A laser driver module that generates a beam of multi-color driver pulses using fewer pump lasers

Abstract

At least one beam of the pump pulses is combined in a non-linear process with a plurality of monochromatic beams, each containing a signal pulse of a unique wavelength. This results in the generation of a population of pulse beams having intermediate-length wavelengths. Next, all the pulses in all the beams within this population are subjected to second harmonic generation, optical parametric amplification, sum frequency generation, or a combination thereof, and the wavelengths of those pulses are decreased to ultraviolet wavelengths, thereby creating driver pulses. Then, a driver beam composed of these wavelength-decreased driver pulses can be focused onto a fuel pellet.

Description

Technical Field

[0001] Government Rights This invention was made with government support under award number DE-NA0003856 awarded by the National Nuclear Security Administration of the Department of Energy and under award number DE-SC0021032 awarded by the Department of Energy's Office of Science. The government has certain rights in this invention.

[0002] This invention relates to inertial confinement fusion energy (IFE), and more particularly, to energy generated by laser-driven inertial confinement fusion. In its most direct sense, this invention relates to a laser driver module for use in generating fusion energy.

Background Art

[0003] Currently, inertial confinement fusion (ICF) is being studied as a power generation technology. In ICF, small fuel pellets are highly compressed to rapidly increase their temperature and pressure. The pellets implode, but a few nanoseconds before that, they generate energy by fusion. (Efforts are currently underway to determine whether it is commercially feasible to capture this energy and use it to supply power.) Compression of the pellets is achieved by focusing powerful laser energy onto the pellets. The device that generates the beam is called a driver, and the driver impinges a driver pulse on the fuel pellet. This invention is a module that generates a driver pulse having appropriate characteristics along with other similar ones.

Summary of the Invention

Problems to be Solved by the Invention

[0004] If the driver pulse is polychromatic, i.e., composed of laser pulses having many different wavelengths, it induces the implosion of the fuel pellet more efficiently. In conventional laser drivers, N lasers are required to generate a polychromatic driver pulse consisting of N pulses each having a different wavelength. High-energy lasers are expensive, and existing laser drivers (such as StarDriver) may have 10 4 or 10 5 laser drivers. It would be advantageous to provide a module for use in a laser driver that generates a polychromatic driver pulse using fewer lasers. **Means for Solving the Problem**

[0005] According to the present invention, at least one beam of the pump pulse is combined in a non-linear process with a plurality of monochromatic beams each containing a low-energy signal pulse of a different wavelength. Thereby, a beam of a population of high-energy pulses of different wavelengths is generated. Next, all the pulses within this population are subjected to second harmonic generation, sum frequency generation, or both, such that the wavelengths of the pulses in those beams are reduced to ultraviolet wavelengths, thereby creating the driver pulse. Then, the driver beam composed of these wavelength-reduced driver pulses can be focused onto the fuel pellet.

[0006] In a first preferred embodiment, the non-linear process is optical parametric amplification. In this process, the signal pulse is amplified, the pump pulse is depleted, and an idler pulse is generated. In subsequent processing steps, both the amplified signal pulse and the idler pulse are converted into ultraviolet driver pulses of different wavelengths.

[0007] In a second preferred embodiment, the non-linear process is itself second harmonic generation or sum frequency generation.

[0008] The first preferred embodiment is a module that can be replicated as needed to generate a driver beam of a driver pulse having the desired polychromatic characteristics.

[0009] The second preferred embodiment uses a single signal source that generates a multi-color primary beam of signal pulses and a plurality of pump sources, each including a pump laser. The signal pulses and the pump pulses are introduced into a matrix of a sum frequency generator. The matrix generates a plurality of driver beams including driver pulses.

[0010] In both preferred embodiments, the signal pulses and the pump pulses have wavelengths between infrared and ultraviolet, and the driver pulses have ultraviolet wavelengths.

