Laser system and method for providing working laser pulses for interaction with targets and associated computer program product

Abstract

The invention relates to a laser system (1) for providing working laser pulses (2, 2') for interaction with targets (3), which pass through a target area (4) periodically or, with the exception of a period error, periodically one after the other, which laser system comprises a laser pulse emitting device (6) for emitting working laser pulses (2, 2'), wherein at least one working laser pulse (2, 2') is assigned to each target (3), and a control device (7) that controls the laser pulse output device (6) and is configured to set the output timing of a working laser pulse (2, 2') such that the working laser pulse, as an ON working laser pulse (2), hits a target (3) in the target area (4) in order to interact with the target (3), or, as an OFF working laser pulse (2'), misses the target (3) in the target area (4) in time so as not to interact with the target (3).

Description

[0001] Laser system and method for providing working laser pulses for interaction with targets and associated computer program product

[0002] The invention relates to a laser system and a method for providing working laser pulses for interaction with targets which pass through a target area periodically or periodically one after the other except for a period error, as well as to an associated computer program product.

[0003] US 2022 / 0317576 A1 discloses a laser system for generating secondary radiation. Laser pulses impinge on a stream of nearly evenly spaced targets to generate the secondary radiation. Based on the detected target position and trajectory, a trigger signal is generated that requests a laser pulse to interact with the target.

[0004] DE 10 2014 017 568 A1 discloses a method for generating amplified output laser pulses at individually specified times, achieved by free triggering using a pulse picker. This involves using a high-power ps laser consisting of a mode-locked seeder with a pulse repetition rate of a few tens of MHz, a pulse picker, an amplifier, a modulator, and possibly a frequency conversion unit. The pulse picker consists of a modulator and a driver, with which at least three levels for different pulse amplitudes can be set downstream of the pulse picker according to a specified value. If the time interval between two requested pulses is greater than the inverse of a nominal pulse repetition rate, the driver switches to an intermediate level, allowing the pulse picker to pass pulses with a predefined and low amplitude to condition the gain of the laser medium for constant laser parameters.Finally, DE 10 2017 210 272 B3 discloses a pulse-on-demand (POD) laser system for generating amplified laser pulses at individually specified times. For example, if laser pulses with different pulse energies are requested, a corresponding energy reduction is achieved by time-controlled partial decoupling of the pulses, depending on their known pulse spacing from the immediately preceding input laser pulse or inserted preceding sacrificial laser pulse.

[0005] The invention is based on the object of specifying a laser system and method as mentioned above, by means of which a working laser pulse intended for interaction with the target can be generated and at the same time controllability with regard to the interaction of the working laser pulses with the target is enabled.

[0006] This object is achieved according to the invention by a laser system for providing working laser pulses for interaction with targets which pass through a target area periodically or periodically one after the other except for a period error, with a laser pulse emission device for emitting working laser pulses, wherein at least one working laser pulse is assigned to each target, and with a control device which controls the laser pulse emission device and is designed to set the emission time of a working laser pulse such that the working laser pulse strikes a target in the target area as an ON working laser pulse in order to interact with the target, or misses the target in the target area as an OFF working laser pulse in order not to interact with the target.

[0007] According to the invention, the ON working laser pulse hits the target positioned in the target area, while the OFF working laser pulse misses the target in the target area. The working laser pulses can be controlled by an external control signal according to a pulse-on-demand (POD) scheme. The division into working and intermediate laser pulses allows for fewer laser power reserves to be maintained compared to the state of the art. The targets pass through the target area in the form of a target stream with low temporal jitter.

[0008] Preferably, the pulse energy of the ON working laser pulses deviates from a pulse energy mean value by less than 3% and in particular by less than 1%, so that the ON working laser pulses have the same or almost the same pulse energy for interaction with the targets.

