 2 , typically between 0.1 and 10 mm 2 , for the generation of laser shocks in a given material, for example for laser shot blasting applications, surface cleaning, generation of ultrasound, spectroscopy, etc.
    By nanosecond pulse, we understand a pulse whose duration is between 1 ns and 100 ns, advantageously between 5 nanoseconds and 20 nanoseconds, which corresponds to a preferred pulse duration for the generation of laser shocks. Said first pulses may include one or a plurality of laser lines.
    The system thus described makes it possible, by reducing the spectral power density (DSP) by reducing the temporal coherence of the pulses upstream of the fiber-optic device, to have very high peak powers for the pulses incident on the material in which wants to generate laser shocks while securing the input and output interfaces of the fiber-optic device. Indeed, the reduction in temporal coherence makes it possible to reduce the PSD with a limited reduction in energy. The reduction of the PSD at almost constant energy or with a small reduction in energy makes it possible to limit the overcurrents attributed to the "speckle" (also called "flicker" or "speckles"), to secure the injection into the fiber device and to limit non-linear effects. The use of a multimode fiber of small diameter is then possible, typically, less than 1 mm, advantageously less than 300 μm, which gives greater flexibility to the fiber-optic device, and therefore easier access to media. confined, with fiber curvature diameters which can be reduced to less than 15 cm.
    According to one or more exemplary embodiments, the time shaping module is configured to reduce the power spectral density so that the light intensity of the pulses is below the stimulated Brillouin backscattering threshold in the fiber device. This limits the loss of light energy due to non-linear effects in the fibers, in particular the Brillouin effect. The Brillouin backscattering threshold decreases when the fiber diameter decreases (and the fiber length increases) and increases when the spectral width of the source becomes greater than the spectral width of the Brillouin line. Thus, by reducing the DSP of the laser pulses, for example by broadening the spectrum or multiplying the laser lines, it is possible to keep a high Brillouin backscattering threshold while reducing the core diameters and / or increasing the fiber length. Indeed, the calculation of the Brillouin threshold takes into account the convolution between the spectral profile of the source and that of the Brillouin gain.
    According to one or more exemplary embodiments, the reduction in DSP is obtained by multiplication of the laser line (s) contained in said first pulses, for example by means of an acousto-optical modulator.
    According to one or more exemplary embodiments, the reduction in DSP is obtained by broadening the spectrum of the laser line (s) contained in said first pulses.
    According to one or more exemplary embodiments, for widening the spectrum of the laser line (s) contained in said first pulses, said time shaping module comprises a reflecting device rotating around a given axis of rotation, and configured to reflect said first incident pulses with Doppler type spectral widening.
    The rotating reflecting device can be oscillating or rotating around said axis of rotation. It includes one or more reflective surfaces. The pulses incident on said reflective surface (s) undergo a spatially variable Doppler shift due to the variable angular speed at each point of said surface (s). Thus, the laser pulses reflected by said rotating reflecting device exhibits a spectral broadening and consequently a reduction in the DSP. In addition, the spatial and temporal coherences of the laser pulses are reduced, which contributes to limiting the speckle and non-linear effects.
    According to one or more exemplary embodiments, the said reflecting surface (s) are arranged in planes perpendicular to the same plane, known as the plane of incidence of the first pulses, comprising the directions of the wave vectors of said first laser pulses incident on the reflecting device rotating and reflected by said rotating reflecting device.
    According to one or more exemplary embodiments, the axis of rotation of said rotating reflecting device is perpendicular to said plane of incidence of said first laser pulses.
    According to one or more exemplary embodiments, said first pulses being emitted at a given repetition frequency, the speed of rotation or of oscillation of said rotating reflecting device is synchronized with the repetition frequency of said first pulses, so that each of said first pulses is incident on a reflecting surface of said reflecting device rotating with a constant angle of incidence.
    According to one or more exemplary embodiments, said rotating reflecting device comprises a simple mirror having a movement of rotation or of oscillation around an axis perpendicular to a plane of incidence of said first laser pulses. For example, the reflecting mirror is arranged so that said first laser pulses are incident on the rotating mirror in a direction perpendicular to the plane of said mirror.
    According to one or more exemplary embodiments, said rotating reflecting device comprises a plurality of reflecting surfaces, two consecutive surfaces forming a non-zero angle, and reflecting mirrors making it possible to return each of said first pulses to each of said reflecting surfaces. For example, the plurality of reflective surfaces are arranged on the faces of a polygon. By multiplying the reflecting surfaces, we can multiply the Doppler enlargement. So for example, with N reflecting surfaces (N> 2) and N-1 deflection mirrors, we multiply by N the Doppler enlargement.
    According to one or more exemplary embodiments, at least one of said reflecting surfaces is non-planar (for example concave or convex). For example, the reflective output surface, that is to say on which the laser pulse is last reflected, is non-planar to introduce a convergence or divergence effect of said pulse.
    According to one or more exemplary embodiments, the light beam formed by said first laser pulses and incident on said reflective surface (s) has dimensions smaller than the dimensions of said reflective surface (s).
    According to one or more exemplary embodiments, the laser pulse generation system further comprises a module for spatial shaping of said first laser pulses upstream of the fiber device.
    According to one or more exemplary embodiments, the spatial shaping module is configured to standardize the spatial power density of said pulses at the input of the fiber device. The standardization of the spatial power density makes it possible to limit the overcurrents in the fiber linked to the Gaussian intensity distribution of a beam for example,
    For example, the module for spatial shaping of the pulses makes it possible to form pulses whose spatial distribution of intensity is of the “top hat” type, that is to say with a spatial variation of the weak intensity, typically limited to +/- 10% (excluding granular effects linked to the Speckle). Spatial shaping of the “top hat” type also makes it possible to adapt the light beam formed by said first pulses to the size of the core of the multimode fiber.
