Device and method for generating a burst in secondary radiation

Abstract

The invention relates to a device (10) for generating a burst in secondary radiation (12), comprising a primary source (14) for generating primary radiation (16) and a secondary source (18) for generating the secondary radiation (12), wherein the device (10) is configured such that the primary radiation (16) impinges on the secondary source (18) and the secondary radiation (12) is generated thereby, wherein the primary source (14) is configured for burst-mode operation in which a plurality of pulse-burst trains (20), which each consist of a plurality of individual pulses (22), are generated, wherein the pulse-burst trains (20) each have a duration in a range between 0.1 ms and 1 s. The invention also relates to a method for generating a burst in secondary radiation (12).

Description

[0001] Title: Device and method for generating a burst in secondary radiation

[0002] Description

[0003] The invention relates to a device for generating a burst in a secondary radiation with features of claim 1 and a method for generating a burst in a secondary radiation with features of the dependent claim.

[0004] A laser-driven secondary radiation source can be used for applications that do not require or accept extremely high single-shot peak powers or high average powers. Particularly in secondary sources for medical applications, it may be necessary to apply a high dose rate temporarily, while a high average power is not desired, as, for example, in the treatment of (cancer) tumors. The object of the present invention is to provide a device and a method for generating secondary radiation, whereby a temporarily high radiation power can be achieved with a comparatively low average power.

[0005] The above problem is solved in the present case by the device for generating a burst in secondary radiation with the features of claim 1. The secondary radiation can consist of photons, electrons, protons and / or neutrons.

[0006] The device comprises a primary source for generating primary radiation and a secondary source for generating secondary radiation. The device is configured such that the primary radiation strikes a target of the secondary source, thereby generating the secondary radiation. The target can be, for example, a gas, a solid, and / or a liquid. The target can be a liquid metal, a solid (dielectric, metallic), and / or a plasma (thin, thick). The primary source is configured for burst-mode operation. In burst-mode operation, several pulse burst trains are generated, each consisting of several individual pulses. The pulse burst trains each have a duration ranging from 0.1 ms (milliseconds) to 1 s (second). The pulse-burst sequences can each have a temporal length (or ).duration) in a range of, in particular, 1 ms to 100 ms .

[0007] This allows for the provision of a relatively large total energy, which does not necessarily have to be deposited in a single, extremely intense laser pulse. Simultaneously, a relatively low (total) average laser power can be provided over longer periods, or high average laser power can be avoided. For example, in medical applications, it can be advantageous to apply a high energy briefly over a short period (essentially a dose rate), while avoiding the application of high average power over extended periods.

[0008] Each individual pulse of a pulse-burst train of primary radiation generates, in particular, a single pulse of a pulse-burst train of secondary radiation. Accordingly, a pulse-burst train of primary radiation and a pulse-burst train of secondary radiation generated from it can have the same number of individual pulses. A pulse-burst train, in particular, represents a packet of individual pulses.

[0009] In ultrashort pulse laser sources (with fs (femtosecond) or ps (picosecond) pulse durations), the peak pulse powers in a laser amplifier path can be limited by nonlinear effects or the damage limits of optical surfaces, i.e., practically energy fluxes per unit area. Temporally splitting the energy of a single pulse into several individual pulses that do not overlap or only slightly overlap in spacetime can shift this limitation by a factor corresponding to the number of individual pulses into which the total energy is distributed.

[0010] Simultaneously, the average laser power can be reduced by a duty cycle, i.e., the quotient of the length of each pulse-burst sequence and a time interval between the individual pulse-burst sequences. The time interval between the individual pulse-burst sequences can, in particular, refer to the duration between the respective start of two temporally adjacent pulse-burst sequences.

[0011] Since both the area of ​​a largest optical surface of laser-active media and the average laser power significantly determine the cost of a laser amplifier chain, cost-optimized laser beam sources can be realized for suitable amplifier architectures that efficiently provide high total energies at reduced average powers.

[0012] An example of an application requiring high total energies over a short period (pulse-burst) but comparatively low average powers is the FLASH treatment method for the radiological (photons, electrons, protons) treatment of tumors. This involves ultrashort and ultrahigh-dose radiation, in which the radiation dose is delivered on timescales of less than one second. As in most medical treatments, high average powers (100 W to 1 kW) of secondary radiation over many seconds are undesirable—if not, as in FLASH, due to excessive radiation exposure, then at least because of potential thermal damage to (healthy) tissue.

