JP2016151694A - Double optical pulse creation device and double optical pulse creation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device that allows a simple configuration to easily create double optical pulses.SOLUTION: A double optical pulse creation device 1 comprises: a polarization split unit 10; and a λ/4 plate 20. The polarization separation unit 10 is configured to: convert an input optical pulse P1 into a first optical pulse P2a and second optical pulse P2b of linear polarization in which respective polarization azimuths are mutually orthogonal; and output the first optical pulse P2a and the second optical pulse P2b in a time-wise mutually separated manner. The λ/4 plate 20 is configured to: receive the first optical pulse P2a and second optical pulse P2b of the linear polarization output from the polarization separation unit 10 in a time-wise mutually separated manner; and output a first optical pulse P3a and second optical pulse P3b of elliptic polarization.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an apparatus and method for generating double light pulses.

  In an ultra-short pulse technology such as femtosecond laser or terahertz light, two optical pulses that are temporally separated from each other are generated, and the polarization state of each optical pulse is controlled, and these two optical pulses are continuously applied to the object. If it can be irradiated, research is expected to proceed in various fields such as material science, biomolecule measurement, information communication, environmental measurement, and medical diagnosis (see Non-Patent Document 1).

  The double optical pulse generation technique described in Non-Patent Document 1 uses a nonlinear optical crystal having a 3-fold rotational symmetry and a waveform shaper. First, the amplitude and polarization state of the double light pulse of the femtosecond laser are determined by the waveform shaper. Then, each laser light pulse is converted into a terahertz light pulse by a nonlinear optical crystal. Thereby, it is said that circularly polarized double terahertz light pulses whose rotational directions are different or the same are obtained.

M. Sato, et al., "Terahertz polarization pulse shaping with arbitrary fieldcontrol," Nature Photonics, Vol. 7, p.724 (2013).

  The double optical pulse generation technique described in Non-Patent Document 1 requires the use of a nonlinear optical crystal having a three-fold rotational symmetry and a waveform shaper. Such nonlinear optical crystals are limited. Further, the waveform shaper has a complicated apparatus configuration, is expensive, and requires an electronic control system.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide an apparatus and method that can easily generate a double light pulse with a simple configuration.

  The double optical pulse generation device of the present invention (1) converts the input optical pulse into linearly polarized first optical pulse and second optical pulse whose polarization directions are orthogonal to each other, and the first optical pulse and the second optical pulse. A polarization separation unit that outputs the first and second light pulses output from the polarization separation unit, and inputs the first and second light pulses respectively. A λ / 4 plate that outputs elliptically polarized light.

  In the double light pulse generation device of the present invention, it is preferable that the time interval between the first light pulse and the second light pulse output from the polarization separation unit is variable. It is preferable that the polarization separation unit is rotatable about an axis parallel to the input direction of the optical pulse to the polarization separation unit. Further, it is preferable that the λ / 4 plate is rotatable around an axis parallel to the input direction of the light pulse to the λ / 4 plate.

  The double light pulse generation device of the present invention is provided on the optical path between the polarization separation unit and the λ / 4 plate, and inputs the first light pulse and the second light pulse output from the polarization separation unit. It is preferable to further include a polarizer that outputs linearly polarized components of specific directions of the first light pulse and the second light pulse to the λ / 4 plate. In this case, it is preferable that the polarizer is rotatable around an axis parallel to the input direction of the light pulse to the polarizer.

  The double optical pulse generator of the present invention receives the first optical pulse and the second optical pulse output from the λ / 4 plate, converts the rotational direction of these elliptically polarized light, and converts the first optical pulse and the second optical pulse. It is preferable to further include a λ / 2 plate that outputs a pulse. In this case, it is preferable that the λ / 2 plate is rotatable about an axis parallel to the input direction of the light pulse to the λ / 2 plate.

  In the double light pulse generation method of the present invention, the input light pulse is converted into linearly-polarized first light pulse and second light pulse whose polarization directions are orthogonal to each other by the polarization separation unit. Optical pulses are temporally separated from each other and output, and the first optical pulse and the second optical pulse output from the polarization separation unit are output as elliptically polarized light by the λ / 4 plate.

