Method for producing fine particle, and system for producing fine particle

Abstract

To provide a method for producing fine particles and a system for producing fine particles which enable the production of fine particles with increased efficiency.SOLUTION: A method for producing fine particles includes an irradiation step for generating fine particles by irradiating a solution 20, mixed with a precursor containing metal atoms, with a first femtosecond pulse laser beam 11 and a second femtosecond pulse laser beam 12 via separate optical paths. For example, the irradiation step comprises: a first irradiation step of applying the first femtosecond pulse laser beam 11 to the solution 20; and a second step of subjecting the solution 20, irradiated in the first irradiation step, to the second femtosecond pulse laser beam 12.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method and a system for producing fine particles. [Background technology]

[0002] It is known that by creating structures using fine particles such as nanoparticles (NPs), phenomena that do not exist in nature can be generated. For example, methods for producing high-performance fine particles have been proposed in order to put the use of fine particles into practical use in thermoelectric conversion elements that do not require a large temperature difference (for example, Patent Documents 1 and 2).

[0003] Patent Document 1 discloses a method for producing nanoparticles, which includes a stirring step of mixing and stirring a base solvent containing metal nanoparticles with a solvent containing a dispersant to form coated nanoparticles in which some of the metal nanoparticles are coated with the dispersant, and a separation step of immersing the coated nanoparticles in the solvent and separating the metal nanoparticles contained in the base solvent from the coated nanoparticles.

[0004] Patent Document 2 discloses a method for producing nanoparticles, which includes a production step of irradiating a base solvent containing a precursor with a femtosecond pulse laser to produce nanoparticles, the production step including an irradiation step of irradiating the base solvent with the femtosecond pulse laser, an acquisition step of acquiring color information of the base solvent irradiated with the femtosecond pulse laser, and a setting step of setting irradiation conditions for the femtosecond pulse laser based on the color information. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6781438 [Patent Document 2] International Publication No. 2022 / 249982 Summary of the Invention [Problem to be solved by the invention]

[0006] Here, while there are high expectations for the use of fine particles, the inability to efficiently generate fine particles has been cited as a problem. In this regard, Patent Document 1 discloses a method for efficiently separating metal nanoparticles from metal nanoparticles on which a coating has been formed, but does not disclose an efficient method for producing fine particles. For this reason, the technology disclosed in Patent Document 1 makes it difficult to efficiently generate fine particles such as metal nanoparticles.

[0007] In addition, the method disclosed in Patent Document 2 discloses a method for setting irradiation conditions that assumes color information. Therefore, with the technology disclosed in Patent Document 2, it is difficult to efficiently generate fine particles such as nanoparticles when the irradiation conditions when color information cannot be acquired or the irradiation conditions before color information is acquired are also taken into consideration.

[0008] The present invention has been devised in view of the above-mentioned problems, and an object of the present invention is to provide a method and system for producing fine particles that can improve the efficiency of producing fine particles. [Means for solving the problem]

[0009] The method for producing microparticles according to the first invention is a method for producing microparticles using a femtosecond pulsed laser, and is characterized by comprising an irradiation step of irradiating a solution containing a precursor containing metal atoms with a first femtosecond pulsed laser beam and a second femtosecond pulsed laser beam, each via a different optical path, to generate microparticles.

[0010] The method for producing microparticles according to the second invention is characterized in that, in the first invention, the irradiation step includes a first irradiation step of irradiating the solution with the first femtosecond pulsed laser light, and a second irradiation step of irradiating the solution irradiated by the first irradiation step with the second femtosecond pulsed laser light.

[0011] The method for producing microparticles according to the third invention is characterized in that, in the second invention, the precursor contains metal ions or complex ions, the first irradiation step generates plasma in the solution by the first femtosecond pulsed laser light to generate intermediate particles based on the precursor, and the second irradiation step generates the microparticles by miniaturizing the intermediate particles by generating self-focusing of the second femtosecond pulsed laser light in the solution, and a plasma region where the plasma is generated is adjacent to or overlaps with a self-focusing region where the self-focusing occurs.

[0012] The fourth invention relates to a method for producing a microparticle, and is characterized in that, in the third invention, the first femtosecond pulsed laser light and the second femtosecond pulsed laser light are irradiated in directions opposite to each other, and the plasma region and the self-focusing region are adjacent to each other.

[0013] The method for producing a microparticle according to the fifth aspect of the present invention is characterized in that, in any one of the first to fourth aspects of the present invention, the first femtosecond pulsed laser light and the second femtosecond pulsed laser light are beams branched from an oscillating light beam of one femtosecond pulsed laser device.

[0014] The method for producing a microparticle according to the sixth invention is characterized in that, in any one of the first to fourth inventions, the optical axis of the first femtosecond pulsed laser beam coincides with the optical axis of the second femtosecond pulsed laser beam.

[0015] A seventh aspect of the present invention relates to a method for producing a microparticle according to any one of the first to fourth aspects of the present invention, wherein the irradiation step is performed by setting the output of the first femtosecond pulsed laser beam and the second femtosecond pulsed laser beam to 0.7 mW or more and setting the laser fluence to 1.0 kJ / cm. 2 As described above, the solution is irradiated.

[0016] The method for producing microparticles according to the eighth invention is characterized in that, in any one of the first to fourth inventions, the irradiation step comprises irradiating the solution with one or more femtosecond pulsed laser beams different from the first femtosecond pulsed laser beam and the second femtosecond pulsed laser beam from different positions to generate the microparticles.

[0017] The method for producing microparticles according to the ninth invention is characterized in that, in any one of the second to fourth inventions, the irradiation step uses a flow path in which the solution flows from upstream to downstream, and sets the irradiation position of the second femtosecond pulsed laser light downstream of the flow path relative to the irradiation position of the first femtosecond pulsed laser light.

[0018] A tenth aspect of the present invention provides the method for producing a microparticle according to the ninth aspect of the present invention, wherein the intensity of the first femtosecond pulsed laser beam is greater than the intensity of the second femtosecond pulsed laser beam.

[0019] The method for producing microparticles according to an eleventh aspect of the present invention is characterized in that, in the first aspect of the present invention, the irradiation step includes splitting an oscillation light of one femtosecond pulsed laser device into the first femtosecond pulsed laser light and the second femtosecond pulsed laser light, and irradiating the solution with the first femtosecond pulsed laser light and the second femtosecond pulsed laser light after passing through different optical paths.

[0020] The method for producing a microparticle according to the 12th invention is characterized in that, in the 11th invention, a difference between the optical path length of the first femtosecond pulsed laser beam and the optical path length of the second femtosecond pulsed laser beam indicates a distance at which they do not interfere with each other.

[0021] The method for producing microparticles according to the thirteenth invention is any one of the first to fourth inventions, characterized in that the irradiation step splits the oscillation light of one femtosecond pulsed laser device into the first femtosecond pulsed laser light and the second femtosecond pulsed laser light via a plurality of focusing lenses that focus only components in one direction, focuses the first femtosecond pulsed laser light at a first focal position of one of the focusing lenses in the solution, and focuses the second femtosecond pulsed laser light at a second focal position of another of the focusing lenses in the solution that is different from the first focal position.

[0022] The system for producing microparticles according to the fourteenth invention is a system for producing microparticles using a femtosecond pulsed laser, characterized in that it comprises a container containing a solution containing a mixture of precursors containing metal atoms, and an optical unit that controls the irradiation directions of a first femtosecond pulsed laser beam and a second femtosecond pulsed laser beam so that they are irradiated onto the container via different optical paths.

[0023] The microparticle manufacturing system of the 15th invention is characterized in that, in the 14th invention, the container includes a flow path through which the solution flows, and the optical unit controls the irradiation position of the second femtosecond pulsed laser light to be downstream of the flow path relative to the irradiation position of the first femtosecond pulsed laser light.

[0024] A fine-particle manufacturing system according to a sixteenth aspect of the present invention is the fourteenth aspect of the present invention, characterized in that the optical section includes one wave plate and two polarizing beam splitters, each of which is coaxially arranged. Effect of the Invention

[0025] According to the first to thirteenth inventions, the irradiation step irradiates the solution with a first femtosecond pulsed laser beam and a second femtosecond pulsed laser beam via different optical paths to generate microparticles. Therefore, a plurality of irradiation conditions suitable for each microparticle generation process can be set using each laser beam. This makes it possible to improve the efficiency of microparticle generation.

[0026] In particular, according to the second invention, in the second irradiation step, the solution irradiated in the first irradiation step is irradiated with a second femtosecond pulsed laser beam. That is, intermediate particles generated based on precursors by the first femtosecond pulsed laser beam are irradiated with a second femtosecond pulsed laser beam, and fine particles can be generated based on the intermediate particles. Therefore, the process of generating fine particles from intermediate particles can be accelerated compared to the case where one femtosecond pulsed laser beam is used. This makes it possible to further improve the efficiency of generating fine particles.

