阅读说明：本技术 大功率激光辐射的快速调制 (Fast modulation of high power laser radiation ) 是由 T·艾达姆 B·利姆珀特 于 2018-03-02 设计创作，主要内容包括：本发明涉及一种用于产生幅度调制的激光辐射的设备,其具有将激光束(1)分成至少两个光束通道的分裂元件(2),放大光束通道之一中的激光辐射的至少一个光放大器(3、7),以及组合元件(9),其将在光束通道中传播的激光辐射(4、8)相干地叠加在至少一个输出光束(14)中。本发明的目的是提供一种设备,利用其可以非常快速地对脉冲或连续激光辐射进行幅度调制,特别是切换,即去激活和再激活。在电子调制信号和切换操作之间只需经过几纳秒的时间。应该实现高的开关对比度。该方法也应适用于高功率。根据本发明,提供至少一个相位调制器(5),其在光束通道之一中位于光放大器(7)的上游,并且根据相位对在光束通道中传播的激光辐射进行时间调制。此外,本发明涉及一种用于激光辐射的幅度调制的方法。(The invention relates to a device for generating amplitude-modulated laser radiation, comprising a splitting element (2) which splits a laser beam (1) into at least two beam paths, at least one optical amplifier (3, 7) which amplifies the laser radiation in one of the beam paths, and a combining element (9) which coherently superimposes the laser radiation (4, 8) propagating in the beam path in at least one output beam (14). It is an object of the invention to provide a device with which pulsed or continuous laser radiation can be amplitude modulated, in particular switched, i.e. deactivated and reactivated, very quickly. Only a few nanoseconds of time need pass between the electronic modulation signal and the switching operation. A high on-off contrast should be achieved. The method should also be suitable for high powers. According to the invention, at least one phase modulator (5) is provided, which is located upstream of the optical amplifier (7) in one of the beam paths and temporally modulates the laser radiation propagating in the beam path as a function of the phase. Furthermore, the invention relates to a method for amplitude modulation of laser radiation.)

1. A method for amplitude modulation of laser radiation, having the following method steps:

-generating a laser radiation,

Splitting the laser radiation into at least two beam channels, an

Coherently combining the laser radiation propagating in the beam path in at least one output beam,

It is characterized in that the preparation method is characterized in that,

The laser radiation propagating in the beam path is time modulated according to relative phase position, so that the output beam is time modulated according to amplitude.

2. the method of claim 1, wherein the laser radiation propagating in at least one beam path is amplified, wherein the laser radiation propagating in the beam path temporally modulates the relative phase position prior to said amplifying.

3. a method according to claim 1 or 2, wherein the relative phase position of the laser radiation propagating in the beam path is feedback controlled.

4. the method of claim 3, wherein the bandwidth of the feedback control is lower than the frequency of the time phase modulation.

5. A method according to claim 3 or 4, characterized in that the time modulation of the relative phase position is performed on the basis of a modulation signal, wherein the nominal value of the feedback control is derived from the modulation signal.

6. Method according to one of claims 1 to 5, characterized in that the generated laser radiation is pulsed laser radiation comprising temporally equidistant laser pulses with a pulse frequency of more than 1kHz, preferably more than 10kHz, more preferably more than 100kHz, particularly preferably more than 1 MHz.

7. The method according to one of claims 1 to 5, characterized in that the generated laser radiation is continuous wave laser radiation.

8. The method according to one of claims 1 to 7, characterized in that the average power of the produced laser radiation is greater than 10W, preferably greater than 100W, and particularly preferably greater than 1 kW.

9. Method according to one of claims 1 to 8, characterized in that the coherent combining takes place in the far field.

10. The method of claim 9, wherein coherent combining also occurs in the near field.

11. The method according to one of claims 1 to 10, characterized in that coherent combination of the laser radiation propagating in the beam path takes place in at least two output beams.

12. The method according to claim 11, characterized in that the laser radiation (4, 8) propagating in the beam path is coherently superimposed in each of the at least two output beams in a different combination.