    According to one or more exemplary embodiments, the laser pulse generation system further comprises at least a first optical amplifier for amplifying said first pulses at the output of the fiber device. Such an optical amplifier can make it possible to compensate for a possible loss of energy resulting from the use of the time shaping module.
    According to one or more exemplary embodiments, the laser pulse generation system further comprises at least one pump light source for the emission of at least one first pump laser beam, intended for the optical pumping of said at least one first amplifier.
    The pump light source comprises for example a laser diode or a set of laser diodes
    The pump source can be continuous or pulsed with a relatively low repetition rate, typically at the repetition frequency of said first laser pulses, that is to say less than a few kilohertz.
    According to one or more exemplary embodiments, the pump source is shaped in time so as to deliver pump pulses whose duration corresponds substantially to the lifetime of the excited level of said at least one first optical amplifier, typically from 1 in the order of a few hundred microseconds. Spatial shaping of the pump beams is also possible, for example to adapt the size of the pump beam to the core diameter of the first multimode fiber.
    According to one or more exemplary embodiments, said at least one pump laser beam is injected into the fiber device, with said first pulses. The transport in the fiber as well as the pumping of the amplifying medium of said at least one first optical amplifier is then copropagative. Alternatively, the optical pumping of the amplifying medium can be transverse to the latter, for example by means of laser diodes.
    According to one or more exemplary embodiments, said laser pulse generation system comprises a plurality of optical amplifiers, arranged for example one behind the other.
    According to one or more exemplary embodiments, the fiber-optic device comprises at the input said first multimode fiber and a set of slightly multimode fibers coupled with said first multimode fiber, forming for example what is called a first "photonic lantern", and in output, a second multimode fiber, coupled with said slightly multimode fibers and comprising a single core for the output of said first laser pulses. Thus, the fiber-optic device comprises two head-to-tail “photonic lanterns”.
    In the present description, slightly multimode fiber is called a fiber comprising less than 10,000 modes, typically between 500 and 10,000 modes. The diameter of the slightly multimode fiber is for example between 0.05 and 0.2 mm. Multimode fiber (input fiber of the photon lantern) has more than 20,000 modes. The diameter of the multimode fiber is for example between 0.5 and 1 mm.
    Such a fiber-optic device, comprising two head-to-tail “photonic lanterns”, allows laser pulses to be transported in slightly multimode fibers of smaller diameter and therefore to gain even more flexibility in the transport of laser pulses, allowing even easier access to confined environments, while keeping a single multimode core at input and output.
    According to one or more exemplary embodiments, the fiber device comprises at least one doped fiber for the optical pre-amplification of said first laser pulses. It can be said first multimode fiber or one or more slightly multimode fibers when using photonic lanterns. Optical pre-amplification further minimizes the amount of energy to be injected into the first multimode fiber.
    According to one or more exemplary embodiments, the laser pulse generation system comprises a second light source for the emission of second laser pulses. The second laser pulses for example have a different wavelength from the first laser pulses. The second laser pulses are advantageously transported by the same fiber device as the first laser pulses. According to one or more exemplary embodiments, the laser pulse generation system comprises a second optical amplifier arranged at the output of said fiber device for the amplification of said second laser pulses.
    According to one or more exemplary embodiments, the system for generating laser pulses further comprises means for focusing said laser pulses of high peak power at the output of the fiber-optic device, for example at the output of said at least one optical amplifier when the latter is present.
    According to one or more exemplary embodiments, the laser pulse generation system further comprises means for moving a distal end of the fiber device. When it is necessary to generate laser shocks at different locations of a material, for example in the case of the treatment of a surface, the material can be moved or the distal end of the fiber device can be moved, i.e. - say the opposite end to the proximal end placed on the side of the source.
    According to a second aspect, the present description relates to a method for generating high peak power laser pulses comprising:
    the emission of first nanosecond laser pulses;
    transporting said first laser pulses by a fiber device comprising at least a first multimode fiber with a single core into which said first laser pulses are injected;
    the temporal shaping of said first laser pulses upstream of the transport by said fiber device, said temporal shaping comprising the reduction of the power spectral density by reduction of the temporal coherence.
    According to one or more exemplary embodiments, said temporal shaping comprises the multiplication and / or widening of the line or lines included in said first pulses.
    According to one or more exemplary embodiments, the method for generating laser pulses further comprises the spatial shaping of said first laser pulses.
    According to one or more exemplary embodiments, said spatial shaping comprises standardizing the spatial distribution of intensity of said first laser pulses.
    According to one or more exemplary embodiments, the method of generating laser pulses further comprises the optical amplification of said first laser pulses by means of at least one first optical amplifier arranged at the output of the fiber device to form said laser pulses of high peak power
    According to one or more exemplary embodiments, the method for generating laser pulses further comprises injecting into said fiber-optic device at least one first pump laser beam for pumping said at least one optical amplifier.
    BRIEF DESCRIPTION OF THE FIGURES
    Other advantages and characteristics of the invention will appear on reading the description, illustrated by the following figures:
    - FIG. 1, a diagram illustrating a pulse generator system of high peak power according to the present description and its implementation in a confined environment;
    - FIGS 2A - 2D, diagrams illustrating the temporal shaping of the pulses upstream of the transport by the fiber-optic device, in an example of a system for generating pulses of high peak power according to the present description, aiming to widen the laser line (s) by Doppler effect;
    - FIG. 3A - 3B, diagrams illustrating the temporal shaping of the pulses upstream of the transport by the fiber device, in an example of a system for generating pulses of high peak power according to the present description, aimed at multiplying the laser lines;
    - FIG. 4A - 4B, diagrams illustrating means for the spatial shaping of the pulses upstream of the transport by the fiber device, in an example of a system for generating pulses of high peak power according to the present description, aimed at forming a beam constant intensity profile;
    - FIG. 5, a diagram of an example of a high peak power pulse generation system according to the present description, further comprising an optical amplifier of said laser pulses at the output of the fiber device;
    - FIG. 6, a diagram of an exemplary embodiment of a fiber-optic device in an example of a peak peak power generation system according to the present description.
