Diffraction device and diffraction method

Abstract

This diffraction device (100) comprises: a supply unit (10) for supplying a gas (V) to a prescribed region (R); a first irradiation unit (20) for irradiating the prescribed region (R) with first laser light (L1) and second laser light (L2); and a second irradiation unit (40) for irradiating the prescribed region (R) with third laser light (L3). The gas (V) contains molecules that resonantly absorb the first laser light (L1), the second laser light (L2), and the third laser light (L3). The first irradiation unit (20) forms interference fringes in the prescribed region (R) by irradiating the prescribed region (R) with the first laser light (L1) and the second laser light (L2) so as to intersect each other in the prescribed region (R), thereby forming compression waves in the gas (V) in the prescribed region (R) due to the interference fringes.

Description

Diffraction device and diffraction method

[0001] The present disclosure relates to a diffraction device and a diffraction method.

[0002] Patent Document 1 describes a diffractive focusing optical element device. This diffractive focusing optical element device includes a gas generation means for supplying a gas containing molecules that resonantly absorb light to form a certain region, and irradiating the region with excitation laser light having a wavelength in the absorption band of the molecules so as to intersect within the region to photoexcite the gas, and having at least one of a focusing optical system and a diverging optical system in at least one of the optical paths of the two excitation laser lights to be intersected, thereby having a photoexcitation means for generating interference fringes with curvature within the region.

[0003] Japanese Patent Application Laid-Open No. 2021-105693

[0004] In the diffractive focusing optical element device described in Patent Document 1 above, the controlled laser light can be diffracted by making the controlled laser light incident on the interference fringes formed in the gas. In such a diffractive focusing optical element device, it is desired to realize a function of blocking the return light of the controlled laser light by rapidly switching between a state where the controlled laser light can be diffracted and a state where the controlled laser light is difficult to be diffracted.

[0005] Therefore, an object of the present disclosure is to provide a diffraction device and a diffraction method capable of controlling the diffraction state at high speed.

[0006] The diffraction apparatus according to this disclosure is a diffraction apparatus comprising: [1] a supply unit for supplying a gas to a predetermined region; a first irradiation unit for irradiating the predetermined region with a first laser beam and a second laser beam; and a second irradiation unit for irradiating the predetermined region with a third laser beam, wherein the gas contains molecules that resonantly absorb the first laser beam, the second laser beam, and the third laser beam; the first irradiation unit irradiates the predetermined region with the first laser beam and the second laser beam so as to intersect each other in the predetermined region, thereby forming interference fringes in the predetermined region, and thereby forming compression waves in the gas in the predetermined region due to the interference fringes; and the second irradiation unit irradiates the predetermined region with the third laser beam after the first laser beam and the second laser beam have been irradiated in the predetermined region, thereby reducing the amplitude of the compression waves.

[0007] The diffraction method according to the present disclosure is [9] "a diffraction method comprising: a supply step of supplying a gas to a predetermined region; a first irradiation step of irradiating the predetermined region with a first laser beam and a second laser beam; and a second irradiation step of irradiating the predetermined region with a third laser beam, wherein the gas contains molecules that resonantly absorb the first laser beam, the second laser beam, and the third laser beam; in the first irradiation step, interference fringes are formed in the predetermined region by irradiating the predetermined region with the first laser beam and the second laser beam so as to intersect each other in the predetermined region, thereby forming compression waves in the gas in the predetermined region due to the interference fringes; and in the second irradiation step, the amplitude of the compression waves is reduced by irradiating the predetermined region with the third laser beam after the first laser beam and the second laser beam have been irradiated in the predetermined region."

[0008] In this diffraction apparatus and method, interference fringes are formed in a predetermined region where gas is supplied, by irradiating it with a first laser beam and a second laser beam so as to intersect each other. The gas contains molecules that resonantly absorb the first laser beam and the second laser beam (and the third laser beam). As a result, compression waves (a state in which areas of high and low gas density are alternately formed in a fringe pattern) are formed in the gas in the predetermined region due to the interference fringes. This makes it possible to diffract the controlled laser beam by, for example, irradiating the predetermined region where the compression waves of the gas are formed (i.e., the controlled laser beam becomes diffractable). These compression waves of the gas are repeatedly generated over time for each irradiation of the first and second laser beams (i.e., spatial modulation of compression and rarefaction over time is repeatedly generated by the compression waves), and the state in which the controlled laser beam can be diffracted is repeatedly generated. In contrast, in this diffraction apparatus and method, a third laser beam is further irradiated onto the predetermined region after the first and second laser beams have been irradiated. As a result, the amplitude of the gas compression wave is reduced after irradiation with the third laser beam. Consequently, the controlled laser beam incident on a predetermined region becomes less susceptible to diffraction (i.e., the controlled laser beam becomes less prone to diffraction). Thus, with this diffraction apparatus and diffraction method, the diffraction state can be controlled at high speed in response to irradiation with the third laser beam.

