Diode laser assembly

Abstract

The invention relates to a diode laser assembly (1) comprising at least one diode laser stack (2a, 2b) and at least one microchannel cooler (3) for active liquid cooling of the at least one diode laser stack (2a, 2b), wherein the diode laser stack (2) is designed in the form of a single-layer diode laser stack (2a) or a multi-layer diode laser stack (2b), wherein a single-layer diode laser stack (2a) has a planar laser bar chip (4) and at least one submount carrier plate (5b) thermally adapted thereto, and a multi-layer diode laser stack (2b) has a plurality of planar laser bar chips (4) and a plurality of submount carrier plates (5) thermally adapted thereto, wherein a planar laser bar chip (4) is thermally conductively connected areally to at least one of the submount carrier plates (5) adjoining thereto. Particularly advantageously, the at least one microchannel cooler (3) has a cooling channel structure (3.1) for active liquid cooling of the at least one diode laser stack (2a, 2b) and is designed for one-sided active cooling of the planar laser bar chips (4) arranged in a multi-layer diode laser stack (2b) or for two-sided active cooling of the planar laser bar chips (4) arranged in a plurality of single-layer or multi-layer diode laser stacks (2a, 2b).

Description

[0001] Diode laser array

[0002] The invention relates to a diode laser arrangement according to the preamble of claim 1.

[0003] Diode laser arrays are fundamentally known in terms of their structure and operation. These arrays comprise a variety of diode lasers or laser diodes, also known as semiconductor lasers or laser emitters. These are industrially manufactured electronic semiconductor components or semiconductor chips used to generate laser radiation.

[0004] Conventional diode lasers or laser emitters, for example, have a resonator length of 1-6 mm and an emitter width of 50-400 pm, which, with good cooling, achieve an optical output power of approximately 10-50 watts.

[0005] Often, so-called NIR (Near Infrared Radiation) diode lasers are used, which are designed to generate laser radiation in a wavelength range of 790 nm to 1080 nm. Known NIR diode lasers, for example, exhibit a conversion efficiency of over 70%, and in some cases even up to 80%, in converting electrical into optical energy.

[0006] To increase the optical output power, several such individual emitters, preferably between 10 and 100, are combined in bar form to create a monolithic semiconductor device. These semiconductor devices are also known as diode laser bars or laser bars. A typical laser bar, for example, has a width of approximately 10 mm. Laser bars have an optical pulse power of over 1000 W and thus generate heat in the range of several thousand watts during continuous wave operation. Continuous operation of a laser bar is therefore only possible to a limited extent, so such laser bars are predominantly operated in pulsed mode, specifically in a "quasi-continuous wave" operating mode. In this mode, the heat input can be reduced by less than 20% compared to continuous operation due to the selected pulse duration to pulse interval ratio.

[0007] To dissipate the remaining heat input, active cooling of such laser bars or plate-shaped laser bar chips is required. For this purpose, the laser bars or plate-shaped laser bar chips are thermally connected to a suitable heat sink, often using so-called "submounts," which are thermally connected to the plate-shaped laser bar chip. These submounts then establish a further thermal connection to another heat sink. Such submounts thus form a "heat sink" themselves, but this heat sink is not actively cooled and therefore its heat absorption capacity is limited.

[0008] For the thermally conductive connection between the laser bar chip and the submount, solder joints such as AuSn or comparable joining methods are typically used, providing sufficient mechanical stability against thermal cycling. For example, thermocompression bonding can also be employed to create the thermally conductive connection. Thermally conductive sintered, adhesive, or clamped connections are also possible. The submount is designed to absorb waste heat and is often made of a material or material mixture whose coefficient of thermal expansion is matched to the plate-shaped laser bar chip. Common materials include CuW, CuMo, Cu-diamond, and similar materials.

[0009] Various cooling concepts are known from the prior art, often employing liquid-cooled heat sinks, particularly so-called microchannel coolers with an integrated cooling channel structure. The liquid cooling medium is supplied and discharged via an inlet and outlet within the microchannel cooler. Such microchannel coolers are made of a thermally conductive material, such as copper. They also frequently exhibit good electrical conductivity to enable the lossless transfer of electrical energy from the microchannel cooler to the semiconductor components mounted on it.

[0010] Effective heat dissipation is achieved, for example, by directly mounting a laser bar chip onto a microchannel cooler via a submount. This allows the waste heat to be dissipated via the shortest possible path. Such arrangements typically have a total height of 2-4 mm, with the microchannel cooler accounting for the largest portion of this height. A liquid cooling medium with a suitable viscosity-heat capacity ratio flows through the integrated cooling channel structure. This medium is often water, but media such as ammonia, liquid nitrogen, or other liquefied gases are also possible. This cooling technology is very efficient and enables heat dissipation from the chip-submount assembly of, for example, 100-200 W of thermal power. A microchannel cooler is therefore required for the active cooling of each laser bar chip.A disadvantage of arranging multiple laser bar chips in a so-called diode laser stack is their considerable height. The average heat dissipation of such liquid-cooled cooling concepts is 100–200 W, enabling a duty cycle of up to 20% for the laser bar chips at an optical pulse power of 1000 W. Laser diode arrangements have also been developed that achieve higher power densities by eliminating the need for such microchannel coolers. In these arrangements, the waste heat is dissipated from the rear of the submount itself and transferred via its thermal interface to a large-area backplane cooler. Up to 30 laser bar chips per cm of height can be implemented in such arrangements, achieving a power density of 30 kW / cm². 2This is achieved in pulsed operation of a laser bar chip with a power output of 1 kW. However, due to the thinness of the often plate-shaped submounts, heat dissipation from the laser bar chip is adversely limited, and such arrangements can therefore only be operated with a duty cycle of approximately 1%. Particularly when using laser emitters with a large resonator length of several millimeters, the heat path across the submount is very long, which significantly reduces the average thermal performance of backplane-cooled laser bar chips as the resonator length increases.

