Method and device for controlling the operation of a laser device, laser device and laser materials processing apparatus

Abstract

The present application relates to method and device for controlling the operation of a laser device, and also to a laser device and to a laser materials processing apparatus. The method for controlling the operation of a laser device for use in a laser materials processing technique comprising the steps: for a first time interval, controlling the laser device so as to emit laser radiation at a first laser power; and after expiry of the first time interval, controlling the laser device so as to emit laser radiation at a second laser power for a second time interval, the second laser power being higher than the first laser power and exceeding a processing threshold value suitable for processing a material in the laser materials processing technique; and c) compensating a delay between the start of the control of the laser device so as to increase the laser power from the first laser power to the second laser power at the beginning of the second time interval and the actual emission of laser radiation at the second laser power independent of the second laser power.

Description

[0001] Nikon SLM Solutions AG - 1 - 30A-167 984

[0002] Method and device for controlling the operation of a laser device, laser device and laser materials processing apparatus

[0003] The present invention generally relates to a method and a device for controlling the operation of a laser device for use in materials processing techniques. Further, the invention relates to laser device which is particularly suitable for being controlled in accordance with the described method. Finally, the invention relates to a laser materials processing apparatus which is equipped with a device for controlling the operation of the laser device and / or a laser device.

[0004] Laser processing encompasses a variety of techniques used in manufacturing and materials processing. Examples for laser processing of materials include, for example, laser cutting, wherein a laser beam is used to cut materials with high precision by melting, burning, or vaporizing the material, laser welding, wherein a laser beam is used to join two or more pieces of material by melting them together at their interface, laser engraving and marking, wherein a laser beam is used to remove material from the surface to create designs, text, or barcodes, laser drilling, wherein a laser beam is used to drill precise holes by vaporizing material in a localized area, laser ablation, wherein a laser beam is used to remove material from a solid surface by vaporizing it, laser cladding, wherein a laser beam is used to melt and deposit a coating material onto a substrate, enhancing surface properties, laser lithography, wherein a laser beam is used to create detailed patterns on substrates, often used in the production of semiconductors, laser surface treatment, wherein a laser beam is used to modify the properties of a surface, such as hardening, annealing, or alloying, laser cleaning, wherein a laser beam is used to remove contaminants, oxides, or coatings from surfaces without damaging the underlying material, and powder bed fusion, wherein a laser beam is used to sinter or melt powder materials layer by layer to create three-dimensional objects. Each of these laser processing methods utilizes the unique properties of laser light, such as high intensity, coherence, and precision, to achieve specific outcomes in a wide range of industrial and technological applications.

[0005] By powder bed fusion, pulverulent, in particular metallic and / or ceramic raw materials can be processed to three-dimensional workpieces of complex shapes. To that end, a raw material powder layer is applied onto a carrier and subjected to laser radiation in a site-selective manner in dependence on the desired geometry of the workpiece that is to be produced. The radiation penetrating into the powder layer Nikon SLM Solutions AG - 2 - 30A-167 984 causes heating and consequently melting or sintering of the raw material powder particles. Further raw material powder layers are then applied successively to the layer on the carrier that has already been subjected to radiation treatment, until the workpiece has the desired shape and size. Powder bed fusion may be employed for the production of prototypes, tools, replacement parts, high value components, or medical prostheses, such as, for example, dental or orthopedic prostheses, on the basis of CAD data. Examples for powder bed fusion techniques include selective laser melting, selective laser sintering, and electron beam melting.

[0006] A laser device is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. Laser devices for use in materials processing applications typically comprises a gain medium where light amplification occurs. It can be a gas, liquid, or solid and contains atoms or molecules that can be excited to higher energy states. A pump source provides energy to excite the atoms or molecules in the gain medium to a higher energy state. This can be electrical energy resulting from electric discharge or diode pumping or optical energy emitted by flash lamps or other lasers. An optical resonator which may, for example, comprise a fully reflective and a partially reflective mirror placed at either end of the gain medium serves to trap photons by reflecting them back and forth through the gain medium, amplifying the light.

[0007] When the pump source, which may operate in a pulsed mode, excites the electrons in the atoms or molecules of the gain medium to higher energy levels, some excited electrons spontaneously fall back to the lower energy state, emitting photons. These photons stimulate other excited electrons to drop to the lower energy state, emitting additional photons with the same phase, frequency, and direction. The emitted photons are reflected back and forth by the mirrors of the optical resonator, passing through the gain medium multiple times, which further amplifies the light through more stimulated emission. The partially reflective mirror allows a portion of the amplified light to escape as the laser beam.

[0008] The operation of laser devices typically involves a delay between the start of the laser device, for example by providing a suitable voltage signal to the pump source, and the actual emission of the laser beam. Delays in laser operation, including a build-up time for reaching a steady state, depend on several parameters. Usual key factors are, for example, the average time a photon stays in the laser cavity before escaping or being absorbed, the time required to achieve a sufficient population inversion in the gain medium, the time it takes for light to travel once around the Nikon SLM Solutions AG - 3 - 30A-167 984 laser cavity and the time it takes for the pump source to effectively excite the gain medium. Further, a pulse duration and a break time between individual pulses when the pump source is operated in a pulsed mode and the laser power influence the delay.

[0009] Further, when a laser device first starts-up or when there is a sudden change in operating conditions, a transient oscillation in the output power, the so-called relaxation peak, occurs before the laser reaches a steady-state operation. Relaxation peaks in lasers are caused by dynamic processes involved in achieving equilibrium between the gain medium's population inversion and photon density in the laser cavity. Factors such as population inversion dynamics, photon density build-up, gain medium response, cavity Q-factor, pump power fluctuations, mode competition, thermal effects, and nonlinear effects all contribute to these transient oscillations.

[0010] Usually, the relaxation peak is very short in duration (a few hundred nanoseconds to a few microseconds). However, the laser power of the relaxation peak is larger (~1.5 to 3 times) than the desired laser power for, for example, materials processing. Additionally, it is possible that during the relaxation peak, the laser's spectrum deviates from the nominal wavelength and is not stable. This might lead to interactions with sensors / measurement instruments that operate within the laser light range, direct and / or indirect interactions with the laser light, or spectral sensitivity within the range of the (short-term) emission wavelengths.