[0011] The present invention will be better understood by reference to the following illustrative and non-limiting drawings.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0013] The figures described below are schematic and distances are not shown to scale. Similar reference numerals indicate similar reference numerals. Further, it will be understood that the laser pulses discussed herein must be precisely shaped to deliver energy with sufficient efficiency. Details of such shaping are not described.

[0014] The First Preferred Embodiment - Figure 1 The signal source, generally designated by reference numeral SS, includes a fiber laser 20 that provides a beam of pump seed signal for laser pump pulses. The pulses of this pump seed signal beam are amplified in a laser preamplifier 30 that supplies a second harmonic generator 40. The output of the second harmonic generator 40 is combined with a beam of laser signal seed pulses generated by a signal seed fiber laser 50. The superposition of these laser beams is input to one or more optical parametric amplifiers (OPA) 60. (If there are multiple OPAs, the OPAs are connected in series.) The OPA 60 generates a polychromatic primary beam of infrared signal pulses. Generating a polychromatic primary beam of infrared signal pulses is a function of the signal source SS. It will be understood that the signal source SS may be configured differently as long as it generates a polychromatic primary beam of infrared signal pulses. The configuration of the signal source SS is not part of the present invention.

[0015] The COPA / SFG pump source PS includes an ytterbium-based fiber laser 80 that generates a beam of pump seed signal. (Other lasers can also be used.) Currently, if a first preferred embodiment of the present invention is intended to be used in ICF, all of the laser amplifiers 30, 90, and 100 can advantageously be neodymium-doped glass adjusted to supply single-shot pulses having a wavelength of 1053 nm. Alternatively, if a first preferred embodiment is intended to be used in inertial fusion energy (IFE), all of the lasers 30, 90, and 100 can advantageously be ytterbium or neodymium-doped yttrium lithium fluoride adjusted to supply multi-Hz pulses having wavelengths of 1047 nm or 1018 nm, respectively. (Other configurations of lasers 30, 90, and 100 are also possible.) This beam is input to a laser preamplifier 90 that supplies a laser power amplifier 100. The beam output from the power amplifier 100 is input to a second harmonic generator 110.

[0016] The second harmonic generator 110 outputs a monochromatic beam including a monochromatic pump pulse having a wavelength between infrared and ultraviolet ( "mid-wavelength"). Generating this beam is a function of the pump source PS. It will be understood that the pump source PS may be configured differently as long as it generates a beam of pump pulses having a mid-wavelength. The configuration of the pump source PS is not part of the present invention. The beam of pump pulses generated by the pump source PS is time-multiplexed and also adjusted with the primary beam of signal pulses. These matters will be described later.

[0017] The polychromatic primary beam from the signal source SS (i.e., the polychromatic beam from the output of the OPA 60) is guided through the optical filter OF. In this example, the optical filter OF is composed of a plurality of filters OF1, OF2,...OF N1 In some embodiments, the filters are series-connected dichroic filters, and the number of filters OF1, OF2...OF N1 is selected to be equal to 1 / 2 of the number of driver pulses of different wavelengths that ultimately make up the polychromatic driver pulse supplied to the fuel pellet (not shown). In other words, if the laser driver is set to supply six different-wavelength driver pulses to the fuel pellet simultaneously, there are three dichroic filters OF1 to OF3. Each of the dichroic filters deflects the secondary beams SB1, SB2,...SB N1 of the signal pulses having a specific selected wavelength and passes all other components of the primary beam to the next dichroic filter SB1, SB2,...SB N1 Each of these secondary beams is monochromatic and contains signal pulses having a single unique wavelength, i.e., a wavelength different from all the wavelengths of the other secondary beams. In this example, the optical filter OF contains the same number of filters OF1, OF2,...OF N1 as the secondary beams SB1, SB2,...SB N1 but this is not necessary. In fact, it is possible to use a single filter as the only filter in the optical filter OF.