[0009] In a preferred embodiment of the invention, the laser pulse delivery device comprises a laser beam source controlled by the control device for generating input laser pulses (seed laser pulses) and an optical amplifier for amplifying input laser pulses to form the working laser pulses and, if necessary, for amplifying further input laser pulses to form intermediate laser pulses present between two working laser pulses. After amplifying an ON working laser pulse to a predetermined pulse energy, the optical amplifier requires a gain-dependent minimum time period to provide the same predetermined pulse energy for an immediately subsequent ON working pulse. This gain-dependent minimum time period is required by the inversion structure required for amplification in the optical amplifier. The minimum possible period duration of the targets is preferably greater than or equal to the gain-dependent minimum time period.The control device is also particularly configured to adjust the emission times and / or the pulse energy of the input laser pulses underlying the OFF working laser pulses and the intermediate laser pulses and thereby the energy stored in the optical amplifier such that the ON working laser pulses each have the same predetermined pulse energy.

[0010] To stabilize the pulse energy of the incoming working laser pulses, the extractable energy of the amplifier system can be adjusted by additional, internally switched intermediate laser pulses (pulse-on-demand). The seed energy of the intermediate laser pulses can be selected to be increasingly larger as the pulse spacing between two working laser pulses increases. To minimize energy loss, the seed energy for the triggered working laser pulses can also be reduced as the pulse spacing between two working laser pulses decreases. By triggering working and intermediate laser pulses with separate energy compensation schemes, a specified energy stability with respect to external reference events (targets) can be ensured, which repeat with an error-prone period.The external control signal requests laser pulses relative to the reference events and controls whether a laser pulse should be triggered before, at the same time as, or after a respective reference event.Preferably, in the event that a current ON working laser pulse immediately follows an ON working laser pulse, the control device is configured to control the laser beam source, to emit the input laser pulse underlying the current ON working laser pulse and, if the time interval between these two working laser pulses is greater than the minimum time period required by the amplification, to emit a further input laser pulse between these two working laser pulses, amplified in the optical amplifier to an intermediate laser pulse, and to adjust its emission time and its pulse energy and thereby the energy stored in the optical amplifier for the current ON working laser pulse such that the current ON working laser pulse has the predetermined pulse energy.

[0011] Preferably, in the event that a current OFF working laser pulse immediately follows an ON working laser pulse, the control device is configured to control the laser beam source to emit the input laser pulse underlying the current OFF working laser pulse, wherein the time interval between the current OFF working laser pulse and the ON working laser pulse is, in particular, less than the gain-dependent minimum time period. The control device can advantageously be configured to adjust the energy of the current OFF working laser pulse via the energy of the underlying input laser pulse such that an ON or OFF working laser pulse immediately following the current OFF working laser pulse can again reach the specified pulse energy after the gain-dependent minimum time period.

[0012] Preferably, in the event that a current OFF working laser pulse immediately follows an OFF working laser pulse, the control device is configured to control the laser beam source, to emit the input laser pulse underlying the current OFF working pulse and, if the time interval between these two working laser pulses is greater than the amplification-related minimum time period, to emit a further input laser pulse between these two working laser pulses, amplified in the optical amplifier to form an intermediate laser pulse.Preferably, in the event that a current ON working laser pulse immediately follows an OFF working laser pulse, the control device is configured to control the laser beam source, to emit the input laser pulse underlying the current ON working pulse and, if the time interval between these two working laser pulses is greater than the minimum time period required by the amplification, to emit a further input laser pulse between these two working laser pulses, amplified in the optical amplifier to an intermediate laser pulse, and to adjust its emission time and its pulse energy and thereby the energy stored in the optical amplifier for the current ON working laser pulse such that the current ON working laser pulse has the predetermined pulse energy.

[0013] The pulse energy of the OFF working laser pulses and / or the intermediate laser pulses is advantageously at most as high as the specified pulse energy of the ON working laser pulses.

[0014] Preferably, an OFF-working laser pulse reaches the target area at least a minimum time interval earlier than the associated target, to ensure that no interaction occurs between the OFF-working laser pulse and the target. This minimum time interval is greater than the minimum possible period duration of the targets.

[0015] In particular, the control device is configured to emit an intermediate laser pulse at least a second minimum time period before an immediately following working laser pulse.

