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    • 专利摘要:
    According to one aspect, the invention relates to a laser device comprising a solid laser amplifier bar (20) having an absorption spectral band comprised in the visible-near-infrared spectral band and at least a first light-emitting module (10A-10D). ) for pumping the solid laser amplifier bar. Each light emitting module comprises a set of light-emitting diodes (LEDs) for emitting a luminous flux in a first spectral band and a light concentrator; the light concentrator comprises a solid bar of fluorescent inorganic material with at least a first illumination surface for receiving the light emitted by the LEDs and an emitting surface for emitting the fluorescence light towards the solid amplifying bar, and wherein the ratio between the illuminating surface and the emitting surface is greater than 100.
    公开号:FR3045965A1
    申请号:FR1562823
    申请日:2015-12-18
    公开日:2017-06-23
    发明作者:Adrien Barbet；Francois Balembois；Amandine Paul；Jean-Philippe Blanchot；Thomas Gallinelli；Sebastien Forget；Sebastien Chenais；Frederic Druon；Patrick Georges
    申请人:EFFILUX；Centre National de la Recherche Scientifique CNRS；Universite Paris Sud Paris 11；Universite Sorbonne Paris Nord Paris 13；Institut dOptique Graduate School；
    IPC主号:
    专利说明:

    CONCENTRATED LIGHT EMITTING MODULE AND LASER DEVICE USING SUCH A MODULE
    STATE OF THE ART
    Technical field of the invention
    The present invention relates to a concentric light emitting module, a laser device comprising an LED pumped solid laser amplifying bar using a concentration light emitting module as well as a laser optical pumping LED emission method.
    State of the art
    Today, in the majority of so-called optically pumped "solid-state lasers", a solid amplifying bar receives light energy from a series of power laser diodes, which are known to be much more powerful than light-emitting diodes or "LEDs". According to the abbreviation Anglo-Saxon "Light-emitting diodes".
    Recent advances in LEDs, in particular thanks to the massive use of LEDs in the field of lighting, have however revived the interest of these sources for optical pumping in laser sources. In addition to their extremely competitive price, LEDs today allow to achieve efficiencies higher than 30% in the visible field, a field in which laser diodes remain expensive and fragile. Recently, applicants have thus demonstrated the feasibility of a solid-state laser device comprising an Nd: YVC> 4 (neodymium-doped yttrium orthovanadate) bar pumped by LED at room temperature (see A. Barbet et al. "Revisiting of LED Pumped Bulb Laser: First Demonstration of Nd: YV04 LED Pumped Laser", Opt.Led., Vol 39, No. 23, 6731, Dec. 2014).
    Despite this, the emittance of LEDs - or illumination (defined as the quotient of light power per unit area) - remains limited because of the quasi-Lambertian emission of these sources. Thus, the emittance is often insufficient to reach the laser thresholds of most solid laser amplifiers.
    One solution for increasing source emittance for the purpose of optical pumping of a laser material is to use a luminescent light concentrator. The article by Ying Yang et al. (The Development of Luminescent Concentrators for Organic Pumping
    Semiconductor lasers "; Adv. Mater. 2009, 21, 3205-3209) thus describes a laser device pumped by means of a luminescent concentrator, a schematic diagram of which is shown in FIG. 1. The laser device 100 comprises a thin layer of an organic semiconductor forming an amplifying medium 104, and a luminescent concentrator formed of an organic layer 102 deposited on a silica substrate 101 and adapted to receive light derived from laser diodes or LEDs, for optical pumping of the organic semiconductor laser. The laser cavity formed in the amplifying medium 104 is shown diagrammatically in FIG. 1 by a double vertical arrow, the optical pumping of the cavity being a transverse pumping. The organic layer 102 is formed of a film of transparent organic material in which fluorescent dyes 103 are dispersed. The dyes absorb the light on the surface of the film and a part (1) of the emitted fluorescence light is collected by a process. total internal reflection ("TIR") to one of the edges of the film. A substantial part (2) of the emitted fluorescence light is, however, lost at the interfaces between the organic layer 102 and the substrate 101 limiting the gain on the emittance (or concentration factor) to factors less than 10, which does not allow not a satisfactory LED optical pumping.
    The present description proposes a luminescent concentrator having a concentration factor greater than 10, making it possible to reach the emittance thresholds required for pumping a laser amplifying bar by means of LEDs.
    SUMMARY OF THE INVENTION
    According to a first aspect, one or more exemplary embodiments relate to a laser device comprising: a solid laser amplifier bar having an absorption spectral band comprised in the visible-near infrared spectral band; at least one first light emitting module for pumping the solid laser amplifying bar, each light emitting module comprising a set of light emitting diodes (LEDs) for emitting in a first spectral band and a light concentrator, the concentrator of light comprising: a solid bar of fluorescent inorganic material with at least a first illumination surface for receiving the light emitted by the LEDs and an emitting surface for emitting the fluorescence light towards the solid amplifier bar, and wherein: the fluorescent inorganic material has an absorption band exhibiting a non-zero overlap with the emission spectral band of the LEDs and an emission band exhibiting a non-zero overlap with the spectral absorption band of the laser amplifier bar.
    In the present description, the visible-near-infrared spectral band is the spectral band generally covered by the LEDs, typically between 360 nm and 940 nm.
    Applicants have shown that the light concentrator thus described allows an optimization of the concentration factor in particular because of the small losses suffered by the fluorescence light emitted into the bar of fluorescent inorganic material and collected towards the emitting surface.
    According to one or more embodiments, the ratio between the illuminating surface and the emitting surface is greater than or equal to 50, advantageously greater than or equal to 100.
    According to one or more embodiments, the bar of fluorescent inorganic material has a substantially rectangular parallelepiped shape, which allows the arrangement of all the LEDs on at least a first illuminating surface, preferably on two illuminating surfaces. .
    According to one or more embodiments, the bar of fluorescent inorganic material has a substantially cylindrical shape, with a circular section, the set of LEDs being arranged all around the cylinder which forms the illumination surface.