  In the double light pulse generation method of the present invention, it is preferable that the time interval between the first light pulse and the second light pulse output from the polarization separation unit is variable. The polarization separation unit is rotatable about an axis parallel to the input direction of the light pulse to the polarization separation unit, and the first and second light pulses in the polarization state corresponding to the rotation direction of the polarization separation unit are λ / It is preferable to output from four plates. The first optical pulse and the second optical pulse in the polarization state according to the rotation direction of the λ / 4 plate, the λ / 4 plate being rotatable about an axis parallel to the input direction of the optical pulse to the λ / 4 plate Is output from the λ / 4 plate.

  In the double light pulse generation method of the present invention, each of the first light pulse and the second light pulse output from the polarization separation unit by the polarizer provided on the optical path between the polarization separation unit and the λ / 4 plate. It is preferable to output a linearly polarized light component having a specific orientation to the λ / 4 plate. In this case, the polarizer is rotatable around an axis parallel to the input direction of the light pulse to the polarizer, and the first light pulse and the second light pulse in the polarization state corresponding to the rotation direction of the polarizer are λ / It is preferable to output from four plates.

  In the double light pulse generation method of the present invention, the rotation direction of the elliptically polarized light of each of the first light pulse and the second light pulse output from the λ / 4 plate by the λ / 2 plate provided at the subsequent stage of the λ / 4 plate. It is preferable to convert and output. In this case, the λ / 2 plate is rotatable about an axis parallel to the input direction of the optical pulse to the λ / 2 plate, and the first optical pulse in the polarization state corresponding to the rotation direction of the λ / 2 plate and the first optical pulse It is preferable to output two light pulses from the λ / 2 plate.

  In the present invention, “light” refers to an electromagnetic wave that can propagate as a beam, and includes an electromagnetic wave in a band from ultraviolet light to terahertz light. “Circularly polarized light” is treated as “elliptically polarized light” having an ellipticity of 1.

  According to the present invention, it is possible to easily generate double light pulses of various polarization states with a simple configuration.

It is a figure which shows the structure of the double optical pulse generation apparatus 1 of 1st Embodiment. 2 is a cross-sectional view of a λ / 4 plate 20. FIG. FIG. 4 is a diagram showing temporal changes in the photoelectric field of optical pulses P3a and P3b output from the λ / 4 plate 20 when the azimuth angle of the λ / 4 plate 20 is 0 °. FIG. 6 is a diagram showing temporal changes in the photoelectric fields of optical pulses P3a and P3b output from the λ / 4 plate 20 when the azimuth angle of the λ / 4 plate 20 is 90 °. It is a figure which shows the structure of the double optical pulse production | generation apparatus 2 of 2nd Embodiment. FIG. 6 shows temporal changes in the photoelectric fields of the light pulses P3a and P3b output from the λ / 4 plate 20 when the azimuth angle of the polarizer 30 is 0 ° and the azimuth angle of the λ / 4 plate 20 is 45 °. FIG. When the azimuth angle of the polarizer 30 is 0 ° and the azimuth angle of the λ / 4 plate 20 is −45 °, the temporal change of the photoelectric field of the light pulses P3a and P3b output from the λ / 4 plate 20 is shown. FIG. When the azimuth angle of the polarizer 30 is 90 ° and the azimuth angle of the λ / 4 plate 20 is 45 °, the temporal change of the photoelectric field of the light pulses P3a and P3b output from the λ / 4 plate 20 is shown. FIG. When the azimuth angle of the polarizer 30 is 90 ° and the azimuth angle of the λ / 4 plate 20 is −45 °, the temporal change of the photoelectric field of the light pulses P3a and P3b output from the λ / 4 plate 20 is shown. FIG. It is a figure which shows the structure of the double optical pulse production | generation apparatus 3 of 3rd Embodiment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. The present invention is not limited to these exemplifications, but is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

(First embodiment)
FIG. 1 is a diagram illustrating a configuration of a double optical pulse generation device 1 according to the first embodiment. The double light pulse generation device 1 includes a polarization separation unit 10 and a λ / 4 plate 20.