[0009] As described above, the compression waves of the gas formed in a predetermined region by the irradiation of the first and second laser beams repeatedly generate spatial modulation of the compression and rarefaction over time. In other words, peaks in the diffraction efficiency of light based on the compression waves of the gas repeatedly occur over time. According to the inventor's findings, by irradiating the predetermined region with a third laser beam at a time between temporally adjacent peaks of diffraction efficiency, it is possible to suitably reduce the amplitude of the compression waves that would have occurred after that time.

[0010] Therefore, the diffraction apparatus according to the present disclosure may also be [2] "the diffraction apparatus according to [1] above, wherein the second irradiation unit irradiates the predetermined region with the third laser light at a time between temporally adjacent peaks of the diffraction efficiency of light based on the compression wave." In this case, as described above, it becomes possible to suitably reduce the amplitude of the compression wave of the gas and to control the diffraction state more reliably.

[0011] The diffraction apparatus according to this disclosure may also be [3] "the diffraction apparatus according to [2] above, wherein the second irradiation unit irradiates the predetermined region with the third laser beam at a time between the time when the first laser beam and the second laser beam are irradiated and the first two peaks of the diffraction efficiency." In this case, the amplitude of the compression wave of the gas after the first peak of the diffraction efficiency can be suitably reduced, making it possible to make the controlled laser beam less susceptible to diffraction. Therefore, it is possible to suitably configure, for example, a regenerative amplifier or an optical switch that operates in single-pulse mode using this diffraction apparatus.

[0012] The diffraction apparatus according to this disclosure may also be [4] "the diffraction apparatus according to [2] or [3] above, wherein the second irradiation unit irradiates the predetermined region with the third laser light in a time range in which the diffraction efficiency is lowest." In this case, it is possible to more reliably reduce the amplitude of the compression wave of the gas.

[0013] The diffraction apparatus according to this disclosure may also be [5] "the diffraction apparatus according to any one of [1] to [4] above, wherein the gas contains ozone, and the first laser beam, the second laser beam, and the third laser beam have central wavelengths at the absorption wavelength of ozone." In this way, by having the gas contain ozone and the first to third laser beams have central wavelengths at the absorption wavelength of ozone, it is possible to suitably form compression waves and reduce the amplitude of compression waves for a gas in a predetermined region.

[0014] The diffraction apparatus according to this disclosure may also be [6] "the diffraction apparatus according to any one of [1] to [5] above, wherein the pulse width of the third laser beam is 1 ps or more and 100 ns or less." In this case, it is possible to suitably reduce the amplitude of compression waves that would have occurred after the time the third laser beam was irradiated. As a result, it is possible to suppress diffraction of the controlled laser beam at times other than the desired time, or to diffract the controlled laser beam only during the desired time period.

[0015] The diffraction apparatus according to this disclosure may be [7] "the diffraction apparatus according to any one of [1] to [6] above, wherein the fluence of the third laser beam is equal to or greater than the fluence of the first laser beam and the second laser beam." In this case, the amplitude of the compression wave of the gas can be reduced more reliably by irradiation with the third laser beam.

[0016] The diffraction apparatus according to this disclosure may be [8] "the diffraction apparatus according to any one of [1] to [7] above, wherein the irradiation area of ​​the third laser beam in the predetermined region includes the irradiation areas of the first laser beam and the second laser beam in the predetermined region." In this case, irradiation with the third laser beam makes it possible to reduce the amplitude of the compression wave of the gas in the entire irradiation area of ​​the first laser beam and the second laser beam.

[0017] This disclosure provides a diffraction apparatus and a diffraction method capable of rapidly controlling the diffraction state.

[0018] Figure 1 is a schematic diagram showing the configuration of the diffraction apparatus according to this embodiment. Figure 2 is a graph showing the time evolution of the spatial temperature distribution and density distribution of a gas. Figure 3 is a graph showing the time evolution of the spatial temperature distribution and density distribution of a gas. Figure 4 is a diagram for explaining the control of the diffraction state. Figure 5 is a diagram for explaining the control of the diffraction state. Figure 6 is a diagram for explaining the control of the diffraction state. Figure 7 is a graph showing the time change of the refractive index modulation amount. Figure 8 is a graph showing the time change of the diffraction efficiency. Figure 9 is a graph showing the time evolution of the spatial temperature distribution and density distribution of a gas according to a modified example.