[0013] The present device is particularly well-suited for such an application. It allows for the realization of highly desirable particle energies (e.g., in the range of 100 MeV (megaelectronvolts) and above for electrons), while maintaining a small size that is manageable, especially for a medical facility. In contrast, a conventional particle accelerator for electron energies in the range of 10 MeV has a length of approximately 1 m (meters). For electron energies of 100 MeV, a conventional particle accelerator can already be several tens of meters long, or even more than 100 meters.

[0014] According to a further development of the device, the primary source can comprise at least one ultrashort pulse laser beam source with a master oscillator power amplifier (MOPA) laser architecture. In this context, a MOPA laser architecture refers to a laser system consisting of at least one laser (seed laser) and at least one laser amplifier for increasing the output power.

[0015] This allows the primary source to be implemented using simple means.

[0016] According to a further development of the device, the individual pulses can have a temporal length (or duration) in a range of 5 fs to 5 ps.

[0017] This allows the individual pulses to be used particularly effectively.

[0018] According to a further development of the device, the number of individual pulses in a pulse-burst train can be in a range of 2 to 10,000,000, in particular 5,000-50,000.

[0019] This allows for further optimization of the pulse-burst trains. According to a further development of the device, a duty cycle can be in the range of 50% to 0.1%. In this context, the duty cycle is the ratio (or...)

[0020] Quotient ) of the duration of a single pulse-burst move to a time interval between pulse-burst moves.

[0021] This allows for further optimization of the burst-mode operation of the primary source.

[0022] According to a further development of the device, the repetition rate of the pulse-burst trains can be at least 10 Hz (Hertz). In particular, the repetition rate of the pulse-burst trains can be in a range of 100 Hz to 10 MHz (Megahertz).

[0023] This allows for further optimization of the burst-mode operation of the primary source.

[0024] According to a further development of the device, the primary radiation can have a wavelength in the range of 500 pm to 2 pm, in particular 1 pm to 2 pm. The primary radiation can have a wavelength of, in particular, greater than 2 pm.

[0025] This allows for further optimization of the burst-mode operation of the primary source.

[0026] According to a further development of the device, the primary source can comprise a laser-active medium. The laser-active medium can be doped with ytterbium (Yb), neodymium (Nd), and / or thulium (Tm). In particular, the primary source can comprise at least one Yb:YAG laser, Nb:YAG laser, and / or Tm:YAG laser. The primary source can also comprise at least one solid-state laser.

[0027] This allows primary radiation to be generated using simple means.

[0028] According to a further development of the device, the secondary source can be configured to generate relativistic electrons using laser wakefield acceleration. These relativistic electrons can constitute the secondary radiation and can be used, in particular, in the FLASH treatment method.

[0029] This allows secondary radiation, consisting in particular of (relativizing) electrons, to be generated using simple means, especially for the FLASH treatment method.

[0030] According to a further development of the device, the primary source can comprise at least one slab amplifier, in particular an InnoSlab amplifier as described, for example, in EP 1181754 Bl. The slab amplifier can be configured as a multi-slab amplifier. In this context, a slab amplifier is defined as a cuboid crystal. It is also conceivable that, alternatively or additionally, the primary source can comprise at least one multipass disk amplifier. The primary source can comprise further amplifiers. The amplifiers of the primary source can form a laser amplifier chain. The primary source can comprise at least one laser amplifier. This allows for amplification of the signal by simple means.

[0031] Primary radiation is converted and the burst-mode operation of the primary source is further optimized.

[0032] According to a further development of the device, the primary source can include at least one compression stage for spectral compression of the individual pulses.

[0033] This allows the pulse duration to be reduced and the burst mode operation of the primary source to be further optimized.

[0034] According to a further development of the device, the primary source can comprise at least one nonlinear post-compression stage. The nonlinear post-compression stage can be configured to add further spectral ranges to the spectrum of the individual pulses by means of self-phase modulation and to at least partially compensate for the spectral temporal chirp of the individual pulses by means of at least one dispersive element. In particular, the nonlinear post-compression stage can be arranged (in the beam direction) downstream of the compression stage.

[0035] This can result in a further reduction in the pulse duration of individual pulses.

[0036] According to a further development of the device, the primary source can comprise at least one first optical pulse source and at least one second optical pulse source, each for generating individual pulses. The individual pulses of the first pulse source and the individual pulses of the second pulse source can be spatially superimposed. Alternatively or additionally, the individual pulses of the first pulse source and the individual pulses of the second pulse source can be temporally shifted relative to each other within a pulse-burst train. The individual pulses of the second pulse source can have a temporal length (or duration) in the range of 5 fs and 1 ps (microseconds).

[0037] Alternatively or additionally, the individual pulses of the first pulse source and the individual pulses of the second pulse source can have different spectral center wavelengths.

