LASER DEVICE WITH AN OPTICAL RESONATOR AND METHOD FOR ADJUSTING THE LASER DEVICE

Abstract

The invention relates to an optical resonator (1) for a laser device (20), in particular for a microchip solid-state laser, comprising an optical medium (4) which is arranged between a first and a second reflective element (2, 3) that are arranged at a distance from one another in a longitudinal direction (P). The optical resonator length is specified by the distance from the first reflective element (2) to the second reflective element (3) in the longitudinal direction (P), the longitudinal extent of the medium (4) arranged between the reflective elements, and the refractive index thereof. According to the invention, the optical resonator length varies in at least one lateral direction (L) running perpendicularly to the longitudinal direction (P). The invention further relates to a laser device (20) comprising such a resonator (1) and to a method for adjusting the laser device (20).

Claims

1. A laser apparatus comprising an optical resonator (1) with an optical medium (4) which is arranged between a first and a second reflection element (2, 3), wherein the first and the second reflection element (2,3) are spaced apart from one another in a longitudinal direction (P), wherein an optical resonator length is defined by a distance of the first reflection element (2) from the second reflection element (3) in the longitudinal direction (P) and a longitudinal extent of the medium (4) arranged therebetween and the refractive index thereof, and a device (21) for coupling a pump laser beam (S) into the optical resonator (1), wherein a coupled-in pump laser beam (S) propagates within the optical resonator (1) parallel to the longitudinal direction (P), wherein the optical resonator length of the optical resonator (1) varies in at least one lateral direction (L) that is perpendicular to the longitudinal direction (P) and the device (21) and the optical resonator (1) are movable with respect to one another such that the position of the coupled-in pump laser beam (S) is changeable at least with respect to the lateral direction (L) that is perpendicular to the longitudinal direction (P).

2. The laser apparatus according to claim 1, wherein the first reflection element and the second reflection element (2, 3) are configured as mirrors having substantially planar mirror surfaces (10, 11) which are tilted with respect to one another in deviation from a plane-parallel arrangement.

3. The laser apparatus according to claim 2, wherein the first reflection element and the second reflection element (2, 3) are arranged at a small angle with respect to one another such that an at least approximately stable resonator is formed.

4. The laser apparatus according to claim 1, wherein the first and/or second reflection element (2, 3) at least include sections sectionally having a curvature for forming a stable resonator.

5. The laser apparatus according to claim 1, wherein the optical medium (4) comprises a laser crystal, having substantially planar front sides (5, 6) that are facing the first reflection element and the second reflection element (2, 3), wherein the substantially front sides (5, 6) extend toward one another in an arrangement that deviates from a plane-parallel arrangement.

6. The laser apparatus according claim 1, wherein the optical medium (4) is fixedly connected to the first and/or the second reflection element (2, 3).

7. The laser apparatus according to claim 1, wherein the first or second reflection element (2, 3) is a saturable absorber (12).

8. A method for adjusting a laser apparatus (20) according to claim 1, wherein a pump laser beam (S) is coupled into the optical resonator (1) such that it propagates within the optical resonator (1) substantially parallel to the longitudinal direction (P), wherein the position of the pump laser beam (S) is changed at least with respect to the lateral direction (L) that is perpendicular to the longitudinal direction (P) to select a region of the optical resonator (1) with a specifiable optical resonator length.

Description

[0036] Possible exemplary embodiments of the invention will be explained in more detail below with reference to the drawings. In the drawing:

[0037] FIG. 1 shows an optical resonator in accordance with a first exemplary embodiment of the invention in a schematic sectional illustration;

[0038] FIG. 2 shows an optical resonator in accordance with a second exemplary embodiment;

[0039] FIG. 3 shows an optical resonator in accordance with a third exemplary embodiment;

[0040] FIG. 4 shows an optical resonator in accordance with a fourth exemplary embodiment;

[0041] FIG. 5 shows an optical resonator in accordance with a fifth exemplary embodiment;

[0042] FIG. 6 shows an optical resonator in accordance with a sixth exemplary embodiment;

[0043] FIG. 7 shows an optical resonator in accordance with a seventh exemplary embodiment;

[0044] FIG. 8 shows an optical resonator in accordance with an eighth exemplary embodiment;

[0045] FIG. 9 shows an optical resonator in accordance with a ninth exemplary embodiment;

[0046] FIG. 10 shows an optical resonator in accordance with a tenth exemplary embodiment;

[0047] FIG. 11 shows an optical resonator in accordance with an eleventh exemplary embodiment;

[0048] FIG. 12 shows an optical resonator in accordance with a twelfth exemplary embodiment;

[0049] FIG. 13 schematically shows a laser apparatus having an optical resonator, shown in FIGS. 1 to 8, and a device for coupling in a pump laser beam;

[0050] FIG. 14 schematically shows a further laser apparatus with one of the optical resonators shown in FIGS. 1 to 12.

