Assembly of luminescent light concentrators, light emission device and method for generating an output beam with a broad spectrum

Abstract

A set of luminescent light concentrators for broad-spectrum emission intended to be pumped by pump radiation having a pump wavelength and comprising: a first luminescent light concentrator (C1), the first concentrator being in a first material adapted to absorb said pump radiation and then emit a first luminescent radiation (L1) having a first central emission wavelength within said first concentrator; a second luminescent light concentrator, attached to the first concentrator, in a second material adapted to absorb said pump radiation and then emit a second luminescent radiation (L2) having a second central emission wavelength greater than the first wavelength within said second concentrator; a third luminescent light concentrator, attached to the second concentrator.in a third material adapted to absorb said pump radiation and then emit a third luminescent radiation (L3) having a third central emission wavelength greater than the second wavelength within said third concentrator, such that said set of concentrators is adapted to emit, through the first output face, an outgoing light emission having the first, second and third central emission wavelengths and formed from a portion of the first, second and third luminescent radiation when the first, second and third luminescent light concentrators absorb said pump radiation. [Fig. 3A]

Description

Title of the invention: Luminescent light concentrator assembly, Light emitting device and Method for generating an output beam with a broad spectrum Technical field

[0001] The present invention relates to the field of luminescent concentrators pumped by a laser source. Prior art

[0002] Luminescent concentrators are light sources combining both high power and high luminance. They are optically pumped materials cut into a parallelepiped shape. They are polished on all faces to allow total internal reflections which will guide the light emitted by the phosphors to the output face.

[0003] It is known from the prior art to carry out the optical pumping of a concentrator by a set of LEDs (see for example Barbet, Adrien, et al. "Light-emitting diode pumped luminescent concentrators: a new opportunity for low-cost solid-state lasers." Optica 3.5 (2016): 465-468.). This configuration is illustrated in [Fig.lA] in which a light emission module ME0 is shown comprising a set of LEDs intended to emit in a given spectral band and a light concentrator CL.

[0004] The concentrator CL is a fluorescent parallelepiped crystal, having at least one illumination face SU, SI2, of dimensions LX w, illuminated by the electroluminescent radiation Ld emitted by the LEDs. The illumination faces SU, SI2 are also called “large faces”. The thickness of the concentrator is noted e.

[0005] The concentrator crystal is configured to absorb said electroluminescent radiation Ld. The luminous flux emitted by the LEDs is directed towards the illumination face. It is absorbed by the phosphors Lum of the fluorescent crystal which are distributed throughout the volume of the crystal and which then emit fluorescence radiation inside the crystal. The emitted rays can be classified into two main categories - trapped rays denoted Lp: these rays are trapped in the crystal due to total internal reflection (TIR) ​​on the different faces of the crystal. These rays exist if the crystal is a parallelepiped with 6 faces parallel in pairs and perpendicular to each other. The trapped rays never leave the crystal, apart from imperfections in the latter. - untrapped rays are the rays that eventually exit the crystal. They are separated into two subcategories: guided rays noted Lg whose characteristic is to be guided by RTI and to exit on one of the faces of the concentrator and unguided rays noted Lout which exit directly from the concentrator without being reflected on the faces.

[0006] For example, the CL concentrator is a fluorescent crystal in the visible (red-orange) like Ce:YAG which absorbs in the blue (around 450 nm), at a wavelength where LEDs are very efficient. The crystal is cut in the form of a plane, lined with hundreds (or even thousands) of LEDs on the two large surfaces and with emission by the edges. These concentrators make it possible to obtain luminance values ​​10 to 20 times higher than that of an LED.

[0007] [Fig.lB] is a representation of the angular diagram of the rays emitted and trapped in the concentrator. The dark caps represent the angles corresponding to the untrapped rays (guided and unguided) and the light areas represent the angles corresponding to the trapped rays. In this representation given as an example, the medium chosen as the concentrator crystal CL is a Ce:YAG crystal (index n2=1.82) having a critical angle of 33° when the ambient medium is air. The percentage of radiation trapped by RTI compared to the untrapped radiation is fixed by the index of the crystal and that of the ambient medium by the Snell-Descartes law.

[0008] Generally speaking, obtaining light emission with a broad spectrum is useful for applications in spectroscopy or pyrometry. However, the light emission of luminescent concentrators is intrinsically spectrally limited by the spectral emission band of their phosphors. For example, fluorescent plastics emit in spectral bands of the order of a few tens of nm at mid-height only in the visible spectrum.

[0009] To obtain a light emission with a large spectral width, it is known to use several luminescent light concentrators as illustrated in Figure 1A, arranged according to the configuration of Figure 2. In the illustration of Figure 2, three concentrators CL1, CL2 and CL3 are arranged side by side and each emit a luminescent emission LGi, LG2, LG3 respectively centered on a central wavelength λ2, 23 different from the other central wavelengths. This configuration is called "transverse assembly". To obtain a broadband emission, it is then necessary to spatially combine the luminescent emissions LGi, LG2, LG3 to form a multi-spectral final beam (see for example patent application WO 2017 / 097762 A1). In reality, the three concentrators CL1, CL2 and CL3 each behave like an individual light pixel.This solution has the disadvantage of requiring an optical mixing device to carry out the combination of the luminescent emissions Ld, LG2, LG3 (not shown in [Fig.2]). In addition, these optical mixing devices introduce spatial inhomogeneities between . the colors in the output beam.

[0010] The invention aims to provide a broadband source using a set of luminescent concentrators which does not require a device external to the concentrators to combine the different wavelengths and with which a light emission is obtained having spatial homogeneity of the distribution of the different wavelengths.

[0011] For this purpose, the invention relates to a set of luminescent light concentrators comprising at least a first, a second and a third concentrator adapted to be optically pumped by a pump wavelength so as to respectively generate a first, a second and a third luminescent radiation having respectively a first, a second and a third central emission wavelength. The concentrators are made of materials adapted so that the set of light concentrators can emit, through a first output face of the first concentrator, an outgoing light emission having the first, the second and the third central wavelength when the first, the second and the third luminescent light concentrator absorb the pump radiation.

[0012] In the configuration of the invention, the set of concentrators allows a spatially homogeneous broadband emission of which several characteristics (duration, spectrum, luminance, geometric extent) are easily controllable. Summary of the invention

[0013] For this purpose, an object of the invention is a set of luminescent light concentrators for broad spectrum emission intended to be pumped by pump radiation having a pump wavelength and comprising: - a first luminescent light concentrator having a first output face, the first concentrator being made of a first material adapted to absorb said pump radiation and then emit a first luminescent radiation having a first central emission wavelength within said first concentrator, - a second luminescent light concentrator, attached to the first concentrator, in a second material adapted to absorb said pump radiation then emit a second luminescent radiation having a second central emission wavelength 22 greater than the first wavelength within said second concentrator, - a third luminescent light concentrator, attached to the second concentrator, in a third material adapted to absorb said pump radiation and then emit a third luminescent radiation having a third central emission wavelength 43 greater than the second wavelength within said third concentrator, the second material being such that the second concentrator has a transmission coefficient greater than 50% for the third luminescent radiation, and the first material being such that the first concentrator has a transmission coefficient greater than 50% for the third luminescent radiation and for the second luminescent radiation so that said set of concentrators is adapted to emit, through the first output face, an outgoing light emission having the first, second and third central emission wavelengths and formed from a portion of the first, second and third luminescent radiation when the first, second and third luminescent light concentrator absorbs said pump radiation.