[0011] In many currently known laser materials processing techniques, a laser device used for generating laser radiation intended to be irradiated onto a material to be processed is repeatedly switched on and off. For example, in powder bed fusion techniques, wherein a laser beam is scanned across a powder bed according to a scan vector pattern so as to site-selectively melt and / or sinter the powder particles of the powder bed in order to generate a three-dimensional object, the laser device is switched on while a scan vector is irradiated and switched off at the end of the irradiation of the scan vector until the next scan vector is irradiated. Further, the laser power for scanning individual scan vectors may vary for example in dependence on whether the scan vector is located in the region of a contour or in the region of an inner volume of a three-dimensional object to be generated. Similarly, in laser cutting techniques, the laser device may be switched off between subsequent cutting steps which may be performed at varying laser powers and in laser welding techniques, the laser device may be switched off between subsequent welding steps which also may be performed at varying laser powers. Nikon SLM Solutions AG - 4 - 30A-167 984

[0012] However, as discussed above, each time the laser device is switched on, a delay between the start of the laser device and the actual emission of the laser beam occurs, wherein a length of the delay depends inter alia on the laser power, the pulse duration and the break time between individual pulses. In particular, a length of the delay increases with an increasing pulse duration and with an increasing break time between individual pulses. Further, the lower the laser power, the longer the delay.

[0013] Additionally, a relaxation peak is observed. An intensity of the relaxation peak depends on the laser power, i.e. the higher the laser power, the higher the maximum intensity of the relaxation peak.

[0014] In laser processing techniques, such as, for example, powder bed fusion, laser delays are typically compensated based on experimentally determined look-up tables for different laser powers at a fixed pulse duration / break time relation. However, as discussed above, the delays not only depend on the laser power, but also on multiple further factors including the pulse duration and the break time between individual pulses which are not considered in current compensation methods.

[0015] Laser devices which are currently used in materials processing techniques typically are not operated at the nominal laser power but at different laser power values below the nominal laser power. The laser power is controlled by controlling a diode current of the pump diodes in a range between 10 % to 100 % of the maximum diode current, wherein a diode current of 100 % of the maximum diode current results in an operation of the laser device at the nominal laser power.

[0016] The invention is directed to the object to provide a method and a device for controlling the operation of a laser device for use in materials processing techniques which allow a mitigation of unwanted effects of a delay and a relaxation peak usually occurring upon start-up of the laser device. Further, the invention is directed to the object to provide a laser device which is particularly suitable for being operated at a low laser power. Finally, the invention is directed at the object to provide a laser materials processing apparatus which is equipped with a device for controlling the operation of the laser device and / or a laser device.

[0017] These objects are addressed by a method for controlling the operation of a laser device as defined in claim 1, a device for controlling the operation of a laser device Nikon SLM Solutions AG - 5 - 30A-167 984 as defined in claim 12, a laser device as defined in claim 13 and a laser materials processing apparatus as defined in claim 16.

[0018] In a method for controlling the operation of a laser device for use in a laser materials processing technique, in a step a), the laser device is controlled, for a first time interval, so as to emit laser radiation at a first laser power. After expiry of the first time interval, in a step b), the laser device is controlled so as to emit laser radiation at a second laser power for a second time interval. The second laser power is higher than the first laser power and exceeds a processing threshold value suitable for processing a material in the laser materials processing technique. In a step c), a delay between the start of the control of the laser device so as to increase the laser power from the first laser power to the second laser power at the beginning of the second time interval and the actual emission of laser radiation at the second laser power is compensated independent of the second laser power.

[0019] The suitability of laser radiation for laser material processing depends on the laser power energy density at the processing site, i.e. on the powder bed surface during laser powder bed fusion or on the workpiece surface during laser cutting or laser welding. The laser power energy density is dependent on the laser power and the laser beam diameter, wherein the laser beam diameter is influenced by the optical system. In the context of the present application, the expression "processing threshold value" defines a minimum laser power which is required for processing a material in a desired manner in a specific laser materials processing technique. For example, in powder bed fusion techniques, the processing threshold value defines the minimum laser power which allows the desired melting and / or sintering of the powder particles of the powder bed. To the contrary, a laser power below the processing threshold value does not result in the specific desired melting and / or sintering of the powder particles of the powder bed. Similarly, in laser cutting or welding techniques, the processing threshold value defines the minimum laser power which allows the desired cutting or welding of a workpiece or material, whereas a laser power below the processing threshold value does not allow a cutting or welding of the workpiece or material.

[0020] In the method for controlling the operation of a laser device, at the beginning of the second time interval, the laser device is not started from a state, in which the laser device does not emit laser power at all, but instead, the laser device is controlled so as to increase the laser power from the first laser power to the second laser power. It has been found by the inventors, that the increase of the laser power from the Nikon SLM Solutions AG - 6 - 30A-167 984 first laser power to the second laser power still involves a delay between the output of a respective signal, for example a suitable voltage signal, to a pump source of the laser device and the actual emission of laser radiation at the second laser power. However, as compared to a control of the laser device so as to emit laser radiation at the second laser power directly upon start-up of the laser device, the dependency of said delay on the second laser power is significantly reduced or even substantially eliminated.

[0021] In order to control the operation of the laser device so as to avoid a state in which the laser device does not emit laser power during the first time interval, it is conceivable that the laser device is not switched off during the first time interval. For example, a power supply and / or the supply of a respective "on" control signal to the laser device may be continued during the first time interval in order to avoid that the laser power emitted by the laser device drops down to zero during the first time interval. It is, however, also conceivable, that the laser device, in particular during a first time interval following a preceding second time interval, is switched off, e.g. by no longer supplying power and / or a respective "on" control signal to the laser device. In this case, the first time interval, however, needs to be short enough that the laser power emitted by the laser device does not drop down to zero during the first time interval or the laser is still in a transition mode. For example, a duration of the first time interval of < 3 ps may ensure that the laser power emitted by the laser device does not drop down to zero during the first time interval.

[0022] Thus, a delay between the start of the control of the laser device so as to increase the laser power from the first laser power to the second laser power at the beginning of the second time interval and the actual emission of laser radiation at the second laser power can be compensated independent of the second laser power. As a result, a compensation algorithm may be simplified. Alternatively or additionally, other parameters than the second laser power or the difference between the first laser power and the second laser power can be considered upon compensating the delay, thus increasing the accuracy of the compensation. Other parameters, i.e. those relating to a beam deflection device, such as a laser scanning device, can also be set in a simplified manner if a constant delay is given which is independent of the second laser power or the difference between the first laser power and the second laser power.

[0023] In addition, as compared to a start-up of the laser device from a state, in which the laser device does not emit laser power, while controlling the laser device so as to Nikon SLM Solutions AG - 7 - 30A-167 984 emit laser radiation at the second laser power, upon increasing the laser power from the first laser power to the second laser power at the beginning of the second time interval, a relaxation peak might be avoided or at least dampened. Thus, irradiation of the material to be processed in the materials processing technique at a laser power exceeding the second laser power is avoided. In summary, the method described herein allows a more accurate control of the laser radiation emitted from the laser device and consequently a more accurate control of a materials processing technique using the laser radiation emitted from the laser device.