    According to one or more exemplary embodiments, the laser device comprises at least a first light emission module arranged for the longitudinal pumping of the solid laser amplifier bar, a transmitting face of said first laser emission module being in contact with a face of bar input solid laser amplifier.
    According to one or more exemplary embodiments, the emitting face of said first longitudinal module is smaller than said input face of the laser amplifier bar.
    According to one or more exemplary embodiments, the laser device comprises at least a first light emission module arranged for transverse pumping of the solid laser amplifying bar.
    According to one or more exemplary embodiments, the laser device comprises at least a second light emitting module, arranged in alignment with the first light emitting module.
    According to one or more exemplary embodiments, the laser device comprises a refraction index matching element arranged between each light emission module and the laser amplifier bar and / or between two light emitting modules arranged in the light emitting module. alignment of one another, the index matching element may comprise a liquid or solid material.
    According to one or more exemplary embodiments, the fluorescent inorganic material is yttrium garnet and cerium-doped aluminum (Ce: YAG).
    According to one or more exemplary embodiments, the LEDs are so-called "flip chip" or "flip chip" LEDs, otherwise known as "Flip-chip" LEDs.
    According to one or more exemplary embodiments, the degree of filling of the LEDs defined by the ratio between the cumulative emitting surface of the LEDs and the illumination surface is greater than 50%, advantageously greater than 60%, advantageously greater than 75%. .
    According to one or more exemplary embodiments, the set of light-emitting diodes (LEDs) are intended to emit a luminous flux of optical power sufficient to trigger an amplified spontaneous emission process at the fluorescence wavelength, in the inorganic bar fluorescent.
    According to a second aspect, one or more exemplary embodiments relate to a laser emission method comprising: the emission of a luminous flux by means of at least a first light emission module, each light emission module comprising a a set of light-emitting diodes (LEDs) emitting in a given emission spectral band and a light concentrator, the light concentrator comprising: a bar of fluorescent inorganic material with at least a first illumination surface receiving the light emitted by the LED and a transmitting surface emitting a fluorescence light to a solid amplifying bar, and wherein: the fluorescent inorganic material has an absorption band having a non-zero overlap with the emission spectral band of the LEDs and a band of emission having a non-zero overlap with the absorption spectral band of the amplifying bar r laser;
    The pumping of the solid laser amplifier bar by means of the luminous flux emitted by the light emission module.
    According to one or more embodiments, the ratio between the illuminating surface and the emitting surface is greater than or equal to 50, advantageously greater than or equal to 100.
    According to one or more exemplary embodiments, the optical power of the luminous flux emitted by the LEDs and received by the first illumination surface is sufficient to trigger an amplified spontaneous emission process at the fluorescence wavelength, in the bar inorganic fluorescent.
    The present invention also relates, according to a third aspect, to an amplified spontaneous emission concentrator.
    According to a third aspect, one or more exemplary embodiments relate to a light emission module for emitting high emittance in a given output transmission spectral band, comprising: a set of light emitting diodes (LEDs) intended to emit in a first emission spectral band a light flux of given optical power; and a light concentrator, comprising: a solid bar of fluorescent inorganic material with at least a first illuminating surface for receiving the luminous flux emitted by the LEDs and an emitting surface for emitting the fluorescence light, and wherein the fluorescent inorganic material has an absorption spectral band exhibiting a non-zero overlap with the emission spectral band of the LEDs; and wherein: the optical power of the light flux that all the LEDs are intended to emit is sufficient to trigger an amplified spontaneous emission process at the fluorescence wavelength, in the fluorescent inorganic bar.
    According to one or more embodiments, the ratio between the illuminating surface and the emitting surface is greater than or equal to 50, advantageously greater than or equal to 100.
    According to one or more exemplary embodiments, the light emission module according to the third aspect is intended for pumping a solid laser amplifier bar.
    BRIEF DESCRIPTION OF THE DRAWINGS Other advantages and characteristics of the invention will appear on reading the description, illustrated by the following figures: FIG. 1 (already described), a block diagram of a concentrator used for pumping an organic semiconductor amplifier medium, according to the prior art; FIG. 2, a diagram of an exemplary laser device according to the present description, comprising a transverse pumping configuration of a solid laser amplifier bar; FIGS. 3A to 3C, diagrams showing different elements of an exemplary laser emission module, adapted in particular for pumping a solid laser amplifier bar; FIG. 4, curves illustrating as a function of the wavelength, the (normalized) emission of the LEDs, the absorption of Ce: YAG, the fluorescence emission (normalized) of Ce YAG, the absorption of Nd: YV04 ; FIG. 5, a diagram of an exemplary laser device according to the present description, comprising a longitudinal pumping configuration of a solid laser amplifier bar; FIG. 6, a diagram of an exemplary laser device according to the present description, comprising a configuration of both longitudinal and transverse pumping of a solid laser amplifier bar; FIGS. 7A and 7B, two diagrams of laser device examples according to the present description, respectively comprising a linear cavity and a ring cavity, with a transverse pumping of the solid laser amplifier bar; FIG. 8 a diagram of an experimental laser device implemented according to an exemplary embodiment of the present description; FIG. 9A and 9B of the experimental curves respectively showing the light energy at the output of the laser device and the small signal laser gain as a function of the energy emitted by the LEDs, in an exemplary embodiment of a laser device as represented in FIG. . 8.
    DETAILED DESCRIPTION
    In the figures, the identical elements are indicated by the same references. For the sake of clarity, the elements are not represented in their actual dimensions and proportions.
    FIG. 2 shows a block diagram of a laser device 200 according to the present description while FIGS. 3A to 3C illustrate an example of a light emission module 10 according to the present description.
    The laser device 200 generally comprises a solid laser amplifier bar 20 with an absorption spectral band comprised in the visible spectral band - near infrared, that is to say an absorption spectral band between 360 nm and 940 nm. nm, for example an amplifying bar made of inorganic material.
    The solid laser amplifier bars are generally formed of matrices doped with luminescent ions, the matrices can be glassy, crystalline or ceramic. The choice of inorganic materials ensures a long service life of the bars because the photo degradation when it exists is much lower than in an organic medium.
