Laser amplifier and laser amplification method

Abstract

To provide a laser amplifier device and a laser amplification method which do not require the spatial separation of each wavelength component in amplified light, and with which it is possible to simplify the optical system for heightening the output of ultrashort pulse light.SOLUTION: A laser amplifier device 1A comprises an amplification unit 2 and a phase adjustment unit 3, the amplification unit 2 including a signal light source 11, an excitation light source 12 and a non-linear optical crystal 13, the non-linear optical crystal 13 including a plurality of crystal portions 13A-13D which are spatially different. The signal light source 11, the excitation light source 12 and the non-linear optical crystal 13 are arranged so that signal light S and excitation light E simultaneously enter each of the plurality of crystal portions 13A-13D, and that at least one of the crystal axis of the plurality of crystal portions 13A-13D and the incident angle of signal light S and the crystal axis of the plurality of crystal portions 13A-13D and the incident angle of excitation light E is different.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a laser amplification device and a laser amplification method. [Background technology]

[0002] For example, a known method for obtaining ultrashort pulsed light on the order of femtoseconds is the mode-locking method, in which laser oscillation is achieved by aligning the phases of each wavelength component in a beam having a wide spectral band. In recent years, there has been an increasing demand for higher output ultrashort pulsed light, and the development of technologies for amplifying laser light having a wide spectral band in conjunction with the mode-locking method has been progressing. One known technology related to such laser amplification is the optical parametric amplification method, in which signal light and pump light are incident on a nonlinear optical crystal to amplify the signal light.

[0003] An example of a laser amplifier using optical parametric amplification is the laser amplifier described in Patent Document 1. This conventional laser amplifier includes a nonlinear optical crystal that transmits signal light and a shaping optical system that shapes pump light and makes it incident on the nonlinear optical crystal. The shaping optical system has an optical array that splits the pump light into a first divided beam and a second divided beam. The shaping optical system also has lenses that focus the first divided beam and the second divided beam on the nonlinear optical crystal so that the angle between the first divided beam and the signal light is different from the angle between the second divided beam and the signal light. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-112706 Summary of the Invention [Problem to be solved by the invention]

[0005] In general, nonlinear optical crystals have a property that their refractive index varies depending on the wavelength of incident light. In response to this property, the laser amplifier described in Patent Document 1 splits pump light while using a single beam of signal light having a wide spectral band, and spatially and temporally overlaps the signal light and pump light when they are incident on the same part of the nonlinear optical crystal. Therefore, in the laser amplifier described in Patent Document 1, the phases of the wavelength components of the amplified signal light (amplified light) are different from each other, and these wavelength components are emitted from the nonlinear optical crystal without being spatially separated. Therefore, when mode-locking is performed using amplified light, it is necessary to spatially separate the wavelength components before adjusting their phases, which may complicate the optical system for increasing the output power of ultrashort pulse light.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a laser amplification device and a laser amplification method that do not require spatial separation of each wavelength component in the amplified light and that can simplify the optical system for increasing the output power of ultrashort pulse light. [Means for solving the problem]

[0007] A laser amplification device according to one aspect of the present disclosure includes an amplifier section that amplifies the intensity of signal light and outputs amplified light, and a phase adjustment section that adjusts the phase of each wavelength component contained in the signal light or the amplified light, wherein the amplifier section has a signal light source that outputs signal light, a pumping light source that outputs pumping light, and a nonlinear optical crystal that emits amplified light in response to the incidence of the signal light and the pumping light, and the nonlinear optical crystal has a plurality of spatially distinct crystal portions, and the signal light source, the pumping light source, and the nonlinear optical crystal are arranged so that the signal light and the pumping light are simultaneously incident on each of the plurality of crystal portions, and at least one of the angles of incidence of the signal light and the crystal axes of the plurality of crystal portions and the angle of incidence of the pumping light is different.

[0008] This laser amplifier can generate amplified light by amplifying the intensity of the signal light by inputting signal light and pump light into a nonlinear optical crystal. In this laser amplifier, the signal light and pump light are simultaneously input to each of multiple spatially distinct crystal portions in the nonlinear optical crystal, and at least one of the angles of incidence of the signal light and the pump light relative to the crystal axes of the multiple crystal portions is different. Therefore, although the phases of the wavelength components of the amplified light output from the nonlinear optical crystal are different from each other, these wavelength components can be output from the nonlinear optical crystal in a spatially separated state. Therefore, this laser amplifier does not require spatial separation of the wavelength components of the amplified light, simplifying the optical system for generating high-power ultrashort pulse light.

[0009] The plurality of crystal portions may be arranged so as to be spatially separated, in which case the wavelength components of the amplified light can be spatially separated more reliably.

[0010] The plurality of crystal portions may be integrally joined, which allows for a reduction in the size of the nonlinear optical crystal and improves the workability of positioning the nonlinear optical crystal relative to the optical system for the signal light and pump light.

[0011] The crystal axes of the multiple crystal portions may be different from one another. In this case, the angles of the signal light and pump light incident on each of the multiple crystal portions can be uniformly determined. This simplifies angle adjustment of the signal light and pump light.

[0012] A single signal light and pump light may be incident on each of the multiple crystal portions. In this case, the optical system for the signal light and pump light can be simplified. Unlike when multiple signal light and pump light are used, changes in optical characteristics due to interference between signal light or pump light can be prevented. In addition, the utilization efficiency of the pump light can be sufficiently ensured.

[0013] A plurality of signal beams may be incident on each of the plurality of crystal portions at equal angles, and a plurality of pump beams may be incident on each of the plurality of crystal portions at equal angles. When the signal beam is divided into a plurality of beams, the wavelength width of each beam becomes appropriately narrower than in the case of a single beam with a wide wavelength width and a narrow time width, and it is possible to prevent the time width of each beam from becoming excessively narrow. This keeps the peak intensities of the signal beam and pump beam within a certain range, thereby preventing damage to the elements that make up the optical system.

[0014] The crystal axes of the plurality of crystal portions may be the same, in which case there is no need to prepare a plurality of crystal portions with different crystal axes, thereby simplifying the configuration of the nonlinear optical crystal.

[0015] A single signal beam may be incident on each of the multiple crystal portions, and multiple pump beams may be incident at different angles. In this case, the optical system for the signal beam can be simplified. Unlike when multiple signal beams are used, changes in optical characteristics due to interference between signal beams can be prevented. Furthermore, the utilization efficiency of the pump beam can be sufficiently ensured.

[0016] A plurality of signal beams may be incident on each of the plurality of crystal portions at different angles, and a single pump beam may be incident on each of the plurality of crystal portions. In this case, the optical system for the pump beam can be simplified. Unlike when multiple pump beams are used, changes in optical characteristics due to interference between the pump beams can be prevented.

[0017] For each of the multiple crystal portions, one of the multiple signal beams and one of the multiple pump beams may be incident at an equal angle, and the other may be incident at a different angle. When the signal beam and the pump beam are divided into multiple beams, the wavelength width of each beam is appropriately narrowed, and it is possible to prevent the time width of each beam from becoming excessively narrow. This keeps the peak intensities of the signal beams and the pump beams within a certain range, thereby preventing damage to the elements that make up the optical system.