[0024] In a particular preferred embodiment of the method for controlling the operation of a laser device, in step c), the delay between the start of the control of the laser device so as to increase the laser power from the first laser power to the second laser power at the beginning of the second time interval and the actual emission of laser radiation at the second laser power is compensated in dependence on the type of the laser device and / or in dependence on at least one parameter of the individual laser device employed in the method. For example, a specific compensation value or equation may be provided for each laser device of interest. Additionally or alternatively, a specific compensation value or equation may be provided in dependence on at least one parameter of the individual laser device employed in the method. Said at least one parameter may, for example, be an operational or structural parameter which, may for example result from tolerances of the laser device setup.

[0025] Preferably, the delay between the start of the control of the laser device so as to increase the laser power from the first laser power to the second laser power at the beginning of the second time interval and the actual emission of laser radiation at the second laser power is compensated exclusively in dependence on the type of the laser device and / or in dependence on at least one parameter of the individual laser device employed in the method. In the case, a single compensation value or equation, which may, e.g. be stored in a lookup table, is sufficient for achieving a sufficient compensation. As a result, the compensation is significantly simplified.

[0026] Preferably, the laser device is operated in a modulated mode. In step c), the delay between the start of the control of the laser device so as to increase the laser power from the first laser power to the second laser power at the beginning of the second time interval and the actual emission of laser radiation at the second laser power may be compensated in dependence on a trigger pulse duration and / or in dependence on a break time between individual trigger pulses. Nikon SLM Solutions AG - 8 - 30A-167 984

[0027] Since it is no longer necessary to consider the laser power, i.e. the actual value of the second laser power, upon compensating, the delay between the start of the control of the laser device so as to increase the laser power from the first laser power to the second laser power at the beginning of the second time interval and the actual emission of laser radiation at the second laser power, a compensation algorithm considering the trigger pulse duration and / or the break time between individual trigger pulses may be employed without unduly complicating the compensation algorithm. As a result, a still more accurate control of the laser radiation emitted from the laser device and consequently a still more accurate control of a materials processing technique using the laser radiation emitted from the laser device is made possible.

[0028] Preferably, the first laser power is below the processing threshold value. In the method for controlling the operation of a laser device, a laser power dependent delay and a relaxation peak occur only during the first time interval. When the first laser power is controlled so as to not exceed the processing threshold value, undesired effects on a material irradiated with laser radiation at the first laser power during the first time interval are prevented or at least mitigated.

[0029] In a particularly advantageous embodiment of the method for controlling the operation of a laser device, the first laser power is selected to be low enough such that also an intensity of the relaxation peak occurring during the first time interval is maintained below the processing threshold value. Such a control of the first laser power ensures that also the maximum peak laser power which is emitted by the laser device due to the relaxation peak does not affect a material irradiated with laser radiation during the first time interval.

[0030] Preferably, the laser device is controlled so as to emit laser radiation at the first laser power during the first time interval while a laser beam is maintained stationary so as to impinge on a stationary impinging site on the material to be processed in the laser materials processing technique. Maintaining the laser beam stationary simplifies the control of the laser device during the first time interval. However, for maintaining the laser beam stationary, the first laser power has to be low enough to ensure that the material to be processed in the laser materials processing technique is not damaged or otherwise affected by the laser beam in the region of the stationary impinging site. Advantageously, this makes additional devices for dissipating laser power, like beam traps, unnecessary. Optionally the laser beam can be maintained stationary so Nikon SLM Solutions AG - 9 - 30A-167 984 as to impinge on a stationary impinging site which is not intended to be processed in the laser materials processing technique.

[0031] The laser device may be controlled so as to emit laser radiation at the first laser power during the first time interval, while a laser beam is scanned across a defined area of a surface of the material to be processed in the laser materials processing technique. Scanning the laser beam across a defined area of the surface of the material to be processed in the laser materials processing technique ensures that the material is not damaged or otherwise affected by a stationary laser beam and hence is particularly advantageous in case the first laser power approaches the processing threshold value.

[0032] During the first time interval, while a laser beam is scanned across a defined area or while a laser beam is maintained stationary on a stationary impinging site and while the laser beam is not used for material processing, calibration procedures or laser beam monitoring procedures could be performed simultaneously. Therefore, adequate laser beam measuring devices could be used to determine laser beam properties of the laser beam like the intensity distribution or for determining the correct alignment of the laser beam or the correct scanning speed.

[0033] In a preferred embodiment of the method for controlling the operation of a laser device, the first time interval directly follows a start-up of the laser device from a switched-off state. The first time interval may, however, also directly follow a preceding second time interval. By controlling the laser device upon start-up from the switched-off state so as to emit laser radiation at the first laser power for the first interval before increasing the laser power to the second laser power during the second time interval the above discussed unwanted effects of a laser power dependent delay and a relaxation peak can be avoided or at least mitigated. By controlling the laser device so as to emit laser radiation at the first laser power after completion of a preceding second time interval results in an operational state of the laser device which might be referred to as a "simmering" operational state. In other words, a state of the laser device, in which the laser device does not emit laser power is avoided. By controlling the first time interval so as to be short enough that the laser power emitted by the laser device does not drop down to zero during the first time interval, the laser may be in a transition mode. The operating time of the laser device may comprise a plurality of subsequent first and second time intervals. Nikon SLM Solutions AG - 10 - 30A-167 984

[0034] The first laser power emitted during different first time intervals may be equal or may vary. Similarly, the second laser power emitted during different second time intervals may be equal or may vary.

[0035] Further, the first laser power emitted during the first time interval may be constant or may vary. For example, during the first time interval, the first laser power may be increased either continuously or stepwise. At the end of the first time interval, the first laser power may approach the second laser power emitted during a subsequent second time interval. Thus, the first laser power emitted during the first time interval may be controlled in such a manner that a kind of laser power ramp up is achieved. For example, a first laser power at the start of the first time interval and / or a (higher) first laser power at the end of the first time interval may remain constant for different first time intervals. Also, the second laser power emitted during the second time interval may be constant or may vary.

[0036] In a preferred embodiment, the first laser power is lower than 10%, preferably lower than 1%, preferably lower than 0,1%, preferably lower than 0,01%, preferably lower than 0,001% and in particular lower than 0,0001% of the nominal power of the laser device. For example, for a laser device having a nominal laser power of 1000 W, the first laser power may not exceed approximately 100 W, approximately 10 W, approximately 1 W, approximately 100 mW, approximately 10 mW or approximately 1 mW. The lower the first laser power, the lower the risk that a material irradiated with laser radiation at the first laser power is affected in an undesired manner. In case the first laser power is selected to be low enough, in particular lower than 1 mW, the laser radiation emitted during the first time interval can be used, for example, for calibration purposes, since the laser power is low enough that irradiated optical elements or measurement instruments are not damaged by the laser radiation. Further, in case the first laser power is selected to be low enough, for example lower than a few mW, laser operation for performing manual calibration procedures with low requirements for personal protective equipment such as laser safety goggles, is made possible.