[0051] Mutually corresponding parts are provided in all figures with the same reference signs.

[0052] FIG. 1 shows an optical resonator 1 in accordance with a first embodiment. The optical resonator 1 comprises a first reflection element 2 and a second reflection element 3. Arranged between the two reflection elements 2, 3 is an optically active medium 4. In the present case, the optically active medium 4 provided for laser amplification is a laser crystal.

[0053] The first reflection element 2 is configured as an output coupling mirror which is separated from the optical medium 4 or from the laser crystal by an air gap 8. The optical medium 4 in turn is separated from the second reflection element 3, which is configured as a rear-side mirror, by a further air gap 9. The laser crystal acting as the optical medium 4 has two front sides 5, 6 which are arranged so as to be plane-parallel with respect to one another. The first reflection element 2, configured as an output coupling mirror, and the second reflection element 3, configured as a rear-side mirror, are arranged such that they are tilted with respect to one another and consequently extend at an acute angle with respect to one another. The further air gap 9, extending between the second reflection element 3 and the front face 6 of the optical medium 4, is wedged-shaped.

[0054] In other embodiments, the air gap 8 between the optical medium 4 and the second reflection element 3 configured as a rear-side mirror is wedge-shaped, or both air gaps 8, 9 are wedge-shaped.

[0055] The optical medium 4 configured as a laser crystal can be coated to achieve a defined reflectance for the signal and/or pump light.

[0056] Either the first or the second reflection element 2, 3 has a high transmittance for the wavelength of the pump light, or of the pump laser beam. In possible alternative embodiments, either the first or the second reflection element 2, 3 is configured as a saturable absorber. The reflection elements 2, 3 of the exemplary embodiment shown in FIG. 2 are mirrors having planar mirror surfaces 10, 11, which are tilted with respect to one another. In another exemplary embodiment, the mirror surfaces 10, 11 have a slight curvature in order to adapt the mode volume used by the laser mode, which is circulating within the optical resonator, to the pump volume defined by the pump laser beam.

[0057] It is to be understood that the schematic illustration shown in FIGS. 1 to 14 in particular of the optical resonator 1 is not to scale. In particular, the tilting of the reflection elements 2, 3 with respect to one another, or the wedge-shaped configuration of the optically active medium 4 and/or the air gaps 8, 9 situated therebetween, are illustrated in strongly exaggerated fashion to illustrate the variation of the resonator length for different positions of the pump laser beam with respect to a lateral direction L. In the actual implementation, in particular in microchip solid-state lasers, the resonator length which is traversed by the pump laser beam per circulation varies only slightly, for example by about 10 nm to 100 nm. The pump laser beam propagates within the optical resonator 1 substantially in the longitudinal direction P. The tilting of the two reflection elements 2, 3 has no noticeable influence on the stability of the optical resonator 1 that is formed.

[0058] FIGS. 2 to 10 show further exemplary embodiments of the optical resonator 1. These exemplary embodiments substantially differ in terms of the specific arrangement of the reflection elements 2, 3 with respect to one another or in terms of the specific geometric embodiment of the optically active medium 4, i.e. the laser crystal. In accordance with various exemplary embodiments, the optical medium 4 is wedge-shaped, i.e. the two front faces 5, 6 of the optical medium 4 do not extend in a plane-parallel arrangement with respect to one another, but at an angle with respect to one another. Such embodiments also define a resonator length which varies for different lateral positions.

[0059] FIG. 2 shows an optical resonator 1 in accordance with a second embodiment. The first reflection element 2, which is configured as an output coupling mirror, is separated from the optically active medium 4 by the air gap 8. The optically active medium 4 in turn is separated from the second reflection element 3, is configured as a rear-side mirror, by the air gap 9. The optically active medium 4 is a wedge-shaped laser crystal.