[0018] The laser amplifier may further include a focusing unit that focuses the amplified light whose phases of the wavelength components have been adjusted by the phase adjusting unit, thereby enabling generation of high-power ultrashort pulsed light without spatially separating the wavelength components in a stage subsequent to the amplification unit.

[0019] The laser amplifier may further include an expander that applies dispersion to the signal light upstream of the nonlinear optical crystal to expand its time width, and a compressor that applies reverse dispersion to the amplified light downstream of the nonlinear optical crystal to compress its time width. In this case, by compressing the time width of the amplified light having high energy obtained by chirped pulse amplification after amplification, it is possible to obtain ultrashort pulse light with high peak intensity. Furthermore, because the amplified light before compression has a relatively wide time width, damage to elements constituting the optical system can be suppressed.

[0020] A laser amplification method according to one aspect of the present disclosure includes an amplification step of amplifying the intensity of the signal light by inputting signal light and pump light into a nonlinear optical crystal, thereby outputting amplified light, and a phase adjustment step of adjusting the phase of each wavelength component contained in the signal light or the amplified light, wherein in the amplification step, the signal light and pump light are simultaneously input into each of a plurality of spatially distinct crystal portions in the nonlinear optical crystal, with at least one of the angles of incidence of the signal light relative to the crystal axes of the plurality of crystal portions and the angle of incidence of the pump light relative to the crystal axes of the plurality of crystal portions being different.

[0021] In this laser amplification method, signal light and pump light are incident on a nonlinear optical crystal, thereby generating amplified light by amplifying the intensity of the signal light. In this laser amplification method, the signal light and pump light are simultaneously incident on each of a plurality of spatially distinct crystal portions in the nonlinear optical crystal, with at least one of the angles of incidence of the signal light and the pump light relative to the crystal axes of the plurality of crystal portions being different. As a result, although the phases of the wavelength components of the amplified light output from the nonlinear optical crystal are different from each other, these wavelength components can be output from the nonlinear optical crystal in a spatially separated state. Therefore, this laser amplification method does not require spatial separation of the wavelength components of the amplified light, thereby simplifying the optical system for generating high-power ultrashort pulse light.

[0022] In the amplification step, a plurality of crystal portions may be arranged so as to be spatially separated, in which case the wavelength components of the amplified light can be spatially separated more reliably.

[0023] In the amplification step, multiple crystal portions may be integrally joined and arranged, which reduces the size of the nonlinear optical crystal and improves the workability of positioning the nonlinear optical crystal relative to the optical system of the signal light and pump light.

[0024] In the amplification step, the crystal axes of the multiple crystal portions may be different from one another. In this case, the angles of the signal light and the pump light incident on each of the multiple crystal portions can be uniformly determined. This simplifies the angle adjustment of the signal light and the pump light.

[0025] In the amplification step, a single signal light and pump light may be incident on each of the multiple crystal portions. In this case, the optical system for the signal light and pump light can be simplified. Unlike when multiple signal light and pump light are used, changes in optical characteristics due to interference between signal light or pump light can be prevented. In addition, the utilization efficiency of the pump light can be sufficiently ensured.

[0026] In the amplification step, the multiple signal beams may be incident on the multiple crystal portions at equal angles to each other, and the multiple pump beams may be incident on the multiple crystal portions at equal angles to each other. When the signal beam is divided into multiple beams, the wavelength width of each beam becomes appropriately narrower than in the case of a single beam with a wide wavelength width and a narrow time width, and it is possible to prevent the time width of each beam from becoming excessively narrow. This keeps the peak intensities of the signal beam and the pump beam within a certain range, thereby preventing damage to the elements that make up the optical system.

[0027] In the amplification step, the crystal axes of the plurality of crystal portions may be the same, which eliminates the need to prepare a plurality of crystal portions with different crystal axes, thereby simplifying the configuration of the nonlinear optical crystal.

[0028] In the amplification step, a single signal beam may be incident on each of the multiple crystal portions, and multiple pump beams may be incident at different angles. In this case, the optical system for the signal beam can be simplified. Unlike when multiple signal beams are used, changes in optical characteristics due to interference between signal beams can be prevented. Furthermore, the utilization efficiency of the pump beam can be sufficiently ensured.

[0029] In the amplification step, multiple signal beams may be incident on multiple crystal portions at different angles, and a single pump beam may be incident on each crystal portion. In this case, the optical system for the pump beam can be simplified. Unlike when multiple pump beams are used, changes in optical characteristics due to interference between pump beams can be prevented.

[0030] In the amplification step, one of the plurality of signal beams and one of the plurality of pump beams may be incident on each of the plurality of crystal portions at an equal angle, and the other may be incident on each of the plurality of crystal portions at a different angle. When the signal beam and the pump beam are divided into a plurality of beams, the wavelength width of each beam is appropriately narrowed, and the time width of each beam can be prevented from becoming excessively narrow. This keeps the peak intensities of the signal beams and the pump beams within a certain range, thereby preventing damage to the elements constituting the optical system.

[0031] The laser amplification method may further include a focusing step of focusing the amplified light whose phases of the wavelength components have been adjusted in the phase adjusting step, thereby making it possible to generate high-power ultrashort pulsed light without spatially separating the wavelength components in a stage subsequent to the amplification unit.

[0032] The laser amplification method may further include an expansion step, which applies dispersion to the signal light to expand its time width as a pre-step of the amplification step, and a compression step, which applies inverse dispersion to the amplified light to compress its time width as a post-step of the amplification step. In this case, by compressing the time width of the amplified light having high energy obtained by chirped pulse amplification after amplification, amplified light with high peak intensity can be obtained. Furthermore, since the amplified light before compression has a relatively wide time width, damage to elements constituting the optical system can be suppressed. [Effects of the Invention]

[0033] According to the present disclosure, spatial separation of the wavelength components in the amplified light is not required, and the optical system for increasing the output of ultrashort pulsed light can be simplified. [Brief explanation of the drawings]