[0011] Large-area diode laser arrays are also known for optical pumping of laser crystals in fiber optic lasers. These "pump modules" operate with a duty cycle of 0.1–10% and achieve pulse powers of several megawatts with a beam area of ​​more than 100 cm². 2 To achieve suitable emission characteristics in the pump modules, micro-optical elements are mounted in front of the laser bar chips. These reduce the beam angle and enable uniform illumination of the laser crystals in a solid-state laser. These pump modules are also cooled with liquids such as water to dissipate heat.

[0012] Based on this, the invention aims to provide a laser diode arrangement that enables effective and active cooling of multiple laser bar chips using a microchannel cooler with a reduced overall height. Furthermore, the invention aims to provide improved heat dissipation and thus more efficient cooling, particularly for laser bar chips with long resonator lengths. This objective is achieved according to the invention by a diode laser arrangement as defined in claim 1.

[0013] Advantageous further developments, details and embodiments of the invention result from the dependent claims, the description and the drawings.

[0014] The essential aspect of the diode laser arrangement according to the invention lies in the fact that the microchannel cooler is designed for one-sided active cooling of the plate-shaped laser bar chips arranged in a multilayer diode laser stack, or for two-sided active cooling of the plate-shaped laser bar chips arranged in several single- or multilayer diode laser stacks. It is particularly advantageous for the laser bar chips to be cooled to be accommodated in one or more diode laser stacks, each of which, together with a thermally adapted submount carrier plate, forms a "single-layer" or "multilayer" diode laser stack according to the invention, wherein a "single-layer" diode laser stack comprises only one laser bar chip and a "multilayer" diode laser stack comprises several laser bar chips.The term "single- or multi-layered" thus indicates the number of laser bar chips present in the respective diode laser stack, which are stacked on top of each other together with one or more submount carrier plates. Advantageously, the laser bar chips are cooled not only in a stack arrangement with a varying number of laser bar chips and submount carrier plates as "heat sink layers" within the stack, but also on one or two sides of the microchannel cooler. For this purpose, the microchannel cooler has a first and / or second flat, planar mounting area, which is preferably located opposite each other to enable a symmetrical design. A planar, thermally conductive connection is established in the respective mounting area between the microchannel cooler and the respective diode laser stack via the submount carrier plate on the free end of the stack, creating a particularly efficient heat transfer.A particularly advantageous aspect of the arrangement according to the invention is that the heat generated in the respective laser bar chip can be transferred to the cooling medium guided by the microchannel cooler via the shortest possible path. In particular, laser bar chips with laser emitters having a large resonator length of several millimeters can be cooled efficiently. This efficient cooling allows the laser bar chip to be operated at high pulse powers.

[0015] In accordance with the invention, a plate-shaped laser bar chip is understood to be a plurality of individual emitters or laser diodes arranged in bar form relative to each other and combined to form a monolithic chip mounted on a semiconductor plate and thus having a plate shape.

[0016] Advantageously, the first and / or second planar and flat mounting area extends along the cooling channel structure in a first and second mounting plane, respectively, which preferably run parallel to each other and to the propagation axis. It is particularly advantageous that the two mounting areas are opposite each other and aligned with each other, especially in the stacking direction of the diode laser stacks.

[0017] Furthermore, for the active cooling of a first and second single-layer diode laser stack, it is advantageous that the free-end submount carrier plate of the first single-layer diode laser stack is thermally connected to the first flat mounting area, and the free-end submount carrier plate of the second single-layer diode laser stack is thermally connected to the second flat mounting area. The described arrangement of the single-layer diode laser stacks, symmetrical to the center plane of the microchannel cooler, enables particularly rapid heat dissipation from the respective laser bar chip via the submount carrier plate into the microchannel cooler.

[0018] In a particularly preferred embodiment of the invention, for active cooling of at least one multilayer diode laser stack, the free-end submount carrier plate of that stack is thermally connected to the first or second planar, flat mounting area. In particular, for active cooling of at least one first and second multilayer diode laser stack, the free-end submount carrier plate of the first multilayer diode laser stack can be thermally connected to the first planar, flat mounting area, and the free-end submount carrier plate of the second multilayer diode laser stack can be thermally connected to the second planar, flat mounting area. These embodiments result in particularly short heat dissipation paths to the microchannel cooler while simultaneously achieving a very low overall height.

[0019] Furthermore, it is advantageous that the first flat mounting area is located on the top side of the microchannel cooler and the second flat mounting area is located on the underside of the microchannel cooler opposite the top side. This symmetrical arrangement results in particularly efficient cooling of the diode laser stacks mounted on it.

[0020] A particularly advantageous multilayer diode laser stack comprises several laser bar chips and several thermally adapted submount carrier plates, which are alternately stacked in a sandwich-like fashion along a stack axis and thermally connected to each other. This provides a thermally adapted submount carrier plate as an intermediate heat storage medium between two laser bar chips, capable of absorbing at least some of the generated waste heat. During pulsed operation, the submount carrier plates act as a temporary heat storage medium for the waste heat generated by the pulse. Between pulses, the absorbed waste heat is dissipated via the diode laser stack to the microchannel cooler. By appropriately dimensioning the thickness of the submount carrier plates, an optimal balance between heat storage during the pulse and heat dissipation during the pulse duration can be achieved.