[0027] In particular, according to the third aspect of the present invention, the plasma region where plasma is generated is adjacent to or overlaps with the self-convergence region where self-convergence occurs. In other words, intermediate particles generated based on the precursor in the plasma region can be easily made to flow to the self-convergence region. Therefore, fine particles can be smoothly generated based on the intermediate particles in the self-convergence region. This makes it possible to further improve the efficiency of fine particle generation.

[0028] In particular, according to the fourth aspect of the present invention, the first femtosecond pulsed laser beam and the second femtosecond pulsed laser beam are irradiated in opposing directions, and the plasma region and the self-focusing region are close to each other. Therefore, compared to a case where the two laser beams do not face each other or the plasma region and the self-focusing region are not close to each other, the reduction period and the ablation period can be shortened, and fine particles can be generated in a short time. This makes it possible to further improve the efficiency of generating fine particles.

[0029] In particular, according to the fifth aspect of the present invention, the first femtosecond pulsed laser beam and the second femtosecond pulsed laser beam are beams branched from an oscillation beam of a single femtosecond pulsed laser device, which makes it possible to reduce the introduction cost and the operation cost of the device compared to the case where a femtosecond pulsed laser device is provided for each laser beam.

[0030] In particular, according to the sixth aspect of the present invention, the optical axis of the first femtosecond pulsed laser beam coincides with the optical axis of the second femtosecond pulsed laser beam. Therefore, it is possible to suppress variations in setting the irradiation position compared to a case where the optical axes of the laser beams are not coincident. This makes it possible to improve the reproducibility in generating microparticles.

[0031] In particular, according to the seventh aspect of the present invention, the irradiation step includes setting the output of the first femtosecond pulsed laser beam and the second femtosecond pulsed laser beam to 0.7 mW or more and the laser fluence to 1.0 kJ / cm. 2 The solution is irradiated with the above-mentioned plasma. This makes it easier to generate sufficient plasma to cause a reduction reaction when generating fine particles, thereby further improving the efficiency of generating fine particles.

[0032] In particular, according to the eighth aspect of the present invention, the irradiation step irradiates the solution with one or more femtosecond pulsed laser beams different from the first femtosecond pulsed laser beam and the second femtosecond pulsed laser beam from different positions to generate microparticles. This makes it possible to set a plurality of irradiation conditions more suitable for each microparticle generation process. This enables more efficient generation of microparticles.

[0033] In particular, according to the ninth aspect of the present invention, the irradiation step sets the irradiation position of the second femtosecond pulsed laser beam downstream of the irradiation position of the first femtosecond pulsed laser beam in the flow path. This makes it easier for the solution to be irradiated with a laser beam suitable for each microparticle generation process. This makes it possible to further improve the efficiency of microparticle generation.

[0034] In particular, according to the tenth aspect of the present invention, the intensity of the first femtosecond pulsed laser beam is stronger than the intensity of the second femtosecond pulsed laser beam. That is, the intensity of the irradiated laser beam can be gradually weakened along the microparticle generation process. Therefore, in the latter half of the microparticle generation process, unnecessary reactions caused by excessive irradiation of the laser beam can be suppressed. This makes it possible to further improve the efficiency of microparticle generation.

[0035] In particular, according to the eleventh aspect of the present invention, the irradiation step irradiates the solution with a first femtosecond pulsed laser beam and a second femtosecond pulsed laser beam along the same optical axis and direction after passing through different paths. Therefore, two types of pulses can be generated in an irradiation area along one axis, and the expansion of the irradiation area can be suppressed. This makes it possible to improve the production efficiency of fine particles while suppressing the increase in size of the production equipment, etc.

[0036] In particular, according to the twelfth aspect of the present invention, the difference between the optical path length of the first femtosecond pulsed laser beam and the optical path length of the second femtosecond pulsed laser beam indicates a distance at which they do not interfere with each other. This makes it possible to maintain the non-thermal effect, which is a feature of the femtosecond pulsed laser. This makes it possible to improve the efficiency of generating fine particles while suppressing the effects of heat caused by laser irradiation.

[0037] In particular, according to the thirteenth aspect of the present invention, the irradiation step focuses the first femtosecond pulsed laser beam at a first focal position in the solution, and focuses the second femtosecond pulsed laser beam at a second focal position different from the first focal position in the solution. This makes it possible to independently control a plurality of microparticle generation regions. This makes it possible to further improve the efficiency of microparticle generation.

[0038] According to the fourteenth to sixteenth inventions, the optical unit controls the irradiation directions of the first femtosecond pulsed laser beam and the second femtosecond pulsed laser beam so that they are irradiated onto the container via different optical paths. Therefore, a plurality of irradiation conditions suitable for each microparticle generation process can be set using each laser beam. This makes it possible to improve the efficiency of microparticle generation.

[0039] In particular, according to the fifteenth aspect of the present invention, the optical unit controls the irradiation position of the second femtosecond pulsed laser beam to be downstream of the irradiation position of the first femtosecond pulsed laser beam in the flow path. This makes it easier for the solution to be irradiated with a laser beam suitable for each microparticle generation process. This makes it possible to further improve the efficiency of microparticle generation.

[0040] In particular, according to the sixteenth aspect of the present invention, the optical unit includes one wave plate and two polarizing beam splitters, each of which is arranged coaxially. Therefore, two types of pulses can be generated for an irradiation area along one axis, and the expansion of the irradiation area can be suppressed. This makes it possible to improve the efficiency of generating fine particles while suppressing the increase in size of the manufacturing equipment, etc. [Brief description of the drawings]

[0041] [Figure 1] FIG. 1(a) is a schematic diagram showing an example of a method for producing microparticles according to the first embodiment, and FIG. 1(b) is a schematic diagram showing a first modified example of the method for producing microparticles according to the first embodiment. [Diagram 2] FIG. 2 is a schematic diagram showing a second modified example of the method for producing fine particles according to the first embodiment. [Diagram 3] FIG. 3 is a diagram showing the relationship between the irradiation time and the measured value of absorbance. [Figure 4] FIG. 4 is a schematic diagram showing an example of the configuration of a microparticle production system according to the first embodiment. [Diagram 5] FIG. 5 is a schematic diagram showing an example of a method and system for producing fine particles according to the second embodiment. [Figure 6] FIG. 6 is a schematic diagram showing a first modified example of the fine particle production method and production system according to the second embodiment. [Figure 7] FIG. 7 is a schematic diagram showing an example of a method and system for producing fine particles according to the third embodiment. [Figure 8] Figure 8(a) is a schematic diagram showing an example of a microparticle manufacturing method and manufacturing system according to the fourth embodiment before switching of the irradiation light, and Figure 8(b) is a schematic diagram showing an example of a first variant of the microparticle manufacturing method and manufacturing system according to the fourth embodiment after switching of the irradiation light. [Figure 9] FIG. 9 is a schematic diagram showing an optical system using a diffractive optical element as a second modified example of the fine particle production method and production system according to the fourth embodiment. [Figure 10] FIG. 10 is a schematic diagram showing an example of a method for converting the intensity distribution of femtosecond pulsed laser light as a third modified example of the fine particle production method and production system according to the fourth embodiment. [Figure 11] FIG. 11 is a schematic diagram showing an example of a method and system for producing fine particles according to the fifth embodiment. [Figure 12] FIG. 12 is a schematic diagram showing an example of a method and system for producing fine particles according to the sixth embodiment. [Figure 13] 13(a) is a schematic side view corresponding to FIG. 12, and FIG. 13(b) is a schematic plan view corresponding to FIG. [Figure 14] Figure 14(a) is a schematic cross-sectional view showing an irradiation area of ​​femtosecond pulsed laser light at the AA section of Figure 13(a), Figure 14(b) is a schematic cross-sectional view showing an irradiation area of ​​femtosecond pulsed laser light at the BB section of Figure 13(b), and Figure 14(c) is a schematic cross-sectional view showing an irradiation area of ​​femtosecond pulsed laser light at the CC section of Figure 13(b). [Figure 15] FIG. 15 is a schematic diagram showing the principle of the method for producing fine particles. [Figure 16] FIG. 16 is a diagram showing the relationship between the irradiation time and the measured value of absorbance in the comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] Hereinafter, an example of a method for producing fine particles and a system for producing fine particles according to an embodiment of the present invention will be described with reference to the drawings.