[0060] The mirror surface 10 of the first reflection element 2, or of the output coupling mirror, extends plane-parallel with respect to the opposite front side 5 of the optical medium 4.

[0061] The second reflection element 3 configured as the rear-side mirror, extends plane-parallel to the opposite front side 6 of the optical medium 4. Alternatively, the front side 6, as is illustrated in the exemplary embodiment in FIG. 3, can be arranged at an angle with respect to the second reflection element 3. Output coupling mirror and rear-side mirror can extend plane-parallel with respect to one another (FIG. 3) or, as is illustrated in FIG. 2, extend at an angle with respect to one another.

[0062] In a fourth embodiment shown in FIG. 4, the first reflection element 2 configured as the output coupling mirror, is connected inseparably to the optical medium 4. The inseparable connection between the optical medium 4 and the first reflection element 2 can be realized, for example, by a dielectric coating on the optical medium 4 configured as the laser crystal, or by bonding or adhesively bonding an output coupling mirror onto the laser crystal.

[0063] The optical medium 4, or the laser crystal, is separated from the second reflection element 3, which serves as a rear-side mirror, by the air gap 9. In this case, the laser crystal is plane-parallel, and the air gap 9 is wedge-shaped. The side of the optically active medium 4 that is opposite the first reflection element 2 can be coated to achieve a defined reflectance for the signal and/or pumped light.

[0064] The first reflection element 2 of the fifth exemplary embodiment shown in FIG. 5 is also connected inseparably to the optical medium 4. In contrast to the example shown in FIG. 4, the second reflection element 3, or the planar mirror surface 11 thereof, is parallel with respect to the opposite front face 6 of the optical medium 4. In the sixth exemplary embodiment of FIG. 6, the mirror surface 11 of the second reflection element 3 extends at an acute angle with respect to the front side 6 of the optical medium 4. In the fifth and in the sixth exemplary embodiments, the optical medium 4 is wedge-shaped, and the front sides thereof extend at an angle with respect to one another.

[0065] In a seventh embodiment, which is illustrated schematically in FIG. 7, the first reflection element 2, which serves as an output coupling mirror, is spaced apart from the optical medium 4 by an air gap 8. The optical medium 4 is plane-parallel, and the air gap 8 is wedge-shaped. The second reflection element 3 configured as rear-side mirror is connected inseparably to the optical medium 4. This can be implemented e.g. by a dielectric coating on the laser crystal or by bonding or adhesive bonding of the rear-side mirror to the laser crystal. The front side 5 of the laser crystal can be coated to achieve a defined reflectance for the signal and/or pumped light.

[0066] In the eighth exemplary embodiment shown in FIG. 8, the first reflection element 2 configured as the output coupling mirror, is separated from the optical medium 4 by the air gap 8. The optical medium 4 is wedge-shaped, and the air gap is, as shown in FIG. 8, plane-parallel or, alternatively, as shown in FIG. 9, wedge-shaped. In the eighth and ninth exemplary embodiments of FIGS. 8 and 9, the second reflection element 3 configured as the rear side mirror, is connected inseparably to the optical medium 4. This can be implemented e.g. by a dielectric coating on the crystal or by bonding or adhesive bonding of a rear-side mirror onto the crystal. The front side 5 of the laser crystal can be coated to achieve a defined reflectance for the signal and/or pumped light. Either the output coupling mirror or the rear-side mirror is adapted to exhibit high transmittance for the pumped light. Either the output coupling mirror or the rear-side mirror may be configured as a saturable absorber. The resonator mirrors are preferably planar, but can also have a curvature which is so small that a stable resonator 1 is formed.

[0067] In a tenth exemplary embodiment, which is schematically illustrated in FIG. 10, the first reflection element 2, which serves as an output coupling mirror, and the second reflection element 3, which serves as a rear-side mirror, are connected inseparably to the optical medium 4 configured as the laser crystal. The first and second reflection elements 2, 3 are implemented by dielectric coating on the optical medium 4. The laser crystal acting as the optical medium 4 also has a wedge-shaped form in the tenth exemplary embodiment. In an alternative exemplary embodiment, the first and second reflection elements 2, 3 are connected to the optical medium 4 by way of bonding or adhesive bonding.

