Optically pumped solid-state laser

Abstract

The invention relates to an optically pumped solid-state laser (1), in which a pump radiation source (100) and a laser resonator (200) are used to form at least one standing wave (320) with an active laser medium (201), which are arranged opposite one another such that the laser resonator (200) can be pumped by the pump radiation source (100), the laser resonator (200) is delimited at a first end by an end mirror (220) for reflecting the standing wave (320) and at a second end by an out-coupling mirror (220) for reflecting the standing wave (320) and coupling out the laser radiation (330), and wherein the laser resonator (200) has at least four reflectors (210) at which the direction of extension of the standing wave (320) changes.

Description

Technical Field

[0001] The present invention relates to an optically pumped solid-state laser, in particular to a surface-emitting optically pumped solid-state laser. Background Art

[0002] Lasers, solid-state lasers and semiconductor lasers are known. In particular, semiconductor lasers with a variety of material systems are currently known, but only certain wavelengths can currently be realized in a simple manner with these material systems. Other wavelengths can be provided by solid-state lasers, in particular by solid-state lasers pumped by means of laser diodes (diode-pumped solid-state (DPSS) lasers). Summary of the invention

[0003] An object of the present invention is to provide an optically pumped solid-state laser which is compact and has a simple construction.

[0004] This object is achieved by an optically pumped solid-state laser having the features of claim 1. Preferred embodiments are indicated in the dependent claims.

[0005] According to one embodiment, an optically pumped solid-state laser comprises a pump radiation source and a laser resonator for forming at least one standing wave with an active laser medium. The pump radiation source and the laser resonator are arranged relative to one another so that the laser resonator can be pumped by the pump radiation source. The laser resonator is bounded at a first end by an end mirror for reflecting the standing wave and at a second end by an output coupling mirror for reflecting the standing wave and coupling out the laser radiation.

[0006] Furthermore, the laser resonator has at least four reflectors at which the extension direction of the standing wave changes.

[0007] The laser resonator can therefore be designed particularly compactly.

[0008] According to one embodiment, the laser medium extends in layers. In particular, the laser medium can extend in layers along a main direction and / or a main plane. Accordingly, the laser medium has, for example, a planar top side and a planar bottom side (preferably parallel to the top side), wherein the area of ​​the possible side faces is much smaller than the area of ​​the top side and the bottom side, for example, at least by a factor, for example 5 times, 10 times, 20 times or 50 times.

[0009] In this case and in general, the reflectors can be arranged in such a way that the standing wave runs in a zigzag manner and passes through the laser medium several times.

[0010] In particular, the standing wave can extend through the laser medium along the extension direction of the standing wave, thereby reflecting at two consecutive reflectors at the top side of the laser medium, thereby extending through the laser medium again, thereby reflecting at two consecutive reflectors at the bottom side of the laser medium, thereby extending through the laser medium again.

[0011] The terms "top side" and "bottom side" here and below describe two at least substantially opposite planar sides of a layered laser medium. Which of the two sides is defined as "upper" or "lower" is arbitrary. The terms "upper" and "lower" are only used to define the same type of orientation in connection with optional other components of the solid-state laser described below.

[0012] Thus, along the direction of the standing wave, the following sequence is generated: laser medium-reflector-reflector-laser medium-reflector-reflector-laser medium. This sequence can be repeated to any length until finally the laser radiation is coupled out via the output coupling mirror or reflected via the end mirror. For example: end mirror-laser medium-reflector-reflector-laser medium-reflector-reflector-laser medium-reflector-reflector-laser medium-reflector-reflector-output coupling mirror.

[0013] The standing wave preferably extends vertically or at least substantially vertically through the laser medium, in particular the layered laser medium. For example, it can pass through the laser medium, in particular the layered laser medium, at an angle of 85 degrees to 95 degrees.

[0014] For example, in each of the sequences described above, the standing wave can extend vertically, or at least substantially vertically, through the lasing medium.

[0015] Two consecutive reflectors can be formed by different parts of a protrusion (particularly a prism) on the laser medium. This is particularly applicable to, but not limited to, two corresponding consecutive reflectors in the above sequence. The protrusion can be shaped so that the standing wave is collimated. The protrusion can be provided as a mirror reflection layer (also called a mirror reflection coating). The protrusion can be composed of a guide medium. There can be a plurality of such protrusions composed of a guide medium on the side (top side or bottom side) of the laser medium. These protrusions can be connected to each other by a guide medium, or these protrusions are not connected by a guide medium.