[0037] A wavelength range of the laser radiation emitted during the first time interval may correspond to a wavelength range of the laser radiation emitted during the second time interval. In other words, the wavelength range of the laser radiation emitted during the first time interval preferably corresponds to the processing wavelength of the laser radiation which is emitted during the second time interval for processing a material in a materials processing technique. Provided that the first laser power is Nikon SLM Solutions AG - 11 - 30A-167 984 low enough, the laser radiation emitted during the first time interval then is particular suitable for calibration purposes, such as, for example, scanner alignment procedures.

[0038] The laser device may be operated in a modulated mode, wherein a trigger pulse duration and / or a break time between individual trigger pulses is controlled so as to minimize a dependency of a delay between the start of the control of the laser device so as to emit laser radiation at the first laser power at the beginning of the first time interval and the actual emission of laser radiation on the first laser power.

[0039] A device for controlling the operation of a laser device for use in a laser materials processing technique is configured to, a) for a first time interval, control the laser device so as to emit laser radiation at a first laser power; b) after expiry of the first time interval, control the laser device so as to emit laser radiation at a second laser power for a second time interval, the second laser power being higher than the first laser power and exceeding a processing threshold value suitable for processing a material in the laser materials processing technique; and c) compensate a delay between the start of the control of the laser device so as to increase the laser power from the first laser power to the second laser power at the beginning of the second time interval and the actual emission of laser radiation at the second laser power independent of the second laser power.

[0040] The device for controlling the operation of a laser device may be configured to perform some or all of the method steps described above with reference to the method for controlling the operation of a laser device.

[0041] For example, the device for controlling the operation of a laser device may be configured to control the laser device such that, in step c), the delay between the start of the control of the laser device so as to increase the laser power from the first laser power to the second laser power at the beginning of the second time interval and the actual emission of laser radiation at the second laser power is compensated in dependence on the type of the laser device and / or in dependence on at least one parameter of the individual laser device employed in the method.

[0042] In particular, the device for controlling the operation of a laser device may be configured to control the laser device such that the laser device is operated in a modulated mode and such that the delay between the start of the control of the laser device so as to increase the laser power from the first laser power to the Nikon SLM Solutions AG - 12 - 30A-167 984 second laser power at the beginning of the second time interval and the actual emission of laser radiation at the second laser power is compensated in dependence on a trigger pulse duration and / or in dependence a break time between individual trigger pulses.

[0043] Further, the device for controlling the operation of a laser device may be configured to control the laser device such that the first laser power is below the processing threshold value. The device for controlling the operation of a laser device may also be configured to control the laser device in such a manner that the first laser power is selected such that an intensity of a relaxation peak occurring during the first time interval is below the processing threshold value.

[0044] Further, the device for controlling the operation of a laser device may be configured to control the laser device such that the laser device emits laser radiation at the first laser power during the first time interval while a laser beam is maintained stationary so as to impinge on a stationary impinging site on the material to be processed in the laser materials processing technique. The device for controlling the operation of a laser device may, however, also be configured to control the laser device in such a manner that the laser device emits laser radiation at the first laser power during the first time interval while a laser beam is scanned across a defined area of a surface of the material to be processed in the laser materials processing technique.

[0045] The first time interval may directly follow a start-up of the laser device from a switched-off state. The first time interval may, however, also directly follow a preceding second time interval.

[0046] The first laser power may be lower than 10%, preferably lower than 1%, preferably lower than 0,1%, preferably lower than 0,01%, preferably lower than 0,001% and in particular lower than 0,0001% of the nominal power of the laser device. A wavelength range of the laser radiation emitted during the first time interval may correspond to a wavelength range of the laser radiation emitted during the second time interval.

[0047] The device for controlling the operation of a laser device may be configured to control the laser device such that the laser device is operated in a modulated mode, wherein a trigger pulse duration and / or a break time between individual trigger pulses is controlled so as to minimize a dependency of a delay between the start of the control of the laser device so as to emit laser radiation at the first laser power at Nikon SLM Solutions AG - 13 - 30A-167 984 the beginning of the first time interval and the actual emission of laser radiation on the first laser power.

[0048] A laser device comprises a gain medium. The gain medium may be any known gain medium in gaseous, liquid, or solid form which contains atoms or molecules that can be excited to higher energy states by a pump source. As a pump source, the laser device comprises a plurality of pump diodes configured to provide pump energy to the gain medium.

[0049] Each of the plurality of pump diodes is connected to at least one current driver. The laser device may comprise a single current driver which is connected to each of the plurality of pump diodes. Alternatively, the laser device may comprise a plurality of current drivers the number of which corresponds to the number of pump diodes such that each current driver may be associated with a pump diode. It is, however, also conceivable, that the laser device comprises a number of current drivers which does not correspond to the number of pump diodes. For example, the number of current drivers may be lower or higher than the number of pump diodes. In such a case, each pump diode should be connected to at least one current driver. The at least one current driver is configured to control at least one of the plurality of pump diodes independent of other ones of the plurality of pump diodes. Preferably, the current driver is configured to control each of the plurality of pump diodes independent of the other ones of the plurality of pump diodes.

[0050] As compared to known laser devices, wherein the laser power is controlled by controlling a diode current of the pump diodes, for example in a range between 10 % to 100 % of the maximum diode current, the laser device described herein allows a control of the laser power by controlling the number of active pump diodes and thus the amount of pump energy supplied to the gain medium. For example, the current driver may activate only a single pump diode or some of the existing pump diodes in case an operation of the laser device at a laser power which is smaller than the nominal laser power is desired. The reduction of the number of active pump diodes allows the operation of the laser device at a low laser power which might not be achievable with currently known laser devices. Further, the individual active pump diodes can be operated in their optimum operational range, i.e. at a high wall plug efficiency (WPE) even if the laser device is operated at a low laser power.

[0051] Due to its capability of being operated at a low laser power, the laser device is particularly suitable for being controlled in accordance with the above described Nikon SLM Solutions AG - 14 - 30A-167 984 method, but not limited thereto. Specifically, the capability of the laser device to be operated at a low laser power can be used to adjust the first laser power which is emitted during the first time interval to a desired low level, either upon start-up of the laser device from a switched off state or when the laser device should be operated in a "simmering" operational state. This may be achieved by an appropriate control of the at least one current driver, for example by means of an above described device for controlling the operation of a laser device.