  The polarization separator 10 converts the input optical pulse P1 into linearly polarized first optical pulse P2a and second optical pulse P2b whose polarization directions are orthogonal to each other, and converts the first optical pulse P2a and the second optical pulse P2b to each other. Separate and output in time. The polarization state of the light pulse P1 input to the polarization separator 10 may be arbitrary. It is preferable that the time interval between the first optical pulse P2a and the second optical pulse P2b output from the polarization separation unit 10 is variable. Further, it is preferable that the polarization separation unit 10 is rotatable around an axis parallel to the input direction of the light pulse P1 to the polarization separation unit 10.

The polarization separation unit 10 can be configured to include a birefringent material (for example, crystal, sapphire, BBO (BaB ₂ O ₄ ) crystal, etc.). The thickness and refractive index of the birefringent material are set according to the time interval between the first light pulse P2a and the second light pulse P2b to be output. For example, increasing the material thickness increases the time interval.

  In addition, the polarization separation unit 10 may include a photoelastic element in which a refractive index is set according to application of stress. In this case, the time interval between the first light pulse P2a and the second light pulse P2b can be set according to the magnitude of the stress.

  In addition, the polarization separation unit 10 may separate the input light pulse by using the first polarization beam splitter to form two light pulses, and synthesize these two light pulses by the second polarization beam splitter. In this case, the first optical pulse P2a output from the second polarizing beam splitter is adjusted by adjusting the difference in optical path length between the two optical pulses from the first polarizing beam splitter to the second polarizing beam splitter. A time interval between the second optical pulse P2b can be set.

  The polarization separation unit 10 preferably outputs the first light pulse P2a and the second light pulse P2b in parallel with each other, and more preferably outputs them coaxially. Even if the output directions of the first light pulse P2a and the second light pulse P2b are parallel to each other but not coaxial, by providing a lens in the subsequent stage of the λ / 4 plate 20, the object of the light pulse irradiation can be obtained. Two light pulses can be irradiated to the common region.

  The λ / 4 plate 20 receives the linearly polarized first optical pulse P2a and the second optical pulse P2b output from the polarization separation unit 10 in terms of time, and receives the elliptically polarized first optical pulse P3a and The second light pulse P3b is output. The λ / 4 plate 20 is preferably rotatable about an axis parallel to the input direction of the light pulses P2a and P2b.

  It is preferable that the λ / 4 plate 20 has a small wavelength dependency. Preferably, the λ / 4 plate 20 is a prism type wave plate, a crystal stack type wave plate, a metal plate stack type wave plate, or the like. In particular, the prism type wave plate can give a set phase change to light of all wavelengths in a wavelength range where the refractive index of the material can be regarded as constant.

  FIG. 2 is a sectional view of the λ / 4 plate 20. The λ / 4 plate 20 shown in the figure is a prism type wave plate. The λ / 4 plate 20 is made of a material that is transparent in the wavelength region of the light pulse P1 and has a high refractive index. When the light pulse P1 is terahertz light, the λ / 4 plate 20 is preferably made of silicon having a refractive index of 3.41 in the wavelength range of terahertz light. The λ / 4 plate 20 has an incident surface 21, an output surface 22, total reflection surfaces 23a to 23d, and holding surfaces 24a to 24f.

  The entrance surface 21 and the exit surface 22 are parallel to each other. The linearly polarized light pulses P2a and P2b are incident on the incident surface 21 perpendicularly. The light pulse incident on the incident surface 21 is sequentially totally reflected on each of the four total reflection surfaces 23a to 23d. Then, elliptically polarized light pulses P3a and P3b are emitted vertically from the emission surface 22. The light pulses P2a and P2b incident on the incident surface 21 and the light pulses P3a and P3b emitted from the emission surface 22 can be coaxial. Therefore, even if the λ / 4 plate 20 is rotated around the axis, the positions of the light pulses P3a and P3b emitted from the emission surface 22 do not change. The holding surfaces 24a to 24f are surfaces that do not contribute to any of the incidence, total reflection, and emission of the light pulse, and are surfaces on which a support member for the arrangement and orientation setting of the λ / 4 plate 20 is brought into contact.

  A phase difference is generated between the p-polarized component and the s-polarized component during total reflection of the light pulse on each of the total reflection surfaces 23a to 23d. The phase difference depends on the incident angles θ1 to θ4 of the light pulses on the total reflection surfaces 23a to 23d and the refractive index ratio between the material of the λ / 4 plate 20 and the surrounding medium (generally air). Therefore, by appropriately setting these, the total sum of the phase differences between the p-polarized component and the s-polarized component generated during the total reflection of the optical pulse on each of the total reflection surfaces 23a to 23d is set to π / 2. Thus, a λ / 4 plate can be formed. Similarly, a λ / 2 plate and a 3λ / 4 plate can be configured.

