Data creation device, light control device, target intensity spectrogram creation device, data creation method, target intensity spectrogram creation method, data creation program, and target intensity spectrogram creation program

Abstract

To shorten the time required for calculating a spectrum phase and intensity spectrum for bringing the time intensity waveform of light closer to a desired waveform.SOLUTION: A fourier transformation unit transforms the first waveform function A2 of a frequency domain to the second waveform function A3 of a time domain. A STFT unit transforms the second waveform function A3 to an intensity spectrogram A41 and a phase spectrogram A42. A spectrogram replacement unit replaces the intensity spectrogram A41 with a preliminarily created intensity spectrogram A43 and constrains the phase spectrogram A42. An inverse STFT unit transforms the intensity spectrogram A43 after replacement and the constrained phase spectrogram A42 to a third waveform function A5 of a time domain. An inverse fourier transformation unit transforms the third waveform function A5 to a fourth waveform function A6 of a frequency domain.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] The present disclosure relates to a data creating device, a light control device, a target intensity spectrogram creating device, a data creating method, a target intensity spectrogram creating method, a data creating program, and a target intensity spectrogram creating program. [Background technology]

[0002] Patent Document 1 and Non-Patent Document 1 disclose a technique for shaping an optical pulse by modulating the spectral phase and / or the spectral intensity using a spatial light modulator (SLM). In Non-Patent Document 1, the spectral phase and the spectral intensity for obtaining a desired optical pulse waveform are calculated using the iterative Fourier method. In Patent Document 1, the wavelength components (frequency components) of the light constituting the time-intensity waveform are controlled. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-036486 A [Non-patent literature]

[0004] [Non-Patent Document 1] M. Hacker, G. Stobrawa, T. Feurer, “Iterative Fourier transform algorithm for phase-only pulse shaping”, Optics Express, Vol. 9, No. 4, pp.191-199,13 August 2001 [Non-Patent Document 2] Olivier Ripoll, Ville Kettunen, Hans Peter Herzig, “Review of iterativeFouriertransform algorithms for beam shaping applications”, Optical Engineering,Vol. 43, No. 11, pp.2549-2556, November 2004 Summary of the Invention [Problem to be solved by the invention]

[0005] One technique for controlling the time waveform of various types of light, such as ultrashort pulsed light, is to modulate the spectral phase and spectral intensity of an optical pulse using an SLM. In this technique, the spectral phase and spectral intensity for bringing the time intensity waveform of the light closer to a desired waveform are calculated, and a modulation pattern for imparting the spectral phase and spectral intensity to the light is presented by an SLM.

[0006] In such a conventional technique, only the shape of the time-intensity waveform can be controlled, and the wavelength components (frequency components) of the light constituting the time-intensity waveform cannot be controlled. In contrast, the technique described in Patent Document 1 makes it possible to control the wavelength components (frequency components) of the light constituting the time-intensity waveform. For example, when generating output light containing multiple light pulses, by making the wavelengths of the multiple light pulses different, it becomes possible to apply the technique to various devices such as laser processing devices, ultra-high speed imaging cameras, and terahertz wave generators. However, the technique described in Patent Document 1 has a problem in that it takes a long time to calculate modulation data for bringing the time-intensity waveform of light closer to a desired waveform.

[0007] The present disclosure aims to provide a data creation device, a light control device, a data creation method, and a data creation program that can shorten the time required to calculate modulation data for making the time intensity waveform of light closer to a desired waveform. The present disclosure also aims to provide a target intensity spectrogram creation device, a target intensity spectrogram creation method, and a target intensity spectrogram creation program that can create a target intensity spectrogram for making the center wavelength different for each of a plurality of pulses. [Means for solving the problem]

[0008] A data creation device according to one embodiment is a device for creating data for controlling an SLM. The data creation device includes a first conversion unit, a second conversion unit, a spectrogram replacement unit, a third conversion unit, a fourth conversion unit, and a data generation unit. The first conversion unit converts a first waveform function in the frequency domain, including an intensity spectrum function and a phase spectrum function, into a second waveform function in the time domain, including a time intensity waveform function and a time phase waveform function. The second conversion unit converts the second waveform function into an intensity spectrogram and a phase spectrogram. The spectrogram replacement unit replaces the intensity spectrogram with a target intensity spectrogram created in advance, and constrains the phase spectrogram. The third conversion unit converts the replaced intensity spectrogram and the constrained phase spectrogram into a third waveform function in the time domain, including a time intensity waveform function and a time phase waveform function. The fourth conversion unit converts the third waveform function into a fourth waveform function in the frequency domain, including an intensity spectrum function and a phase spectrum function. In this data creation device, the first conversion unit, the second conversion unit, the third conversion unit, and the fourth conversion unit repeatedly operate in this order while replacing the first waveform function of the first conversion unit with the fourth waveform function of the fourth conversion unit. The data generation unit generates data based on the phase spectrum function of the fourth waveform function obtained after the repeated operations.

[0009] A data creation method according to one embodiment is a method for creating data for controlling an SLM. This data creation method includes a first conversion step, a second conversion step, a spectrogram substitution step, a third conversion step, a fourth conversion step, and a data generation step. In the first conversion step, a first waveform function in the frequency domain, including an intensity spectrum function and a phase spectrum function, is converted into a second waveform function in the time domain, including a time intensity waveform function and a time phase waveform function. In the second conversion step, the second waveform function is converted into an intensity spectrogram and a phase spectrogram. In the spectrogram substitution step, the intensity spectrogram is replaced with a target intensity spectrogram created in advance, and the phase spectrogram is constrained. In the third conversion step, the replaced intensity spectrogram and the constrained phase spectrogram are converted into a third waveform function in the time domain, including a time intensity waveform function and a time phase waveform function. In the fourth conversion step, the third waveform function is converted into a fourth waveform function in the frequency domain, including an intensity spectrum function and a phase spectrum function. In this data creation method, the first conversion step, the second conversion step, the third conversion step, and the fourth conversion step are repeated in this order while replacing the first waveform function in the first conversion step with the fourth waveform function in the fourth conversion step. In the data generation step, data is generated based on the phase spectrum function of the fourth waveform function obtained after the repeated operations.

[0010] A data creation program of one embodiment is a program for creating data for controlling an SLM. This data creation program causes a computer to execute a first conversion step, a second conversion step, a spectrogram substitution step, a third conversion step, a fourth conversion step, and a data generation step. In the first conversion step, a first waveform function in the frequency domain including an intensity spectrum function and a phase spectrum function is converted into a second waveform function in the time domain including a time intensity waveform function and a time phase waveform function. In the second conversion step, the second waveform function is converted into an intensity spectrogram and a phase spectrogram. In the spectrogram substitution step, the intensity spectrogram is replaced with a target intensity spectrogram created in advance, and the phase spectrogram is constrained. In the third conversion step, the replaced intensity spectrogram and the constrained phase spectrogram are converted into a third waveform function in the time domain including a time intensity waveform function and a time phase waveform function. In the fourth conversion step, the third waveform function is converted into a fourth waveform function in the frequency domain including an intensity spectrum function and a phase spectrum function. In this data creation program, the first conversion step, the second conversion step, the third conversion step, and the fourth conversion step are repeated in this order while replacing the first waveform function in the first conversion step with the fourth waveform function in the fourth conversion step. In the data generation step, data is generated based on the phase spectrum function of the fourth waveform function obtained after the repeated operations.

[0011] In these data creation devices, data creation methods, and data creation programs, the intensity spectrogram is replaced with a target intensity spectrogram created in advance, and calculations are repeatedly performed between the frequency domain, the time domain, and the spectrogram while constraining the phase spectrogram. According to the research of the present inventors, this makes it possible to reduce the time required to calculate modulation data for approximating the time intensity waveform of light to a desired waveform, compared to the technology described in Patent Document 1. Furthermore, it is possible to improve the calculation accuracy of the modulation data.