    For the sake of consistency, identical elements are identified by the same references in the different figures.
    DETAILED DESCRIPTION
    In the present description, we are interested in the generation of pulses of high peak power, suitable for the generation of laser shocks in a material.
    The interaction of high illumination pulses (light power delivered per unit area), typically of the order of a few million watts per cm 2 , with a material, causes a sudden heating of the illuminated surface and its vaporization under forms a plasma that relaxes. This is called laser shock. Laser shock is a mechanism in which the light material interaction time is very short, typically a few tens of nanoseconds, and therefore there is no significant rise in temperature of the part to be treated as for the processes. laser cutting or laser welding. The laser shock can be favored in one direction thanks to a confinement layer. Indeed, in the absence of a confinement layer, the extension of the laser shock takes place on 4π steradians.
    More precisely, in the case of laser shot peening (or “laser shock peening”), the laser shock thus created makes it possible to introduce with very high precision residual compressive stresses deep on a material. This ultimately improves fatigue resistance by delaying the initiation and propagation of cracks. A confinement layer also makes it possible to promote the relaxation of the plasma towards the inside of the part to be treated and to improve the effectiveness of the treatment.
    In the case of LIBS (abbreviation of the English expression "Light Induced Breakdown Spectroscopy"), the laser shock causes vaporization of the surface to be treated. The atoms and the ions ejected are carried in excited energy levels and emit, while being de-excited, a spectrum made up of atomic lines, whose wavelength makes it possible to identify the elements present and whose intensity is proportional to the concentration of emitting atoms.
    In the case of cleaning by ablation, the plasma created on the surface under the effect of radiation relaxes, thus causing fractionation and expulsion of dirt without damaging the surface to be cleaned.
    In the control by ultrasound generated by laser, one uses the ultrasonic wave formed by the plasma resulting from the interaction pulses - matter. The ultrasonic wave travels through the material and is reflected at the interfaces. The deformation of the material upon arrival of the ultrasonic wave can be analyzed using an interferometer coupled to a second laser beam. This analysis can provide several characteristics related to the material, namely its thickness, its microscopic structure, or even possible underlying defects for example.
    FIG. 1 presents a diagram illustrating a system 10 for generating pulses of high peak power according to the present description and its implementation within a confined medium 11.
    The system 10 comprises, in an enclosure 100 which can be air-conditioned and isolated from dust and moisture, at least a first light source 101 for the emission of first laser pulses I L.
    The light source 101 is for example a pulsed laser, emitting pulses of duration between 1 and 100 ns advantageously between 5 and 20 ns. The light source emits for example at 1.064 μm (emission wavelength of neodymium lasers (Nd): YAG) or at 1.030 μm (emission length of ytterbium lasers (Yb): YAG). The light source 101 can include, without limitation, a solid laser, a fiber laser, a semiconductor laser, a disc laser or a combination of such lasers.
    The light source can emit laser pulses with a single laser line or with a plurality of laser lines.
    Several light sources can also be provided, for example at different wavelengths for the emission of first pulses and at least second pulses at different wavelengths.
    The system 10 can also include, within the enclosure 100, a time shaping module 102 and / or a spatial shaping module 103, intended for example to reduce the temporal and / or spatial coherence of the first laser pulses and / or to form pulses with a substantially constant intensity profile. These spatial and / or temporal shaping modules aim in particular to reduce overcurrents or “hot spots” at the input of the fiber device and to limit non-linear effects. Examples of a temporal and spatial formatting module will be described in the following description.
    In the example shown in FIG. 1, at the output of the temporal 102 and spatial shaping modules 103, the first laser pulses are injected into a fiber device 110. The fiber device 110 allows the transport of the laser pulses emitted by the said light source or sources; it can comprise a single multimode fiber with a single core arranged to receive said laser pulses. In other examples, it may include several optical fibers, always with a first multimode optical fiber comprising a single core adapted to receive all of the laser pulses.
    When the system 10 is used for example for laser shot blasting purposes, it is also possible to provide for the formation of the confinement layer, a water nozzle 14 supplied by a water tank and a pump 12 delivering water to the nozzle 14 by means of a pipe 13. Water is not obligatory and the confinement layer can just as easily be obtained by means of a gel, a paint or a solid material transparent to the length of pulse wave (for example Quartz). It is also possible to dispense with the confinement layer, but this reduces the depth of the prestressing induced by the laser peening process. The containment layer is also not useful in applications other than laser shot blasting.
    The system 10 may also include means for moving (not shown) a distal end of the fiber device. When it is necessary to generate laser shocks at different locations of a material, for example in different areas of a surface in the case of the treatment of a surface, the material can be moved or the distal end of the device can be moved fiber, that is to say the end opposite to the proximal end placed on the side of the source and thus carry out a spatial scanning of the surface to be treated by laser pulses.
    The system 10 can also comprise, according to an exemplary embodiment, an optical component 115 for the spatial shaping of the pulses at the output of the fiber device. The optical component 115 is for example a diffractive optical component, for example of the DOE (for "Diffractive Optic Element") type, a microlens system, an optical condenser, a Powel lens. In the case of a spatial scan of the part to be treated by laser pulses, this shaping can make it possible, for example, to adapt to the geometry of the part to be treated in order to minimize the overlap between the different zones of the part that we want to light up and thus gain speed.
    FIGS. 2A - 2D on the one hand and 3A - 3B on the other hand, illustrate different means of temporal shaping of the pulses upstream of the transport by the fiber-optic device, in an example of a system for generating pulses of high peak power according to the present description, aimed at reducing the power spectral density (DSP) of the laser pulses, either by widening the laser lines, or by multiplying the laser lines contained in the pulses.