  Next, the operation of the double light pulse generation device 1 of the present embodiment will be described, and the double light pulse generation method of the present embodiment will be described. Assume that the input optical pulse P1 is linearly polarized light. At this time, the direction of the linearly polarized light of the light pulses P2a and P2b output from the polarization separation unit 10 corresponds to the direction of the optical axis of the polarization separation unit 10. The amplitude ratio of the light pulses P2a and P2b output from the polarization separation unit 10 is in accordance with the azimuth of the optical axis of the polarization separation unit 10 with respect to the direction of linear polarization of the light pulse P1. The rotation directions of the elliptically polarized light of the light pulses P3a and P3b output from the λ / 4 plate 20 are opposite to each other. The rotation direction, the rotation start position, the ellipticity, and the elliptical direction of the elliptically polarized light of the light pulses P3a and P3b output from the λ / 4 plate 20 are high speeds of the λ / 4 plate 20 with respect to the linearly polarized light direction of the light pulses P2a and P2b. It depends on the direction of the axis.

  Therefore, the amplitude ratio, the rotation direction, the rotation start position, the ellipticity, and the ellipticity of the optical pulses P3a and P3b output from the double optical pulse generation device 1 are set by setting the orientation of the polarization separator 10 and the orientation of the λ / 4 plate 20. The direction can be controlled. Note that the rotation direction is the direction in which the orientation of the photoelectric field vector rotates. The rotation start position is the direction of the photoelectric field vector at the rising edge of the optical pulse. The ellipse orientation is the orientation of the major axis of the ellipse.

  3 and 4 are diagrams showing temporal changes in the photoelectric fields of the light pulses P3a and P3b output from the λ / 4 plate 20 when the azimuth angle of the λ / 4 plate 20 is set to various values. In any of the figures, the azimuth angle of the optical axis of the polarization separating unit 10 is set to 45 ° with reference to the azimuth of the linearly polarized light of the light pulse P1. FIG. 3 shows a case where the azimuth angle of the λ / 4 plate 20 is 0 °. FIG. 4 shows a case where the azimuth angle of the λ / 4 plate 20 is 90 °. These drawings show the amplitude and direction of the photoelectric field of the optical pulses P3a and P3b output from the λ / 4 plate 20 at time t, with the two axes orthogonal to the traveling direction of the optical pulse as the x-axis and the y-axis. As shown in these drawings, the rotation direction and rotation start position of the circularly polarized light of the optical pulses P3a and P3b output from the λ / 4 plate 20 can be changed according to the change in the azimuth angle of the λ / 4 plate 20. it can.

  As described above, in the present embodiment, the two optical pulses P3a and P3b that are temporally separated from the λ / 4 plate 20 and output by adjusting the azimuth angles of the polarization separation unit 10 and the λ / 4 plate 20 are output. Various polarization states can be set. In this embodiment, it is only necessary to rotate the polarization separation unit 10 and the λ / 4 plate 20 in order to control the polarization states of the light pulses P3a and P3b. Therefore, double light having various polarization states can be easily obtained with a simple configuration. Pulses can be generated.

  A 3λ / 4 plate may be used in place of the λ / 4 plate 20. Also in this case, substantially equivalent effects can be obtained.

(Second Embodiment)
FIG. 5 is a diagram illustrating a configuration of the double light pulse generation device 2 according to the second embodiment. The double light pulse generation device 2 includes a polarization separation unit 10, a λ / 4 plate 20, and a polarizer 30. Compared with the configuration of the double optical pulse generation device 1 of the first embodiment shown in FIG. 1, the double optical pulse generation device 2 of the second embodiment shown in FIG. 5 is different in that it further includes a polarizer 30. To do.

  The polarizer 30 is provided on the optical path between the polarization separator 10 and the λ / 4 plate 20. The polarizer 30 receives the optical pulses P2a and P2b output from the polarization separation unit 10 and outputs linearly polarized components of specific directions of these optical pulses P2a and P2b to the λ / 4 plate 20. The polarizer 30 is preferably rotatable about an axis parallel to the input direction of the light pulse.

