JP6659339B2 - Pulse light generation device and pulse light generation method - Google Patents

Description

  The present invention relates to a pulse light generation device and a pulse light generation method.

  Non-Patent Document 1 discloses a technique for generating pulse light (ultra-short pulse light) having an extremely short time width.

Yoshihisa Hiromoto et al., "Terahertz Technology Overview", Terahertz Technology Forum, 2007 edition

  For example, terahertz pulsed light can be generated by applying excitation pulsed light to a photoconductive antenna, a crystal element, or the like to cause a nonlinear optical effect. Such a nonlinear optical effect occurs more remarkably as the rise or fall of the time intensity waveform of the excitation pulse light is steeper (that is, as the maximum value of the time derivative of the intensity is larger). When generating the terahertz pulse light, the peak intensity (or the peak value of the spectrum intensity) of the time waveform of the terahertz pulse light increases as the rise or fall of the time intensity waveform of the excitation light pulse becomes steeper.

  As a method of sharpening the rise or fall of the time intensity waveform of the pulse light, for example, there is a method of shortening the time width of the pulse light as much as possible and increasing the peak value. According to the recognition of the inventor, the minimum value of the time width of the pulse light is uniquely determined by the unique spectral bandwidth and the shape of the spectrum intensity waveform of the pulse light. In particular, a pulse light having a short time width equal to the theoretical limit value and having a high peak value is called a TL (Transform limited) pulse.

  FIG. 15A is a graph showing the spectrum intensity waveform G11 and the spectrum phase waveform G12 of the TL pulse, where the horizontal axis indicates the wavelength, the left vertical axis indicates the intensity, and the right vertical axis indicates the phase. FIG. 15B is a graph showing an example of the time waveform of the TL pulse, in which the horizontal axis represents time and the vertical axis represents intensity. As shown in FIG. 15A, the TL pulse is generated when the spectral phase waveform G12 is constant (flat) regardless of the wavelength.

  As described above, the minimum value of the time width of the pulse light is theoretically determined by the TL pulse. Therefore, according to the above-described concept, the limit of the magnitude of the nonlinear optical effect is obtained when the excitation pulse light is a TL pulse. However, if the rise or fall of the time intensity waveform of the pulse light can be made steeper, the nonlinear optical effect can be more remarkably generated. If the nonlinear optical effect can be generated more remarkably, there is a great advantage for an optical device utilizing the nonlinear optical effect, for example, the peak intensity of the time waveform of the terahertz pulse light can be further increased.

  The present invention has been made in view of such a problem, and provides a pulse light generation device and a pulse light generation method that can make the rise or fall of the time intensity waveform of pulse light steeper than the TL pulse. The purpose is to provide.

In order to solve the above-described problem, a first pulsed light generation device according to the present invention includes a spectral element that splits light, and a spatial light modulation that is optically coupled to the spectral element and that modulates the phase of light after splitting. And a light conversion element which is optically coupled to the spatial light modulator and converts the modulated light into pulsed light. When the spatial light modulator makes the spectral phase waveform of the pulse light non-linear and point-symmetric with respect to a certain wavelength ω0 and makes the rising of the pulse light steep , at least the full width at half maximum of the spectral intensity waveform of the pulse light is obtained. If the spectral phase waveform of the pulsed light is one of monotonically increasing and monotonically decreasing within the wavelength range, and the falling edge of the pulsed light is steep, the spectral phase waveform of the pulsed light is monotonically increased and monotonically reduced within the wavelength range. And the other .

In addition, a second pulsed light generation device according to the present invention includes a spectral element that splits light, and a spatial light modulator that is optically coupled to the spectral element and that modulates the phase of light after splitting. The spectroscopic element receives the modulated light and converts it into pulsed light. When the spatial light modulator makes the spectral phase waveform of the pulse light non-linear and point-symmetric with respect to a certain wavelength ω0 and makes the rising of the pulse light steep , at least the full width at half maximum of the spectral intensity waveform of the pulse light is obtained. If the spectral phase waveform of the pulsed light is one of monotonically increasing and monotonically decreasing within the wavelength range, and the falling edge of the pulsed light is steep, the spectral phase waveform of the pulsed light is monotonically increased and monotonically reduced within the wavelength range. And the other .

