LASER LIGHT SOURCE UNIT, ILLUMINATION APPARATUS AND METHOD FOR GENERATING LASER LIGHT

Abstract

A laser light source unit for vehicles, with a resonator containing a first end mirror and a second end mirror, between which an active laser medium is arranged, and with a pump device for generating pump radiation, which can be introduced into the resonator via the first end mirror, wherein a rotatable birefringent medium is arranged in the resonator such that, according to a rotation of the birefringent medium, preferred radiation of different wavelengths is stimulated in the active laser medium.

Claims

1. A laser light source unit for an illumination apparatus for vehicles, the laser light source comprising: a resonator having a first end mirror and a second end mirror; an active medium arranged between the first end mirror and the second end mirror; a pump to generate pump radiation that is adapted to be introduced into the resonator via the first end mirror; and a rotatable birefringent medium arranged in the resonator such that, according to a rotation of the birefringent medium, preferred radiation having different wavelengths is stimulated in the active laser medium.

2. The laser light source unit according to claim 1, wherein the birefringent medium is formed such that at twice the passage through the birefringent medium, exclusively the preferred radiation with a specific wavelength has phase balance and a substantially identical polarization direction, and wherein the preferred radiation with the particular wavelength is in phase and has the same polarization direction before and after twice the passage through the birefringent medium.

3. The laser light source unit according to claim 1, wherein the birefringent medium is designed as a birefringent plate which is arranged at a Brewster angle to an optical axis of the active laser medium.

4. The laser light source unit according to claim 1, wherein the pump device is designed such that the pump device radiates pump radiation of a first wavelength, wherein the first end mirror and the second end mirror are designed to be highly transmissive for the pump radiation of the first wavelength, wherein the first end mirror is designed to be highly reflective for the preferred radiation of a second wavelength and/or a third wavelength and/or a fourth wavelength, and wherein the second end mirror is designed to be partially transmissive and/or partially reflective for the preferred radiation of the second wavelength and/or the third wavelength and/or the fourth wavelength.

5. The laser light source unit according to claim 4, wherein, according to the rotational position of the birefringent medium, the laser light that is coupled out by the second end mirror corresponds to an additive color mixture of the pump radiation of the first wavelength and the preferred radiation of the second wavelength and/or the third wavelength and/or the fourth wavelength.

6. The laser light source unit according to claim 1, wherein the pump device comprises a laser diode for emitting the pump radiation in a blue wavelength as a first wavelength, and wherein the active laser medium includes a praseodymium-doped crystal material.

7. The laser light source unit according to claim 1, wherein the birefringent medium is assigned a setting device for the rotation of the former about the optical axis with a constant speed, so that the preferred radiation of a plurality of wavelengths of the pump radiation of the first wavelength is superimposed on the emitting laser light.

8. The laser light source unit according to claim 1, wherein the first end mirror is flat and the second end mirror of the resonator is spherical.

9. An illumination apparatus for vehicles comprising: a laser light source unit according to claim 1; and a radiation direction of a same upstream optical unit for generating a predetermined distribution of light.

10. A method for generating laser light, the method comprising: introducing pump radiation from an outside into an active laser medium which is arranged between two end mirrors and is coupled out at one of the end mirrors as laser light; and transmitting radiation within the resonator on the way between the active laser medium and the second end mirror, passed twice through a birefringent medium, each with a change in the polarization direction after passage through the birefringent medium, wherein after twice the passage through the birefringent medium, exclusively preferred radiation of a specific wavelength is in phase and has the same polarization direction as before twice the passage through the birefringent medium.

11. The method according to claim 10, wherein the birefringent medium is rotated at a speed about the optical axis, which is greater than a minimum speed, so that laser light of a white color is generated by the additive color mixing of wavelengths of the preferred radiation stimulated selectively in the different rotational positions of the birefringent medium and the pump radiation introduced into the active laser medium from the outside.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

[0018] FIG. 1 is a schematic structure of a laser light source unit;

[0019] FIG. 2 is a plan view of a circular birefringent medium with an illustration of preferred radiation of different wavelengths; and

[0020] FIG. 3 is an emission spectrum of the emitted laser light of white light color, wherein the birefringent medium is operated at a minimum speed.