  In the second embodiment, the two light pulses input to the λ / 4 plate 20 are linearly polarized light in the same direction. Therefore, the rotation directions of the elliptically polarized light of the two optical pulses P3a and P3b output from the double optical pulse generation device 1 of the first embodiment are opposite to each other, whereas the double optical pulse of the second embodiment is The rotation directions of the elliptically polarized light of the two light pulses P3a and P3b output from the generation device 2 are the same.

  In the present embodiment, two optical pulses P3a and P3b that are temporally separated and output from the λ / 4 plate 20 by adjusting the azimuth angles of the polarization separation unit 10, the λ / 4 plate 20, and the polarizer 30 are output. Various polarization states can be set. In this embodiment, in order to control the polarization states of the light pulses P3a and P3b, it is only necessary to rotate the polarization separation unit 10, the λ / 4 plate 20, and the polarizer 30, so that various polarizations can be easily made with a simple configuration. A double light pulse of state can be generated. Further, by making the polarizer 30 provided on the optical path between the polarization separation unit 10 and the λ / 4 plate 20 detachable, the two lights that are separated from the λ / 4 plate 20 in time and output. The rotation directions of the elliptically polarized light of the pulses P3a and P3b can be reversed or the same.

  FIGS. 6 to 9 show the temporal relationship of the photoelectric fields of the light pulses P3a and P3b output from the λ / 4 plate 20 when the azimuth angle of the polarizer 30 and the azimuth angle of the λ / 4 plate 20 are set to respective values. It is a figure which shows a change. In any of the figures, the azimuth angle of the optical axis of the polarization separating unit 10 is set to 45 ° with reference to the azimuth of the linearly polarized light of the light pulse P1. FIG. 6 shows a case where the azimuth angle of the polarizer 30 is 0 ° and the azimuth angle of the λ / 4 plate 20 is 45 °. FIG. 7 shows a case where the azimuth angle of the polarizer 30 is 0 ° and the azimuth angle of the λ / 4 plate 20 is −45 °. FIG. 8 shows a case where the azimuth angle of the polarizer 30 is 90 ° and the azimuth angle of the λ / 4 plate 20 is 45 °. FIG. 9 shows a case where the azimuth angle of the polarizer 30 is 90 ° and the azimuth angle of the λ / 4 plate 20 is −45 °. These drawings show the amplitude and direction of the photoelectric field of the optical pulses P3a and P3b output from the λ / 4 plate 20 at time t, with the two axes orthogonal to the traveling direction of the optical pulse as the x-axis and the y-axis. As shown in these drawings, the rotation direction and the rotation start position of the circularly polarized light of the optical pulses P3a and P3b output from the λ / 4 plate 20 according to changes in the azimuth angles of the λ / 4 plate 20 and the polarizer 30, respectively. Can be changed.

(Third embodiment)
FIG. 10 is a diagram illustrating a configuration of the double light pulse generation device 3 according to the third embodiment. The double light pulse generation device 3 includes a polarization separation unit 10, a λ / 4 plate 20, and a λ / 2 plate 40. Compared with the configuration of the double optical pulse generator 1 of the first embodiment shown in FIG. 1, the double optical pulse generator 3 of the third embodiment shown in FIG. 10 further includes a λ / 2 plate 40. Is different.

  The λ / 2 plate 40 is provided at the subsequent stage of the λ / 4 plate 20. The λ / 2 plate 40 receives the elliptically polarized first light pulse P3a and the second light pulse P3b output from the λ / 4 plate 20, converts the rotation direction of these elliptically polarized light, and converts the first light pulse P4a. And the second optical pulse P4b is output. The λ / 2 plate 40 is preferably rotatable about an axis parallel to the input direction of the light pulses P3a and P3b. According to the setting of the azimuth angle of the λ / 2 plate 40, the rotation start position of the elliptically polarized light of the two optical pulses P4a and P4b output from the λ / 2 plate 40 can be changed.

  In the configuration of the double optical pulse generation device 2 of the second embodiment, the λ / 2 plate 40 may be provided after the λ / 4 plate 20.