[0016] According to one embodiment, the output coupling mirror and / or the end mirror comprises or consists of one or more layers on the (preferably layered) laser medium. These layers can be formed directly on the laser medium, for example on the top side or the bottom side of the laser medium, or as an alternative, at least one further layer can extend between the laser medium and the output coupling mirror and / or the end mirror.

[0017] According to one embodiment, the solid-state laser further comprises a (preferably layered) guide medium arranged at the side of the laser medium for guiding the standing wave, wherein at least two reflectors are formed as protrusions of the guide medium. The protrusions can be provided with a mirror-reflecting layer.

[0018] In this case, it is advantageous if the mirror-reflective layer is not arranged on the lasing medium but on the guide medium. Otherwise, carrier exchanges can occur between excited state levels in the lasing medium and the conduction band of the layer, which in turn lead to non-radiative recombination and efficiency losses, in particular through plasmon excitation. It is particularly advantageous if the mirror-reflective layer is a layer containing a metal or a layer consisting of one metal or a plurality of metals.

[0019] Preferably, the solid-state laser comprises two such guiding media, one guiding medium at the top side of the lasing medium and another guiding medium at the bottom side of the lasing medium.

[0020] According to one embodiment, the solid-state laser has an upper (preferably layered) guiding medium arranged on the top side of the laser medium and used to guide the standing wave with a plurality of protrusions, each protrusion forming two reflectors, and the solid-state laser has a lower (preferably layered) guiding medium arranged on the bottom side of the laser medium and used to guide the standing wave with a plurality of protrusions, each protrusion forming two reflectors.

[0021] Guide media with reflectors can simplify the manufacture of solid-state lasers. The upper and lower guide media can be connected to the laser medium by means of index-matched materials, for example by lamination or bonding. In this case, the guide media can be provided in the form of a wafer for a plurality of lasers and the guide media can already be applied to the wafer before singulation. This method is also referred to as wafer level processing.

[0022] The guide medium can contain glass or consist of glass.

[0023] The outcoupling mirror can be arranged on the top side of the upper guide medium and the end mirror can be arranged on the bottom side of the lower guide medium.

[0024] The output coupling mirror can include one or more layers. The end mirror can also be designed to include one or more layers.

[0025] In particular, the output coupling mirror can include one or more layers on the top side of the upper guide medium or on the top side of the laser medium, or can be composed of one or more layers on the top side of the upper guide medium or on the top side of the laser medium, and the end mirror can include one or more layers on the bottom side of the lower guide medium or on the bottom side of the laser medium, or can be composed of one or more layers on the bottom side of the lower guide medium or on the bottom side of the laser medium.

[0026] According to one embodiment, the end mirror is designed as an incoupling mirror, and the pump radiation source and the laser resonator are arranged opposite one another in such a way that the pump radiation is coupled into the laser resonator via the incoupling mirror.

[0027] This can be achieved by using a wavelength selective mirror as end mirror, which is transmissive for the pump radiation and highly reflective for the laser radiation.

[0028] The output coupling mirror can also be a wavelength selective mirror. As a result, the wavelength of the laser can be stabilized. In particular, the reflectivity of the output coupling mirror can have a maximum at the main wavelength of the laser radiation and decrease in the direction of wavelengths longer and / or shorter than the main wavelength, thereby stabilizing the wavelength.

[0029] According to one embodiment, the solid-state laser comprises a wavelength-selective reflective coating arranged on at least one reflector, which serves to stabilize the main wavelength of the laser radiation. To achieve this, due to the reflective coating, the reflectivity of the at least one reflector can have a maximum at the main wavelength and decrease in the direction of wavelengths longer and / or shorter than the main wavelength.

[0030] According to one embodiment, the solid-state laser further comprises a housing. The housing can be sealed and can be formed by a carrier, a layered laser medium and a frame, which connects the carrier to the layered laser medium. The frame can comprise one or more side walls. The pump radiation source can be arranged in the housing, in particular on the carrier, for example on the carrier top side.

[0031] The carrier can be a PCB (printed circuit board), a ceramic carrier, a metal substrate or a QFN (quad flat no-lead package) substrate. The pump radiation source can be welded or bonded to the carrier.

