Lighting device comprising a pump radiation source

Abstract

According to the present disclosure, an illumination apparatus includes a pump radiation source for emitting pump radiation, a phosphor element for converting the pump radiation into conversion light and a carrier, on which the phosphor element is mounted, which carrier is made of a carrier material which is transparent at least for the pump radiation and has a refractive index n.sub.carrier. The pump radiation passes through the carrier, exits at an exit surface of the carrier and is then incident on a pump radiation input coupling surface of the phosphor element that is arranged at the exit surface. The pump radiation in the carrier is incident on the exit surface of the carrier with a centroid direction, which centroid direction is inclined with respect to a surface normal on the exit surface by an exit angle .sub.out0, and .sub.out<.sub.c with .sub.c=arcsin(1/n.sub.carrier).

Claims

1. An illumination apparatus (1), comprising a pump radiation source (2) for emitting pump radiation (3), a phosphor element (5) for converting the pump radiation (3) into conversion light (14,16) and a carrier (6), on which the phosphor element (5) is mounted, which carrier (6) is made of a carrier material which is transparent at least for the pump radiation (3) and has a refractive index n.sub.carrier, wherein the pump radiation (3) passes through the carrier (6), exits at an exit surface (12) of the carrier (6) and is then incident on a pump radiation input coupling surface (13) of the phosphor element (5) that is arranged at the exit surface (12), wherein the pump radiation (3) in the carrier (6) is incident on the exit surface (12) of the carrier (6) with a centroid direction (22), which centroid direction (22) is inclined with respect to a surface normal (21) on the exit surface (12) by an exit angle (20) .sub.out0, wherein .sub.out<.sub.c with .sub.c=arcsin (1/n.sub.carrier); and wherein, in a condition of the phosphor element (5) being dismounted from the carrier (6) and optically decoupled from light exiting the exit surface (12), a lower limit angle of the exit angle (20) is given by .sub.outarcsin.

2. The illumination apparatus as claimed in claim 1, having a reflection surface which faces the pump radiation input coupling surface such that at least a part of a backscattered conversion light which is emitted at the pump radiation input coupling surface is reflected at the reflection surface back in the direction of the phosphor element.

3. The illumination apparatus as claimed in claim 2, wherein the reflection surface is interrupted by a hole-shaped interruption through which the pump radiation propagates from the pump radiation source to the pump radiation input coupling surface of the phosphor element.

4. The illumination apparatus as claimed in claim 2, wherein the reflection surface has the shape of a concave mirror, viewed from the pump radiation input coupling surface of the phosphor element.

5. The illumination apparatus as claimed in claim 4, wherein the reflection surface is spherical, wherein a surface centroid of the pump radiation input coupling surface has a distance d, extending along a surface normal on the pump radiation input coupling surface, from the spherical reflection surface, and a sphere on which the spherical reflection surface is based has a radius R, wherein 0.8.Math.R<d<1.2.Math.R.

6. The illumination apparatus as claimed in claim 4, wherein the carrier is configured as a plano-convex lens, the convex lateral surface of which includes an entry surface at which the pump radiation enters the carrier, and at the planar side of which the phosphor element is arranged, wherein a reflection layer forming the reflection surface is applied on the convex lateral surface of the carrier and partially covers it.

7. The illumination apparatus as claimed in claim 4, wherein an entry surface of the carrier at which the pump radiation enters the carrier and the reflection surface are arranged at a distance from one another via a gas volume through which the part of the backscattered conversion light that is reflected at the reflection surface back in the direction of the phosphor element passes.

8. The illumination apparatus as claimed in claim 7, wherein the carrier is configured as a plane-parallel plate.

9. The illumination apparatus as claimed in claim 8, wherein the carrier, which is configured as a plane-parallel plate, is put together with a reflector forming the reflection surface.

10. The illumination apparatus as claimed in claim 1, wherein the pump radiation is incident on an entry surface of the carrier in linearly polarized fashion at an entry angle .sub.in 0, and a polarization plane, formed by vectors of the electric field, is inclined with respect to a plane of incidence by at most 20.

11. The illumination apparatus as claimed in claim 10, wherein the carrier is configured as a plane parallel plate, wherein 0.5.0.Math..sub.B.sub.in1.3.Math..sub.B, with .sub.B=arCtan(n.sub.carrier/1).

12. The illumination apparatus as claimed in claim 1, wherein the pump radiation has, immediately upstream of the exit surface, a cross-sectional profile whose maximum extent, along a wide axis, corresponds to at least 1.2 times an extent along a narrow axis, which is perpendicular to the former, wherein the narrow axis is inclined with respect to a plane of incidence by at most 20.