[0018] All of the pump beam of pump pulses from the pump source PS and all of the second-order beams of the signal pulses are input into a collinear optical parametric amplifier (COPA) 120. The COPA 120 has N stages C1, C2... C N1 and N1 is equal to the number of second-order beams from the signal source SS. Each stage C1, C2... C N1 is a crystal of, for example, lithium triborate, potassium dihydrogen phosphate (KDP), or potassium dihydrogen phosphate deuterated (DKDP). (Other materials are also possible.) When the pump pulse from the pulse source PS interacts with the signal pulse in one of the stages C1, C2... C N1 a non-linear interaction occurs, generating three pulses. One is the amplified signal pulse, another is the depleted pump pulse, and the third is the idler pulse having a frequency that is the difference in frequency between the signal pulse and the pump pulse. The amplified signal pulse and the idler pulse are paired. Both have a mid-wavelength.

[0019] As described above, one component of such each interaction is a signal pulse having a unique frequency, that is, a frequency different from the frequencies of all other signal pulses. Thus, each of the N stages C1, C2... C N1 within the COPA 120 will generate two beams including pairs of pulses of a unique wavelength, a beam composed of the amplified signal pulse and a beam composed of the idler pulse. Thus, the COPA 120 doubles the number of beams of unique frequencies from the multi-color beam generated by the signal source SS.

[0020] The multi-color pulse beam generated by the COPA 120 is then directed towards the timing stage 130. As will become clear below, the timing stage 130 makes it possible to synchronize the group of pump pulses with the groups of signal pulses and idler pulses within a subsequent multi-stage sum frequency generator SFG. First, the structure and operation of the sum frequency generator SFG will be generally described.

[0021] The sum frequency generator SFG has a plurality of stages S1, S2,... S connected in seriesN1 It includes. (The number of stages in the sum frequency generator SFG may be different from the number of stages in COPA 120.) Each of the stages S1, S2,... S N1 is, for example, a crystal of lithium triborate, potassium dihydrogen phosphate, or potassium dihydrogen phosphate-d. (Other materials are also possible.) Each beam pair, that is, the pair of the amplified signal pulse and the idler pulse, interacts with the pump pulse in one of the stages S1, S2,... S N1 In this non-linear interaction, the amplified signal pulse and the idler pulse are converted into two new ultraviolet driver pulses. One of these driver pulses has a frequency equal to the sum of the frequencies of the original amplified signal pulse and the pump pulse, and the other driver pulse has a frequency equal to the sum of the frequencies of the idler pulse and the pump pulse. Therefore, in this first preferred embodiment, the infrared signal pulses and pump pulses generated by lasers 20 and 80 are used to create ultraviolet driver pulses. The ultraviolet pulses are more suitable for use as driver pulses. The ultraviolet pulses deliver more useful energy to the fuel pellet than the infrared pulses.

[0022] As described above, the timing stage 130 is arranged between the COPA 120 and the sum frequency generator SFG. This is necessary because the paired amplified signal pulse and idler pulse must reach the sum frequency generator simultaneously with the corresponding SFG pump pulse. The timing stage 130 can include two or more dichroic mirrors 132 and 134 (two are shown for simplicity) but may not include them, and the paired amplified signal pulse, idler pulse, and SFG pump pulse are adjusted so that they can catch up with each other and enter the sum frequency generator SFG simultaneously.

[0023] As described above, the pump source PS time-division multiplexes the generation of pump pulses. This is necessary because the pump pulses are used at different positions at different times. The first group of pump pulses is used to generate pairs of amplified signal pulses and idler pulses in the COPA 120, and subsequent groups of pump pulses are used to generate driver pulses in the sum frequency generator SFG. Further, the generation of pump pulses by the pump source PS and the generation of signal pulses by the signal source SS must be synchronized so that the interaction between them can occur as intended. The multiplexing and synchronization means 136 (including a computer system) is operably connected to both the pump source PS and the signal source SS to perform these functions. (For clarity, the stages C1, C2... C N1 of the COPA 120 are shown phase-matched only for a single pair of amplified signal pulses and idler pulses. It may be possible to configure these stages C1, C2... C N1 to function for two or more such pairs.) The driver pulses exiting the sum frequency generator SFG are directed towards the optical output port 138. Upon exiting the optical output port, the driver pulses enter the beam delivery and demultiplexing system 140.