[0021] A preferred configuration is a multilayer diode laser stack comprising two to five laser bar chips and two to six thermally matched submount carrier plates, arranged alternately in a sandwich-like structure. Similarly, a single-layer diode laser stack comprises one laser bar chip and one or two thermally matched submount carrier plates. This described sandwich-like structure is particularly advantageous to implement using appropriate coating and soldering processes.

[0022] In a preferred embodiment, the first and second mounting levels are perpendicular to the stacking axis and / or parallel to the propagation axis. With this mounting level arrangement and a two-sided configuration of the microchannel cooler, particularly high cooling performance was achieved.

[0023] The thermally adapted submount carrier plates are particularly advantageous when manufactured from a material with a coefficient of thermal expansion matched to that of the laser bar chip. Furthermore, the thermally adapted submount carrier plates are advantageously made from an electrically conductive material. This ensures not only optimal heat dissipation but also enables the series connection of the laser bar chips within the diode laser stack.

[0024] In the case of two-sided active cooling of single- or multi-layer diode laser stacks, these are preferably arranged symmetrically to a central plane of the microcooler.

[0025] In a particularly preferred embodiment, the laser bar chips and submount carrier plates integrated into a diode laser stack form an electrical series circuit. In the case of double-sided mounting of two diode laser stacks, the two diode laser stacks can also be connected in series with each other. This enables a simple and efficient supply of the electrical energy required for operation to the laser bar chips.

[0026] The laser diode arrangement has a first and second connection contact for connecting the laser diode arrangement to an electrical power supply source, wherein at least the first connection contact is formed by a metallization or metal layer electrically insulated from the microchannel cooler by an insulating layer. The second connection contact can be formed by the microchannel cooler itself or a further metallization or metal layer can be provided on the underside of the microchannel cooler, which is electrically insulated from the microchannel cooler by a further insulating layer. These measures also enable the simplest possible power supply and the use of the diode laser arrangement according to the invention for building a diode laser stack. A single- or multi-part diode laser stack can also be terminated at the end of the stack facing away from the microchannel cooler by a free-end submount carrier plate.In the case of single-sided mounting, a submount carrier plate can also be provided in the unoccupied mounting area.

[0027] It is particularly advantageous that the thickness of a submount carrier plate in the diode laser stack is dimensioned in such a way that the heat generated by the adjacent laser bar chip during a pulse duration is approximately completely absorbed.

[0028] For example, the thickness of a plate-shaped laser bar chip is between 80 and 120 pm, for example 100 pm, and these can have an emission width of approximately 10 mm with a resonator length of 1 to 10 mm.

[0029] The thickness of a submount carrier plate is preferably between 100 and 600 pm, i.e., it has a multiple thickness compared to the laser bar chips.

[0030] Bond wires are particularly advantageous for contacting the laser bar chips, either directly or via a free-end submount carrier plate. Alternatively, contact can be made using a contact foil, which is connected to the laser bar chips or the submount carrier plate by soldering or thermal compression bonding.

[0031] It is also particularly advantageous to have an optical arrangement downstream of each diode laser stack in the beam path of the diode laser radiation. The diode laser radiation emerging from the laser bar chips is shaped by micro-optics provided in the optical arrangement in such a way that the divergence angles in the fast and slow axes are aligned. The optical arrangement can also include an optical element acting as a cylindrical lens, which reduces the divergence of the generated diode laser radiation in the fast-axis direction.

[0032] A laser bar chip is preferably thermally and electrically connected to at least one submount carrier plate via a preferably cycle-resistant solder joint. Alternatively, the laser bar chip can be thermally and electrically connected to at least one submount carrier plate via a thermocompression bonding process.

[0033] Further developments, advantages, and possible applications of the invention will also become apparent from the following description of exemplary embodiments and from the figures. All features described and / or illustrated are, individually or in any combination, fundamentally the subject matter of the invention, irrespective of their compilation in the claims or their cross-reference. The content of the claims is also incorporated into this description. Brief description of the drawings

[0034] The invention will be explained in more detail below with reference to exemplary embodiments in conjunction with the drawings. The drawings show...

[0035] Fig. 1 shows an exemplary schematic cross-sectional view through a diode laser arrangement according to the invention for the active cooling of two single-layer diode laser stacks;

[0036] Fig. 2 is an exemplary schematic sectional view through a device according to the invention.

[0037] Diode laser arrangement for active cooling of a multilayer diode laser stack;

[0038] Fig. 3 shows an exemplary schematic top view of the inventive

[0039] Diode laser arrangement according to Figure 2;

[0040] Fig. 4 shows an exemplary schematic cross-sectional view through a diode laser arrangement according to the invention for the active cooling of two multilayer diode laser stacks;

[0041] Fig. 5 shows an exemplary schematic sectional view through a

[0042] Diode laser stack comprising three diode laser arrangements according to the invention as shown in Figure 4,

[0043] Fig. 6 shows, by way of example, a schematic section view of a section through the first mounting area of ​​a diode laser arrangement according to the invention.

[0044] Fig. 7 shows, by way of example, a schematic section view of a section through the second mounting area of ​​a diode laser arrangement according to the invention and

[0045] Fig. 8 shows an exemplary schematic sectional view through a diode laser arrangement according to the invention for active cooling, comprising a multilayer diode laser stack and a contact film. Ways of implementing the invention

[0046] Identical reference numerals are used in the figures for identical or similarly functioning elements of the invention. Furthermore, for the sake of clarity, only those reference numerals necessary for describing the respective figure are shown in the individual figures. The invention is also illustrated in the figures by means of schematic views. In particular, these schematic representations serve to explain the fundamental principle of the invention.

[0047] Fig. 1 shows a schematic sectional view through a diode laser arrangement 1 according to the invention with at least one microchannel cooler 3 for active cooling of several laser bar chips 4, wherein the arrangement of the laser bar chips 4 is preferably formed as a so-called “diode laser array”.

