Patent Application
20140369023
The present application is a national stage entry according to 35 U.S.C. §371 of PCT application No.: PCT/EP2012/068553 filed on Sep. 20, 2012, which claims priority from German application No.: 102011085978.0 filed on Nov. 9, 2011, and is incorporated herein by reference in its entirety.
Various embodiments relate to a laser-phosphor device having a laser array, for example a laser diode array, the radiation of which is directed onto a phosphor layer in order to stimulate the latter to shine. The term laser array is intended to mean an arrangement of a multiplicity of lasers. The individual lasers of the laser array may be the same as one another or different to one another
The related art discloses laser-phosphor devices in which a laser spot is generated on a phosphor layer by means of various optics, so that the phosphor layer is excited and emits light. Such laser-phosphor devices are used, for example, as light sources. In this case, the laser radiation is guided through primary optics and through an optical system, before it strikes the phosphor layer. The laser radiation collimated by the primary optics is in this case focused through the optical system to form a laser spot. The converted light generated at the position of the spot on the phosphor is delivered through a converging optical system to an application.
The idea of using laser radiation is that it can be concentrated onto a small area (spot) and generates useful light with a high luminous density there with the aid of a phosphor. The converging optical system therefore only processes light from the region of the spot. Any displacement or enlargement of the spot therefore leads to a reduction of the useful light. These displacements or enlargements of the spot may, for example, be caused by placement, shape and position tolerances of the lasers and of the primary optics.
Various embodiments provide a laser-phosphor device in which the tolerances, in particular position tolerances, of the primary optics collimating the laser radiation have up to a certain extent no effects on the position and size of the laser spot on the phosphor.
In the laser-phosphor device according to the disclosure, laser radiation (for example coherent light, i.e. laser radiation in the visible range, or coherent electromagnetic radiation in the ultraviolet (UV) or infrared (IR) range) of a laser array can be transmitted via primary optics and via an imaging optical system onto a phosphor layer. The laser array has a multiplicity of lasers, for example laser diodes, which can emit laser radiation with the same wavelength and/or different wavelengths. The imaging optical system is configured in such a way that the part, passed through by the laser beam, of a plane which extends perpendicularly to the optical axis of the system and lies at least in the vicinity of the primary optics, preferably in the primary optics or in the light path immediately after the primary optics, can be imaged with reduction onto the phosphor layer. In other words, the spot generated by the optical imaging system is the reduced optical image of the radiation distribution in the aforementioned plane through which the laser beam passes, i.e. ultimately the radiation distribution of the primary optics. In this way, small position deviations of the primary optics can be tolerated since they do not lead to any enlargement or position displacement of the spot, but merely alter the angle of incidence of the laser light on the phosphor.
In this case, it has been found advantageous for the imaging to take place with reduction approximately on a scale of 1:40.
In order to collimate respective light emitted by the assigned laser, preferably a laser diode, the primary optics preferably have a multiplicity of converging lenses, a converging lens being assigned to each laser or laser diode. In other words, the primary optics are preferably configured as an array of collimated primary optical elements, preferably converging lenses, which corresponds to the laser array.
In a preferred refinement, each converging lens includes two convexly curved surfaces, one of which is aspherical.
The optical imaging of the laser-phosphor device according to the disclosure is preferably telecentric on both sides.
In a preferred variant, the imaging optical system has a positive lens or positive lens group, a negative lens or negative lens group, and a subsequent positive lens or positive lens group.
In another preferred variant, the imaging optical system consists of a telescope arrangement having two mirrors (reflecting telescope).
In this case, the multiplicity of laser diodes may be arranged in annularly around the convexly curved mirror.
In a first variant, the hollow mirror arrangement has a concavely curved hollow mirror having a central opening.
In a second variant, the hollow mirror arrangement has a multiplicity of hollow mirrors, a hollow mirror being assigned to each laser diode.
In another variant, the output takes place laterally, for example in the manner of a newtonian or Nasmyth telescope arrangement.
In order to avoid hot spots on the phosphor, which could occur owing to sharp imaging of the individual laser diodes or of the assigned converging lenses, the imaging may be slightly defocused so that the imaging is a little blurred and the irradiation strength distribution is rendered uniform. Furthermore, in this context it is advantageous for the lasers with the assigned primary optical elements to be arranged uniformly, preferably hexagonally or rectangularly, particularly in a square.
The disclosure is not limited to laser diodes, but may include all types of laser light sources, i.e. for example: gas lasers, solid-state lasers, fiber lasers. Furthermore superluminescent diodes having essentially parallel beam emission are also intended to be included here under the term laser.
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:
The following detailed description refers to the accompanying drawing that show, by way of illustration, specific details and embodiments in which the disclosure may be practiced.
These are distributed uniformly on the array 2 with the format 40 mm*60 mm.
Each laser diode 1 of the laser diode array 2 is assigned a biconvex converging lens 4, the twenty-four converging lenses 4 forming primary optics 6 in the form of a primary lens array. Via the converging lenses 4, each of which has a diameter of 6 mm, the light of each assigned laser diode 1 is collimated. An imaging optical system consisting of the lenses 8, 10 and 12 images the surface of the primary lens array on a reduced scale as a spot (14) on the phosphor (28, see also
With a maximum angle divergence of ±0.5° relative to the optical axis (which corresponds to the horizontal in the plane of the drawing) of the light after the primary optics 6 amounts to about 20° on the selected imaging scale of 1:40 of the full angle of incidence on the phosphor layer. With a maximum lateral centering error (i.e. in a plane perpendicular to the plane of the drawing) of 20 μm for one or more of the converging lenses 4 of the primary optics 6, the divergence is increased by 0.6°, i.e. up to ±1.1°. Nevertheless, according to the disclosure the position and the size of the spot 14 on the phosphor layer 28 does not change; it is merely that the angle of incidence increases from 20° (with divergence of ±0.5° to 50° (corresponding to a divergence of ±1.1°. The imaging optical system 8, 10, 12 or 108, 116, 110, 118, 112, 120, respectively, is configured in such a way that these 50° are still transmitted on the spot side. In this way, the effects of the position tolerances of the converging lenses 4 of the primary optics 6 are eliminated, assuming that the extent of the tolerances is not so great that the imaging optical system can no longer transmit the light.
Similarly, the position and the size of the spot (14) on the phosphor layer (28) is preserved by the arrangement according to the disclosure even if centering errors due to adjustment inaccuracies of one or more converging lenses (4) of the primary optics (6) parallel to the optical axis, and adjustment inaccuracies due to tilting of the primary lenses, occur.
In the third embodiment, the primary lens plane through which the laser radiation of the laser diodes (201) passes is imaged on a reduced scale by means of a reflecting telescope-like arrangement. First, the light oriented parallel by the converging lenses 204 is reflected by a concavely curved hollow mirror 236 into a central region inside the annular laser diode arrangement. Arranged there, there is a convexly curved mirror 238 by which the light rays are directed in a collimate fashion through an opening 240 of the hollow mirror 236.
In a variant which is not represented, the mirror 238 is likewise concave.
In the third embodiment as well, the arrangement of laser diodes 201 is imaged in the form of a spot of reduced size on the phosphor layer (neither shown in
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2011 085 978.0 | Nov 2011 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2012/068553 | 9/20/2012 | WO | 00 | 5/8/2014 |