13. A method as claimed in claim 11 or 12, characterized in that the temporal modulation of the relative phase position of the laser radiation propagating in the beam path is converted by coherent combination into a temporal modulation of the power splitting ratio of the laser radiation propagating in the beam path into the output beam.

14. A device for generating amplitude-modulated laser radiation has

A splitting element (2) splitting the laser beam (1) into at least two beam channels,

A combining element (9) which coherently superimposes the laser radiation (4, 8) propagating in the beam path in at least one output beam (14),

It is characterized in that the preparation method is characterized in that,

At least one phase modulator (5), which phase modulator (5) temporally modulates the laser radiation propagating in the beam path in one of the beam paths as a function of the phase.

15. The apparatus according to claim 14, characterized by at least one optical amplifier (3, 7), the at least one optical amplifier (3, 7) amplifying the laser radiation in one of the beam channels, wherein the phase modulator (5) is upstream of the optical amplifier (7).

16. The apparatus according to claim 14 or 15, wherein the splitting element (2) comprises a polarizing beam splitter or an intensity beam splitter.

17. Device according to one of claims 14 to 16, characterized in that the combination element (9) comprises at least one polarizing beam splitter or at least one intensity beam splitter or at least one partial mirror.

18. The apparatus according to one of claims 14 to 17, characterized by a feedback control circuit with a controller (18) that controls the relative phase position of the laser radiation (4, 8) propagating in the beam path.

19. The apparatus according to claim 18, characterized in that the phase modulator (5) temporally modulates the laser radiation in accordance with a modulation signal (6) fed to the phase modulator (5), wherein the controller (18) derives a nominal value of the feedback control in accordance with the modulation signal (6).

20. Device according to claim 18 or 19, characterized in that the feedback control circuit comprises a hans-coullard detector as measuring device (11) for detecting the relative phase position.

21. The apparatus according to one of claims 18 to 20, characterized in that the feedback control circuit has a variable delay as an adjusting element (17) arranged in one of the beam channels.

22. The apparatus according to one of claims 14 to 21, characterized in that the phase modulator (5) is an electro-optical modulator.

23. The apparatus according to one of claims 14 to 22, characterized in that the combining element (9) coherently superimposes the laser radiation (4, 8) propagating in the beam path in at least two output beams.

24. The apparatus according to claim 23, characterized in that the combining element (9) coherently superimposes the laser radiation (4, 8) propagating in the beam path in different combinations in each of the at least two output beams.

25. The device according to claim 23 or 24, characterized in that the combination element (9) converts the temporal modulation of the relative phase position of the laser radiation (4, 8) propagating in the beam path into a temporal modulation of the power splitting ratio of the laser radiation (4, 8) propagating in the beam path into the output beam.

Technical Field

The invention relates to a method for amplitude modulation of laser radiation, comprising the following method steps:

-generating a laser radiation,

Splitting the laser radiation into at least two beam channels, an

Coherently combining the laser radiation propagating in the beam path in at least one output beam.

The invention further relates to a device for generating amplitude-modulated laser radiation, comprising

a splitting element which splits the laser beam into at least two beam paths, an

a combining element coherently superimposing the laser radiation propagating in the beam path in at least one output beam.

Background

in recent years, short pulse lasers have become multifunctional tools in high precision material processing. Ultrashort laser pulses (pulse length <10ps) have advantages over longer laser pulses (pulse length in the range of a few nanoseconds) due to the low heat input into the workpiece (so-called cold ablation). The processing speed depends on the pulse frequency of the laser. In order to perform cost-effective material processing, laser systems with high repetition rates have been developed in recent years. This also means an increase in average power for a given pulse energy.

Many applications in material processing require that the laser pulses or even the entire pulse train of a pulsed laser system be deactivated in a targeted manner, or that a continuous laser signal be required in order to have its power corrected as quickly as possible. This type of application may exist, for example, if a machining scanner controlling the position of the focal point of the laser beam has to move the beam between two points without any laser radiation impinging on the surface of the workpiece to be machined during the movement.