[0038] This allows for further optimization of the burst-mode operation of the primary source.

[0039] The device may include a control unit. The control unit may be configured to control the timing of the first and / or the second pulse source. The control unit may be configured to generate and / or modulate the bursts according to a predetermined pattern, for example by controlling a modulator and / or controlling the first and / or second pulse source.

[0040] According to a further development of the device, the intervals between the individual pulses can vary. In particular, the intervals between the individual pulses can be non-equidistant. The intervals between the individual pulses can be tailored to advantageous properties for the generation process of the secondary radiation.

[0041] A pulse burst train can, for example, be broken down into several partial pulse burst trains, each possibly with a different number of individual pulses, occurring in quick succession.

[0042] The intervals between individual pulses within a pulse burst train can exhibit a complex pattern that, in particular, encodes time information which can be utilized with suitable instrumental or mathematical methods.

[0043] This allows for further optimization of the burst-mode operation of the primary source.

[0044] At least two individual pulses within a pulse-burst sequence can have different intensities. Likewise, it is conceivable that at least two pulse-burst sequences can have different intensities. The primary source can be configured to adjust the intensity of individual, and especially multiple, individual pulses and / or pulse-burst sequences.

[0045] The above problem is solved by a method for generating secondary radiation with the features of the dependent claim. The method comprises the following steps:

[0046] Generating primary radiation in a burst-mode operation, in which several pulse-burst trains, each consisting of several individual pulses, are generated.

[0047] Secondary radiation is generated by directing primary radiation onto a secondary source. A device as described above is used to carry out this process. For the advantages achievable with this method, please refer to the descriptions of the device. The measures described in connection with the device and / or those explained below can be used to further develop the process.

[0048] Further features, details and advantages of the invention will become apparent from the wording of the claims and from the following description of exemplary embodiments with reference to the drawings. The drawings show:

[0049] Fig. 1 shows a schematic representation of a device for generating secondary radiation;

[0050] Fig. 2 shows a diagram of several pulse-burst sequences of the device according to Figure 1 according to a first embodiment;

[0051] Fig. 3 shows a diagram of several pulse-burst sequences of the device according to Figure 1 according to a second embodiment;

[0052] Fig. 4 shows a diagram of a pulse-burst train of the device according to Figure 1 according to a third embodiment.

[0053] In the following description and in the figures, corresponding components and elements are designated by the same reference symbols. For clarity, not all reference symbols are shown in every figure. Figure 1 shows a schematic representation of a device 10 for generating secondary radiation 12. The device 10 comprises a primary source 14 for generating a

[0054] Primary radiation 16 and a secondary source 18 for generating the secondary radiation 12 .

[0055] The device 10 is configured such that the primary radiation 16 strikes a target of the secondary source 18, thereby generating the secondary radiation 12. The primary source 14 is configured for burst-mode operation. In burst-mode operation, several pulse-burst trains 20 are generated, each pulse-burst train 20 consisting of several individual pulses 22. The pulse-burst trains 20 each have a duration in the range of 0.1 ms to 1 s. The pulse-burst trains 20 can each have a duration in the range of 1 ms to 100 ms.

[0056] The primary source 14 can include at least one ultrashort pulse laser beam source 24 with a master oscillator power amplifier laser architecture.

[0057] The wavelength of the primary radiation 16 can lie in a range from 1 pm to 2 pm. In particular, the primary radiation 16 can have a wavelength greater than 2 pm.

[0058] The primary source 14 (or the ultrashort pulse laser beam source 24) can comprise a laser-active medium. The laser-active medium can be doped with ytterbium, neodymium, and / or thulium. The primary source 14 can, in particular, comprise at least one Yb:YAG laser, Nb:YAG laser, and / or Tm:YAG laser. In particular, the ultrashort pulse laser beam source 24 can be configured as a Yb:YAG laser, Nb:YAG laser, and / or Tm:YAG laser.

[0059] The primary source 14 can comprise at least one slab amplifier 26. The primary source 14 can comprise an amplifier chain consisting of multiple amplifiers.

[0060] The primary source 14 can include at least one compression stage 28 for spectral compression of the individual pulses 22.

[0061] The primary source 14 can include at least one nonlinear post-compression stage 30. The nonlinear post-compression stage 30 can be configured to add further spectral ranges to a spectrum of the individual pulses 22 by means of self-phase modulation and to at least partially compensate for the spectral, temporal chirp of the individual pulses 22 by means of at least one dispersive element.