[0019] Hereinafter, a diffraction apparatus and diffraction method according to one embodiment will be described with reference to the drawings. In the description of the drawings, the same or corresponding elements are denoted by the same reference numerals, and redundant explanations may be omitted.

[0020] Figure 1 is a schematic diagram showing the configuration of a diffraction apparatus according to this embodiment. The diffraction apparatus 100 shown in Figure 1 is for diffracting a controlled laser beam Lin. The diffraction apparatus 100 includes a supply unit 10 for supplying gas V to a predetermined region R, a first irradiation unit 20 for irradiating the predetermined region R with a first laser beam L1 and a second laser beam L2, and a second irradiation unit 40 for irradiating the predetermined region R with a third laser beam L3.

[0021] The supply unit 10 includes a gas supply unit 11, a flow path element 12, and a gas suction unit 13. The gas supply unit 11 is, for example, a pump that supplies gas V containing molecules that resonately absorb the first laser beam L1, the second laser beam L2, and the third laser beam L3. Gas V is, for example, a gas containing ozone. The concentration of ozone in gas V is, for example, 50 mJ / cm² of ultraviolet laser light. ２ The value can be set to a level sufficient for absorption by a gas layer with a thickness of 3 mm to 10 mm (for example, around 1% to 3%).

[0022] When supplying gas V containing ozone in the gas supply unit 11, one example of a method for generating the ozone-containing gas V is to place oxygen O into a space gap that generates dielectric barrier discharge. ２ By supplying a raw material gas containing ozone and discharging it, ozone O ３ A method for generating a gas containing oxygen may also be used. More specifically, a method comprising a pair of metal electrodes arranged in a parallel plate shape and a pair of dielectrics placed between the metal electrodes, wherein oxygen is supplied from a raw gas source such as an oxygen cylinder or air tank. ２A raw material gas containing ozone (such as high-concentration oxygen or dehumidified air) is introduced into the space gap between a pair of dielectrics by a diaphragm pump, and a high-frequency high voltage is applied to a pair of metal electrodes by a high-frequency power supply. For example, a 13 MHz, 100 W power supply is used for the high-frequency power supply. The method for generating the ozone-containing gas V is not limited to the above embodiment, and may also be an electrolytic method or an ultraviolet lamp method. Alternatively, the ozone-containing gas V may be generated as a high-concentration ozone gas by vaporizing liquid ozone, for example.

[0023] The flow channel element 12 forms a flow channel through which the gas supplied from the gas supply unit 11 flows. The flow channel element 12 has an opening 14 to expose a part of the flow channel to the outside. The predetermined region R is the region exposed to the outside from the opening 14. The gas suction unit 13 is, for example, a pump that sucks in the gas that has flowed through the flow channel of the flow channel element 12.

[0024] The first irradiation unit 20 irradiates a gas V flowing through a predetermined region R of a flow channel formed by the flow channel element 12 with a first laser beam L1 and a second laser beam L2. More specifically, the first irradiation unit 20 includes an excitation light source 21 and an interference optical system 30. The interference optical system 30 includes a beam splitter 22 and reflectors 23A to 23F. The excitation light source 21 outputs laser beam L for exciting the gas V. If the gas V containing molecules that resonantly absorb the laser beam L is a gas containing ozone, the laser beam L (i.e., the first laser beam L1 and the second laser beam L2) can have a center wavelength that is particularly strong at the absorption wavelength of ozone (for example, a wavelength of 230 nm to 280 nm).

[0025] The beam splitter 22 receives the laser light L output from the excitation light source 21, splits the laser light L into a first laser beam L1 and a second laser beam L2, and emits them.

[0026] The reflectors 23C, 23D, 23E, and 23F are arranged in sequence on the optical path of the first laser beam L1 emitted from the beam splitter 22. The reflectors 23C, 23D, 23E, and 23F sequentially reflect the first laser beam L1, thereby causing the first laser beam L1 to enter a predetermined region R.

[0027] The reflectors 23A, 23B, and 23F are arranged in order on the optical path of the second laser beam L2 emitted from the beam splitter 22. The reflectors 23A, 23B, and 23F sequentially reflect the second laser beam L2, causing the second laser beam L2 to be incident on a predetermined region R. The reflectors 23A to 23F guide the first laser beam L1 and the second laser beam L2 so that they intersect in the predetermined region R, and irradiate the predetermined region R with the first laser beam L1 and the second laser beam L2.