[0034] [Figure 1] 1 is a schematic diagram showing the relationship between a nonlinear optical crystal used in optical parametric amplification and the optical axis of an incident beam. [Figure 2] 1A and 1B are diagrams illustrating a design example of amplified light using optical parametric amplification. [Figure 3] 1 is a schematic diagram illustrating a configuration of a laser amplifier device according to a first embodiment of the present disclosure. [Figure 4] 3A to 3C are schematic diagrams showing waveforms of wavelength, phase, and time of signal light and pump light before amplification in the first embodiment. [Figure 5] 4A to 4C are schematic diagrams showing waveforms of wavelength, phase, and time of signal light after amplification in the first embodiment. [Figure 6] 4A to 4C are schematic diagrams showing waveforms of wavelength, phase, and time of amplified light after phase adjustment in the first embodiment. [Figure 7] 3 is a schematic diagram showing the time waveform of ultrashort pulsed light obtained in a light collecting section in the first embodiment. FIG. [Figure 8] FIG. 4 is a schematic diagram illustrating a configuration of a laser amplifier device according to a second embodiment of the present disclosure. [Figure 9] 10A and 10B are schematic diagrams showing waveforms of wavelength, phase, and time of signal light and pump light before amplification in the second embodiment. [Figure 10] FIG. 10 is a schematic diagram illustrating a configuration of a laser amplifier device according to a third embodiment of the present disclosure. [Figure 11] FIG. 10 is a schematic diagram illustrating a configuration of a laser amplifier device according to a fourth embodiment of the present disclosure. [Figure 12] 10A and 10B are schematic diagrams showing waveforms of wavelength, phase, and time of signal light and pump light before amplification in the fourth embodiment. [Figure 13] FIG. 10 is a schematic diagram illustrating a configuration of a laser amplifier according to a fifth embodiment of the present disclosure. [Figure 14] FIG. 10 is a schematic diagram illustrating a configuration of a laser amplifier according to a sixth embodiment of the present disclosure. [Figure 15] 13A and 13B are schematic diagrams showing waveforms of wavelength, phase, and time of signal light before expansion in the sixth embodiment. [Figure 16] 13A and 13B are schematic diagrams showing waveforms of wavelength, phase, and time of signal light after expansion in the sixth embodiment. [Figure 17] 13A and 13B are schematic diagrams showing waveforms of wavelength, phase, and time of signal light after amplification in the sixth embodiment. [Figure 18] 13A and 13B are schematic diagrams showing waveforms of wavelength, phase, and time of signal light after phase adjustment in the sixth embodiment. [Figure 19] 13A and 13B are schematic diagrams showing waveforms of wavelength, phase, and time of compressed signal light in the sixth embodiment. [Figure 20] FIG. 20 is a schematic diagram showing the time waveform of ultrashort pulsed light obtained in a focusing unit in the sixth embodiment. [Figure 21]FIG. 12 is a schematic diagram illustrating a configuration of a laser amplifier device according to a seventh embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0035] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a laser amplification device and a laser amplification method according to one aspect of the present disclosure will be described in detail below with reference to the drawings. [Principle of laser amplification disclosed herein]

[0036] First, the principles of the laser amplifier and laser amplification method according to this embodiment will be described. The laser amplifier and laser amplification method according to this embodiment are configured by applying optical parametric amplification, which amplifies signal light by injecting signal light and pumping light into a nonlinear optical crystal. Furthermore, the laser amplifier and laser amplification method according to this embodiment apply mode-locking to amplified light obtained by amplifying the intensity of signal light using optical parametric amplification, and are capable of generating high-power ultrashort pulse light, for example, on the order of femtoseconds.

[0037] In general laser amplification methods, the wavelength of the amplified laser light is determined by the medium used, but in optical parametric amplification, the wavelength of the amplified laser light can be selected by adjusting the cut angle of the nonlinear optical crystal or the angles of the signal light and pump light incident on the nonlinear optical crystal.

[0038] 1 is a schematic diagram showing the relationship between a nonlinear optical crystal used in optical parametric amplification and the optical axis of an incident beam. As shown in the figure, in a nonlinear optical crystal 101, signal light 102 is propagated in a direction at an angle θ1 that satisfies the phase matching angle with respect to a certain crystal axis direction (here, the c-axis), and pump light 103 is propagated in a direction at an angle θ2 that satisfies the phase matching angle with respect to the propagation direction of the signal light 102, thereby enabling optical parametric amplification of the signal light 102. Therefore, for example, if multiple nonlinear optical crystals 101 with slightly different crystal cut angles are prepared, the wavelength bands (amplification bands) of the amplified light obtained by amplifying the intensity of the signal light 102 can be made different for each of the multiple nonlinear optical crystals 101.

[0039] Figure 2 shows an example of a design of amplified light using optical parametric amplification. In this figure, the horizontal axis represents the crystal cut angle (°) and the vertical axis represents wavelength (nm). Curve K in the figure indicates the amplifiable wavelength when pump light is incident at a predetermined angle (corresponding to θ2 in Figure 1) relative to signal light incident parallel to the crystal cut angle (the angle corresponding to θ1 in Figure 1). In the example of Figure 2, the angular shift between the signal light and pump light is 2.6°, and the wavelength of the pump light is 527 nm. In addition, in the example of Figure 2, five nonlinear optical crystals 101A to 101E with different cut angles were prepared, and these nonlinear optical crystals 101A to 101E were bonded together to verify the expandability of the amplification bandwidth of the signal light. The cut angles of the nonlinear optical crystals 101A to 101E were 21.70°, 21.66°, 21.62°, 21.58°, and 21.54°, respectively.

[0040] From the results in Figure 2, when optical parametric amplification is performed using five nonlinear optical crystals 101A to 101E with different cut angles, the amplification band of signal light 102 is estimated to be approximately 280 nm. For example, when optical parametric amplification is performed using only nonlinear optical crystal 101A, the amplification band of signal light 102 is estimated to be approximately 100 nm. In this way, it can be seen that when multiple nonlinear optical crystals 101 with slightly different cut angles are prepared, the amplification bands of signal light 102 in each nonlinear optical crystal 101 are combined, making it possible to expand the amplification band of signal light 102.

[0041] In the mode-locking method, by aligning the phases of pulsed light in a wider wavelength range, it is possible to further narrow the time width. For example, in the case of signal light 102 that was optically parametrically amplified using only nonlinear optical crystal 101A, the time width of the ultrashort pulsed light obtained by mode-locking was approximately 10 fs, whereas in the case of signal light 102 that was optically parametrically amplified using nonlinear optical crystals 101A to 101E, the time width of the ultrashort pulsed light obtained by mode-locking was narrowed to approximately 4 fs. Below, various embodiments of a laser amplification device and a laser amplification method configured based on this principle will be described in detail. [First embodiment]

[0042] 3 is a schematic diagram showing the configuration of a laser amplification device according to a first embodiment of the present disclosure. As shown in the figure, a laser amplification device 1A according to the first embodiment is configured to include an amplification unit 2, a phase adjustment unit 3, and a focusing unit 4. The amplification unit 2 is a part that executes an amplification step of amplifying the intensity of signal light S and outputting amplified light A. The amplification unit 2 includes a signal light source 11 that outputs signal light S, a pumping light source 12 that outputs pumping light E, and a nonlinear optical crystal 13 that emits amplified light A in response to the incidence of signal light S and pumping light E.

[0043] The signal light S is light to be amplified by the laser amplifier 1, and is pulsed light in this example. The signal light source 11 may be, for example, a titanium sapphire laser, an Er-doped laser, an Nd-doped laser, an Yb-doped laser, a Tm-doped laser, a Cr-doped laser, an Fe-doped laser, or a supercontinuum light. In this embodiment, a plurality of (four) signal light beams S1 to S4 are incident on the nonlinear optical crystal 13 from the signal light source 11. The optical axes of the signal light beams S1 to S4 are aligned in a line in a direction perpendicular to the direction in which these optical axes extend. The angles of incidence of the signal light beams S1 to S4 on the nonlinear optical crystal 13 are equal to one another. The signal light beams S1 to S4 may be output from a plurality of signal light sources 11, or may be signal light S from a single signal light source 11 separated by a separation optical system or the like.