[0043] (First embodiment: Method for producing fine particles) The method for producing fine particles according to this embodiment uses a femtosecond pulse laser. The fine particles include a plurality of particles having a particle diameter of, for example, 1 nm or more and 100 nm or less. The fine particles may include particles having a particle diameter of, for example, a median diameter (median diameter: D50) of 1 nm or more and 50 nm or less, and may also include particles having an average particle diameter of, for example, 1 nm or more and 50 nm or less. In the following description, "intermediate particles" are used to refer to intermediate substances used in producing fine particles. Intermediate particles refer to substances having a larger median diameter or average particle diameter than the fine particles that are finally produced, and the particle diameter of the intermediate particles may be within the above range, for example.

[0044] The median diameter or average particle diameter can be measured, for example, by using a particle size distribution measuring instrument, such as a known particle size distribution measuring instrument using a dynamic light scattering method (e.g., Zetasizer Ultra manufactured by Malvern Panalytical, etc.).

[0045] First, the principle of a method for producing nanoparticles (NP: Nano Particles) by irradiating a solution 20 containing a mixture of precursors containing metal ions or complex ions with femtosecond pulsed laser light will be described with reference to Fig. 15 and Fig. 16. In the following description, femtosecond pulsed laser light may be simply referred to as laser light.

[0046] For example, as shown in Fig. 15, when a solution 20 in which multiple metal ions are dissolved is irradiated with femtosecond pulsed laser light 1, plasma is generated in the region shown by the approximately rectangular shape in the figure. In addition, the optical Kerr effect occurs with the generation of plasma, and thus a self-convergence phenomenon occurs in which the femtosecond pulsed laser light 1 repeatedly converges as if there were a convex lens (Kerr lens) in multiple approximately elliptical regions continuing in one direction from the approximately rectangular region in the figure. In addition, self-phase modulation also occurs at the same time as the self-convergence phenomenon occurs.

[0047] In the generated plasma, intermediate particles of the alloy are generated by a reduction reaction in the area with the highest brightness. At this time, the outer diameter of the intermediate particles is, for example, about 1 nm to 20 nm. The generated intermediate particles move within the solution 20, for example, by stirring the solution 20, and are miniaturized by a laser ablation reaction that occurs when the intermediate particles are irradiated again with the femtosecond pulse laser beam 1, generating fine particles with an outer diameter of about 2 nm.

[0048] Fig. 16 is data showing the relationship between the irradiation time of the femtosecond pulsed laser beam 1 shown in Fig. 15 and the measurement value (absorbance). As shown in Fig. 16, the period from the start of irradiation with the femtosecond pulsed laser beam 1 during which the absorbance of the solution 20 rises steeply is considered to be the reduction period, and the period during which the absorbance reaches its maximum value and then gradually decreases to reach a convergence state is considered to be the ablation period.

[0049] Here, the inventors have found that, as one method for improving the production efficiency of fine particles, it is desirable for the absorbance shown in FIG. 16 to rise more steeply and reach a convergent state more quickly.

[0050] 1(a) and 1(b) are schematic diagrams showing a method for producing fine particles according to the present embodiment. The method for producing fine particles includes an irradiation step.

[0051] In the irradiation step, a first laser beam 11 (first femtosecond pulsed laser beam 11) and a second laser beam 12 (second femtosecond pulsed laser beam 12), which are oscillation beams of a femtosecond pulsed laser, are irradiated onto a solution 20 containing a mixture of precursors via different optical paths to generate microparticles. In this case, a plurality of irradiation conditions suitable for each microparticle generation process can be set using each of the laser beams 11 and 12. This makes it possible to improve the efficiency of generating microparticles.

[0052] In the irradiation step, for example, as shown in FIG. 1(a), two laser beams 11 and 12 are irradiated so as to face each other. High-luminance plasma regions 100a and 100b formed by the two laser beams 11 and 12 are close to each other. As in the description of FIG. 15, the substantially rectangular regions in FIG. 1(a) indicate the plasma regions 100a and 100b, and a plurality of substantially elliptical regions continuing in one direction from the plasma regions 100a and 100b indicate self-focused regions or self-phase-modulated regions for the two laser beams 11 and 12, respectively. Here, for example, when the output of each of the two laser beams 11 and 12 is 0.7 mW or more and the laser fluence is 1.0 kJ / cm2, 2 In the case where the above ratio is satisfied, it is possible to easily generate sufficient plasma to cause a reduction reaction when generating the particles, thereby making it possible to further improve the efficiency of generating the particles.

[0053] 2 shows a state in which the second laser beam 12 is decentered compared to FIG. 1(a) in order to make it easier to understand the relative positional relationship between the two laser beams 11 and 12. This shows the state before the two laser beams 11 and 12 are irradiated in opposite directions.

[0054] By adjusting the focusing positions of the two laser beams 11 and 12, the plasma region 100a generated by the first laser beam 11 and the plasma region 100b generated by the second laser beam 12 are brought closer to each other and are formed so as to at least partially overlap each other, as shown in FIG. 1(b).

[0055] Fig. 3 shows data indicating the relationship between the irradiation time of the femtosecond pulse laser and the measurement value (absorbance) in the irradiation step. That is, the data shown is obtained when irradiating with the two laser beams 11 and 12 shown in Fig. 1(a) and Fig. 1(b). The data in Fig. 3 can be obtained by measuring the solution 20 using an ultraviolet-visible spectrophotometer (FLAME, manufactured by Ocean Photonics K.K.).

[0056] The absorbance in FIG. 3 is the absorbance at a specific wavelength, and the wavelength corresponds to a microparticle of a specific shape or size. Therefore, a state in which the absorbance does not change even when irradiated with the femtosecond pulsed laser light 1 indicates a convergence state in which the shape or size of the microparticle does not change. The characteristic of the absorbance shown in FIG. 3 is that the rise in absorbance is steep, and the convergence state is reached at the same time as the maximum value of the absorbance is reached. Therefore, the characteristic of the absorbance shown in FIG. 3 is shorter in both the reduction period and the ablation period than the characteristic of the absorbance shown in FIG. 16, so it can be determined that the microparticles are generated in a short time. Therefore, it is possible to improve the generation efficiency of the microparticles.

[0057] The rise of the reduction period becomes steeper if the femtosecond pulsed laser light 1 is stronger, but it is not a linear relationship. More specifically, the intensity distribution of the femtosecond pulsed laser light 1 that generates nonlinearity is not uniform but is roughly Gaussian, and the threshold light intensity that contributes to the reduction reaction is considerably lower than the maximum intensity of the Gaussian distribution. In this case, the light that exceeds the threshold does not contribute to the reduction reaction of the ions. Therefore, even if the femtosecond pulsed laser light 1 is divided to half its intensity, the slope of the rise will not be less than half if the light that does not contribute to the reduction reaction can be reduced by saturation.

[0058] Therefore, for example, by splitting the femtosecond pulsed laser beam 1 into two to form two high-intensity plasma regions 100a and 100b, the reduction reaction starts more rapidly, which means that particles can be generated more efficiently than by irradiating a single femtosecond pulsed laser beam 1.

[0059] Another method for quickly completing the reduction reaction is to mix an additive into the solution 20. Basically, what hinders the reduction reaction is oxidation, so by adding a material that counteracts the oxidizing species that are generated when water is decomposed by plasma, the reduction reaction can be completed in a shorter time.

[0060] As in the comparative example of FIG. 16, it takes time for the intermediate particles generated by the reduction reaction to move to the region where the ablation reaction occurs due to the stirring of the solution 20, whereas by configuring the method for producing fine particles according to the present embodiment shown in FIG. 1(a) and the like, the plasma region 100a with high brightness due to the first laser light 11 and the self-converging region where the second laser light 12 is self-converged or the self-phase-modulated region overlap or are close to each other, making it unnecessary to move the intermediate particles, or the intermediate particles generated based on the precursor in the plasma region 100a can be easily made to flow to the self-converging region or the self-modulating region, and it is considered that the reduction reaction and the ablation reaction converge almost simultaneously. In this case, the generation of fine particles based on the intermediate particles in the self-converging region or the self-modulating region can be smoothly performed. This makes it possible to further improve the generation efficiency of fine particles.

[0061] For example, the irradiation step may include a first irradiation step and a second irradiation step. In the first irradiation step, the solution 20 is irradiated with the first laser light 11. In the second irradiation step, the solution 20 irradiated with the first laser light 11 in the first irradiation step is irradiated with the second laser light 12. That is, the intermediate particles generated based on the precursor by the first femtosecond pulsed laser light 11 are irradiated with the second femtosecond pulsed laser light 12, and fine particles can be generated based on the intermediate particles. In this case, the process of generating fine particles from intermediate particles can be accelerated compared to the case where one femtosecond pulsed laser light 1 is used. This makes it possible to further improve the generation efficiency of fine particles. In this case, the flow of the solution 20 can be controlled using, for example, a stirrer, and the first irradiation step and the second irradiation step can be performed in this order with the irradiation positions of the two laser lights 11 and 12 fixed.

