Optimized Light Emitting Device

Abstract

A solid fluorescent material or a solid scintillator material CL is included, and the incident light Ld is absorbed in the material, and then luminescent light L L A light-emitting device 1 adapted to emit a luminescent light capture portion L p A part of the light, called the ray, is captured by total internal reflection in the material, and the material is divided into two parallel faces, called the large faces FE1 and FE2, along the horizontal plane xy, and two parallel faces, called the side faces FE2 and FE3. [0010] The material includes faces FL1, FL2, FL3, and FL4 of TIFF2024522785000042.tif18166, and forms vertices S2, S3, and S4 between two adjacent side faces and the larger face, the material has a normal to the side face that is invariant with rotation by an angle of 2π / n in a horizontal plane about a z-axis perpendicular to the horizontal plane, the material has a vertex S1 called a chamfered virtual vertex that forms a surface called a chamfered vertex SB1, or has an edge called a virtual edge S1S5 between the two side faces, where a surface of a chamfered edge SB1 is formed by chamfering, and a portion of the captured light passes through the chamfered vertex to form an output beam L S and forming a normal to the chamfered surface [0025] A light-emitting device, wherein TIFF2024522785000043.tif14166 is parallel to the sum of the normals of the planes forming the imaginary surface within a range of ±10°.

Description

[Technical field]

[0001] The present invention relates to the field of light concentrators, and more particularly to the extraction of light emitted within a light concentrator. [Background technology]

[0002] Light emitting diodes (LEDs) have many applications in the field of lighting. However, the brightness of LEDs is limited to values ​​that make them unsuitable for some applications.

[0003] One solution to improve the brightness of LEDs is to use LED-excited luminescent concentrators (see, for example, Non-Patent Document 1). These concentrators are, for example, crystals that emit fluorescent light in the visible range (red to orange), such as Ce:YAG, which absorbs in the blue range (around 450 nm), at wavelengths where LEDs are very efficient. The crystals are cut in the shape of a plane, and hundreds (or even thousands) of LEDs are lined up on both of their large surfaces, emitting light at the edges. These concentrators can achieve brightness values ​​10 to 20 times higher than LEDs.

[0004] Fig. 1A shows an example of a light emitting module ME0 based on a collector crystal CL, known in the prior art. Fig. 1A shows a schematic perspective view of the light emitting module ME0. The light emitting module ME0 comprises a set of LEDs emitting in a first spectral band and a collector CL. The collector CL is a fluorescent parallelepiped crystal and has at least one illumination surface SI1, SI2 of dimensions LxW illuminated by the electroluminescent radiation Ld emitted by the LEDs. The illumination surfaces SI1, SI2 are also called "large surfaces". The thickness of the collector is denoted e.

[0005] The collector crystal is configured to absorb said electroluminescent radiation Ld. The luminous flux emitted by the LED and directed towards the illumination surface is absorbed by the luminophores Lum of the fluorescent crystal distributed throughout the mass of the crystal and emits fluorescent radiation inside the crystal. The emitted light rays can be broadly divided into two categories: - Capture ray (L pThese rays are trapped inside the crystal by total internal reflection (TIR) ​​on the various faces of the crystal. These rays exist if the crystal is a parallelepiped with six faces, two of which are parallel and two of which are perpendicular to each other. The trapped rays never leave the crystal. - Untrapped rays are rays that ultimately exit the crystal. They can be divided into two subcategories: guided rays L, which are guided by the RTI and emerge at one of the faces of the collector. g , and non-guided rays L emerging directly from the collector without being reflected by any surface. out .

[0006] FIG. 1B shows the angular distribution of all rays emitted and captured within the collector. The dark caps represent the uncaptured rays (guided L g and uninduced L out ), and the bright areas represent the angles corresponding to the captured rays L p represents the angle corresponding to the critical angle θ of the crystal. In this example, the medium chosen for the focusing crystal CL is a Ce:YAG crystal (refractive index n=1.82) with a critical angle of 33° when the surrounding medium is air. The proportion of radiation captured by the RTI compared to that not captured is determined by the refractive index of the crystal and that of the surrounding medium by the Snell-Descartes law:

[0007] For the parallelepiped collector of FIG. 1A, assuming an exit refractive index n=1 (air) and a collector refractive index n=1.82 (e.g. YAG), the percentage of light exiting at the exit face SE is 8%. The remaining light either exits at other faces (5×8%) or remains trapped inside the collector by total internal reflection (52%) (see FIG. 1B). For a parallelepiped collector of diamond (n=2.4) in air, the percentage of trapped rays increases to 73%. To increase the efficiency, it is known to those skilled in the art to place a reflecting mirror on the face opposite the exit face. However, the efficiency in each direction of the parallelepiped remains limited to a maximum of 2×8%=16% for Ce:YAG and 2×4.5%=9% for diamond.

[0008] Light extraction from luminescent crystals has been an important topic in the field of scintillators for the past 50 years (see non-patent document 2). It has been the subject of many publications with diverse ideas for extraction. This point is of paramount importance in the field of scintillator crystals, since they often have a high refractive index (e.g. Ce:YAG n=1.83, BGO n=2.15), making the light captured by total internal reflection (52% for Ce:YAG and 65% for BGO in parallelepiped geometry) very important.

[0009] This subject has appeared again in another scientific field, in quantum optics, the emission of single photons in diamonds containing nitrogen-vacancy (NV) centers. Here again, different solutions for light extraction are being considered. This point is particularly important in diamond (73% of the light rays are captured by the parallelepiped) since diamond has a very high refractive index (n=2.4).

[0010] Once the light has been extracted, it needs to be made usable. Typically, significant extraction means that the numerical aperture of the output beam is very large. The use of immersion microscopes is the first solution to collect the fluorescence of the NV centers and propagate the radiation to a detector. However, there is still a need to improve the light extraction of diamonds with NV centers.