    A reduction in the DSP makes it possible to limit the nonlinear effects in the fiber or fibers of the fiber device 110 and to reduce the temporal coherence of the laser pulses, which makes it possible to limit the overcurrents.
    For example, the applicant has shown that it could be advantageous in a system for generating high peak power laser pulses according to the present description, to reduce the DSP so as to be found, for a given fiber diameter and a given length of the fiber device, below the stimulated Brillouin backscatter threshold in the fiber device.
    Indeed, under the effect of temperature, the molecules that make up the optical fiber make small displacements around their original position. This results in the appearance of phonons which modify the refractive index of the fiber core, in the form of low amplitude acoustic waves. When a light wave passes through this medium, it is diffused by these acoustic waves and the diffusion is accompanied by a Doppler effect due to the mobility of the acoustic waves (spontaneous Brillouin effect). When the scattered wave propagates in the same direction as the incident optical wave we speak of a Stokes wave. When the scattered wave propagates in a direction opposite to the incident wave, we speak of an antiStokes wave.
    When the incident wave is very energetic, by interfering with the Stokes wave, it will create an intensity modulation and a network of highly contrasted indices in the fiber. This phenomenon, called electrostriction, is accompanied by stimulated diffusion which has an exponential gain for the anti-Stokes wave; we are talking about the Stimulated Brillouin Gain. The stimulated wave is backscattered in the form of a counter-propagating wave thus causing significant energy losses for the wave transmitted in the fiber.
    The stimulated Brillouin gain only appears for a guided light intensity in the fiber greater than a threshold intensity called the Brillouin threshold (P t h). Beyond the Brillouin threshold, the intensity of the backscattered wave increases exponentially. The Brillouin threshold is defined by (see for example P. Singh et al. “Nonlinear scattering effects in optical fibers”, Progress In Electromagnetics Research, PIER 74, 379-405, 2007):
    21. K. A e ff Δν ® Δν Β th de-Leff Av s
    Where A e ff is the effective area of the core of the fiber, L e ff is the effective length of the fiber, K is a constant linked to the polarization of the transported radiation which can vary from 1 to 2 and ge is the Brillouin gain, Δν is the width of the spectrum injected of said first pulses into the fiber (spectral range of the DSP) and Avb is the width of the Brillouin gain. For a monochromatic wave and at room temperature, the Brillouin gain has a width of the order of 20 MHz. Thus, if the incident spectrum is shifted (or widened) by more than 20 MHz, the stimulated Brillouin effect tends to decrease. In other words, the more monochromatic the light waves (with great temporal coherence) the more easily the stimulated Brillouin effect appears.
    The above equation shows that for small fiber core diameters of the fiber device (which is sought to gain flexibility), the Brillouin threshold is lowered. To increase the Brillouin threshold, it is possible, for example, to seek to broaden the spectrum of the laser line (s) contained in the laser pulses injected into the fiber device or to multiply this or these line (s).
    FIGS 2A to 2D illustrate examples of modules for temporal shaping of the first adapted laser pulses allowing the broadening of the spectrum of the laser line (s) contained in said first pulses.
    The spectral broadening of the laser line (s) makes it possible, as previously explained, to reduce the non-linear effects in the fiber or fibers of the fiber device, in particular the stimulated Brillouin effect, but also to limit the risk of overcurrents due to speckle phenomena. Indeed, if we broaden the spectrum, we reduce the temporal coherence and the capacity of light to interfere. This reduces the contrast of speckle grains and therefore overcurrents.
    In the examples illustrated in FIGS 2A to 2D, the time shaping module 102 comprises a reflecting device rotating around a given axis of rotation, configured to reflect said first incident pulses with spectral widening of the Doppler type.
    In the example illustrated in FIG. 2A, the rotating reflecting device comprises a simple mirror 22, arranged in a plane perpendicular to a plane of incidence H of the first pulses II. The mirror 22 is rotated about an axis of rotation 221 perpendicular to the plane of incidence H and contained in the plane of the mirror. The rotating mirror can have a rotary or oscillating movement around the axis of rotation 221. If it is assumed that the pulses are emitted with a given repetition frequency, the speed of rotation or of oscillation of the mirror is synchronized so that each pulse is incident on the mirror 22 with the same angle of incidence. For example, the angle of incidence is 0 ° from normal to the mirror, as shown in FIG. 2A. the angle of incidence is not necessarily zero but a zero angle is more advantageous in the case of a simple mirror.
    In the example of FIG. 2A, a polarization separator element 20 associated with a quarter-wave plate 21 makes it possible to separate on the one hand the pulses incident on the rotating mirror 22 and on the other hand the pulses reflected by the mirror 22.
    As shown that FIG. 2A, the pulses incident on the rotating mirror 22 for example have a spectrum So centered on an optical frequency Vo and with a given spectral fineness (curve 201). In addition, curve 202 schematically indicates the spatial distribution of the intensity I (r) of an incident pulse (thin line) and the spatial distribution of the optical frequency v (r) (thick line). As can be seen on curve 202, the spatial distribution of the optical frequency is constant, for example equal to vo.
    When a laser pulse is incident on the rotating mirror 22, it undergoes a shift of Doppler frequency Au D variable with the spatial profile of the beam. Indeed, spatially, each point of the incident beam on the rotating mirror undergoes a Doppler shift induced by the angular speed of the mirror δθ / δί. However, the angular speed varies as a function of the distance r between a mirror point and the axis of rotation.
    The curve 204 thus schematically illustrates the variation of the frequency v (r) of the reflected pulse resulting from the Doppler frequency shift Au D variable as a function of
    r.
    Denote by Df the diameter of the incident beam on the rotating mirror. The upper part of the beam at a distance r = D / 2 undergoes a negative Doppler shift: ùv D O = υ ο ~ U l where vo and vi are respectively the optical frequencies of the beam at distances r = Q and r = D / 2 of the axis of rotation. The lower part of the beam at the distance r = -D / 2 undergoes a positive Doppler shift:
    = v 2 - v 0 , where v2 is the optical frequency of the beam at the distance r = -D / 2 from the axis of rotation. Note that the center of the beam located at a distance r = 0 from the axis of rotation undergoes a zero Doppler shift.