[0014] According to an embodiment of the whole of the invention, a first spectral range of transparency of the first material associated with said outgoing light emission comprises a second spectral range of transparency of the second material associated with said outgoing light emission which itself comprises a third spectral range of transparency of the third material associated with said outgoing light emission.

[0015] According to an embodiment of the whole of the invention, an absorption coefficient of the second material for the first central emission wavelength and an absorption coefficient of the third material for the second central emission wavelength 22 is greater than 5 cmA and preferably greater than or equal to 10 cm-[

[0016] According to an embodiment of the assembly of the invention, the assembly comprises a fourth luminescent light concentrator attached to the first concentrator by its first output face, the fourth concentrator having a second output face and being made of a fourth material suitable for: - absorbing said pump radiation or additional pump radiation having an additional pump wavelength ^p' less than said pump wavelength then - emitting a fourth luminescent radiation having a fourth central emission wavelength ^4 lower than the first wavelength within said fourth concentrator, the fourth material being such that the fourth concentrator has a transmission coefficient greater than 50% for the first, second and third luminescent radiation, so that said light concentrator assembly is adapted to emit, through the second output face, a secondary light emission having the first, second, third and fourth wavelength when the first, second, third and fourth luminescent light concentrator absorbs said pump radiation and / or the additional pump radiation.

[0017] Another object of the invention is a light emission device comprising: - a laser source adapted to generate an incident laser beam, - an optical pumping cavity comprising at least one opening so that the incident beam can pass through said at least one opening and form said pump radiation by reflection and / or diffusion within the optical pumping cavity, - a set of luminescent light concentrators according to the invention arranged in the optical pumping cavity and such that the first, second and third luminescent light concentrators are capable of absorbing said pump radiation and then said set of luminescent light concentrators emits said outgoing light emission.

[0018] According to one embodiment, the light emission device of the invention comprises a non-imaging optical device attached to the first output face or the second output face in order to collect rays by reducing a solid angle of said outgoing light emission or said secondary light emission so as to form an output beam having the first, second and third wavelength or having the first, second, third and fourth wavelength.

[0019] According to an embodiment of the light emission device of the invention, the laser source operates in pulsed mode delivering pulses of duration tp, and in which the first luminescent radiation has a first lifetime Ti, the second luminescent radiation has a second lifetime r2, and the third luminescent radiation has a third lifetime ' 3, and in which r^> T2<> sirp <T^ r2, ou dans lequel Tp 2, ^3. De manière préférentielle, le premier matériau est adapté pour qu’il existe une fenêtre temporelle d’une durée prédéterminée supérieure à 5 ns dans laquelle une répartition d’une intensité de la première, de la deuxième et de la troisième longueur d’onde dans ladite émission sortante est constante, pour une intensité de ladite émission sortante supérieure à 20% d’une intensité maximale de ladite émission sortante supérieure obtenue pendant une impulsion de durée tp

[0020] According to an embodiment of the light emission device of the invention, a reflection coefficient of walls of the optical pumping cavity is greater than 90% for the first central emission wavelength 2] and the second wavelength central emission wave d2.

[0021] According to one embodiment of the light emission device of the invention, the optical pumping cavity comprises a diffusing medium arranged between reflective walls of the optical pumping cavity so that the incident beam can pass through said at least one opening and form said pump radiation by reflection on the reflective walls and by diffusion within the diffusing medium. Preferably, the optical pumping cavity comprises a first opening adapted to be traversed by the incident beam, and a second and a third opening connected by a channel arranged in the diffusing medium, said set of luminescent light concentrators being arranged within the channel which is adapted to allow circulation of a fluid making it possible to cool said set of luminescent light concentrators when it absorbs said pump radiation.More preferably, the device comprises a first light converter element arranged in the optical pumping cavity and adapted to absorb said pump radiation and / or the incident beam and then emit so-called complementary pump radiation having the fourth central emission wavelength, an absorption coefficient of the first, second and third material for the fourth central emission wavelength / 4 associated with the first, second and third luminescent radiation respectively being greater than 5 cm1 so that the first, second and third concentrator absorb the complementary pump radiation and then emit the first, second and third luminescent radiation respectively.

[0022] According to an embodiment of the light emission device of the invention, the laser source is adapted to simultaneously generate said incident beam having the pump wavelength λp and an additional incident beam having the additional pump wavelength λP', and the optical pump cavity comprising a first opening adapted to be crossed by the incident beam and a first additional opening adapted to be crossed by the additional incident beam so as to form, by reflection and / or diffusion within the optical pump cavity, said additional pump radiation then being absorbed by the fourth concentrator.

[0023] According to an embodiment of the light emission device of the invention, TP < TY r2- t3 and T} > T2 > T2 and in which the incident beam does not comprise the pump wavelength ^P but has an additional pump wavelength A / \c device then comprising a second light converter element arranged in the optical pump cavity between the channel and the diffusing medium and adapted to absorb the incident beam then emit an intermediate incident beam having the pump wavelength, said intermediate incident beam forming said pump radiation by reflection and / or diffusion within the optical pump cavity. Preferably, the optical pump cavity is separated into a first and a second chamber, the first chamber comprising the first opening adapted to be crossed by a first portion of the incident beam and comprising the first, second and third concentrator and comprising the second light converter element, the second chamber comprising a first additional opening adapted to be crossed by a second portion of the incident beam and comprising the fourth concentrator and not comprising the second light converter element.

[0024] According to an embodiment of the light emission device of the invention, the optical pumping cavity diffusely reflects a percentage greater than or equal to 90% of the incident radiation and has a reflection coefficient greater than 90%, preferably greater than 95% for the incident radiation. Preferably, a surface of the optical cavity where the incident radiation is reflected is made of spectralon or polytetrafluoroethylene.

[0025] According to one embodiment of the light emission device of the invention, the laser source and the optical pumping cavity are adapted so that a fluence of the pump radiation within the light concentrator is less than 5 J / cm2, preferably less than or equal to 1 J / cm2.

[0026] Another object of the invention is a method for generating an output beam with a broad spectrum with a set of luminescent light concentrators according to the invention, said method comprising the following steps: - generating a laser beam called an incident beam with a laser source, - directing the incident beam through at least one opening formed in an optical pump cavity adapted to form said pump radiation by reflection and / or diffusion of the incident beam within the optical pump cavity, - absorbing said pump radiation with said set of concentrators arranged in the optical pumping cavity so as to emit said outgoing light emission through the first output face, - collecting rays from said outgoing light emission by reducing a solid angle associated with the outgoing light emission so as to form an output beam. Brief description of the drawings

[0027] Other characteristics, details and advantages of the invention will emerge from reading the description given with reference to the appended drawings given by way of example and which represent, respectively:

[0028] [Fig.lA] a schematic view of an example of a light emission module known from the prior art,

[0029] [Fig.lB] a representation of the rays emitted in a luminescent concentrator, known from the prior art,

[0030] [Fig.2], a schematic view of an example of a light emitting module broad spectrum known from the prior art,

[0031] [Fig.3A], a schematic view of a set of concentrators according to the invention,

[0032] [Fig.3B], a schematic perspective view of the first concentrator only of the set of concentrators according to the invention,

[0033] [Fig.4A], three emission spectra associated respectively with the first, the second and to the third luminescent radiation emitted respectively by the first, the second and the third material of the assembly according to the invention

[0034] [Fig.4B], a comparison of the absorption band of the first material according to the example of [Fig.4A] and the associated emission spectrum on the one hand, and the absorption band of the third material and the associated emission spectrum according to the example of [Fig.4A] on the other hand,