[0016] Preferably, the laser beam source is configured to provide the input laser pulses with a constant pulse energy.

[0017] In order to be able to individually adjust the pulse energy of the input pulses and thus the pulse energy of the working and intermediate laser pulses, an optical modulator controlled by the control device is preferably arranged upstream of the optical amplifier. This optical modulator modulates the input laser pulse energy accordingly, e.g., by modulating the amplitude or clipping the pulse edges. The optical modulator can be, for example, an AOM (acousto-optic modulator) or an EOM (electro-optic modulator). The system can also include an amplifier chain or a frequency converter connected downstream of the optical amplifier, and the device for adjusting the pulse energy can be arranged upstream of or between the amplifiers.

[0018] Particularly preferably, the laser system has a pulse selector (e.g. AOM or EOM) arranged between the optical amplifier and the target area, which is controlled by the control device in order to select the intermediate laser pulses from the further beam path of the working laser pulses. This ensures that the intermediate laser pulses cannot accidentally hit a target. Preferably, the selected intermediate laser pulses are destroyed internally, e.g. by means of a beam trap. Alternatively, the input laser pulses underlying the intermediate laser pulses can have a different wavelength. After being amplified in a broadband optical amplifier, the intermediate laser pulses are selected out at a pulse selector designed as a spectral filter. It is also possible to trigger an intermediate laser pulse with a suitable polarization, which is then selected out after the optical amplifier at a pulse selector designed as a polarization filter.

[0019] Further preferably, the control device is configured to emit at least one intermediate pulse if the time interval between the next working laser pulse to be emitted and the previous working laser pulse is greater than a predetermined maximum duration, which is greater than the gain-dependent minimum time period and can, for example, be twice the minimum time period. In this case, the control device triggers an intermediate laser pulse, for example after the gain-dependent minimum time period, which has the energy of the ON working laser pulse and prevents too much energy from being stored in the optical amplifier. For larger time intervals between two working laser pulses, a corresponding number of intermediate laser pulses are inserted, each spaced, for example, at a distance equal to the gain-dependent minimum time period, so that too much energy is not stored in the optical amplifier.Preferably, each target is assigned a control signal from which the arrival time of the target in the target area can be determined, and the control device is configured to emit an ON or an OFF working laser pulse based on the respective control signal.

[0020] In a further aspect, the invention also relates to a method for providing working laser pulses for interaction with targets which pass through a target area periodically or periodically one after the other except for a period error, comprising the following method steps:

[0021] - Emitting at least one working laser pulse for each target; and

[0022] - Setting a delivery time of the at least one working laser pulse by means of a control device such that the working laser pulse either strikes a target in the target area as an ON working laser pulse in order to interact with the target, or misses the target in the target area as an OFF working laser pulse in order not to interact with the target.

[0023] Preferably, the ON or OFF working laser pulses are emitted based on control signals that are assigned to the respective targets and from which the respective arrival time of the targets in the target area can be determined.

[0024] Finally, the invention also relates to a control program product which has code means adapted to carry out all steps of the method according to the invention when the program runs on a control device of the laser system according to the invention.

[0025] Further advantages of the invention will become apparent from the description and the drawings. Likewise, the above-mentioned and further-described features can be used individually or in combination. The embodiments shown and described are not intended to be exhaustive, but rather serve as examples for describing the invention. It shows:

[0026] Fig. 1 shows an embodiment of a laser system according to the invention for providing working laser pulses for interaction with periodically emitted targets; and Figs. 2a-2d show an exemplary temporal representation of the temporal energy control of the laser system according to the invention when alternating between working laser pulses that hit the targets and working laser pulses that miss the targets.

[0027] The laser system 1 shown in Fig. 1 serves to provide working laser pulses 2, 2' for interaction with targets 3, which are periodically generated with a period duration t p or up to a period error At p periodically, i.e. in the form of a target current with low temporal jitter, pass through a target area 4 one after the other.

[0028] Secondary radiation 5 (e.g., EUV radiation) can be generated by the interaction of the working laser pulses 2 with the targets 3 in the target area 4. For example, the target material is or comprises tin.