[0028] As a result, a spatial periodic intensity distribution (interference fringes) is obtained in a predetermined region R due to the interference of the first laser beam L1 and the second laser beam L2. The spacing of these interference fringes is, for example, several μm, but can be varied. The reflecting mirrors 23A to 23F can be arranged so that the optical path lengths of the first laser beam L1 and the second laser beam L2 from the beam splitter 22 to the predetermined region R are approximately the same. The first laser beam L1 and the second laser beam L2 can be incident on the predetermined region R so that they have the same intensity. In order to increase the visibility of the interference fringes, it is desirable that the intensities of the first laser beam L1 and the second laser beam L2 be the same, but interference fringes can be formed even if they are not the same intensity.

[0029] Interference between the first laser beam L1 and the second laser beam L2 forms interference fringes in a predetermined region R, resulting in the formation of compression waves in the gas V within that region R. As shown in Figure 2(a), the temperature T and density ρ of the gas V in the predetermined region R are assumed to be spatially constant before irradiation with the first laser beam L1 and the second laser beam L2. In the graphs of Figures 2 and 3, the dashed line represents the temperature T of the gas V, and the solid line represents the density ρ.

[0030] In that state, as shown in Figure 2(b) (time t = 0 ns), when the first laser beam L1 and the second laser beam L2 are irradiated onto the gas V in a predetermined region R and interference fringes are formed in the predetermined region R, light absorption of the first laser beam L1 and the second laser beam L2 occurs in the gas V in accordance with the interference fringes, causing high and low temperature waves W1 (a state in which high and low temperature regions of the gas V are alternately formed in a fringe-like pattern) to be spatially formed in the gas V.

[0031] Subsequently, as shown in Figure 2(c) (for example, at time t = 80 ns), as time evolves, the higher temperature parts of gas V expand and the lower temperature parts of gas V compress, resulting in the spatial formation of compression waves W2 (a state in which parts of gas V with high and low density ρ are alternately formed in a striped pattern) that are in opposite phase to the high and low waves W1 of gas V. Furthermore, as shown in Figure 2(d) and (e) (for example, at times t = 160 ns and 240 ns), as time evolves further, spatial modulation of the density ρ of gas V by the compression waves W2 and spatial modulation of the temperature T by the high and low waves W1 alternately occur repeatedly.

[0032] In this way, the first irradiation unit 20 irradiates a predetermined region R with a first laser beam L1 and a second laser beam L2 so that they intersect in the predetermined region R, thereby forming interference fringes in the predetermined region R, and creating compression waves W2 in the gas V in the predetermined region R due to these interference fringes. The repetition time period of the spatial modulation of compression and rarefaction caused by these compression waves W2 depends on the interference fringe spacing.

[0033] As shown in Figure 1, when a compression wave W2 is formed in a gas V in a predetermined region R, controlled laser light Lin output from a predetermined optical system So is irradiated onto the predetermined region R, causing diffraction of the controlled laser light Lin and generating diffracted laser light Lo. The laser light Lo may be used for laser processing of the workpiece 50, for example, by irradiating the workpiece 50. The optical system So is, for example, a laser light source including an amplifier. A portion of the laser light Lo irradiated onto the workpiece 50 may become scattered and reflected light Lp. Therefore, it is desirable to suppress the return of a portion of the scattered and reflected light Lp to the optical system So, etc., as reflected light.

[0034] The second irradiation unit 40 includes a light source 41 and a reflector 42. The light source 41 outputs a third laser beam L3. The reflector 42 reflects the third laser beam L3 output from the light source 41, thereby causing the third laser beam L3 to be incident on a predetermined region R.

[0035] The second irradiation unit 40 reduces the amplitude of the compression wave W2 by irradiating the predetermined region R with a third laser beam L3 after the first laser beam L1 and the second laser beam L2 have been irradiated onto the predetermined region R. That is, as shown in Figure 3(a) (for example, at time t = 160 ns), when the second irradiation unit 40 irradiates the gas V in the predetermined region R with the third laser beam L3, light absorption of the third laser beam L3 occurs in the gas V, and as a result the lower temperature parts of the gas V are heated more efficiently than the higher temperature parts, the amplitude of the high and low wave W1 (difference in temperature) is reduced. As a result, as shown in Figure 3(b) (for example, at time t = 240 ns), the amplitude of the compression wave W2 of the gas V, which is formed in accordance with the high and low wave W1 as it evolves over time, is also reduced (difference in density). In the illustrated example, the second irradiation unit 40 uniformly irradiates the high and low temperature parts of the gas V with the third laser beam L3.