DETAILED DESCRIPTION

[0021] A laser light source unit 1 according to the invention can be used in illumination apparatuses for vehicles, for example as headlights or for example as interior lighting in vehicles. Alternatively, the laser light source unit 1 can also be used in other lights for other purposes.

[0022] The laser light source unit 1 includes a pump device 2 for generating pump radiation 3, and a resonator 4. The resonator 4 has a first end mirror 5 on a side facing the pump device 2 and a second end mirror 6 on a side facing away from the pump device 2. Between the first end mirror 5 and the second end mirror 6 of the resonator 4, an active laser medium 7 and a birefringent medium 8 are arranged. In the present exemplary embodiment, the active laser medium 7 is arranged between the first end mirror 5 and the birefringent medium 8. The birefringent medium 8 is arranged between the active laser medium 7 and the second end mirror 6.

[0023] The first end mirror 5 serves as an input mirror for the pump radiation 3. The second end mirror 6 serves as an output mirror for emitting laser light 9 in a radiation direction A.

[0024] Along an optical axis 10 of the laser light source unit 1, the pump device 2, the first end mirror 5, the active laser medium 7, the birefringent medium 8 and the second end mirror 6 are thus arranged one behind the other.

[0025] The birefringent medium 8 can also be arranged in the radiation direction A behind the active laser medium 7 so that it is positioned between the active laser medium 7 and the first end mirror.

[0026] The pump device 2 comprises a laser diode, which emits pump radiation 3 of a first wavelength 11, namely a blue wavelength. For example, FIG. 3 shows the emission spectrum of the white laser light 9, wherein in addition to the first wavelength 11 (blue), a second wavelength 12 (green wavelength), a third wavelength 13 (orange wavelength) and a fourth wavelength 14 (red wavelength) are specified. The term wavelength used here also stands synonymously for wavelength ranges which comprise several wavelengths for a specific light color, as is shown, for example, by the emission spectrum of the laser medium 7 shown in FIG. 3.

[0027] The active laser medium 7 is designed as a praseodymium-doped crystal material, for example praseodymium-doped yttrium lithium fluoride crystal material (Pr 3+:YLF) and emits an emission spectrum. The active laser medium can also be formed of another crystal material. The Pr:YLF crystal should be used in particular to generate green and red wavelengths.

[0028] The first end mirror 5 and the second end mirror 6 are designed to be highly transmissive for the pump radiation 3 of the first wavelength 11. The transmittance for the first wavelength 11 is preferably 100% or just below 100% (close to 100%).

[0029] The first end mirror 5 is highly reflective for the second wavelength 12 and/or third wavelength 13 and/or fourth wavelength 14 and/or for a further wavelength which is different from the first wavelength 11. The first end mirror 5 preferably has a degree of reflection of 100% or just below 100%. The second end mirror 6 is partially transmissive and/or partially reflective for the second wavelength 12 and/or third wavelength 13 and/or fourth wavelength 14 and/or for a further wavelength that differs from the first wavelength 11. For this purpose, the second end mirror 6 preferably has a degree of reflection in a range from 96% to 100%. The degree of reflection of the second end mirror 6 for the second wavelength 12, third wavelength 13, fourth wavelength 14 and/or further wavelengths different from the first wavelength 11 is smaller than in the first end mirror 5, since radiation of the second wavelength 12 and/or the third wavelength 13 and/or fourth wavelength 14 must be coupled out of the second end mirror 6.

[0030] The first end mirror 5 is preferably designed as a flat end mirror and the second end mirror 6 preferably as a spherical mirror. As a result, adjustment can be simplified and the resonator 4 can be designed in a stable manner.

[0031] The birefringent medium 8 is provided for color control of the laser light 9 emitted by the laser light source unit 1. Said medium is produced as a birefringent crystal plate, preferably made of a silicon material. The birefringent crystal plate 8 has two parallel flat sides at which radiations enter and exit. The birefringent crystal plate 8 is arranged inclined at a Brewster angle s to the optical axis 10, so that the radiation arriving from the active laser medium 7 strikes the birefringent crystal plate 8 at the Brewster angle s. The Brewster angle s is preferably optimized for the green wavelength 12, so that the blue wavelength 11 and the red wavelength 14 can also strike the crystal plate 8 at an angle close to the Brewster angle s. This way, unwanted light losses can be minimized for a relatively wide wavelength range.