[0029] The laser system 1 comprises a laser pulse delivery device 6 for generating the working laser pulses 2, 2' and a control device 7, by means of which the delivery of the working laser pulses 2, 2' by the laser pulse delivery device 6 can be triggered and / or controlled at specific times. For example, it can be provided that the laser pulse delivery device 6 delivers a working laser pulse 2, 2' as a single laser pulse or in the form of a laser pulse packet (laser burst) when the control device 7 receives a corresponding control signal. This allows working laser pulses 2, 2' with individual pulse energy to be specifically requested at specific times, which can be implemented, for example, using known pulse-on-demand concepts.

[0030] As shown in Fig. 1, the laser pulse output device 6 comprises, for example, a laser beam source 8 controlled by the control device 7 for generating input laser pulses 9 with preferably constant pulse energy and an optical amplifier 10 for amplifying input laser pulses 9 to form the working laser pulses 2, 2' and, if necessary, for amplifying further input laser pulses 9 to form intermediate laser pulses 11, which can be selected out of the further beam path of the working laser pulses 2, 2' by means of an optional pulse selector 16 and therefore do not arrive at the target area 4. The pulse selector 16 is arranged between the optical amplifier 10 and the target area 4 and is controlled by the control device 7 in order to deflect the intermediate laser pulses 11 from the beam path of the working laser pulses 2, 2' and, for example, feed them to a beam trap 17. This ensures that the intermediate laser pulses 11 cannot accidentally hit a target 3.Preferably, the pulse selector 16 is an AOM or EOM.

[0031] If an input laser pulse 9 was converted into a working laser pulse 2, 2' with a given pulse energy E nO m, the optical amplifier 10 requires a gain-related minimum time period T m in for a new inversion setup to provide the same predetermined pulse energy Enom for an immediately following working pulse 2, 2'. The minimum possible period t p -At p the targets

[0032] 3 is greater than or equal to the gain-dependent minimum time period Tmin. The input laser pulses 9 underlying the working and intermediate laser pulses 2, 2', 11 can be either a single laser pulse or a laser pulse packet (laser burst).

[0033] The laser pulse delivery device 6 optionally has an optical modulator 12 arranged upstream of the optical amplifier 10 for individually adjusting the pulse energy of the input laser pulses 9, thus adjusting the pulse energy of the working and intermediate laser pulses 2, 2', 11 accordingly. The optical modulator 12 is controlled by the control device 7 to adjust the desired pulse energy of the input laser pulses 9, for example, by modulating the amplitude or trimming the pulse edges, and can be designed, for example, as an AOM or EOM.

[0034] To feed the targets 3 into the target area 4, the laser system 1 can have a target delivery device 13, by means of which the targets 3 are delivered in such a way that they periodically reach the target area 4 with the period duration t p ±At pone after the other. For example, the targets 3 can be released from the target release device 13 in the form of individual drops and in the direction of gravity, i.e. downwards in Fig. 1, and pass through the target area 4 from top to bottom. A target detection device (e.g. a camera) 14 can also be arranged downstream of the target release device 13, which at the latest in the target area

[0035] 4 detects an emitted target 3 and in particular also its target geometry, for example by means of image recognition, and delivers a corresponding external control signal 15 to the control device 7. From the control signals, the respective arrival time of the targets 3 in the target area 4 can be determined. Based on the control signal 15, the control device 7 then controls the laser pulse emitter 6 to emit a working laser pulse 2, 2'. However, if the time interval between the working laser pulse 2, 2' to be emitted and the previous working laser pulse 2, 2' is greater than a predetermined maximum duration, which is greater than the gain-dependent minimum time period Tmin and e.g. 2*T min, an intermediate laser pulse 11 is preferably triggered by the control device 7, e.g. after the gain-related minimum time period Tmin, which has the energy of the ON working laser pulse 2 and prevents too much energy from being stored in the optical amplifier 10. For longer time intervals between two working laser pulses of n*T m in (n>=2) n-1 additional intermediate pulses 11 are inserted at intervals of Tmin so that not too much energy is stored in the optical amplifier 10.