    The laser amplifier bar 20, for example an amplification bar made of inorganic material, is formed of a material included, for example, in the following group of materials:
    Titanium ion doped matrices belonging to the family of oxides (e.g. titanium doped sapphire Ti: Al2O3) or glasses (for example silicate or phosphate);
    Matrices doped with neodymium ions belonging to the family of glasses (for example silicate or phosphate), garnets (eg Nd: YAG, Nd: GGG), vanadates (egNd: YV04, NdiGdVCL), aluminates (eg Nd: YAP), fluorides (eg Nd: YLF), tungstates, molybdates or beryllates (eg Nd: KGW (CaWCL), Nd: NaLa (MoC> 4) 2, Nd: La2Be2C> 5) or ceramics;
    Chromium ion-doped matrices belonging to the fluoride family (eg Cr: LiSAF, Cr: LiSGAF, Cr: LiCAF), oxides (such as ruby, alexandrite, BeAbCb or emerald, Be3Ab (Si03) 6 ), garnets (eg Cr: GSGG), silicates (eg Cr: Forsterite) or tungstates (eg CnZnWCL);
    Matrices doped with praseodymium ions belonging to the fluoride family (eg Pr: YLF, Pr: LLF, Pr: KYF), aluminates (eg Pr: YAP, YAIO3), garnets (eg Pr: LuAG, Pr: YAG), glasses (eg Pr: ZBLAN);
    Matrices doped with ytterbium ions belonging to the family of glasses (for example silicate or phosphate fibers), garnets (eg Yb: YAG, Yb: LuAG), fluorides (eg Yb: YLF, Yb: CaF2), tungstates (eg Yb: KYW (KY (WO4) 2), Yb: KGW (KG (WO4) 2)), aluminates (eg Ybxalgo (CaGdAlCL), Ybxalyo (CaYAlCl)), oxides (eg Yb: Lu2C> 3, Yb: Y2C> 3, Yb: Sc2C> 3), borates (eg Yb: YCOB), silicates (eg Yb: YSO) or ceramics;
    Erbium-doped matrices belonging to the family of glasses (for example silicate or phosphate fibers or ZBLAN fibers), garnets (eg Er: YAG, Er / Cr: YSGG), oxides (eg ErAbCh) or aluminates (eg Er: YAP); Thulium doped matrices belonging to the family of glasses (such as, for example, silicate or phosphate fibers or ZBLAN fibers), garnets (e.g. Tm: YAG), fluorides (e.g. Tm: YLF);
    Holmium-doped matrices belonging to the family of glasses (such as, for example, silicate or phosphate fibers or ZBLAN fibers), garnets (e.g. Ho: YAG), fluorides (e.g. Ho: YLF);
    Any codoped matrix involving two of the ions mentioned above (e.g. Nd / Cr: YAG, Nd / Ce: YAG, Yb / Er: YAG);
    In general, any matrix among oxides, fluorides, borates, silicates, aluminates, tungstates, garnets, glasses, beryllates, molybdates or ceramics doped by a luminescent ion or a combination of luminescent ions among trivalent rare earth ions (such as Nd3 +, Er3 +, Ho3 +, Ce3 +, Tm3 +, Pr3 +, Gd3 +, Eu3 +, Yb3 +), divalent rare earth ions (such as Sm2 +, Dy2 +, Tm2 +) or metal ions (such as than Cr3 +, Ni2 +, Co2 +, Ti3 +, V2 +)
    In this example, the laser amplifier bar 20 is arranged within a laser cavity formed by two mirrors, a first mirror 21, called a cavity-bottom mirror, having a high reflection coefficient, typically greater than 99% over the length of the mirror. wave of the laser emission and a second mirror 22 said output mirror through which the laser flux is emitted. One and / or the other of the mirrors 21 and 22 may be replaced in a known manner by reflective treatments directly deposited on the faces of the amplifier bar.
    In the example illustrated in FIG. 2, the laser device also comprises a diffuser 23 adapted to recycle the unused pump energy and homogenize the pump illumination in the amplifying bar 20.
    The laser device 200 furthermore comprises at least one light emission module 10 for pumping the solid laser amplifier bar 20, the emission module comprising a solid bar made of fluorescent inorganic material, as will be detailed hereinafter. In the example of FIG. 2, several transmission modules referenced 10a, 10b, 10c, 10d, are arranged next to each other so as to allow transverse optical pumping of the solid amplification bar 20 over a large part of its length.
    According to one or more exemplary embodiments, the laser device 200 comprises an adaptation element 30 of the refractive index, in particular between a light emission module 10a-10d and the laser amplifier bar 20 with which the transmission module bright is in contact. The adaptation element of the refractive index makes it possible, as will be detailed in more detail in the remainder of the description, to eliminate the losses of fluorescent light at the interfaces with the emitting surface (s) of the bars of fluorescent inorganic material. of which are formed light emission modules and increase the critical angle for which one has total internal reflection, which has the effect of letting out more rays ("emptying"). The adaptation element of the refractive index may comprise a liquid or solid material, or between the liquid and the solid (oils or glues more or less viscous). The refractive index matching element may comprise, for example, an index oil, such as those used in immersion microscope objectives, whose refractive indices are between 1.4 and 1.85. The refractive index matching member may also include an adhesive that dries after exposure to UV rays, thereby forming a solid element.
    In the case where the laser amplifier bar 20 and the massive bar of fluorescent inorganic material have comparable crystallographic properties, it is possible to stick them by molecular adhesion; the index adaptation is then obtained without external element between the two media.
    FIGS. 3A and 3B illustrate an example of light emission module 10 according to the present description, particularly adapted to the pumping of a laser amplifier bar as shown in FIG. 2. FIGS. 3A and 3B schematically show respectively perspective and side views of the same module 10. FIG. 3C illustrates an LED submodule of which all the LEDs are formed.
    Each light emitting module 10 comprises a set of light-emitting diodes 13, or LEDs, intended to emit in a first spectral band and a light concentrator 11. In this example, the LEDs are arranged in the form of sub-modules 12, one of which example is shown in FIG. 3C.