13. The illumination apparatus as claimed in claim 1, wherein the pump radiation, upstream of the carrier, passes through a converging lens that has an optical axis, wherein the pump radiation is incident on the converging lens with an offset with respect to the optical axis, i.e. a central axis of the beam with the pump radiation is offset with respect to the optical axis upstream of the converging lens.

14. The illumination apparatus as claimed in claim 1, having a plurality of pump radiation sources which are each configured for emitting pump radiation in the form of a beam, wherein, to the extent that two of the beams are rotationally symmetric relative to one another with a rotational axis that is perpendicular to the pump radiation input coupling surface, a rotational angle on which said rotational symmetry is based differs from 180.

15. The use of an illumination apparatus as claimed in claim 1 for illumination.

16. The illumination apparatus as claimed in claim 1, further comprising an illumination optical unit (17) optically coupled to light exiting the phosphor element (5) and having a light collection aperture angle that is not in excess of two times said lower limit angle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present disclosure will be explained in more detail below with reference to exemplary embodiments, wherein, within the context of the coordinate claims, the individual features can also be essential to the present disclosure in a different combination, and, furthermore, a distinction is not always specifically drawn between the different claim categories.

(2) In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the disclosed embodiments. In the following description, various embodiments described with reference to the following drawings, in which:

(3) FIG. 1A shows a first illumination apparatus according to the present disclosure having a pump radiation source and a phosphor element in a partially cut side view during normal operation;

(4) FIG. 1B shows a schematic illustration, in supplementation of FIG. 1A, for illustrating the angle during the pump radiation input coupling;

(5) FIG. 2 shows the illumination apparatus in accordance with FIG. 1A in the case of an error, specifically if a phosphor element is not present;

(6) FIG. 3 shows a second illumination apparatus according to the present disclosure in a partially cut side view, specifically likewise in the case of an error similar to FIG. 2.

DETAILED DESCRIPTION

(7) FIG. 1 shows an illumination apparatus 1 according to the present disclosure having a pump radiation source 2, specifically a laser diode, for emitting pump radiation 3. Immediately downstream of the pump radiation source 2, the pump radiation 3 passes through a converging lens 4, which focuses the beam with the pump radiation 3. Downstream of the converging lens 4, the pump radiation 3 is guided onto a phosphor element 5, which is applied directly onto a carrier 6.

(8) The carrier 6 is a plane-parallel plate made of sapphire, which has been inserted into a reflector that has the shape of half a hollow sphere. A correspondingly shaped injection molded part 7 made of polycarbonate, which is coated on the inside with a silver layer 8, forms the reflector. The silver layer 8 forms a reflection surface 9 that faces the carrier 6 and the phosphor element 5 and the function of which will become clear in the context of the operation of the illumination apparatus 1 described below.

(9) In order to be able to couple the pump radiation 3 into the just described arrangement, the injection molded part 7 includes an interruption 10 through which the pump radiation 3 can pass inside from outside the hollow sphere. The pump radiation 3 then enters the carrier 6 at an entry surface 11, exits at an opposite exit surface 12, and is then incident on a pump radiation input coupling surface 13 of the phosphor element 5. The phosphor element 5 is made of cerium-doped yttrium aluminum garnet (YAG:Ce) and is excited with the pump radiation (in the present case, blue pump light having a dominant wavelength of 450 nm).

(10) Upon this excitation, the phosphor element 5 emits a conversion light 14 at a conversion light output coupling surface 15 that is located opposite the pump radiation input coupling surface 13. However, upon excitation with the pump radiation 3, conversion light is emitted in principle omnidirectionally, that also means a backscattered conversion light 16 is emitted at the pump radiation input coupling surface 13. In order to also make this useful for the illumination, the reflection surface 9 is provided, at which the backscattered conversion light 16 is reflected and in this way guided back in the direction of the phosphor element 5. The conversion light 14, which was originally emitted at the conversion light output coupling surface 15, is then focused, together with the thus recycled backscattered conversion light 16, using an illumination optical unit 17 (only schematically indicated in the present case) and guided to the illumination application. In a simple case, the illumination optical unit can also merely be a plane-parallel plate, or such a plane-parallel plate can form the first optical element of the optical unit, in that case a combination with a plurality of lenses is preferred.

(11) FIG. 1B shows a schematic detail view of FIG. 1A, specifically for illustrating the angles during the pump radiation guidance. The pump radiation 3 is coupled into the carrier 6 obliquely with respect to the entry surface 11 (FIG. 1A) of the carrier 6 such that it is incident on the exit surface 12 (cf. FIG. 1A) of the carrier 6 at an exit angle 20 (.sub.out). The exit angle 20 is the one between a surface normal 21 on the exit surface of the carrier 6 and a centroid direction 22 which the pump radiation 3 has within the carrier 6. The exit angle 20 is here smaller than the critical angle .sub.c for total internal reflection (34 for sapphire); yet at the same time it is 33, with the latter angle being obtained from arcsin((1/n.sub.Saphir).Math.sin(77)).