[0048] The diode laser arrangement 1 is designed to generate a preferably planar diode laser radiation DLS, which propagates in a propagation direction or along a propagation axis z.

[0049] The diode laser arrangement 1 is operated in pulsed mode, specifically in a so-called "quasi continuous wave" (qcw) operating mode. This means that the diode laser arrangement 1 according to the invention does not generate a continuous diode laser radiation (DLS), but rather a pulsed one, which propagates in a specific direction or along the propagation axis z. The diode laser radiation (DLS) has a predetermined pulse duration and pulse width, which can be adjusted depending on the application. Preferably, the diode laser arrangement 1 is operated at a duty cycle of 0.1% to 10%, where the duty cycle describes the ratio of pulse duration to pulse period, and the pulse period is the sum of the pulse duration and the pulse interval.

[0050] The diode laser arrangement 1 can, for example, form a pump module for generating a planar pump beam for a solid-state laser with large-area laser crystals. Such pump modules exhibit, for example, a pump power of several megawatts with a beam area of ​​more than 100 cm². 2 The invention can also be used in a corresponding amplifier module for such solid-state lasers.

[0051] The diode laser arrangement 1 according to the invention comprises at least one or more diode laser stacks 2a, 2b and at least one microchannel cooler 3 for active liquid cooling of the at least one diode laser stack 2a, 2b. In the exemplary embodiments, one microchannel cooler 3 is provided per diode laser arrangement 1, the inventive concept also including the provision of several microchannel coolers.

[0052] According to the invention, the microchannel cooler 3 is designed for the one- or two-sided active cooling of one or more plate-shaped laser bar chips 4 provided in the diode laser stacks 2a, 2b. Thus, according to the invention, one- or two-sided mounting of one or more diode laser stacks 2a, 2b on a microchannel cooler 3 is provided, wherein this mounting is particularly symmetrical. The arrangement is preferably symmetrical about a central plane of the microchannel cooler 3, which runs along or parallel to the propagation axis z.

[0053] A diode laser stack 2a, 2b comprises one or more plate-shaped laser bar chips 4 and one or more thermally adapted submount carrier plates 5, wherein thermal adaptation in the sense of the invention means the production of the submount carrier plates 5 from a material which has a coefficient of thermal expansion adapted to the material of the laser bar chip 4.

[0054] Preferably, materials such as CuW, CuMo, Cu-diamond, or comparable materials are used to manufacture the submount carrier plates 5. Furthermore, the submount carrier plates 5 are electrically conductive, so that an electrical connection can also be established between two laser bar chips 4 or between a laser bar chip 4 and the microchannel cooler 3 by means of a submount carrier plate 5.

[0055] For example, a laser bar chip 4 has a thermal conductivity of approximately 60 watts / mK, and in comparison, a submount carrier plate 5 has a thermal conductivity of approximately 180 watts / mK, i.e., the thermal conductivity of the submount carrier plate 5 is two or three times that of the laser bar chip 4, depending on the respective thickness of the plate-shaped laser bar chip 4 and / or the submount carrier plate 5.

[0056] According to the invention, a diode laser stack 2a, 2b can be configured as a single-layer diode laser stack 2a or a multi-layer diode laser stack 2b, wherein a single-layer diode laser stack 2a comprises a plate-shaped laser bar chip 4 and at least one thermally adapted submount carrier plate 5, and a multi-layer diode laser stack 2b comprises several plate-shaped laser bar chips 4 and several thermally adapted submount carrier plates 5. The term "single-layer" or "multi-layer" thus indicates the number of plate-shaped laser bar chips 4 contained in the respective diode laser stack 2a, 2b. Figure 1 shows, for example, two single-layer diode laser stacks 2a, each with a plate-shaped laser bar chip 4, and Figure 2 shows a multi-layer diode laser stack 2b with, for example, five plate-shaped laser bar chips 4.

[0057] In the context of the invention, a plate-shaped laser bar chip 4 is understood to be a plurality of individual emitters or laser diodes arranged in a bar shape relative to one another and combined to form a monolithic chip mounted on a semiconductor wafer, thus having a plate shape. Preferably, a plate-shaped laser bar chip 4 has between 10 and 100 individual emitters or laser diodes. The laser diodes are arranged along a bar longitudinal axis x, which runs perpendicular to the propagation axis and the stacking axis y.

[0058] Furthermore, the at least one microchannel cooler 3 for one- or two-sided active liquid cooling of the diode laser stack(s) 2a, 2b has a cooling channel structure 3.1 and at least one first planar, flat mounting area 3.2, which extends along the cooling channel structure 3.1 in a first mounting level MEI. In a preferred embodiment, a second planar, flat mounting area 3.3 is provided, which preferably also extends along the cooling channel structure 3.1 in a second mounting level ME2.

[0059] Particularly preferably, the first and second mounting levels MEI, ME2 are arranged parallel to each other and formed on the top and bottom surfaces of the microchannel cooler 3, respectively, in an edge-side section of the microchannel cooler 3 in the region of the cooling channel structure 3.1. The top and bottom surfaces of the microchannel cooler 3 can also be stepped, so that, for example, the first and second mounting levels MEI, ME2 can be formed in a thickness-reduced section of the microchannel cooler 3 on the top or bottom surface. In the embodiment according to Figure 1, for example, the first and second mounting levels MEI, ME2 are provided in such a thickness-reduced section of the microchannel cooler 3, specifically at the free end and edge, respectively.