    The light concentrator 11 is formed of a bar of fluorescent inorganic material with at least a first illumination surface 14, 14 'intended to receive the light emitted by the LEDs and an emitting surface 15 intended to emit the fluorescence light towards the solid amplification bar 20. The inorganic fluorescent material has an absorption band exhibiting a non-zero overlap with the emission spectral band of the LEDs and an emission band exhibiting a non-zero overlap with the spectral band of absorption of the bar laser amplifier. Thus, the luminous flux emitted by the LEDs and directed towards the illumination surface (s) is absorbed by the fluorescent inorganic material which in turn emits a fluorescence light collected and directed by means of a total reflection mechanism. internal to the emitting surface 15. The fluorescence light thus emitted allows pumping the laser amplifier bar 20.
    The bar of inorganic fluorescent material may be formed of a scintillator crystal type material, and for example:
    Matrices doped with cerium ions belonging to the garnets family (eg Ce: YAG, Ce: LuAG), fluorides (eg Ce: YLF, Ce: LiCAF), aluminates (eg Ce: YAP), silicates (eg Ce: LSAS, Ce: LYSO, Ce: LSO or Ce: GSO), aluminates (eg Ce: Sr3A1206), nitrides (eg Ce: LaCeSi6Nll (called Ce: LSN)), oxides (eg Ce: YAM, Y4A1209);
    Matrices doped with europium ions belonging to the fluoride family (eg Eu: CaF), garnets (eg Eu: Lu AG or Eu: YAG), silicates (eg Eu: M2SiO4 or M = Ca, Sr or Ba), sulfides (eg Eu: SrS), aluminates (eg Eu: Sr3A1206), oxides (eg Eu: SrB407), nitrides (eg Eu: SrSiO2N2);
    Therbium ion doped matrices belonging to the family of silicates (e.g. Tb: GOS); Thallium ion doped matrices belonging to the iodide family (e.g. Tl: NaI (thallium doped sodium iodide), Tl: CsI (thallium doped cesium iodide));
    Sodium ion doped matrices belonging to the iodide family (e.g. Na: CsI (sodium doped cesium iodide));
    Any previously cited template involving two of the above doping ions (e.g. Nd / Cr: YAG, Nd / Ce: YAG, Yb / Er: YAG);
    In general, any matrix, among oxides, fluorides, sulphides, nitrides, borates, silicates, aluminates, tungstates, garnets, glasses, beryllates, molybdates or even ceramics, doped with an ion or a combination of ions among the trivalent rare earth ions (such as Nd3 +, Er3 +, Ho3 +, Ce3 +, Tm3 +, Pr3 +, Gd3 +, Eu3 +, Yb3 +, Dy3 +), the divalent rare earth ions (such as Pd2 +, Mn2 +, Eu2 +, Sm2 +, Dy2 +, Tm2 +) or metal ions (such as Cr3 +, Ni2 +, Co2 +, Ti3 +, V2 +).
    The bar of inorganic fluorescent material may be formed of a material of the laser material type, for example: Ti: Sa, Ruby, Nd: YAG, Nd / Cr: YAG, Nd / Ce: YAG, CrLiSAF, Cr: LiGAF, Cr: LiCAF, Alexandrite, DCM, Emerald, materials doped with praseodymium ions such as YLF, LLF, KYF, YA10, LuAG, YAG, YAP matrices); with YV04 = Yttrium orthovanadate, YAG = Yttrium aluminum garnet, YLF = lithium yttrium fluoride, YAP = yttrium perovskite aluminum, GSO = gadolinium oxyorthosilicate, LSO = lutetium oxyorthosilicate, YAP = yttrium aluminate, BaF2 = barium fluoride, CsF = cesium fluoride.
    The crystals mentioned above are the best-known examples and / or used, but the fluorescent inorganic material may be formed of a laser material chosen from the list mentioned above with reference to the material of which the solid amplification bar is formed.
    Each sub-module of LEDs comprises in this example a subset of LEDs arranged in a matrix on a printed circuit so as to optimize the filling ratio defined here by the ratio between the cumulative emitting surface of the LEDs and the surface illuminated bar (illumination surface 14 and / or 14 '). Advantageously, the desired filling ratio is greater than 50%, advantageously greater than 60%, advantageously greater than 75%, which amounts to a filling ratio of 50% to increase the incident emittance on the illuminating surface. by a factor of 1.5.
    In the example of FIG. 3C, the LEDs are wire-wired LEDs with a gold wire soldered to the top of the LED, which brings current to the semiconductor material. Each sub-module comprises 25 LEDs, each chip is spaced 300 μm from its neighbor in one direction and 800 μm in the other.
    According to another exemplary embodiment, the LEDs may be so-called "flip chip" or "flip chip" LEDs, otherwise known as "Flip-chip" LEDs according to the English expression. In this type of LED, the light emitting surface is opposed to the wiring surface, unlike wire-wire LEDs, in which the transmitting surface and the wiring surface for welds (or contacts) are in the same direction. In Flip-chip LEDs, balls or bumps are generally used for welding to the housing, and this technology makes it possible to further increase the density of the useful emission surfaces of the T, ED on each submodule.
    The concentration factor C of the concentrator 11 can be defined as the ratio between the output emittance Eout (in W / cm2) and the incident emittance Ein (in W / cm2), where the output emittance Eout is defined by the output light power Pout emitted by the emission surface of the concentrator divided by the emission surface Sout of the concentrator (referenced 15, 15 'in the example of FIG 3A) and the incident emittance Ein is defined by the incident light power Pin emitted by the LEDs and received by the illumination surface divided by the illuminating surface Sin (referenced 14, 14 'in the example of FIG 3A) of the concentrator. In practice, because of the very small distance between the LED emission surfaces and the illuminating surface of the bar of fluorescent inorganic material, all the light power emitted by the LEDs is received by the illuminating surface and the power Incident light Pin can be determined by the cumulative optical power emitted by all LEDs.