Further, the pulse light generation method according to the present invention includes a first step of splitting light, a second step of modulating the phase of the light after splitting, and a third step of converting the modulated light into pulse light. Including. Then, in the second step, when the spectral phase waveform of the pulsed light is nonlinear and point-symmetric with respect to a certain wavelength ω0 and the rising of the pulsed light is sharp , at least the full width at half maximum of the spectral intensity waveform of the pulsed light and one of the monotonic increase and monotonic decrease the spectral phase waveform of the pulsed light in the wavelength range of, in the case of a steep fall of the pulse light is monotonically increasing and monotonic spectral phase waveform of the pulsed light in the wavelength range The other of the decreases .

  The inventor tried to make the spectrum phase waveform flat in the TL pulse into various shapes in order to make the rise or fall of the time intensity waveform of the pulse light steeper than the TL pulse. As a result, as described above, when the spectral phase waveform is non-linear and point-symmetric with respect to a certain wavelength ω0, and further, is monotonically increasing or decreasing within at least the full width at half maximum wavelength range of the spectral intensity waveform, the pulse It has been found that one of the rise and fall of the time intensity waveform of light is steeper than the TL pulse, and the other is slower than the TL pulse. In addition, it was confirmed that the time width of the pulse light was slightly wider than that of the TL pulse light.

  As described above, according to the above apparatus and method, one of the rise and fall of the time intensity waveform of the pulse light can be made steeper than the TL pulse, so that the nonlinear optical effect can be more remarkably generated. . Therefore, for example, when the terahertz pulsed light is generated using the nonlinear optical effect, the peak intensity of the time waveform of the terahertz pulsed light can be further increased as compared with the case where the TL pulsed light is used as the excitation light.

  In the above apparatus and method, the wavelength ω0 may be included in the wavelength range of the full width at half maximum of the spectral intensity waveform of the pulsed light. Thereby, one of the rise and fall of the time intensity waveform of the pulse light can be more steeply formed than the TL pulse.

  In the above apparatus and method, the spectral phase waveform may be sigmoidal. Alternatively, the spectral phase waveform may be an n-th order function (n is a positive odd number). Alternatively, the spectral phase waveform may be a k-th order function (k is a positive real number excluding a positive odd number). Alternatively, the spectral phase waveform corresponds to a linear sum of at least two of a sigmoid function, an n-th order function (n is a positive odd number), and a k-th order function (k is a positive real number excluding a positive odd number). It may be shaped. Accordingly, a spectrum phase waveform that is non-linear and point-symmetric with respect to a certain wavelength ω0 and that is monotonically increasing or monotonically decreasing within a wavelength range of at least the full width at half maximum of the spectrum intensity waveform can be suitably realized.

  In the above device, the spectral element may include a diffraction grating or a prism. Thereby, the light provided to the spatial light modulator can be appropriately split.

  In the above device, the light conversion element may include a condenser lens. Thereby, the light modulated by the spatial light modulator can be suitably converted into pulsed light.

  According to the pulse light generation device and the pulse light generation method of the present invention, the rise or fall of the time intensity waveform of the pulse light can be steeper than the TL pulse.