[0062] <Solution 20> The solution 20 refers to a liquid obtained by mixing a precursor and a liquid. As the liquid, water may be used, or a mixture of water and alcohol may be used. By irradiating the solution 20 with the laser light 1, fine particles containing metal atoms contained in the precursor are generated.

[0063] Here, when a liquid containing only a precursor and water is used as the solution 20, the solution 20 is irradiated with the femtosecond pulsed laser light 1, and the water contained in the solution 20 reacts to generate reduced species such as hydrated electrons and hydrogen radicals (H·), as well as oxidized species such as hydroxide radicals (OH·) and hydrogen peroxide (H2O2). The inventors have found that while the reduced species contribute to the generation of fine particles, the oxidized species inhibit the reduction reaction of metal ions and complex ions that directly affect the generation of fine particles, and the time required to generate fine particles may be delayed. The inventors have also found that when a liquid containing only a precursor and alcohol is used as the solution 20, the time required to generate fine particles is significantly delayed. One possible reason for this is that the time required to generate fine particles may be delayed because reduced species based on the decomposition reaction of water cannot be generated.

[0064] In contrast, in this embodiment, for example, a solution 20 in which a precursor, alcohol, and water are mixed is used. At this time, the oxidizing species that inhibit the reduction reaction of the precursor reacts with the alcohol. Therefore, it is possible to suppress the inhibition of the reduction reaction of metal ions, complex ions, etc. contained in the precursor. In addition to the above, the alcohol that reacts with the oxidizing species changes to a reducing compound, so that it is possible to promote the reduction reaction of the precursor. That is, by using the above-mentioned solution 20, it is possible to efficiently generate fine particles. As a result, it is possible to optimize the irradiation time of the femtosecond pulse laser light 1, and to suppress the structural change of the fine particles. Therefore, it is possible to suppress the deterioration of the quality of the fine particles.

[0065] As the alcohol, a secondary alcohol such as 2-propanol (IPA: isopropyl alcohol) is used. Compared to the case where a primary alcohol is used, a secondary alcohol is more likely to maintain a stable state of radicals due to hyperconjugation. In addition, a secondary alcohol is more likely to react with oxidizing species than a case where a tertiary alcohol is used. For these reasons, the use of a secondary alcohol as the alcohol makes it possible to further promote the reduction reaction of the precursor.

[0066] In addition, polyhydric alcohols such as glycerin and sorbitol may be used as the alcohol. In this case, the number of reaction sites with the oxidizing species can be increased compared to the case where a monohydric alcohol is used. Therefore, by using a polyhydric alcohol as the alcohol, it is possible to further promote the reduction reaction of the precursor.

[0067] <Precursor> The precursor includes, for example, a metal salt. In this case, for example, the precursor may include a plurality of metal salts each having a different metal. In this case, the concentration of each metal salt mixed in the solution 20 can be easily controlled, so that the content of each metal contained in the generated alloy microparticles can be easily controlled.

[0068] The concentration of the metal salts mixed in the solution 20 is, for example, 1.0×10 -5 mоl·dm -3 Above 1.0×10 -1 mоl·dm -3 or less, and can be set arbitrarily depending on the application of the fine particles to be produced.

[0069] The metal salt contains a known compound containing a metal ion, and any material can be contained depending on the application. For example, known metal salts such as H2PtCl6·6H2O, FeCl3·6H2O, and NiCl2·6H2O can be used.

[0070] For example, the redox potential of the metal ions contained in the metal salt may be negative. In this case, for example, a material containing a base metal is used as the metal salt. Here, when a metal salt containing metal ions with a negative redox potential is used, there is a concern that oxidation may occur as the fine particles are generated. In contrast, according to this embodiment, the oxidation reaction of the fine particles can be suppressed by the action of a reducing substance generated by the oxidation reaction of the alcohol contained in the solution 20. This makes it possible to generate fine particles that have been difficult to generate in the past. Therefore, it is possible to further expand the uses of the fine particles.

[0071] The "oxidation-reduction potential" refers to a known value described in, for example, "Analytical Chemistry Data Book (Maruzen Publishing)" etc. Furthermore, the "base metal" refers to metals whose metal ion oxidation-reduction potentials are classified as negative values, and refers to lithium, potassium, calcium, sodium, magnesium, aluminum, zinc, iron, nickel, tin, and lead.

[0072] In addition to the above, for example, the precursor may include solid particles. In this case, for example, the precursor may include a plurality of solid particles each having a different metal. The solid particles have a median diameter (or average particle diameter) larger than the median diameter (or average particle diameter) of the generated fine particles. The solid particles have a median diameter (or average particle diameter) of, for example, 50 nm or more and about 200 μm.

[0073] Unlike the metal salts described above, the solid particles do not contain materials that are not contained in the fine particles, such as chlorine, etc. Therefore, it is possible to suppress the generation of unnecessary materials that are generated along with the generation of the fine particles.

[0074] (First embodiment: Microparticle manufacturing system) The microparticle production system according to this embodiment includes a container 2, an irradiation device 3, and an optical unit 30, as shown in FIG. 4, for example. The container 2 contains a solution 20. The optical unit 30 controls the irradiation directions of the first laser light 11 and the second laser light 12 so that the container 2 is irradiated via different optical paths. In this case, a plurality of irradiation conditions suitable for each microparticle production process can be set using each of the laser lights 11 and 12. This makes it possible to improve the efficiency of microparticle production. The microparticle production system can be used in the above-mentioned microparticle production method.

[0075] For example, Fig. 4 shows an example of the optical unit 30 used in the microparticle production system according to this embodiment. Fig. 4 shows a configuration example in which one laser beam 1 is split into two beams and the two beams are irradiated in opposing directions onto a container 2 using the optical unit 30. That is, the optical unit 30 may include at least one of a wedge prism 301, a half prism 302, and mirrors 303, 304, 305, 306, and 307 shown in Fig. 4, for example.

[0076] In the configuration shown in Figure 4, light emitted from an irradiation device 3 (femtosecond pulse laser device) is dispersed by a wedge prism 301, and femtosecond pulse laser light 1 of a specific wavelength is reflected by a mirror 303 and split into two directions via a half prism 302.

[0077] The split laser beams 1 are respectively reflected by mirrors 304 and 306, and further reflected by mirrors 305 and 307, and enter the solution 20 contained in the container 2. Here, the two laser beams 1 reflected by mirrors 305 and 307 (i.e., the two laser beams 11 and 12) are adjusted, for example, so that their optical axes coincide with each other.

[0078] Here, "the optical axes coincide with each other" includes the case where there is a certain degree of misalignment between the optical axes of the two laser beams 11, 12. For example, if the degree of coincidence between the beams of the two opposing laser beams 11, 12 is such that the angular difference is 1 minute or less and the parallel decentering is 20 μm or less, a significant decrease in the generation efficiency of the fine particles is unlikely to occur.

[0079] In this way, by splitting the laser beam 1 into multiple beams, it is possible to reduce the introduction cost of the device and the operating cost of the device, compared to the case where a femtosecond pulse laser device is provided for each of the laser beams 11 and 12. Also, compared to the case where the optical axes of the laser beams 11 and 12 are not aligned, it is possible to suppress variations in setting the irradiation positions. This allows fine particles to be generated with high efficiency.

[0080] 4, one laser beam 1 is split into two or more beams and irradiated in opposing directions using one irradiation device 3, but the microparticle manufacturing system according to this embodiment does not need to be limited to this configuration. For example, the irradiation step may use a plurality of irradiation devices 3 to irradiate the container 2 with a plurality of laser beams 1 via different optical paths (e.g., opposing irradiation). In addition, when modulating the intensity ratio of transmission and reflection of the half prism 302, for example, a wave plate may be used.

[0081] According to this embodiment, in the irradiation step, the solution 20 is irradiated with a first femtosecond pulsed laser beam 11 (first laser beam 11) and a second femtosecond pulsed laser beam 12 (second laser beam 12) via different optical paths to generate microparticles. Therefore, a plurality of irradiation conditions suitable for each microparticle generation process can be set using each of the laser beams 11 and 12. This makes it possible to improve the efficiency of generating microparticles.

[0082] Furthermore, according to this embodiment, in the second irradiation step, the solution 20 irradiated in the first irradiation step is irradiated with the second laser beam 12. That is, the intermediate particles generated based on the precursor by the first laser beam 11 are irradiated with the second laser beam 12, and fine particles can be generated based on the intermediate particles. Therefore, the process of generating fine particles from intermediate particles can be accelerated compared to the case where one femtosecond pulse laser beam 1 is used. This makes it possible to further improve the efficiency of generating fine particles.