    Thus, the concentration factor C can be defined by:
    (1) Where ηο / ο is the optical efficiency of the concentrator and G is the concentrator shape ratio defined by the ratio of illuminating and emitting surfaces. The optical efficiency ηο / ο can be expressed as the product of various parameters summarized in equation (2) below: 77o / 0 = V exc1! PLQyVtIR.V extr (2) Where r exc is the excitation efficiency of the fluorescent inorganic material (defined as the ratio between the light power absorbed by the fluorescent inorganic material and the light power Pin emitted by the LEDs); ηρυ3Υ represents the photoluminescence efficiency (or "PhotoLuminescence Quantum Yield" as the English expression); the parameter η ™ represents the total internal reflection efficiency on the faces 14 and 14 '. It is determined by the percentage of fluorescence light in total internal reflection with respect to all of the light emitted by the medium; and ηεχΐΓ is the extraction efficiency of the fluorescence light; it is determined by the percentage of light actually coming out of the concentrator by the face 15 or 15 'with respect to the quantity of light propagating in total internal reflection. The excitation efficiency η6χε takes into account both the absorption capacity of the fluorescent inorganic material and the losses at the interfaces 14 and 14 'of the incident light power. The photoluminescence efficiency qpLQY measures the percentage of retransmission of the light power absorbed. In the case of the inorganic fluorescent materials mentioned above, ηρι. <3Υ is often greater than 0.9.
    The total internal reflection efficiency ητπι depends on the critical total internal reflection angle θC according to the equation 0C = Arcsin (ne / nc), where nc is the refractive index of the concentrator at the fluorescence wavelength and is the index of refraction of the environment. All rays having an angle of incidence greater than 0C are in total internal reflection. We therefore try to reduce this angle to increase η ™. Advantageously, a fluorescent inorganic material of high nc index, greater than 1.4 and advantageously greater than 1.6, will be chosen immersed in a low index environment, such as air.
    Thus, crystals such as Ce: YAG (yttrium garnet and cerium-doped aluminum), BGO (bismuth germanate, index 2.15), CdWCL (cadmium tungstate, index 2.3), TiiAfiCL (titanium: sapphire) , Nd: YAG, Nd: YV04 and EuiSnAbOi, are particularly suitable because they have a refractive index greater than or equal to 1.7. The extraction efficiency of the fluorescence light r | Cxtr takes into account the ratio of the rays which intercept the faces 15 and 15 'with respect to all rays propagating in total internal reflection on 14 and 14'. On these rays, qextr takes into account all the losses sustained during the propagation in the concentrator: residual absorption, diffusion by defects or impurities in the matrix or exit of rays by non-useful faces, other than 14, 14 ', 15 and 15 '. Finally, qcxtr takes into account the proportion of rays coming out from the faces 15 and 15 '. To maximize qcxtr one seeks to limit the losses by propagation: thus, one can choose a fluorescent inorganic material with a very good crystalline quality and low linear losses (lower than 2.10 "2 cm" 1). Thus, crystals such as Ce: YAG (yttrium garnet and doped cerium, index 1.83), BGO (bismuth germanate, index 2.15), CdWCL (cadmium tungstate, index 2.3), ThAhCb (titanium: sapphire, index 1.76), Nd: YAG (yttrium and neodymium-doped aluminum garnet, index 1.83), Nd: YVC> 4 (neodymium-doped yttrium orthovanadate, index 2.2) and EmSnAhO6 (europium doped aluminum and strontium oxide, index 1.7) are particularly suitable.
    To maximize qextr also seeks to limit the total internal reflection on the faces 15 and 15 '. Thus, it is sought to limit the index jump between the concentrator and the laser medium.
    According to an exemplary embodiment, it is sought that the concentrator and the laser medium have the same index and are of the same physical nature in order to be bonded to one another by molecular adhesion (for example Ce: YAG for the concentrator and Nd: YAG for the laser medium).
    According to another exemplary embodiment, an index matching element as defined above can also be used to limit the index jump relative to an intermediate passage in the air.
    Applicants have shown that the output can be significantly increased between a configuration in which the concentrator is surrounded by air and a configuration in which there is index material between the concentrator and the laser bar. The increase in light emission depends on the index of the chosen concentrator, the material chosen for the refractive index matching element and the index of the chosen laser material.
    For example, in the case of Ce: YAG (index around 1.83), if using a glue of index 1.8 with a laser material index greater than 1.8 (such as NdiYVCL), the light emission at the output can be increased by a factor of 7 (neglecting the losses in the Ce: YAG), and by a factor of 5 to 6 (if they are taken into consideration).
    Thus, guided by the formulas (1) and (2), by choosing a ratio of form greater than or equal to 100, a fluorescent inorganic material of very good crystalline quality, of high index (such as Ce: YAG) and using a refractive index matching element between the concentrator and the laser medium, it is possible to obtain concentration factors greater than 50.
    In the example of FIG. 3A and 3B, the bar of fluorescent inorganic material 11 has a substantially rectangular parallelepiped shape defined by 3 dimensions, the length L which is the largest dimension of the bar, and the dimensions et and h of the faces 15, 15 'located at the ends of the bar, where £ (width) is the largest dimension of the faces 15, 15 'and h (thickness) is the smallest dimension of the faces 15, 15'.
    Alternatively, the bar of fluorescent inorganic material 11 may have a cylindrical shape for example, with faces at the ends of the bar of circular shape. This geometry makes it possible to limit the losses via the useless surfaces, other than 14, 14 ', 15 and 15'. In this case, it is possible to arrange the LEDs all around the bar to form a single illumination surface.
    According to one or more embodiments, the two faces 15 and 15 'located at the ends of bar fluorescent inorganic material 11 are emitting faces, as shown in FIG. 3B.
    Alternatively, it is possible to have a mirror or a reflective treatment at the wavelength of the fluorescence light, or more generally any system for returning the fluorescence light specularly or diffuse on one of the two faces 15 or 15 so that it has only one emitting surface, which doubles the output emittance in the case where there is an intermediate medium composed of air between the concentrator and the laser amplifier bar.
    As a general rule, the dimensions of the emitting surface 15 and / or 15 'are chosen according to the application.