[0012] In the above data creation device, the first waveform function of the first conversion unit at the beginning of the repetition may be a waveform function for an initial optical pulse, and the target intensity spectrogram may be an intensity spectrogram for an optical pulse train including a plurality of optical pulses having a time difference from each other and different central wavelengths. Similarly, in the above data creation method and data creation program, the first waveform function of the first conversion step at the beginning of the repetition may be a waveform function for an initial optical pulse, and the target intensity spectrogram may be an intensity spectrogram for an optical pulse train including a plurality of optical pulses having a time difference from each other and different central wavelengths. In these cases, the central wavelength can be made different for each of the plurality of output pulses, making it possible to apply the present invention to various devices such as laser processing devices, ultra-high speed imaging cameras, and terahertz wave generators.

[0013] In the above data creation device, the target intensity spectrogram may be set so that, when the full width at half maximum of the wavelength band of the light input to the SLM is λw, the full width at half maximum λs of the wavelength band of each of the multiple optical pulses is greater than (λw / 4) and smaller than (6·λw / 5), and the central wavelength interval λd of the multiple optical pulses is greater than 0 and smaller than (4·λw / 5). Similarly, in the above data creation method and data creation program, the target intensity spectrogram may be set so that, when the full width at half maximum of the wavelength band of the light input to the SLM is λw, the full width at half maximum λs of the wavelength band of each of the multiple optical pulses is greater than (λw / 4) and smaller than (6·λw / 5), and the central wavelength interval λd of the multiple optical pulses is greater than 0 and smaller than (4·λw / 5). In this case, the time waveform of the multiple optical pulses generated can be accurately brought close to the target time waveform.

[0014] A light control device according to one embodiment includes a light source, a spectroscopic element, an SLM, and an optical system. The light source outputs input light. The spectroscopic element disperses the input light. The SLM modulates the spectral phase of the dispersed input light and outputs modulated light. The optical system combines the wavelength components of the modulated light. The SLM modulates at least one of the spectral phase and the spectral intensity of the input light based on data created by any one of the data creation devices described above. According to this light control device, by controlling the SLM based on data created by any one of the data creation devices described above, it is possible to reduce the time required to calculate modulation data for approximating the time intensity waveform of the output light to a desired waveform. Furthermore, it is possible to improve the calculation accuracy of the modulation data.

[0015] A target intensity spectrogram creation device according to one embodiment is a device for creating a target intensity spectrogram for a light pulse train including a plurality of light pulses having a time difference and different center wavelengths from each other, the target intensity spectrogram being used for creating data for controlling an SLM. The target intensity spectrogram creation device includes a waveform function setting unit, a fifth conversion unit, a sixth conversion unit, and a target generation unit. The waveform function setting unit sets a target waveform function in the frequency domain including an intensity spectrum function and a phase spectrum function for each light pulse. The fifth conversion unit converts the target waveform function of each of the plurality of light pulses into a fifth waveform function in the time domain including a time intensity waveform function and a time phase waveform function. The sixth conversion unit generates an intensity spectrogram from the fifth waveform function of each of the plurality of light pulses. The target generation unit generates a target intensity spectrogram by superimposing the intensity spectrograms of each of the plurality of light pulses.

[0016] A target intensity spectrogram creation method according to one embodiment is a method for creating a target intensity spectrogram for a light pulse train including a plurality of light pulses having a time difference and different center wavelengths, the target intensity spectrogram being used for creating data for controlling an SLM. The target intensity spectrogram creation method includes a waveform function setting step, a fifth conversion step, a sixth conversion step, and a target generation step. In the waveform function setting step, a target waveform function in the frequency domain including an intensity spectrum function and a phase spectrum function is set for each light pulse. In the fifth conversion step, the target waveform function of each of the plurality of light pulses is converted into a fifth waveform function in the time domain including a time intensity waveform function and a time phase waveform function. In the sixth conversion step, an intensity spectrogram is generated from the fifth waveform function of each of the plurality of light pulses. In the target generation step, a target intensity spectrogram is generated by superimposing the intensity spectrograms of each of the plurality of light pulses.

[0017] A target intensity spectrogram creation program according to one embodiment is a program for creating a target intensity spectrogram for a light pulse train including a plurality of light pulses having a time difference and different center wavelengths, the target intensity spectrogram being used for creating data for controlling an SLM. The target intensity spectrogram creation program causes a computer to execute a waveform function setting step, a fifth conversion step, a sixth conversion step, and a target generation step. In the waveform function setting step, a target waveform function in the frequency domain including an intensity spectrum function and a phase spectrum function is set for each light pulse. In the fifth conversion step, the target waveform function of each of the plurality of light pulses is converted into a fifth waveform function in the time domain including a time intensity waveform function and a time phase waveform function. In the sixth conversion step, an intensity spectrogram is generated from the fifth waveform function of each of the plurality of light pulses. In the target generation step, a target intensity spectrogram is generated by superimposing the intensity spectrograms of each of the plurality of light pulses.

[0018] According to the target intensity spectrogram creating device, the target intensity spectrogram creating method, and the target intensity spectrogram creating program, it is possible to suitably create a target intensity spectrogram for making the center wavelength different for each of a plurality of pulses. Effect of the Invention

[0019] According to the data creation device, light control device, data creation method, and data creation program of the present disclosure, it is possible to reduce the time required to calculate modulation data for approximating the time intensity waveform of light to a desired waveform. Also, according to the target intensity spectrogram creation device, target intensity spectrogram creation method, and target intensity spectrogram creation program of the present disclosure, it is possible to create a target intensity spectrogram for differentiating the center wavelength for each of multiple pulses. [Brief description of the drawings]