[0024] Since the driver pulses exiting the sum frequency generator SFG are temporally separated, the beam delivery and demultiplexing system 140 is required. It will be recalled that in order to most efficiently transfer energy to the target pellet, the groups of driver pulses must be combined into a single multi-color pulse. To achieve this, a pair of beamline filters is used to create beamlines of different lengths. The beamline filters are adjusted to cause the previously generated driver pulses to travel in a beamline that is longer than the beamline for the subsequently generated driver pulses. Thus, for example, a driver pulse of one color is generated at time t1, a driver pulse of a second color is generated at a later time t2, and a driver pulse of a third color is generated at a still later time t N Let us assume. Dichroic mirrors D1, D2,... D NPairs guide these driver pulses along beamlines BL1, BL2, ... BL N The driver pulse generated at time t1 is advanced along the longest beamline BL1 and thus takes the longest time to reach the output of system 140. The driver pulse generated at time t2 is advanced along the shorter beamline BL2 and thus takes less time to reach the output of system 140. And the driver pulse generated at time t N advances along an even shorter beamline BL N and thus takes even less time to reach the output of system 140. By appropriately adjusting the lengths of beamlines BL1, BL2, ... BL N , all driver pulses can reach the output of system 140 substantially simultaneously.

[0025] In this first preferred embodiment, system 140 is disposed after output port 138. This is a design choice and is not essential.

[0026] Second harmonic generator 110, collinear optical parametric generator 120, and sum frequency generator SFG do not operate at 100% efficiency. Residual pump power can be recovered using a photovoltaic device and reused to generate inertial fusion energy (i.e., improve the optical - electrical "wall plug" efficiency of the laser driver), or the photoelectric power can be used to preheat the working fluid in the fusion plant in the form of cogeneration (i.e., improve the overall efficiency of the fusion plant). Importantly, this approach does not require additional power to manage the heat load required by other laser driver approaches.

[0027] The Second Preferred Embodiment - Figure 2 The second preferred embodiment shown in FIG. 2 is different from the first preferred embodiment shown in FIG. 1 but is basically similar. The second preferred embodiment is similar to the signal source SS and has a signal source injection that generates a multi-color signal beam including multi-color signal pulses. This beam operates in the same way as the optical filter OF operates, that is, a plurality of secondary single-color beams B1, B2,... B N are directed towards an optical filter (not shown) that creates

[0028] However, while the first preferred embodiment uses a single pump source PS, the second preferred embodiment uses a plurality (here three are shown, but not limited to this, and any number can be used) of parallel pump sources PS A PS B ... PS N The pump pulses generated by each of the pump sources PS A PS B ... PS N are both single-color and unique, that is, the pump pulse generated by the pump source PS A has a wavelength different from the wavelengths of the pump pulses generated by the pump sources PS B and PS C

[0029] The pump sources PS A PS B ... PS M may optionally differ from the pump source PS in two other respects. Here, each of the pump sources PS A PS B ... PS M is a diode-pumped solid-state laser. (Materials suitable for these pump sources are shown in FIG. 2, but other materials may also be suitable.) Also, in the first embodiment, the pump source PS includes a second harmonic generator 110. In this second preferred embodiment, each pump source PS A PS B ... PS N ​is connected to three second harmonic / sum frequency generation matrices, one of which has the first second harmonic generator and the other two do not. For example, each pump source is connected to matrices M1, M2, and MM. Second harmonic generation or sum frequency generation generated a mid-wavelength pump beam that pumps the serially connected sum frequency generators. For example, matrix M1 has the first second harmonic generator SHG1 followed by serially connected sum frequency generators SFG111, SFG112, and SFG11N. M1 also has two sum frequency generators SFG12 and SFG13 that create two different pump wavelengths by mixing the output of pump laser DPSSL-1 (connections not shown in FIG. 2 for clarity) with DPSSL-2 and DPSSL-M, respectively.