[0036] Thus, the diffraction apparatus 100 can switch between two states: one in which a compression wave W2 is formed in the gas V of the predetermined region R by irradiating the predetermined region R with a first laser beam L1 and a second laser beam L2, thereby allowing the controlled laser beam Lin to be diffracted; and another in which, after the first laser beam L1 and the second laser beam L2 have been irradiated, a third laser beam L3 is irradiated onto the predetermined region R, thereby reducing the amplitude of the compression wave W2 and making it difficult (or not) for the controlled laser beam Lin to be diffracted.

[0037] In other words, as shown in Figure 4, in the initial state before the first laser beam L1, the second laser beam L2, and the third laser beam L3 are irradiated onto the predetermined region R, compression waves W2 are not formed in the gas V of the predetermined region R, so the controlled laser beam Lin is not diffracted in the predetermined region R. For this reason, the controlled laser beam Lin emitted from the predetermined region R does not enter the workpiece 50.

[0038] Subsequently, as shown in Figure 5, the first irradiation unit 20 irradiates a predetermined region R with the first laser beam L1 and the second laser beam L2, thereby forming a compression wave W2 in the gas V of the predetermined region R. At this time, the second irradiation unit 40 is not irradiating with the third laser beam L3. In this case, as shown in Figure 7(a), a refractive index modulation amount G1 corresponding to the compression wave W2 is generated in the predetermined region R. Here, the time t1 at which the controlled laser beam Lin is irradiated is the time when the density modulation structure of the compression wave W2 is at its maximum, and the time when the diffraction efficiency is at its maximum. As a result, the controlled laser beam Lin is diffracted in the predetermined region R, generating diffracted laser beam Lo, which is irradiated onto the workpiece 50.

[0039] The time at which the first laser beam L1 and the second laser beam L2 are irradiated is defined as time t0, and the time t1 at which the controlled laser beam Lin is irradiated is defined as the first peak of the refractive index modulation amount G1 from time t0.

[0040] Subsequently, as shown in Figure 6, the second irradiation unit 40 irradiates a predetermined region R with the third laser beam L3, thereby reducing the amplitude of the compression wave W2 of the gas V. At this time, the first irradiation unit 20 is not irradiating with the first laser beam L1 and the second laser beam L2. In this case, as shown in Figure 7(b), after time t2 when the third laser beam L3 is irradiated, the peak of the refractive index modulation amount G1 decreases (for example, the peak disappears) in accordance with the reduction in the amplitude of the compression wave W2, resulting in a different refractive index modulation amount G2. Therefore, after time t2, the controlled laser beam Lin is not diffracted in the predetermined region R and does not incident on the workpiece 50. The diffraction state is controlled in the diffraction device 100 as described above.

[0041] Figure 8 is a graph showing the relationship between the diffraction efficiency of light based on compression waves and time. As shown in Figure 8, the second irradiation unit 40 can irradiate a predetermined region R with the third laser beam L3 at a time between temporally adjacent peaks of the diffraction efficiency G3 of light based on the compression wave W2. In the illustrated example, the second irradiation unit 40 irradiates the predetermined region R with the third laser beam L3 at time t2, between the first two peaks P1 and P2 of the diffraction efficiency G3, from the time when the first laser beam L1 and the second laser beam L2 are irradiated (time t0).

[0042] In particular, the second irradiation unit 40 can irradiate the third laser beam L3 to a predetermined region R in a time range (time t2) where the diffraction efficiency G3 is the lowest. The time range where the diffraction efficiency G3 is the lowest is, for example, a time range where the diffraction efficiency G3 is about 20% or less of the peak P1. In other words, by irradiating the third laser beam L3 to the predetermined region R in the time range where the diffraction efficiency G3 is about 20% or less of the peak P1, the amplitude of the coarse dense wave W2 can be effectively reduced. As a result, the peaks P2 and P3 that could occur in the diffraction efficiency G3 when the third laser beam L3 is not irradiated are reduced, resulting in a different diffraction efficiency G4. Therefore, in this case, it is possible to efficiently diffract the controlled laser beam Lin only in the vicinity of the first peak P1.