[0020] [Figure 1] 1 is a diagram illustrating a schematic configuration of a light control device according to a first embodiment. [Diagram 2] FIG. 2 is a diagram illustrating a configuration of an optical waveform control unit included in the optical control device. [Diagram 3] FIG. 2 shows the modulation surface of an SLM. [Figure 4] (a) shows the spectral waveform of a single-pulse input light, and (b) shows the time intensity waveform of a single-pulse input light. [Diagram 5] (a) shows the spectral waveform of the output light when a square-wave spectral phase modulation is applied in the SLM. (b) shows the temporal intensity waveform of the output light when a square-wave spectral phase modulation is applied in the SLM. [Figure 6] 1A is a diagram showing a spectrogram of a band-controlled multi-pulse, (b) is a diagram showing the time waveform of an optical pulse train, and (c) is a diagram showing the spectrum obtained by combining three optical pulses. [Figure 7]1A is a diagram showing a spectrogram of a multipulse that is not band-controlled, (b) is a diagram showing the time waveform of an optical pulse train, and (c) is a diagram showing the spectrum obtained by combining three optical pulses. [Figure 8] FIG. 2 is a diagram illustrating an example of a hardware configuration of a data creation device. [Figure 9] FIG. 2 is a block diagram showing an internal configuration of a spectrum design unit. [Figure 10] FIG. 13 is a block diagram showing a calculation procedure of a phase spectrum function in a spectrum design unit. [Figure 11] FIG. 13 is a diagram showing, by means of formulas, a calculation procedure of a phase spectrum function in the spectrum design unit. [Figure 12] 1A is a graph showing an example of an initial spectral function, and FIG. 1B is a graph showing a second waveform function in the first rotation obtained by Fourier transforming the initial spectral function shown in FIG. [Figure 13] 12(a) is an intensity spectrogram transformed from the second waveform function shown in FIG. 12(b), (b) is a phase spectrogram transformed from the second waveform function shown in FIG. 12(b), (c) is an example of a target intensity spectrogram, and (d) is a constrained phase spectrogram. [Figure 14] 13(a) is a graph showing a schematic diagram of a third waveform function in the first round obtained by performing an inverse STFT on the target intensity spectrogram and phase spectrogram shown in FIG. 13(c) and (d). (b) is a graph showing a schematic diagram of a fourth waveform function in the first round obtained by performing an inverse Fourier transform on the third waveform function shown in (a). [Figure 15] 14(a) is a graph showing a schematic representation of a first waveform function at the third rotation after FIG. 14(b), and (b) is a graph showing a schematic representation of a second waveform function at the third rotation obtained by Fourier transforming the first waveform function shown in (a). [Figure 16](a) An intensity spectrogram at the third revolution, converted from the second waveform function shown in FIG. 15(b). (b) A phase spectrogram at the third revolution, converted from the second waveform function shown in FIG. 15(b). (c) A target intensity spectrogram at the third revolution. (d) A constrained phase spectrogram at the third revolution. [Figure 17] 16(a) is a graph showing a schematic diagram of a third waveform function in the third round obtained by performing an inverse STFT on the target intensity spectrogram and phase spectrogram shown in FIG. 16(c) and (d). (b) is a graph showing a schematic diagram of a fourth waveform function in the third round obtained by performing an inverse Fourier transform on the third waveform function shown in (a). [Figure 18] 1A and 1B are spectrograms showing the initial spectral function and target intensity spectrograms used in the examples, respectively; [Figure 19] 11 is a graph showing the relationship between the number of iterations until the calculation results converge and the calculation accuracy with respect to the design value, obtained in the example. [Figure 20] (a) shows an intensity spectrogram at the first round of iterative calculation in the data creation device of the embodiment, (b) shows an intensity spectrogram when the calculation result has converged in the data creation device of the embodiment, and (c) shows an intensity spectrogram when the calculation result has converged in the data creation device described in Patent Document 1. [Figure 21] 11 is a graph showing the relationship between the central wavelength interval between adjacent optical pulses and the calculation accuracy with respect to the design value. [Figure 22] 1 is a graph showing the relationship between the bandwidth of an optical pulse, the central wavelength interval, and the calculation accuracy with respect to the design value. [Diagram 23] 1 is a graph showing the relationship between the bandwidth of an optical pulse, the central wavelength interval, and the calculation accuracy with respect to the design value. [Figure 24] 1 is a graph showing the relationship between the bandwidth of an optical pulse, the central wavelength interval, and the calculation accuracy with respect to the design value. [Diagram 25]23 is a graph showing a range, determined from the graph of FIG. 22, in which the RMS value is 2×10 −4 or less for a combination of bandwidth and central wavelength interval. [Figure 26] 24 is a graph showing a range, determined from the graph of FIG. 23, in which the RMS value is 2×10 −4 or less for a combination of bandwidth and central wavelength interval. [Figure 27] 25 is a graph showing a range, determined from the graph of FIG. 24, in which the RMS value is 4×10 −4 or less for a combination of bandwidth and central wavelength interval. [Figure 28] FIG. 2 is a block diagram showing the functional configuration of an apparatus for creating a target intensity spectrogram. [Figure 29] 19(a) is a graph showing a target waveform function for one of the optical pulses shown in Figure 18; (b) is a graph showing a time domain waveform function generated from the target waveform function shown in (a); [Diagram 30] 29(a) shows an intensity spectrogram generated from the waveform function shown in FIG. 29(b), and (b) shows a target intensity spectrogram obtained by superimposing the intensity spectrograms for three optical pulses. [Diagram 31] 1 is a flow chart illustrating a method for creating a target intensity spectrogram. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, an embodiment will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are given the same reference numerals, and duplicated description will be omitted.

[0022] 1 is a diagram illustrating a schematic configuration of a light control device 1 according to an embodiment of the present disclosure. The light control device 1 of this embodiment generates, from an input light La, an output light Lb having an arbitrary time intensity waveform different from that of the input light La. As illustrated in FIG. 1, the light control device 1 includes a light source 2, an optical waveform control unit 3, and a data creation device 20.

[0023] The light source 2 outputs the input light La to be input to the optical waveform control unit 3. The input light La is, for example, continuous light. Alternatively, the light source 2 is, for example, a laser light source such as a solid-state laser light source, and the input light La (initial optical pulse) is, for example, a coherent single optical pulse. The light source 2 is, for example, a femtosecond laser, and in one embodiment, an LD direct pumping type Yb:YAG pulse laser. The time waveform of the optical pulse is, for example, a Gaussian function. The full width at half maximum (FWHM) of the optical pulse is, for example, within a range of 10 fs to 10000 fs, and in one example, is 100 fs. The input light La has a certain bandwidth and includes multiple continuous wavelength components. In one embodiment, the bandwidth of the input light La is 10 nm, and the center wavelength of the input light La is 800 nm.

[0024] The optical waveform control unit 3 has an SLM 14, and receives a control signal SC from a data creation device 20 at the SLM 14. The optical waveform control unit 3 converts the input light La from the light source 2 into output light Lb having an arbitrary time-intensity waveform. The control signal SC is generated based on data for controlling the SLM 14, i.e., data including the intensity of a complex amplitude distribution or the intensity of a phase distribution. The data is, for example, a Computer-Generated Hologram (CGH).

[0025] 2 is a diagram showing an example of the configuration of the optical waveform control unit 3. The optical waveform control unit 3 has a diffraction grating 12, a lens 13, a spatial light modulator (SLM) 14, a lens 15, and a diffraction grating 16. The diffraction grating 12 is a dispersive element in this embodiment, and is optically coupled to the light source 2. The SLM 14 is optically coupled to the diffraction grating 12 via the lens 13. The diffraction grating 12 spatially separates a plurality of wavelength components contained in the input light La into wavelength components. Note that instead of the diffraction grating 12, other optical components such as a prism may be used as the dispersive element.

[0026] Input light La is obliquely incident on diffraction grating 12 and is split into multiple wavelength components. Light L1 containing these multiple wavelength components is condensed by lens 13 for each wavelength component, and is imaged on the modulation surface of SLM 14. Lens 13 may be a convex lens made of a light-transmitting material, or may be a concave mirror having a concave light-reflecting surface.

[0027] The SLM 14 shifts the phases of the multiple wavelength components output from the diffraction grating 12 from one another in order to convert the input light La into the output light Lb. To this end, the SLM 14 receives a control signal SC from the data generating device 20 and simultaneously performs phase modulation and intensity modulation of the light L1. The SLM 14 may perform only phase modulation or only intensity modulation. The SLM 14 is, for example, of a phase modulation type. In one embodiment, the SLM 14 is of a liquid crystal on silicon (LCOS) type. Although the SLM 14 is of a transmissive type in the figure, the SLM 14 may also be of a reflective type. The spatial light modulator 14 is not limited to a phase modulation type spatial light modulator, but may also be an intensity modulation type spatial light modulator such as a digital micro mirror device (DMD) or a phase-intensity modulation type spatial light modulator.

[0028] FIG. 3 is a diagram showing the modulation surface 17 of the SLM 14. As shown in FIG. 3, on the modulation surface 17, a plurality of modulation regions 17a are arranged along a direction AA, and each modulation region 17a extends in a direction AB intersecting the direction AA. The direction AA is the direction of light dispersion by the diffraction grating 12. This modulation surface 17 acts as a Fourier transform surface, and each of the plurality of modulation regions 17a is incident on a corresponding wavelength component after dispersion. The SLM 14 modulates the phase and intensity of each incident wavelength component in each modulation region 17a independently from other wavelength components. Note that since the SLM 14 in this embodiment is a phase modulation type, intensity modulation is realized by a phase pattern (phase image) presented on the modulation surface 17.

[0029] Each wavelength component of modulated light L2 modulated by SLM 14 is collected to one point on diffraction grating 16 by lens 15. Lens 15 and diffraction grating 16 function as an optical system that collects modulated light L2. Lens 15 may be a convex lens made of a light-transmitting member, or a concave mirror having a concave light-reflecting surface. Diffraction grating 16 functions as a multiplexing optical system that multiplexes each wavelength component after modulation. That is, the multiple wavelength components of modulated light L2 are collected and multiplexed by lens 15 and diffraction grating 16 to become output light Lb. When SLM 14 is a reflective type, lenses 13 and 15 may be formed of a common lens, and diffraction gratings 12 and 16 may be formed of a common diffraction grating.