If pulse frequencies in the kHz range (intervals between laser pulses in the μ s-ms range) are used, a series of modulation techniques exist in the prior art for deactivating and reactivating the laser beam or significantly changing its power. In addition to mechanical switching methods, these methods include electro-optical, acousto-optical and opto-optical switches (see w.koechner, "Solid state laser Engineering," new york, Springer, 6 th edition).

The technical requirements for the case where the laser emission has to be deactivated and reactivated (or its power significantly modified) rapidly, i.e. within a switching time significantly less than 1 μ s, between two laser pulses (pulse frequency > >1MHz, the interval between laser pulses < <1 μ s) of a high pulse repetition rate laser system or in a continuous emitting laser (continuous wave laser, also called cw laser), are significantly higher. In these cases, it is necessary to use a modulation mechanism that is capable of deactivating and reactivating (or significantly changing the power of) the laser within a time interval that is shorter than the pulse interval following the occurrence of the modulation signal provided by the electronic control system.

An essential aspect here is that, for example in material processing, it is generally necessary to have a high average power and/or a high pulse energy.

Therefore, the modulation principle must provide a high contrast and must also be suitable for high powers and as efficient as possible.

Another essential aspect is that the power modulation and/or deactivation or reactivation of the laser pulse or the entire pulse train must not have any negative effect on the laser system used, for example on the inversion level of the laser oscillator or laser amplifier, which would otherwise lead to undesired and uncontrollable power fluctuations.

disclosure of Invention

Against this background, it is an object of the present invention to provide a method and a corresponding device, by means of which pulsed or continuous laser radiation can be amplitude-modulated, in particular switched, i.e. deactivated and reactivated, very rapidly. A high on-off contrast should be achieved. Furthermore, the method should be suitable for high powers, i.e. for average powers of the laser radiation of more than 10W, and preferably significantly more than, i.e. more than 100W to more than 1 kW. The modulation should contain as little losses as possible (high efficiency).

The invention achieves this object starting from a method of the type described above in that the laser radiation propagating in the beam path is already time-modulated according to the relative phase positions before amplification, so that the output beam is time-modulated according to the amplitude.

According to the invention, the laser radiation is first generated at low power using a suitable laser system. The laser radiation is then split into at least two beam channels. For the purposes of the present invention, splitting into at least two beam channels means splitting the laser radiation into at least two spatially separated beam paths. In at least one beam channel, preferably in all beam channels, the laser radiation propagating in the respective beam channel can be amplified. For this purpose, an optical amplifier of a type known per se is used. After amplification, the high-power laser radiation propagating in the beam path is coherently combined into an output beam or output beams. By splitting the laser radiation into at least two beam paths and subsequent coherent combination, an interferometer is produced which can be constructed, for example, in the manner of a Mach-Zehnder (Mach-Zehnder) interferometer or in the manner of a Michelson (Michelson) interferometer. In this case, each beam channel forms an interferometer branch, wherein in at least one interferometer branch, preferably in all interferometer branches, the laser radiation propagating there can be amplified in each case. In the output beams, the amplified laser radiation is combined, resulting in the radiation power of the individual beams being added.

In one possible embodiment, a plurality of output light beams is produced, at least one of which is modulated according to the invention.

The present invention is based on the following findings: the laser radiation propagating in the beam path may be time-modulated according to the relative phase position before amplification. Phase modulators not suitable for high power, such as electro-optic modulators or EOMs for short, may be used for this purpose.