    In the case of the rotating mirror shown in FIG. 2A, it can be shown that the total amplitude of the Doppler enlargement Av D is maximized when Df ~ D M (Dm diameter of the mirror). In this case the amplitude of the Doppler shift is equal to:
    / D f (~ Df 2nD M δθ Δυ 0 = Δ „ 0 (ν) _ Δ „ 0 δθ speed of rotation or oscillation in RPM (1 RPM = 2π rad / min = 2π / 60 rad / s) , λ wavelength In this example, we assume that Av D (γ) and Av D correspond to the Doppler shifts undergone at each end of the mirror.
    Thus, it is possible to associate with each spatial coordinate r of the beam a resulting optical frequency which is specific to it. This spatially variable Doppler effect results in a spectral broadening of the laser line of the pulses (S3 spectrum), as illustrated on curve 203.
    FIGS 2B to 2D illustrate other examples of rotating reflecting devices. In these examples, the rotating reflecting device comprises several reflecting surfaces arranged for example along the faces of a polygon. The rotating reflecting device also comprises fixed mirrors for reflecting laser pulses, making it possible to return each pulse from one rotating reflecting surface to the next. The reflecting surfaces and the reflecting mirrors are for example arranged in planes perpendicular to a plane of incidence Π comprising the directions of the wave vectors of the incident and reflected pulses, in order to maximize the Doppler shift effect. The reflecting surfaces have a rotational or oscillating movement about a central axis of rotation, perpendicular to the plane of incidence, for example an axis passing through the barycenter of the polygon, in this example an axis of symmetry of the polygon. In the examples presented below, each face of the rotating polygon forms a reflecting surface; thus, the rotating reflecting device comprises N reflecting surfaces and N-1 deflection mirrors. It is also possible to have N reflecting surfaces (N> 2) on a limited number of sides of the polygon and always N-1 deflection mirrors. The applicant has shown that this particular configuration of "rotating polygon" makes it possible to multiply Doppler enlargement.
    In the example of FIG. 2B, the rotating reflecting device 23 comprises 4 reflecting surfaces 231 arranged in a square, in rotation about an axis of symmetry 232 and 3 reflecting mirrors 233; In the example of FIG. 2C, the rotating reflecting device 24 comprises 6 reflecting surfaces 241 arranged in a hexagon, in rotation around an axis of symmetry 242, and 5 reflecting mirrors 243; In the example of FIG. 2D, the rotating reflecting device 25 comprises 8 reflecting surfaces 251 arranged in an octagon, rotating around an axis of symmetry 252, and 7 deflecting mirrors 253. In general, the rotating reflecting device may comprise N reflecting surfaces, with N between 2 and 10 and N-1 deflection mirrors. In the examples illustrated in FIGS 2B to 2D, we denote respectively S4, S5, Se the resulting spectra (curves 205, 206, 207 respectively).
    As illustrated in FIGS 2B - 2D, the laser pulses I L are incident on a reflecting surface of the polygon with an angle Θ relative to the normal to the surface. The laser pulses are synchronized in time with the rotation or the oscillation of the rotating reflecting device so that each incident pulse has the same angle of incidence with one of the reflecting surfaces.
    In order to maximize the spectral spread by Doppler effect, it can be provided that the light beam formed by laser pulses incident on each reflecting surface has a diameter less than or equal to:
    Df = D M .sin (<z) .cos (0)
    Where D m is an external diameter of the polygon in a direction perpendicular to the axis of rotation and a is the half angle between the center of the polygon and one of these facets The rotating reflecting device has an angular speed δθ, Θ is the angle beam incidence compared to normal to a reflective facet. Each rotating facet will shift the frequency of the radiation reflected thereon by Doppler effect. As in the example in FIG. 2A, the Doppler shift undergone by the beam is different according to the spatial profile of the beam. Indeed, spatially, each point of the incident beam on a reflecting face undergoes a Doppler shift induced by the angular speed of the reflecting face. In the case where the beam arrives in a direction perpendicular to the axis of rotation, the total amplitude of the Doppler enlargement can be maximized. It is then determined by the expression below:
    / Dr / Dr 2πΰ Μ δθ kv D = Δυ 0 I - 1 - Δυ ΰ I - 1 =. sin (a) cos (0) -
    Thanks to the polygon geometry of the rotating reflecting device, the light pulses can be reflected on each of the reflecting faces of the polygon and it is possible to multiply the spectral spreading effect by Doppler effect. Thus, for a polygon having N reflecting faces, the spectrum of an incident line on the rotating reflecting device will undergo an enlargement due to the Doppler effect expressed as follows:
    Ν.2πΰ Μ δθ
    Av d = -------. sin (cr) cos (0) -
    For example, we consider laser pulses at 1064 nm with a pulse duration of 20 ns and whose spectrum is limited by Fourier transform (spectral width 50 MHz). If the laser source is synchronized in time with an octagon rotating at 55,000 rpm (rpm = rotation per minute, i.e. 5,760 rad / s) with an outside diameter of 40 mm so that the angle of incidence between the laser beam and the normal to the polygons surface is always equal to θ = 11.25 ° and the pulses of reflect on the 8 reflecting sides of the polygon then the spectrum of the laser will be spread over approximately 690 MHz. The rotating reflecting device will thus have broadened the incident spectrum by a factor of 13.