[0035] [Fig.4C], the transmission curve as a function of the wavelength of the first, of the second and third material according to the example of [Fig.4A] respectively,

[0036] [Fig.5A], an example of a spectrum emitted by an assembly according to the invention illustrated in [Fig.5B] and comprising four luminescent concentrators

[0037] [Fig.5C], a comparison of the four absorption bands, of the first, of the second, of the third material and the fourth material according to the example of [Fig.5A]

[0038] [Fig.6], a schematic view of a light emitting device according to the invention comprising the assembly according to the invention, optically pumped by a laser source via an optical pumping cavity,

[0039] [Fig.7], a schematic view of a light emitting device according to the invention comprising a diffusing pumping cavity of cylindrical shape of length adapted to the length of the assembly according to the invention

[0040] [Fig.8], a schematic view of a light emitting device according to a mode of embodiment of the invention with a non-imaging extractor device at the output,

[0041] [Fig.9], a schematic view of a light emitting device according to a mode of realization of the invention

[0042] [Fig. 10], a schematic view of a light emitting device according to one embodiment of the invention

[0043] [Fig. 11], a schematic view of a light emitting device according to one embodiment of the invention

[0044] In the figures, unless otherwise indicated, the elements are not to scale. Description of the embodiments

[0045] Figure 3A shows a schematic side view of a set 1 of concentr luminescent light transformers according to the invention. The assembly 1 according to the invention is intended to be optically pumped by pump radiation RP having a pump wavelength by means which will be detailed later in the description of [Fig.6].

[0046] As will be explained later, the assembly 1 comprises three luminescent light concentrators C1, C2 and C3 making it possible to obtain an outgoing light emission Lout having a broad, spatially homogeneous spectrum over the entire surface of the output face and this without requiring optical elements external to the assembly 1 to achieve the combination of the different wavelengths. This configuration is called “longitudinal assembly” as opposed to the “transverse assembly” configuration illustrated in FIG. 2 because, in the invention, a portion of the radiation forming the outgoing light emission Lout passes through the assembly 1 along its total length Lct.

[0047] The first concentrator Cl is in a first material comprising phosphors Lum adapted to absorb the pump radiation RP then to emit the first luminescent radiation Li having a first central emission wavelength within the first concentrator. L denotes the lifetime of the luminescent radiation Li and a face of the first concentrator Cl through which the outgoing light emission Lout having a broad spectrum is emitted is called the first output face FS1.

[0048] [Fig. 3B] illustrates a schematic perspective view of the first concentrator C1 only, when it is optically pumped. As a non-limiting example, in the embodiment of [Fig. 3B], the first concentrator C1 is a rectangular parallelepiped of length Lci, width Wi and thickness ei having two large faces FE1, FE2 and four lateral faces FS1, FC, FL1, FL2.

[0049] As mentioned above, in a manner known per se, a portion LSi of the luminescent radiation Li passes through the first output face FS1 of the first concentrator CL. This portion Lsi comprises the guided portion reflected on the faces of the concentrator and the unguided portion associated with the first output face FS1 passing directly through the latter, without being reflected on the faces of the concentrator.

[0050] As illustrated in Figure 3A, the second concentrator C2 is attached to the first concentrator CL. The second concentrator C2 is in a second material adapted to absorb the pump radiation and then emit the second luminescent radiation L2 having a second central emission wavelength 2? within the second concentrator. We note r2 the lifetime of the second luminescent radiation L2. This second central emission wavelength 22 is greater than the first wavelength / ½ in order to allow the transmission of a portion LS2 of the second luminescent radiation L2 towards the first concentrator.

[0051] For example, the concentrators C1 and C2 are joined by means of an optical glue having a refractive index which is adapted to maximize the extraction of the second luminescent radiation and its transmission from the second concentrator C2 to the first concentrator C1.

[0052] Finally, the assembly 1 comprises the third concentrator C3 attached to the second concentrator. The third concentrator C3 is made of a third material suitable for absorbing the pump radiation and then emitting the third luminescent radiation L3 within the third concentrator. The lifetime of the third luminescent radiation L3 is noted. The third luminescent radiation L3 has a third central emission wavelength ^3 greater than the second wavelength in order to allow the transmission of a portion Ls3 of the third luminescent radiation L3 to the second concentrator.

[0053] For example, the concentrators C2 and C3 are joined by means of an optical glue having a refractive index which is adapted to maximize the extraction of the third luminescent radiation and its transmission from the third concentrator C2 to the second concentrator C2.

[0054] Preferably, the first and second materials are such that > 5¾ in order to ensure minimal absorption of the second wavelength by the first concentrator CL Similarly, preferably, the second and third materials are such that in order to ensure minimal absorption of the third wavelength by the first second concentrator C2.

[0055] In order to allow the formation of an outgoing light emission Lmtt having a broad, spatially homogeneous spectrum over the entire surface of the first output face FS1, the second material is such that the second concentrator has a transmission coefficient T23 greater than 50% (and preferably greater than 90%) for the third luminescent radiation. This transmission coefficient T23 is calculated for a “longitudinal” crossing of the second concentrator by the third luminescent radiation along its length Cc2 (i.e. from the third concentrator to the first along the direction 3' in FIG. 3A). Thus, a portion of the outgoing emission Ls3 emitted by the third concentrator will be transmitted by the second concentrator to the first concentrator.

[0056] In addition, the first material is such that the first concentrator has a transmission coefficient Ti3 greater than 50% (and preferably greater than 90%). for the third luminescent radiation and a transmission coefficient Tn greater than 50% (and preferably greater than 90%) for the second luminescent radiation. Here again, the transmission coefficient Ti3 is calculated for a “longitudinal” crossing of the first concentrator by the third luminescent radiation along its length Lc} (i.e. from the second concentrator to the first then through the first output face FS 1 along the direction y in Figure 3A). Thus, a portion of the outgoing emission Ls3 emitted by the third concentrator will be transmitted by the first concentrator through the first output face FS1 in the outgoing light emission LMlt.

[0057] Similarly, the transmission coefficient Tn is calculated for a “longitudinal” crossing of the first concentrator by the second luminescent radiation along its length Lcr so that a portion of the outgoing emission Ls2 emitted by the second concentrator is transmitted by the first concentrator through the first output face FS1 in the outgoing light emission Lout.

[0058] The set 1 of concentrators of the invention is therefore adapted to emit, through the first output face FS1, an outgoing light emission Lmi( formed from a portion of the first, second and third luminescent radiation when the first, second and third luminescent light concentrator absorbs the pump radiation. This outgoing light emission Lûut has the first, second and third central emission wavelength. Thus, the invention makes it possible to combine the first, second and third material so that the outgoing light emission Loul is spectrally homogeneous over the entire surface of the face FS1 exiting the source (Fig. 5). The third wavelength emitted by the third concentrator then perfectly overlaps the other wavelengths and ^1 emitted by the two other concentrators C2 and Cl encountered successively.

[0059] As a non-limiting example, [Fig.4A] illustrates three emission spectra SE1, SE2 and SE3 associated respectively with the first, second and third luminescent radiation emitted respectively by the first, second and third materials which are fluorescent plastics emitting on spectral bands of the order of a few tens of nm at mid-height in the red, blue and green respectively.

[0060] The assembly of set 1 must take into account the spectral positions of the emission and absorption bands of the fluorophores. To illustrate this point, [Fig.4B] compares on the one hand the absorption band BAI of the first material according to the example of [Fig.4A] and the associated emission spectrum SE1, and on the other hand the absorption band BA3 of the third material and the associated emission spectrum SE3 according to the example of [Fig.4A].