According to the invention, the phase modulator is integrated into an interferometer arrangement for amplitude modulation formed by a beam path. Temporal modulation, i.e., a change in the relative phase position of the radiation propagating in a beam path (i.e., an interferometer branch), causes a corresponding change in the state of interference in the coherent combination, resulting in amplitude modulation of the output beam. Phase modulation (e.g., by EOM) allows high switching speeds and fast reaction times that meet the above requirements.

the optical amplifier, which is arranged in the beam path, i.e. upstream of the coherent combination, is continuously exposed to laser radiation with a constant average power. Due to the modulation imprinted according to the invention, only the phase changes over time. This results in the inversion level in each optical amplifier remaining constant over time. Thus, all available laser pulses have the same pulse energy. The amplitude modulation according to the invention does not cause any undesired power fluctuations during amplification. Useful laser pulses are those that correspond to phase modulation that constructively interfere with the output beam.

According to the invention, the laser radiation can be switched on or off or modulated in the nanosecond range (or even faster) by modulating the phase in the following manner: such that the laser radiation of the respective beams interferes with the output beam either completely constructively or completely destructively. Also, continuous amplitude modulation is possible because the relative phase positions of the respective beams correspondingly produce only partial constructive interference in the output beam.

The main advantage of the invention is that it can be implemented entirely using commercially available components.

Coherent combination of laser radiation propagating in a beam path used according to the present invention can be divided into two categories, namely, a filled aperture (superposition of beams in the near and far fields) and a tiled aperture (superposition only in the far field). The method according to the invention can be applied to both categories, preferably using filled aperture combining, because of the higher combining or extinction efficiency compared to the tiled aperture principle.

the laser radiation may be pulsed at any pulse length and pulse frequency. The laser radiation may have any wavelength as long as suitable components are available. The laser radiation may also be continuously emitted continuous wave laser radiation (cw laser radiation).

The method according to the invention is particularly suitable for the modulation of pulsed laser radiation, i.e. of laser radiation comprising laser pulses which are equally spaced in time, the pulse frequency of the laser pulses being greater than 1kHz, preferably greater than 10kHz, more preferably greater than 100kHz, and particularly preferably greater than 1 MHz. In all the above frequency ranges, modulation with pulse accuracy is possible as a result of the invention.

The modulation technique according to the invention is particularly suitable for high powers. The average power of the laser radiation generated may be greater than 10W, preferably greater than 100W, particularly preferably even greater than 1 kW.

In a preferred embodiment of the method according to the invention, the relative phase position of the laser radiation propagating in the beam path is controlled. For this purpose, a further phase adjustment element may be used. Also, a phase modulator (e.g., EOM) for modulation may be used for feedback control. In a practical system, fluctuations in optical path length inevitably occur in the beam path, for example due to thermal expansion. This results in fluctuations in the relative phase position of the laser radiation propagating in the beam path at the location of the coherent combination. This in turn leads to undesirable fluctuations in the power in the output beam. By controlling the relative phase positions, the difference in optical path length in the beam path is stabilized. Thus, stable emission in the output beam can be obtained even at the maximum output power in spite of external influence on the system. Here, the bandwidth of the feedback control may be (significantly) smaller than the frequency of the time-phase modulation according to the invention. The fluctuations caused by external influences usually have a much lower frequency than the modulation frequency.

The feedback control should be configured such that it does not act against the phase modulation according to the invention. As soon as the relative phase position of the laser radiation is to be adjusted by a modulation deviating from the nominal value of the feedback control, the feedback control which is independent of the phase modulation counteracts the modulation (after a time period predetermined by the bandwidth of the feedback control).

The time modulation of the relative phase position is conveniently performed in dependence on the modulation signal. The modulation signal is a signal predetermined by a superordinate control system which can directly predetermine the relative phase to be adjusted, or can predetermine the amplitude of the output beam. In the latter case, the modulation signal has to be converted into a control signal for the phase modulator used (e.g. EOM) according to a relation between amplitude and relative phase position predetermined by the modulation principle. In the case of controlling the relative phase position, the current nominal value of the feedback control should conveniently track the modulation signal to ensure that the feedback control does not oppose the desired modulation. If the modulation frequency is within or less than the bandwidth of the feedback control used to stabilize the interferometer, the current nominal value of the feedback control should correspond to the relative phase position to be adjusted according to the predetermined modulation signal.