[0011] A similar problem arises in the field of scintillator crystals, which convert very high energy incident radiation (X-rays or gamma rays) into visible radiation that can be detected by "classical" detectors such as photomultiplier tubes or photodiodes. The scintillator must meet several constraints: - High sensitivity is required since the detected light flux must be maximized to enable the detection of rare events, - The detector must be fast so that it can distinguish events that are very close in time, - The scintillator must give an identical response to all absorbed X or gamma photons arriving at a certain energy. This response is called "photopic". The method to quantify the quality of this response is "energy resolution". It consists in classifying the events recorded in the scintillator by the intensity of the emission from the scintillator and creating a histogram. The energy resolution strongly depends on the operating conditions of the scintillator and its geometry. The resolution also strongly depends on the light that can be extracted. It depends on the reflectivity of the faces and the nature of the surface condition (polished or scattering). Coupling in optical fibers reduces the energy resolution because the useful light flux becomes less important for the coupling efficiency. Light extraction efficiency is therefore a key issue in this field.

[0012] The present invention aims to alleviate certain problems of the prior art. To this end, an object of the present invention is a light emitting device comprising a solid phosphor or scintillator crystal that includes a chamfered apex or chamfered edge with normals oriented in a way adapted to recycle multiple captured light rays, thus increasing the light extraction efficiency of the device and increasing the power and brightness of the output beam passing through the chamfered apex or chamfered edge. [Prior art documents] [Non-patent literature]

[0013] [Non-Patent Document 1] 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 [Non-Patent Document 2] CM Ankenbrandt and EMLent “Increasing the light collection efficiency of scintillation counters”, RSI Vol 34 No6 p647(1963) Summary of the Invention

[0014] To this end, the object of the invention according to a first variant is a light-emitting device comprising a solid fluorescent or scintillator material, adapted to absorb incident light in said material and then emit luminescent light, a part of said luminescent light (called the captured part) being captured by total internal reflection in said material, said material being arranged along two parallel faces, called the large faces, along a horizontal plane xy, and along two parallel faces, called the side faces.

[0015]

number

[0016] and forming a vertex between two adjacent side surfaces and the larger surface, the material has a normal to the side surface that is invariant upon rotation through an angle of 2π / n in the horizontal plane about a z-axis perpendicular to the horizontal plane, the material has a vertex called a virtual chamfered vertex (forming a surface called a virtual chamfered vertex), some of the rays of the captured portion pass through the virtual chamfered vertex to form an exit beam, and the normal to the virtual chamfered vertex is parallel to the sum of the normals of the surfaces forming the virtual vertex within ±10°.

[0017] In a preferred embodiment of the first variant, the material is a rectangular parallelepiped.

[0018] In a preferred embodiment of the first variant, the angular coordinates of the normal to the chamfered vertex in the xyz coordinate system are (α=±45°; β=±35.3°)±10°.

[0019] Another object of the invention according to a second variant is a light-emitting device comprising a solid fluorescent or scintillator material, adapted to absorb incident light in said material and then emit luminescent light, a part of said luminescent light, called the captured part, being captured by total internal reflection in said material, said material being arranged along two parallel faces, called the large faces, along a horizontal plane xy, and along two parallel faces, called the side faces.

[0020]

number

[0021] The material includes a surface having a normal to the side surface that is invariant with rotation in the horizontal plane about a z-axis perpendicular to the horizontal plane by an angle of 2π / n, the material having an edge between two side surfaces, called a virtual edge, that is chamfered to form a chamfered edge surface, a portion of the light rays of the captured portion pass through the chamfered edge to form an exit beam, and a normal to the apex of the chamfer is parallel to the sum of the normals of the two side surfaces that form the virtual edge within a range of ±10°.

[0022] In a preferred embodiment of the invention conforming to the first and second variants, the device comprises a plurality of reflectors covering said chamfered edge or said side surface except for said chamfered apex.

[0023] In a preferred embodiment of the invention, compatible with the first and second variants, the material has an extinction coefficient α of the luminescent light such that 1 / α>>2L, where L is the maximum distance between two parallel sides.

[0024] In a preferred embodiment of the invention compatible with the first and second variants, the material is a diamond crystal having nitrogen vacancy centres and said incident radiation is emitted by a laser irradiating at least one face of the crystal.

[0025] In a preferred embodiment of the invention, which is compatible with the first and second variants, the side faces are perpendicular to the larger faces.

[0026] In a preferred embodiment of the invention conforming to the first and second variants, the device comprises a tapered conical adapter attached at its so-called upstream end adjacent to said chamfered edge or apex and an optical fiber connected to the so-called downstream end of said tapered adapter, said tapered adapter matching the numerical aperture of the output beam to the numerical aperture of the optical fiber.

[0027] In a preferred embodiment of the invention, which is compatible with all previous variants and embodiments, the ratio of the surface of the chamfered edge or chamfered apex to the surface of the face of the material is lower than 1 / 10, preferably lower than 1 / 100, more preferably lower than 1 / 1000.

[0028] Another object of the invention is an x-ray or gamma ray imaging system comprising an x-ray or gamma ray source and a detector including: - a plurality of identical light-emitting devices according to any of the preceding claims arranged to form an array, the material of each device being a solid scintillator; - a plurality of photodiodes respectively disposed on opposite sides of the chamfered edge or the chamfered apex of the material of each device. [Brief description of the drawings]

[0029] Other characteristics, details and advantages of the invention will become apparent from the description made with reference to the accompanying drawings, given by way of example and representing respectively:

[0030] [Figure 1A] FIG. 1A shows a light emitting module known in the prior art. [Figure 1B] FIG. 1B shows an angular diagram of all the rays emitted and captured within a prior art light collector. [Figure 2A] FIG. 2A shows a light-emitting device according to a first variant of the invention. [Figure 2B]FIG. 2B shows a 3D angular representation of all the rays emitted and trapped within the crystal of the first variant of the invention. [Figure 2C] FIG. 2C shows the trajectories of light rays emitted by a luminophore within the crystal of the first variant of the invention. [Diagram 3] FIG. 3 is a diagram showing escape cones Lg, Lout, and Ls in a plane using angular coordinates (α, β) in an xyz coordinate system. [Figure 4A] FIG. 4A shows a light-emitting device according to a second variant of the invention. [Figure 4B] FIG. 4B shows a 3D angular representation of all the rays emitted and trapped within the crystal of the second variant of the invention. [Figure 4C] FIG. 4C is a diagram showing angle coordinates in the xyz coordinate system. [Figure 4D] FIG. 4D is a diagram showing escape cones Lg, Lout, and Ls in a plane using angular coordinates (α, β) in an xyz coordinate system. [Figure 5A] FIG. 5A shows the brightness of the output beam and the extraction efficiency as a function of the attenuation coefficient α for various crystal configurations. [Figure 5B] FIG. 5B shows the brightness of the output beam and the extraction efficiency as a function of the attenuation coefficient α for various crystal configurations. [Figure 5C] FIG. 5C illustrates a variation of the configuration used in FIGS. 5A and 5B. [Figure 6A] FIG. 6A shows a light-emitting device according to a second variant of the invention, in which the crystal has six sides. [Figure 6B] FIG. 6B is a diagram showing the angular distribution of all the rays emitted and trapped within the crystal of FIG. 6A. [Figure 7A] FIG. 7A shows various crystal configurations coupled to an optical fiber via a tapered conical adapter. [Figure 7B]FIG. 7B shows the light extraction efficiency as a function of the upstream end diameter φu for the various crystal configurations shown in FIG. 7A. [Figure 8] FIG. 8 shows a detector including a number of identical light-emitting devices according to the first or second variant of the invention.

[0031] In the drawings, elements are not drawn to scale unless otherwise noted. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] 2A and 4A show respectively a light-emitting device 1 according to a first and a second variant of the invention. The device 1 according to the invention comprises a light collector CL which is a solid phosphor crystal or a solid scintillator crystal, in which the luminescent light L L In another embodiment, the light collector is not a crystal but another material, such as glass. For simplicity, the following description of the device of the present invention uses a crystal, but the present invention also relates to a device in which the luminescence light L is generated within the crystal. L It will be appreciated that the concentrator may be made of another material adapted to absorb the incident light Ld that induces the emission of light.

[0033] The crystal contains two parallel faces, FE1 and FE2, called the major faces, along the horizontal plane xy, and four parallel faces, FL1, FL2, FL3, and FL4, called the lateral faces.

[0034]

number

[0035] These sides form vertices S1, S2, S3, S4, and S5 between the two adjacent sides and the larger face.

[0036]

number

[0037] Side FL i (see FIG. 2C). As an illustrative example, in FIGS. 2A and 4A, the crystal CL is rectangular and n=4. However, those skilled in the art will recognize that the invention also applies to crystals having numbers greater than n=4 (see, for example, FIG. 6A).

[0038] As known to those skilled in the art, the captured portion of the luminescent light, L p A portion of the light, called L, is trapped by total internal reflection within the crystal. As mentioned above, the ratio of trapped to untrapped light is determined by the refractive index of the crystal and the refractive index of the surrounding medium, according to the Snell-Descartes law. The trapped light is L p These rays are captured inside the crystal by total internal reflection (TIR) ​​at the various faces of the crystal. The uncaptured rays are the rays that eventually leave the crystal. They can be divided into two subcategories: guided rays L that are guided by TIR at the larger face or side and emerge at one of the faces of the collector. g , and non-guided rays L emerging directly from the collector without being reflected by any surface. out .

[0039] The present invention aims to create an artificial escape cone associated with trapped light rays of the structure within a predetermined angular range and "recycle" those rays to increase the light extraction efficiency and thus increase the brightness and power of the beam exiting the crystal of the present invention compared to that previously achieved with prior art crystals. The term "recycle" in this specification refers to allowing trapped light rays within a predetermined angular range to escape the crystal, thereby increasing the light extraction efficiency and power of the beam exiting the crystal. s This means increasing the brightness and power of the LD, but this is only possible after incoherent superposition of those beams in the crystal.

[0040] For this purpose, the crystal of the present invention has a normal to said side surface that is invariant to a rotation through an angle of 2π / n in the horizontal plane xy about the z-axis perpendicular to the horizontal plane. In the exemplary views of Figures 2A and 4A, n=4, and the normal to the side surface is invariant to a rotation through an angle of π / 2 about the z-axis.

[0041] To increase the light extraction efficiency, according to a first variant of the invention (shown in FIG. 2A), the crystal has an edge between the two side surfaces FL1, FL2. This edge, called the virtual edge S1, S5, is chamfered, so that it forms a surface called the chamfered edge SB1. Its normal

[0042]

number

[0043] lies in the plane of the larger surface, as do the other normals to the side surfaces (see further). This chamfered edge AB1 defines the exit surface. The captured portion of the rays passing through the chamfered edge is called the exit beam L s Form.

[0044] According to a second variant of the invention (shown in FIG. 4A), the crystal has a vertex called virtual vertex S1. This vertex is chamfered so that it forms a surface called chamfered vertex SB1. Its normal

[0045]

number

[0046] is not in the plane of the larger surface. Its orientation is chosen to take advantage of the symmetry of the structure (see further). This chamfered vertex SB1 defines the exit surface. The captured portion of the rays that pass through this chamfered vertex are called the exit beam L s Form.

[0047] In each variant, the normal to the chamfered vertex or edge

[0048]

number

[0049] has a predetermined orientation adapted to "recycle" the most captured light rays, thus increasing the light extraction efficiency by taking advantage of the symmetry of the structure. Indeed, as will be explained later, the direction of the normal to the chamfered apex or edge is an important parameter that controls the predetermined angular range of captured light rays that can exit the crystal through the exit face (chamfered edge or apex).

[0050] The first variant exploits the symmetry of the structure of the crystal in a plane. More precisely, in the first variant of the invention, the normal to the chamfered edge

[0051]

number

[0052] is parallel to the sum of the normals of the nearest sides (i.e., the faces that form the imaginary edge). This means that

[0053]

number

[0054] but

[0055]

number

[0056] The allowable range of normal directions is determined by the size of the escape cone and the loss of structure:

[0057]

number

[0058] and

[0059]

number

[0060] A maximum angle between is allowed of + / - 10°. Angles greater than 10° reduce light recycling and undesirably reduce the light extraction efficiency of the crystalline CL.