    In addition, in addition to spreading the spectrum and reducing the temporal coherence of the laser pulses, the different spatial coordinates of the beam are associated with different spectral components, which makes it possible to reduce the spatial coherence. Such a temporal shaping module therefore makes it possible to minimize the overcurrent peaks due to the spatio-temporal coherence of the source. In addition, for a beam at 1064 nm of 20 ns and diameter 15 mm, the diffraction limit is around 67 prad. However during the duration of the pulse, if the polygon of 8 facets rotating at 55000 RPM (5760 rad / s), the beam undergoes a scanning during its duration of 20 ns equal to 115 prad, that is approximately 2 times the diffraction limit . This will help minimize the speckle contrast.
    FIGS. 3A - 3B illustrate examples of module 102 for time shaping aimed at multiplying the laser line (s) of the laser pulses injected into the fiber device.
    These examples allow a multiplication of laser lines leading to a decrease in temporal coherence. This allows in particular to increase the Brillouin threshold and decrease the contrast of the speckle at the input of the fiber device.
    The example of FIG. 3 A is based on the use of an acousto-optical modulator 33 (MAO, or AOM according to the abbreviation of the Anglo-Saxon expression "acousto-optic modulator"), using the acousto-optical effect to diffract and change the optical frequency of light by sound waves (usually close to radio frequencies).
    More specifically, the module 102 comprises a polarization splitter cube 31 which transmits the linearly polarized laser pulses I L , of spectrum So, to the acousto-optical modulator 33. The modulator 33 receives a signal from a polychromatic radiofrequency electric generator 32 Diffracted beams Fi, F 2 , ... come from the modulator 33. If N radiofrequencies constitute the polychromatic RF signal delivered by the generator 32 and supplying the acousto-optical modulator 33, it is possible to have up to N diffracted beams in N different directions at the output of the modulator 33. Each diffracted beam is associated with a direction and has undergone a spectral shift corresponding to one of the N radiofrequencies constituting the polychromatic RF signal delivered by the generator 32. The higher the RF frequency important the greater the spectral and angular shift undergone by the beam at the output of the modulator 33. Thus, a range of discrete beams are emitted at the output of the modulator 33. This range of discrete beams can be recollimated by an optical system 34, for example an optical lens. The beams thus collimated pass through a quarter-wave plate 34 which transforms the linear polarization into a circular polarization. A mirror 36 is arranged at the output of the quarter-wave plate to form a self-collimation configuration. This optical configuration allows a reverse return of the beams to the modulator 33. The return pulses cross again the plate 35. They then have a polarization at 90 ° from the initial polarization. Following the opposite path, they again pass through the lens 34 to be routed into the modulator 33. The beams will again undergo angular and spectral shifts, the spectral shift on the return being added to the spectral shift suffered on the outward journey. Each of the spectrally shifted beams is returned to the polarization splitter cube 31 and directed towards the fiber device (not shown in FIG. 3A). The resulting spectrum Si is widened, as illustrated in the diagram in FIG. 3 A due to the different lines formed by the module 102 thus represented.
    For example, if the polychromatic radiofrequency signal comprises 3 distinct radiofrequencies Vi, V2, V3, typically between 35 MHz and 350 MHz, the spectrum Si of output pulses will include a comb of optical frequencies vo + 2vi, vo + 2v 2 , Vo + 2v 3 , where Vo is the central optical frequency of the pulses emitted by the source 101. On the other hand, the output beam will have a single direction. If the laser pulses from the source 101 already include a plurality of lines, these lines will each be multiplied as described above. Note that the bandwidth of the optical amplifiers envisaged is much greater than the shifts made by the MAOs, the laser pulses resulting from this time shaping can be amplified by the optical amplifier. For example, an Nd: YAG crystal has an amplification bandwidth of almost 30 GHz around 1064 nm.
    Another arrangement for multiplying the lines of the first laser pulses is illustrated in FIG. 3B.
    In this example, the time shaping module comprises an amplitude or phase modulator 37 configured to modulate the incident pulses II in intensity.
    The amplitude or phase modulator 37 comprises for example a Pockels cell. If the intensity is modulated with a polychromatic radio frequency signal 38, the spectrum S2 at the module output will be enriched with the spectral components originating from the polychromatic RF signal 38. This has the effect of broadening the spectrum by multiplying the laser lines and the spectral density power of the pulses from the source 101.
    The reduction of the DSP resulting from the multiplication of the laser lines as described in the examples above can range from a factor of 2 to a factor of 10. Thus, for example, it is possible, from a fine spectrum of spectral width 100 MHz typically, obtain pulses whose total spectral width at the input of the fiber-optic device is of the order of several hundred MHz, which makes it possible to significantly reduce the Brillouin gain.
    Of course, the methods presented above for the reduction of PSD are not exhaustive and can be combined.
    FIGS. 4A and 4B illustrate examples of spatial shaping of the laser pulses I L upstream of the transport by the fiber device.
    These two examples aim to form a profile beam of substantially uniform intensity, of the “top hat” type. For example, we can look for a spatial variation of the light intensity is +/- 10% excluding granular effects linked to the speckle.
    FIG. 4A thus illustrates a first example of a shaping module 103 comprising a DOE (for "Diffractive Optical Element") 41 associated with an optical system 42, for example an optical lens, to achieve spatial shaping adapted to the size and to the geometry of the fiber.
    In FIG. 4A, the profile Po represents the profile of the intensity of the laser pulses emitted by a laser source, for example of the Gaussian type. The applicant has shown that with a Pi profile of the “top hat” type, as shown in FIG. 4A, the risk of overcurrents during propagation in the fiber device is reduced. The spatial shaping of the beam in the image plane of the optical system 42 corresponds to the spatial Fourrier transform of the phase mask imposed by the DOE 41 convoluted with the spatial Fourier transform of the spatial distribution of beam intensity at the level of the DOE. Thus, the phase mask imposed by the DOE 41 is calculated so that the result of this convolution forms a “top hat” intensity distribution, the diameter D of the beam being proportional to the focal distance f of the optical system 42.
    FIG. 4B illustrates another variant of a spatial shaping module 103. In this example, the spatial shaping is carried out by means of a pair of microlens arrays 43, 44 and a converging lens 44.