[0030] The region in front of the lens 15 (spectral region) and the region behind the diffraction grating 16 (time domain) are in a Fourier transform relationship with each other, and phase modulation in the spectral domain affects the time intensity waveform in the time domain. Therefore, the output light Lb has a desired time intensity waveform different from that of the input light La according to the modulation pattern of the SLM 14. Here, FIG. 4(a) shows, as an example, the spectral waveform (spectral phase G11 and spectral intensity G12) of the single-pulse input light La, and FIG. 4(b) shows the time intensity waveform of the input light La. Also, FIG. 5(a) shows, as an example, the spectral waveform (spectral phase G21 and spectral intensity G22) of the output light Lb when a square-wave spectral phase modulation is applied in the SLM 14, and FIG. 5(b) shows the time intensity waveform of the output light Lb. In Fig. 4(a) and Fig. 5(a), the horizontal axis indicates wavelength (nm), the left vertical axis indicates the intensity value (arbitrary unit) of the intensity spectrum, and the right vertical axis indicates the phase value (rad) of the spectrum phase. In Fig. 4(b) and Fig. 5(b), the horizontal axis indicates time (femtoseconds), and the vertical axis indicates the light intensity (arbitrary unit). In this example, a rectangular wave-shaped phase spectrum waveform is given to the output light Lb, so that the single pulse of the input light La is converted into a double pulse accompanied by higher-order light as the output light Lb. Note that the spectrum and waveform shown in Fig. 5 are just one example, and the time intensity waveform of the output light Lb can be shaped into various shapes by various combinations of the spectrum phase and the spectrum intensity.

[0031] When the output light Lb is an optical pulse train including a plurality of optical pulses, the optical pulse train may be a group of single pulses generated by dividing the spectrum constituting the input light La into a plurality of wavelength bands and using each of the wavelength bands. In this case, there may be overlapping portions at the boundaries between the plurality of wavelength bands. In the following description, such an optical pulse train may be referred to as a "band-controlled multi-pulse."

[0032] Fig. 6 is a diagram showing an example of a band-controlled multi-pulse. In this example, an optical pulse train Pb consisting of three optical pulses Pb1 to Pb3 is shown. Fig. 6(a) is a spectrogram in which the horizontal axis indicates time and the vertical axis indicates wavelength, and the optical intensity is represented by the shade of color. Fig. 6(b) shows the time waveform of the optical pulse train Pb. The time waveform of each of the optical pulses Pb1 to Pb3 is, for example, a Gaussian function.

[0033] As shown in FIG. 6(a) and FIG. 6(b), the peaks of the three optical pulses Pb1 to Pb3 are spaced apart in time, and the propagation timings of the three optical pulses Pb1 to Pb3 are shifted from one another. In other words, one optical pulse Pb2 has a time delay with respect to one optical pulse Pb1, and another optical pulse Pb3 has a time delay with respect to the other optical pulse Pb2. However, the tails of adjacent optical pulses Pb1 and Pb2 (or Pb2 ​​and Pb3) may overlap with each other. The time interval (peak interval) of adjacent optical pulses Pb1 and Pb2 (or Pb2 ​​and Pb3) is, for example, within a range of 10 fs to 10000 fs, and is, for example, 2000 fs. The FWHM of each optical pulse Pb1 to Pb3 is, for example, within a range of 10 fs to 5000 fs, and is, for example, 300 fs.

[0034] Fig. 6(c) shows the spectrum obtained by combining the three optical pulses Pb1 to Pb3. As shown in Fig. 6(c), the spectrum obtained by combining the three optical pulses Pb1 to Pb3 has a single peak, but referring to Fig. 6(a), the central wavelengths of the three optical pulses Pb1 to Pb3 are shifted from one another. The spectrum having a single peak shown in Fig. 6(c) is almost the same as the spectrum of the input light La.

[0035] The peak wavelength interval between adjacent optical pulses Pb1, Pb2 (or Pb2, Pb3) is determined by the spectral bandwidth of the input light La, and is generally within a range of twice the full width at half maximum. In one example, when the spectral bandwidth of the input light La is 10 nm, the peak wavelength interval is 5 nm. As a specific example, when the central wavelength of the input light La is 800 nm, the peak wavelengths of the three optical pulses Pb1 to Pb3 can be 795 nm, 800 nm, and 805 nm, respectively.

[0036] Fig. 7 is a diagram showing an example of a multi-pulse that is not band-controlled. In this example, an optical pulse train Pd consisting of three optical pulses Pd1 to Pd3 is shown. Fig. 7(a) is a spectrogram similar to Fig. 6(a), in which the horizontal axis indicates time and the vertical axis indicates wavelength, and the optical intensity is represented by the shade of color. Fig. 7(b) shows the time waveform of the optical pulse train Pd. Fig. 7(c) shows the spectrum obtained by combining the three optical pulses Pd1 to Pd3.

[0037] 7(a)-(c), the peaks of the three optical pulses Pd1-Pd3 are spaced apart in time, but the central wavelengths of the three optical pulses Pd1-Pd3 are the same. The optical waveform control unit 3 of this embodiment is not limited to such an optical pulse train Pd, but can generate an optical pulse train Pb in which the central wavelengths of the optical pulses Pb1-Pb3 are different from one another, as shown in FIG.

[0038] Referring again to Fig. 1, the data creation device 20 is electrically connected to the SLM 14, creates data on a phase modulation pattern for making the time intensity waveform of the output light Lb closer to a desired waveform, and provides the SLM 14 with a control signal SC including the phase modulation pattern. The data creation device 20 of this embodiment causes the SLM 14 to present a phase pattern for phase modulation that gives the output light Lb a spectral phase and spectral intensity for obtaining the desired waveform. To this end, the data creation device 20 has a spectrogram setting unit 21, a spectrum design unit 22, and a data generation unit 23.

[0039] The data generating device 20 may be provided separately from a device that provides the control signal SC to the SLM 14. In this case, the data generating device 20 provides data regarding the phase modulation pattern to the device that provides the control signal SC to the SLM 14. The data generating device 20 may be, for example, a personal computer; a smart device such as a smartphone or a tablet terminal; or a computer having a processor such as a cloud server.

[0040] Fig. 8 is a diagram that shows a schematic example of a hardware configuration of the data creation device 20. As shown in Fig. 8, the data creation device 20 can be physically configured as a normal computer including a processor (CPU) 61, main storage devices such as a ROM 62 and a RAM 63, input devices 64 such as a keyboard, a mouse and a touch screen, output devices 65 such as a display (including a touch screen), a communication module 66 such as a network card for transmitting and receiving data to and from other devices, and an auxiliary storage device 67 such as a hard disk.

[0041] The computer processor 61 can realize each function of the data creation device 20 by the data creation program. Therefore, the data creation program causes the computer processor 61 to operate as the spectrogram setting unit 21, the spectrum design unit 22, and the data generating unit 23 in the data creation device 20. The modulation pattern calculation program is stored in a storage device (storage medium) inside or outside the computer. The storage device may be a non-transitory recording medium. Examples of the recording medium include recording media such as flexible disks, CDs, and DVDs, recording media such as ROMs, semiconductor memories, cloud servers, and the like.

[0042] The spectrogram setting unit 21 accepts input of data relating to a desired intensity spectrogram (target intensity spectrogram) from an operator. The operator inputs data relating to a target intensity spectrogram prepared in advance to the spectrogram setting unit 21. Alternatively, the spectrogram setting unit 21 may hold a target intensity spectrogram in advance, or may be provided with the target intensity spectrogram from a device (described later) that creates a target intensity spectrogram. The data relating to the target intensity spectrogram is provided to the spectrum design unit 22. The spectrum design unit 22 calculates a phase spectrum function suitable for realizing the provided target intensity spectrogram.

[0043] The data generator 23 calculates a phase modulation pattern (e.g., a computer-generated hologram) to be applied to the output light Lb in the optical waveform controller 3 based on the phase spectrum function found in the spectrum designer 22, and generates data related to the phase modulation pattern. Then, a control signal SC including the calculated phase modulation pattern is provided to the SLM 14. The SLM 14 is controlled based on the control signal SC.