[0032] The pump radiation source can comprise a semiconductor laser. In particular, the device can contain one or more semiconductor lasers, in particular one or more surface emitting semiconductor lasers, such as a VCSEL (Vertical Cavity Surface Emitting Laser) array.

[0033] In the case of the above-mentioned shell, the pump radiation source can include one or more surface emitting semiconductor lasers arranged on a carrier, or be composed of one or more surface emitting semiconductor lasers arranged on a carrier, in particular one or more VCSELs (Vertical Cavity Surface Emitting Laser) or HCSELs (Horizontal Cavity Surface Emitting Laser), such as a VCSEL array.

[0034] The laser can be based on a GaN (gallium nitride) material system.

[0035] According to one embodiment, the laser medium comprises a laser crystal or consists of a laser crystal. The crystal can be doped with a rare earth metal, in particular Tb3+ or Pr3+.

[0036] The laser medium can be a planar laser crystal. The crystal can have a thickness of 0.2 mm to 2 mm inclusive.

[0037] Solid-state lasers can be used, for example, in spectrometers or in augmented reality glasses (also called AR glasses) or in virtual reality glasses (also called VR glasses). BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The present invention is described in more detail below with reference to the accompanying drawings, which schematically show:

[0039] Figure 1 shows an optically pumped solid-state laser according to a first embodiment,

[0040] FIG2 shows an optically pumped solid-state laser according to a second embodiment,

[0041] Figure 3 An optically pumped solid-state laser according to a third embodiment is shown. DETAILED DESCRIPTION

[0042] exist Figure 1In FIG. 1 , an optically pumped solid-state laser 1 according to a first embodiment is shown. The essential components of the solid-state laser 1 are a pump radiation source 100 and a laser resonator 200. In the present case, the pump radiation source 100 is a vertical cavity surface emitting laser (VCSEL) based on GaN. As a further alternative, for example, any other semiconductor laser, in particular some other vertical emitting laser, such as a horizontal cavity surface emitting laser (HCSEL), or even an edge emitting semiconductor laser, or even an array of these lasers can also be used. The pump radiation source 100 is arranged relative to the laser resonator 200 so that the pump radiation 310 emitted by the pump radiation source 100 is coupled into the laser resonator 200 via the end mirror 220, and the laser resonator 200 is correspondingly pumped by the pump radiation 310 of the pump radiation source 100.

[0043] The input coupling mirror 220 is a frequency selective mirror which has a high transmittance in the blue spectral range, so that the pump radiation 310 can be coupled into the laser resonator 200. At the same time, the input coupling mirror 220 has a high reflectivity for the longer wavelength laser radiation 330 (or standing wave 320) to be generated, and forms an end mirror 220 arranged at the end of the laser resonator 200 and for reflecting the standing wave 320 to be formed in the laser resonator 200. At the second end of the laser resonator 200, the laser resonator is bounded by an output coupling mirror 230 which has a relatively high reflectivity in the spectral range of the laser radiation 330, so that the standing wave 320 can be formed in the resonator 200, and at the same time the laser radiation 330 can be coupled out of the laser resonator 200 via the output coupling mirror 230.

[0044] As mentioned above, the input coupling mirror 220 is a frequency selective mirror. In the present case, the input coupling mirror 220 is a frequency selective multilayer mirror, the individual layers of which are coated on the bottom side 203 of the lasing medium. The output coupling mirror is coated on the top side 202 of the lasing medium.

[0045] The laser resonator 200 includes four reflectors 210 at which the propagation direction of the standing wave 320 changes. Accordingly, the standing wave 320 extends multiple times in a zigzag manner through the laser medium 201, which is configured as a layer in the current embodiment. Two of the reflectors 210 are formed by prisms 212 arranged on the top side 202 and the corresponding bottom side 203 of the laser medium 201. The standing wave 320 extends substantially vertically through the layered laser medium 201.

[0046] The solid-state laser 1 according to the first exemplary embodiment further comprises a collimator lens 240 , by means of which the divergent pump radiation 310 is collimated into a nearly parallel beam before being coupled into the laser resonator 200 via the incoupling mirror 220 .