It is a figure showing roughly composition of a pulse light generation device concerning one embodiment of the present invention. FIG. 3 is a diagram illustrating a modulation surface of the spatial light modulator. 5 is a graph showing an example of a spectral phase waveform given to pulsed light by a spatial light modulator. (A) shows a comparison between the time waveform of the pulse light having the spectrum phase waveform and the spectrum intensity waveform shown in FIG. 3 and the time waveform of the TL pulse. (B) The time differential waveform of each graph of (a) is shown. 5 is a graph showing an example of three spectral phase waveforms according to a combination of α and β in Expression (1). 11 is a graph showing another example of a spectral phase waveform given to pulsed light by a spatial light modulator. It is a graph which shows the example of three spectrum phase waveforms according to the combination of a and n of Numerical formula (2). It is a graph which shows another example of the spectrum phase waveform given to the pulse light by the spatial light modulator. It is a graph which shows the example of three spectrum phase waveforms according to the combination of a and k of Numerical formula (3). It is a graph which shows another example of the spectrum phase waveform given to the pulse light by the spatial light modulator. It is a graph which shows the example of three spectrum phase waveforms according to the combination of b and c of Formula (4). It is a graph which shows the example of the spectrum phase waveform linearly approximated by dividing into a some area. It is a flowchart which shows a pulse light generation method. 9 shows a configuration of a pulsed light generation device according to a modification. (A) is a graph showing a spectrum intensity waveform and a spectrum phase waveform of a TL pulse. (B) A graph showing an example of a time waveform of a TL pulse.

  Hereinafter, embodiments of a pulse light generation device and a pulse light generation method according to the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

  FIG. 1 is a diagram schematically illustrating a configuration of a pulse light generation device 1A according to an embodiment of the present invention. The pulse light generation device 1A of the present embodiment generates pulse light Ld from the input light La with a steep rise or fall of the time intensity waveform (that is, a large absolute value of the time change rate). As shown in FIG. 1, the pulse light generation device 1A includes a light source 2, an optical system 10, and a control unit 20.

  The light source 2 outputs input light La input to the optical system 10. The light source 2 is, for example, a laser light source such as a solid-state laser light source, and the input light La is, for example, a coherent pulse light.

  The optical system 10 includes a spectral element 12, a curved mirror 14, and a spatial light modulator (SLM) 16. The spectral element 12 is optically coupled to the light source 2, and the SLM 16 is optically coupled to the spectral element 12 via the curved mirror 14. The spectroscopic element 12 splits the input light La for each wavelength component. The spectral element 12 includes, for example, a diffraction grating formed on a plate surface. Alternatively, the spectral element 12 may include a prism. The input light La enters the light-splitting element 12 obliquely and is split into a plurality of wavelength components by the action of diffraction or refraction. The light Lb after splitting composed of the plurality of wavelength components reaches the curved mirror 14. The light Lb is reflected by the curved mirror 14 and reaches the SLM 16.

  The SLM 16 modulates the phase of the split light Lb in order to generate the pulse light Ld in which the rise or fall of the time intensity waveform is steep. The SLM 16 has a plurality of pixels arranged one-dimensionally or two-dimensionally, and modulates the light Lb dispersed by the spectral element 12 for each pixel. In one embodiment, SLM 16 is of the liquid crystal on silicon (LCOS) type. FIG. 2 is a diagram illustrating the modulation surface 17 of the SLM 16. The modulation surface 17 is composed of a plurality of pixels arranged two-dimensionally. FIG. 2 shows a modulation region 17a in which a plurality of pixels are arranged along a certain direction B for easy understanding. A plurality of modulation regions 17a are arranged along a direction A intersecting with the direction B. This direction A is the direction of the spectral separation by the spectral element 12. Therefore, each of the split wavelength components is input to each of the plurality of modulation regions 17a. The SLM 16 modulates the phase of each input wavelength component in each modulation area 17a.

  The modulated light Lc composed of each wavelength component modulated by the SLM 16 is reflected again by the curved mirror 14 and reaches the spectral element 12. At this time, the curved mirror 14 functions as a condensing optical system that condenses the modulated light Lc. Further, the spectral element 12 functions as a multiplexing optical system, and multiplexes each of the modulated wavelength components. That is, a plurality of wavelength components of the modulated light Lc are condensed and multiplexed with each other by the spectral element 12 and converted into pulsed light Ld.