[0060] In the assembled state, the first and / or second mounting level MEI, ME2 of the microchannel cooler 3 preferably run perpendicular to the stack axis y of the diode laser stack(s) 2a, 2b mounted thereon. The cooling channel structure 3.1 is integrated into the microchannel cooler 3 and is designed to hold a liquid cooling medium. Water is suitable as a liquid cooling medium, but other liquids with a suitable ratio of heat capacity and viscosity can also be used, such as ammonia, liquid nitrogen, or other liquefied gases that exhibit corresponding suitability. The mounting areas 3.3, 3.4 are formed on the top and bottom surfaces of the microchannel cooler 3, respectively. Active cooling in the mounting areas 3.3, 3.4 is achieved by means of the microchannel cooler 3 via the liquid cooling medium contained within it.

[0061] The microchannel cooler 3 is made of a material with good electrical and thermal conductivity, such as copper or similar materials, and has a layered or monolithic structure. Suitable manufacturing processes, such as direct copper bonding, can be used for its production. The microchannel cooler 3 is preferably essentially cuboidal in shape, with its central plane extending along the propagation axis z. The microchannel cooler 3 has a relatively small thickness of a few millimeters and, in comparison, large top and bottom surfaces.

[0062] To supply the liquid cooling medium into the cooling channel structure 3.1, the microchannel cooler 3 has an inlet 3.4 and to discharge the liquid cooling medium an outlet 3.5, which are preferably arranged in a rear region of the microchannel cooler 3 opposite the mounting areas 3.2, 3.3. Preferably, the inlet and outlet 3.4, 3.5 are provided on the top or bottom of the microchannel cooler 3.

[0063] The inlet and outlet 3.4, 3.5 are formed by preferably circular bores in the region of the top or bottom of the microchannel cooler 3, through which the respective liquid cooling medium can be supplied to or discharged from the cooling channel structure 3.1. Ring-shaped sealing elements 8 can preferably be provided to seal the inlet and outlet 3.4, 3.5 or the bores.

[0064] The inlet and outlet 3.4, 3.5 can also be designed as through-holes extending from the top to the bottom of the microchannel cooler 3, thus enabling a series connection of several microchannel coolers 3.

[0065] The laser diode arrangement 2 further comprises a first and / or second connection contact 6, 6' for connecting the laser diode arrangement 2 to an electrical power supply source or for supplying and removing electrical current. The first connection contact 6 can, for example, be formed by a metallization or metal layer that is formed over a surface area on the top side of the microchannel cooler 3. This metallization or metal layer is connected to the microchannel cooler 3 via an insulating layer 7 and is thus electrically insulated from the microchannel cooler 3. This metallization or metal layer forms a so-called cover contact. Due to the microchannel cooler 3 being made of an electrically conductive material, the second connection contact 6' can be formed by the underside of the microchannel cooler 3 itself, which also forms a surface cover contact 6'.Alternatively, further metallization can also be applied to the underside of the microchannel cooler 3.

[0066] A metal layer is provided which is connected to the microchannel cooler 3 or its underside via a further insulating layer 7'. This further metal layer then also forms a cover contact 6'.

[0067] In the present embodiment according to Figure 1, for example, the first connection contact 6 is provided for connecting the electrical negative terminal n, which is connected to the top of the microchannel cooler 3 via the insulating layer 7. Similarly, the second connection contact 6' is provided for connecting the electrical positive terminal p, which is connected to the underside of the microchannel cooler 3 via a further insulating layer 7'.

[0068] In contrast, in the embodiment shown in Figure 2, the second connection contact 6' is formed by the underside of the microchannel cooler 3 itself. Figure 4 again shows an embodiment with a first and second connection contact 6, 6', each formed by a metallization or metal layer connected to the microchannel cooler 3 via an insulating layer 7, 7'.

[0069] The diode laser stack 2a, 2b each has a sandwich-like structure, i.e., one or more plate-shaped laser bar chips 4 and one or more submount carrier plates 5 are stacked alternately along a stacking axis y in a sandwich-like arrangement. In each diode laser stack 2a, 2b, two consecutive laser bar chips 4 are thermally connected to each other via a thermally matched submount carrier plate 5, or each submount carrier plate 5 is thermally and electrically connected to exactly one top or bottom surface of a laser bar chip 4.

[0070] Each plate-shaped laser bar chip 4 has an upper n-terminal surface for connecting the negative terminal and an opposing lower p-terminal surface for connecting the positive terminal. These are not explicitly shown in the figures.

[0071] For active cooling of a first and second single-layer diode laser stack 2a, a submount carrier plate 5 of the first single-layer diode laser stack 2a is thermally connected to the first planar, flat mounting area 3.2, and a free-end submount carrier plate 5 of the second single-layer diode laser stack 2a is thermally connected to the second planar, flat mounting area 3.3. A corresponding arrangement is shown in Figure 1, in which the first and second single-layer diode laser stacks 2a each have only one laser bar chip 4 and one submount carrier plate 5. However, it is also conceivable that the first and second single-layer diode laser stacks 2a also have a further submount carrier plate 5, which is arranged on the top side of the laser bar chip 4 facing away from the cooling channel body 3 in the first and / or second single-layer diode laser stack 2a.Thus, the first and second single-layer diode laser stack 2a comprises a laser bar chip 4 and two submount carrier plates 5.

[0072] In a further embodiment of the invention, for active cooling of at least one multilayer diode laser stack 2b, the free-end submount carrier plate 5 of that stack is thermally connected to the first or the second planar, flat mounting area 3.2, 3.3. When connected to the first mounting area 3.2, the laser bar chips 4 in the multilayer diode laser stack 2b are oriented such that their p-type contact surfaces face the microchannel cooler 3 or the first mounting area 3.2, respectively. Similarly, when connected to the second mounting area 3.3, the laser bar chips 4 in the multilayer diode laser stack 2b are oriented such that their n-type contact surfaces face the microchannel cooler 3 or the second mounting area 3.3, respectively; that is, on the underside of the microchannel cooler 3, the p-type contact surfaces face away from the microchannel cooler 3.