(12) The illumination optical unit 17 has an aperture angle of 150, consequently a used light cone, that is to say the conversion light guided via the illumination optical unit 17 (including partially non-converted pump radiation) has a half-opening angle of 75. With the just mentioned lower limit for the exit angle 20 it is possible to ensure that, in the case of an error if the phosphor element 5 falls off the carrier 6, the pump radiation is not, or at least not to any major extent, coupled into the illumination optical unit 17. As is schematically indicated by the dashed line in FIG. 1B, the pump radiation in this case is refracted past the illumination optical unit 17, and dangerous propagation of focused pump radiation via the illumination optical unit 17 can be avoided. Reference is also made to the detailed discussion in the introductory part of the description.

(13) FIG. 2 illustrates the case of the error further in detail for the illumination apparatus of FIG. 1A, wherein the representation is based on a raytracing simulation by the inventor. The phosphor element has fallen off, and for this reason the pump radiation, as is explained with reference to FIG. 1B, is laterally refracted at the exit surface 12 of the carrier 6. In the underlying simulation, losses at the boundary surfaces are additionally taken into account, because reflections occur both at the entry surface 11 and at the exit surface 12 (Fresnel losses). The reflection coefficients are below 20%, but even this portion of the pump radiation can become a problem in the case of propagation via the illumination optical unit 17. Even if an anti-reflective coating is applied at the boundary surfaces of the carrier 6, the reflections cannot be entirely avoided.

(14) In FIG. 2, a corresponding portion of the pump radiation reflected at the exit surface 12 of the carrier 6, said portion making up around 10% of the pump radiation that is incident on the exit surface 12 (with respect to the radiant power), is denoted with the reference sign 25. This pump radiation reflected at the exit surface 12 is incident on the reflection surface 9, is reflected here back in the direction of the carrier 6, passes through it, and is refracted out of the used light cone due to the symmetric setup like the pump radiation that originally exited at the exit surface 12, only to the other side (to the top left in the figure). In summary, even taking into account reflection losses occurring in reality in the case of an error, it is possible for propagation of the pump radiation via the illumination optical unit 7 to be avoided.

(15) During normal operation, i.e. with the phosphor element 5 present, the entire pump radiation 3 is not converted in the phosphor element 5, but a non-converted part of the pump radiation 3 together with the conversion light 14 (and also with the recycled backscattered conversion light 16) forms the illumination light. The non-converted pump radiation is in this case, however, scattered in the phosphor element 5, i.e. fanned out, therefore does not propagate in a focused form in the illumination optical unit 17.

(16) The oblique coupling of the pump radiation 9 onto the entry surface 11 of the carrier 6 is furthermore also advantageous in as far as the pump radiation 3 is linearly polarized, specifically p-polarized. That means, a polarization plane including the vectors of the electric field of the pump radiation thus coincides with the plane of incidence (in the present case the drawing plane). This is advantageous in as far as in that case, with increasingly inclined input coupling, the reflection coefficient that determines the Fresnel losses (at the transition air/sapphire) decreases from around 10% to what is known as the Brewster angle .sub.B, cf. also the statements in the introductory part of the description.

(17) FIG. 3 shows a further illumination apparatus 1 according to the present disclosure, which corresponds to that in accordance with FIG. 1A as far as the pump radiation source 2, the converging lens 4 and also the relative arrangement of phosphor element 5 and illumination optical unit 17 are concerned. The pump radiation 3 is guided to the phosphor element 5, similar to the description regarding FIG. 1B. In the possible case of an error, i.e. if the phosphor element is not present, the pump radiation is then refracted from the used light cone, as in the case of the above-described embodiment. In general, in the context of this disclosure, identical reference signs denote parts having the same function, and, to this extent, reference is always also made to the description relating to the other figures.

(18) In the illumination apparatus in accordance with FIG. 3, the carrier 30 provided is not a plane-parallel plate, but a hemisphere made of sapphire. Arranged on the planar side of it is the phosphor element 5, while the convex side is coated with a reflection layer 32 made of silver that forms a reflection surface 31. The resulting reflection surface 31 is, like the above-mentioned reflection surface 9, spherical and serves for recycling the backscattered conversion radiation 16 and a part of the pump radiation that is scattered back at the pump radiation input coupling surface 13. In the present case, the pump radiation 3 is coupled in perpendicularly to the spherical-convex lateral surface of the hemisphere.

(19) While the disclosed embodiments have been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the disclosed embodiments as defined by the appended claims. The scope of the disclosed embodiments is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.