    Thus, in the case of longitudinal pumping application of a laser amplifier bar, it will be sought to reduce these dimensions to correspond to the size of an intracavity laser mode, typically less than a few millimeters, preferably less than 1 millimeter. In practice, in the case of a rod of fluorescent inorganic material 11 of rectangular section, the width ε should be adapted to the size of at least one LED, typically greater than one millimeter while the thickness h can be more small, preferably less than one millimeter, even more preferably less than 500 μηι, typically less than a few hundred pm, for example of the order of a hundred pm.
    In the case of the transverse pumping application of a laser amplifier bar, it will be sought to reduce the thickness h of the bar to correspond to the dimension of an intracavity laser mode, ie typically a thickness h of between 100 μm and 2 μm. mm, advantageously between 100 pm and 1 mm. The width may be greater than in the case of longitudinal pumping. The minimum value of the width ε may be defined by the size of an LED and the maximum dimension by the growth technology of the scintillator crystal in the case where the bar of inorganic fluorescent material is formed of such a crystal. Typically, one will seek a width greater than 1 mm, preferably greater than 5 mm, preferably greater than 10 mm, which makes it possible to maximize the number of LEDs in the dimension of the width.
    In one or other of the applications (longitudinal pumping or transverse pumping), the length L of the bar of inorganic fluorescent material is chosen as large as possible to maximize the emitting surface. However, it is limited by the choice of the fluorescent inorganic material and in particular the growth technology in the case of a scintillating crystal. It is also limited by losses in the fluorescent inorganic medium. With linear losses less than 2.10 -2 cm -1, a length L greater than 100 mm, advantageously greater than 200 mm, or even greater than 300 mm will be sought, which makes it possible to maximize the number of LEDs in the dimension of the length.
    It is also possible to provide two bars of fluorescent inorganic material arranged one behind the other, or more, in order to increase the total effective length.
    In all cases, the dimensions of the bar may be adapted to maintain a high ratio between the illumination surface and the emitting surface (s), that is to say greater than or equal to 50, advantageously greater than or equal to 100.
    The choice of fluorescent inorganic material is made according to the use sought for the light emission module 10 and in particular the spectral absorption band of the laser amplifier bar 20.
    FIG. 4 thus illustrates by way of example as a function of the wavelength, the emission curve 41 of LED whose emission is centered in blue at 435 nm, the absorption curve 42 of Ce: YAG which can the bar of fluorescent inorganic material is formed, the emission curve 43 of Ce: YAG and the absorption curve 44 of the Nd: YVC> 4 of which the laser amplifying bar may be formed.
    The inventors have shown that the combined use of these 3 components, LED, fluorescent inorganic material bar in Ce: YAG and Nd: YVC> 4 laser amplifier bar made it possible to produce an LED pumped laser system.
    Moreover, thanks to the light emission module according to the present description, it is possible by adapting the luminous flux emitted by the LEDs to the illuminating surfaces of a bar made of a specific fluorescent inorganic material, to reach the thresholds of intensity of the fluorescence light allowing an amplified spontaneous emission effect (or ASE for "Amplified Spontaneous Emission" according to the English expression) at the fluorescence wavelength, in the fluorescent inorganic bar. This effect makes it possible to considerably increase the intensity of the luminous flux at the output of the emission face.
    Indeed, the stimulated emission and the spontaneous emission are in competition. The spontaneous emission (which forms the fluorescence) is characterized by a flow rate (probability per second) A, called the Einstein coefficient, equal to the inverse of the lifetime of the doping ions. The stimulated emission is characterized by a flow rate (probability per second) σ.Ι, where σ is the stimulated emission cross section of the dopant ions and I is the luminous intensity at the fluorescence wavelength, in the bar in fluorescent inorganic material.
    In order to have a significant amplified spontaneous emission, it is interesting to compare the spontaneous emission rate and the stimulated emission rate. The amplified spontaneous emission becomes significant if σ.Ι> A.
    This condition requires an incident emittance by the LEDs strong enough to obtain a sufficient signal I and a choice of laser materials such that the Α / σ ratio is as small as possible. With the power of current LEDs, the applicants have shown that it is possible to obtain amplified spontaneous emission with certain materials forming the bar of fluorescent inorganic material, for example crystals of Nd: YVO4 or Nd: YAG.
    With this effect, it is thus possible to achieve concentration factors much higher than a conventional concentrator, typically 10 to 100 times larger.
    Such a light emission module will be particularly advantageous for pumping a laser amplifier bar. It may find other applications, requiring high luminance light sources especially in the field of lighting, or spectroscopy. The set of variants concerning the choice of the fluorescent inorganic material, the shape of the bar of fluorescent inorganic material or the dimensions of the bar apply to the light emission module thus described.
    FIG. 5 illustrates another example of a laser device according to the present description.
    The laser device comprises in this example at least one light emission module 10a arranged to allow longitudinal pumping of the solid laser amplifier bar 20.
    The longitudinal pumping allows a better overlap between the pump beam and the intracavity laser mode; the pump beam is also absorbed over a greater distance, which increases the absorption of the pump beam.
    The laser amplifier bar is arranged in a cavity formed by a cavity bottom mirror 21 and an exit mirror 22. The cavity bottom mirror 21 is in this example a dichroic mirror (or a treatment deposited on one side of the laser amplifier bar) adapted to pass the pump beam, that is to say in this example the light beam from the transmission module 10A, and reflect the light flux at the laser emission wavelength . As in the example of FIG. 2, an index matching element 30 allows an adaptation of the refractive index between the light emitting module 10a and the laser amplifier bar 20.
    In this example, the emitting surface (not shown in FIG 5) of the light emitting module 10a is advantageously smaller than the input face of the amplifier bar so that all the flux emitted by the transmission module 10a is useful for pumping the laser bar. Advantageously, the emitting surface thus covers less than 100%, advantageously less than 80% of the input face of the laser amplifier bar.
    Advantageously, as illustrated in FIG. 5, the laser device comprises two light emitting modules 10a, 10b or more, aligned one behind the other and advantageously separated by an adaptation element of the refractive index 30.