[0036] For technical details regarding the coupling of targets 3 into the target area 4 to generate secondary radiation 5, please refer to the scientific publication "Light sources for high-volume manufacturing EUV lithography: technology, performance, and power scaling", I. Fomenkov et al., Advanced Optical Technologies 6(3): 173-186, DOI: 10.1515 / aot-2017-0029.

[0037] Figs. 2a-2d show an exemplary representation of the temporal energy control of the laser system 1 when alternating between working laser pulses 2, which hit the targets 3 in the target area 4, and working laser pulses 2', which miss the targets 3 in the target area 4 in time.

[0038] Fig. 2a shows the targets 3 output by the target output device 13, which are positioned in the target area 4 at times tj-i, t, tj+i, tj+2, and tj+3. The targets 3 used to generate secondary radiation 5 are referred to as ON targets, and the targets 3 that are not used to generate secondary radiation 5—e.g., due to an excessive period error, suboptimal target geometry, or to modulate the power of the secondary beam source or to omit working pulses—are referred to as OFF targets.

[0039] As shown in Fig. 2b, each target 3 is assigned a working pulse 2, 2'. The working pulses that hit an assigned ON target 3 in the target area 4 in order to interact with the ON target 3 are referred to as ON working laser pulses 2, and the working laser pulses that miss an assigned OFF target 3 in the target area 4 in order not to interact with the OFF target 3 are referred to as OFF working laser pulses 2'. The ON working pulses 2 are requested by the control device 7 at the times tj-i and tj+3 in order to interact with the ON targets 3 in the target area 4, and each have the same predetermined pulse energy E nOm. Preferably, the pulse energy of the ON working laser pulses 2 deviates from a predetermined pulse energy average by less than 3% and in particular by less than 1%. The OFF working pulses 2', however, are requested by the control device 7 at least a minimum time interval Ati earlier than the associated OFF targets 3 are positioned in the target area 4, thus in the present case at the times tj+i-Ati, tj+2-Ati, with individually adjustable pulse energy, which, however, is not greater than the predetermined pulse energy E nO m of the ON working pulses 2. The minimum time interval Ati is chosen so that no interaction occurs between the OFF working laser pulse 2' and the OFF target 3.

[0040] As shown in Fig. 2c, the control device 7 can, if required, request an intermediate laser pulse 11 at least a second minimum time interval Δt2 before an ON or OFF working laser pulse 2, 2', i.e. in the present case at the times t1-Δt2, tj+2-Δt1-Δt2 and tj+3-Δt2, with individually adjustable pulse energy, which, however, is not greater than the predetermined pulse energy E nO m of the ON working pulses 2. The timing and pulse energy of the OFF working laser pulses 2' and the intermediate laser pulses 11 are selected such that, on the one hand, the energy E stored in the optical amplifier 10 for the ON working laser pulses 2 is always the same in order to adjust the ON working laser pulses 2 in the optical amplifier 10 to the same predetermined pulse energy E nO m, and on the other hand, as little power reserves as possible must be kept in the optical amplifier 10.

[0041] Fig. 2d shows the corresponding time profile of the energy E stored in the optical amplifier 10. In this case, the control device 7, as described below, adjusts the emission times and / or the pulse energy of the input laser pulses 9 underlying the OFF working laser pulses 2' and the intermediate laser pulses 11 and thereby adjusts the energy E stored in the optical amplifier 10 such that the ON working laser pulses 2 each have the same predetermined pulse energy E nO m.

[0042] 1 . If a current ON working laser pulse 2 (here at time t,) immediately follows an ON working laser pulse 2 (here at time tn):

[0043] The control device 7 requests the current ON working laser pulse 2 with pulse energy Enom at the time of the ON target 3 and, if, as in this case, the time interval between the two ON working laser pulses 2 is greater than the minimum gain-free time period Tmin, i.e., tj-tj-1 >Tmin, an intermediate laser pulse 11 between these two working laser pulses, here at time -Δt2. The request time and pulse energy of the intermediate laser pulse 11 are set by the control device 7 such that the energy E stored in the optical amplifier 10, which decreases due to the amplification of the intermediate laser pulse 11, has increased again at the time such that the current ON working laser pulse 2 is amplified to the specified pulse energy Enom.