[0083] Furthermore, according to this embodiment, the plasma region 100a where plasma is generated is adjacent to or overlaps with the self-convergence region where self-convergence occurs. That is, the intermediate particles generated based on the precursor in the plasma region 100a can be easily made to flow to the self-convergence region. Therefore, the generation of fine particles based on the intermediate particles in the self-convergence region can be smoothly performed. This makes it possible to further improve the generation efficiency of fine particles.

[0084] Furthermore, according to this embodiment, the first femtosecond pulsed laser beam 11 and the second femtosecond pulsed laser beam 12 are irradiated in opposing directions, and the plasma region 100a and the self-focusing region are close to each other. Therefore, compared to a case where the two laser beams 11 and 12 do not face each other, or the plasma region 100a and the self-focusing region are not close to each other, the reduction period and the ablation period can be shortened, and fine particles can be generated in a short time. This makes it possible to further improve the efficiency of generating fine particles.

[0085] According to this embodiment, the first laser beam 11 and the second laser beam 12 are beams branched from an oscillation beam of one femtosecond pulse laser device (irradiation device 3). Therefore, compared to a case where an irradiation device 3 is provided for each of the laser beams 11 and 12, it is possible to reduce the introduction cost of the device and the operating cost of the device.

[0086] Furthermore, according to this embodiment, the optical axis of the first laser beam 11 coincides with the optical axis of the second laser beam 12. Therefore, it is possible to suppress variations in setting the irradiation position compared to a case where the optical axes of the laser beams 11 and 12 are not coincident. This makes it possible to improve the reproducibility in generating fine particles.

[0087] According to the present embodiment, the irradiation step is performed by setting the output of the first femtosecond pulsed laser beam 11 and the second femtosecond pulsed laser beam 12 to 0.7 mW or more and the laser fluence to 1.0 kJ / cm. 2 The above is irradiated onto the solution 20. This makes it possible to easily generate sufficient plasma to cause a reduction reaction when generating fine particles, thereby making it possible to further improve the efficiency of generating fine particles.

[0088] Furthermore, according to this embodiment, the optical unit 30 controls the irradiation directions of the first femtosecond pulsed laser beam 11 and the second femtosecond pulsed laser beam 12 so that they are irradiated onto the container 2 via different optical paths. This makes it possible to set a plurality of irradiation conditions suitable for each microparticle generation process using each laser beam. This makes it possible to improve the microparticle generation efficiency.

[0089] Second embodiment Hereinafter, an example of a method for producing microparticles and a system for producing microparticles according to the second embodiment will be described. The difference between this embodiment and the above-mentioned embodiment is that the container 2 includes a flow path 21. Note that the description of the same contents as those of the above-mentioned embodiment will be omitted.

[0090] Fig. 5 is a schematic diagram showing an example of a method for producing fine particles according to this embodiment. Fig. 5 shows an example in which two laser beams 11 and 12 are irradiated to a flow path 21 in which a solution 20 flows from an upstream 21a to a downstream 21b. In this way, fine particles can be continuously produced by irradiating the solution 20 with two laser beams 11 and 12 while the solution 20 is flowing in the container 2. When the solution 20 contains a plurality of metal atoms, fine particles of an alloy can be produced.

[0091] Here, the flow path 21 may have a shape that allows the solution 20 to flow from "bottom to top" based on the installation surface 99, or may have a shape that allows the solution 20 to flow from "top to bottom" or in a substantially horizontal direction along the installation surface 99. In particular, by making the flow of the solution 20 "bottom to top (the direction of the arrow in FIG. 5)" based on the installation surface 99 of the container 2, the flow rate of the solution 20 can be easily controlled. For example, the flow path 21 may include a configuration in which a regulator 22 such as a flow rate control valve is disposed to control the flow rate of the solution 20. Here, when multiple metal atoms are dissolved in the solution 20, the speed at which the alloy becomes fine particles differs depending on the type of metal ion. For this reason, the flow rate of the solution 20 can be appropriately changed by the regulator 22 to optimize the flow rate so as to maximize the generation efficiency. The solution 20 with the optimal flow rate may be irradiated with two laser beams 11 and 12 with fixed irradiation positions to generate fine particles. This makes it possible to further improve the generation efficiency of fine particles.

[0092] 5, by making the portion (flow path 21) of the container 2 where the two laser beams 11 and 12 are irradiated narrower than the other portions, the reduction reaction and ablation reaction of the precursor caused by the two laser beams 11 and 12 can occur almost instantaneously. In this case, the reduction period and ablation period can be shortened, and the microparticles can be generated in a short time. This makes it possible to further improve the efficiency of generating the microparticles.

[0093] In this way, by providing a flow path 21 in the container 2 and irradiating the solution 20 flowing in one direction within the flow path 21 with two laser beams 11 and 12, it is possible to continuously generate microparticles. In addition, by irradiating the solution 20 containing a plurality of metal atoms flowing in one direction within the flow path 21 with two laser beams 11 and 12, it is possible to continuously generate alloy microparticles. This makes it possible to improve the productivity of the microparticles.

[0094] For example, the irradiation step may use the flow path 21 to set the irradiation position of the second femtosecond pulsed laser light 12 on the downstream 21b side of the irradiation position of the first femtosecond pulsed laser light 11. In this case, it is possible to easily irradiate the solution 20 with the two laser lights 11 and 12 suitable for each generation process of the fine particles in order along the flow path 21 of the solution 20. This makes it possible to further improve the generation efficiency of the fine particles. In addition, the optical unit 30 may control the irradiation position of the second femtosecond pulsed laser light 12 to the downstream 21b side of the flow path 21 from the irradiation position of the first femtosecond pulsed laser light 11. In this case, it is possible to easily irradiate the solution 20 with the laser lights 11 and 12 suitable for each generation process of the fine particles. This makes it possible to further improve the generation efficiency of the fine particles.

[0095] When the irradiation positions of the laser beams 11 and 12 are set as described above, the intensity of the first laser beam 11 may be stronger than that of the second laser beam 12. That is, the intensity of the irradiated laser beams 11 and 12 can be gradually weakened along the process of generating the microparticles. In this case, it is possible to suppress unnecessary reactions caused by excessive irradiation of the second laser beam 12 in the latter half of the process of generating the microparticles. This makes it possible to further improve the efficiency of generating the microparticles. In this case, the laser beams 11 and 12 having an intensity distribution as shown in FIG. 10 described later may be used.

[0096] The system for producing microparticles according to this embodiment may also include a known pump. For example, the solution 20 can be automatically injected or collected by using an automated pump. For example, a piston pump, a parts pump, a peristaltic pump, a diaphragm pump (with a check ball), etc. can be used. These pumps can adjust the flow rate and pressure, allowing for highly accurate fluid control.

[0097] For example, one method (recovery step) for recovering and extracting the microparticles generated by the above method from the solution 20 is to use high-frequency vibration. In this method, an ultrasonic disperser is used to disperse the microparticles in the liquid by high-frequency vibration, and the microparticles are mixed uniformly to facilitate separation. This makes it possible to extract the microparticles with a high recovery rate.

[0098] Other separation methods include magnetic separation and electrophoresis. Magnetic separation is effective when the particles are magnetic, and is a method of extracting the particles by using an external magnetic field. Another method is to generate an electric field and move the particles from the solution 20 by electrophoresis. By combining these methods, it is possible to extract the particles with higher accuracy.

[0099] FIG. 6 is a schematic diagram showing an example of the method for producing the above-mentioned fine particles. FIG. 6 shows an example of a configuration used when generating a solution 44 (including the solution 20), irradiating the solution with two laser beams 11 and 12 to generate fine particles, and then recovering the fine particles. More specifically, first, a first metal atom (e.g., a first metal ion 42) and a second metal atom (e.g., a second metal ion 43) are mixed in a solvent 41 (e.g., a liquid containing water) to generate a solution 44. Then, a regulator 45 is controlled so that the solution 44 flows through the container at an optimal flow rate. When the solution 44 passes through an irradiation station 46 (corresponding to the flow path 21 of the container 2 described above), the solution 44 is irradiated with two fixed laser beams 11 and 12 to generate fine particles of an alloy. The generated fine particles are recovered by a recovery cylinder 47, and then separated fine particles 49 are taken out by an ultrasonic disperser 48.

[0100] In this manner, it becomes possible to produce high-performance alloy particles with high efficiency.

[0101] According to this embodiment, in the irradiation step, the irradiation position of the second laser beam 12 is set on the downstream 21b side of the flow path 21 from the irradiation position of the first laser beam 11. This makes it easier for the solution 20 to be irradiated with the laser beams 11 and 12 suitable for each microparticle generation process. This makes it possible to further improve the efficiency of microparticle generation.