[0052] The at least one current driver may be configured to activate at least some of the plurality of pump diodes in an alternated manner such that the operation time of the pump diodes during their life cycle is substantially equal. For example, in a laser device which has a nominal laser power of 1000 W and comprises four 250 W pump diodes and which typically is operated at a laser power of 500 W, two of the four pump diodes at a time may be operated in an alternated manner such that all pump diodes during their life-cycle experience a substantially equal operation time.

[0053] The laser device may comprise at least one high power pump diode. Alternatively or additionally, the laser device may comprise at least one low power pump diode. In case the laser device is equipped with at least one low power pump diode, the laser device can be operated at a particularly low laser power. In case the laser device comprises high power and low power pump diodes, the laser devices can be operated at high laser powers or low laser powers as desired in a particularly efficient manner by activating the respective pump diodes. Preferably, the laser device comprises a plurality of high power pump diodes and / or a plurality low power pump diodes. The at least one high power pump diode may be connected to a high power current driver. Alternatively or additionally, the at least one low power pump diode may be connected to a low power current driver. Associating a high power pump diode with a high power current driver and / or associating a low power pump diode with a low power current driver allows an optimum control and hence an operation of the diodes at an optimum efficiency.

[0054] The laser device may comprise a single high power current driver which is connected to each of a plurality of high power pump diodes. Alternatively, the laser device may comprise a plurality of high power current drivers the number of which corresponds to the number of high power pump diodes such that each high power current driver may be associated with a high power pump diode. It is, however, also conceivable, that the laser device comprises a number of high power current drivers which does not correspond to the number of high power pump diodes. For example, the number Nikon SLM Solutions AG - 15 - 30A-167 984 of high power current drivers may be lower or higher than the number of high power pump diodes. In such a case, it is preferable that each high power pump diode is connected to at least one high power current driver.

[0055] Similarly, the laser device may comprise a single low power current driver which is connected to each of a plurality of low power pump diodes. Alternatively, the laser device may comprise a plurality of low power current drivers the number of which corresponds to the number of low power pump diodes such that each low power current driver may be associated with a low power pump diode. It is, however, also conceivable, that the laser device comprises a number of low power current drivers which does not correspond to the number of low power pump diodes. For example, the number of low power current drivers may be lower or lower than the number of low power pump diodes. In such a case, it is preferable that each low power pump diode is connected to at least one low power current driver. It is alco conceivable that a low power current driver is connected to a high power pump diode.

[0056] A laser materials processing apparatus comprises an above described device for controlling the operation of the laser device and / or an above described laser device. The laser materials processing apparatus may, for example, be a laser cutting apparatus, a laser welding apparatus, a laser engraving apparatus, a laser drilling apparatus, a laser cladding apparatus, a laser lithography apparatus, a laser surface treatment apparatus, a laser cleaning apparatus or a powder bed fusion apparatus.

[0057] Preferred embodiments of the invention will be described in greater detail with reference to the appended schematic drawings wherein

[0058] Figure 1 shows an exemplary laser materials processing apparatus which is designed in the form of a powder bed fusion apparatus;

[0059] Figure 2 shows a diagram wherein a pump diode voltage observed upon start-up of a laser device is plotted against the time for different laser powers;

[0060] Figure 3 shows a diagram wherein a pump diode voltage observed during a first time interval which directly follows a start-up of the laser device and a second time interval following the first time interval is plotted against the time, wherein, during the first time interval, the laser device is operated at a first laser power of 15% of the Nikon SLM Solutions AG - 16 - 30A-167 984 nominal laser power, and wherein, during the second time interval, the laser device is operated at different second laser powers which are higher than the first laser power; and

[0061] Figure 4 shows the structure of a laser device which is suitable for use, for example, in the laser materials processing apparatus of figure 1.

[0062] Figure 1 shows an exemplary laser materials processing apparatus 100 which is designed in the form of a powder bed fusion apparat for producing a three- dimensional work piece by an additive manufacturing process. The laser materials processing apparatus 100 may, however, also be designed, for example, in the form of a laser cutting apparatus, a laser welding apparatus, a laser engraving apparatus, a laser drilling apparatus, a laser cladding apparatus, a laser lithography apparatus, a laser surface treatment apparatus or a laser cleaning apparatus.

[0063] In the exemplary embodiment of figure 1, the apparatus 100 comprises a carrier 102 and a powder application device 104 for applying a raw material powder onto the carrier 102. The raw material powder may be a metallic powder but may also be a ceramic powder or a plastic material powder or a powder containing different materials. The powder may have any suitable particle size or particle size distribution. It is, however, preferable to process powders of particle sizes < 100 |im. The carrier 102 and the powder application device 104 are accommodated within a process chamber 106 which is sealable against the ambient atmosphere. The carrier 102 is displaceable in a vertical direction into a built cylinder 108 so that the carrier 102 can be moved downwards with increasing construction height of a work piece 110, as it is built up in layers from the raw material powder on the carrier 12. The carrier 102 may comprise a heater and / or a cooler.

[0064] The apparatus 100 further comprises an irradiation system 10 for selectively irradiating laser radiation onto a raw material powder layer applied onto the carrier 102. In the embodiment of an apparatus 100 shown in figure 1, the irradiation system 10 comprises a laser device 12 which is configured to emit a laser beam 14. An optical unit 16 for guiding and processing the laser beam 14 emitted by the laser device 12 is associated with the laser device 12. It is, however, also conceivable that the irradiation system 10 is configured to emit two or more radiation beams. Nikon SLM Solutions AG - 17 - 30A-167 984

[0065] The optical unit 16 comprises two lenses 18 and 20 which in the embodiment shown in figure 1 both have positive refractive power. The lens 18 is configured to collimate the laser light emitted by the laser device 12, such that a collimated or substantially collimated radiation beam is generated. The lens 20 is configured to focus the collimated (or substantially collimated) laser beam 14 on a desired position in a z- direction. The optical unit 16 further comprises a pivotable scanner mirror 22 which serves to deflect the laser beam 14 and hence scan the laser beam 14 in a x- direction and a y-direction across an irradiation plane I which, during operation of the apparatus 100 typically is defined by a surface of a raw material powder layer applied onto the carrier 102 so as to be selectively irradiated.

[0066] An optical detection device 24 which in the embodiment shown in figure 1 is designed in the form of a camera is arranged in the process chamber 106, for observing the laser beam 14 and / or for observing irradiated regions after irradiation by the laser beam 14. The optical detection device 24 may be part of a melt pool observation device, but also may be a separate device. The optical detection device 24 may also be capable of detecting reflected laser radiation that is reflected from the irradiation plane I back into the optical unit and / or the optical detection device 24 may also be capable of detecting radiation that originates from the point of incidence of the laser beam 14 in the irradiation plane I when the laser beam 14 impinges the irradiation plane I. The optical detection device 24 may also be part of the optical unit 16 and may be arranged in such a way that it can detect radiation that enters the optical unit 16.