[0044] The pumping light E is light used to amplify the signal light S, and here, like the signal light S, is pulsed light. The pumping light source 12 may be, for example, a titanium sapphire laser, an Er-doped laser, an Nd-doped laser, a Yb-doped laser, a Tm-doped laser, a Cr-doped laser, or an Fe-doped laser. In this embodiment, a plurality of (four) pumping lights E1 to E4 are incident on the nonlinear optical crystal 13 from the pumping light source 12. The optical axes of the pumping lights E1 to E4 are aligned in a direction perpendicular to the direction in which the optical axes extend. The angles of incidence of the pumping lights E1 to E4 with respect to the nonlinear optical crystal 13 are equal to each other. The pumping lights E1 to E4 may be output from a plurality of pumping light sources 12, or may be pumping light E from a single pumping light source 12 separated by a separation optical system or the like.

[0045] The nonlinear optical crystal 13 is a part that emits amplified light A by the incidence of signal light S and pumping light E due to the nonlinear optical effect. Examples of the nonlinear optical crystal 13 include BBO (β-BaB2O4) crystal, LBO (LiB3O5) crystal, and CLBO (CsLiB6O 10) crystal, YCOB (YCa4O(BO3)3) crystal, GaSe crystal, AgGaS2 crystal, AgGaSe2 crystal, LiInS2 crystal, LiInSe2 crystal, etc. can be used. The nonlinear optical crystal 13 has a plurality of spatially distinct crystal portions 13A to 13D. "Spatially distinct" means that they are arranged so as not to overlap each other in the in-plane direction of the beam cross section of the signal light S. In this embodiment, the plurality of crystal portions 13A to 13D are aligned in a line with a small gap between them along the direction in which the optical axes of the signal light S1 to S4 are aligned. The plurality of crystal portions 13A to 13D may be integrally bonded by an adhesive or the like, or may be arranged simply in contact with each other without the use of an adhesive or the like.

[0046] The above-mentioned signal light source 11, pumping light source 12, and nonlinear optical crystal 13 are arranged so that the signal light S and the pumping light E are simultaneously incident on each of the multiple crystal portions 13A to 13D, and at least one of the incident angle between the crystal axis of the multiple crystal portions 13A to 13D and the signal light S and the incident angle between the crystal axis of the multiple crystal portions 13A to 13D and the pumping light E is different.

[0047] In this embodiment, the signal light S and the pump light E are incident on the nonlinear optical crystal 13 from different directions. The difference in the angle of incidence between the signal light S1-S4 and the pump light E1-E4 with respect to the nonlinear optical crystal 13 (the angle corresponding to θ2 in FIG. 1) is, for example, 2.6°. Furthermore, in this embodiment, the crystal axes of the multiple crystal portions 13A-13D are different from one another. That is, the multiple crystal portions 13A-13D have different crystal cut angles. Here, the cut angles of the crystal portions 13A-13D (the angle corresponding to θ1 in FIG. 1) are 21.65°, 21.63°, 21.61°, 21.59°, and 21.57°, respectively.

[0048] Signal light S1 to S4 and pump light E1 to E4 are simultaneously incident on each of the multiple crystal portions 13A to 13D. Specifically, signal light S1 and pump light E1 are simultaneously incident on crystal portion 13A, and signal light S2 and pump light E2 are simultaneously incident on crystal portion 13B. Furthermore, signal light S3 and pump light E3 are simultaneously incident on crystal portion 13C, and signal light S4 and pump light E4 are simultaneously incident on crystal portion 13D.

[0049] Amplified light A1 to A4, which is obtained by amplifying the intensities of signal light S1 to S4, is emitted from each of the multiple crystal portions 13A to 13D. The emission optical axis of each of the amplified light A1 to A4 coincides with the optical axis of the signal light S1 to S4 before amplification. In this embodiment, as described above, the nonlinear optical crystal 13 has multiple spatially distinct crystal portions 13A to 13D. Therefore, each of the amplified light A1 to A4 is emitted from each of the multiple crystal portions 13A to 13D in a state where it is spatially separated from one another.

[0050] Although not shown, idler lights having wavelengths different from those of the pre-amplified signal lights S1 to S4 may be generated in correspondence with the signal lights S1 to S4, in addition to the amplified lights A1 to A4, when the signal lights S1 to S4 pass through the nonlinear optical crystal 13. The optical axes of these idler lights are shifted from the optical axes of the pre-amplified signal lights S1 to S4, respectively, but these idler lights can also be used as amplified light.

[0051] The phase adjustment unit 3 is a part that performs a phase adjustment step of adjusting the phase of each wavelength component contained in the signal light S or the amplified light A. The phase adjustment unit 3 can be configured, for example, by a spatial light phase modulator such as an LCOS-SLM, a deformable mirror, a femtosecond pulse shaper, or an acousto-optic programmable dispersion filter. In this embodiment, the phase adjustment units 3 are respectively disposed on the optical axes of the amplified lights A1 to A4 between the nonlinear optical crystal 13 and the focusing unit 4, and adjust the phases so that the phases of the wavelength components contained in the amplified lights A1 to A4 are aligned with each other. In this embodiment, when the amplified lights A1 to A4 enter the focusing unit 4, they pass through an optical window 15 of the vacuum chamber 14, which will be described later. For this reason, it is preferable that the phase adjustment unit 3 adjusts the phase of each wavelength component contained in the amplified lights A1 to A4 while taking into account the phase shift caused by passing through the optical window 15.

[0052] The phase adjustment unit 3 only needs to function to align the phases of the wavelength components contained in the amplified light A when the amplified light A enters the focusing unit 4 located downstream of the nonlinear optical crystal 13, and the phases of the wavelength components contained in the amplified light A do not necessarily have to be aligned after passing through the phase adjustment unit 3. Therefore, the phase adjustment unit 3 may be located upstream of the nonlinear optical crystal 13. For example, the phase adjustment unit 3 may be located on the optical axis of each of the signal lights S1 to S4 between the signal light source 11 and the nonlinear optical crystal 13. In this case, the phase of each wavelength component contained in the signal lights S1 to S4 can be adjusted by taking into consideration both the phase shift due to passage through the nonlinear optical crystal 13 and the phase shift due to passage through the optical window 15.

[0053] The focusing unit 4 is a part that executes the focusing step of focusing the amplified light A, the phases of which have been adjusted by the phase adjustment unit 3. The focusing unit 4 is composed of, for example, a focusing lens 16 disposed in the vacuum chamber 14. The focusing lens 16 is, for example, a convex lens. The focusing unit 4 may also be composed of a concave mirror. The amplified light A1 to A4, the phases of which have been aligned by the phase adjustment unit 3, enters the vacuum chamber 14 through optical windows 15 disposed corresponding to the optical axes of the amplified light A1 to A4, and is focused to a single point by the focusing lens 16. By focusing the amplified light A1 to A4, the phases of which have been aligned to a single point, the wavelength components of the amplified light A1 to A4 are combined to become broadband light, and high-power ultrashort pulsed light P is generated at the focusing point.

[0054] 4 to 6 are diagrams showing the waveforms of the wavelength, phase, and time of the signal light S, pumping light E, and amplified light A at various positions in the laser amplifier 1A. Fig. 4 is a diagram showing the waveforms of the wavelength, phase, and time of the signal light S emitted from the signal light source 11 and the pumping light E emitted from the pumping light source 12 (i.e., the signal light S and pumping light before amplification).