[0032] The birefringent medium 8 is thus arranged inclined and not perpendicular to the optical rule axis 10. The birefringent medium 8 is rotatably supported about the optical axis 10.

[0033] According to the rotational position of the birefringent medium 8, preferred radiation 15 can be set with a specific second wavelength 12 or third wavelength 13 or fourth wavelength 14, which in each case is in phase and has the same polarization direction after twice the passage through the birefringent medium 8. If the birefringent medium 8, for example, is brought to a rotational position in which the fourth wavelength 14 (red wavelength) is brought into an active position 16 according to FIG. 2, the preferred radiation 15 is exclusively formed by the red wavelength 14. This means that the red wavelength 14 is stimulated or amplified in the active laser medium 7, while radiation of another wavelength, for example green wavelength 12, orange wavelength 13, is not stimulated. The radiation of the green wavelength 12 and the orange wavelength 13 formed back in the direction of the active laser medium 7, which the birefringent medium 8 transmitted starting from the active laser medium 7, which was then reflected at the second end mirror 6 and which then again the birefringent medium 8 transmitted in the direction of the active laser medium 7, is not in phase and does not have the same polarization direction as the radiation of the green wavelength 12 or the orange wavelength 13 entering from the active laser medium 7 into the birefringent medium. The birefringent medium 8 has the ability that, having passed through the latter twice, only the preferred radiation 15 of a specific wavelength 12, 13, 14 is in phase and has the same polarization direction, but not the other radiation. Only the preferred radiation 15 is stimulated in the active laser medium 7, while the radiation of other wavelengths is not stimulated.

[0034] According to the rotational position of the birefringent medium 8, the active laser medium 7 can thus be stimulated with a specific wavelength 12, 13, 14. This preferred radiation 15 with the determined green wavelength 12 or orange wavelength 13 or red wavelength 14 is then additively mixed with the pump radiation 3 of blue wavelength 11 to obtain laser light 9 of a light color thereby determined, which is emitted by the laser light source unit 1 in the radiation direction A.

[0035] If the birefringent medium 8 is rotated continuously in one rotational direction D at a speed which is greater than or equal to a minimum speed, preferred radiation 15 of a green wavelength 12, of an orange wavelength 13 and of a red wavelength 14 can be generated in short time intervals, so that laser light 9 of white light color is emitted by additive color mixing with the pump radiation 3 of the blue wavelength 11. The emission spectrum according to FIG. 3 includes this white laser light 9. The minimum speed of the birefringent medium 8 depends on the perceptive ability of the human eye.

[0036] A setting device is coupled to the birefringent medium 8 so that a defined angle of rotation and/or a specific speed can be set for the birefringent medium 8.

[0037] An optical unit for forming the illumination apparatus can be arranged in the radiation direction A in front of the laser light source unit 1. The optical unit has, for example, a liquid crystal panel with a number of individually controllable pixels arranged in a matrix. By controlling the pixels, a predetermined light distribution, for example a low beam distribution, can be set. For this purpose, the pixels of the liquid crystal panel are imaged into the area in front of the vehicle via a downstream lens unit. If necessary, a traffic area detection unit can be provided, which provides sensor data about the presence and location of another traffic object in the area in front of the vehicle. According to the current position of this traffic object, the pixels of the liquid crystal panel can then be controlled so that the area of the generated light distribution in which the traffic object is located is not illuminated and thus a glare-free area of the light distribution is generated. This glare-free area can be tracked to the changed relative position of the traffic object with respect to the vehicle, so that the entire area in front of the vehicle is illuminated, with the exception of the glare-free area in which the traffic object is currently located (glare-free high beam distribution).

[0038] A further lens device for expanding the laser light 9 emitted by the laser light source unit 1 is preferably provided in the radiation direction A behind the liquid crystal panel.

[0039] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.