    The inventors have shown experimentally that putting two bars of fluorescent inorganic material one behind the other makes it possible to remarkably increase the concentration factor C (experimentally, an increase in the concentration factor of a ratio greater than 1.5 was obtained). It is observed that positioning two bars one behind the other is more effective than using a single bar with a reflective element at the fluorescence wavelength on a face 15 '. Advantageously, it will be possible to arrange two bars of fluorescent inorganic material one behind the other, for example two identical bars with optimized dimensions. The concentration factor can be further increased with a reflective element at the fluorescence wavelength positioned at the end of the second bar. Other configurations of longitudinal and / or transverse pumping by means of light emitting modules according to the present description are of course possible.
    FIG. 6 thus illustrates a laser device comprising a laser amplifier bar 20 arranged in a cavity (21, 22) and comprising both longitudinal and transverse pumping by means of light emission modules 10a-10j according to the present description.
    Advantageously, a refractive index matching element 30 may be arranged between each of the transmission modules in contact with the laser amplifier bar and said transmission module and between two light emission modules.
    As previously explained, two bars of fluorescent inorganic material can advantageously be arranged one behind the other, or more preferably, the number being limited by considerations of spatial space and losses.
    Moreover, the number of light emission modules in contact with the laser amplifier bar for transverse pumping is limited only by the size of the laser amplifier bar.
    FIGS. 7A and 7B show laser device variants with respectively a linear cavity and a ring cavity. In the example of FIG. 7A (linear cavity), there are two mirrors 21, 22. In the example of FIG. 7B (ring cavity), there are 2 laser beams output. In these configurations, the signal propagates by total internal reflection in the laser amplifier bar 20, limiting the losses at each reflection on the interfaces of the crystal forming the laser amplifier bar. The polygon structure with N sides, allows to pump by more than 2 sides. Moreover, in the case where the optical axis is not in the plane of the crystal, one can increase the thickness of the latter to obtain greater gains.
    In both cases, the pumping is transverse and carried out by means of light emission modules 10a-10j.
    In these configurations, there are no matching elements between the light emission modules and the laser crystal 20 so as not to frustrate the total internal reflection in the crystal 20. The light emission modules are distant from the each other, limiting congestion problems. The thickness of the laser device thus obtained is small (typically of the order of 1 mm for example), which allows the crystal 20 to be effectively cooled.
    As illustrated in FIGS. 7A and 7B, it is possible to arrange light emitting modules one behind the other, with an element 30 for matching the refractive index between the modules.
    First experimental results have been validated by the applicants with a laser device, a diagram of which is shown in FIG. 8. FIG. 8 illustrates a side view of the laser device, the laser signal being emitted upwards.
    In this example, the laser amplifier bar 20 is a crystal of Nd: YVC> 4 doped 1 at.%, Of dimensions 2x2x20 mm3, polished on 2 lateral faces, the two others are frosted. The laser faces are anti-reflective (AR) treated for one, and highly reflective (HR) for the other, all at the laser wavelength (1064 nm). The orientation of the crystal is called "a-cut", that is to say that it is oriented so that the axis c is perpendicular to the axis of laser propagation. The laser cavity is plano-concave. The cavity bottom mirror 21 is provided by the HR treatment of the crystal and the output coupler 22 (partially transparent mirror) is concave (with a radius of curvature that can vary between 100 mm and 500 mm). The reflectivity of the output coupler can vary from the RH (reflection higher than 99.5%) to 20% transmission at the laser emission wavelength. The cavity length of 22 mm (approximately the length of the crystal) can be varied to a little less than the radius of curvature of the output coupler (using a coupler with a radius of curvature of 500 mm, the cavity can be stable up to a length of about 500 mm).
    The light emission module 10 comprises a bar of fluorescent inorganic material 11 of Ce: YAG of dimensions 1x9x100 mm3 to form the light concentrator. All its faces are polished so as to guarantee total internal reflection. One of the two polished lateral faces of the laser amplifier bar 20 (2 × 20 mm 2) is glued by means of the matching element 30 (UV glue having an optical index estimated between 1.5 and 1.6) to one both sides of the bar of inorganic material 11 (1x9 mm2) In this way, the light concentrator pumps the laser crystal transversely over a large part of its length. With the adaptation element 30, the concentration factor is estimated to be 20.
    The light emission module 10 also comprises a set of LEDs 13, arranged in the form of fourteen modules 12 of 25 LEDs each (only one line of 6 modules is shown in FIG 8 for the sake of clarity), arranged on the basis of FIG. and the other of the bar made of inorganic material 11, making it possible to obtain 350 LEDs on the module 10. The LEDs are powered and controlled by electronic cards making it possible to deliver to the LEDs electrical pulses of variable duration (5 μs, 100 μs). s, 1 ms and 3 ms) as well as variable electric currents (several current calibres between 3 A and 4 A). An external trigger sets the repetition frequency of the LEDs. The concentrator is sandwiched on both sides with the subsets of LEDs 12, the subsets being brought closer together. Everything is in a mechanical pumping head for mechanical maintenance.
    The LED panels and the concentrator can be cooled (or not) separately (or not) by means of a circulation of water indicated by the arrows A and B.
    FIGS. 9A and 9B respectively show the laser energy and the small signal gain obtained by means of a laser device as shown in FIG. 8, depending on the energy emitted by the LEDs. The energy curves are obtained using an XPL-12 thermal power meter from Gentec®.
    More specifically, FIG. 9A represents curves 91, 92, 93, 94 showing the output energy of the laser (which exits through the output coupler, the partially transparent mirror) as a function of the energy emitted by the LEDs, for different transmissions of the couplers output, respectively 1%, 2%, 3% and 5%.
    FIG. 9B represents the energy of the LEDs necessary to reach the laser threshold (which depends on the transmission of the coupler used, indicated in percentages in FIG 9B). The more transparent the coupler is, the more losses it introduces and therefore the higher the threshold. These first experimental results show that it is possible to make a laser device with a coupler having a transmission of 20%.
    Although described through a number of detailed exemplary embodiments, the laser device and the laser emission method described above include various alternatives, modifications, and enhancements which will be apparent to those skilled in the art, it being understood that these various variants, modifications and improvements fall within the scope of the invention, as defined by the following claims.