[0061] [Fig.4B] shows that it is possible to select fluorescent media having overall only one absorption band. Taking into account the energy levels of the molecules (or atoms) considered, all wavelengths greater than those in the absorption band will be transmitted without being absorbed. This is true as long as the matrix comprising the fluorophores does not absorb, which is the case for PMMA-type plastics in the visible range for example.

[0062] Furthermore, [Fig.4B] illustrates that, for a given material, the emission band and the absorption band are always very close to each other spectrally. For example, they are separated by about 20 nm to 40 nm for fluorescent plastics emitting in the visible. Depending on the materials, it is the "absorption-emission" ensemble which shifts as observed in [Fig.4B] between the absorption band BAI of the first material and the associated emission spectrum SE1 and the absorption band B A3 of the third material and the associated emission spectrum SE3.

[0063] Finally, the absorption and emission bands are often slightly overlapped, which creates an effect called "reabsorption".

[0064] It is understood that the placement of the materials relative to each other in set 1 is a function of their emission spectrum and their absorption band. For simplicity, an emission spectrum is characterized by its central emission wavelength noted [Fig.4C] illustrates the transmission curve CTI, CT2, CT3 as a function of the wavelength of the first, second and third material according to the example of [Fig.4A] respectively. The transparency range of each luminescent material is defined by two limits as illustrated in [Fig.4C]: - an upper limit formed by a wavelength of interest noted 2max which corresponds to the highest wavelength desired in the spectrum of the outgoing light emission, and - a lower limit, noted 4râ 6 which corresponds to the wavelength for which the transmission of the material is equal to 90% of the value of 2max. Thus, for shorter wavelengths the material becomes absorbent.

[0065] We recall that > ​​4»« z, and that these two quantities are quite close.

[0066] It is possible to find media which remain totally transparent for wavelengths greater than 4»n / ,. Thus, the transparency ranges of the different media to be considered all have the same which depends on the device.

[0067] As observed in Figure 4C, in set 1 of the invention, the transparency spectral ranges are included in each other in order to allow a broad spectrum emission: [;Wn3, lmax] c 4^] C [4,^, Xmax\. In other words, in set 1 of the invention, a first spectral range [4w«l' ^ma>•] of transparency of the first material associated with the outgoing light emission comprises a second spectral range Àmax ] of transparency of the second material associated with the outgoing light emission which itself comprises a third spectral range [2miw3, of transparency of the third material associated with the outgoing light emission.

[0068] As ^3 > ^mzrt3, then is in the transparency band of the third material but also necessarily in that of the second and first materials. This means that the third radiation can pass through the first and second materials without undergoing significant attenuation

[0069] To have maximum transmission of the entire spectrum emitted by the different media, it is therefore necessary for the media to be placed one after the other in decreasing order of Àmi„ (therefore so that the material having the widest transparency band is closest to the output (i.e. on the right in the illustration of [Fig.3A].

[0070] In the direction opposite to the output (i.e. from right to left in the illustration of FIG. 3A), the luminescent radiation has a central emission wavelength which may not be included in the spectral transparency ranges of the media crossed. Thus, the first central emission wavelength, for example, is not included in the second spectral transparency range. (nor in the third spectral range of transparency [2 / win3, Also, the first luminescent radiation is absorbed by the second material. Similarly, the second luminescent radiation is absorbed by the third material. In other words, the second material is pumped by the first luminescent radiation and the third material is pumped by the second luminescent radiation.

[0071] The light Lconv exiting through the face FC opposite the output face FS1 therefore only contains the emission spectrum of the concentrator closest to the output (i.e. the third luminescent radiation in the illustration of figure 3A). This face FC therefore allows a conversion of the wavelengths from to A.

[0072] For a second and a third sufficiently absorbent material, for example with an absorption coefficient of the second material for the first central emission wavelength, then the first luminescent radiation emitted by the first concentrator C1 travels a short distance in the second concentrator C2 before being totally absorbed. This absorption zone becomes an emitting zone of a second luminescent radiation called “secondary” centered on the wavelength and a part of this second “secondary” luminescent radiation centered on the wavelength / U therefore leaves towards the face of FS1 exit.

[0073] This is an internal "self-pumping" of the assembly 1 making it possible to increase the conversion efficiency of the assembly 1 of the invention and to increase the number of spectral components of the outgoing light emission.

[0074] To ensure this internal self-pumping effect, according to a preferred embodiment, an absorption coefficient % । of the second material for the first central emission wavelength and an absorption coefficient a32 of the third material for the second central emission wavelength 22 are greater than 5 cm-1 and preferably greater than or equal to 10 cm-1. For the sake of clarity, it is explicitly specified that the absorption coefficient a2i of the second material is associated with the emission of the second “secondary” luminescent radiation centered on the wavelength ^2 and that the absorption coefficient a32 of the third material is associated with the emission of the third “secondary” luminescent radiation centered on the wavelength ^3.

[0075] Since the second and third "secondary" luminescent radiation pass through a very small thickness of the second and third concentrator respectively, the reabsorption effects limiting the spectral width are reduced. Thus, the self-pumping of the assembly 1 contributes to increasing the number of spectral components and to "smoothing" the overall spectrum of the outgoing light emission Li)ut.

[0076] This result is illustrated in [Fig.5A] which presents an example of spectrum emitted by an assembly 1 according to the invention comprising four luminescent concentrators C1-C4 illustrated in [Fig.5B].

[0077] Compared to the assembly of Figure 3A, the assembly of Figure 5B comprises a fourth concentrator C4 attached to the first concentrator C1 by its first output face FS1. The face of the fourth concentrator opposite the face of the fourth concentrator which is opposite the first output face FS1 is called the second output face FS2. The fourth concentrator is made of a fourth material suitable for absorbing the pump radiation and then emitting a fourth luminescent radiation L4 having a fourth central emission wavelength A within the fourth concentrator, less than the first wavelength. The lifetime of the fourth luminescent radiation L4 is noted r4.

[0078] The fourth material is such that the fourth concentrator has a transmission coefficient (calculated for a crossing of the fourth concentrator along its length in the y direction) greater than 50% for the first, second and third luminescent radiation. Thus, the assembly 1 of [Fig.5B] is adapted to emit, through the second output face FS2, a secondary light emission Lout>2 having the first, second, third and fourth wavelengths when the first, second, third and fourth luminescent light concentrator absorbs pump radiation.

[0079] As a non-limiting example, in the example of Figure 5A the fourth concentrator C4 comprises fluorophores making it possible to emit in the blue ( = 435 finite) - Figure 5C is a comparison of the four absorption bands BA1-BA4, of the first, second, third material and fourth material according to the example of Figure 5A. It is observed that it is possible to pump these four materials by a single pump wavelength, for example Ap = 355 nm as illustrated in [Fig.4C].

[0080] Let us now return to the description of [Fig.5A]. The latter presents a comparison of the STI spectrum emitted by set 1 of [Fig.5B] (which comprises four concentrators C1-C4 comprising fluorophores emitting respectively in green, orange, red and blue) with an ST2 spectrum which is a sum of the blue, green, orange, red spectra emitted independently by the fluorophores of each of the concentrators C1-C4 of set 1 of [Fig.5B].