[0055] As shown in the figure, the signal light S1 to S4 have different center wavelengths, for example, in the range of 700 nm to 1100 nm. The phases of the signal light S1 to S4 are roughly constant within each wavelength band and are aligned with each other. The time width of the signal light S1 to S4 is roughly inversely proportional to its own wavelength width, for example, in the range of 10 fs to 1 ps. In this embodiment, the pump light E1 to E4 have the same center wavelength, but the center wavelengths of the pump light E1 to E4 may be different from each other. The phases of the pump light E1 to E4 are roughly constant within each wavelength band and are aligned with each other. The time width of the pump light E1 to E4 is, for example, in the range of 1 ps to 1 ns.

[0056] In the example of Fig. 4, signal light S1 has a center wavelength of 800 nm, a wavelength width of 100 nm, and a time width (full width at half maximum) of 10 fs, signal light S2 has a center wavelength of 885 nm, a wavelength width of 70 nm, and a time width (full width at half maximum) of 16 fs, signal light S3 has a center wavelength of 945 nm, a wavelength width of 50 nm, and a time width (full width at half maximum) of 26 fs, and signal light S4 has a center wavelength of 984 nm, a wavelength width of 28 nm, and a time width (full width at half maximum) of 50 fs, and pump light E1 to E4 have a center wavelength of 527 nm, a wavelength width of 0.1 nm, and a time width (full width at half maximum) of 10 ps.

[0057] Each wavelength component of the signal light S may have a band wider than the wavelength band amplified in the amplifier 2. That is, the wavelength bands of the signal light S1 to S4 may overlap with each other. In this case, the wavelength bands of the amplified light A after being focused by the focuser 4 are continuous, and the temporal waveform of the obtained ultrashort pulsed light P can be made to approximate a Gaussian distribution or a Sinc function distribution. Even when the wavelength bands of the signal light S1 to S4 do not overlap with each other, by making the wavelength bands close to each other, it is possible to obtain ultrashort pulsed light with a temporal waveform different from a Gaussian distribution.

[0058] 5 is a diagram showing a schematic diagram of the wavelength, phase, and time waveform of amplified light A (i.e., amplified signal light S) output from nonlinear optical crystal 13. As shown in the figure, the intensity of amplified light A1 to A4 output from nonlinear optical crystal 13 increases relative to signal light S1 to S4 due to optical parametric amplification. Meanwhile, since nonlinear optical crystal 13 has a property in which the refractive index varies depending on the wavelength of the incident light, the phases of the wavelength components of amplified light A1 to A4 are delayed according to the wavelength components of signal light S1 to S4, and are shifted from each other. The time width of amplified light A1 to A4 is maintained at the same time as the time width of signal light S1 to S4, but the peak positions of the time waveforms are shifted according to the wavelength difference.

[0059] 6 is a diagram schematically showing the wavelength, phase, and time waveform of amplified light A after phase adjustment. As shown in the figure, in amplified light A1 to A4 after phase adjustment, the intensity before phase adjustment is maintained, while the phases of the wavelength components generated during amplification in nonlinear optical crystal 13 are aligned with each other. Amplified light A1 to A4, whose wavelength components have been phase-aligned, is focused by focusing unit 4, whereby high-power ultrashort pulsed light P with a time width (full width at half maximum) of approximately several fs to 100 fs is generated, as shown in FIG.

[0060] As described above, the laser amplifier 1A can generate amplified light A by amplifying the intensity of the signal light S by inputting signal light S and pump light E into the nonlinear optical crystal 13. In the laser amplifier 1A, the signal light S and pump light E are input to each of a plurality of spatially distinct crystal portions 13A-13D in the nonlinear optical crystal 13, and both the angle of incidence of the signal light S relative to the crystal axes of the plurality of crystal portions 13A-13D and the angle of incidence of the pump light E relative to the crystal axes of the plurality of crystal portions 13A-13D are different. Therefore, although the phases of the wavelength components of the amplified light A1-A4 output from the nonlinear optical crystal 13 are different from one another, these wavelength components can be output from the nonlinear optical crystal 13 in a spatially separated state. Therefore, the laser amplifier 1A does not require spatial separation of the wavelength components of the amplified light A1-A4, and therefore does not require the placement of optical components such as a diffraction grating in the optical system, thereby simplifying the optical system for increasing the output power of the ultrashort pulse light P.

[0061] In the laser amplifier 1A, the multiple crystal portions 13A-13D are arranged so as to be spatially separated. This allows the wavelength components of the amplified light A1-A4 to be spatially separated more reliably. When the multiple crystal portions 13A-13D are integrally bonded with an adhesive or the like, the nonlinear optical crystal 13 can be made smaller. Furthermore, the workability of positioning the nonlinear optical crystal 13 relative to the optical system of the signal light S and the pumping light E can be improved.

[0062] In the laser amplifier 1A, the crystal axes of the multiple crystal portions 13A-13D are different from one another. The multiple signal beams S1-S4 and the multiple pump beams E1-E4 are incident on the multiple crystal portions 13A-13D at equal angles, respectively. By making the crystal axes of the multiple crystal portions 13A-13D different from one another, the angles of the signal beams S1-S4 and the pump beams E1-E4 incident on the multiple crystal portions 13A-13D can be uniformly determined. This simplifies angle adjustment of the signal beam S and the pump beam E. Furthermore, by dividing the signal beam S into multiple beams, the wavelength width of each beam becomes appropriately narrower than in the case of a single beam with a wide wavelength width and a narrow time width, preventing the time width of each beam from becoming excessively narrow. This keeps the peak intensities of the signal light S1 to S4 and the pump light E1 to E4 within a certain range, thereby preventing damage to the elements that make up the optical system.

[0063] The laser amplifier 1A is provided with a focusing unit 4 that focuses amplified light A1 to A4, the phases of which have been adjusted by the phase adjustment unit 3. This makes it possible to generate high-power ultrashort pulsed light P without spatially separating the wavelength components in a stage subsequent to the amplification unit 2. [Second embodiment]

[0064] 8 is a schematic diagram showing the configuration of a laser amplifier according to a second embodiment of the present disclosure. As shown in the figure, a laser amplifier 1B according to the second embodiment differs from the first embodiment in that a single beam of signal light S and pumping light E is incident on each of a plurality of crystal portions 13A to 13D. The crystal axes of the plurality of crystal portions 13A to 13D are different from each other, as in the first embodiment.

[0065] In the laser amplifier 1B, as shown in FIG. 9, the signal light S has a wide wavelength band of 200 nm or more, for example, in the range of 700 nm to 1100 nm. The phase of the signal light S is approximately constant within each wavelength band. The time width of the signal light S is inversely proportional to its own wavelength width, for example, in the range of 10 fs to 1 ps. Here, the time width of the signal light S is, for example, 4.5 fs. The wavelength, phase, and time waveform of the pump light E are similar to those of the pump lights E1 to E4 in the first embodiment.

[0066] In laser amplifier 1B, a single signal light S is used, and therefore amplified light A emitted from nonlinear optical crystal 13 appears to be a single beam. However, because the crystal axes of the multiple crystal portions 13A-13D are different from one another, the actual amplified light A can be regarded as a collection of amplified light A1-A4 emitted from each of the multiple spatially distinct crystal portions 13A-13D. Although the phases of the wavelength components of amplified light A1-A4 are different from one another (see FIG. 5), amplified light A1-A4 are emitted from each of the multiple crystal portions 13A-13D from nonlinear optical crystal 13 in a spatially separated state.