[0061] The second variant of the invention makes full use of the symmetry of the structure. Thus, in the second variant of the invention, the normals to the chamfered vertices

[0062]

number

[0063] is parallel to the sum of the normals of all the nearest faces (i.e., the faces that form the virtual vertex). This means that

[0064]

number

[0065] but

[0066]

number

[0067] This means that it is proportional to (

[0068]

number

[0069] is the normal to the large face FE1 that forms the virtual vertex). The allowable range of normal directions depends on the size of the escape cone and the loss of structure:

[0070]

number

[0071] and

[0072]

number

[0073] A maximum angle between is allowed of + / - 10°. Angles greater than 10° reduce light recycling and undesirably reduce the light extraction efficiency of the crystalline CL.

[0074] Figures 2B and 4B show 3D angular views of all rays emitted and trapped within the crystal CL. As in Figure 1B, the dark caps represent the non-trapped rays (induced L g and uninduced L out ) The medium intensity region represents the angle corresponding to the capture ray L p The bright areas within the medium intensity region are the escape cone 1 of the beveled surface and its image created by the surface of the crystal that is considered as a reflecting mirror (e.g., the effect of total internal reflection). s The rays that form are mainly composed of trapped rays, whose direction belongs to the escape cone or the image of the escape cone due to the structure. Without the chamfered edge or apex, these rays would not have left the crystal. In this example diagram, the medium chosen for the focusing crystal CL is a Ce:YAG crystal (refractive index n=1.82), and the critical angle for the surrounding medium air is 33°.

[0075] As can be seen in Figure 2B, the chamfered edge creates one escape cone (1) and three images (2-3-4), while in Figure 4B, the chamfered apex creates one escape cone and seven images (2-3-4-5-6-7-8). The area of ​​the escape cone in the angular representations of Figures 2B and 4B (i.e., the angular range over which the trapped beam exits the crystal) is determined by the critical angle of the TIR. In other words, the exit beam L s The maximum angle of the escape cone of the light rays that form is the critical angle θ c Therefore, it is determined by the refractive index of the crystal and the refractive index of the surrounding medium according to the Snell-Descartes law. Figures 3 and 4D show that for efficient light extraction,

[0076]

number

[0077] We will explain why the direction of the escape cone, which is an axis parallel to the axis of the escape cone, is important. In the first variant of the invention, it is the sum of the normals (

[0078]

number

[0079] ), or in the second variant of the invention, it is not parallel to the sum of the normals (

[0080]

number

[0081] ), the escape cone of the chamfered facet and its image may overlap with the escape cone of the other facet. Minimizing this overlap is important to achieve efficient light extraction.

[0082] FIG. 2C shows the trajectory of a ray emitted by a luminophore SP1 in a crystal CL. As an example, this ray has a trajectory in a direction 1 within an escape cone 1 along a horizontal plane xy, and the normal to the chamfered edge is O xyz It has angular coordinates (α=45°; β=0°) in the coordinate system (α is the angle in the plane xy and β is the angle with respect to the z axis). As mentioned before, for this shape, the normal to the chamfered edge is

[0083]

number

[0084] is the sum of the normals of the nearest sides (

[0085]

number

[0086] ) for simplicity, let us call this normal the "optimal normal". Considering the rectangular shape of the crystal, the light ray changes direction six times before leaving the crystal. From FIG. 2C it can be seen that the original cone of the light ray, the escape cone 1, is transformed due to the TIR on the side into cone image 2, then cone image 3, then cone image 4, then cone image 3, then cone image 2, then cone image 1, and then exits through the chamfered edge AB1. With the same light ray direction, the same exit point can be achieved by using luminophores SP2 emitting in direction 2 at cone image 2, or by using luminophores SP3 emitting in direction 3 at cone image 3, or by using luminophores SP4 emitting in direction 4 at cone image 4. This figure shows the light L exiting through the chamfered edge in the first variant of the invention. s is derived from four distinct cones of light. The chamfered edge therefore "recycles" the four escape cones and incoherently combines the rays from these four cones to produce the exit beam L s can be formed.

[0087] In contrast, in the prior art crystal of FIG. 1A, the light emerging from one of the sides is only available from one cone of light. If a reflector is placed on the face opposite the exit face in the prior art crystal of FIG. 1A, the light from said exit face is still only available from two cones of light. Thus, theoretically, for a rectangular crystal, the first variant of the invention (FIG. 2A) can provide a light extraction efficiency that is four times higher than that of the prior art crystal of FIG. 1A. Note that the light extraction efficiency is calculated based on the light intensity of the exit beam L. s The power output of the structure is expressed as the total power output (L p +L out +L g ) is calculated by dividing it by

[0088] As an example, for the crystal CL in FIG. 4A, the angular coordinates of the normal to the chamfered vertex in the xyz coordinate system are (α=45°; β=35.3°). FIG. 4C shows the coordinates in that coordinate system. For a rectangular crystal, this is the normal to the chamfered edge.

[0089]

number

[0090] is the sum of the normals of all the nearest faces (

[0091]

number

[0092] ), which means that the normal must be parallel to the x-axis and y-axis directions. Another representation of said normal is the coordinate (1,1,1) in the xyz coordinate system. For simplicity, we will call this normal the "optimum normal". For a crystal with a rectangular shape and a chamfered vertex S1, the direction of this normal ensures a minimum overlap between the angles forming the escape cone made by the chamfered vertex and the angles forming the cone of uncaptured rays. The images of escape cone 1 by the crystal faces are cones 2, 5, and 4. The images of cone 2 are cones 1, 6, and 3, the images of cone 3 are cones 2, 7, and 4, and the images of cone 4 are cones 3, 8, and 1. Thus, by multiple imaging, the chamfered vertex SB1 of crystal CL in FIG. 4A produces eight cones of light for the exit beam L. s Theoretically, for a crystal of rectangular parallelepiped shape, the second variant of the invention can thus lead to a light extraction efficiency that is 8 times higher than that of the prior art crystal of FIG.