[0081] Figure 5A shows that the spectral bands where there are "holes" between the central emission wavelengths λ (at 74) are more marked in the ST2 spectrum than in the STI spectrum. In addition, the STI spectrum is enriched with spectral components always lower than the emission peak considered. This is the signature of a reabsorption effect in the concentrators taken separately, an effect limited by self-pumping. The STI spectrum of set 1 of [Fig.5B] is therefore smoother than the ST2 spectrum.

[0082] [Fig.6] illustrates another object of the invention which is a light emission device 10 according to the invention comprising the assembly 1 according to the invention, optically pumped by a laser source SL via an optical pumping cavity CP.

[0083] The laser source SL is adapted to generate an incident beam FI. According to a first alternative of the invention, the source SL generates an incident beam FI having the pump wavelength 2^. According to a second alternative of the invention, the source SL generates an incident beam FI not having the pump wavelength Ap, the latter then being generated within the cavity by light conversion (see for example [Fig.9]).

[0084] This SL source is not specific to the invention and can be any laser source known to those skilled in the art.

[0085] Preferably, the SL source is a pulsed source delivering laser pulses of duration tp- A pulsed SL source makes it possible to obtain an outgoing light emission Lout of higher peak power than a continuous laser source, while reducing thermal problems within the concentrator. In the embodiment where the SL laser source operates in pulsed mode, it is preferable that the SL laser source and the optical pump cavity (via its characteristics reflection characteristics of the incident beam) are adapted so that a fluence (or energy density) of the pump radiation within the concentrators of set 1 is less than 5 J j cm ï , preferably less than or equal to 1 J / cm 2 . Indeed, the laser optical damage threshold is typically between 5 J / cm 2 and 10 J j cm 2 for a pulsed laser delivering 10 ns pulses, depending on the experimental conditions.

[0086] According to one embodiment, the laser source SL is a Q-switched laser source. As a non-limiting example, the laser source SL is a frequency-tripled Q-switched Nd:YAG laser delivering pulses with an energy of 15 rnJ at 355 nm and with a pulse duration rP — 5 ns and with a rate of 20 Hz.

[0087] The optical pumping cavity CP has a surface SR adapted to reflect the incident beam FL. The surface SR of the cavity CP defines a volume comprising the assembly 1 and in which the laser source SL is not included. The volume defined by the surface SR of the cavity CP comprises at least one opening 01 so that the incident beam can pass through the opening 01 and be reflected and / or diffused a plurality of times on the surface SR of the optical pumping cavity, thus creating pump radiation RP.

[0088] According to one embodiment, as illustrated in Figure 6, the surface SR of the cavity CP defines a closed volume. By “closed volume”, it is meant here that the surface SR of the cavity CP is entirely closed with the exception of one or more openings having a total surface ST such that LL < 5%, preferably less than SR < 1%. The use of a closed cavity avoids losses suffered by the incident beam FI during its propagation in the cavity CP, which is essential for generating an outgoing light emission Ls with high peak power, while limiting the pump power density within the light concentrators of set 1.

[0089] The assembly 1 is arranged in the cavity CP so as to absorb the pump radiation RP then emit the outgoing light emission Lout through the output face FS1 of the first concentrator CL.

[0090] The optical pump cavity CP allows the pump radiation RP to pass through the concentrators C1-C3 a plurality of times, which increases the absorption of the pump radiation RP by these concentrators. Thus, simultaneous pumping of all the concentrators is allowed and the peak power of the outgoing light emission Lout is increased. By using a cavity with a surface having a high reflection or scattering coefficient resulting in multiple reflections / scatterings on the surface of the cavity CP and therefore multiple passages in the concentrators, the optical pump cavity CP allows the pump radiation RP to pass through the concentrators C1-C3 a plurality of times, which increases the absorption of the pump radiation RP by these concentrators. trators C1-C3, it is possible to use concentrators C1-C3 in materials having an absorption length for the incident beam FI much smaller than the thickness of these concentrators. For example, it is possible to use a first material of the first concentrator Cl with an absorption coefficient of the order of cm-1 or a fraction of cnr* and a thickness ei of the order of mn\ implying an absorption length at least 10 times greater than the thickness of the first concentrator Cl.

[0091] In addition, the cavity CP makes it possible to "distribute" the pumping on all the faces of the concentrators C1-C3 simultaneously, without resorting to complex optical systems allowing the light to be distributed on the different lateral faces. Thus, the power density (or fluence in the pulsed case) of the pump radiation RP on the faces of each concentrator (and within the concentrators) is limited and the problems of thermal effect, optical damage threshold and photobleaching of the phosphors Lum of this concentrator are avoided. Conversely, pumping each concentrator C1-C3 directly with a respective portion of the incident beam FI would result in a much higher power density in the pumped area which could cause optical damage and photobleaching problems. For example, a fluorescent medium using organic molecules pumped by laser is limited in luminance and power because of the aforementioned effects.

[0092] The distribution of the pumping on all the lateral faces also makes it possible to limit the surface area of ​​the large pumping faces and therefore to limit the width Wi of the first concentrator, in particular in order to have a first output face FS1 that is as symmetrical as possible (ideally a square).

[0093] Thus, the light emission device 10 of the invention makes it possible to generate an outgoing light emission Lmit having a broad, spatially homogeneous spectrum over the entire surface of the first output face FS1. Furthermore, the device makes it possible to obtain an outgoing light emission Lout of high power and a small extent by optimizing the pump power density within the concentrator. For this, it is essential that the laser source SL is located outside the cavity CP so that it does not obstruct the multiple reflections of the incident beam FI on the surface SR of the cavity CP, which would reduce the power of the effective pump radiation RP pumping the assembly 1.

[0094] In a first approximation, the device 10 according to the invention works for any shape of concentrators C1-C3 as long as they have the same section (i.e. identical dimensions along the zx plane according to the example of FIG. 3A). However, the shape of the concentrators directly influences the outgoing light emission Lm(t, in particular its luminance and its geometric extent. In addition, the length of each concentrator of the set 1 can be adapted to "dose" the desired amount of radiation in a color. It is therefore preferable to choose a concentrator shape suitable for: - produce a significant concentrating effect of the luminescent radiation by total internal reflections in the structure. Thus, the luminance of the outgoing light emission Lout is increased. This parameter is controlled by the ratio Li / ei between the length and the thickness of the first concentrator in the example of [Fig.3A], - produce an outgoing light emission LCMt with a geometric extent adapted to the chosen application. This parameter is controlled by the shape and dimension of the output face FS1.

[0095] Also, preferably, the concentrators are in the form of a "rod", that is to say a parallelepiped having a length at least 5 times, preferably 10 times, still preferably 20 times, greater than its width and its thickness in order to achieve a significant "concentrating" effect by total internal reflections in the structure. The length of each concentrator is however limited by the propagation losses which are intrinsic to the concentrator. It is therefore preferable to find an optimal compromise between maximum concentrating effect and high propagation losses.

[0096] Even more preferably, the output face FS1 has a square or close to a square shape with an area adapted to the imaging system which will follow the source (for example a few mm2).

[0097] In a preferred embodiment, the surface of the optical pumping cavity CP diffusely reflects a percentage greater than or equal to 90% of the incident radiation and has a reflection coefficient greater than 90%, preferably greater than 95% for the incident radiation. Thus, the most homogeneous pump radiation possible is obtained and efficiently pumps a larger volume of the concentrators. This characteristic is critical to guarantee a high peak power of the outgoing light emission Ls while limiting the volume density of pump power within each concentrator.Conversely, a surface of the optical pump cavity CP specularly reflecting a majority of the incident beam would generate less homogeneous pump radiation which could lead to hot spots in each concentrator where the power volume density could exceed the threshold for optical damage or photobleaching.