[0102] Furthermore, according to this embodiment, the intensity of the first laser beam 11 is stronger than the intensity of the second laser beam 12. That is, the intensities of the irradiated laser beams 11 and 12 can be gradually weakened along the process of generating the microparticles. Therefore, in the latter half of the process of generating the microparticles, unnecessary reactions caused by excessive irradiation of the laser beam 12 can be suppressed. This makes it possible to further improve the efficiency of generating the microparticles.

[0103] Furthermore, according to this embodiment, the optical unit 30 controls the irradiation position of the second femtosecond pulsed laser beam 12 to be downstream of the irradiation position of the first femtosecond pulsed laser beam 11 in the flow path 21. This makes it easier for the solution 20 to be irradiated with the laser beams 11 and 12 suitable for each microparticle generation process. This makes it possible to further improve the efficiency of microparticle generation.

[0104] Third embodiment Hereinafter, an example of a method for producing microparticles and a system for producing microparticles according to the third embodiment will be described. The difference between this embodiment and the above-mentioned embodiment is that three or more laser beams are irradiated onto the solution 20. Note that the description of the same contents as those of the above-mentioned embodiment will be omitted.

[0105] Fig. 7 is a schematic diagram showing a method for producing fine particles according to a third embodiment. As shown in Fig. 7, in this embodiment, three laser beams 11, 12, and 13 are irradiated from three different directions. In this case, a plurality of irradiation conditions more suitable for each fine particle generation process can be set. This enables more efficient generation of fine particles. The third laser beam 13 may be, for example, a branched beam from any one of the laser beams 1, 11, and 12.

[0106] More specifically, the high-luminance plasma regions 100a, 100b, and 100c (approximately rectangular regions in the figure) of the three laser beams 11, 12, and 13 overlap or are close to each other, and the self-converging or self-modulating regions (continuous approximately elliptical regions in the figure) of the other laser beams 11, 12, and 13 different from the laser beams 11, 12, and 13 overlap or are close to each other. As a result, the self-converging or self-modulating regions formed by the three laser beams 11, 12, and 13 overlap or are close to the high-luminance plasma regions 100a, 100b, and 100c. This configuration enables more efficient generation of fine particles.

[0107] In this embodiment, the case where three laser beams 11, 12, and 13 are used has been described, but the present invention is not limited to this. For example, even when three or more laser beams (e.g., an odd number of three or more) are used, highly efficient generation of fine particles is possible.

[0108] According to this embodiment, in the irradiation step, the solution 20 is irradiated from different positions with the first femtosecond pulsed laser beam 11 and one or more other femtosecond pulsed laser beams 13 different from the second femtosecond pulsed laser beam 12, thereby generating microparticles. This enables more efficient generation of microparticles.

[0109] (Fourth embodiment) Hereinafter, an example of a method for producing fine particles and a system for producing fine particles according to the fourth embodiment will be described. The difference between the above-described embodiment and this embodiment is that the irradiation destination of the laser light 1 is switched using a switching mirror 311 included in the optical unit 31. Note that a description of the same contents as those of the above-described embodiment will be omitted.

[0110] The system for producing fine particles according to this embodiment includes an optical unit 31 including a switching mirror 311 and half prisms 312 and 313, as shown in Fig. 8(a) and Fig. 8(b), for example. Fig. 8(a) and Fig. 8(b) are schematic diagrams showing an example of the method for producing fine particles according to this embodiment. The method for producing fine particles according to this embodiment uses an optical unit 31 that can switch the irradiation of one laser light 1 to two or more solutions 20 by the switching mirror 311.

[0111] 8(a) and 8(b), a plurality of irradiation stations 318, 319 in which solutions 20 are placed are provided as targets for irradiation with the laser beam 1. By switching a switching mirror 311, the optical path of the laser beam 1 is switched and the laser beam 1 is branched into two directions at each of the half prisms 312, 313. The two branched laser beams 11, 12 are irradiated onto the solution 20 placed in the desired irradiation station 318, 319, and fine particles are generated.

[0112] FIG. 8(a) shows a state in which the solution 20 arranged in the irradiation station 318 is irradiated with two laser beams 11 and 12, and FIG. 8(b) shows a state in which the switching mirror 311 is switched from the state of FIG. 8(a) to irradiate the solution 20 arranged in another irradiation station 319 with the laser beams 11 and 12. As shown in FIG. 8(b), the solution 20 in the irradiation station 318 can be replaced while the laser beams 11 and 12 are being irradiated to the other irradiation station 319. In this way, the solution 20 can be easily replaced by switching the optical path without stopping the oscillation of the femtosecond pulse laser. This makes it possible to further improve the generation efficiency of the fine particles. The solution 20 may be replaced for each container 2 containing the solution 20, or only the solution 20 may be replaced.

[0113] In this embodiment, the λ / 2 plates 314-317 may be disposed before the solution 20 is irradiated with the laser beams 11 and 12. In this case, the polarization of the irradiated laser beams 11 and 12 can be controlled by adjusting the rotation of the λ / 2 plates 314-317. For example, when P-polarized light has a better efficiency of generating fine particles, it is possible to irradiate the laser beam with P-polarized light. The electric field at the focal point of the linearly polarized P-polarized or S-polarized light is perpendicular to the laser incidence direction. In this case, the electrons surrounding the atoms are vigorously shaken by the electric field vibration compared to, for example, circularly polarized light, and plasma is generated more efficiently, so that fine particles can be manufactured more efficiently.

[0114] The above-mentioned embodiment can be modified in various ways. For example, the container 2 for the solution 20 may be one suitable for producing fine particles. Alternatively, an optical element disposed close to the container 2 for the solution 20 may be further used. For example, when the amount of the solution 20 to be irradiated with the laser beams 11 and 12 is small, an optical component having a function of concentrating the laser beams 11 and 12 in one direction perpendicular to the optical axis and making the intensity distribution uniform in the other direction perpendicular to the optical axis when the laser beams 11 and 12 are incident on a specific surface of the container 2 with an optical axis perpendicular to the specific surface is preferable. Here, "uniform" means that the intensity distribution is more uniform than a Gaussian distribution, and does not necessarily have to be strictly uniform.

[0115] The system for producing fine particles may include an optical unit 32 including at least one of a diffractive optical element 321 and a normal lens 322, as shown in Fig. 9, for example. When irradiating the two laser beams 11 and 12 onto the solution 20, the optical unit 32 is arranged such that the diffractive optical element 321 and the lens 322 are arranged in this order along the optical paths of at least one of the two laser beams 11 and 12. In the example of Fig. 9, the diffractive optical element 321 can change the pattern formation only in the Y-direction component to provide cylindrical imaging performance. Specifically, by using the diffractive optical element 321 to focus the X-direction components of the laser beams 11 and 12 into a normal Gaussian beam, and expanding the energy near the center of the Gaussian beam for the Y-direction components as shown by a pair of diagonal lines in the figure, the beams are then incident on a normal lens 322, whereby only the Y-direction components of the laser beams 11 and 12 that have passed through the normal lens 322 can be changed into a uniform top-hat pattern as shown in the intensity distribution in the lower right of Fig. 9, and the X-direction components can be converted into strongly focused light as shown in the intensity distribution in the lower left of Fig. 9. Note that a configuration using only the diffractive optical element 321 is also possible, and a metalens may be used instead of the diffractive optical element 321.

[0116] In addition to the above, for example, as shown in FIG. 10, the light intensity distribution may be converted into two types using a metalens or the like. In this case, for example, among the laser light 1, the light with higher intensity (first intensity) may be the first femtosecond pulsed laser light 11, and the light with lower intensity (second intensity) may be the second femtosecond pulsed laser light 12. By converting the intensity of the laser light 1 described above, it is possible to suppress the decrease in reproducibility caused by the adjustment of the optical axis, compared to the case where the laser light is split into the laser lights 11 and 12 using an optical system. In addition to the above, since there is no need to prepare two femtosecond pulsed laser devices, it is possible to reduce manufacturing costs.

[0117] Fifth embodiment Hereinafter, an example of a method for producing microparticles and a system for producing microparticles according to the fifth embodiment will be described. The difference between the above-mentioned embodiment and this embodiment is that two laser beams 11 and 12 having different optical path lengths are irradiated onto the solution 20 along coaxial optical paths using two polarizing beam splitters 332 and 333 included in the optical unit 33. Note that a description of the same contents as those of the above-mentioned embodiment will be omitted.

[0118] In the irradiation step in this embodiment, the oscillation light of one femtosecond pulse laser device (irradiation device 3) is split into a first laser light 11 and a second laser light 12. After that, the first laser light 11 and the second laser light 12 are caused to pass through different optical paths, and then irradiated onto the solution 20 along the same optical axis and direction. At this time, for example, the optical axis indicates an optical axis that overlaps with the traveling direction of the laser light 1 oscillated from the irradiation device 3. In this case, two types of pulses can be generated for an irradiation area along one axis, and the expansion of the irradiation area can be suppressed. This makes it possible to improve the generation efficiency of fine particles while suppressing the increase in size of the manufacturing device, etc.