[0068] In a further aspect of the invention, the optical resonator 1 in a includes additional discrete optical elements, such as active Q-switches or saturable absorbers 12. Such a modification of the optical resonator 1 is provided independently of the specific configuration thereof, in particular all the geometries shown in FIGS. 1 to 10 are possible. The reflection elements 2, 3 in each of the examples shown may be adapted as saturable absorbers.

[0069] FIGS. 11 and 12 schematically illustrate the eleventh and the twelfth exemplary embodiments of the invention. The optical medium 4 is a doped laser crystal having a plurality of sections 4a, 4b, which differ in terms of the type of doping and/or their doping concentration. The first section 4a serves as an amplifier medium which generates the optical gain. The second section 4b is a saturable absorber 12. Both sections 4a, 4b are connected inseparably to one another.

[0070] In another exemplary embodiment, one of the two sections 4a, 4b is undoped. The first section 4a and the second section 4b are doped with doping atoms or ions of the same chemical element, and in an alternative embodiment with doping atoms or ions of different chemical elements.

[0071] In a possible exemplary embodiment, which is not illustrated in more detail, the optical medium 4 additionally has an undoped section which serves for improving the heat dissipation from the laser-active first section 4a. Additionally, coatings may be applied between the different crystal sections to attain a defined reflectance for the signal and/or pumped light.

[0072] As shown by way of example in FIGS. 11 and 12, the sections 4a, 4b may be cube-shaped or wedge-shaped. In particular, the laser-active first section 4a can have, as is shown in FIG. 11, two plane-parallel opposite front faces, and the saturable absorber 12 can be wedge-shaped. In the twelfth exemplary embodiment (FIG. 12), the laser-active first section 4a is wedge-shaped and the saturable absorber 12 is cube-shaped with plane-parallel opposite front faces.

[0073] FIGS. 13 and 14 schematically illustrate a laser apparatus 20 having one of the optical resonators 1 described above. FIGS. 13 and 14 show merely by way of example the specific exemplary embodiment of FIG. 10, wherein it is to be understood that all other optical resonators 1 as described herein before can be used analogously in the laser apparatus 20.

[0074] The laser apparatus 20 has the optical resonator 1 which defines an optical resonator length which varies in dependence on the lateral positioning of a pump laser beam S that has been coupled in. The pump laser beam S can be coupled into the optical resonator 1 using the device 21, wherein the positioning of the pump laser beam S can be specified in particular with respect to the lateral direction L. In other words, the device 21 and the optical resonator 1 are movable relative to one another such that the region that is traversed by the pump laser beam S during circulation in the resonance space can specifically be selected. The relative positioning of the device 21 and of the optical resonator 1 thus defines the effective resonator length and the spectral mode spacing of the resonator modes to be amplified.

[0075] In FIG. 13, the adjustment of the laser apparatus 20 is effected by displacing the optical resonator 1 in the lateral direction L with respect to a spatially fixed device 21, which provides the pump laser beam S. This is indicated in FIG. 13 by way of the double-headed arrow 22.

[0076] In FIG. 14, the laser apparatus 20 is adjusted by moving the device 21 with respect to the spatially fixed optical resonator 1. A region of the optical resonator 1 having a suitable resonator length is also selected here by adjusting the position of the pump laser beam S with respect to the lateral direction L.

[0077] The invention has been described above with reference to preferred exemplary embodiments. However, it is to be understood that the invention is not limited to the specific configuration of the exemplary embodiments shown, it is understood that the competent person skilled in the art can derive variations on the basis of the description without departing from the essential concept of the invention. In particular, independently of the specific coniguration of the optical resonator 1 shown in FIGS. 1 to 12, at least one of the two reflection elements 2, 3 may be configured as a saturable absorber 12. Any front faces 5, 6 of the optical medium 4 may be provided with coatings to adapt the reflectance for the pump and/or for the signal light in a way suitable for the laser amplification. Furthermore, the schematically illustrated resonators 1 may have a slight curvature such that they comply with the stability criteria.

LIST OF REFERENCE SIGNS

[0078] 1 optical resonator [0079] 2 first reflection element [0080] 3 second reflection element [0081] 4 optical medium [0082] 5 front face [0083] 6 front face [0084] 8 air gap [0085] 9 air gap [0086] 10 mirror surface [0087] 11 mirror surface [0088] 12 saturable absorber [0089] 20 laser apparatus [0090] P longitudinal direction [0091] L lateral direction [0092] S pump laser beam