In a preferred embodiment of the method according to the invention, the coherent combination of the laser radiation propagating in the beam path takes place in at least two output beams. This embodiment is based on the consideration that a large number of applications (for example in material processing) require a flexible division of the laser power into individual spatially separated processing stations or output ports. This both reduces the cost of purchase and significantly increases the throughput and the range of processing options for the overall processing system used, as compared to using a single laser at each processing station for individual processing.

The implementation of a device with multiple output beams is advantageously achieved according to the invention using a method of coherently combining multiple (at least two) beam channels. This is possible for both continuous and pulsed laser radiation. The relative phase position of the laser radiation of the individual channels to be coherently superposed here determines the distribution of the power in two or more possible output beams. In other words, coherent combining allows converting a temporal modulation of the relative phase position of the laser radiation propagating in the beam path into a temporal modulation of the power ratio of the splitting of the laser radiation propagating in the beam path into the output beam.

Also in this embodiment, the stabilization of the relative phase position also advantageously occurs for a stable output power, in order to compensate for fluctuations, for example due to thermal or acoustic disturbances in the individual beam channels. In order to redistribute the output work between the output beamsIn accordance with the invention, it is necessary to make targeted modifications to the relative phase positions between the individual beam channels and, if the reallocation is to be maintained for longer than the time corresponding to the stable bandwidth, it is also necessary to correct the stable nominal value of the coherent combination. In order to stabilize the output power distribution in the output beam corresponding to the phase position of the laser radiation in the beam path, conventional stabilization methods may be used, e.g. LOCSET and LOCS

Conveniently, in the above-described exemplary embodiments, the laser radiation propagating in the beam path coherently and differently superposes, i.e. coherently and in different combinations, in each of the at least two output beams, for example in such a way that: with a given phase difference between the two beam paths, there is constructive interference in the first output beam and destructive interference in the second output beam.

In the simplest example of the combination of two beam paths, the above approach allows flexible allocation of output power over the two output beams. A change in relative phase position of pi (starting from ideal constructive interference in the first output beam and ideal destructive interference in the second output beam) can move the output power completely to the second output beam and be used there for the application. All intermediate power values can likewise be set by appropriate selection of the phase positions. It should be noted that this approach increases the maximum possible power of a single output beam compared to the emission of a single laser. Assuming a combined efficiency of 100%, each output beam may emit 0% to 200% of the power of the single emission.

Various elements may be employed to change the relative phase positions in the beam paths depending on the desired speed of redistribution of power across the different output beams. For example, a piezo-driven mirror in the delay section allows modifying the power distribution in the kHz range and the electro-optical modulator in the GHz range, so that the laser radiation can be redistributed with pulse accuracy onto different output beams.

One particular application scenario is to turn off the laser radiation at one or more processing stations (e.g., to exchange workpieces). During this transition time, the laser power can be transferred to other processing stations for efficient use.

The object on which the invention is based is also achieved by a device of the type mentioned above in that at least one phase modulator is provided which temporally modulates the phase of the laser radiation propagating in one of the beam paths.

As passive, low-loss and stable-performance splitting and/or combining elements, polarizing beam splitters (e.g. thin-film polarizers) or intensity beam splitters are suitable, e.g. commercially available with high quality and low cost. Diffractive elements (e.g. gratings) are also possible as splitting and/or combining elements.

Conveniently, the apparatus according to the invention has a feedback control circuit that controls the relative phase position of the laser radiation propagating in the beam path in order to stabilize the optical path length in the beam path in the event of an inevitable external influence, for example as described above. As measuring means for detecting the relative phase position, the feedback control circuit may comprise, for example, a Hans-Kurad of a type known per seA detector. As an adjusting element, the feedback control circuit may comprise, for example, a delay arranged in one of the beam paths, which delay may be varied (for example by means of a piezo actuator). In this way, feedback control can be implemented particularly simply. However, the adjusting element may also be the phase modulator itself, in which case the modulation signal and the control signal from the controller superimposed thereon are fed to the phase modulator.