[0098] For example, the surface of the optical cavity is made of Spectralon or polytetrafluoroethylene. Spectralon has a reflection coefficient of 99% for a spectral range from 400 nm to 1500 nm. This implies that the incident beam FI can be reflected by scattering 100 times before losing 63% of its power.

[0099] As a non-limiting example, in the example of [Fig.6], the pumping cavity CP is a sphere of diameter D comprising two openings O1, O2.

[0100] It is important to note that the shape of the cavity can adapt to the geometry of the concentrators. For example, in the embodiment of [Fig.7], the pumping cavity CP is a cylindrical diffusing cavity having a length adapted to the length Lct of the assembly 1. In this compact structure, the direct illumination of the concentrators by the laser source SL is avoided by diffusion of the incident beam FI upon entry into the pumping cavity thanks to a diffusing medium MD arranged in the cavity CP. In order to complete the confinement of the light inside the cavity, the latter is covered with a reflective layer SR. According to the embodiment of [Fig.7], the cavity CP is adapted to allow air to circulate to cool the concentrator heating up due to optical pumping.

[0101] For certain applications, it is very important to know the spectral composition of the emitted signal as a function of time with a resolution of up to one nanosecond. This spectral composition must be stable over time. In other words, it is desirable to obtain a constant distribution of the intensity of the first, second and third wavelengths in the outgoing light emission, over a sufficiently long period and with a sufficiently high intensity of the outgoing light emission.

[0102] With a pulsed SL laser source, two scenarios are possible to ensure this temporal stability of the wavelength distribution over a sufficiently long time window: - the laser pulse of duration tp is sufficiently short compared to the lifetimes rt' r2' r3 of the phosphors of the materials of set 1, or - the lifetime of the fluorophores of each material of set 1 is decreasing from the material emitting the smallest central emission wavelength (i.e. the material of the rightmost concentrator in the illustration of the figures of the invention).

[0103] By "a sufficiently long time window" is meant here over a duration greater than or equal to min(Tp, ty

[0104] Also, according to a first embodiment, the laser source SL operates in pulsed mode delivering pulses of duration Tp > r2. Thus, the duration of the pulse is long enough to ensure that there is a time window for which a distribution of an intensity of the first, second and third wavelengths in the outgoing emission is constant. More precisely, this time window is of duration rp- max(rj, t^).

[0105] According to a second embodiment, in order to ensure this temporal stability, the SL laser source operates in pulsed mode delivering pulses of duration TP < T T2, and we have the first, second and third material which are adapted so that > ​​T?,. These conditions are necessary to allow obtaining a constant distribution of the intensity of the first, second and third wavelength in the outgoing light emission.

[0106] In the second embodiment, despite the aforementioned conditions, if ri is not sufficiently large compared to r2, then it is possible that this constant distribution is obtained for an intensity of the outgoing light emission that is very low compared to the maximum intensity generated during the pump pulse tp. To avoid this, the first material is adapted so that is sufficiently large compared to r2 so that a distribution of the intensity of the first, second and third wavelengths in the outgoing emission is constant and this for an intensity of the outgoing light emission greater than 20% of the maximum intensity of the upper outgoing emission obtained during the pump pulse* The spectral composition of the outgoing light emission is then stable on a signal of high light intensity.

[0107] The inventors determined that a first material having a lifetime L at least twice as long as r2 was sufficient to obtain a constant distribution of the different wavelengths in the outgoing light emission, while ensuring a sufficiently high intensity of the outgoing light emission.

[0108] Thanks to the use of a first material generating a first luminescent radiation having a lifetime longer than the duration of the pump pulses, it is for example possible to generate broad spectrum light pulses of around a hundred nanoseconds despite an SL laser source delivering pulses of a few nanoseconds for example.

[0109] In a manner known per se, the luminescent emission in the concentrators is Lambertian. Also, the solid angle of emission of the outgoing light emission Lmft is equal to 77 sr which makes it difficult to use this broad spectrum radiation for practical purposes, for example when it is desired to couple it to a conventional optical system. To overcome this problem, in the embodiment illustrated in [Fig.8], the light emission device 10 comprises a non-imaging optical device ONI attached to the first output face FS1. The non-imaging optical device ONI makes it possible to collect rays of the outgoing light emission by reducing a solid angle associated with the outgoing light emission so as to form an output beam FS having the first, second and third wavelengths.

[0110] This non-imaging optical device ONI is preferably bonded to the first output face FS1 with an adhesive with an index close to the index of the concentrator Cl to maximize the extraction efficiency of the outgoing light emission LMit. Another advantage linked to the use of the non-imaging optical device ONI attached to the first output face FS1 is that it allows the mechanical maintenance of the assembly 1 within the cavity CP without using an additional mechanical element which would reduce the effective pump power.

[0111] According to one embodiment, the non-imaging optical device ONI is a parabolic concentrator (concentrator parabolic compound in English) attached to the first output face FS1 using a photo-polymerizable UV glue in order to extract a maximum of light trapped in the first concentrator C1 and to straighten the rays in the output beam FS. As a non-limiting example, the parabolic concentrator ONI has an input diameter of 2.5 mm attached to the face FS1 and an output diameter of 5 mm. The solid angle at the output of the parabolic concentrator ONI is estimated at sr and the geometric extent of the output beam is therefore of the order of 0.1 cm 2 sr.

[0112] More generally, it is preferable for the non-imaging optical device ONI to have a structure adapted so that a solid angle of the output beam is less than or equal to y sr in order to facilitate the use of the output radiation of the device 10. Thus, the output beam FS shaped by the non-imaging optical device ONI can be coupled into a conventional optical device (not shown) in order to provide a beam usable by an optical system of low numerical aperture for example.

[0113] [Fig. 9] illustrates an embodiment of the invention of the device 10 in which the assembly 1 comprises four concentrators C1-C4 as illustrated in the embodiment of [Fig. 5B]. In the embodiment of [Fig. 9], the device 10 comprises a first light converter element EC making it possible to carry out “complementary” pumping of the assembly 1. For this, the light converter element EC is arranged in the optical pumping cavity and is adapted to absorb the pump radiation RP and / or the incident beam and then emit so-called complementary pump radiation RPC pumping several of the concentrators of the assembly 1.

[0114] According to one embodiment, the light converter element EC is made of the same material as the fourth concentrator C4 so that the complementary pump radiation RPC has the fourth central emission wavelength A which pumps the concentrators C1-C3 so that they emit respectively the first, the second and the third luminescent radiation. By way of example, an absorption coefficient of the first, the second and the third material for the fourth central emission wavelength / 4 associated with the first, the second and the third radiation read is considered optimal. minescent radiation respectively greater than 5 cmA so that the first, second and third concentrators absorb the complementary pump radiation and then emit the first, second and third luminescent radiation respectively.

[0115] According to the example of [Fig.5B], the converter element EC will have the effect of converting a pump radiation RP in the UV into blue around 440 nm, wavelength which is absorbed by the concentrators C1-C3 (respectively with fluorophores emitting in the green, orange and red) Thus, it is a cascade of pump wavelength external to the concentrators.

[0116] The converter element EC may be in the form of powder which lines the interior of the cavity CP or the interior of a perforated cylinder in which the assembly 1 is inserted (see [Fig. 11]).