[0044] Fig. 9 is a block diagram showing an internal configuration of the spectrum design unit 22. As shown in Fig. 9, the spectrum design unit 22 has a Fourier transform unit (first transform unit) 25, a spectrogram transform unit (second transform unit) 26, a spectrogram substitution unit 27, a spectrogram inverse transform unit (third transform unit) 28, and an inverse Fourier transform unit (fourth transform unit) 29. The spectrum design unit 22 calculates a phase spectrum function on which the modulation pattern is based, using a calculation method described below. Fig. 10 is a block diagram showing a calculation procedure of the phase spectrum function in the spectrum design unit 22. Fig. 11 is a diagram showing the calculation procedure of the phase spectrum function in the spectrum design unit 22 by using mathematical expressions.

[0045] First, an initial spectral function A1, that is, an initial intensity spectral function A0(ω) and a phase spectral function Φ0(ω) which are functions of frequency ω, are prepared. In one example, these intensity spectral function A0(ω) and phase spectral function Φ0(ω) respectively represent the intensity spectrum and the spectral phase of the input light La, but are not limited to this. FIG. 12(a) is a graph that shows the intensity spectral function A0(ω) and the phase spectral function Φ0(ω) as an example of the initial spectral function A1. In FIG. 12(a), a graph G31 shows the intensity spectral function A0(ω), and a graph G32 shows the phase spectral function Φ0(ω). The horizontal axis shows the wavelength, and the vertical axis shows the intensity value of the intensity spectral function or the phase value of the phase spectral function.

[0046] The first waveform function A2 is expressed by the following formula (1), where n is the repetition number (n=1, 2, . . . , N) and i is an imaginary number. In the first round (n=1), the initial spectral function A1 is set to the first waveform function A2. That is, Φ1(ω)=Φ0(ω) of the first waveform function A2 in the first round of repetition.

number

number

[0047] Next, the spectrogram conversion unit 26 of the spectrum design unit 22 performs a Short-Time Fourier Transform (STFT) on the second waveform function A3 (arrow B2 in the figure, second conversion step), thereby obtaining an intensity spectrogram A41 and a phase spectrogram A42 expressed by the following formula (3).

number

[0048] The process in the spectrogram conversion unit 26 for converting the second waveform function A3 into the intensity spectrogram A41 and the phase spectrogram A42 is not limited to STFT, and may be other processes. The process of converting a time waveform into a spectrogram is called time-frequency conversion, including STFT. In the time-frequency conversion, a composite signal such as a time waveform is subjected to frequency filtering or numerical calculation (multiplication with a shifted window function to derive a spectrum for each time) to generate three-dimensional information consisting of time, frequency, and the strength of the signal component (intensity spectrum). In this embodiment, the conversion result (time, frequency, intensity spectrum) is defined as a "spectrogram". In addition to STFT, time-frequency conversion includes wavelet conversion (Haar wavelet conversion, Gabor wavelet conversion, Mexican hat wavelet conversion, Morlet wavelet conversion), etc.

[0049] Next, the spectrogram replacement unit 27 of the spectrum design unit 22 replaces the intensity spectrogram A41 with a previously created intensity spectrogram A43 (target intensity spectrogram) and constrains the phase spectrogram A42 (arrow B3 in the figure, spectrogram replacement step). The intensity spectrogram A43 is provided from the spectrogram setting unit 21 (see FIG. 1). Constraining the phase spectrogram A42 means that the phase spectrogram A42 is not changed (left as is). As a result, the above formula (3) is replaced with the following formula (4). TSG(ω,t) is the target intensity spectrogram function.

number

[0050] Next, the spectrogram inverse transform unit 28 of the spectrum design unit 22 performs an inverse STFT on the intensity spectrogram A43 and the phase spectrogram A42 (arrow B4 in the figure, third transform step). Note that here too, as with the spectrogram transform unit 26, a time-frequency transform other than STFT may be used. As a result, a time-intensity waveform function a' shown by the following formula (5) is obtained. n (t) and the time-phase waveform function φ' n A third waveform function A5 in the time domain including (t) is obtained, where n=1 at the first round.

number

[0051] Next, the inverse Fourier transform unit 29 of the spectrum design unit 22 performs an inverse Fourier transform from the time domain to the frequency domain on the third waveform function A5 (arrow B5 in the figure, fourth transformation step). As a result, the intensity spectrum function A n (ω) and the phase spectrum function Φ' n A fourth waveform function A6 in the frequency domain including (ω) is obtained. Note that n=1 in the first round.

number

[0052] Thereafter, spectrum design unit 22 replaces phase spectral function Φ1(ω) of first waveform function A2 with phase spectral function Φ'1(ω) of the fourth waveform function while constraining intensity spectral function A0(ω) of first waveform function A2 (i.e., Φ2(ω)=Φ'1(ω) of first waveform function A2; see arrow B6 in the figure). Then, the operations of Fourier transform unit 25, spectrogram conversion unit 26, spectrogram substitution unit 27, spectrogram inverse conversion unit 28, and inverse Fourier transform unit 29 described above are repeated N times until the phase spectral function converges. In this way, spectrum design unit 22 replaces phase spectral function Φ1(ω) of first waveform function A2 with phase spectral function Φ'1(ω) of the (n+1)th round while constraining intensity spectral function A0(ω) of first waveform function A2. n+1 (ω) is the phase spectrum function Φ' of the fourth waveform function at the nth cycle n While replacing with (ω), Fourier transform unit 25, spectrogram transform unit 26, spectrogram substitution unit 27, spectrogram inverse transform unit 28, and inverse Fourier transform unit 29 repeatedly operate in this order.

[0053] FIG. 15(a) is a graph showing the intensity spectrum function A0(ω) (graph G71) and the phase spectrum function Φ3(ω) (graph G72) of the first waveform function A2 in the third round (n=3) after FIG. 14(b). It can be seen that the waveform of the phase spectrum function Φ3(ω) has changed from the first round. FIG. 15(b) is a graph showing the time intensity waveform function a3(t) (graph G81) and the time phase waveform function φ3(t) (graph G82) of the second waveform function A3 in the third round, which are Fourier transformed from the first waveform function A2 shown in FIG. 15(a). FIGS. 16(a) and 16(b) are graphs showing the intensity spectrogram A41 and the phase spectrogram A42 in the third round, which are transformed from the second waveform function A3 shown in FIG. 15(b). It can be seen that three optical pulses Pb1 to Pb3 having a time difference from each other and different central wavelengths start to be generated. FIG. 16(c) is a diagram showing an intensity spectrogram A43 in the third revolution, which is the same as the intensity spectrogram A43 in the first revolution shown in FIG. 13(c). FIG. 16(d) is a diagram showing a constrained phase spectrogram A42 in the third revolution, which is the same as the phase spectrogram A42 in FIG. 16(b). FIG. 17(a) is a graph that typically shows a time intensity waveform function a'3(t) (graph G91) and a time phase waveform function φ'3(t) (graph G92) of the third waveform function A5 in the third revolution, which are inverse STFT-processed from the intensity spectrogram A43 and the phase spectrogram A42 shown in FIG. 16(c) and (d). FIG. 17(b) is a graph showing a schematic representation of the intensity spectrum function A3(ω) (graph G101) and the phase spectrum function Φ'3(ω) (graph G102) of the fourth waveform function A6 at the third rotation, which is obtained by inverse Fourier transform from the third waveform function A5 shown in FIG. 17(a).

[0054] By repeating the above-mentioned operation, the phase spectrum function Φ' is calculated so that the intensity spectrogram A41 gradually approaches the intensity spectrogram A43. n (ω) is corrected. Finally, the phase spectrum function Φ' included in the fourth waveform function A6 is N(ω) is the desired spectral phase solution Φ result (ω). This spectral phase solution Φ result (ω) is provided to the data generator 23.

[0055] The data generating unit 23 calculates the spectral phase solution Φ result Data relating to a phase modulation pattern (for example, a computer generated hologram) for imparting a spectral phase and / or a spectral intensity based on (ω) to the output light Lb is calculated (data generating step).