[0067] In this laser amplifier 1B, similarly to the first embodiment, spatial separation of the wavelength components in the amplified light A1 to A4 is not required, and there is no need to place optical components such as a diffraction grating in the optical system, so the optical system for increasing the output of the ultrashort pulse light P can be simplified.

[0068] Furthermore, in the laser amplifier 1B, a single beam of signal light S and pumping light E is incident on each of the multiple crystal portions 13A to 13D. This configuration eliminates the need to use multiple signal light sources 11 and pumping light sources 12, simplifying the optical system for the signal light S and pumping light E. It also makes it easier to adjust the optical axes of the signal light S and pumping light E. By using a single beam of signal light S, it is possible to accurately adjust the phase in the phase adjustment unit 3. Unlike when multiple beams of signal light S and pumping light E are used, it is possible to prevent changes in optical characteristics due to interference between the signal light S or between the pumping light E. It is also possible to fully ensure the utilization efficiency of the pumping light E. [Third embodiment]

[0069] 10 is a schematic diagram showing the configuration of a laser amplifier according to a third embodiment of the present disclosure. As shown in the figure, a laser amplifier 1C according to the third embodiment differs from the first embodiment in that the crystal axes of the multiple crystal portions 13A to 13D are the same.

[0070] In the laser amplifier 1C, the nonlinear optical crystal 13 is composed of a crystal whose crystal axis is oriented in one direction. The cut angle of the crystal portion (the angle corresponding to θ1 in FIG. 1) is, for example, 21.65°. Although the nonlinear optical crystal 13 appears to be a single crystal, it can be regarded as an aggregate of multiple crystal portions 13A to 13D whose crystal axis directions are the same. In the laser amplifier 1C, the wavelengths, phases, and time waveforms of the signal light S and pumping light E are similar to those of the signal light S1 to S4 and pumping light E1 to E4 in the first embodiment (see FIG. 4).

[0071] On the other hand, in the laser amplifier 1C, the signal light beams S1-S4 are incident on the crystal portions 13A-13D at equal angles, and the pump light beams E1-E4 are incident on the crystal portions 13A-13D at different angles. In the example of Fig. 10, the angles of the pump light beams E1-E4 relative to the signal light beams S1-S4 incident on the crystal portions 13A-13D are 1.9°, 2.0°, 2.1°, and 2.5°, respectively (the angle corresponding to θ2 in Fig. 1). This makes it possible to amplify each wavelength component contained in the signal light S even if the crystal axis directions of the crystal portions 13A-13D are the same.

[0072] In this laser amplifier 1C, as in the first embodiment, there is no need to spatially separate the wavelength components of the amplified light A1 to A4, and there is no need to place optical components such as a diffraction grating in the optical system, so the optical system for increasing the output of the ultrashort pulse light P can be simplified.

[0073] Furthermore, in the laser amplifier 1C, the multiple signal light beams S1 to S4 are incident on each of the multiple crystal portions 13A to 13D at equal angles, and the multiple pump light beams E1 to E4 are incident on each of the multiple crystal portions 13A to 13D at different angles. By dividing the signal light S into multiple beams in this way, the wavelength width of each beam becomes appropriately narrower than in the case of a single beam with a wide wavelength width and a narrow time width, and it is possible to prevent the time width of each beam from becoming excessively narrow. This keeps the peak intensities of the signal light S and the pump light E within a certain range, thereby preventing damage to the elements that make up the optical system.

[0074] In this embodiment, it is sufficient that one of the plurality of signal beams S1 to S4 and the plurality of pump beams E1 to E4 is incident on each of the plurality of crystal portions 13A to 13D at an equal angle, and the other is incident on each of the plurality of crystal portions 13A to 13D at a different angle. Therefore, it is also possible to have each of the plurality of signal beams S1 to S4 incident on each of the plurality of crystal portions 13A to 13D at a different angle, and each of the plurality of pump beams E1 to E4 incident on each of the plurality of crystal portions 13A to 13D at an equal angle. In this case, it is preferable to dispose an angle adjustment mechanism for aligning the optical axes of the amplified beams A1 to A4 output from nonlinear optical crystal 13 on the optical path between nonlinear optical crystal 13 and light collecting unit 4. [Fourth embodiment]

[0075] 11 is a schematic diagram showing the configuration of a laser amplifier according to a fourth embodiment of the present disclosure. As shown in the drawing, a laser amplifier 1D according to the fourth embodiment differs from the third embodiment in that the signal light S is a single beam.

[0076] In the laser amplifier 1D, as shown in FIG. 12, the signal light S has a wide wavelength band of 200 nm or more, for example, in the range of 700 nm to 1100 nm. The phase of the signal light S is approximately constant within each wavelength band. The time width of the signal light S is inversely proportional to its own wavelength width, for example, in the range of 10 fs to 1 ps. Here, the time width of the signal light S is, for example, 4.5 fs. The wavelengths, phases, and time waveforms of the pumping lights E1 to E4 are similar to those of the pumping lights E1 to E4 in the first embodiment.

[0077] In the laser amplifier 1D, a single beam of signal light S is incident on each of the multiple crystal portions 13A-13D, and multiple beams of pump light E1-E4 are incident at different angles. In the example of Fig. 11, the angles (corresponding to θ2 in Fig. 1) of the multiple beams of pump light E1-E4 relative to the signal light S1-S4 incident on each of the multiple crystal portions 13A-13D are 1.9°, 2.0°, 2.1°, and 2.5°. This makes it possible to amplify each wavelength component contained in the signal light S even if the crystal axis directions of the multiple crystal portions 13A-13D are the same.

[0078] Because the laser amplifier 1D uses a single signal light S, the amplified light A emitted from the nonlinear optical crystal 13 appears as a single beam. However, in each of the multiple crystal portions 13A-13D, only the portion of the signal light S that passes through the respective incident positions of the pumping light E1-E4 is amplified. Therefore, the actual amplified light A can be regarded as a collection of amplified light A1-A4 emitted from each of the multiple spatially different crystal portions 13A-13D. The difference in intensity between the amplified and non-amplified portions of the signal light S is, for example, approximately 1000 times. Although the phases of the wavelength components of the amplified light A1-A4 are different from each other (see FIG. 5), the amplified light A1-A4 are emitted from each of the multiple crystal portions 13A-13D from the nonlinear optical crystal 13 in a spatially separated state.

[0079] In this laser amplifier 1D, as in the first embodiment, there is no need to spatially separate the wavelength components of the amplified light A1 to A4, and there is no need to place optical components such as a diffraction grating in the optical system, so the optical system for increasing the output of the ultrashort pulse light P can be simplified.

[0080] In the laser amplifier 1D, a single signal light S is used for each of the multiple crystal portions 13A to 13D, eliminating the need to use multiple signal light sources 11 and simplifying the optical system for the signal light S. Also, it becomes easier to adjust the optical axis of the signal light S. By using a single signal light S, the phase can be adjusted with high precision in the phase adjustment unit 3. Unlike when multiple signal lights S are used, it is possible to prevent changes in optical characteristics due to interference between the signal lights S. Furthermore, the utilization efficiency of the pump light E can be fully ensured. [Fifth embodiment]

[0081] 13 is a schematic diagram showing the configuration of a laser amplifier according to a fifth embodiment of the present disclosure. As shown in the drawing, a laser amplifier 1E according to the fifth embodiment differs from the third embodiment in that a single pumping light E is used.