  The control unit 20 includes a computer 21 including a processor and a memory and a controller 22 including a processor and a memory. The computer 21 is, for example, a personal computer or a smart device, and controls operations of the light source 2 and the like by a processor. The controller 22 controls a modulation amount for each of the plurality of pixels in accordance with a modulation pattern in which control values corresponding to the plurality of pixels of the SLM 16 are two-dimensionally distributed. More specifically, the controller 22 is electrically connected to the computer 21 and the SLM 16 and sends a control signal including a phase modulation pattern for sharpening the rise or fall of the time intensity waveform of the pulse light Ld of the SLM 16 to the SLM 16. To provide. Hereinafter, the spectral phase waveform given to the pulsed light Ld to sharpen the rise or fall of the time intensity waveform will be described in detail.

FIG. 3 is a graph showing an example of a spectral phase waveform given to the pulse light Ld by the SLM 16. A graph G21 shows a spectrum phase waveform of the pulse light Ld, and a graph G22 shows a spectrum intensity waveform of the pulse light Ld. The shape of the spectrum intensity waveform shown here is a Sech ² type. The horizontal axis indicates the wavelength (unit: nm), the left vertical axis indicates the spectrum intensity (arbitrary unit), and the right vertical axis indicates the spectrum phase (unit: rad).

  As shown in FIG. 3, the SLM 16 makes the spectrum phase waveform G21 of the pulsed light Ld nonlinear with respect to the wavelength, and includes the wavelength ω0 (800 nm in the figure) included in the wavelength range of the full width at half maximum W of the spectrum intensity waveform G22. ) (Hereinafter referred to as condition A). Here, the point symmetry is an expression when a graph of a spectrum phase waveform is grasped as a graphic, in other words, it can be said that it is antisymmetric with respect to the wavelength ω0. Anti-symmetry means that the result of performing a certain transformation on an element is equal to the result of applying the opposite sign to the original element (in terms of real numbers, the absolute value is the same and the sign is opposite). Also called alternation or skew symmetry. That is, assuming that the phase value corresponding to the wavelength ω0 in the spectral phase waveform is φ0, when the spectral phase waveform in the wavelength region smaller than the wavelength ω0 is inverted around the phase value φ0 and further inverted around the wavelength ω0, This means that it matches the spectral phase waveform in the wavelength region larger than the wavelength ω0.

Further, the SLM 16 makes the spectrum phase waveform G21 of the pulse light Ld monotonically increase or decrease (hereinafter, referred to as condition B) within the wavelength range of at least the full width at half maximum W of the spectrum intensity waveform G22. FIG. 3 shows a sigmoid function-like spectrum phase waveform as an example of a spectrum phase waveform satisfying these conditions A and B. Equation (1) represents a sigmoid function-like spectral phase waveform Phase (ω). α and β are arbitrary real numbers.

  FIG. 4A shows a time waveform (graph G31) of the pulse light Ld having the spectrum phase waveform G21 and the spectrum intensity waveform G22 shown in FIG. 3 and a time waveform of the TL pulse shown in FIG. (Graph G32) is shown. FIG. 4B shows a comparison between the time derivative waveform (graph G41) of the graph G31 in FIG. 4A and the time derivative waveform (graph G42) of the graph G32 in FIG. 4A. As shown in FIGS. 4 (a) and 4 (b) (particularly, see FIG. 4 (b)), with respect to the rise, the maximum value of the time derivative of the pulse light Ld is larger than the maximum value of the time derivative of the TL pulse. This indicates that the pulse light Ld is steeper than the TL pulse. On the other hand, regarding the fall, the minimum value of the time derivative of the TL pulse is smaller than the minimum value of the time derivative of the pulse light Ld, and the TL pulse is steeper than the pulse light Ld. With respect to the pulse time width, the pulse light Ld is slightly longer than the TL pulse.