[0056] The effects obtained by the data creation device 20, data creation method, and data creation program of the present embodiment described above will be described. In this embodiment, the intensity spectrogram A41 is replaced with a target intensity spectrogram A43 created in advance, and calculations are performed repeatedly between the frequency domain, the time domain, and the spectrogram while constraining the phase spectrogram A42. According to the research of the present inventor, this makes it possible to obtain a spectral phase solution Φ for bringing the time intensity waveform of the output light Lb closer to a desired waveform, compared to the technology described in Patent Document 1. result This reduces the time required to calculate the spectral phase solution Φ result The calculation accuracy of (ω) can be improved.

[0057] Here, an example will be described. The inventor calculated data on a phase modulation pattern for generating an optical pulse train Pb including three optical pulses Pb1 to Pb3 having a time difference and different central wavelengths from an input light La that is a single optical pulse with a Gaussian time waveform, using the data generating device 20 of this embodiment and the data generating device described in Patent Document 1. FIG. 18(a) is a spectrogram showing an initial spectral function A1 used in this example. This spectrogram includes a single optical pulse Pb0, the central wavelength of which is 800 nm, and the wavelength band (full width at half maximum) λw of which is 10 nm. FIG. 18(b) is a diagram showing a target intensity spectrogram A43 used in this example. This intensity spectrogram A43 includes three optical pulses Pb1 to Pb3, the wavelength band (full width at half maximum) λs of each optical pulse is 5 nm, the time interval between adjacent optical pulses is 2 ps, and the central wavelength interval λd of adjacent optical pulses is 2 nm.

[0058] FIG. 19 is a graph showing the relationship between the number of iterations N (horizontal axis, scale is logarithmic) until the calculation result converges, obtained by this example, and the calculation accuracy (vertical axis, RMS value) with respect to the design value. Graph G111 in the figure shows the relationship obtained by the data creation method of this embodiment, and graph G112 shows the relationship obtained by the data creation device described in Patent Document 1. Note that FIG. 20(a) shows an intensity spectrogram at the second round of iterative calculation in the data creation device 20 of this embodiment. FIG. 20(b) shows an intensity spectrogram when the calculation result converges in the data creation device 20 of this embodiment. FIG. 20(c) shows an intensity spectrogram when the calculation result converges in the data creation device described in Patent Document 1.

[0059] 19, it can be seen that, according to the data creation device 20 of this embodiment, the calculation result converges with a significantly smaller number of iterations N, as compared with the data creation device described in Patent Document 1. The time required for calculation was 952 minutes in the data creation device described in Patent Document 1, whereas it was 6.7 minutes in the data creation device 20 of this embodiment. It can also be seen that the RMS value in the data creation device 20 of this embodiment is significantly smaller than the RMS value in the data creation device described in Patent Document 1. That is, according to the data creation device 20, data creation method, and data creation program of this embodiment, the spectral phase solution Φ result (ω), i.e., the time required to calculate the modulation data, can be significantly reduced. In addition, the spectral phase solution Φ result The calculation accuracy of (ω), in other words, the calculation accuracy of the modulation data, can be significantly improved.

[0060] As in this embodiment, the first waveform function A2 of the Fourier transform unit 25 (first conversion step) at the beginning of the repetition may be a waveform function for the initial optical pulse Pb0, and the intensity spectrogram A43 may be an intensity spectrogram for an optical pulse train Pb including a plurality of optical pulses Pb1 to Pb3 having a time difference and different central wavelengths from one another. In this case, the central wavelength can be made different for each of the plurality of output pulses, which makes it possible to apply the present invention to various devices such as laser processing devices, ultra-high speed imaging cameras, and terahertz wave generators.

[0061] Here, when generating an optical pulse train Pb including a plurality of optical pulses Pb1 to Pb3, suitable values ​​of the bandwidth (full width at half maximum) λs of each optical pulse Pb1 to Pb3 in the intensity spectrogram A43 and the central wavelength interval λd of adjacent optical pulses will be considered. Fig. 21 is a graph showing the relationship between the central wavelength interval λd (nm) of adjacent optical pulses and the calculation accuracy (RMS value) with respect to the design value. Note that the wavelength band λw (equal to the wavelength band of the input light La) of the optical pulse Pb0 of the initial spectral function A1 is set to 10 nm, the bandwidth λs of each optical pulse Pb1 to Pb3 is set to 10 nm, and the repetition number N is set to 50.

[0062] 21, the calculation accuracy for the design value depends on the central wavelength interval λd between adjacent optical pulses. In addition, when the central wavelength interval λd is in the range of 5 nm, i.e., smaller than (λw / 2), the RMS value is 1.0×10 -4 and the calculation accuracy is sufficiently high. Furthermore, when the central wavelength interval λd is 2.5 nm, i.e., in the vicinity of (λw / 4), the RMS value is the smallest, and the calculation accuracy is the highest.

[0063] 22 to 24 are graphs showing the relationship between the bandwidth λs of each optical pulse, the central wavelength interval λd, and the calculation accuracy (RMS value) with respect to the design value. FIG. 22 shows a case where the number of optical pulses included in the optical pulse train Pb is 3, and the bandwidth λw of the optical pulse Pb0 of the first waveform function A2 at the beginning of the repetition is 10 nm. FIG. 23 shows a case where the number of optical pulses included in the optical pulse train Pb is 3, and the bandwidth λw is 20 nm. FIG. 24 shows a case where the number of optical pulses included in the optical pulse train Pb is 2, and the bandwidth λw is 10 nm. In FIG. 22 to 24, the peak intensities of the multiple optical pulses constituting the optical pulse train Pb are equal to each other. In FIG. 22 to 24, the curves G121 to G126 show cases where the central wavelength interval λd is 1 nm, 2 nm, 4 nm, 5 nm, 8 nm, and 12 nm, respectively. 22 to 24, regardless of the central wavelength interval λd, the calculation accuracy for the design value depends on the bandwidth λs of each of the optical pulses Pb1 to Pb3. Moreover, the smaller the central wavelength interval λd, the smaller the minimum value of the calculation accuracy.

[0064] Figure 25 shows the RMS value of 2×10 for the combination of bandwidth λs and central wavelength interval λd obtained from the graph in Figure 22. -4 25 is a graph showing the range in which the RMS value is 2×10-4 From this graph, when the number of optical pulses included in the optical pulse train Pb is 3 and the bandwidth λw is 10 nm, the RMS value is 2×10 -4 The ranges of the bandwidth λs and central wavelength spacing λd below can be expressed as (λw / 2)<λs<λw and 0<λd<(4 λw / 5), respectively.

[0065] Figure 26 shows the RMS value of 2×10 for the combination of bandwidth λs and central wavelength interval λd obtained from the graph in Figure 23. -4 26 is a graph showing the range in which the RMS value is 2×10 -4 From this graph, when the number of optical pulses included in the optical pulse train Pb is 3 and the bandwidth λw is 20 nm, the RMS value is 2×10 -4 The ranges of the bandwidth λs and the central wavelength interval λd below can be expressed as (λw / 4)<λs<λw and 0<λd<(λw / 5), respectively.

[0066] Figure 27 shows the RMS value of 4×10 for the combination of bandwidth λs and central wavelength interval λd obtained from the graph in Figure 24. -4 27 is a graph showing the range in which the RMS value is 4×10 -4 From this graph, when the number of optical pulses included in the optical pulse train Pb is 2 and the bandwidth λw is 10 nm, the RMS value is 4 × 10 -4The ranges of bandwidth λs and central wavelength spacing λd can be expressed as (4·λw / 5)<λs<(6·λw / 5) and 0<λd<(4·λw / 5), respectively.

[0067] To sum up the above results, it is preferable that the target intensity spectrogram A43 is set so that when the full width at half maximum of the wavelength band of the light (input light La) input to SLM 14 is λw, the full width at half maximum λs of the wavelength band of each of the multiple optical pulses is greater than (λw / 4) and smaller than (6 λw / 5), and the central wavelength interval λd of the multiple optical pulses is greater than 0 and smaller than (4 λw / 5). In this case, the time waveform of the multiple optical pulses generated can be made to accurately approximate the target time waveform.