[0093] However, to achieve this theoretical limit of light extraction efficiency, it is necessary that there is no overlap between the angles forming the escape cone created by the chamfered edge or apex and the angles forming the cone of untrapped rays. Indeed, if such an overlap exists, light rays propagating in the crystal at angles within the overlap range will "leak" out of the crystal through the side or large facets and will not contribute to increasing the brightness and power of the output beam, thus resulting in a relative decrease in light extraction efficiency. This means that this theoretical limit is more easily achieved using crystals with a higher refractive index (e.g. diamond), because the critical angle θ c , leaving more "space" in the escape cone formed by the chamfered edge or the refractive index. Clearly, this theoretical limit on the light extraction efficiency is ultimately determined by the critical angle θ c and is limited by the Snell-Descartes law.

[0094] FIG. 3 shows the escape cone L using the angular coordinates (α, β) in the xyz coordinate system. g , Lout and L s The bright areas between the cones are the captured rays L p This figure is taken as an example for a diamond crystal with a rectangular shape and chamfered edges with optimal normals, for the first variant of the invention. For diamond, assuming that the surrounding medium is air, the critical angle is θ c = 24.6°. From Figure 3, the four escape cones L s and their positions relative to the other cones are known. Figure 3 shows that the optimal normal is g and chamfered edge AB1 makes escape cone L s It can be shown that the overlap between the escape cones L is minimized. s The center of the escape cone L g It is aligned with the center of the escape cone L g In the first variant of the invention with a rectangular crystal and an optimum normal, the critical angle θ c If is less than 22.5°, the escape cone L g , L out and Escape Cone L s There will be no overlap between them.

[0095] FIG. 4D shows the escape cone L using the angular coordinates (α, β) in the xyz coordinate system. g , L out , and L s 4D is a planar representation of the diamond crystal of FIG. 4A. This figure is taken as an example of a rectangular diamond crystal with a chamfered apex having an optimal normal, in accordance with the second variant of the present invention. From FIG. 4D, the eight escape cones L formed by the chamfered apex can be seen. s , and their positions relative to the other cones are known. Unlike Fig. 3, in Fig. 4D, the optimal normal is g and the escape cone L formed by the chamfered edge AB1. s It can be seen that the escape cone L sThe center of is on the line β=35°, and the escape cone L g As an example, in a second variant of the invention, for a rectangular crystal with a normal to a chamfered vertex having angular coordinates of (α=45°; β=35.3°) in the xyz coordinate system, the critical angle θ c but,

[0096]

number

[0097] If less than L, escape cone L g +L out and Escape Cone L s There will be no overlap between them.

[0098] Escape Cone L g +L out and Escape Cone L s If there is an overlap between the angle ranges, in one embodiment of the present invention, the device 1 includes multiple reflectors covering the side surfaces except for the chamfered edges or chamfered apexes. This allows light rays propagating at inner angles that overlap with the angle range to be recycled and exit through the chamfered edges or apexes instead of leaking out of the crystal through the side surfaces or larger faces. If the reflectors cover the appropriate faces of the crystal, the light extraction efficiency of the device can be increased up to the theoretical limit mentioned above. In this specification, a reflector means a reflective surface with a reflectance of luminescent light higher than 50%, preferably higher than 90%, and more preferably higher than 99%.

[0099] In a preferred embodiment of the invention, the normal to the side surface lies in the horizontal plane xy (the plane of the large face). This means that the side surface is perpendicular to the large face. In this configuration, the escape cone of the side surface is self-imaged by the large face, which is considered as a reflecting mirror. This shape is advantageous to optimally recycle the captured rays through the chamfered edge or apex and achieve the highest possible light extraction. In fact, if the side surface is not perpendicular to the large face, the image of the escape cone of the side surface by the large face is not equal to their escape cone. Thus, if there are n side surfaces, there are n escape cones associated with those sides and n images made by reflection on other faces of the crystal. This means that if the side surface is not perpendicular to the large face, it is more complicated to achieve no overlap between the escape cone of the chamfered face and its image by reflection and the 2n escape cones associated with the side surface (i.e. the n "real" escape cones and the n images by reflection). Thus, for some shapes and given refractive indices of crystals, the above-described embodiments in which the side surfaces are perpendicular to the large faces can achieve higher light extraction efficiencies than those in which the side surfaces are not perpendicular to the large faces.

[0100] 5A and 5B respectively represent the brightness of the exit beam and the extraction efficiency as a function of the attenuation coefficient α of the crystal for various configurations. The various configurations are shown in FIG. 5C. The calculations were performed using analytical equations. In all exemplary configurations, the crystal is a rectangular Ce:YAG crystal with dimensions w=14 mm; L=100 mm; t=1 mm (see FIG. 5C for dimensions). In FIGS. 5A and 5B, the C0 and C0' curves are obtained from calculations based on a configuration corresponding to the top configuration in FIG. 5C, where the reflector covers the entire side surface SE' and the reflector covers the side surface SE partially. That is to say, an uncovered surface ("exit surface") is defined from which the exit beam leaves. This configuration, called "prior art configuration", is not an embodiment of the invention and recycles two escape cones thanks to the reflector. The C1 and C1' curves are obtained from calculations based on a first variant of the invention, has an optimal normal and corresponds to the middle configuration in FIG. 5C. Finally, the C2 and C2' curves are obtained from calculations according to a second variant of the invention, have optimal normals and correspond to the bottom configuration of FIG. 5C.