[0044] If the time interval between the two ON working laser pulses 2 is equal to the gain-free minimum time period Tmin, i.e. tj-tj-i =T min, no intermediate laser pulse 11 needs to be requested by the control device 7. A time interval between two ON working laser pulses 2 smaller than the gain-free minimum time period Tmin, i.e. tj-tj-i <T m in, however, is inadmissible and is not permitted by the control device 7 or is evaluated as an OFF working laser pulse, and the pulse energy is adjusted depending on the distance from the minimum time period Tmin, as described below under 2.

[0045] 2. If a current OFF working laser pulse 2' (here at time tj+i -Ati ) immediately follows an ON working laser pulse 2 (here at time ti):

[0046] The control device 7 requests the current OFF-working laser pulse 2' at the time tj+i-Ati. The time interval between the current OFF-working laser pulse 2' and the previous ON-working laser pulse 2, i.e. (tj+i-Ati)-, is selected to be no greater than the gain-free minimum time period Tmin, so that the current OFF-working laser pulse 2' is at most equal to the specified pulse energy E nomis amplified. The request time and pulse energy of the current OFF-working laser pulse 2' are preferably adjusted by the control device 7 such that the energy E stored in the optical amplifier 10, which decreases due to the amplification of the current OFF-working laser pulse 2', has increased again after the amplification-free minimum period Tmin to such an extent that an immediately following ON- or OFF-working laser pulse 2, 2' is amplified to the predetermined pulse energy Enom. As shown, the pulse energy of the current OFF-working laser pulse 2' does not exceed the predetermined pulse energy E nO m of the ON working laser pulses 2. If a current OFF working laser pulse 2' (here at time tj+2-Ati) immediately follows an OFF working laser pulse 2' (here at time tj+i -Ati ):

[0047] The control device 7 requests the current OFF-working laser pulse 2' e.g. with pulse energy Enom at the time tj+2-Ati and, if as in the present case the time interval between these two OFF-working laser pulses is greater than the gain-free minimum time period Tmin, i.e. (tj+2-Ati )-(tj+i-Ati )>T m in, between these two working laser pulses, here at time (tj+2-Ati)-At2, an intermediate laser pulse 11 is applied. The request time and pulse energy of the intermediate laser pulse 11 are set by the control device 7 such that the energy E stored in the optical amplifier 10, which decreases due to the amplification of the intermediate laser pulse 11, has increased again at time tj+2-Ati to such an extent that the current OFF working laser pulse 2' is amplified to the predetermined pulse energy Enom or even to a lower pulse energy.

[0048] As shown, the stored energy E before the amplification of the intermediate laser pulse 11 can increase to an energy level that may be higher than the amplification of the ON working laser pulses 2 to the specified pulse energy Enom. However, the pulse energy of the intermediate pulse 11 does not exceed the specified pulse energy E nom of the ON working laser pulses 2. If a current ON working laser pulse 2 (here at time tj+3) immediately follows an OFF working laser pulse 2' (here at time tj+2-Ati ):

[0049] The control device 7 requests the current ON working laser pulse 2 with pulse energy Enom at time tj+3 and, if, as in the present case, the time interval between these two working laser pulses is greater than the gain-free minimum time period Tmin, i.e. (tj+3)-(tj+2-Ati)>Tmin, an intermediate laser pulse 11. The request time and pulse energy of the intermediate laser pulse 11 are set by the control device 7 such that the energy E stored in the optical amplifier 10, which decreases due to the amplification of the intermediate laser pulse 11, has increased again at time tj+3 to such an extent that the current ON working laser pulse 2 reaches the specified pulse energy E nO m. As shown, the stored energy E before the amplification of the intermediate laser pulse 11 can increase to an energy level which can be higher than when the working laser pulses are amplified to the specified pulse energy E nOm. However, the pulse energy of the intermediate pulse 11 does not exceed the specified pulse energy of the ON working laser pulses 2.