[0043] The third laser beam L3, similar to the first laser beam L1 and the second laser beam L2, has a central wavelength that is particularly strong in the absorption wavelength of ozone (for example, having a wavelength of 230 nm to 280 nm). Also, the pulse width of the third laser beam L3 is in the nanosecond region (for example, 1 ns or more and 100 ns or less), or in the picosecond to nanosecond region (for example, 1 ps or more and 100 ns or less). Furthermore, the fluence and pulse energy of the third laser beam L3 are, for example, equal to or greater than those of the first laser beam L1 and the second laser beam L2, and are respectively 10 mJ / cm ２ or more (as an example, 60 mJ / cm ２ ) and 1 mJ or more.

[0044] Also, the third laser beam L3 can be irradiated to the entire irradiation region of the first laser beam L1 and the second laser beam L2 in the predetermined region R. In other words, the irradiation region of the third laser beam L3 can be made to include the irradiation regions of the first laser beam L1 and the second laser beam L2 in the predetermined region R. As an example, the irradiation region of the third laser beam L3 is equal to or greater than the irradiation regions of the first laser beam L1 and the second laser beam L2, and is, for example, 10 mm × 10 mm or more.

[0045] Incidentally, as an example, as shown in FIG. 1, the diffraction device 100 may include a control unit 35. The control unit 35 controls the first irradiation unit 20 and the second irradiation unit 40 to control the timing of irradiation of the first laser beam L1 and the second laser beam L2, and the timing of irradiation of the third laser beam L3, thereby performing control of the diffraction state as described above. The control unit 35 can be configured as, for example, a computer device including a processor, a memory, a storage, a communication device, and the like. Further, in the control unit 35, the processor executes software (program) read into the memory or the like, controls reading and writing of data in the memory and the storage, and communication by the communication device, thereby performing various processes for controlling each unit such as the first irradiation unit 20 and the second irradiation unit 40.

[0046] Next, the diffraction method according to the present embodiment will be described. In this diffraction method, first, as shown in FIGS. 1 and 4, a gas is supplied to the predetermined region R (step S 101: supply step). In step S 101, the first laser beam L1 and the second laser beam L2 are not irradiated, and the third laser beam L3 is not irradiated.

[0047] Subsequently, as shown in FIGS. 1 and 5, the first laser beam L1 and the second laser beam L2 are irradiated onto the predetermined region R (step S 102: first irradiation step). In step S 102, the first laser beam L1 and the second laser beam L2 are irradiated onto the predetermined region R so as to intersect each other in the predetermined region R, thereby forming interference fringes in the predetermined region R, and forming a density wave W2 in the gas V in the predetermined region R due to the interference fringes. In step S 102, the third laser beam L3 is not irradiated.

[0048] Subsequently, as shown in FIGS. 1 and 6, the third laser beam L3 is irradiated onto the predetermined region R (step S 103: second irradiation step). In step S 103, after the first laser beam L1 and the second laser beam L2 are irradiated onto the predetermined region R, the third laser beam L3 is irradiated onto the predetermined region R, thereby reducing the amplitude of the density wave W2.

[0049] As described above, in the diffraction apparatus 100 and diffraction method according to this embodiment, interference fringes are formed in a predetermined region R to which gas V is supplied, by irradiating the region R with first laser light L1 and second laser light L2 so as to intersect each other. Gas V contains molecules that resonantly absorb the first laser light L1 and second laser light L2 (and third laser light L3). As a result, compression waves W2 caused by the interference fringes are formed in the gas V in the predetermined region R.

[0050] As a result, by injecting the controlled laser beam Lin into a predetermined region R where a compression wave of the gas V is formed, it becomes possible to diffract the controlled laser beam Lin (i.e., the controlled laser beam Lin becomes diffractable). This compression wave W2 of the gas V is repeatedly generated in time with each irradiation of the first laser beam L1 and the second laser beam L2 (i.e., spatial modulation of compression and rarefaction in time is repeatedly generated by the compression wave W2), and the state in which the controlled laser beam Lin can be diffracted is repeatedly generated.

[0051] In contrast, in the diffraction apparatus 100 and diffraction method according to this embodiment, a third laser beam L3 is further irradiated onto a predetermined region R after the first laser beam L1 and the second laser beam L2 have been irradiated onto it. As a result, the amplitude of the compression wave W2 of the gas V is reduced after irradiation with the third laser beam L3. Consequently, the controlled laser beam Lin incident on the predetermined region R becomes less susceptible to diffraction (i.e., the controlled laser beam Lin becomes less susceptible to diffraction). Thus, according to the diffraction apparatus 100 and diffraction method according to this embodiment, the diffraction state can be controlled at high speed in response to the irradiation of the third laser beam L3.