[0073] A corresponding arrangement is shown in Figure 2. In this embodiment, the free-end submount carrier plate 5 of the multilayer diode laser stack 2b is connected to the first planar, flat mounting area 3.2, whereas in the opposite second planar, flat mounting area 3.3, only a submount carrier plate 5 is provided on its own, i.e., without a laser bar chip 4, preferably for stability reasons. Figure 3 shows a top view of a diode laser arrangement 1.

[0074] Figure 4 shows another embodiment in which a multilayer diode laser stack 2b is mounted on the microchannel cooler 3 in both the first and the second planar, flat mounting area 3.2, 3.3 as described above.

[0075] The multilayer diode laser stacks 2b shown in Figures 2 and 4, for example, comprise four laser bar chips 4 and four submount carrier plates 5. It is understood that the multilayer diode laser stacks 2b can have a different number of laser bar chips 4 and the associated four submount carrier plates 5 without this departing from the inventive concept.

[0076] The multi-layer diode laser stack 2b can also be terminated at the stack end used by the microchannel cooler 3, analogous to the single-layer diode laser stack 2a, via a submount carrier plate 5. Particularly preferably, when single- or multi-layer diode laser stacks 2a, 2b are mounted on both sides of the microchannel cooler 3, they have a symmetrical structure.

[0077] The single- or multi-layer diode laser stacks 2a, 2b are thus mounted on one or both sides of the mounting areas 3.2, 3.3 of the microchannel cooler 3 in such a way that the entire diode laser stack 2 is actively liquid-cooled.

[0078] The thickness of the submount carrier plate 5 in the diode laser stack 2a, 2b is preferably selected such that the heat emitted by the respective laser bar chip 4 during pulsed operation is absorbed by the adjacent submount carrier plate(s) 5 in such a way that the temperature of the further laser bar chip 4 provided in the diode laser stack 2a, 2b remains unaffected. The submount carrier plate 5 thus forms a thermal storage medium. During the longer pulse interval compared to the pulse duration, this extended period is then used to transfer the heat generated in the diode laser stack 2a, 2b through the entire stack to the microchannel cooler 3, and in particular the waste heat temporarily stored in the respective submount carrier plate 5. This is particularly possible when operating the pulsed diode laser array with a "duty cycle" of 0.1-10%.

[0079] The laser bar chips 4 preferably have an emission width of approximately 10 mm and a resonator length of 1 to 10 mm. The thickness of the plate-shaped laser bar chips 4 is, for example, between 80 and 120 pm, preferably approximately 100 pm, and is chosen to be as small as possible to minimize thermal resistance during heat conduction through the laser bar chips 4. The wavelength of the laser bar chips 4 is preferably in the range of 800–900 nm, although laser bar chips 4 with shorter or longer wavelengths can also be used. To achieve the highest possible output power per laser bar chip 4, laser diodes with a fill factor greater than 50% are preferably used.

[0080] The thickness of the submount carrier plate 5 is preferably between 100 and 600 µm, meaning that 10 to 30 laser bar chips 4 can be arranged per cm of installation height, so that with an optical signal power of 1 kW per laser bar chip 4, power densities of up to 10 to 30 kW / cm² are possible. 2 can be achieved.

[0081] The thermally and electrically conductive connection between the laser bar chip 4 and the submount carrier plates 5, or between the submount carrier plate 5 and the microchannel body 3, is preferably made by means of a preferably cycle-resistant solder joint 12, for example made of AuSn or a comparable solder material. The solder material is applied to the submount carrier plate 5 in the form of preforms or as a coating, and the plate-shaped laser bar chip 4 to be joined is placed on it, preferably flush with the surface. The actual connection of the components is then made via a soldering process in which the melting point of the solder used is exceeded. A thermocompression bonding process can also be used instead of a solder joint 12.

[0082] Figure 6 shows a schematic section view of a section through the first mounting area 3.2 of a diode laser arrangement 1 according to the invention, in which a multilayer diode laser stack 2b comprising two laser bar chips 4 and three submount carrier plates 5 is mounted, wherein the laser bar chips 4 are each connected to at least one submount carrier plate 5 via a solder connection 12 and the free-end submount carrier plate 5 is also connected to the microchannel cooler 3, namely its first mounting area 3.2, via a solder connection 12.

[0083] Similarly, Figure 7 shows a schematic section view through the second mounting area 3.3 of a diode laser arrangement 1 according to the invention, on which a multilayer diode laser stack 2b comprising two laser bar chips 4 and three submount carrier plates 5 is mounted in the second mounting level ME2.

[0084] The orientations of the n- and p-connection surfaces of the submount carrier plates 5 can be clearly seen in Figures 6 and 7 based on the beam exit point. In Figure 6, the p-connection surfaces of the submount carrier plates 5 point towards the microchannel cooler 3, whereas in Figure 7 they point away from the microchannel cooler 3.

[0085] The laser bar chips 4 are contacted, for example, via bond wires 9, 9', which establish an electrically conductive connection between the first and second connection contacts 6, 6' and the respective outer submount carrier plate 5 and laser bar chip 4. Corresponding bond wires 9, 9' are shown, for example, in Figures 1 to 7.