[0067] A control unit 26 is provided for controlling either exclusively the operation of the laser device 12 or also for controlling further components of the apparatus 100 such as, for example, the entire irradiation system 10 and / or the powder application device 104. The control unit 26 comprises a computer-readable recording medium on which a computer program product comprising program code portions is stored.

[0068] A controlled gas atmosphere, preferably an inert gas atmosphere is established within the process chamber 106 by supplying a shielding gas to the process chamber 106 via a process gas inlet 112. After being directed through the process chamber 106 and across the raw material powder layer applied onto the carrier 102, the gas is discharged from the process chamber 106 via a process gas outlet 114. The process gas may be recirculated from the process gas outlet 114 to the process gas inlet 112 and thereupon may be cooled or heated and / or filtered in order to remove particulate impurities discharged from the process chamber 106 with the process gas Nikon SLM Solutions AG - 18 - 30A-167 984 stream before the process gas re-enters the process chamber 106 via the process gas inlet 112.

[0069] During operation of the apparatus 100 for producing a three-dimensional work piece, a layer of raw material powder is applied onto the carrier 102 by means of the powder application device 104. In order to apply the raw material powder layer, the powder application device 104 is moved across the carrier 102, for example under the control of the control unit 26. Then, for example again under the control of the control unit 26, the layer of raw material powder is selectively irradiated in accordance with a geometry of a corresponding layer of the work piece 110 to be produced by means of the irradiation device 10. The steps of applying a layer of raw material powder onto the carrier 102 and selectively irradiating the layer of raw material powder in accordance with a geometry of a corresponding layer of the work piece 110 to be produced are repeated until the work piece 110 has reached the desired shape and size.

[0070] The laser beam 14 is scanned across the raw material powder layer according to a scan vector pattern which is defined, for example, by the control unit 26, so as to site-selectively melt and / or sinter the powder particles of the powder bed in order to generate the work piece 110. The laser device 12, which is operated in a modulated mode, necessarily is switched on while a scan vector is irradiated. However, at the end of the irradiation of the scan vector, in currently known apparatuses 100, the laser device 12 usually is switched off until the next scan vector is irradiated. As a result, the laser device 12 is switched on and off for each scan vector to be irradiated. Further, the laser power for scanning individual scan vectors usually varies, for example in dependence on whether a scan vector is located in the region of a contour or in the region of an inner volume of the work piece 110 to be generated.

[0071] Each start-up of the laser device 12 from the switched-off state involves a delay between the start of the laser device 12, e.g. by providing a suitable voltage signal to a pump source of the laser device 12, and the actual emission of the laser beam 14. Further, the laser power for scanning individual scan vectors may vary for example in dependence on whether the scan vector is located in the region of a contour or in the region of an inner volume of a workpiece 110 to be generated.

[0072] Figure 2 shows a diagram wherein a pump diode voltage observed upon start-up of a laser device is plotted against the time for different laser power levels of 15% of the Nikon SLM Solutions AG - 19 - 30A-167 984 nominal laser power, 25% of the nominal laser power, 50% of the nominal laser power, 75% of the nominal laser power and 100% of the nominal laser power. Figure 2 reveals, that the delay between the start of the laser device 12 at a time 0 and the actual observation of a pump diode voltage which indicates the emission of a laser beam 14 strongly depends on the laser power. The higher the laser power, the shorter the delay between the start of the laser device 12 and the actual emission of the laser beam 14. Additionally, a relaxation peak R is observed, wherein an intensity of the relaxation peak R also depends on the laser power. In general, the higher the laser power, the higher the maximum intensity of the relaxation peak R.

[0073] Further parameters which influence the delay between the start of the laser device 12 and the actual emission of the laser beam 14 when the laser device 12 is operated in a modulated mode, are the trigger pulse duration and the break time between individual trigger pulses. In particular, a length of the delay increases with an increasing trigger pulse duration and with an increasing break time between individual trigger pulses.

[0074] During operation of the apparatus 100, the operation of a laser device 12, by means of the control unit 26, is controlled such that, in a step a), the laser device 12, for a first time interval, emits laser radiation at a first laser power. This may be achieved by not switching-off the laser device 12 during the first time interval, for example, by continuing a power supply and / or a suppy of a respective "on" control signal to the laser device 12. It is, however, also conceivable, that the laser device 12, in particular during a first time interval following a preceding second time interval, is switched off, e.g. by no longer supplying power and / or a respective "on" control signal to the laser device. In this case, the first time interval, however, is short enough that the laser power emitted by the laser device does not drop down to zero during the first time interval or is still in a transition state. For a example, a duration of the first time interval of < 3 ps may ensure that the laser power emitted by the laser device does not drop down to zero during the first time interval.

[0075] After expiry of the first time interval, in a step b), the control unit 26 controls the laser device 12 so as to emit laser radiation at a second laser power for a second time interval. The second laser power is higher than the first laser power and exceeds a processing threshold value suitable for processing, i.e. melting and / or sintering the raw material powder appied onto the carrier 102. During the second time interval, the laser beam 14 is scanned across the surface of the raw material Nikon SLM Solutions AG - 20 - 30A-167 984 powder on the carrier 102 along a scan vector of the scan vector pattern defined for generating the work piece 110.

[0076] To the contrary, the first laser power is below the processing threshold value. Thus, during the first time interval, undesired effects on the raw material powder due to being exposed to the radiation beam 14 emitted by the laser device 12 are prevented or at least mitigated. In particular, the first laser power is selected to be low enough such that also an intensity of the relaxation peak R occurring during the first time interval is maintained below the processing threshold value. Such a control of the first laser power ensures that also the maximum peak laser power which is emitted by the laser device 12 due to the relaxation peak does not affect the raw material powder on the carrier 102 during the first time interval.

[0077] The first laser power emitted during the first time interval may be constant or may vary. For example, during the first time interval, the first laser power may be increased such that the first laser power approaches the second laser power emitted during a subsequent second time interval.

[0078] The laser device 12 may be controlled so as to emit laser radiation at the first laser power during the first time interval while the laser beam 14 is maintained stationary so as to impinge on a stationary impinging site on raw material powder on the carrier 102. Maintaining the laser beam stationary simplifies the control of the laser device 12 during the first time interval. However, in case the laser beam 14 should be maintained stationary during the first time interval, the first laser power should be selected to be low enough to ensure that the raw material powder on the carrier 102 affected in an undesired manner by the laser beam 14 in the region of the stationary impinging site. In particular in case the first laser power approaches the processing threshold value, it is therefore also conceivable to control the laser device 12 so as to emit laser radiation at the first laser power during the first time interval while a laser beam 14 is scanned across a defined area of a surface of the raw material powder on the carrier 102.