As a phase modulator for fast switching, EOM is preferably employed. There are commercially available EOMs with switching times in the ns range. Thus, a fast amplitude modulation meeting the requirements in the field of laser-based material processing (see above) can be achieved. According to the present invention, an EOM (e.g., a fiber EOM) designed for low power, which is available on the market at low cost, can be used as a phase modulator.

The device according to the invention allows to deactivate and reactivate the laser beam between two laser pulses of a high repetition rate short pulse laser. The device according to the invention thus allows switching times in the range of only a few nanoseconds. As mentioned above, the continuously emitted (cw) laser radiation can also be modulated steplessly correspondingly rapidly.

Drawings

Exemplary embodiments of the present invention are explained in more detail below with reference to the accompanying drawings. These show the following:

FIG. 1: a schematic view of the device according to the invention in a first embodiment,

FIG. 2: schematic view of a device according to the invention in a second embodiment with multiple output beams.

Detailed Description

In fig. 1, an input pulse train 1 is generated using a laser system (not shown) and split into two (or more) beam channels using a splitting element 2 in the form of a beam splitter. Fig. 1 shows a 1-to-2 beam splitter (e.g., a polarizing beam splitter). An intensity beam splitter (e.g., 50/50 beam splitter, segmented mirror, or 1-to-N beam splitter, such as a diffractive element) is also possible. More than two beam paths may be obtained by a cascade arrangement of 1 to 2 beam splitters or using 1 to N beam splitters. The spatially separated bursts 4 and 8 pass through optical amplifiers 3 and 7 or amplifier chains to achieve the required power. In one of the beam paths there is a phase modulator 5 (e.g. pockels cell/EOM) which imprints a temporal phase pattern on the pulse train 8. This is predetermined by the external modulation signal in the form of the control voltage 6. According to the invention, the phase pattern determines the modulation depth of the amplitude modulation. At the combining element 9, the laser radiation 4, 8 propagating in the beam path is coherently superimposed in a single output beam. It is essential here that the optical path difference between the beam paths is smaller, preferably much smaller, than the coherence length of the laser radiation.

In the polarization combination explained with the aid of the exemplary embodiment of fig. 1, the combination element 9 is a polarizing element (for example, a polarizing beam splitter or a thin-film polarizer). During the superposition at the combining element 9, the total radiation power of the p-polarized beam in the first beam path (pulse train 8) and the total power of the s-polarized beam in the second beam path (pulse train 4) are first combined to form the output beam. If the relative phase position of the laser radiation 4, 8 propagating in the two beam channels is equal to zero (or an integer multiple of 2 pi), the interference is maximally constructive and the output radiation is characterized by linear polarization, the polarization orientation being tilted by 45 °. Now, the wave plate 12 is used to rotate the orientation to the p-polarization of the subsequent polarizer 13 (any polarizing element, e.g. a grating compressor with polarization dependent transmission). This state represents the maximum amplitude of the laser radiation in the output beam. If the relative phase position of the laser radiation in the two laser channels varies due to phase modulation, the constructive interference will decrease with a corresponding decrease in the amplitude of the output beam. This forms the basis for the amplitude modulation principle according to the invention. If the subsequent polarizer 13 is omitted, it can be used to modulate the polarization state with pulse accuracy, although the described arrangement cannot be used to modulate the amplitude.

In practical conditions, fluctuations in the optical path length occur in the beam path, which leads to fluctuations in the corresponding polarization state and thus to fluctuations in the power of the output beam. Thus, in the exemplary embodiment of FIG. 1, a portion of the combined laser beam is directed by beam splitter 10 toAnd a detector (HCD) 11. This analyses the polarization state and thus the relative phase position of the laser radiation 4, 8 propagating in the two beam channels. The HCD 11 is used to generate an error signal which is used to control and thus stabilise the difference in optical path length in the beam path.