[0101] In both Fig. 5A and Fig. 5B, the surface of the exit face (uncovered surface in prior art configuration A, chamfered edge in C1 curve, and chamfered apex in C2 curve) is

[0102]

number

[0103] In the calculation of FIG. 5A, it is assumed that the emission of the exit beam immediately after the exit surface is Lambertian, and the brightness value is α=0 cm -1 The output beam L of the prior art configuration A in the case s Divided by the brightness value of

[0104] From FIG. 5A and FIG. 5B,

[0105]

number

[0106] It can be seen that in this case, the first and second variants of the invention provide a slightly better extraction efficiency and a brighter exit beam than the prior art configuration A. However,

[0107]

number

[0108] For α=5.10, the first and second variants of the present invention provide significantly better extraction efficiency and a much brighter output beam than prior art configuration A. -4 cm -1 In the case of the conventional configuration A, the output beam L s The brightness of the exit beam L in the first variant of the invention is 0.75 ua. s The brightness of the exit beam L in the second variant of the invention is 1.5 ua. s The brightness is 2.5ua. α=5.10 -4 cm -1 In the case of α=2.10, the extraction efficiency in the configuration A of the prior art is 14%, whereas in the first variant of the invention it is 24% and in the second variant of the invention it is 38%. -4 cm -1 In this case, the light extraction efficiency reaches over 50% for the second variant of the invention, but is still only 15% for configuration A of the prior art.

[0109] It is shown that the light rays exiting through the chamfered edge or apex of the crystal of the present invention have a longer average path than the light rays exiting from the side surface SE of the prior art crystal of Fig. 1 A. This explains why the effect of increasing the attenuation coefficient α on the brightness and extraction efficiency is relatively larger in the first and second variants of the present invention than in the prior art configuration A.

[0110] The surface of the chamfered edge or vertex is the average path L of the light rays that exit through the chamfered edge or vertex. meanIt will be noted that the average length directly affects the normal length. For example, in the case of the second variant of the invention (the bottom configuration in FIG. 5C) with optimal normals, the average length is

[0111]

number

[0112] where s2 is the area of ​​the chamfered apex. Preferably, and in order to obtain even greater benefit from the advantages provided by the configuration of the present invention, the crystal CL of the present invention has an extinction coefficient α of the luminescent light such that 1 / α>>2L. In the more general case where the crystal shape is not rectangular, L is the maximum distance between two parallel sides.

[0113] 5A and 5B show that both the brightness value of the exit beam and the light extraction efficiency value are higher for the configuration of the second variant of the invention than for the configuration of the first variant of the invention. As α becomes smaller, the gap between the two configurations becomes larger. This is due to the fact that the escape cone L recycled in the second variant of the invention g The number of escape cones L recycled in the first variant of the invention is 8. g This can be explained by the fact that it is twice the number four.

[0114] FIG. 6A shows a light-emitting device 1 according to a second variant of the invention, in which the crystal CL has six parallel sides, two by two. In this embodiment, n=6, and the normals to the sides are invariant upon rotation by an angle of π / 3 in the horizontal plane about the z axis. The normal to the chamfered vertex S1 is the sum of the normals of the three faces forming the vertex (

[0115]

number

[0116] ) which is the "optimal" normal for this shape. FIG. 6B displays the angular diagram of all rays emitted and trapped in the crystal CL of FIG. 6A. As shown in FIG. 6B, taking into account the shape of the crystal, the chamfered apex creates 12 artificial escape cones. Thus, theoretically, the second variant of the invention can be realized by using the escape cone L g , L out , L s If there is no overlap between the crystals, this can result in a light extraction efficiency that is 12 times higher than the light extraction efficiency of the prior art crystal of FIG. 1A.

[0117] In an embodiment of the invention that is compatible with the first and second variants of the invention, the crystal is a diamond containing nitrogen vacancy centers. NV (nitrogen vacancy) centers are impurities that are produced by irradiation in diamond and are used for their fluorescent properties. In this embodiment, the incident radiation Ld is emitted by a laser that illuminates at least one of the large faces. Typically, they absorb green light and emit red light. Considering the refractive index n=2.4 of diamond, the light that passes through the parallelepiped faces and exits into air corresponds to 4.5% of the total light. Usually, the light is collected by a confocal microscope. For example, with a numerical aperture of 1.35 (immersion objective), the collected light corresponds to a maximum of 8.6% of the emitted light. The sensitivity of the experiment depends on the amount of signal that is collected, and many strategies have been tried to increase this value. Thus, the diamond crystal CL of the invention can dramatically increase the light extraction efficiency. As an example, in the second variant of the invention, a rectangular crystal in ambient air and an optimal normal allows the recycling of eight escape cones in the exit beam Ls. This means that the light extraction efficiency is 4.5 x 8 = 36% in this example.

[0118] Control of the surface size of the chamfered apex allows the use of photodetectors with smaller surfaces that have the very short response times required for experiments with NV centers (lifetimes of about 10 ns, interrogation sequences of transitions in the μs range) while still collecting maximum light flux.

[0119] FIG. 7A shows various configurations of crystals coupled to an optical fiber FO via a tapered conical adapter TC.

[0120] The bottom configuration in Fig. 7A shows an embodiment of the invention that is compatible with the first and second variants of the invention. The rectangular crystal in Fig. 7A shown as an illustrative example is according to the second variant of the invention and includes a chamfered apex with an optimum normal. In this embodiment, the device 1 comprises a tapered conical adapter TC attached to the so-called upstream end adjacent to the chamfered edge or apex. "Attached" means that the upstream end is glued, for example with a very thin thickness of an intermediate medium of refractive index n'. The device 1 comprises an optical fiber FO connected to the so-called downstream end of the tapered adapter. The tapered adapter TC is connected to the output beam L s The numerical aperture of the optical fiber is f It is adapted so that the rays of the output beam are guided into the optical fiber by the TIR on that face. In a preferred embodiment, the face of the adapter is L s To improve the reflectivity of the beam, it is treated with a metallic or dielectric coating.

[0121] To ensure the preservation of etendue (or throughput), the upstream end diameter φ u and the downstream end diameter φ d are related by the following relationship:

[0122]

number

[0123] (wherein n is the refractive index of the crystal CL, θ m is the collection angle inside the crystal of the ray guided in the fiber.) If a glue with refractive index n' is used as the intermediate medium, then:

[0124]

number

[0125] To collect more light than would be possible by directly coupling the fiber into the luminous medium, the numerical aperture at the input of the cone must be larger than the numerical aperture at the output. This is called φ u <φ d The upstream end φ u It should be noted that the diameter of θ is limited by a minimum value that depends on the refractive index n' of the intermediate medium. If the numerical aperture of the adapter is sufficient to collect all possible angles, then θ' m = 90°, we need:

[0126]

number

[0127] The top configuration in Figure 7A is a prior art configuration ("prior art configuration B") in which the fiber is simply placed at the output side of the crystal ("butt coupled"), and has an aperture adapter TC and a reflecting mirror M2 on the face opposite the adapter to increase the collected flux.