  DESCRIPTION OF SYMBOLS 1-3 ... Double light pulse production | generation apparatus, 10 ... Polarization separation part, 20 ... (lambda) / 4 board, 30 ... Polarizer, 40 ... (lambda) / 2 board.

Claims (16)

A polarization separation unit that converts the input optical pulse into linearly polarized first optical pulse and second optical pulse whose polarization directions are orthogonal to each other, and temporally separates and outputs the first optical pulse and the second optical pulse. When,
A λ / 4 plate that inputs the first light pulse and the second light pulse output from the polarization separation unit and outputs each of the first light pulse and the second light pulse as elliptically polarized light,
A double optical pulse generator.   The double optical pulse generation device according to claim 1, wherein a time interval between the first optical pulse and the second optical pulse output from the polarization separation unit is variable.   3. The double light pulse generation device according to claim 1, wherein the polarization separation unit is rotatable about an axis parallel to an input direction of the light pulse to the polarization separation unit.   4. The double optical pulse generation device according to claim 1, wherein the λ / 4 plate is rotatable about an axis parallel to an input direction of the optical pulse to the λ / 4 plate. 5.   A first light pulse and a second light pulse, which are provided on an optical path between the polarization separation unit and the λ / 4 plate and output from the polarization separation unit, are input, and the first light pulse and the second light pulse are input. 5. The double light pulse generation device according to claim 1, further comprising a polarizer that outputs a linearly polarized light component in a specific direction of each light pulse to the λ / 4 plate.   6. The double optical pulse generation device according to claim 5, wherein the polarizer is rotatable around an axis parallel to an input direction of the optical pulse to the polarizer.   A λ / 2 plate that inputs the first optical pulse and the second optical pulse output from the λ / 4 plate, converts the rotational direction of the elliptically polarized light, and outputs the first optical pulse and the second optical pulse. The double light pulse generation device according to any one of claims 1 to 6, further comprising:   The double optical pulse generation device according to claim 7, wherein the λ / 2 plate is rotatable about an axis parallel to an input direction of the optical pulse to the λ / 2 plate. The polarization separation unit converts the input optical pulse into linearly polarized first optical pulse and second optical pulse whose polarization directions are orthogonal to each other, and temporally separates the first optical pulse and the second optical pulse from each other. Output,
With the λ / 4 plate, the first light pulse and the second light pulse output from the polarization separator are output as elliptically polarized light,
Double light pulse generation method.   The method of generating a double light pulse according to claim 9, wherein a time interval between the first light pulse and the second light pulse output from the polarization separation unit is variable. The polarization separation unit is rotatable around an axis parallel to the input direction of the light pulse to the polarization separation unit,
Outputting a first light pulse and a second light pulse in a polarization state corresponding to the rotation direction of the polarization separation unit from the λ / 4 plate;
The double light pulse generation method according to claim 9 or 10. The λ / 4 plate is rotatable around an axis parallel to the input direction of the light pulse to the λ / 4 plate,
Outputting a first light pulse and a second light pulse in a polarization state corresponding to the rotation direction of the λ / 4 plate from the λ / 4 plate;
The double light pulse generation method according to any one of claims 9 to 11.   A linearly polarized light component in a specific direction of each of the first light pulse and the second light pulse output from the polarization separation unit is obtained by a polarizer provided on an optical path between the polarization separation unit and the λ / 4 plate. The double light pulse generation method according to claim 9, wherein the double light pulse is output to the λ / 4 plate. The polarizer is rotatable around an axis parallel to the input direction of the light pulse to the polarizer,
Outputting a first light pulse and a second light pulse in a polarization state corresponding to the rotation direction of the polarizer from the λ / 4 plate;
The double light pulse generation method according to claim 13.   The rotation direction of the elliptically polarized light of each of the first optical pulse and the second optical pulse output from the λ / 4 plate is converted and output by a λ / 2 plate provided at a subsequent stage of the λ / 4 plate. Item 15. The double light pulse generation method according to any one of Items 9 to 14. The λ / 2 plate is rotatable about an axis parallel to the input direction of the light pulse to the λ / 2 plate,
Outputting a first light pulse and a second light pulse in a polarization state corresponding to the rotation direction of the λ / 2 plate from the λ / 2 plate;
The double light pulse generation method according to claim 15.

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