[0062] The primary source 14 can comprise at least one first optical pulse source and at least one second optical pulse source, each for generating individual pulses 22. The individual pulses 22 of the first pulse source and the individual pulses 22 of the second pulse source can be spatially superimposed.

[0063] Alternatively or additionally, the individual pulses 22 of the first pulse source and the individual pulses 22 of the second pulse source can be temporally shifted relative to each other within a pulse-burst train 20. The individual pulses 22 of the second pulse source can have a temporal duration in the range of 5 fs and 1 ps. Alternatively or additionally, the individual pulses 22 of the first pulse source and the individual pulses 22 of the second pulse source can have different spectral centroid durations.

[0064] Secondary source 18 can be configured to generate relativistic electrons using laser wakefield acceleration. It is also conceivable that secondary radiation 12 from secondary source 18 could comprise photons and / or neutrons.

[0065] The device can include a control unit 13. The control unit 13 can be configured for the timing control of the first and / or the second pulse source. The control unit 13 can be configured for generating and / or modulating the bursts according to a predefined pattern, for example, by controlling a modulator and / or controlling the first and / or second pulse source. The control unit 13 can, for example, be operated by a person. It is also conceivable that the control unit 13 performs the timing control automatically.

[0066] The individual pulses 22 can have a temporal length (or duration) in a range of 5 fs to 5 ps.

[0067] The number of individual pulses 22 in a pulse burst train 20 can be in a range of 2 to 10,000,000, in particular 5,000 to 50,000.

[0068] A duty cycle can range from 50% to 0.1%. In this context, the duty cycle refers to the ratio or quotient between a single pulse-burst cycle 20 and the time interval between individual pulse-burst cycles 20 (e.g., two consecutive pulse-burst cycles 20).

[0069] The repetition rate of the pulse-burst trains 20 can be at least 10 Hz. In particular, the repetition rate of the pulse-burst trains 20 can be in a range of 100 Hz to 10 MHz.

[0070] The intervals between the individual pulses 22 can differ. In particular, the intervals between the individual pulses 22 cannot be equidistant.

[0071] It is conceivable that the intensity of the individual pulses 22, as well as the interval between two temporally adjacent (or consecutive) individual pulses 22, can be set or varied as desired.

[0072] Figure 2 shows a diagram of several pulse-burst sequences 20 of the device 10 according to Figure 1, based on a first embodiment. The intensity 32 is plotted against the time 34 of the primary radiation 16.

[0073] Six pulse-burst sequences 20, each consisting of two individual pulses 22, are shown. All six pulse-burst sequences 20 are identical in design. The first individual pulse 22 of each pulse-burst sequence 20 has a (significantly) higher intensity 32 than the second individual pulse 22 that follows it. The duration of a pulse-burst sequence 20 is indicated by a double arrow and the reference symbol 15. The interval between two adjacent pulse-burst sequences 20 is indicated by a double arrow and the reference symbol 17. The duration of a single individual pulse 22 is indicated by two arrows and the reference symbol 19.

[0074] The duty cycle is formed here by the quotient between the time duration 15 of a pulse-burst train 20 and the time duration 17 and time duration 15 of a distance between the two adjacent pulse-burst trains 20 .

[0075] Figure 3 shows a diagram of several pulse-burst sequences 20 of the device 10 according to Figure 1, based on a second embodiment. Here too, the intensity 32 is plotted against the time 34 of the primary radiation 16.

[0076] Three pulse-burst trains 20, each consisting of twelve individual pulses 22, are shown. The first, third, fifth, seventh, ninth, and eleventh individual pulses 22 of each pulse-burst train 20 are identical in form and exhibit a (significantly) higher intensity than the second, fourth, sixth, eighth, tenth, and twelfth individual pulses 22 of the respective pulse-burst train 20. The second, fourth, sixth, eighth, tenth, and twelfth individual pulses 22 of the respective pulse-burst train 20 are identical in form.

[0077] The first and last pulse-burst trains 20 are identical in form. The individual pulses 22 of the second (or middle) pulse-burst train 20 each exhibit a higher intensity 32 than the individual pulses 22 of the first and last pulse-burst trains 20.

[0078] In the present case, the duration 15 of the respective pulse-burst trains 20 and the duration 17 of the respective intervals between two adjacent pulse-burst trains 20 are each indicated by a double arrow.

[0079] Figure 4 shows a diagram of a pulse-burst train 20 of the device 10 according to Figure 1 according to a third embodiment. Here too, the intensity 32 is plotted against the time 34 of the primary radiation 16.