[0119] For example, the difference between the optical path length of the first laser light 11 and the optical path length of the second laser light 12 indicates a distance at which they do not interfere with each other. Here, when the difference in the optical path length indicates a distance at which the laser lights interfere with each other, the pulse width of the combined light beam of each laser light becomes large. At this time, the non-thermal effect, which is a characteristic of the femtosecond pulse laser, is lost, and the effect of heat associated with laser irradiation may occur. In this case, there is a concern that the generation efficiency of the fine particles may be reduced. In contrast, the difference in the optical path length in this embodiment indicates a distance at which the laser lights 11 and 12 do not interfere with each other. Therefore, it is possible to maintain a state in which the non-thermal effect, which is a characteristic of the femtosecond pulse laser, is maintained. This makes it possible to improve the generation efficiency of the fine particles while suppressing the effect of heat associated with laser irradiation.

[0120] For example, as shown in FIG. 11, the optical unit 33 includes one wave plate 331 and two polarizing beam splitters 332 and 333, which are arranged on the same axis. In this case, two types of pulses can be generated for an irradiation area along one axis, and the expansion of the irradiation area can be suppressed. This makes it possible to improve the production efficiency of fine particles while suppressing the increase in size of the manufacturing equipment, etc. The optical unit 33 may include, for example, two mirrors 334 and 335.

[0121] The wave plate 331 changes the state of polarization of the laser light 1 oscillated from the irradiation device 3. As the wave plate 331, for example, a half-wave plate (HWP: Half-Wave Plate) can be used, and a known wave plate can be used depending on the application.

[0122] The first polarizing beam splitter 332 splits the laser light 1, whose polarization state has been changed, into a first laser light 11 and a second laser light 12. In this case, for example, the first laser light 11 exhibits a horizontal linear polarization component based on the laser light 1 (for example, an arrow indicating the up and down directions on the paper surface of FIG. 11), and the second laser light 12 exhibits a vertical linear polarization component based on the laser light 1 (for example, a circle indicating the front and back directions on the paper surface of FIG. 11).

[0123] The second polarizing beam splitter 333 combines the split laser beams 11 and 12. The laser beams 11 and 12 combined by the second polarizing beam splitter 333 travel along the same optical axis and in the same direction. At this time, a difference occurs in the optical path length of each of the laser beams 11 and 12 because the laser beams 11 and 12 have traveled different paths.

[0124] The two mirrors 334, 335 are used, for example, to guide the optical path of the second laser beam 12 branched via the first polarizing beam splitter 332 to the second polarizing beam splitter 333. By using the two mirrors 334, 335, for example, the optical path of the second laser beam 12 can be set longer than the optical path of the first laser beam 11, and a difference in optical path length between the laser beams 11 and 12 can be generated. Note that instead of the two mirrors 334, 335, known optical elements may be used.

[0125] For example, when the optical unit 33 is arranged in a configuration as shown in FIG. 11, the difference in optical path length of each of the split laser beams 11 and 12 can be set based on twice the distance h between the first polarizing beam splitter 332 and the mirror 334, and can be set to, for example, 2×h / c (c: speed of light). Here, the shortest distance for preventing the pulses of each of the laser beams 11 and 12 from interfering with each other can be calculated from the pulse width of the laser beam 1. For example, when the pulse width f of the laser beam 1 is 100 fs and the repetition frequency ω is 1 kHz, the shortest distance is 15 μm. Therefore, by setting the difference in optical path length of each of the laser beams 11 and 12 to be larger than the shortest distance of 15 μm, it is possible to maintain a state in which the non-thermal effect is maintained.

[0126] According to this embodiment, in the irradiation step, the first laser beam 11 and the second laser beam 12 are caused to travel through different paths, and then irradiated onto the solution 20 along the same optical axis and direction. Therefore, two types of pulses can be generated in an irradiation area along one axis, and the expansion of the irradiation area can be suppressed. This makes it possible to improve the production efficiency of fine particles while suppressing the increase in size of the manufacturing equipment, etc.

[0127] Furthermore, according to this embodiment, the difference between the optical path length of the first laser beam 11 and the optical path length of the second laser beam 12 indicates a distance at which they do not interfere with each other. Therefore, it is possible to maintain a state in which the non-thermal effect, which is a feature of the femtosecond pulse laser, is maintained. This makes it possible to improve the generation efficiency of fine particles while suppressing the influence of heat caused by laser irradiation.

[0128] According to this embodiment, the optical unit 33 includes one wave plate 331 and two polarizing beam splitters 332 and 333, which are arranged on the same axis. Therefore, two types of pulses can be generated for an irradiation area along one axis, and the expansion of the irradiation area can be suppressed. This makes it possible to improve the generation efficiency of fine particles while suppressing the increase in size of the manufacturing device, etc.

[0129] Sixth embodiment Hereinafter, an example of a method for producing fine particles and a system for producing fine particles according to the sixth embodiment will be described. The difference between this embodiment and the above-mentioned embodiments is that the laser light 1 is branched using a plurality of condenser lenses 341, 342 included in the optical unit 34. Note that a description of the same contents as those of the above-mentioned embodiment will be omitted.

[0130] The microparticle production system according to this embodiment includes an optical unit 34 including condenser lenses 341 and 342 and movable units 343 and 344, as shown in Fig. 12. Fig. 12 is a schematic diagram showing an example of a microparticle production method and a microparticle production system according to this embodiment. The microparticle production method according to this embodiment uses an optical unit 35 that splits the irradiation of one laser beam 1 into two laser beams 11 and 12 by the condenser lenses 341 and 342.

[0131] The condenser lenses 341 and 342 are lenses that condense only components in one direction. For example, a known cylindrical lens is used as the condenser lenses 341 and 342, and a plurality of lenses having substantially the same shape may be used, or lenses having different shapes may be used. The condenser lens 341 is fixed on a movable part 343 so as to intersect with the optical axis of the laser light 1, for example. The condenser lens 342 is fixed on a movable part 344 so as to intersect with the optical axis of the laser light 1, for example. The condenser lenses 341 and 342 are disposed adjacent to each other in the optical axis direction of the laser light 1 (Z direction in FIG. 12). In addition, each of the movable parts 343 and 344 is movable forward f1 or backward f2 in the optical axis direction of the laser light 1, for example.

[0132] The condenser lens 341 is, for example, a plano-convex lens (plano-convex cylindrical lens) that bulges in the optical axis direction when viewed in the X direction, i.e., in a side view. The condenser lens 342 is, for example, a plano-convex lens (plano-convex cylindrical lens) that bulges in the optical axis direction when viewed in the Y direction, i.e., in a plan view. That is, each of the condenser lenses 341, 342 is, for example, a pair of plano-convex lenses of substantially the same shape that are oriented in directions that differ from each other by 90° with the optical axis as the axis of rotation. In this case, based on the laser light 1, a first component in one direction and a second component in a direction perpendicular to the component in one direction can be branched.

[0133] 13(a) and 13(b) show an example of the irradiation step using the optical unit 34. Figures 13(a) and 13(b) are schematic diagrams showing an example of the irradiation step in the method for producing fine particles according to this embodiment as viewed in the X direction and the Y direction, respectively.

[0134] For example, in the irradiation step, as shown in Fig. 13(a), a part of the laser beam 1 is branched as a first laser beam 11 via a condenser lens 341. Thereafter, the laser beam 11 that has passed through the condenser lens 341 is caused to travel in the Z direction while being contracted in the Y direction through a condenser lens 342, and is focused in the solution 20 in the container 2, which is the first focal position of the condenser lens 341. At this time, the first laser beam 11 exhibits, for example, a horizontal component (component in the X direction in Fig. 13) based on the laser beam 1. As a result, the first focal position in the solution 20 becomes a plasma region fa where plasma is generated by the laser beam 11.

[0135] In the irradiation step, as shown in FIG. 13(b), at least a part of the laser beam 1 transmitted through the condenser lens 341 is branched as the laser beam 12 via the condenser lens 342. After that, the laser beam 12 that has passed through the condenser lens 342 is caused to advance in the Z direction while being reduced in diameter in the X direction, and is focused in the solution 20 in the container 2, which is the second focal position of the condenser lens 342. At this time, the second laser beam 12 exhibits, for example, a vertical component (component in the Y direction in FIG. 13) based on the laser beam 1. As a result, the second focal position in the solution 20 becomes a plasma region fb where plasma is generated by the laser beam 12. Note that a self-converging region fc is formed by each of the laser beams 11 and 12 between the plasma regions fa and fb.