[0082] In the laser amplifier 1E, the wavelengths, phases, and time waveforms of the signal lights S1 to S4 are similar to those of the signal lights S1 to S4 in the first embodiment (see FIG. 4). Also, the wavelengths, phases, and time waveforms of the pumping light E are similar to those of the pumping light E in the second embodiment (see FIG. 9).

[0083] In the laser amplifier 1E, the signal light beams S1 to S4 are incident on the crystal portions 13A to 13D at different angles. In the example of FIG. 13, the angles of the signal light beams S1 to S4 relative to the cut angles of the crystal portions 13A to 13D (angles corresponding to θ1 in FIG. 1) are 0°, 0.04°, 0.07°, and 0.1°, respectively. Furthermore, the angles of the signal light beams S1 to S4 relative to the pump light E incident on the crystal portions 13A to 13D (angles corresponding to θ2 in FIG. 1) are 2.5°, 2.46°, 2.43°, and 2.4°, respectively. This makes it possible to amplify each wavelength component contained in the signal light S even if the crystal axis directions of the crystal portions 13A to 13D are the same.

[0084] In this laser amplifier 1E, similarly to the first embodiment, spatial separation of the wavelength components of the amplified light A1 to A4 is not required, and there is no need to arrange optical components such as a diffraction grating in the optical system, so that the optical system for increasing the output of the ultrashort pulsed light P can be simplified. Furthermore, in the laser amplifier 1E, a single pumping light E is used for each of the multiple crystal portions 13A to 13D, so there is no need to use multiple pumping light sources 12, and the optical system for the pumping light E can be simplified. Furthermore, adjustment of the optical axis of the pumping light E is also easy. Unlike when multiple pumping lights E are used, changes in optical characteristics due to interference between the pumping lights E can be prevented.

[0085] In the laser amplifier 1E, the angles of incidence of the signal light beams S1 to S4 onto the crystal portions 13A to 13D are different from one another, and therefore the directions in which the optical axes of the amplified light beams A1 to A4 output from the nonlinear optical crystal 13 extend are also different from one another. Therefore, in the laser amplifier 1E, it is preferable to dispose an angle adjustment mechanism 18, which aligns the optical axes of the amplified light beams A1 to A4 output from the nonlinear optical crystal 13, on the optical path between the nonlinear optical crystal 13 and the focusing unit 4. The angle adjustment mechanism 18 can be configured, for example, by an optical mirror, an electro-optical modulator, an acousto-optical modulator, or the like. [Sixth embodiment]

[0086] 14 is a schematic diagram showing the configuration of a laser amplifier according to a sixth embodiment of the present disclosure. As shown in the figure, a laser amplifier 1F according to the sixth embodiment differs from the first embodiment in that it further has a so-called chirped pulse amplification function.

[0087] More specifically, the laser amplifier 1F further includes a pulse stretcher (stretching unit) 21 and a pulse compressor (compression unit) 22 in addition to the configuration of the laser amplifier 1A. The pulse stretcher 21 is a device that performs an expansion step of applying dispersion to the signal light S to expand its time width, and is arranged on the upstream side of the nonlinear optical crystal 13. The pulse compressor 22 is a device that performs a compression step of applying reverse dispersion to the amplified light A to compress its time width, and is arranged on the downstream side of the nonlinear optical crystal 13. In the example of FIG. 14 , the pulse stretcher 21 is arranged on the optical path of the signal light S between the signal light source 11 and the nonlinear optical crystal 13, and the pulse compressor 22 is arranged on the optical path of the amplified light A between the phase adjustment unit 3 and the vacuum chamber 14.

[0088] In the laser amplifier 1F, as shown in FIG. 15, the signal light S before expansion has a wide wavelength band exceeding the range of, for example, 700 nm to 1100 nm. The phase of the signal light S is approximately constant within each wavelength band. The time width of the signal light S is inversely proportional to the width of each wavelength band, for example, within the range of several fs to 1 ps. Here, the time width of the signal light S is, for example, 4.5 fs. The wavelengths, phases, and time waveforms of the pumping light E1 to E4 are similar to those of the pumping light E1 to E4 in the first embodiment (see FIG. 4).

[0089] 16, the time width of the expanded signal light S is expanded by a pulse expander 21 and the expanded signal light S is divided into a plurality of signal lights S1 to S4 having the same wavelength width. The wavelength width and phase of the signal lights S1 to S4 are maintained as they were before expansion, while the time width is expanded to about 10 ps to 1 ns. Here, the time width of the signal lights S1 to S4 is, for example, 1 ns.

[0090] As shown in Fig. 17, the amplified light A1 to A4 output from the nonlinear optical crystal 13 has an increased intensity relative to the signal light S1 to S4 due to optical parametric amplification, and is divided into four beams with different wavelength widths and center wavelengths. The phase of each wavelength component of the amplified light A1 to A4 is delayed according to the wavelength. For example, the shorter the wavelength, the greater the amount of phase delay, and therefore, a shift occurs in the phase of each wavelength component of the amplified light A1 to A4 according to the wavelength difference. The amplified light A1 to A4 each have a different time width according to the wavelength width.

[0091] As shown in FIG. 18, the amplified light A1 to A4 after phase adjustment maintains its intensity before the phase adjustment, while the phases of the wavelength components generated during amplification in the nonlinear optical crystal 13 are aligned with each other. As shown in FIG. 19, the amplified light A1 to A4 after compression maintains its wavelength width and phase from before compression, while its time width is narrowed to approximately 10 fs to 1 ps. The amplified light A1 to A4 after compression also have different time widths depending on their wavelength widths. By focusing the amplified light A1 to A4, whose wavelength components have been aligned in phase, using the focusing unit 4, high-power ultrashort pulse light P with a time width (full width at half maximum) of approximately several fs to 100 fs is generated, as shown in FIG. 20. The laser amplifier 1F using chirped pulse amplification is capable of generating ultrashort pulse light P with a peak intensity approximately four orders of magnitude higher than that of the laser amplifier 1A.

[0092] In this laser amplifier 1F, similarly to the first embodiment, spatial separation of the wavelength components in the amplified light A1 to A4 is not required, and there is no need to arrange optical components such as a diffraction grating in the optical system, which simplifies the optical system for increasing the output of the ultrashort pulse light P. Furthermore, in the laser amplifier 1F, the time width of the amplified light A1 to A4, which has high energy obtained by chirped pulse amplification, is compressed after amplification, thereby obtaining ultrashort pulse light P with high peak intensity. Furthermore, because the amplified light A1 to A4 before compression has a relatively wide time width, damage to the elements that make up the optical system can be suppressed. [Seventh embodiment]

[0093] 21 is a schematic diagram showing the configuration of a laser amplifier according to a seventh embodiment of the present disclosure. As shown in the figure, a laser amplifier 1G according to the seventh embodiment differs from the first embodiment in that signal light S and pumping light E are simultaneously incident on each of a plurality of crystal portions 13A to 13D from the same direction.