[0128] The central configuration in FIG. 7A (called prior art configuration A′) corresponds to prior art configuration A and has a reflector placed at the exit surface to concentrate the light on the exit area where the adapter TC is located.

[0129] FIG. 7B shows the diameter φ of the upstream end for various configurations of the crystal shown in FIG. 7A. u 1 represents the light extraction efficiency as a function of .

[0130] The curves in FIG. 7B that correspond to the embodiment of the invention shown in the bottom diagram of FIG. 7A are curves C21 and C22.

[0131] In the calculation of the C21 curve, the core of the fiber (or its "precursor" by the cone) is inscribed in the face of the exit area, i.e. the chamfered edge or apex ("C21 configuration"). In this case, the fiber does not collect all the rays leaving the exit face.

[0132] In the calculation of the C22 curve, the fiber core completely contains the exit area ("C22 configuration"). In this case, all rays exiting from the chamfered edge or vertex are coupled into the fiber. However, the tradeoff is that the exit area is 1 / 4 the size of the C21 configuration. Therefore, the exit probability through this area is much lower, and the propagation length through the medium before finding an exit is longer.

[0133] The curve corresponding to prior art configuration A' in FIG. 7B is curve C0'' in FIG. 7A.

[0134] The curve corresponding to prior art configuration B in FIG. 7B is curve C01 in FIG. 7A.

[0135] In the three configurations shown in FIG. 7A as examples for calculating the curves in FIG. 7B, the crystal is rectangular in shape with dimensions w=2.5 mm, L=50 mm, t=1 mm, and α=2.10. -3 cm -1 The optical fiber core diameter is 1 mm and the numerical aperture is ON f = 0.5. Calculations were performed assuming no overlap between the escape cones.

[0136] In FIG. 7B, the vertical line VLx VL =0.5 mm, curves C0, C01, C22, and C21 are plotted against efficiency values ​​(φ u <x VL ) and the efficiency value achievable without an intermediate medium (φ u >x VL This vertical line is given by Eq1. As an illustrative example, in FIG. 7B, n'=1.4.

[0137] Curve C01 in FIG. 7B shows that the prior art configuration a) has a very low efficiency (about 1%). u =φ dFor φ = 1 mm (equivalent to a coupling without an adapter cone), the embodiment of the invention (see curves C21 and C22) already gives an 8-fold improvement over the coupling of the prior art configuration A (C01 curve) and a 2-fold improvement over the coupling of the prior art configuration A' (C0'' curve). u = 0.5 mm, this improvement factor is 18 for the C22 configuration and 24 for the C21 configuration. Finally, for φ u = 0.4 mm, the improvement factor is 32 for the C21 configuration.

[0138] FIG. 7B shows the output beam L in the optical fiber. s This clearly shows the advantages offered by using a crystal of the invention having bevelled edges or apexes in combination with an adapter TC to achieve high extraction efficiencies.

[0139] From FIG. 7B, the upstream end φ u It can be seen that the smaller the diameter of the crystal CL, the better the C21 configuration of the present invention is compared to the C22 configuration. This is due to the fact that the average path distance of the light rays inside the crystal CL before exiting from the chamfered end or apex is longer in the C22 configuration than in the C21 configuration. Thus, the propagation loss of the C22 limits the extraction efficiency.

[0140] Another object of the invention relates to scintillator crystals. As mentioned before, the energy resolution of a scintillator depends heavily on the light extraction efficiency of the crystal. Scintillators are often assembled in arrays to perform X-ray / gamma imaging. For compactness, parallelepiped crystals are most often chosen. An important parameter for this imaging method is the pixel density, with each scintillator in the array representing a pixel. In fact, in the case of scattering surfaces, the crystals must be optically separated from each other by a reflector to avoid "crosstalk", i.e. light emitted by a first crystal exiting the face of a second crystal and being detected as light coming from the second crystal.

[0141] In order to alleviate certain problems of the prior art, another object of the invention is an X-ray or gamma-ray imaging system comprising an X-ray or gamma-ray source and a detector Det. The detector Det is shown in FIG. 8 and comprises a number of identical light-emitting devices 1 according to the first or second variant of the invention. The crystal of each device shown as an illustrative example is according to the second variant of the invention and comprises a chamfered apex. In the embodiment of FIG. 8, the crystal of each device is a solid-state scintillator. The devices 1 are arranged to form an array and form a pixelated detector for the incident radiation Ld emitted by the X-ray or gamma-ray source. To collect the visible exit beam passing through the chamfered edge or apex, the imaging system comprises a number of photodiodes PD respectively arranged opposite the chamfered edge or chamfered apex of the crystal of each device. That is to say, in the imaging system of the invention, one pixel is formed by a device 1 and its corresponding photodiode PD. Preferably, all faces of the crystal are optically polished.

[0142] A crucial advantage of an imaging system using the detector of FIG. 8 compared to prior art scintillator detector arrays is that crosstalk is not an issue. This is due to the fact that in the detector Det, the only rays that leave the chamfered edge or chamfered apex and are detected by each photodiode are the captured rays from the crystals located on the opposite side of the photodiode. In fact, the uncaptured rays that leave any given face from any crystal of the array are identical and have the same escape cone, and therefore will not be captured by another crystal of the array. Thus, an uncaptured ray that leaves any crystal of the array will propagate through all the crystals of the detector that are on its path and will not be detected by any photodiode PD, depending on the position of the photodiode PD.