[0050] For the case not shown in Fig. 2, that the time interval of a working laser pulse 2, 2' to be emitted from the previous working laser pulse 2, 2' is greater than a predetermined maximum duration, which is greater than the gain-related minimum time period Tmin and e.g. 2*T m in, the control device 7, e.g. after the gain-related minimum time period Tmin, triggers an intermediate laser pulse 11 which has the energy of the ON working laser pulse 2 and prevents too much energy from being stored in the optical amplifier 10. For longer time intervals between two working laser pulses of n*T m in (n>=2) n-1 additional intermediate pulses 1 are inserted at intervals of Tmin so that not too much energy is stored in the optical amplifier 10.

Claims

Patent claims 1. Laser system (1) for providing working laser pulses (2, 2') for interaction with targets (3), which pass through a target area (4) periodically or periodically one after the other except for a period error, comprising a laser pulse emission device (6) for emitting working laser pulses (2, 2'), wherein at least one working laser pulse (2, 2') is assigned to each target (3), and comprising a control device (7) controlling the laser pulse emission device (6) and configured to set the emission time of a working laser pulse (2, 2') such that the working laser pulse, as an ON working laser pulse (2), strikes a target (3) in the target area (4) in order to interact with the target (3), or as an OFF working laser pulse (2'), misses the target (3) in the target area (4) in order not to interact with the target (3).

2. Laser system according to claim 1, characterized in that the pulse energy (Enom) of the ON working laser pulses (2) deviates from a pulse energy mean value by less than 3% and in particular by less than 1%.

3. Laser system according to claim 1 or 2, characterized in that the laser pulse output device (6) comprises a laser beam source (8) controlled by the control device (7) for generating input laser pulses (9) and an optical amplifier (10) for amplifying input laser pulses (9) to form the working laser pulses (2, 2') and, if required, for amplifying further input laser pulses (9) to form intermediate laser pulses (11) which are present between two working laser pulses, wherein the optical amplifier (10), after amplification of an ON-working laser pulse (2) to a predetermined pulse energy (Enom), requires a gain-related minimum time period (Tmin) in order to obtain the same predetermined pulse energy (E nom), and wherein the control device (7) is designed to determine the emission times and / or the pulse energy of the input laser pulses (9) underlying the OFF working laser pulses (2') and the intermediate laser pulses (11) and thereby the energy stored in the optical amplifier (10). Energy so that the ON working laser pulses (2) each have the same specified pulse energy (E nO m).

4. Laser system according to claim 3, characterized in that the control device (7) is configured, when a current ON-working laser pulse (2) immediately follows an ON-working laser pulse (2), to control the laser beam source (8), to emit the input laser pulse (9) underlying the current ON-working laser pulse (2) and, if the time interval between these two working laser pulses is greater than the amplification-related minimum time period (Tmin), to emit a further input laser pulse (9) amplified in the optical amplifier (10) to an intermediate laser pulse (11) between these two working laser pulses and to adjust its emission time and its pulse energy and thereby the energy (E) stored in the optical amplifier (10) for the current ON-working laser pulse (2) such that the current ON-working laser pulse (2) has the predetermined pulse energy (E nO m).

5. Laser system according to claim 3 or 4, characterized in that the control device (7) is set up, when a current OFF working laser pulse (2') immediately follows an ON working laser pulse (2), to control the laser beam source (8) to emit the input laser pulse (9) underlying the current OFF working laser pulse (2'), wherein the time interval between the current OFF working laser pulse (2') and the ON working laser pulse (2) is in particular smaller than the gain-related minimum time period (Tmin).

6. Laser system according to claim 5, characterized in that the control device (7) is designed to adjust the energy of the current OFF working laser pulse (2') via the energy of the underlying input laser pulse (9) in such a way that an ON or OFF working laser pulse (2, 2') immediately following the current OFF working laser pulse (2') again reaches the predetermined pulse energy (E nom) can be achieved.