  FIG. 5 is a graph showing an example of three spectral phase waveforms according to the combination of α and β in Expression (1). The graph G51 in the figure shows the case where α = 0.51, β = 1.96, the graph G52 shows the case where α = 0.01, β = 0.96, the graph G53 shows α = 29.01, The case where β = 0.81 is shown. The present inventor has confirmed that when α and β are at least these values, the rising edge of the pulse light Ld is steeper than that of the TL pulse. Further, according to this sigmoid function-like spectrum phase waveform, it was found that there was a condition (α, β) in which the slope of the pulse light Ld was 11% or more larger than the slope of the TL pulse.

  In the above example, the spectrum phase waveform has a monotonically increasing sigmoid type phase within the wavelength range of the full width at half maximum W of the spectrum intensity waveform G22. Become. Conversely, in the case of a sigmoid phase in which the spectral phase waveform is monotonically decreasing within the wavelength range of the full width at half maximum W, the pulse light Ld is steeper with respect to the fall than the TL pulse.

FIG. 6 is a graph showing another example of the spectral phase waveform given to the pulse light Ld by the SLM 16. Also in this example, as in FIG. 3, the SLM 16 realizes a spectrum phase waveform satisfying the conditions A and B. As an example of such a spectral phase waveform, FIG. 6 shows spectral phase waveforms G61 and G62 having an n-th order function (n is a positive odd number). Specifically, a graph G61 shows a case where n = 3, and a graph G62 shows a case where n = 5. Equation (2) represents an n-th order function-like spectral phase waveform Phase (ω). a is an arbitrary real number.

  According to the spectrum phase waveform of the n-th order function when a <0 as described above, the rising edge of the pulse light Ld is steeper than that of the TL pulse. On the other hand, regarding the falling, the TL pulse is steeper than the pulse light Ld. When a> 0, the steepness of the rise and fall is reversed. With respect to the pulse time width, the pulse light Ld is slightly longer than the TL pulse.

FIG. 7 is a graph showing an example of three spectral phase waveforms according to the combination of a and n in Expression (2). A graph G71 in the figure shows a case where a = −4.6 × 10 ⁻⁴ and n = 3, a graph G72 shows a case where a = −2.0 × 10 ⁻⁶ and n = 5, and a graph G73 shows The case where a = −1.6 × 10 ⁻⁸ and n = 7 is shown. The present inventor has confirmed that, when a and n are at least these values, the pulse light Ld is steeper with respect to the rise than the TL pulse. Further, according to the n-th order function-like spectral phase waveform, it has been found that there is a condition (a, n) in which the slope of the pulse light Ld is 7% or more larger than the slope of the TL pulse.

FIG. 8 is a graph showing still another example of the spectral phase waveform given to the pulse light Ld by the SLM 16. Also in this example, as in FIG. 3, the SLM 16 realizes a spectrum phase waveform satisfying the conditions A and B. As an example of such a spectral phase waveform, FIG. 8 shows a spectral phase waveform of a k-th order function (k is a positive real number excluding a positive odd number). Specifically, a graph G81 shows a case where k = 1.25, and a graph G82 shows a case where k = 2.5. Equation (3) represents a k-th order function-like spectral phase waveform Phase (ω). a is an arbitrary real number.

  According to the spectral phase waveforms G81 and G82 of the k-th order function as described above, the rising edge of the pulse light Ld is steeper than that of the TL pulse. On the other hand, regarding the falling, the TL pulse is steeper than the pulse light Ld. With respect to the pulse time width, the pulse light Ld is slightly longer than the TL pulse.

FIG. 9 is a graph showing an example of three spectral phase waveforms according to the combination of a and k in Expression (3). A graph G91 in the figure shows a case where a = −1.13 × 10 ⁻² and k = 2, a graph G92 shows a case where a = −3.0 × 10 ⁻⁵ and k = 4, and a graph G93 shows The case where a = −1.7 × 10 ⁻³ and k = 2.5 is shown. The present inventor has confirmed that, when a and k are at least these values, the rising edge of the pulse light Ld is steeper than that of the TL pulse. In addition, according to the k-th order function-like spectral phase waveform, it has been found that there is a condition (a, k) in which the slope of the pulse light Ld is 17% or more larger than the slope of the TL pulse.