[0068] [Create target intensity spectrogram] Next, an apparatus, method, and program for creating a target intensity spectrogram A43 used to create data for controlling the SLM 14 will be described. FIG. 28 is a block diagram showing the functional configuration of an apparatus 100 for creating an intensity spectrogram A43. The apparatus 100 creates a target intensity spectrogram A43 for an optical pulse train Pb including a plurality of optical pulses (for example, the above-mentioned optical pulses Pb1 to Pb3) having a time difference from one another and different central wavelengths. As shown in FIG. 28, the apparatus 100 includes a waveform function setting unit 101, a Fourier transform unit (fifth transform unit) 102, a spectrogram conversion unit (sixth transform unit) 103, and a target generation unit 104. The apparatus 100 may have the same hardware configuration (see FIG. 6) as the above-mentioned data creation apparatus 20. In this case, the processor 61 of the computer can realize each function of the above-mentioned apparatus 100 by a target intensity spectrogram creation program. Therefore, the target intensity spectrogram creation program causes the computer processor 61 to operate as a waveform function setting unit 101 , a Fourier transform unit 102 , a spectrogram conversion unit 103 , and a target generation unit 104 .

[0069] The waveform function setting unit 101 sets a target waveform function in the frequency domain including an intensity spectrum function and a phase spectrum function for each optical pulse. For example, the waveform function setting unit 101 sets a target waveform function for optical pulse Pb1, sets another target waveform function for optical pulse Pb2, and sets yet another target waveform function for optical pulse Pb3. The parameters of the target waveform function include, for example, the following: a) The shape of the intensity spectral function of each light pulse (e.g. Gaussian) b) The spectral energy content of the intensity spectrum function of each light pulse c) The bandwidth (full width at half maximum) of the intensity spectral function of each optical pulse, λs d) The central wavelength of the intensity spectral function of each light pulse e) Phase spectrum function of each optical pulse When the spectral phase of each optical pulse is linear with respect to frequency, the slope of the linear function corresponds to the time shift amount of each optical pulse. Fig. 29(a) is a graph showing the intensity spectral function G131 and phase spectral function G132 of the target waveform function for the optical pulse Pb2 shown in Fig. 18 as an example of the target waveform function. In Fig. 29(a), the horizontal axis indicates wavelength (nm) and the vertical axis indicates the intensity value (arbitrary unit) of the intensity spectral function G131 and the phase value (rad) of the phase spectral function G132. Since this example is a target waveform function for the optical pulse Pb2 located at the center of the three optical pulses Pb1 to Pb3 that are equally spaced in time, the slope of the phase spectral function G132 (i.e., the time shift amount) is set to zero.

[0070] The Fourier transform unit 102 transforms the target waveform function of each of the multiple optical pulses into a time domain waveform function (fifth waveform function) including a time intensity waveform function and a time phase waveform function. Fig. 29(b) is a graph showing a time intensity waveform function G141 and a time phase waveform function G142 generated from the target waveform function shown in Fig. 29(a) as an example of a time domain waveform function. In Fig. 29(b), the horizontal axis indicates time (fs), and the vertical axis indicates the intensity value (arbitrary unit) of the time intensity waveform function G141 and the phase value (rad) of the time phase waveform function G142.

[0071] The spectrogram conversion unit 103 generates an intensity spectrogram from the waveform function in the time domain of each of the multiple optical pulses. Fig. 30(a) is a diagram showing an intensity spectrogram generated from the waveform function shown in Fig. 29(b) as an example of an intensity spectrogram. Note that the method of creating the intensity spectrogram and the definition of the spectrogram are the same as those explained in the spectrogram conversion unit 26 of the spectrum design unit 22 described above. Also, the spectrogram conversion unit 103 may use other time-frequency transformations (e.g., wavelet transformations) instead of STFT.

[0072] The target generation unit 104 generates an intensity spectrogram A43 by superimposing the intensity spectrograms of the multiple optical pulses on one another. FIG. 30(b) is a diagram showing, as an example, an intensity spectrogram A43 obtained by superimposing the intensity spectrograms of three optical pulses Pb1 to Pb3 on one another. Note that the target generation unit 104 may multiply the superimposed intensity spectrograms of the multiple optical pulses by a correction coefficient. The correction coefficient is, for example, a coefficient for bringing the spectral intensity distribution of the created target intensity spectrogram A43 closer to the spectral intensity distribution of the optical pulse of the input light La.

[0073] 31 is a flowchart showing a method for creating the intensity spectrogram A43. The target intensity spectrogram creating program of this embodiment causes a computer to execute the following steps.

[0074] First, in the waveform function setting step S1, a target waveform function in the frequency domain including an intensity spectrum function and a phase spectrum function is set for one of the multiple optical pulses. In the Fourier transform step (fifth transform step) S2, the target waveform function of the one optical pulse is converted into a time domain waveform function (fifth waveform function) including a time intensity waveform function and a time phase waveform function. In the spectrogram transform step (sixth transform step) S3, an intensity spectrogram is generated from the time domain waveform function generated in the Fourier transform step S2. In the target generation step S4, the intensity spectrogram generated in the spectrogram transform step S3 is superimposed on the target intensity spectrogram. The above waveform function setting step S1, Fourier transform step S2, spectrogram transform step S3, and target generation step S4 are repeated the same number of times as the number of optical pulses (step S5). As a result, an intensity spectrogram A43 is generated. This is not limiting, and for example, multiple light pulses may be processed collectively in the waveform function setting step S1, the Fourier transform step S2, and the spectrogram conversion step S3, and then the generated multiple intensity spectrograms may be superimposed in the target generation step S4.

[0075] According to the above-described device 100, method, and program for creating the intensity spectrogram A43, it is possible to suitably create the intensity spectrogram A43 for varying the center wavelength for each of the multiple pulses included in the optical pulse train Pb.

[0076] The data creation device, light control device, target intensity spectrogram creation device, data creation method, target intensity spectrogram creation method, data creation program, and target intensity spectrogram creation program according to the present disclosure are not limited to the above-mentioned embodiments, and various other modifications are possible. For example, in the above-mentioned embodiments, the case where an optical pulse train including a plurality of optical pulses having a time difference and different central wavelengths is generated has been mainly described, but the device, method, and program according to the present disclosure are also effective in the case where an optical pulse train including a plurality of optical pulses having a time difference and equal central wavelengths is generated. In addition, the device, method, and program according to the present disclosure are also effective in the waveform control of light other than an optical pulse train, such as when shaping the time waveform of a single optical pulse. [Explanation of symbols]

[0077] 1...light control device, 2...light source, 3...optical waveform control unit, 12...diffraction grating, 13...lens, 14...spatial light modulator (SLM), 15...lens, 16...diffraction grating, 17...modulation surface, 17a...modulation region, 20...data creation device, 21...spectrogram setting unit, 22...spectrum design unit, 23...data generation unit, 25...Fourier transform unit (first transform unit), 26...spectrogram conversion unit (second transform unit), 27...spectrogram replacement unit, 28...spectrogram inverse conversion unit (third transform unit), 29...inverse Fourier transform unit (fourth transform unit), 61...processor (CPU), 62...ROM, 63...RAM, 64...input device, 65...output device, 66...communication module, 67...auxiliary storage device, 100...device, 101... Waveform function setting unit, 102...Fourier transform unit (fifth transform unit), 103...spectrogram conversion unit (sixth transform unit), 104...target generation unit, A1...initial spectral function, A2...first waveform function, A3...second waveform function, A5...third waveform function, A6...fourth waveform function, A41...intensity spectrogram, A42...phase spectrogram, A43...target intensity spectrogram, L1...light, L2...modulated light, La...input light, Lb...output light, Pb...optical pulse train, Pb0, Pb1 to Pb3...optical pulse, Pd...optical pulse train, Pd1 to Pd3...optical pulse, S1...waveform function setting step, S2...Fourier transform step, S3...spectrogram conversion step, S4...target generation step, SC...control signal.