    权利要求:
    Claims (13)
    [1" id="c-fr-0001]
    A laser device comprising: a solid laser amplifier bar (20) having an absorption spectral band in the visible-near-infrared spectral band; at least one first light emitting module (10a-10d) for pumping the solid laser amplifying bar, each light emitting module comprising a set of light-emitting diodes (LEDs) for emitting a luminous flux in a first spectral band and a light concentrator, the light concentrator comprising: a solid bar (11) of fluorescent inorganic material with at least a first illumination surface (14, 14 ') for receiving the light emitted by the LEDs and an emitting surface (15, 15 ') for emitting the fluorescence light towards the solid laser amplifying bar, and wherein: the fluorescent inorganic material has an absorption band having a non-zero overlap with the emission spectral band of the LEDs and an emission band having a non-zero overlap with the spectral absorption band of the laser amplifier bar; and o the ratio of the illuminating surface to the emitting surface is greater than or equal to 100.
    [2" id="c-fr-0002]
    2. Laser device according to claim 1, comprising at least a first light emitting module arranged for the longitudinal pumping of the solid laser amplifier bar, a transmitting face of said first laser emission module being in contact with an input face of solid laser amplifier bar.
    [3" id="c-fr-0003]
    3. Laser device according to claim 2, wherein the emitting face of said first longitudinal module is smaller than said input face of the laser amplifier bar.
    [4" id="c-fr-0004]
    4. Laser device according to any one of the preceding claims, comprising at least a first light emitting module arranged for transverse pumping of the solid laser amplifier bar.
    [5" id="c-fr-0005]
    5. Laser device according to any one of the preceding claims, comprising at least a second light emitting module, arranged in alignment with the first light emitting module.
    [6" id="c-fr-0006]
    6. Laser device according to any one of the preceding claims, comprising a refraction index matching element arranged between each light emission module and the laser amplifier bar and / or between two light emitting modules arranged in the alignment of each other.
    [7" id="c-fr-0007]
    Laser device according to any of the preceding claims, wherein the fluorescent inorganic material is yttrium garnet and cerium-doped aluminum (Ce: Y AG).
    [8" id="c-fr-0008]
    8. Laser device according to any one of the preceding claims, wherein the LEDs are "Flip-chip" LEDs.
    [9" id="c-fr-0009]
    9. Laser device according to any one of the preceding claims, wherein the filling rate of the LEDs defined by the ratio between the cumulative emission area of the LEDs and the illumination surface is greater than 50%, preferably greater than 60. %, advantageously greater than 75%.
    [10" id="c-fr-0010]
    10. Laser device according to any one of the preceding claims, wherein the set of light-emitting diodes (LEDs) are intended to emit a light flux of optical power sufficient to trigger a wavelength amplified spontaneous emission process. fluorescence, in the fluorescent inorganic bar.
    [11" id="c-fr-0011]
    A laser emission method comprising: emitting a light flux by means of at least a first light emitting module, each light emitting module comprising a set of light-emitting diodes (LEDs) emitting in a strip given emission spectral and light concentrator, the light concentrator comprising: a bar of fluorescent inorganic material with at least a first illumination surface receiving the light emitted by the LEDs and an emitting surface emitting a fluorescence light to a solid amplifying bar, and wherein: the fluorescent inorganic material has an absorption band having a non-zero overlap with the emission spectral band of the LEDs and an emission band exhibiting a non-zero overlap with the spectral band of absorption of the laser amplifier bar; and o the ratio of the illuminating surface to the emitting surface is greater than or equal to 100; The pumping of the solid laser amplifier bar by means of the luminous flux emitted by the light emission module.
    [12" id="c-fr-0012]
    The laser emission method according to claim 11, wherein: the optical power of the light flux emitted by the LEDs and received by the first illumination surface is sufficient to trigger a wavelength amplified spontaneous emission process. fluorescence, in the fluorescent inorganic bar.
    [13" id="c-fr-0013]
    A light emitting module for high emittance emission in a given output emission spectral band, comprising: a set of light-emitting diodes (LEDs) for emitting in a first emission spectral band a luminous flux of given optical power; and a light concentrator, comprising: a solid bar of fluorescent inorganic material with at least a first illuminating surface for receiving the luminous flux emitted by the LEDs and an emitting surface for emitting the fluorescence light, and wherein the fluorescent inorganic material has an absorption spectral band exhibiting a non-zero overlap with the emission spectral band of the LEDs; the ratio between the illuminating surface and the emitting surface is greater than or equal to 100; and o the optical power of the luminous flux that all the LEDs are intended to emit is sufficient to trigger an amplified spontaneous emission process at the fluorescence wavelength, in the fluorescent inorganic bar.
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    同族专利:
    公开号 | 公开日
    FR3045965B1|2018-05-11|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    US20050063197A1|2003-08-07|2005-03-24|Nightingale John L.|System and method utilizing guided fluorescence for high intensity applications|
    US20150303641A1|2014-04-17|2015-10-22|Colorado School Of Mines|Led pumped laser device and method of use|WO2022008310A1|2020-07-07|2022-01-13|Centre National De La Recherche Scientifique|3d concentrator|
    FR3108798A1|2020-03-24|2021-10-01|Centre National De La Recherche Scientifique|T-shaped laser pumping device|
    WO2021191221A1|2020-03-24|2021-09-30|Centre National De La Recherche Scientifique|T-shaped laser pumping device|
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    2016-12-16| PLFP| Fee payment|Year of fee payment: 2 |
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    2017-12-08| PLFP| Fee payment|Year of fee payment: 3 |
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    2021-09-10| ST| Notification of lapse|Effective date: 20210806 |
    优先权:
    申请号 | 申请日 | 专利标题
    FR1562823A|FR3045965B1|2015-12-18|2015-12-18|CONCENTRATED LIGHT EMITTING MODULE AND LASER DEVICE USING SUCH A MODULE|
    FR1562823|2015-12-18|FR1562823A| FR3045965B1|2015-12-18|2015-12-18|CONCENTRATED LIGHT EMITTING MODULE AND LASER DEVICE USING SUCH A MODULE|
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