  According to the spectral phase waveform of the k-th order function in the case of a <0 as described above, the pulse light Ld is steeper with respect to the rise than the TL pulse. On the other hand, regarding the falling, the TL pulse is steeper than the pulse light Ld. When a> 0, the steepness of the rise and fall is reversed.

FIG. 10 is a graph showing still another example of the spectral phase waveform given to the pulse light Ld by the SLM 16. Also in this example, as in FIG. 3, the SLM 16 realizes a spectrum phase waveform satisfying the conditions A and B. As an example of such a spectral phase waveform, FIG. 10 shows a sinusoidal spectral phase waveform G101. Equation (4) represents a sinusoidal spectral phase waveform Phase (ω). b and c are arbitrary real numbers.

  According to the sinusoidal spectrum phase waveform of b> 0 as shown in FIGS. 10 and 12, the spectrum phase waveform monotonically increases within the wavelength range of the full width at half maximum W of the spectrum intensity waveform G22. Regarding the rise, the pulse light Ld is steeper than the TL pulse. On the other hand, regarding the falling, the TL pulse is steeper than the pulse light Ld. On the other hand, when b <0, the steepness of the rise and fall is reversed. With respect to the pulse time width, the pulse light Ld is slightly longer than the TL pulse.

  FIG. 11 is a graph showing an example of three spectral phase waveforms according to the combination of b and c in Expression (4). The graph G111 in the figure shows the case where b = 0.285 and c = 0.345, the graph G112 shows the case where b = 0.615 and c = 0.225, and the graph G113 shows the case where b = 2.865. The case where c = 0.09 is shown. The present inventor has confirmed that when b and c are at least these values, the rising edge of the pulse light Ld is steeper than that of the TL pulse. Further, according to the sine function-like spectrum phase waveform, it was found that there was a condition (b, c) in which the slope of the pulse light Ld was larger than the slope of the TL pulse by 11.3% or more.

In each of the examples described above, the case where the spectral phase waveform is a curve is shown. However, the spectral phase waveform may be linearly approximated by dividing it into a plurality of sections. It can be sharpened. As an example, FIG. 12 shows a spectrum obtained by dividing the sigmoid function-like spectrum phase waveform (α = 0.51, β = 1.96) shown in FIG. 3 into three sections and performing linear approximation in each section. 19 shows a phase waveform G121. Note that, also in this example, the spectrum phase waveform G121 satisfies the conditions A and B as in FIG. Equation (5) represents a spectral phase waveform Phase (ω) of a linear approximation type of a sigmoid function. y0, y1, b are arbitrary real numbers. A graph G121 in FIG. 12 shows a case where y0 = 0, y1 = 1.96, and b = 0.199.

  According to the spectrum phase waveform obtained by linearly approximating the sigmoid function as described above, the spectrum phase waveform monotonically increases within the wavelength range of the full width at half maximum W of the spectrum intensity waveform G22. At this time, regarding the rising, the pulse light Ld is steeper than the TL pulse. On the other hand, regarding the falling, the TL pulse is steeper than the pulse light Ld. With respect to the pulse time width, the pulse light Ld is slightly longer than the TL pulse.

  The spectral phase waveform is not limited to each of the above examples. For example, a sigmoid function (see FIG. 3), an n-th function (see FIG. 6), a k-th function (see FIG. 8), a sine function (see FIG. 10), and a shape corresponding to a linear sum of at least two of these linear approximation functions. Further, for example, the sum may be the sum of a phase pattern that enables generation of a multi-pulse and the phase pattern that enables steepening. Even in such a case, the pulse light Ld can be steeper than the TL pulse with respect to the rise or fall.