[0094] 21, multiple (four) pumping lights E1 to E4 output from pumping light source 12 first travel in a direction perpendicular to the optical axes of signal lights S1 to S4 output from signal light source 11. Then, pumping lights E1 to E4 are combined with signal lights S1 to S4 by beam combining unit 20 arranged on the optical axes of the signal lights S1 to S4, respectively, and enter nonlinear optical crystal 13 coaxially with the signal lights S1 to S4. A dichroic mirror, for example, can be used as beam combining unit 20.

[0095] In this embodiment, the signal light S and the pumping light E are incident on the nonlinear optical crystal 13 from the same direction. Therefore, the difference in the angle of incidence between the signal light S1 to S4 and the pumping light E1 to E4 with respect to the nonlinear optical crystal 13 (the angle corresponding to θ2 in FIG. 1) is 0°. Furthermore, the cut angles of the crystal portions 13A to 13D (the angle corresponding to θ1 in FIG. 1) are 22.98°, 22.94°, 22.90°, and 22.86°, respectively.

[0096] In this laser amplifier 1G, similarly to the first embodiment, spatial separation of the wavelength components in the amplified light A1 to A4 is not required, and there is no need to arrange optical components such as a diffraction grating in the optical system, which simplifies the optical system for increasing the output of the ultrashort pulsed light P. Furthermore, a portion is formed in which the signal light S1 to S4 and the pump light E1 to E4 are coaxial, which allows the optical system of the device to be made smaller. [Explanation of symbols]

[0097] 1A to 1G...laser amplifier, 2...amplification section, 3...phase adjustment section, 4...focusing section, 11...signal light source, 12...excitation light source, 13...nonlinear optical crystal, 13A to 13D...crystal section, 21...pulse stretcher (stretching section), 22...pulse compressor (compression section), S, S1 to S4...signal light, E, E1 to E4...excitation light, A, A1 to A4...amplified light.

Claims

1. an amplifier that amplifies the intensity of the signal light and outputs amplified light; a phase adjusting unit that adjusts the phase of each wavelength component included in the signal light or the amplified light, The amplifier unit includes a signal light source that outputs the signal light; an excitation light source that outputs excitation light; a nonlinear optical crystal that emits the amplified light in response to the signal light and the pumping light being incident thereon; the nonlinear optical crystal has a plurality of spatially distinct crystal portions; The signal light source, the pumping light source, and the nonlinear optical crystal are arranged in a laser amplification device such that the signal light output from the signal light source and the pumping light output from the pumping light source, both of which are pulsed light, are incident simultaneously on each of the plurality of crystal portions without passing through a diffraction grating, and at least one of the angles of incidence of the signal light and the crystal axes of the plurality of crystal portions and the angle of incidence of the pumping light is different.

2. 2. A laser amplifier according to claim 1, wherein the plurality of crystal portions are arranged in a spatially separated manner.

3. 2. A laser amplifier according to claim 1, wherein said plurality of crystal portions are integrally bonded together.

4. 4. The laser amplifier according to claim 1, wherein the crystal axes of the plurality of crystal portions are different from one another.

5. 5. A laser amplifier according to claim 4, wherein the signal light and the pumping light are incident on each of the plurality of crystal portions as a single beam.

6. 5. A laser amplifier according to claim 4, wherein the plurality of signal beams and the plurality of pump beams are incident on each of the plurality of crystal portions at equal angles to one another.

7. 4. The laser amplifier according to claim 1, wherein the crystal axes of the plurality of crystal portions are the same.

8. 8. A laser amplifier according to claim 7, wherein a single beam of said signal light is incident on each of said plurality of crystal portions, and a plurality of beams of said pumping light are incident at mutually different angles.

9. 8. A laser amplifier according to claim 7, wherein the plurality of signal beams are incident on each of the plurality of crystal portions at angles different from one another, and the pumping beam is incident as a single beam.

10. 8. A laser amplifier according to claim 7, wherein one of the plurality of signal lights and one of the plurality of pumping lights are incident on each of the plurality of crystal portions at an equal angle to each other, and the other is incident on each of the plurality of crystal portions at a different angle to each other.

11. 11. The laser amplifier according to claim 1, further comprising a focusing section that focuses the amplified light whose phases of the wavelength components have been adjusted by the phase adjusting section.

12. an expansion unit that disperses the signal light in a stage preceding the nonlinear optical crystal to expand its time width; 12. The laser amplifier according to claim 1, further comprising a compressor that compresses the time width by applying reverse dispersion to the amplified light in a stage subsequent to the nonlinear optical crystal.

13. An amplifying step of amplifying the intensity of the signal light by making the signal light output from the signal light source and the pumping light output from the pumping light source incident on a nonlinear optical crystal, and outputting amplified light; a phase adjusting step of adjusting the phase of each wavelength component included in the signal light or the amplified light, In the amplification step, the signal light output from the signal light source and the pumping light output from the pumping light source, both of which are pulsed light, are simultaneously incident on each of a plurality of spatially distinct crystal portions in the nonlinear optical crystal without passing through a diffraction grating, while at least one of the angles of incidence of the signal light and the crystal axes of the plurality of crystal portions and the angle of incidence of the pumping light and the crystal axes of the plurality of crystal portions is made different.

14. 14. The laser amplification method according to claim 13, wherein the plurality of crystal portions are arranged in a spatially separated manner in the amplifying step.

15. 14. The laser amplification method according to claim 13, wherein the amplifying step comprises integrally combining and arranging the plurality of crystal portions.

16. 16. The laser amplification method according to claim 13, wherein in the amplifying step, the crystal axes of the plurality of crystal portions are made different from one another.

17. 17. The laser amplification method according to claim 16, wherein in the amplifying step, the signal light and the pumping light are incident as single beams on each of the plurality of crystal portions.

18. 17. The laser amplification method according to claim 16, wherein in the amplifying step, the plurality of signal beams are incident on each of the plurality of crystal portions at equal angles to one another, and the plurality of pumping beams are incident on each of the plurality of crystal portions at equal angles to one another.

19. 16. The laser amplification method according to claim 13, wherein in the amplifying step, the crystal axes of the plurality of crystal portions are aligned with one another.

20. 20. The laser amplification method according to claim 19, wherein in the amplifying step, a single beam of the signal light is made incident on each of the plurality of crystal portions, and a plurality of beams of the pump light are made incident at mutually different angles.

21. 20. The laser amplification method according to claim 19, wherein in the amplifying step, the signal light beams are incident on the crystal portions at mutually different angles, and the pump light beam is incident as a single beam.

22. 20. The laser amplification method according to claim 19, wherein, in the amplifying step, one of the plurality of signal lights and one of the plurality of pumping lights are incident on each of the plurality of crystal portions at an equal angle to each other, and the other is incident on each of the plurality of crystal portions at a different angle to each other.

23. 23. The laser amplification method according to claim 13, further comprising a focusing step of focusing the amplified light whose phases of the wavelength components have been adjusted by the phase adjusting step.

24. an expansion step of dispersing the signal light to expand its time width as a pre-process of the amplification step; 24. The laser amplification method according to claim 13, further comprising a compression step, as a post-processing step of said amplifying step, of compressing a time width by giving inverse dispersion to said amplified light.

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