[0143] By making the area of ​​the chamfered edges or chamfered apexes of the crystal smaller than the area of ​​the lateral surfaces between the chamfered edges or chamfered apexes, it is possible to use photodiodes with smaller surfaces that have a very short response time while still collecting maximum light flux.Thus, preferably, the surface of the photodiode and the surface of the chamfered edges or apexes are smaller than the surface of the lateral surfaces between the chamfered edges or apexes.

[0144] The ratio of the surface of the chamfered edge or the surface of the chamfered vertex to the total surface of the crystal CL (S bev / S tot ) is an important parameter for controlling the so-called "concentrator effect" that concentrates the luminescent light into an output beam with a large luminous flux. bev / S tot The smaller the ratio of S, the greater the luminous flux of the output beam (assuming that the propagation losses do not compensate for the concentrator effect). In fact, a small S bev / S tot The ratio "pushes" the luminescence light out through a small exit area while recycling many trapped rays and allowing the crystal CL to be excited through a large facet with a relatively large area. Furthermore, as mentioned above, a smaller S bev / S tot The use of the ratio is useful for adapting the emission area to that of any photodetector having a small surface to ensure a very short response time.

[0145] Therefore, preferably, in all embodiments of the present invention, S bev / S tot The ratio is less than 1 / 10, preferably less than 1 / 100, and more preferably less than 1 / 1000. Through simulations and experiments, the inventors have found that the S ratio is less than 1 / 10. bev / S tot The use of the ratio allows for a sufficient light collection effect of the luminescent light while maintaining a S of less than 1 / 100, preferably less than 1 / 1000. bev / S totIt has been determined that the selection of the ratio allows for a greater luminous flux of the exit beam.

[0146] The following table shows selected embodiments using a parallelepiped crystal CF with chamfered edges, using different parameters and different materials. In the following examples, the edges are at the surface t 2 (useful in most applications to provide a symmetric exit beam) and bev / S tot The ratio can be estimated as follows:

[0147]

number

[0148] [Table 1]

[0149] As mentioned above, the shape of the parallelepiped structure encourages the light rays to be recycled within the structure until they exit through the chamfered edges. The following ratios and dimensions result in a crystal CL with an exit surface that is particularly suitable for combination with photodetectors for various applications.

Claims

1. It contains a solid fluorescent material or a solid scintillator material (CL), in which incident light (Ld) is absorbed and then luminescent light (L Ｌ A light-emitting device (1) adapted to emit light having a wavelength of 100 nm, The luminescent light capture portion (L ｐ ), is captured in the material by total internal reflection, The material has two parallel faces (FE1, FE2) along the horizontal plane xy, called the large faces, and two parallel faces (FE1, FE2) along the horizontal plane xy, called the side faces. [0010] faces (FL1, FL2, FL3, FL4) forming vertices (S2, S3, S4) between two adjacent sides and the larger face; the material has a normal to the side surface that is invariant with rotation through an angle of 2π / n within the horizontal plane about a z-axis perpendicular to the horizontal plane; The material has a vertex (S1) called the virtual chamfered vertex which forms a surface called the chamfered vertex (SB1), A portion of the captured light beam passes through the chamfered apex to form an exit beam (L Ｓ ) is formed, The normal to the chamfered vertex ( [0025] ) is parallel to the sum of the normals of the faces forming said virtual vertex within a range of ±10°.

2. The device of claim 1 , wherein the material is a rectangular solid.

3. 3. The device of claim 1, wherein the angular coordinates of the normal to the chamfered vertex in the xyz coordinate system are (α=±45°; β=±35.3°)±10°.

4. It contains a solid fluorescent material or a solid scintillator material (CL), in which incident light (Ld) is absorbed and then luminescent light (L Ｌ A light-emitting device (1) adapted to emit light having a wavelength of 100 nm, The luminescent light capture portion (L ｐ ), is captured in the material by total internal reflection, The material has two parallel faces (FE1, FE2) along the horizontal plane xy, called the large faces, and two parallel faces (FE1, FE2) along the horizontal plane xy, called the side faces. [0030] The surface (FL1, FL2, FL3, FL4) the material has a normal to the side surface that is invariant with rotation through an angle of 2π / n within the horizontal plane about a z-axis perpendicular to the horizontal plane; said material has an edge between two side surfaces, called a virtual edge (S1S5), which is chamfered to form a surface of a chamfered edge (SB1); A portion of the captured light beam passes through the chamfered edge to form an exit beam (L Ｓ ) is formed, The normal to the chamfered vertex ( [0045] ) is parallel to the sum of the normals of the two side surfaces forming said virtual edge within a range of ±10°.

5. The device of claim 1 , 2 or 4 , comprising a plurality of reflectors covering the side surfaces except for the chamfered edges or the chamfered vertices.

6. 5. The device according to claim 1, 2 or 4, wherein the material has an extinction coefficient α of the luminescent light such that 1 / α>>2L, where L is the maximum distance between two parallel sides.

7. 5. The device according to claim 1, 2 or 4, wherein the material is a diamond crystal having nitrogen vacancy centers and the incident radiation (Ld) is generated by a laser irradiating at least one face of the crystal.

8. 5. The device of claim 1, 2 or 4, wherein the side surface is perpendicular to the larger surface.

9. a tapered cone adapter attached to the so-called upstream end adjacent the chamfered edge or apex, and an optical fiber connected to the so-called downstream end of the tapered adapter; 5. The device of claim 1, 2 or 4, wherein the tapered adapter matches the numerical aperture of the output beam to the numerical aperture of the optical fiber.

10. 5. A device according to claim 1, 2 or 4, wherein the ratio of the surface of the chamfered edge or apex to the surface of the face of the material is lower than 1 / 10.

11. 11. The device according to claim 10, wherein said ratio is lower than 1 / 100, preferably lower than 1 / 1000.

12. 1. An X-ray or gamma ray imaging system comprising an X-ray or gamma ray source and a detector (Det) including: a plurality of light-emitting devices (1) according to claim 1, claim 2 or claim 4 arranged to form an array, the material of each device being a solid scintillator; - a number of photodiodes (PD) arranged on opposite sides of the chamfered edge or the chamfered apex of the material of each device; An imaging system comprising:

Images