  Here, a pulse light generation method using the pulse light generation device 1A will be described with reference to the flowchart shown in FIG. First, the input light La is split by the spectroscopic element 12 (first step S1). Next, the phase of the split light Lb is modulated by the SLM 16 (second step S2). Subsequently, the modulated light Lc is converted into pulsed light Ld by the spectroscopic element 12 (third step S3). In the second step S2, the spectral phase waveform of the pulsed light Ld is nonlinear and point-symmetric with respect to a certain wavelength ω0 (condition A), and is monotonic within at least the wavelength range of the full width at half maximum W of the spectral intensity waveform of the pulsed light Ld. The phase of the light Lb is modulated so as to increase or monotonically decrease (condition B).

  Effects obtained by the pulse light generation device 1A and the pulse light generation method of the present embodiment described above will be described. The inventor tried to make the spectrum phase waveform flat in the TL pulse into various shapes in order to make the rise or fall of the time intensity waveform of the pulse light steeper than the TL pulse. As a result, when the spectrum phase waveform satisfies both the conditions A and B described above, one of the rise and fall of the time intensity waveform of the pulse light becomes steeper than the TL pulse and the other becomes gentler than the TL pulse. I found that.

  According to the pulse light generation device 1A and the pulse light generation method of the present embodiment, since the SLM 16 performs the phase modulation of the light Lb so that the pulse light Ld satisfies the conditions A and B, the rise of the time intensity waveform of the pulse light Ld And the falling edge can be steeper than the TL pulse. As a result, the nonlinear optical effect can be more remarkably generated. As a result of the numerical calculation, it was confirmed that according to the present embodiment, the gradient of the time intensity waveform of the pulse light Ld can be increased by about 10 to 17% as compared with the TL pulse light.

  As an example of the effect of the present embodiment, high efficiency generation of THz (terahertz) light is given. Considering, for example, the case where a photoconductive antenna is used as a method of generating THz light, the time waveform or spectrum of the THz light is generally determined by the current density Jpc (t) and the temporal change of the photoconductivity σ (t). Since the temporal change of the photoconductivity σ (t) is determined based on the intensity profile I (t) of the pulsed light, it is considered that the steepness of the time waveform of the pulsed light contributes to the improvement of the generation intensity of THz light and the expansion of the spectrum band. . Further, even when the THz light is generated using the nonlinear optical crystal, the generation intensity of the THz light is proportional to the second derivative of the intensity profile I (t). It is considered that this contributes to the improvement of the generation intensity of THz light and the expansion of the spectrum band in the same manner as described above. It should be noted that various technologies using other nonlinear optical effects (laser processing, laser microscope measurement, etc.) are expected to achieve higher efficiency and higher accuracy.

  Further, as in the present embodiment, the wavelength ω0 may be included in the wavelength range of the full width at half maximum W. Thereby, one of the rise and fall of the time intensity waveform of the pulse light Ld can be more reliably made steeper than the TL pulse.

(Modification)
FIG. 14 shows a configuration of a pulse light generation device 1B according to a modification of the above embodiment. This pulse light generation device 1B is different from the above embodiment in the form of a light conversion element. That is, in the above embodiment, the spectroscopic element 12 receives the modulated light Lc and converts it into the pulsed light Ld. However, the pulsed light generation device 1B of this modified example is optically coupled to the SLM 16 and It further includes a light conversion element 18 that converts light Lc into pulsed light Ld. In addition, such a light conversion element 18 is suitably realized by including, for example, a condenser lens.

  The pulse light generation device and the pulse light generation method according to the present invention are not limited to the above-described embodiment, and various other modifications are possible. For example, in the above embodiment, a sigmoid function or the like is shown as an example of the spectrum phase waveform that satisfies the conditions A and B. Can be adopted.