    The first microlens array 43 (focal distance F gi ) divides the incident beam into a multitude of sub-beams. The second matrix of microlenses 44 (focal distance F g2 ) in combination with the converging lens 45 plays the role of a matrix of objectives which superimposes the images of each of the sub-beams in a plane called "homogenization plane" located at the focal length F L of the converging lens. By modifying the distance between the two microlens arrays, the size of the shaping is changed. The geometry of the microlenses taken individually gives the shape of the image after the homogenization plane.
    Spatial shaping as described by means of FIGS 4A, 4B makes it possible, by comparison with a Gaussian profile, to reduce the overcurrents at the input of the multimode fiber during propagation in the fiber device. Indeed, for the same energy and the same beam diameter, a circular “top hat” profile has a peak intensity lower than a Gaussian profile.
    The reduction of overcurrents on the power profile of the laser pulses can also be obtained by reducing the temporal coherence of the pulses, as explained above.
    FIG. 5 illustrates an example of a system 50 according to the present description comprising all or part of the elements described with reference to FIG. 1 and further comprising at least a first optical amplifier 120 arranged at the output of said fiber device 110 for the optical amplification of said first laser pulses. Optionally, several optical amplifiers can be arranged in series. At the output of said optical amplifier (s), spatial shaping of the amplified pulses is possible by means of an element 115, as described with reference to FIG. 1.
    The system 50 can also include at least a second laser amplifier for amplifying second laser pulses emitted by a second source at a wavelength different from the first source, if necessary.
    The system 50 also includes a light source 104 for the emission of a pump beam Ip. The wavelength of the pump light source 104 depends on the wavelength of the pulses emitted by the source 101 and on the optical amplifier 120 used. For example, if the laser source 101 emits at a wavelength around 1064 nm and the amplifier crystal of the optical amplifier 120 is an Nd: YAG crystal, the pump source 104 may emit pump beams to a wavelength around 800 nm. If the laser source 101 emits at a wavelength around 1030 nm, and the amplifier crystal is of the Yb: YAG type, then the pump source 104 can emit the pump beams at a wavelength around 980 nm.
    The pump laser source advantageously comprises one or more laser diodes.
    The pump laser source 104 can emit pump beams in continuous (CW) or quasi-continuous (QCW) regime.
    A temporal shaping by means of a temporal shaping module 105 allows for example to modulate the pump beams in intensity. Thus, for example, the pump beams are modulated at the repetition frequency of said first pulses. They can be maintained at a constant or almost constant light intensity for a given duration, for example of the order of time of the excited levels of the rare earth ions which serve for the amplification phenomenon of the optical amplifier 120. Once this Over time, the intensity of the pump beams can be reduced to zero. Spatial shaping of the pump bundles is also possible, for example by means of a spatial shaping module 106, which for example makes it possible to secure the injection of the pump bundles into the fiber device 110 by adapting the size from the optical mode of the pump beam to the core diameter of the first multimode fiber.
    When using pump laser diodes, time shaping is done by acting directly on the electrical control of the diode.
    In the example of FIG.5, the pump beam Ip is injected into the fiber device 110 with the laser pulses I L by means of mirrors 107, 108, the blade 108 being for example a dichroic blade. The pump beam Ip is copropagative with the laser pulses I L , that is to say that the pump beam is injected into the fiber device 110. Copropagative pumping is particularly advantageous in order to maximize the overlap between the laser beam of pump and the laser pulses to be amplified. Thus the amplification process is more efficient and optimizes the pump energy required.
    Alternatively, the optical pumping can be transverse, carried out for example by means of individual fiber laser diodes. This variant makes it possible to bring more pump energy by using, for example, an optical fiber per pump diode.
    In all cases, as previously described, spatial shaping of the pulses at the output of the amplifier 120 is possible, for example by means of a component 115 as described with reference to FIG. 1, for example a diffractive optical component, for example of the DOE type (for “Diffractive Optic Element”), a microlens system, an optical condenser, a Powel lens.
    FIG. 6 shows a diagram of an exemplary embodiment of a fiber-reinforced device 60 in which two components known as "photonic lantern" are arranged head to tail.
    Each component or "photonic lantern" connects a multimode fiber core (at least 20,000 modes) to several slightly multimode fibers (less than 10,000 modes) having cores of smaller diameters. The arrangement of these components is for example described in the article by D. Noordegraaf. et al. (“Multi-mode to single mode conversion in a 61 port photonic lantern”, Optics Express, Vol. 18, No. 5 (2010) pp. 4673 - 4678.). Thus, the fiber device 60 described in FIG. 6 comprises as input said first multimode fiber 61, a set of slightly multimode fibers 62 coupled with said first multimode fiber, and as output, a second multimode fiber 63, coupled with said slightly multimode fibers and comprising a single core for the output of said first laser pulses. There may for example be between 10 and 20, advantageously between 10 and 100 slightly multimode fibers.
    Such a device can have transmission losses, typically less than 15%, but has great flexibility due to the use of slightly multimode fibers of smaller diameter (typically between 50 μm and 200 μm). Furthermore, the losses can be compensated by using fibers 62 doped between the single-core injection and coupling sections (61, 63). These losses could also be compensated, according to a variant, by means of an optical amplifier at the output of the fiber-optic device.
    Thus, it is possible by means of the fiber device 60 to inject high energy laser pulses (typically> 300 mJ for 10 ns pulses) into a single core and to propagate said pulses to the area to be treated over several smaller diameter fibers. Once the multi-fiber transport function has been performed, the optical radiation can be amplified, for example by means of the optical amplifier 120 as described in FIG. 5, then delivered to the surface to be treated. By delivering energy from a single core, the amplification and / or shaping of the beam by a diffractive optical component, for example of the DOE type, microlens system, optical condenser, Powel lens, is facilitated.