[0052] As described above, the compression wave W2 of the gas V formed in a predetermined region R by irradiation with the first laser beam L1 and the second laser beam L2 repeatedly generates spatial modulation of the compression and rarefaction over time. In other words, the peak of the optical diffraction efficiency G3 based on the compression wave W2 of the gas V repeatedly occurs over time. According to the inventor's findings, by irradiating the predetermined region R with the third laser beam L3 at a time between temporally adjacent peaks of the diffraction efficiency G3, it is possible to suitably reduce the amplitude of the compression wave W2 that would have occurred after that time.

[0053] Therefore, in the diffraction apparatus 100 according to this embodiment, the second irradiation unit 40 can irradiate a predetermined region R with a third laser beam L3 at a time between temporally adjacent peaks of the optical diffraction efficiency G3 based on the compression wave W2. In this case, as described above, it is possible to suitably reduce the amplitude of the compression wave W2 of the gas V and to more reliably control the diffraction state.

[0054] Furthermore, in the diffraction apparatus 100 according to this embodiment, the second irradiation unit 40 can irradiate a predetermined region R with a third laser beam L3 at time t2 between the first two peaks P1 and P2 of the diffraction efficiency G3 from the time the first laser beam L1 and the second laser beam L2 are irradiated. In this case, the amplitude of the compression wave W2 of the gas V after the first peak P1 of the diffraction efficiency G3 can be suitably reduced, making it difficult for the controlled laser beam Lin to be diffracted. Therefore, it is possible to suitably configure, for example, a regenerative amplifier or an optical switch that operates in single-pulse mode using the diffraction apparatus 100.

[0055] Conventionally, to suppress reflected light, an isolator utilizing the Faraday effect is used as an element to prevent the backflow of laser light. In this case, since a solid medium element is used, the damage threshold for laser light is small, and the element cross-section needs to be large. Also, since this element often utilizes polarization rotation, it can only be used with polarized light. In contrast, the diffraction apparatus 100 according to this embodiment can suppress reflected light without controlling the polarization of the controlled laser light Lin (i.e., it does not depend on the polarization state of the controlled laser light Lin). That is, the diffraction apparatus 100 can be operated with any polarization state of the controlled laser light Lin. Furthermore, the diffraction apparatus 100 can also be used for decoupling ASE light between laser light amplifications.

[0056] Furthermore, in the diffraction apparatus 100 according to this embodiment, the second irradiation unit 40 can irradiate a predetermined region R with a third laser beam L3 during a time range in which the diffraction efficiency G3 is at its lowest. In this case, it is possible to more reliably reduce the amplitude of the compression wave W2 of the gas V.

[0057] Furthermore, in the diffraction apparatus 100 according to this embodiment, the gas V may contain ozone, and the first laser beam L1, the second laser beam L2, and the third laser beam L3 may have central wavelengths at the absorption wavelength of ozone. In this way, by having the gas V contain ozone and the first laser beam L1, the second laser beam L2, and the third laser beam L3 have central wavelengths at the absorption wavelength of ozone, it is possible to suitably form compression waves W2 and reduce the amplitude of compression waves W2 for the gas V in a predetermined region R.

[0058] Furthermore, in the diffraction apparatus 100 according to this embodiment, the pulse width of the third laser beam L3 may be 1 ps or more and 100 ns or less. In this case, it is possible to suitably reduce the amplitude of the compression wave W2 that would have been generated after the time the third laser beam L3 was irradiated. As a result, it is possible to suppress diffraction of the controlled laser beam Lin at times other than the desired time, or to diffract the controlled laser beam Lin only during the desired time period.

[0059] Furthermore, in the diffraction apparatus 100 according to this embodiment, the fluence of the third laser beam L3 may be greater than or equal to the fluence of the first laser beam L1 and the second laser beam L2. In this case, irradiation with the third laser beam L3 makes it possible to more reliably reduce the amplitude of the compression wave W2 of the gas V.

[0060] Furthermore, in the diffraction apparatus 100 according to this embodiment, the pulse energy of the third laser beam L3 may be greater than or equal to the pulse energies of the first laser beam L1 and the second laser beam L2. In this case, the amplitude of the compression wave W2 of the gas V can be reduced more reliably.