[0086] Instead of bond wires 9, 9', contact foils 6" in the form of connection contacts 6, 6' formed by metallization or a metal layer can also be used. These foils are connected to the laser bar chip 4 either directly or via an external submount carrier plate 5. The contact foils 6" are connected either by means of a solder joint 12 or by means of thermal compression bonding. Figure 8 shows an exemplary schematic sectional view through a diode laser arrangement 1 comparable to Figure 2, in which, instead of bond wires 9, the multilayer diode laser stack 2b is contacted by means of a contact foil 6" which is electrically connected via a free-end submount carrier plate 5.

[0087] The individual laser bar chips 4 within a diode laser stack 2b are connected in series to each other, i.e. the respective contact surfaces of the laser bar chips 4 are each connected to each other via a submount carrier plate 5, the series connection being continued via the electrically conductive microchannel cooler 3 in the case of double-sided assembly of the microchannel cooler 3.

[0088] Figure 5 shows an example of a stacked, sandwich-like arrangement of several diode laser assemblies 1 according to the invention, connected in series. Such an arrangement is often also referred to as a diode laser stack. For this purpose, the second terminal 6' of each diode laser assembly is electrically connected to the adjacent terminal via a plate-shaped spacer contact element 10. For example, more than 100 laser bar chips 4 can also be operated in a circuit in a corresponding series connection.

[0089] Furthermore, each diode laser arrangement 1 can be assigned at least one optical arrangement 11, 11' which extends along the bar longitudinal axis x and / or stack axis y and is arranged downstream of the laser bar chips 4 in the beam path. The optical arrangement 11, 11' shapes the laser radiation DLS emerging from the laser bar chips 4 via appropriately provided micro-optics such that the divergence angle in the fast-axis and slow-axis of the generated laser radiation DLS can be adjusted. For example, the divergence of the generated radiation in the fast-axis direction is reduced by means of an optical element designed as a cylindrical lens. The profile of the emitted laser radiation DLS in the slow-axis direction can also be adjusted with further optical elements, with the aim of achieving the most homogeneous distribution of the laser radiation DLS possible.

[0090] The micro-optics of the optical arrangement 11, 11' can be made of optical glass, in particular fused silica, which has a low absorption coefficient at the laser wavelength used, so that beam shaping is accompanied by the lowest possible power losses. In a preferred embodiment, the micro-optics of the optical arrangement 11, 11' are provided with an AR coating to keep the power losses as low as possible.

[0091] The aforementioned micro-optics are permanently connected to the diode laser arrangement 1 using suitable joining methods such as gluing or soldering, and are aligned or adjusted accordingly in the beam path. Furthermore, several stacked arrangements of multiple diode laser arrangements 1 according to the invention, as shown in Figure 5, can be combined into modules in which several such stacked arrangements are arranged side by side and / or one above the other, forming a matrix-like structure. This allows the creation of a large-area, nearly monolithic pump module with an output area of ​​several hundred cm². 2 Such modules may exhibit this feature. They preferably have multiple circuits to provide independent power distribution within the modules. This allows the power distribution to be configured for specific applications.

[0092] In a diode laser stack, the inlets and outlets 3.3, 3.4 of the microchannel coolers 3 of the individual diode laser arrangements 1 can be configured as aligned through-holes, each connected to the other via a sealing element 8, preferably O-ring-shaped sealing elements 8, thus creating a closed coolant circuit. The through-holes of the stacked microcoolers 3 preferably form a common inlet and outlet channel.

[0093] The invention has been described above using exemplary embodiments. It is understood that numerous modifications and adaptations are possible without departing from the underlying inventive concept.

[0094] Reference symbol list

[0095] 1 Laser diode array 2a Single-layer diode laser stack 2b Multi-layer diode laser stack

[0096] 3 Microchannel coolers 3.1 Cooling channel structure

[0097] 3.2 First flat and level mounting area

[0098] 3.3 Second flat and level mounting area

[0099] 3.4 Admission

[0100] 3.5 Outlet 4 Laser bar chip

[0101] 5 Submount carrier plate 6 First connection contact

[0102] 6' second connection contact 6" contact foils

[0103] 7 Insulation layer T further insulation layer

[0104] 8 sealing elements 9 bonding wires

[0105] 9 additional bond wires 10 spacer contact element

[0106] 11 Optical arrangement IV further optical arrangement 12 Solder connections

[0107] DLS diode laser radiation MEI first mounting level ME2 second mounting level n electrical negative pole P electrical positive pole x bar longitudinal axis y stacking axis z propagation axis

Claims

Patent claims 1. Diode laser arrangement (1) comprising at least one diode laser stack (2a, 2b) and at least one microchannel cooler (3) for active liquid cooling of the at least one diode laser stack (2a, 2b), wherein the diode laser stack (2) is configured as a single-layer diode laser stack (2a) or a multi-layer diode laser stack (2b), wherein a single-layer diode laser stack (2a) comprises a plate-shaped laser bar chip (4) and at least one thermally adapted submount carrier plate (5) thereto, and a multi-layer diode laser stack (2b) comprises several plate-shaped laser bar chips (4) and several thermally adapted submount carrier plates (5) thereto, wherein a plate-shaped laser bar chip (4) is thermally connected over its entire surface to at least one adjoining submount carrier plate (5), wherein the at least a microchannel cooler (3) for active liquid cooling of the at least one diode laser stack (2a, 2b) a cooling channel structure (3.1) characterized in that the microchannel cooler (3) is designed for one-sided active cooling of the plate-shaped laser bar chips (4) arranged in a multilayer diode laser stack (2b) or for two-sided active cooling of the plate-shaped laser bar chips (4) arranged in several single- or multilayer diode laser stacks (2a, 2b).

2. Diode laser arrangement (1) according to claim 1, characterized in that the at least one microchannel cooler (3) has a first and / or second planar, flat mounting area (3.2, 3.3) which extends along the cooling channel structure (3.1) in a first or second mounting plane (MEI, ME2).