[0079] The first laser power is lower than 10%, preferably lower than 1%, preferably lower than 0,1%, preferably lower than 0,01%, preferably lower than 0,001% and in particular lower than 0,0001% of the nominal power of the laser device. For example, for a laser device 12 having a nominal laser power of 1000 W, the first laser power may not exceed approximately 100 W, approximately 10 W, approximately 1 W, approximately 100 mW, approximately 10 mW or approximately Nikon SLM Solutions AG - 21 - 30A-167 984

[0080] 1 mW. The lower the first laser power, the lower the risk that the raw material powder irradiated with the laser beam 14 at the first laser power is affected in an undesired manner. Further, in case the first laser power is selected to be low enough, in particular lower than 1 mW, the laser radiation emitted during the first time interval can be used, for example, for calibration purposes, since the laser power is low enough that irradiated optical elements or measurement instruments are not damaged by the laser radiation. Further, in case the first laser power is selected to be low enough, e.g. lower than a few mW, laser operation for performing manual calibration procedures with low requirements for personal protective equipment such as laser safety goggles, is made possible.

[0081] A wavelength range of the laser radiation emitted during the first time interval corresponds to a wavelength range of the laser radiation emitted during the second time interval. In other words, the wavelength range of the laser radiation emitted during the first time interval corresponds to the processing wavelength of the laser radiation which is emitted during the second time interval for processing, i.e. melting and / or sintering the raw material powder on the carrier. Provided that the first laser power is low enough, the laser radiation emitted during the first time interval then is particular suitable for calibration purposes, such as, for example, scanner alignment procedure.

[0082] The operation of a laser device 12, by means of the control unit 26, is controlled in such a manner that the laser device 12, at the beginning of the second time interval, is not started from a state, in which the laser device 12 does not emit laser power. Instead, the laser device 12 is controlled so as to increase the laser power from the first laser power to the second laser power.

[0083] A diagram, wherein the pump diode voltage observed during the first time interval which directly follows a start-up of the laser device 12 and the second time interval following the first time interval is plotted against the time is shown in figure 3. In the exemplary diagram of figure 3, during the first time interval, the laser device 12 is operated at a first laser power of 15% of the nominal laser power. During the second time interval, the laser device 12 is operated at different second laser powers of between 15% and 100% of the nominal laser power.

[0084] Figure 3 reveals that the increase of the laser power from the first laser power to the second laser power still involves a delay between the output of a respective signal, e.g. a suitable voltage signal, to a pump source of the laser device 12 and the actual Nikon SLM Solutions AG - 22 - 30A-167 984 emission of laser radiation at the second laser power. However, as compared to a control of the laser device 12 so as to emit laser radiation at the second laser power directly upon start-up of the laser device 12, the dependency of said delay on the second laser power is significantly reduced or even substantially eliminated. In fact, an equal or at least similar delay is observed independent of the value of the second laser power.

[0085] In addition, a relaxation peak is observed only upon start-up of the laser device 12 during the first time interval, whereas an increase of the laser power from the first laser power to the second laser power at the beginning of the second time interval does not cause a further relaxation peak. Thus, irradiation of the raw material powder on the carrier 102 at a laser power exceeding the second laser power is avoided.

[0086] At the beginning of the operation of the laser device 12, the first time interval directly follows the start-up of the laser device 12 from a switched-off state. During continued operation of the laser device 12, the first time interval may, however, also directly follow a preceding second time interval. In other words, after the second time interval, the laser device 12 is controlled so as to avoid that the laser power emitted by the laser device 12 drops down to zero. Instead, the laser device is controlled so as to reduce the laser power from the second laser power to the first laser power such that the laser device 12, during the first time interval directly following a preceding second time interval, is maintained in a "simmering" operational state. In other words, the operating time of the laser device comprises a plurality of subsequent first and second time intervals.

[0087] During each second time interval, the laser beam 14 is scanned across the surface of the raw material powder on the carrier 102 along a scan vector of the scan vector pattern defined for generating the work piece 110. After completion of the scan vector, the laser device 12 is controlled so as to reduce the laser power from the second laser power to the first laser power for a first time interval before the laser power again is increased to the second laser power to scan a further scan vector during a further second time interval.

[0088] The first laser power emitted during different first time intervals may be equal or may vary. The second laser power emitted during different second time intervals typically varies in dependence on the location of the scan vector in the scan vector Nikon SLM Solutions AG - 23 - 30A-167 984 pattern, i.e. in dependence on whether the scan vector is located in the region of a contour or in the region of an inner volume of the work piece 110 to be generated.

[0089] During operation of the laser device 12, a trigger pulse duration and / or a break time between individual trigger pulses is controlled so as to a dependency of a delay between the start of the control of the laser device 12 so as to emit laser radiation at the first laser power at the beginning of the first time interval and the actual emission of laser radiation on the first laser power.

[0090] The operation of a laser device 12, by means of the control unit 26, further is controlled such that, in a step c), the delay between the start of the control of the laser device 12 so as to increase the laser power from the first laser power to the second laser power at the beginning of the second time interval and the actual emission of laser radiation at the second laser power is compensated independent of the second laser power. Instead, the delay between the start of the control of the laser device so as to increase the laser power from the first laser power to the second laser power at the beginning of the second time interval and the actual emission of laser radiation at the second laser power is compensated in dependence on a trigger pulse duration and / or in dependence on a break time between individual trigger pulses. Since it is no longer necessary to consider the laser power, a compensation algorithm considering the trigger pulse duration and / or a break time between individual trigger pulses is not unduly complicated while a more accurate control of the laser radiation emitted from the laser device 12 is made possible.

[0091] The structure of a laser device 12 which is particularly suitable for use, for example, in the laser materials processing apparatus 100 of figure 1 is shown in figure 4. The laser device 12 comprises a gain medium 28 which in the exemplary embodiment of the laser device 12 shown in figure 4 is designed in the form of a Yb doped fibre. As a pump source, the laser device 12 comprises a plurality of pump diodes 30a, 30b configured to provide pump energy to the gain medium 28. In particular, the laser device 12 comprises a plurality of high power pump diodes 30a and a plurality of low power diodes 30b. The pump diodes 30a, 30b are connected to the gain medium 28 via respective pump couplers 32.