7. Laser system according to one of claims 3 to 6, characterized in that the control device (7) is set up, when a current OFF working laser pulse (2') immediately follows an OFF working laser pulse (2'), to control the laser beam source (8), to emit the input laser pulse (9) on which the current OFF working pulse (2') is based and, if the time interval between these two working laser pulses is greater than the amplification-related minimum time period (Tmin), to emit a further input laser pulse (9) between these two working laser pulses, amplified in the optical amplifier (10) to form an intermediate laser pulse (11).

8. Laser system according to one of claims 3 to 7, characterized in that the control device (7) is configured, when a current ON-working laser pulse (2) immediately follows an OFF-working laser pulse (2'), to control the laser beam source (8), to emit the input laser pulse (9) underlying the current ON-working pulse (2) and, if the time interval between these two working laser pulses is greater than the amplification-related minimum time period (Tmin), to emit a further input laser pulse (9) amplified in the optical amplifier (10) to an intermediate laser pulse (11) between these two working laser pulses, and to adjust its emission time and its pulse energy and thereby the energy stored in the optical amplifier (10) for the current ON-working laser pulse (2) such that the current ON-working laser pulse (2) has the predetermined pulse energy (E nO m).

9. Laser system according to one of claims 3 to 8, characterized in that the pulse energy of the OFF working laser pulses (2') and / or the intermediate laser pulses (11) is at most as high as the predetermined pulse energy (E nO m) the ON working laser pulses (2).

10. Laser system according to one of claims 3 to 9, characterized in that an OFF working laser pulse (2') reaches the target area (4) by at least a minimum time interval (Ati ) earlier than the associated target (3) in order to ensure that no interaction takes place between the OFF working laser pulse (2') and the target (3).

11. Laser system according to one of claims 3 to 10, characterized in that the control device (7) is arranged to emit an intermediate laser pulse (11) by at least a second minimum time period (Δt2) before an immediately following working laser pulse (2, 2').

12. Laser system according to one of claims 3 to 11, characterized in that the laser beam source (8) is arranged to provide the input laser pulses (9) with a constant pulse energy.

13. Laser system according to one of claims 3 to 12, characterized in that an optical modulator (12) controlled by the control device (7) is arranged upstream of the optical amplifier (10) in order to adjust the pulse energy of the input laser pulses (9) and thereby the pulse energy of the OFF working laser pulses (2') and the intermediate laser pulses (11).

14. Laser system according to one of claims 3 to 13, characterized in that a pulse selector (16) is arranged between the optical amplifier (10) and the target area (4), which selects the intermediate laser pulses (11) from the further beam path of the working laser pulses (2, 2').

15. Laser system according to one of claims 3 to 14, characterized in that the control device (7) is designed to emit at least one intermediate pulse (11) if the time interval between the next working laser pulse (2, 2') to be emitted and the previous working laser pulse (2, 2') is greater than a predetermined maximum duration, which is greater than the gain-related minimum time period (Tmin).

16. Laser system according to one of the preceding claims, characterized in that each target (3) is assigned a control signal (15) and the control device (7) is configured to emit an ON or an OFF working laser pulse (2, 2') based on the respective control signal (15).

17. Method for providing working laser pulses (2, 2') for interaction with targets (3), which are periodically or periodically pass through a target area (4) one after the other, with the following process steps: - emitting at least one working laser pulse (2, 2') for each target (3); and - Setting a delivery time of the at least one working laser pulse (2, 2') by means of a control device (7) such that the working laser pulse either strikes a target (3) in the target area (4) as an ON working laser pulse (2) in order to interact with the target (3), or misses the target (3) in the target area (4) as an OFF working laser pulse (2') in order not to interact with the target (3).

18. Method according to claim 17, characterized in that the ON and OFF working laser pulses (2, 2') are emitted based on control signals (15) which are respectively assigned to the targets (3).

19. Control program product comprising code means adapted to carry out all steps of the method according to claim 17 or 18 when the program runs on a control device (7) of the laser system (1) according to one of claims 1 to 16.

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