[0117] An additional advantage of the CP pumping chamber is to allow external "self-pumping" of the assembly 1. With the use of a diffusing and / or multi-reflecting CP pumping chamber, it is possible to use the external self-pumping of the assembly 1 to improve the conversion efficiency between the pump radiation RP and the outgoing light emission Lout. Indeed, as illustrated in Figure 5C, since the absorption bands of the concentrators of an assembly are different, it may be difficult to find a common and optimal intersection between the absorption bands to pump all the concentrating media with a single light source. As shown in Figure 5C, if pumping in the UV at λp = 355 nm is well suited for the concentrator C4 emitting in the blue, it is however less optimal for the concentrators C1-C3 emitting respectively in the green, orange or red.However, in the case of a parallelepiped concentrator with index n=1.5 surrounded by air, 12% of the emitted luminescent radiation exits on each face. The four lateral faces therefore emit nearly 50% of the total intensity of the luminescent radiation emitted by each concentrator in the pumping chamber. This light can therefore be absorbed by a concentrator under the wavelength conditions described previously. This external self-pumping effect therefore makes it possible to multiply the pumping wavelengths and therefore allows a more efficient conversion of the incident beam FL. Thus, a weak absorption of the pump wavelength by a concentrator can be compensated for by the absorption of other wavelengths generated by the other concentrators.

[0118] As a non-limiting example, in the illustration of Figure 9, the first luminescent radiation leaving the first concentrator via the side faces is referenced This radiation can then pump the second and third concentrators using the pumping chamber CP so that they emit respectively in orange and in red. Similarly, in the illustration of Figure 9, the second luminescent radiation leaving the second concentrator through the side faces is referenced Lng2. This radiation C^pcut then pumps the third concentrator through the pumping chamber CP so that it emits in the red. To facilitate this external self-pumping, it is preferable that the reflection coefficient of the reflective walls SR of the optical pumping cavity CP is greater than 90% for the first central emission wavelength and for the second central emission wavelength 22.

[0119] Figure 10 illustrates an embodiment of the device 10 of the invention, in which the assembly 1 comprises four concentrators C1, C2, C3 and C4 emitting for example respectively in green, orange, red and blue. In the embodiment of Figure 10, by way of example, it is considered that the materials are such that the lifetime of the luminescent radiation emitted by each concentrator is equal, that is to say that Ti~ ri~ r3~ ^4. It is then possible to have a synchronized emission of the concentrators, if a single pumping source is available, common to all the concentrators.

[0120] In the embodiment of FIG. 10, the laser source SL is adapted to simultaneously generate the incident beam FI having the pump wavelength A? and an additional incident beam FI' having an additional pump wavelength, for example by non-linear optical conversion.

[0121] As an example, the laser source SL generates the incident beam FI from the second harmonic of a Nd:YAG laser (532 nm) to pump the first, second and third concentrators C1, C2 and C3 emitting in the green, orange and red respectively. In addition, the laser source SL generates the additional incident beam FF from the third harmonic of the Nd:YAG laser (355 nm) to pump the fourth concentrator C4 emitting in the blue (and possibly the first concentrator emitting in the green). The second and third harmonics being synchronized by construction, this pumping at two wavelengths is synchronized.

[0122] The optical pumping cavity CP comprises a first opening 01 adapted to be crossed by the incident beam F1 to form the pump radiation RP by reflection and / or diffusion in the cavity CP thanks to the diffusing medium MD. In addition, the cavity CP comprises a first additional opening 01' adapted to be crossed by the additional incident beam FF so as to form, by reflection and / or diffusion within the optical cavity thanks to the diffusing medium MD, additional pump radiation absorbed by the fourth concentrator.

[0123] Due to pumping and wavelength conversions, some of the pump radiation is lost as heat at the concentrator assembly 1. trators. To control the temperature of the assembly 1, it is preferable to evacuate the heat. This can be achieved by an air flow passing through the optical pumping cavity CP over its entire length. Also, according to the embodiment of [Fig. 10], the optical pumping cavity CP comprises a second 02 and a third opening 03 connected by a channel CN ​​arranged in the diffusing medium MD and the assembly 1 is arranged within the channel CN. This channel is adapted to allow circulation of a fluid (for example air) making it possible to cool the assembly 1 when it absorbs the pump radiation and the additional pump radiation.

[0124] Thus, the device 10 of figure 10 allows easy generation of an output beam FS having a broad spectrum formed from the peaks centered at ^3 and 24 by judiciously choosing the radiation pumping the assembly 1 so as to optimize its absorption by the concentrators.

[0125] [Fig. 11] illustrates an embodiment of the device 10 of the invention optimized in order to control the duration of the light emission in the case where the concentrators are in materials such that the lifetimes of the luminescent radiation are not equal.

[0126] In this embodiment, the assembly 1 comprises four concentrators C1, C2, C3 and C4 such that T4 > > r2 > (with 1 4 the lifetime of the fourth radiation luminescent L4 emitted by the fourth concentrator). In addition, the laser source SL emits pulses of duration tp in pulsed mode so that Tp < b The laser source SL is adapted to emit an incident beam which does not include the pump wavelength λp but which has an additional pump wavelength ^P'.

[0127] Just like the device of [Fig.10], in the embodiment of [Fig.11], the cavity CP comprises a diffusing medium MD within which is formed, between the openings 02 and 03, the channel CN ​​which comprises the assembly 1.

[0128] To produce a device 10 with temporal control of the spectrum, it is necessary that the additional pump wavelength Ap- interacts only with the concentrator C4 having the greatest lifetime. The solution of [Fig.l 1] consists of separating the pumping into two parts: a direct pumping part for the concentrator C4 and a cascade pumping part for the following concentrators C1-C3 via a light converter element EC' which is made of the same material as the concentrator C4

[0129] The optical pumping cavity CP is separated into a first chamber CPI and a second chamber CP2. The first chamber CPI comprises the first, second and third concentrators C1, C2 and C3 and comprises the first opening O1 adapted to be crossed by a first portion Fil of the incident beam FL

[0130] The second chamber CP2 comprises the fourth concentrator C4 and comprises a first additional opening 01' adapted to be crossed by a second portion FI2 of the incident beam.

[0131] In order to generate the pump wavelength from the additional pump wavelength ^P-, the device 10 comprises the light converter element EC' which is made of the same material as the concentrator C4. The element EC' is arranged in the first chamber CPI only, between the channel CN ​​and the diffusing medium MD. It is adapted to absorb the first portion Fil of the incident beam and then emit an intermediate incident beam FII having the pump wavelength ^p. Thus, the intermediate incident beam FII forms the pump radiation by reflection and / or diffusion within the first chamber CPI of the cavity CP.

[0132] The second chamber CP2 does not include the light converter element EC' and is optically separated from the first chamber CPI so that the second portion FI2 pumps only the fourth concentrator C4.

[0133] Thus, the device 10 of the embodiment of [Fig. 10] allows optimal temporal control of the spectrum of the output beam FS.