[0030] Each of the secondary beams is supplied to nine sum frequency generators. For example, secondary beam B1 is supplied to sum frequency generators SFG111, SFG121, SFG131, SFG221, SFG211, SFG231, SFGMM1, SFG2M1, and SFG1M1. It will be apparent that the matrix configuration of the second preferred embodiment generates N×M driver pulses, scales well, and can be more multi-color than that generated by the first preferred embodiment. As shown, using three different injection wavelengths and three different high-energy pump lasers, this embodiment generates nine different wavelengths in nine output beams, each consisting of three time-multiplexed pulses.

[0031] As shown, the second preferred embodiment has three beam transmission and demultiplexing systems 140A, 140B, and 140C, which operate in the same manner as system 140. All of these systems 140A, 140B, and 140C supply the optical output port 138A.

[0032] As described above, the preferred embodiments of the present invention have been described, but this description is not limiting and is merely illustrative. The scope of the present invention is defined only by the following claims.

Claims

1. A method for generating a multi-color driver pulse for use in generating fusion energy, comprising: a) combining at least one beam of infrared pump pulses with a plurality of monochromatic beams each containing a signal pulse of a unique wavelength in a non-linear process to generate a population of beams containing pulses; and b) reducing the wavelength of all the pulses in all the beams within the population to an ultraviolet wavelength using second harmonic generation, sum frequency generation, or both. A method as described above.

2. The method according to claim 1, wherein the combining step is performed in a collinear optical parametric amplifier.

3. The method according to claim 1, wherein the combining step is performed in a second harmonic generator or a sum frequency generator.

4. The method according to claim 1, wherein the combining step is performed in a matrix of sum frequency generators composed of serially connected sum frequency generators.

5. A laser driver module for generating fusion energy, comprising: a) a signal source for generating a multi-color primary beam of N time-multiplexed multi-color signal pulses; and b) An optical filter that separates the multi-color signal pulses in the primary beam into monochromatic secondary beams of a plurality of N １ signal pulses, each secondary beam including a monochromatic signal pulse having a single wavelength different from the wavelengths of the signal pulses in all other secondary beams; c) a pump source for generating a monochromatic beam of pump pulses. d) A multi-stage collinear optical parametric amplifier, wherein the optical parametric amplifier has N １ stages, and each stage includes a non-linear optical element that receives a unique one of the monochromatic second-order beams of the pump pulse beam and the N １ signal pulse beams, a multi-stage collinear optical parametric amplifier; e) multiplexing and synchronization means operably connected to the signal source and the pump source, the multiplexing and synchronization means causing the signal source to generate a primary beam of time-division multiplexed signal pulses and the pump source to generate a beam of 2N １ time-division multiplexed pump pulses, N １ of which pulses are used in the optical parametric amplifier and N １ of which pulses are used in a sum-frequency generator arranged downstream of the optical parametric amplifier, synchronizing the generation of the signal pulses and the generation of the pump pulses so as to simultaneously receive a signal pulse and a pump pulse corresponding to each stage of the optical parametric amplifier, thereby generating an amplified signal pulse paired with an idler pulse, multiplexing and synchronization means; f) An N-stage sum frequency generator arranged downstream of the optical parametric amplifier, where each of the N stages receives a unique pair of an amplified signal and an idler pulse together with a pump pulse and includes a non-linear optical element that generates 2N unique driver pulses of a short wavelength. The N-stage sum frequency generator; ２ and ２ ２ ２ ​​​ g) inserted between the optical parametric amplifier and the sum frequency generator, and delays the pump pulse to temporally synchronize the pump pulse with N pairs of an amplified signal and an idler pulse for sum frequency generation, a time delay stage, ２ and h) the 2N ２ synchronizing and combining means for receiving the individual short-wavelength pulses and synchronizing and combining them so as to reach the optical output simultaneously for all of them A laser driver module as described above.