[0047] In this embodiment, the laser medium 201 is a laser crystal doped with a rare earth metal. In particular, Tb3+ or Pr3+ can be suitable for doping. With the aid of this material, a laser crystal 201 can be produced which can be excited with the aid of blue radiation from a GaN-based pump radiation source and emits in the green spectral range (Tb3+) or the corresponding orange spectral range (Pr3+). Current semiconductor lasers cannot reach these spectral ranges.

[0048] In FIG. 2 , an optically pumped solid-state laser 1 according to a second embodiment is shown. The optically pumped solid-state laser comprises components of the solid-state laser 1 according to the first embodiment. In addition, the solid-state laser 1 according to the second embodiment comprises an upper guide medium 215 and a lower guide medium 214, wherein the prism 212 is integrally formed in the guide medium 214, 215. For example, the guide media 214, 215 can be manufactured as an integral glass element together with the prism 212, respectively. In order to manufacture the laser resonator 200, the guide media 214, 215 and the laser medium 201 can be directly joined or bonded to each other. For example, the laser medium 201 can be bonded to the upper guide medium 215 first, and the lower guide medium 214 can then be bonded to the final semi-finished product.

[0049] In this embodiment, the output coupling mirror 230 is covered on the top side of the upper guide medium 215, and the input coupling mirror 220 is covered on the bottom side 203 of the laser medium 201. As a further alternative, the input coupling mirror 220 can also be covered on the bottom side of the lower guide medium 214, and / or the output coupling mirror 230 can be covered on the top side of the laser medium 201.

[0050] In contrast to the solid-state laser 1 of the first exemplary embodiment, the solid-state laser 1 according to the second exemplary embodiment also has a preferably sealed housing 400. The housing comprises a carrier 410, on which the VCSEL 100 is arranged, and a frame 420, which connects the carrier 410 to the laser resonator 200. Accordingly, the carrier 410, the frame 420 and the laser resonator 200 form a housing 400, within which the VCSEL 100 serving as a pump radiation source is arranged.

[0051] Furthermore, in the case of the solid-state laser 1 according to the second embodiment, a wavelength selective reflective coating 211 is arranged on the reflector 210, which stabilizes the main wavelength of the laser radiation 330. The reflective coating is designed so that the reflectivity of the reflector 210 is maximum at the main wavelength (target wavelength) of the laser radiation 330 and decreases in the direction of wavelengths longer and / or shorter than the main wavelength. In this way, the temperature drift of the wavelength of the solid-state laser 1 can be reduced.

[0052] Such a frequency selective reflective coating 211 can be obtained by applying a multilayer mirror. By also designing the output coupling mirror 230 to be frequency selective accordingly, a further stabilization of the main wavelength of the laser radiation can be achieved, which means that its reflectivity has a maximum at the main wavelength and decreases in the direction of longer and / or shorter wavelengths.

[0053] exist Figure 3 In FIG. 1 , an optically pumped solid-state laser 1 according to a third embodiment is shown. The laser is constructed identically to the laser according to the second embodiment, except for the following differences:

[0054] The solid-state laser 1 according to the third embodiment does not have a collimating lens 240. Instead, the first two reflectors 210 are not formed by a prism 212, but by a protrusion with a curved edge 213. The above-mentioned edge collimates the standing wave, so that the collimating lens 240 is not necessary. As a further alternative, it is also possible to replace the further prism with a suitable protrusion 213 with a curved edge, so that a collimated laser radiation 330 is produced overall. In the case of the third embodiment, the input coupling mirror 220 is covered onto the lower guide medium 214.

[0055] List of reference numerals:

[0056] 1: Optically pumped solid-state lasers

[0057] 100: Pump radiation source

[0058] 200: Laser resonator

[0059] 201: Laser Media

[0060] 202: Top side of laser medium

[0061] 203: Bottom side of laser medium

[0062] 210: Reflector

[0063] 211: Reflective coating

[0064] 212: Prismatic protrusion

[0065] 213: Raised with curved edges

[0066] 214: Lower guide medium

[0067] 215: Upper guide medium

[0068] 220: End mirror, input coupling mirror

[0069] 230: Output coupling mirror

[0070] 240: Collimating lens

[0071] 310: Pump Radiation

[0072] 320: Standing Wave

[0073] 330: Laser radiation

[0074] 400: Shell

[0075] 410: Carrier

[0076] 420: Framework.