[0136] That is, in the irradiation step, laser light 1, which is an oscillation light of one femtosecond pulsed laser device, is split into a first femtosecond pulsed laser light 11 and a second femtosecond pulsed laser light 12 via focusing lenses 341 and 342, and the first femtosecond pulsed laser light 11 is focused at a first focal position of one focusing lens 341 in the solution 20, while the second femtosecond pulsed laser light 12 is focused at a second focal position of another focusing lens 342, which is different from the first focal position, in the solution 20. In this case, a plurality of microparticle generation regions can be controlled independently. This makes it possible to further improve the efficiency of microparticle generation.

[0137] In the irradiation process, the movable parts 343 and 344 may be moved forward f1 or backward f2 to move and adjust the plasma regions fa and fb in the optical axis direction. In this case, plasma can be generated at a position where the generation of fine particles is not progressing. This makes it possible to further improve the generation efficiency of fine particles.

[0138] 14(a) to 14(c) show the AA cross section of FIG. 13(a), and the BB and CC cross sections of FIG. 13(b), respectively. The plasma region fa is, for example, as shown in FIG. 14(a), approximately spindle-shaped and extended in the X direction in the cross section in the Z direction. This is because the laser beam 11 is a horizontal component based on the laser beam 1, and travels in the Z direction while being contracted in the Y direction, and is focused at the first focal position. The plasma region fb is, for example, as shown in FIG. 14(b), approximately spindle-shaped and extended in the Y direction in the cross section in the Z direction. This is because the laser beam 12 is a vertical component based on the laser beam 1, and travels in the Z direction while being contracted in the X direction, and is focused at the second focal position. The self-focusing region fc is, for example, as shown in FIG. 14(c), approximately elliptical in the cross section in the Z direction. This is because the self-focusing of the laser beams 11 and 12 influence each other.

[0139] Further, the focusing lenses 341 and 342 may be, other than the above-mentioned plano-convex lens, a convex meniscus lens (convex meniscus cylindrical lens), a biconvex lens (biconvex cylindrical lens), an aspheric lens, a diffractive lens such as a diffractive optical element, a Fresnel lens, or a metalens, and a reflective focusing element such as a concave mirror. Further, one of the focusing lenses 341 and 342 may be a focusing lens that focuses components in all directions, instead of a focusing lens that focuses components in one direction only. In this case as well, the laser beam 1, which is the oscillation beam of one femtosecond pulsed laser device, is branched into a first femtosecond pulsed laser beam 11 and a second femtosecond pulsed laser beam 12, and the first femtosecond pulsed laser beam 11 is focused at a first focal position, and the second femtosecond pulsed laser beam 12 is focused at a second focal position, so that a plurality of microparticle generation regions can be controlled independently. This makes it possible to further improve the efficiency of generating fine particles.

[0140] According to this embodiment, in the irradiation step, the first femtosecond pulsed laser beam 11 is focused at a first focal position in the solution 20, and the second femtosecond pulsed laser beam 12 is focused at a second focal position different from the first focal position in the solution 20. This makes it possible to independently control a plurality of microparticle generation regions. This makes it possible to further improve the efficiency of microparticle generation.

[0141] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0142] 1. Femtosecond pulsed laser light (laser light) 11 First Laser Beam 12 Second laser beam 13 The third laser light 2 containers 20 solution 21 Flow Path 21a Upstream 21b downstream 22 Regulator 3 Irradiation device 30 Optics Department 301 Wedge Prism 302 Half Prism 303~307 Mirror 31 Optics Department 311 Switching mirror 312, 313 Half Prism 314~317 λ / 2 plate 318, 319 Irradiation Station 32 Optics Department 321 Diffractive Optical Elements 322 Lens 33 Optics Department 331 Wave plate 332, 333 Polarizing Beam Splitter 334, 335 Mirror 34 Optics Department 341, 342 Condenser lens 343, 344 Moving parts 41 Solvents 42 First metal ion 43 Second Field Metal Ions 44 Solution 45 Regulator 46 Irradiation Station 47 Diffraction Cylinder 48 Ultrasonic disperser 49 Separated fine particles 99 Installation surface 100a, 100b, 100c Plasma region f1 forward f2 backward fa, fb Plasma region fc self-convergence region

Claims

1. A method for producing a microparticle using a femtosecond pulse laser, comprising the steps of: The method includes an irradiation step of irradiating a solution containing a precursor containing metal atoms with a first femtosecond pulsed laser beam and a second femtosecond pulsed laser beam via different optical paths to generate fine particles. A method for producing fine particles, comprising the steps of:

2. The irradiation step includes: a first irradiation step of irradiating the solution with the first femtosecond pulsed laser light; a second irradiation step of irradiating the solution irradiated in the first irradiation step with the second femtosecond pulsed laser light; Contains The method for producing fine particles according to claim 1,

3. The precursor comprises a metal ion or a complex ion, the first irradiation step generates plasma in the solution by the first femtosecond pulsed laser light to generate intermediate particles based on the precursor; the second irradiation step generates the microparticles by miniaturizing the intermediate particles by generating self-focusing of the second femtosecond pulsed laser light in the solution; The plasma region where the plasma is generated is adjacent to or overlaps with the self-focusing region where the self-focusing occurs. The method for producing fine particles according to claim 2,

4. the first femtosecond pulsed laser beam and the second femtosecond pulsed laser beam are irradiated in directions opposite to each other, The plasma region and the self-focusing region are close to each other. The method for producing fine particles according to claim 3,

5. The first femtosecond pulsed laser light and the second femtosecond pulsed laser light are beams branched from an oscillation beam of one femtosecond pulsed laser device. The method for producing microparticles according to any one of claims 1 to 4, characterized in that

6. The optical axis of the first femtosecond pulsed laser beam coincides with the optical axis of the second femtosecond pulsed laser beam. The method for producing microparticles according to any one of claims 1 to 4, characterized in that

7. In the irradiation step, the output of the first femtosecond pulsed laser beam and the second femtosecond pulsed laser beam are set to 0.7 mW or more, and the laser fluence is set to 1.0 kJ / cm. 2 The solution is then irradiated with The method for producing microparticles according to any one of claims 1 to 4, characterized in that

8. The irradiating step includes irradiating the solution with one or more femtosecond pulsed laser beams different from the first femtosecond pulsed laser beam and the second femtosecond pulsed laser beam from different positions, thereby generating the microparticles. The method for producing microparticles according to any one of claims 1 to 4, characterized in that

9. The irradiation step includes using a flow path in which the solution flows from upstream to downstream, and setting an irradiation position of the second femtosecond pulsed laser light downstream of the flow path relative to an irradiation position of the first femtosecond pulsed laser light. The method for producing fine particles according to any one of claims 2 to 4, characterized in that

10. The intensity of the first femtosecond pulsed laser beam is greater than the intensity of the second femtosecond pulsed laser beam. The method for producing fine particles according to claim 9,

11. The irradiation step includes: Oscillation light from one femtosecond pulse laser device is split into the first femtosecond pulse laser light and the second femtosecond pulse laser light, the first femtosecond pulsed laser light and the second femtosecond pulsed laser light are caused to travel through different optical paths, and then irradiated onto the solution along the same optical axis and direction. The method for producing fine particles according to claim 1,

12. a difference between the optical path length of the first femtosecond pulsed laser beam and the optical path length of the second femtosecond pulsed laser beam indicates a distance at which they do not interfere with each other; The method for producing fine particles according to claim 11,

13. The irradiation step includes: Oscillation light from one femtosecond pulse laser device is split into the first femtosecond pulse laser light and the second femtosecond pulse laser light via a plurality of focusing lenses that focus only a component in one direction; focusing the first femtosecond pulsed laser light at a first focal position of one of the focusing lenses in the solution, and focusing the second femtosecond pulsed laser light at a second focal position of another of the focusing lenses in the solution that is different from the first focal position. The method for producing microparticles according to any one of claims 1 to 4, characterized in that

14. A system for producing microparticles using a femtosecond pulse laser, comprising: A vessel containing a solution containing a mixture of precursors containing metal atoms; an optical unit that controls directions of irradiation of a first femtosecond pulsed laser beam and a second femtosecond pulsed laser beam so that the first femtosecond pulsed laser beam and the second femtosecond pulsed laser beam are irradiated onto the container via different optical paths; A system for producing fine particles, comprising:

15. The container includes a flow path through which the solution flows, the optical unit controls an irradiation position of the second femtosecond pulsed laser beam to be downstream of an irradiation position of the first femtosecond pulsed laser beam in the flow path. The system for producing microparticles according to claim 14,

16. The optical section includes one wave plate and two polarizing beam splitters arranged coaxially. The system for producing microparticles according to claim 14,

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