Claims

1. Claims Set (1) of luminescent light concentrators for broad spectrum emission intended to be pumped by pump radiation (RP) having a pump wavelength ^p and comprising: - a first luminescent light concentrator (Cl) having a first output face (FS1), the first concentrator being in a first material adapted to absorb said pump radiation then emit a first luminescent radiation (Li) having a first central emission wavelength within said first concentrator, - a second luminescent light concentrator, attached to the first concentrator, in a second material adapted to absorb said pump radiation then emit a second luminescent radiation (L2) having a second central emission wavelength 22 greater than the first wavelength within said second concentrator, - a third luminescent light concentrator, attached to the second concentrator, in a third material adapted to absorb said pump radiation then emit a third luminescent radiation (L3) having a third central emission wavelength ^3 greater than the second wavelength within said third concentrator, the second material being such that the second concentrator has a transmission coefficient greater than 50% for the third luminescent radiation, and the first material being such that the first concentrator has a transmission coefficient greater than 50% for the third luminescent radiation and for the second luminescent radiation so that said set of concentrators is adapted to emit, through the first output face, an outgoing light emission having the first, second and third central emission wavelength and formed from a portion of the first, second and third luminescent radiation when the first, second and third luminescent light concentrators absorb said pump radiation.

2. Set of luminescent light concentrators according to the preceding claim, in which a first spectral range of transparency of the first material associated with said outgoing light emission comprises a second spectral range of transparency of the second material associated with said outgoing light emission which itself comprises a third spectral range of transparency of the third material associated with said outgoing light emission.

3. A set of luminescent light concentrators according to claim 1 or 2, wherein an absorption coefficient of the second material for the first central emission wavelength and an absorption coefficient of the third material for the second central emission wavelength is greater than 5 cm1 and preferably greater than or equal to 10 cm1.

4. Set of luminescent light concentrators according to any one of the preceding claims, comprising a fourth luminescent light concentrator attached to the first concentrator by its first output face, the fourth concentrator having a second output face (FS2) and being made of a fourth material adapted to: - absorb said pump radiation or additional pump radiation having an additional pump wavelength shorter than said pump wavelength then - emit fourth luminescent radiation (L4) having a fourth central emission wavelength ^4 shorter than the first wavelength within said fourth concentrator, the fourth material being such that the fourth concentrator has a transmission coefficient greater than 50% for the first, second and third luminescent radiation,such that said light concentrator assembly is adapted to emit, through the second output face, a secondary light emission having the first, second, third and fourth wavelengths when the first, second, the third and fourth luminescent light concentrators absorb said pump radiation and / or the additional pump radiation.

5. Light emission device (10) comprising: - a laser source (SL) adapted to generate an incident laser beam (FI), - an optical pumping cavity (CP) comprising at least one opening (01, 02) so that the incident beam can pass through said at least one opening and form said pump radiation (RP) by reflection and / or diffusion within the optical pumping cavity, - a set of luminescent light concentrators according to any one of claims 1 to 4 arranged in the optical pumping cavity and such that the first, second and third luminescent light concentrators are capable of absorbing said pump radiation and then said set of luminescent light concentrators emits said outgoing light emission.

6. Device according to the preceding claim, comprising a non-imaging optical device attached to the first output face or the second output face in order to collect rays by reducing a solid angle of said outgoing light emission or said secondary light emission so as to form an output beam (FS) having the first, second and third wavelength or having the first, second, third and fourth wavelength.

7. Device according to claim 5 or 6, in which the laser source (SL) operates in pulsed mode delivering pulses of duration tp, and in which the first luminescent radiation has a first lifetime ri, the second luminescent radiation has a second lifetime T2, and the third luminescent radiation has a third lifetime and in which r r3 if T p T br 2, T 3 or in which Tp> T2, T^.

8. Device according to the preceding claim, in which the first material is adapted so that there is a time window of a duration predetermined greater than 5 ns in which a distribution of an intensity of the first, second and third wavelengths in said outgoing emission is constant, for an intensity of said outgoing emission greater than 20% of a maximum intensity of said upper outgoing emission obtained during a pulse of duration

9. Device according to any one of claims 5 to 8, wherein a reflection coefficient of reflective walls (SR) of the optical pumping cavity (CP) is greater than 90% for the first central emission wavelength and the second central emission wavelength d2.

10. Device according to any one of claims 5 to 9, in which the optical pumping cavity comprises a diffusing medium (MD) arranged between reflecting walls (SR) of the optical pumping cavity so that the incident beam can pass through said at least one opening and form said pump radiation (RP) by reflection on the reflecting walls and by diffusion within the diffusing medium (MD).

11. Device according to the preceding claim, in which the optical pumping cavity comprises a first opening adapted to be crossed by the incident beam, and a second and a third opening connected by a channel (CN) arranged in the diffusing medium, said set of luminescent light concentrators being arranged within the channel which is adapted to allow circulation of a fluid making it possible to cool said set of luminescent light concentrators when it absorbs said pump radiation.

12. Device according to the preceding claim comprising a set of concentrators according to claim 4, the device comprising a first light converter element arranged in the optical pump cavity and adapted to absorb said pump radiation and / or the incident beam and then emit so-called complementary pump radiation having the fourth central emission wavelength, an absorption coefficient of the first, second and third material for the fourth central emission wavelength / 4 associated with the first, second and third luminescent radiation respectively being greater than 5 cnr1 so that the first, second and third concentrator absorb the complementary pump radiation and then emit respectively the first, second and third luminescent radiation.

13. Device according to claim 11 or 12 comprising a set of concentrators according to claim 4, in which the laser source is adapted to simultaneously generate said incident beam having the pump wavelength and an additional incident beam having the additional pump wavelength ^P', the optical pump cavity comprising a first opening adapted to be crossed by the incident beam and a first additional opening adapted to be crossed by the additional incident beam so as to form, by reflection and / or diffusion within the optical pump cavity, said additional pump radiation then being absorbed by the fourth concentrator.

14. Device according to claim 7 combined with claim 11, in which Tp < T h r2, and Tj > t2 > f3 and in which the incident beam does not comprise the pump wavelength but has an additional pump wavelength ^P' the device then comprising a second light converter element arranged in the optical pump cavity between the channel and the diffusing medium and adapted to absorb the incident beam then emit an intermediate incident beam (FII) having the pump wavelength, said intermediate incident beam forming said pump radiation (RP) by reflection and / or diffusion within the optical pump cavity.

15. Device according to the preceding claim comprising a set of concentrators according to claim 4, in which the optical pumping cavity is separated into a first (CPI) and a second (CP2) chamber, the first chamber comprising the first opening adapted to be crossed by a first portion of the incident beam and comprising the first, the second and the third concentrator and comprising the second light converter element, the second chamber comprising a first additional opening adapted to be crossed by a second portion of the incident beam and comprising the fourth concentrator and not comprising the second light converter element.

16. Device according to any one of claims 5 to 15, in which the optical pumping cavity (CP) diffusely reflects a percentage greater than or equal to 90% of the incident radiation and has a reflection coefficient greater than 90%, preferably greater than 95% for incident radiation.

17. Device according to the preceding claim, in which a surface of the optical cavity where the incident radiation is reflected is made of spectralon or polytetrafluoroethylene.

18. Device according to any one of claims 5 to 16, in which the laser source (SL) and the optical pumping cavity are adapted so that a fluence of the pump radiation within the light concentrator is less than 5 J / cm2, preferably less than or equal to 1 J / cm2.

19. Method for generating an output beam with a broad spectrum with a set of luminescent light concentrators according to claim 1, said method comprising the following steps: - generating a laser beam called incident beam (FI) with a laser source (SL), - directing the incident beam through at least one opening (01, 02) formed in an optical pump cavity (CP) adapted to form said pump radiation (RP) by reflection and / or diffusion of the incident beam within the optical pump cavity, - absorbing said pump radiation (RP) with said set of concentrators arranged in the optical pump cavity so as to emit said outgoing light emission through the first output face, - collecting rays of said outgoing light emission by reducing a solid angle associated with the outgoing light emission so as to form an output beam (FS).

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