Claims

1. An optically pumped solid-state laser (1), comprising: - a source of pump radiation (100), and - a laser resonator (200) for forming at least one standing wave with an active laser medium (201) extending in a layer, wherein the pump radiation source (100) and the laser resonator (200) are arranged relative to one another so that the laser resonator (200) can be pumped by the pump radiation source (100), wherein the laser resonator (200) is bounded at a first end by an end mirror (220) for reflecting the standing wave (320) and at a second end by an output coupling mirror (230) for reflecting the standing wave (320) and coupling out laser radiation (330), The laser resonator (200) has at least four reflectors (210), at which the extension direction of the standing wave (320) changes. The end mirror, the output coupling mirror and the reflector are arranged relative to the laser medium so that the standing wave (320) extends through the laser medium (201) along the propagation direction of the standing wave, and then reflects the standing wave at two consecutive reflectors (210) at the top side (202) of the laser medium (201), and then the standing wave extends through the laser medium (201) again, and then reflects the standing wave at two consecutive reflectors (210) at the bottom side (203) of the laser medium (201), and then the standing wave extends through the laser medium again.

2. The solid-state laser (1) according to claim 1, wherein: The two continuous reflectors (210) at the top side of the laser medium are formed by different parts of an upper protrusion (212, 213) consisting of a guide medium on the laser medium (201).

3. The solid-state laser (1) according to claim 1 or 2, wherein: The two continuous reflectors (210) at the bottom side of the laser medium are formed by different parts of a lower protrusion (212, 213) consisting of a guide medium on the laser medium (201).

4. The solid-state laser (1) according to any one of claims 2 to 5, configured such that the standing wave (320) extends substantially vertically through the laser medium (201).

5. The solid-state laser (1) according to any one of the preceding claims, wherein: The output coupling mirror (230) and / or the end mirror (220) comprises a layer on the laser medium (201).

6. The solid-state laser (1) according to any one of the preceding claims, comprising an upper guide medium (215) arranged on the top side (202) of the laser medium (201), the upper guide medium having a plurality of protrusions (212, 213), each of which forms two of the reflectors (210), and the solid-state laser further comprising a lower guide medium (215) arranged on the bottom side (203) of the laser medium (201), the lower guide medium having a plurality of protrusions (212, 213), each of which forms two of the reflectors (210).

7. The solid-state laser (1) according to claim 6, wherein: The output coupling mirror (230) is arranged on the top side of the upper guide medium (215), and / or the end mirror (220) is arranged on the bottom side of the lower guide medium (214).

8. The solid-state laser (1) according to any of the preceding claims, further comprising a carrier (410) and a frame (420), wherein the pump radiation source (100) is arranged on the carrier, and wherein the frame connects the carrier (410) to the layered laser medium (201), so that the carrier (410), the frame (420) and the laser medium (201) form a preferably sealed housing (400), in which the pump radiation source (100) is arranged.

9. The solid-state laser (1) according to any one of the preceding claims, wherein: The pump radiation source (100) comprises a semiconductor laser, which is preferably based on a GaN material system.

10. The solid-state laser (1) according to claim 8 and 9, wherein The semiconductor laser is a surface emitting semiconductor laser arranged on a carrier (410).

11. The solid-state laser (1) according to any one of the preceding claims, wherein: The end mirror (220) is designed as an incoupling mirror (220), and the pump radiation source (100) and the laser resonator (200) are arranged opposite one another so that the pump radiation (310) is coupled into the laser resonator (200) via the incoupling mirror (220).

12. The solid-state laser (1) according to any one of the preceding claims, wherein: The laser medium (201) comprises a laser crystal doped with a rare earth metal, in particular Tb3+ or Pr3+, or the laser medium is composed of a laser crystal doped with a rare earth metal, in particular Tb3+ or Pr3+.

13. The solid-state laser (1) according to any of the preceding claims, comprising a wavelength selective reflective coating (211) which is arranged on at least one of the reflectors (210) and is suitable for stabilizing the main wavelength of the laser radiation.

14. The solid-state laser (1) according to claim 13, wherein: Due to the reflective coating (211), the reflectivity of at least one of the reflectors (210) has a maximum at the main wavelength and decreases in the direction of wavelengths longer and / or shorter than the main wavelength.

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