    Furthermore, the fact that the input and the outputs of the fiber-optic device are multimode fibers with cores of large diameters (typically between 300 μm and 1 mm) secures the sensitivity to damage induced by laser for the input and output faces. of the fiber device.
    Although described through a number of detailed exemplary embodiments, the methods and systems for generating high peak power pulses include various variants, modifications and improvements which will be apparent to those skilled in the art, being it is understood that these different variants, modifications and improvements are part of the scope of the invention, as defined by the claims which follow.
    权利要求:
    Claims (15)
    [1" id="c-fr-0001]
    1. System (10) for generating pulses of high peak power comprising:
    at least a first light source (101) for the emission of first laser pulses (I L ) nanoseconds comprising one or more laser line (s);
    - a fiber device (110) for transporting said first laser pulses, comprising at least a first multimode fiber with a single core arranged to receive said first laser pulses;
    - A module (102) for temporal shaping of said first laser pulses, arranged upstream of the fiber device, configured to decrease the power spectral density of said pulses by reducing temporal coherence.
    [2" id="c-fr-0002]
    2. The laser pulse generation system according to claim 1, wherein said time shaping module (102) comprises spectrum widening means configured to widen the spectrum of the laser line (s) contained in said first pulses.
    [3" id="c-fr-0003]
    The laser pulse generation system according to claim 2, wherein said spectrum widening means comprises a reflecting device rotating (22-25) about a given axis of rotation, configured to reflect said first incident pulses with Doppler type spectral broadening.
    [4" id="c-fr-0004]
    4. The laser pulse generation system according to claim 3, wherein said rotating reflecting device comprises at least a first reflecting surface having a rotational or oscillating movement around said axis of rotation.
    [5" id="c-fr-0005]
    5. The laser pulse generation system according to claim 4, wherein said first pulses being emitted with a given repetition frequency, the speed of rotation or oscillation of said at least one reflecting surface is synchronized with said repetition frequency. first pulses such that each of said first pulses is incident on said at least one reflecting surface with a constant angle of incidence.
    [6" id="c-fr-0006]
    6. Laser pulse generation system according to claim 4, in which said rotating reflecting device comprises N reflecting surfaces (N> 2) and N - 1 deflection mirrors configured to return each of said first pulses to each of said reflecting surfaces, all of said reflecting surfaces exhibiting a rotational or oscillating movement around said axis of rotation.
    [7" id="c-fr-0007]
    7. A laser pulse generation system according to any one of the preceding claims, in which said time shaping module (102) comprises means configured to multiply the laser line (s) contained in said first pulses.
    [8" id="c-fr-0008]
    8. A laser pulse generation system according to claim 1, further comprising a module (103) for spatial shaping of said first laser pulses, arranged upstream of the fiber device, configured to standardize the spatial density of power of said pulses.
    [9" id="c-fr-0009]
    9. The laser pulse generation system according to claim 1, further comprising at least a first optical amplifier (120) arranged at the output of said fiber device for the optical amplification of said first laser pulses.
    [10" id="c-fr-0010]
    10. The laser pulse generation system according to claim 1, in which said fiber-optic device (110) comprises at input said first multimode fiber, a set of slightly multimode fibers coupled with said first multimode fiber, and in output, a second multimode fiber, coupled with said slightly multimode fibers and comprising a single core for the output of said first laser pulses.
    [11" id="c-fr-0011]
    11. Laser pulse generation system according to any one of the preceding claims, in which said fiber device (110) comprises at least one doped fiber for the optical pre-amplification of said first laser pulses.
    [12" id="c-fr-0012]
    12. A method of generating high peak power laser pulses comprising: the emission of first nanosecond laser pulses;
    transporting said first laser pulses by a fiber device comprising at least a first multimode fiber with a single core into which said first laser pulses are injected;
    5 - the temporal shaping of said first laser pulses upstream of transport by the fiber device, said temporal shaping comprising the reduction of the power spectral density by reduction of the temporal coherence of said first laser pulses.
    [13" id="c-fr-0013]
    13. Method for generating laser pulses according to claim 12,
    10 further comprising the spatial shaping of said first laser pulses upstream of the transport by the fiber device, said spatial shaping comprising the standardization of the spatial power density of said first laser pulses.
    [14" id="c-fr-0014]
    14. Method for generating laser pulses according to any one of claims 12 or 13, further comprising the optical amplification of said first
    [15" id="c-fr-0015]
    15 laser pulses by means of at least a first optical amplifier arranged at the output of the fiber device to form said laser pulses of high peak power.
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    同族专利:
    公开号 | 公开日
    US20210273397A1|2021-09-02|
    WO2019233900A1|2019-12-12|
    JP2021525970A|2021-09-27|
    CN112544018A|2021-03-23|
    FR3081738B1|2020-09-04|
    EP3804050A1|2021-04-14|
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    优先权:
    申请号 | 申请日 | 专利标题
    FR1854860A|FR3081738B1|2018-06-05|2018-06-05|METHODS AND SYSTEMS FOR THE GENERATION OF LASER PULSES OF HIGH PEAK POWER|
    FR1854860|2018-06-05|FR1854860A| FR3081738B1|2018-06-05|2018-06-05|METHODS AND SYSTEMS FOR THE GENERATION OF LASER PULSES OF HIGH PEAK POWER|
    CN201980052362.6A| CN112544018A|2018-06-05|2019-05-31|Method and system for generating high peak power laser pulses|
    US16/972,514| US20210273397A1|2018-06-05|2019-05-31|Methods and systems for generating high peak power laser pulses|
    JP2020568267A| JP2021525970A|2018-06-05|2019-05-31|High peak power laser pulse generation method and high peak power laser pulse generation system|
    PCT/EP2019/064225| WO2019233900A1|2018-06-05|2019-05-31|Methods and systems for generating high peak power laser pulses|
    EP19731607.8A| EP3804050A1|2018-06-05|2019-05-31|Methods and systems for generating high peak power laser pulses|
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