  1A, 1B: pulse light generation device, 2: light source, 10: optical system, 12: spectral element, 14: curved mirror, 17: modulation surface, 17a: modulation area, 18: light conversion element, 20: control unit, La ... input light, Lc ... modulated light, Ld ... pulsed light, W ... full width at half maximum.

Claims (15)

A light-splitting element for splitting light;
A spatial light modulator that is optically coupled to the spectroscopic element and modulates the phase of the light after the spectroscopy;
An optical conversion element that is optically coupled to the spatial light modulator and converts the modulated light into pulsed light,
The spatial light modulator sets the spectral phase waveform of the pulse light to be nonlinear and point-symmetric with respect to a certain wavelength ω0, and when the rising of the pulse light is steep , At least in the wavelength range of the full width at half maximum, the spectral phase waveform of the pulse light is one of monotone increase and monotone decrease , and when the fall of the pulse light is steep, the spectrum of the pulse light in the wavelength range A pulsed light generation device, wherein the phase waveform is the other of monotonically increasing and monotonically decreasing . A light-splitting element for splitting light;
A spatial light modulator that is optically coupled to the spectral element and modulates the phase of the light after the spectral separation,
The spectroscopic element receives the modulated light and converts it into pulsed light,
The spatial light modulator sets the spectral phase waveform of the pulse light to be nonlinear and point-symmetric with respect to a certain wavelength ω0, and when the rising of the pulse light is steep , At least in the wavelength range of the full width at half maximum, the spectral phase waveform of the pulse light is one of monotone increase and monotone decrease , and when the fall of the pulse light is steep, the spectrum of the pulse light in the wavelength range A pulsed light generation device, wherein the phase waveform is the other of monotonically increasing and monotonically decreasing .   The pulse light generation device according to claim 1, wherein the wavelength ω0 is included in a wavelength range of the full width at half maximum.   The pulse light generation device according to claim 1, wherein the spectrum phase waveform has a sigmoid function.   The pulse light generation device according to any one of claims 1 to 3, wherein the spectrum phase waveform is an n-th order function (n is a positive odd number).   The pulse light generation device according to any one of claims 1 to 3, wherein the spectrum phase waveform is a k-th order function (k is a positive real number excluding a positive odd number).   The spectral phase waveform has a shape corresponding to a linear sum of at least two functions of a sigmoid function, an n-th function (n is a positive odd number), and a k-th function (k is a positive real number excluding a positive odd number). The pulse light generation device according to any one of claims 1 to 3.   The pulse light generation device according to any one of claims 1 to 7, wherein the dispersive element includes a diffraction grating or a prism.   The pulse light generation device according to claim 1, wherein the light conversion element includes a condenser lens. A first step of dispersing light;
A second step of modulating the phase of the separated light;
Converting the modulated light into pulsed light; and
In the second step, when the spectral phase waveform of the pulse light is nonlinear and point-symmetric with respect to a certain wavelength ω0, and the rising of the pulse light is steep , at least the spectral intensity waveform of the pulse light is When the spectral phase waveform of the pulse light is one of monotonically increasing and monotonically decreasing within the full width at half maximum and the falling edge of the pulse light is steep, the spectral phase of the pulse light is within the wavelength range. A pulsed light generation method in which the waveform is the other of a monotone increase and a monotone decrease .   The pulse light generation method according to claim 10, wherein the wavelength ω0 is included in a wavelength range of the full width at half maximum.   The pulse light generation method according to claim 10, wherein the spectrum phase waveform has a sigmoid function.   The pulse light generation method according to claim 10, wherein the spectrum phase waveform has an n-th order function shape (n is a positive odd number).   The pulse light generation method according to claim 10, wherein the spectral phase waveform is a k-th order function (k is a positive real number excluding a positive odd number).   The spectral phase waveform has a shape corresponding to a linear sum of at least two functions of a sigmoid function, an n-th function (n is a positive odd number), and a k-th function (k is a positive real number excluding a positive odd number). The pulse light generation method according to claim 10 or 11, wherein

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