[0080] A single pulse burst train 20 is depicted. Each pair of successive individual pulses 22 exhibits a different intensity 32. The preceding individual pulse 22 has a (significantly) higher intensity 32 than the subsequent individual pulse 22. In this case, the individual pulses 22 in the (temporal) middle of the pulse burst train 20 exhibit a higher intensity than the individual pulses 22 at the two (temporal) ends of the pulse burst train 20.

[0081] In the present case, the duration 15 of the individual pulse-burst train 20 is indicated by a double arrow.

[0082] The following describes a method for generating a

[0083] Secondary radiation 12 described:

[0084] The method comprises the following steps: Generating a primary radiation 16 in a burst-mode operation, in which several pulse-burst trains 20, each consisting of several individual pulses 22, are generated. Generating the secondary radiation 12 by directing the primary radiation 16 onto a secondary source 18, wherein a device 10 according to the above descriptions, in particular the device 10 shown in Figures 1 to 4, is used to carry out the method.

Claims

Patent claims 1. Device (10) for generating a burst in a secondary radiation (12) comprising: a primary source (14) for generating a primary radiation (16), a secondary source (18) for generating the secondary radiation (12), wherein the device (10) is configured such that the primary radiation (16) hits a target of the secondary source (18) and thereby generates the secondary radiation (12), wherein the primary source (14) is configured for burst-mode operation in which several pulse-burst trains (20), each consisting of several individual pulses (22), are generated, wherein the pulse-burst trains (20) each have a temporal length in the range of 50 ns to 1 s, in particular in the range of 1 ms to 500 ms.

2. Device (10) according to claim 1, characterized in that the primary source (14) comprises at least one ultrashort pulse laser beam source (24) with a master oscillator power amplifier laser architecture.

3. Device (10) according to claim 1 or 2, characterized in that the individual pulses (22) have a temporal length in a range of 5 fs to 5 ps.

4. Device (10) according to one of the preceding claims, characterized in that a number of the individual pulses (22) in a pulse-burst train (20) in a The range is from 2 to 10,000,000, especially 5,000-50,000.

5. Device (10) according to one of the preceding claims, characterized in that a duty cycle of a single pulse-burst train (20) divided by a time interval of the pulse-burst trains (20) is in a range of 50% to 0.1%.

6. Device (10) according to one of the preceding claims, characterized in that the repetition rate of the pulse-burst moves (20) is at least 10 Hz, especially in a range of 100 Hz to 10 MHz.

7. Device (10) according to one of the preceding claims, characterized in that the primary radiation (16) has a wavelength in a range of 1 pm to 2 pm, in particular greater than 2 pm.

8. Device (10) according to one of the preceding claims, characterized in that the primary source (14) comprises a laser-active medium, wherein the laser-active medium is doped with ytterbium, neodymium and / or thulium, in particular wherein the primary source (14) comprises at least one Yb:YAG laser, Nb:YAG laser and / or Tm:YAG laser.

9. Device (10) according to one of the preceding claims, characterized in that the secondary source (18) is configured to generate relativistic electrons by means of laser wakefield acceleration.

10. Device (10) according to one of the preceding claims, characterized in that the primary source (14) comprises at least one slab amplifier (26), in particular InnoSlab.

11. Device (10) according to one of the preceding claims, characterized in that the primary source (14) includes at least one compression stage (28) for spectral compression of the individual pulses (22).

12. Device (10) according to one of the preceding claims, characterized in that the primary source (14) comprises at least one nonlinear post-compression stage (30), wherein the nonlinear post-compression stage (30) is designed to add further spectral ranges to a spectrum of the individual pulses (22) by means of self-phase modulation and to compensate at least partially for the spectral temporal chirp of the individual pulses (22) by means of at least one dispersive element.

13. Device (10) according to one of the preceding claims, characterized in that the primary source (14) comprising at least one first optical pulse source and at least one second optical pulse source, each for generating single pulses (22), wherein the single pulses (22) of the first pulse source and the single pulses (22) of the second pulse source are spatially superimposed, temporally shifted relative to each other within a pulse-burst train (20), and the single pulses (22) of the second pulse source have a temporal length in the range of 5 fs and 1 ps and / or exhibit different spectral focus durations.

14. Device (10) according to one of the preceding claims, characterized in that the intervals between the individual pulses (22) are different.

15. Method for generating a burst in a secondary radiation (12) comprising the steps: Generating a primary radiation (16) in a burst-mode operation in which several pulse-burst trains (20) each consisting of several individual pulses (22) are generated; Generating the secondary radiation (12) by directing the primary radiation (16) onto a secondary source (18) , wherein a device (10) according to one of the preceding claims is used to carry out the method.

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