The relative phase position adjusted by the phase modulator 5 as a function of the control voltage 6 must in each case be predetermined as a nominal control value for the feedback control of the stabilized interferometer. This is particularly important if a relatively large number of laser pulses are to be attenuated. The reaction time of the feedback control is determined by the speed of the regulating element 17. For example, if the adjustment element 17 is an EOM, the reaction time may be in the nanosecond range; if the adjusting element 17 is configured by, for example, a piezo-driven mirror in the delay section, a reaction time in the millisecond range can be obtained. A wide range of reaction times can be tolerated because the intrinsic phase fluctuations due to external influences are slow (typically in the range of 1000Hz or less).

the error signal in this exemplary embodiment is fed to a controller 18, which controller 18 controls the relative phase position of the laser radiation propagating in the beam path. In an exemplary embodiment, a separate element, for example a piezo-driven mirror in the delay section in one of the two beam paths, is used as the adjusting element 17. Alternatively, the error signal may be fed directly to the phase modulator 5, in which case the error signal is suitably superimposed on the control voltage 6. The control voltage 6 is also fed to the controller 18. The control voltage 6 provides a nominal value of current to the controller 18 for feedback control of the relative phase position.

Thus, stable emission can be obtained at the output terminal in spite of external influence on the system. The relative phase position is stabilized to a nominal value predetermined by the control voltage 6.

As described above, a change in the relative phase position of the laser radiation in the beam path results in a reduction in the amplitude of the output beam, so that maximum constructive interference no longer occurs. If the phase difference is pi (or 3 pi, 5 pi, etc.), a linear polarization of the laser radiation is again obtained downstream of the combination element 9, wherein the polarization orientation is rotated by 90 deg. (compared to the case without phase difference). Therefore, if the position of the wave plate 12 on the polarizer 13 is not changed, complete extinction can be achieved. The amplitude drops to a minimum value.

In order to change the amplitude rapidly (with pulse precision), the corresponding phase jumps are impressed by the phase modulator 5. No additional phase-imprinted laser pulses may be used as the usable radiation 14 in the output beam. The pulses with the additional impressed phase are attenuated so that they are partially deflected at the polarizer 13 or completely deflected in the case of a phase jump pi and form a branched pulse train 15, which can be used in addition or absorbed in the beam trap 16.

The method according to the invention can also be implemented with more than two beam paths, wherein either a plurality of phase modulators is used or, in the case of a cascaded splitting of the laser radiation into beam paths, for example after a first 1-to-2 splitting, the phase is modulated in the beam path and the modulated laser radiation is then split into further beam paths. Asymmetric splitting is also possible, for example laser radiation is split into one phase-modulated high-power beam path and a plurality of unmodulated low-power beam paths.

In the exemplary embodiment of fig. 2, the laser radiation of a signal source (e.g. a laser oscillator or a preamplifier system) (not shown) is split into a plurality of beam channels by means of a beam splitter S as splitting element. In an exemplary embodiment, the optical amplifier V_1-V₄In each of the four beam paths. With a phase modulator phi positioned upstream of each amplifier₁-Φ₄Such as an electro-optic modulator. Mirror and beam combiner K₁-K₃The shown arrangement (e.g. partially reflecting mirror or polarizing beam splitter) is used as a combining element. The invention allows all four output beams P to be used₁-P₄In which the laser radiation propagating in the beam path is coupled by means of mirrors and a beam combiner K₁-K₃Are coherently superimposed. According to phase modulator phi₁-Φ₄At four output beams P, based on the power of the single beam path₁-P₄Respectively, a power distribution of 0-200% is obtained at P₂And P₃Even a power distribution of 0-400% is obtained.

In the exemplary embodiment of fig. 2, as in the exemplary embodiment of fig. 1, in practice a feedback control of the phase position of the laser radiation propagating in the beam path should again be provided to compensate for fluctuations due to environmental influences (thermal and acoustic disturbances). This feedback control is not shown in fig. 2.

The method shown in fig. 2 can be extended to any number of N beam channels and M output beams, where M can be between 2 and N.