3. Diode laser arrangement (1) according to claim 2, characterized in that, for active cooling of a first and second single-layer diode laser stack (2a), the free-end submount carrier plate (5) of the first single-layer diode laser stack (2) is thermally connected to the first planar, flat mounting area (3.2) and the free-end submount carrier plate (5) of the second single-layer diode laser stack (2a) is thermally connected to the second planar, flat mounting area (3.3).

4. Diode laser arrangement (1) according to claim 2 or 3, characterized in that, for active cooling of at least one multilayer diode laser stack (2b), its free-end submount carrier plate (5) is thermally connected to the first or second planar, flat mounting area (3.2, 3.3).

5. Diode laser arrangement (1) according to one of claims 2 to 3, characterized in that, for active cooling of at least one first and second multilayer diode laser stack (2b), the free-end submount carrier plate (5) of the first multilayer diode laser stack (2b) is thermally connected to the first planar and flat mounting area (3.2) and the free-end submount carrier plate (5) of the second multilayer diode laser stack (2b) is thermally connected to the second planar and flat mounting area (3.3).

6. Diode laser arrangement (1) according to one of claims 2 to 5, characterized in that the first planar and flat mounting area (3.2) is formed on a top side of the microchannel cooler (3) and the second planar and flat mounting area (3.3) is formed on a bottom side of the microchannel cooler (3) opposite the top side.

7. Diode laser arrangement (1) according to one of the preceding claims, characterized in that a multilayer diode laser stack (2b) comprises several laser bar chips (5) and several thermally adapted submount carrier plates (5) which are alternately sandwich-like stacked along a stacking axis (y) and are thermally conductively connected to each other.

8. Diode laser arrangement (1) according to claim 7, characterized in that a multilayer diode laser stack (2b) preferably comprises two to five laser bar chips (5) and two to six thermally adapted submount carrier plates (5).

9. Diode laser arrangement (1) according to one of the preceding claims, characterized in that a single-layer diode laser stack (2a) comprises a laser bar chip (5) and one or two thermally adapted submount carrier plates (5).

10. Diode laser arrangement according to one of the preceding claims, characterized in that the first and second mounting plane (MEI, ME2) is perpendicular to the stacking axis (y) and / or parallel to the propagation axis (z).

11. Diode laser arrangement (1) according to one of the preceding claims, characterized in that the thermally adapted submount carrier plates (5) are made of a material which has a coefficient of thermal expansion adapted to the material of the laser bar chip (4).

12. Diode laser arrangement (1) according to one of the preceding claims, characterized in that the thermally adapted submount carrier plates (5) are made of an electrically conductive material.

13. Diode laser arrangement (1) according to one of the preceding claims, characterized in that, in the case of two-sided active cooling of the single- or multi-layer diode laser stacks (2a, 2b), these are arranged symmetrically to a central plane of the microchannel cooler (3).

14. Diode laser arrangement (1) according to one of the preceding claims, characterized in that the laser bar chips (4) and submount carrier plates (5) included in a diode laser stack (2a, 2b) form an electrical series circuit.

15. Diode laser arrangement (1) according to claim 14, characterized in that in the case of a two-sided mounting of two diode laser stacks (2a, 2b) the two diode laser stacks (2a, 2b) are also connected in series to each other.

16. Diode laser arrangement (1) according to one of the preceding claims, characterized in that the laser diode arrangement (1) has a first and second connection contact (6, 6') for connecting the laser diode arrangement (2) to an electrical power supply source, wherein at least the first connection contact (6) is formed by means of a metallization or metal layer electrically insulated from the microchannel cooler (3) by an insulating layer (7).

17. Diode laser arrangement (1) according to claim 16, characterized in that the second connection contact (6') is formed by the microchannel cooler (3) itself or a further metallization or metal layer is provided on the underside of the microchannel cooler (3) which is electrically insulated from the microchannel cooler (3) by a further insulating layer (7').

18. Diode laser arrangement (1) according to one of the preceding claims, characterized in that a one- or multi-part diode laser stack (2a, 2b) is terminated at the stack end facing away from the microchannel cooler (3) via a free-end submount carrier plate (5).

19. Diode laser arrangement (1) according to one of the preceding claims, characterized in that the thickness of a submount carrier plate (5) in the diode laser stack (2a, 2b) is dimensioned such that the heat generated by the adjacent laser bar chip (4) during a pulse duration is approximately completely absorbed.

20. Diode laser arrangement (1) according to one of the preceding claims, characterized in that the thickness of a plate-shaped laser bar chip (4) is between 80 and 120 pm, for example 100 pm and / or these have an emission width of approximately 10 mm with a resonator length of 1 to 10 mm.

21. Diode laser arrangement (1) according to one of the preceding claims, characterized in that the thickness of a submount carrier plate (5) is between 100 - 600pm.

22. Diode laser arrangement (1) according to one of the preceding claims, characterized in that bond wires (9, 9') or a contact foil (6") are provided for contacting the laser bar chips (4) either directly or via a free-end submount carrier plate (5).

23. Diode laser arrangement (1) according to one of the preceding claims, characterized in that an optics arrangement (11, 11') is arranged downstream of each diode laser stack (2a, 2b) in the beam path of the diode laser radiation (DLS).

24. Diode laser arrangement (1) according to one of the preceding claims, characterized in that a laser bar chip (4) is thermally and electrically connected to at least one submount carrier plate (5) via a preferably cycle-resistant solder joint (12).

25. Diode laser arrangement (1) according to one of the preceding claims, characterized in that a laser bar chip (4) is thermally and electrically connected to at least one submount carrier plate (5) via a thermocompression bonding process.

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