6. The driver module according to claim 5, wherein the signal pulses in the primary beam have an infrared wavelength, the beam of pump pulses has a mid-wavelength, and the laser driver pulse has an ultraviolet wavelength.

7. The driver module according to claim 5, wherein the primary beam is output from a non-linear optical parametric amplifier within the signal source.

8. The N of the collinear optical parametric amplifier １ The driver module according to claim 5, wherein the N stages are connected in series.

9. The N of the sum frequency generator ２ The driver module according to claim 5, wherein the N stages of the sum frequency generator are connected in series, each stage outputs a unique pair of laser driver pulses, and each pair includes a signal pulse and an idler pulse.

10. The N ２ There is an optical path between each of the non-linear optical elements in the sum frequency generator and the optical output means, and the synchronization of the laser driver pulses is achieved by selectively changing the lengths of the respective optical paths. The driver module according to claim 5.

11. The driver module according to claim 5, wherein each optical path includes a beam line filter and a beam line extending from the beam line filter to the optical output means.

12. The driver module according to claim 5, wherein the beam line filter is a grating or a dichroic mirror or a polarizer.

13. The driver module according to claim 5, wherein the pump pulse is generated by a single laser system operating at a wavelength of 1053 nm or 1047 nm.

14. The driver module according to claim 5, wherein the non-linear optical element is made of lithium triborate, potassium dihydrogen phosphate, or deuterated potassium dihydrogen phosphate.

15. The optical synchronization means is N ２ The driver module according to claim 5, comprising N dichroic mirrors or wavelength selection elements.

16. The driver module according to claim 5, wherein each optical path includes a dichroic mirror.

17. The driver module according to claim 5, wherein the pump source comprises exactly one pump laser.

18. N １ is N ２ The driver module according to claim 5, which is equal to

19. N １ and N ２ The driver module according to claim 5, wherein they are not equal and can be less than N.

20. A laser driver for generating fusion energy, comprising: a) a signal source for generating a multi-color primary beam of multi-color signal pulses; b) an optical filter for separating the multi-color signal pulses in the primary beam into a plurality of N single-color secondary beams of signal pulses, each secondary beam including a single-color signal pulse having a single wavelength different from the wavelengths of the signal pulses in all other secondary beams; c) a plurality of M pump sources, each pump source generating a beam of pump pulses; d) a plurality of sum-frequency generator matrices each composed of a plurality of sum-frequency generators connected in series, each sum-frequency generator receiving a beam of pump pulses from one of the pump sources and a single-color secondary beam of signal pulses; e) means for time-synchronizing the ultraviolet driver pulses from the sum-frequency generator matrix. A laser driver.

21. A method for generating short-wavelength driver pulses for use in generating fusion energy, comprising: a) using a signal source to generate a multi-color primary beam of signal pulses; b) using only one pump laser to generate a temporally multiplexed beam of pump pulses; c) non-linearly interacting the single-color signal pulses from the multi-color primary beam with specific pump pulses, each such interaction generating an amplified signal pulse paired with an idler pulse; d) generating short-wavelength driver pulses by non-linearly interacting the paired amplified signal pulse and idler pulse with a pump pulse; e) simultaneously arriving the driver pulses at a target position. A method.

22. The method according to claim 21, wherein the non-linear interaction between the single-color signal pulse and the pump pulse occurs in an optical parametric amplifier.

23. The method according to claim 21, wherein the non-linear interaction of the amplified signal pulse, the idler pulse, and the pump pulse occurs in a sum-frequency generator.

24. A method for generating short-wavelength driver pulses for use in generating fusion energy, a) generating a first group and a second group of pump pulses using only one pump laser; b) using the pump pulses of the first group in a collinear optical parametric amplifier; c) using the pump pulses of the second group in a sum frequency generator disposed downstream of the collinear optical parametric amplifier; d) synchronizing the driver pulses output from the sum frequency generator to reach a target position simultaneously; A method comprising the steps above.

Images