[0061] Furthermore, in the diffraction apparatus 100 according to this embodiment, the irradiation area of ​​the third laser beam L3 in a predetermined region R may also include the irradiation areas of the first laser beam L1 and the second laser beam L2 in the predetermined region R. In this case, irradiation with the third laser beam L3 makes it possible to reduce the amplitude of the compression wave W2 of the gas V throughout the entire irradiation area of ​​the first laser beam L1 and the second laser beam L2.

[0062] The above embodiments illustrate one aspect of the present invention. Therefore, the present invention is not limited to the above embodiments and can be modified as needed.

[0063] For example, in the above embodiment, an example was described in which the second irradiation unit 40 uniformly irradiates the high-temperature and low-temperature portions of the gas V with the third laser beam L3 (see Figure 3(a)). However, as shown in Figure 9(a), the second irradiation unit 40 may selectively irradiate the portions of the gas V with the third laser beam L3 to the portions with relatively low temperatures. In this case, the portions of the gas V with relatively low temperatures are effectively heated, and the amplitude of the high and low temperature waves W1 of the gas V is more reliably reduced. As a result, as shown in Figure 9(b), the amplitude of the compression wave W2 of the gas V is more reliably reduced.

[0064] Furthermore, in the above embodiment, the light sources for the first laser beam L1 and the second laser beam L2 (excitation light source 21) and the light source for the third laser beam L3 (light source 41) are configured separately. However, the diffraction apparatus 100 may be configured to output the first laser beam L1, the second laser beam L2, and the third laser beam L3 from a single light source.

[0065] 10... Supply unit, 20... First irradiation unit, 40... Second irradiation unit, L1... First laser beam, L2... Second laser beam, L3... Third laser beam, R... Determined region, V... Gas, W2... Compression wave.

Claims

1. A diffraction apparatus comprising: a supply unit for supplying gas to a predetermined region; a first irradiation unit for irradiating the predetermined region with a first laser beam and a second laser beam; and a second irradiation unit for irradiating the predetermined region with a third laser beam, wherein the gas contains molecules that resonantly absorb the first laser beam, the second laser beam, and the third laser beam; the first irradiation unit irradiates the predetermined region with the first laser beam and the second laser beam so as to intersect each other in the predetermined region, thereby forming interference fringes in the predetermined region and creating compression waves in the gas in the predetermined region due to the interference fringes; and the second irradiation unit reduces the amplitude of the compression waves by irradiating the predetermined region with the third laser beam after the first laser beam and the second laser beam have been irradiated in the predetermined region.

2. The diffraction apparatus according to claim 1, wherein the second irradiation unit irradiates the predetermined region with the third laser light at a time between temporally adjacent peaks of the diffraction efficiency of light based on the compression wave.

3. The diffraction apparatus according to claim 2, wherein the second irradiation unit irradiates the predetermined region with the third laser light at a time between the time when the first laser light and the second laser light are irradiated and the first two peaks of the diffraction efficiency.

4. The diffraction apparatus according to claim 2 or 3, wherein the second irradiation unit irradiates the predetermined region with the third laser light during a time range in which the diffraction efficiency is lowest.

5. The diffraction apparatus according to any one of claims 1 to 4, wherein the gas contains ozone, and the first laser beam, the second laser beam, and the third laser beam have a central wavelength at the absorption wavelength of ozone.

6. The diffraction apparatus according to any one of claims 1 to 5, wherein the pulse width of the third laser beam is 1 ps or more and 100 ns or less.

7. The diffraction apparatus according to any one of claims 1 to 6, wherein the fluence of the third laser beam is equal to or greater than the fluence of the first laser beam and the second laser beam.

8. The diffraction apparatus according to any one of claims 1 to 7, wherein the irradiation area of ​​the third laser light in the predetermined region includes the irradiation areas of the first laser light and the second laser light in the predetermined region.

9. A diffraction method comprising: a supply step of supplying a gas to a predetermined region; a first irradiation step of irradiating the predetermined region with a first laser beam and a second laser beam; and a second irradiation step of irradiating the predetermined region with a third laser beam, wherein the gas contains molecules that resonantly absorb the first laser beam, the second laser beam, and the third laser beam; in the first irradiation step, interference fringes are formed in the predetermined region by irradiating the predetermined region with the first laser beam and the second laser beam so as to intersect each other in the predetermined region, thereby forming compression waves in the gas in the predetermined region due to the interference fringes; and in the second irradiation step, the amplitude of the compression waves is reduced by irradiating the predetermined region with the third laser beam after the first laser beam and the second laser beam have been irradiated in the predetermined region.

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