[0092] Each of the plurality of pump diodes 30a, 30b is connected to at least one current driver 34a, 34b. In particular, each of the plurality of high power pump diodes 30a is connected to a high power current driver 34a whereas each of the plurality of low power pump diodes 30b is connected to a low power current driver 34b. Nikon SLM Solutions AG - 24 - 30A-167 984

[0093] The at least one current driver 30a, 30b is configured to control at least one of the plurality of pump diodes 30a, 30b independent of other ones of the plurality of pump diodes 30a, 30b. In particular, the high power current driver 34a is configured to control each of the plurality of high power pump diodes 30a independent of the other high power pump diodes 30a and also independent of the low power pump diodes 30b. Similiarly, the low power current driver 34b is configured to control each of the plurality of low power pump diodes 30b independent of the other low power pump diodes 30b and also independent of the high power pump diodes 30a.

[0094] The above described structure of the laser device 12, allows a control of the laser power by controlling the number of active pump diodes 30a, 30b and thus the amount of pump energy supplied to the gain medium. For example, the current drivers 34a, 34b may activate only a single pump diode 30a, 30b or some of the pump diodes 30a, 30b in case an operation of the laser device 12 at a laser power below the nominal laser power is desired. The presence of low power pump diodes 30b makes it possible that the laser device 12 can be operated at a particularly low laser power. As a result, the laser device 12 is particularly suitable to emit a low first laser power during a first time interval either upon start-up of the laser device from a switched off state or when the laser device should be operated in a "simmering" operational state as described above.

[0095] The additional provision of high power pump diodes allow the laser device 12 to be operated at high laser powers or low laser powers as desired in a particularly efficient manner by activating the respective pump diodes 30a, 30b via the associated high power and low power current drivers 34a, 34b. Further, each of the current drivers 34a, 34b is configured to activate at least some of the plurality of pump diodes 30a, 30b in an alternated manner such that the operation time of the pump diodes 30a, 30b during their life cycle is substantially equal.

Claims

Nikon SLM Solutions AG - 25 - 30A-167 984Claims1. Method for controlling the operation of a laser device (12) for use in a laser materials processing technique, the method comprising the steps: a) for a first time interval, controlling the laser device (12) so as to emit laser radiation at a first laser power; b) after expiry of the first time interval, controlling the laser device (12) so as to emit laser radiation at a second laser power for a second time interval, the second laser power being higher than the first laser power and exceeding a processing threshold value suitable for processing a material in the laser materials processing technique; and c) compensating a delay between the start of the control of the laser device (12) so as to increase the laser power from the first laser power to the second laser power at the beginning of the second time interval and the actual emission of laser radiation at the second laser power independent of the second laser power.

2. The method of claim 1, wherein, in step c), the delay between the start of the control of the laser device (12) so as to increase the laser power from the first laser power to the second laser power at the beginning of the second time interval and the actual emission of laser radiation at the second laser power is compensated in dependence on the type of the laser device (12) and / or in dependence on at least one parameter of the individual laser device (12) employed in the method.

3. The method of claim 1 or 2, wherein the laser device (12) is operated in a modulated mode and wherein, in step c), the delay between the start of the control of the laser device (12) so as to increase the laser power from the first laser power to the second laser power at the beginning of the second time interval and the actual emission of laser radiation at the second laser power is compensated in dependence on a trigger pulse duration and / or in dependence on a break time between individual trigger pulses.

4. The method of anyone of claims 1 to 3, wherein the first laser power is below the processing threshold value.

5. The method of anyone of claims 1 to 4,Nikon SLM Solutions AG - 26 - 30A-167 984 wherein the first laser power is selected such that an intensity of a relaxation peak occurring during the first time interval is below the processing threshold value.

6. The method of anyone of claims 1 to 5, wherein the laser device (12) is controlled so as to emit laser radiation at the first laser power during the first time interval while a laser beam is maintained stationary so as to impinge on a stationary impinging site on the material to be processed in the laser materials processing technique.

7. The method of anyone of claims 1 to 6, wherein the laser device (12) is controlled so as to emit laser radiation at the first laser power during the first time interval while a laser beam is scanned across a defined area of a surface of the material to be processed in the laser materials processing technique.

8. The method of anyone of claims 1 to 7, wherein the first time interval directly follows a start-up of the laser device (12) from a switched-off state and / or wherein the first time interval directly follows a preceding second time interval.

9. The method of anyone of claims 1 to 8, wherein the first laser power is lower than 10%, preferably lower than 1%, preferably lower than 0,1%, preferably lower than 0,01%, preferably lower than 0,001% and in particular lower than 0,0001% of the nominal power of the laser device (12).

10. The method of anyone of claims 1 to 9, wherein a wavelength range of the laser radiation emitted during the first time interval corresponds to a wavelength range of the laser radiation emitted during the second time interval.

11. The method of anyone of claims 1 to 10, wherein the laser device (12) is operated in a modulated mode and wherein a trigger pulse duration and / or a break time between individual trigger pulses is controlled so as to minimize a dependency of a delay between the start of the control of the laser device (12) so as to emit laser radiation at the first laser power at the beginning of the first time interval and the actual emission of laser radiation on the first laser power.Nikon SLM Solutions AG - 27 - 30A-167 98412. Device (26) for controlling the operation of a laser device (12) for use in a laser materials processing technique, the device being configured to: a) for a first time interval, control the laser device (12) so as to emit laser radiation at a first laser power; b) after expiry of the first time interval, control the laser device (12) so as to emit laser radiation at a second laser power for a second time interval, the second laser power being higher than the first laser power and exceeding a processing threshold value suitable for processing a material in the laser materials processing technique; and c) compensate a delay between the start of the control of the laser device (12) so as to increase the laser power from the first laser power to the second laser power at the beginning of the second time interval and the actual emission of laser radiation at the second laser power independent of the second laser power.

13. Laser device (12) comprising:- a gain medium (28); and- a plurality of pump diodes (30a, 30b) configured to provide pump energy to the gain medium, wherein each of the plurality of pump diodes (30a, 30b) is connected to at least one current driver (34a, 34b), and wherein the at least one current driver (34a, 34b) is configured to control at least one of the plurality of pump diodes (30a, 30b) independent of other ones of the plurality of pump diodes (30a, 30b).

14. Laser device (12) according to claim 13, wherein the at least one current driver (34a, 34b) is configured to activate at least some of the plurality of pump diodes (30a, 30b) in an alternated manner such that the operation time of the pump diodes (30a, 30b) during their life cycle is substantially equal.

15. Laser device (12) according to claim 13 or 14, wherein the laser device (12) comprises at least one high power pump diode (30a) and / or at least one low power pump diode (30b), wherein the at least one high power pump diode (30a) is connected to a high power current driver (34a) and / or wherein the at least one low power pump diode (30b) is connected to a low power current driver (34b).

16. Laser materials processing apparatus (100) comprising:Nikon SLM Solutions AG - 28 - 30A-167 984- a device for controlling the operation of the laser device (12) according to claim 12 and / or a laser device (12) according to any one of claims 13 to 15.

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