Claims

1. 1. An apparatus for generating data for controlling a spatial light modulator, comprising: a first converter for converting a first waveform function in the frequency domain, which includes an intensity spectrum function and a phase spectrum function, into a second waveform function in the time domain, which includes a time intensity waveform function and a time phase waveform function; a second converter for converting the second waveform function into an intensity spectrogram and a phase spectrogram; a spectrogram replacement unit that replaces the intensity spectrogram with a pre-created target intensity spectrogram and constrains the phase spectrogram; a third transform unit that transforms the replaced intensity spectrogram and the constrained phase spectrogram into a third waveform function in the time domain including a time intensity waveform function and a time phase waveform function; a fourth transform unit that transforms the third waveform function into a fourth waveform function in the frequency domain including an intensity spectrum function and a phase spectrum function; A data generating unit that generates the data; Equipped with the first converter, the second converter, the spectrogram replacement unit, the third converter, and the fourth converter repeatedly operate in this order while replacing the phase spectral function of the first waveform function with the phase spectral function of the fourth waveform function; The data generating unit generates the data based on a phase spectrum function of the fourth waveform function obtained after a repetitive operation.

2. the first waveform function of the first converter at the beginning of the repetition is a waveform function for an initial optical pulse; 2. The data creation device according to claim 1, wherein the target intensity spectrogram is an intensity spectrogram for a light pulse train including a plurality of light pulses having a time difference from one another and different central wavelengths.

3. 3. The data creation device according to claim 2, wherein the target intensity spectrogram is set so that, when a full width at half maximum of a wavelength band of light input to the spatial light modulator is λw, a full width at half maximum λs of the wavelength band of each of the plurality of optical pulses is greater than (λw / 4) and less than (6·λw / 5), and a central wavelength spacing λd of the plurality of optical pulses is greater than 0 and less than (4·λw / 5).

4. A light source that outputs input light; A spectroscopic element that splits the input light; a spatial light modulator that modulates a spectral phase of the input light after separation and outputs modulated light; an optical system for multiplexing each wavelength component of the modulated light; Equipped with 4. A light control device, wherein the spatial light modulator modulates at least one of a spectral phase and a spectral intensity of the input light based on the data generated by a data generation device according to claim 1.

5. 1. An apparatus for generating a target intensity spectrogram for use in generating data for controlling a spatial light modulator, the target intensity spectrogram being related to a light pulse train including a plurality of light pulses having a time difference from one another and different central wavelengths, the apparatus comprising: a waveform function setting unit that sets a target waveform function in a frequency domain including an intensity spectral function and a phase spectral function for each of the optical pulses; a fifth transform unit that transforms the target waveform function of each of the plurality of optical pulses into a fifth waveform function in the time domain including a time intensity waveform function and a time phase waveform function; a sixth converter that generates an intensity spectrogram from the fifth waveform function of each of the plurality of optical pulses; a target generator that generates the target intensity spectrogram by superimposing the intensity spectrograms of the plurality of optical pulses; A target intensity spectrogram creating device comprising:

6. 1. A method of generating data to control a spatial light modulator, comprising the steps of: a first transformation step of transforming a first waveform function in the frequency domain, which includes an intensity spectral function and a phase spectral function, into a second waveform function in the time domain, which includes a time intensity waveform function and a time phase waveform function; a second transformation step of transforming the second waveform function into an intensity spectrogram and a phase spectrogram; a spectrogram substitution step of replacing the intensity spectrogram with a pre-created target intensity spectrogram and constraining the phase spectrogram; a third transformation step of transforming the replaced intensity spectrogram and the constrained phase spectrogram into a third waveform function in the time domain including a time intensity waveform function and a time phase waveform function; a fourth transformation step of transforming the third waveform function into a fourth waveform function in the frequency domain including an intensity spectral function and a phase spectral function; A data generation step of generating the data; Including, repeating the first conversion step, the second conversion step, the third conversion step, and the fourth conversion step in this order while replacing the first waveform function in the first conversion step with a fourth waveform function in the fourth conversion step; The data generating step generates the data based on a phase spectrum function of the fourth waveform function obtained after a repetitive operation.

7. the first waveform function of the first conversion step at the beginning of the iteration is a waveform function for an initial optical pulse; 7. The data creation method according to claim 6, wherein the target intensity spectrogram is an intensity spectrogram for a light pulse train including a plurality of light pulses having a time difference from one another and different central wavelengths.

8. 8. The data creation method according to claim 7, wherein the target intensity spectrogram is set such that, when a full width at half maximum of a wavelength band of light input to the spatial light modulator is λw, a full width at half maximum λs of the wavelength band of each of the plurality of optical pulses is greater than (λw / 4) and less than (6·λw / 5), and a central wavelength spacing λd of the plurality of optical pulses is greater than 0 and less than (4·λw / 5).

9. 1. A method for generating a target intensity spectrogram for use in generating data for controlling a spatial light modulator, the target intensity spectrogram being for a light pulse train including a plurality of light pulses having different central wavelengths and a time difference therebetween, the method comprising: a waveform function setting step of setting a target waveform function in a frequency domain including an intensity spectral function and a phase spectral function for each of the optical pulses; a fifth transformation step of transforming the target waveform function of each of the plurality of optical pulses into a fifth waveform function in the time domain including a temporal intensity waveform function and a temporal phase waveform function; a sixth transformation step of generating an intensity spectrogram from the fifth waveform function of each of the plurality of optical pulses; a target generating step of generating the target intensity spectrogram by superimposing the intensity spectrograms of each of the plurality of light pulses; A method for constructing a target intensity spectrogram, comprising:

10. A program for creating data for controlling a spatial light modulator, a first transformation step of transforming a first waveform function in the frequency domain, which includes an intensity spectral function and a phase spectral function, into a second waveform function in the time domain, which includes a time intensity waveform function and a time phase waveform function; a second transformation step of transforming the second waveform function into an intensity spectrogram and a phase spectrogram; a spectrogram substitution step of replacing the intensity spectrogram with a pre-created target intensity spectrogram and constraining the phase spectrogram; a third transformation step of transforming the replaced intensity spectrogram and the constrained phase spectrogram into a third waveform function in the time domain including a time intensity waveform function and a time phase waveform function; a fourth transformation step of transforming the third waveform function into a fourth waveform function in the frequency domain including an intensity spectral function and a phase spectral function; A data generation step of generating the data; Run the following on your computer: repeating the first conversion step, the second conversion step, the third conversion step, and the fourth conversion step in this order while replacing the first waveform function in the first conversion step with a fourth waveform function in the fourth conversion step; a data creation program for generating the data based on a phase spectrum function of the fourth waveform function obtained after the repeated operation, in the data generating step;

11. the first waveform function of the first conversion step at the beginning of the iteration is a waveform function for an initial optical pulse; 11. The data creation program according to claim 10, wherein the target intensity spectrogram is an intensity spectrogram relating to a light pulse train including a plurality of light pulses having a time difference from one another and different central wavelengths.

12. 12. The data creation program according to claim 11, wherein the target intensity spectrogram is set so that, when a full width at half maximum of a wavelength band of light input to the spatial light modulator is λw, a full width at half maximum λs of the wavelength band of each of the plurality of optical pulses is greater than (λw / 4) and less than (6·λw / 5), and a central wavelength spacing λd of the plurality of optical pulses is greater than 0 and less than (4·λw / 5).

13. A program for creating a target intensity spectrogram for use in creating data for controlling a spatial light modulator, the target intensity spectrogram being related to an optical pulse train including a plurality of optical pulses having a time difference from one another and different central wavelengths, the program comprising: a waveform function setting step of setting a target waveform function in a frequency domain including an intensity spectral function and a phase spectral function for each of the optical pulses; a fifth transformation step of transforming the target waveform function of each of the plurality of optical pulses into a fifth waveform function in the time domain including a temporal intensity waveform function and a temporal phase waveform function; a sixth transformation step of generating an intensity spectrogram from the fifth waveform function of each of the plurality of optical pulses; a target generating step of generating the target intensity spectrogram by superimposing the intensity spectrograms of each of the plurality of light pulses; A target intensity spectrogram generating program that causes a computer to execute the above.

Images