JP2004212071A - Apparatus and method for measuring tertiary nonlinear optical characteristic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus and a method for measuring a tertiary nonlinear reception rate spectrum by a single irradiation with pulses. <P>SOLUTION: The apparatus for measuring a tertiary nonlinear reception rate spectrum comprises: a positive chirp irradiation means (3) for irradiating a sample (6) with positive chirp pulses (L3); a negative chirp irradiation means (4) for irradiating the sample (6) with negative chirp pulses (L4); and a light reception means (5) for receiving diffraction light (L5) from the inside of the sample (6). The wavelength of the positive chirp pulse (L3) monotonously decreases from the start to the end of pulses, the wavelength of the negative chirp pulse (L4) monotonously increases, the wavelength bands of the positive and negative chirp pulses (L3, L4) are overlapped and superposed in the sample (6) that enters at a specific angle, and the light reception means (5) is arranged in a vector direction obtained by subtracting the wavenumber vector of the negative chirp pulses (L4) from the wavenumber vector being two times larger than the wavenumber vector of the positive chirp pulse (L3). <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an apparatus and a method for measuring a third-order nonlinear optical characteristic that characterizes a third-order nonlinear optical process.
[0002]
[Prior art]
The third-order nonlinear optical process is a third-harmonic generation (THG) that generates light having three times the frequency of incident light, and light intensity-dependent refraction in which the refractive index of a material changes according to the intensity of incident light. Rate is a process that causes nonlinear effects such as two-photon absorption (TPA) that simultaneously absorbs two photons. In particular, the light-intensity-dependent refractive index has been studied for the next practical use of Dense Wavelength Division Multiplexing (DWDM), which is a communication system for multiplexing a plurality of lights having different wavelengths into an optical fiber. This is an important phenomenon that may be applied to an ultra-high-speed optical switch required for time-division multiplexing (TDM) optical communication. In addition, two-photon absorption has been increasingly applied to light restriction that protects a photodetector from high-density laser light pulses, and to optical microfabrication, which is a method for manufacturing photonic crystals and optical integrated circuits.
[0003]
The third-order nonlinear optical process is characterized by a ^third- order nonlinear susceptibility χ ⁽³⁾ . The third-order nonlinear susceptibility χ ⁽³⁾ is a complex tensor quantity and depends on the frequency and polarization direction of the light involved, and is specifically expressed by χ ⁽³⁾ (−ω; ω, ω, −ω). It is. Here, the description on the right side of the symbol “;” indicates the angular frequency of the three incident photons, and the description on the left side of the symbol “;” indicates the angular frequency of the output photon. Therefore, for various applications as described above, for various materials such as semiconductors, ultrafine metal particles, and π-conjugated organic compounds, measurement of the third-order nonlinear susceptibility χ ⁽³⁾ (−ω; ω, ω, −ω) and its measurement Elucidation of the relationship between the structure of a substance (especially the electronic structure) and the third-order nonlinear optical process has been studied based on the measurement results.
[0004]
The third-order nonlinear susceptibility χ ⁽³⁾ (−ω; ω, ω, −ω) depends on the frequency as well as the refractive index, which is a linear susceptibility. It is very important to elucidate the relationship with third-order nonlinear optical processes. For example, the perturbation theory of quantum mechanics allows the nonlinear susceptibility based on electronic polarization to be approximated by the product of the energy difference between the electronic states of the material and the transition moment. It becomes possible to know the electronic structure.
[0005]
There are various methods for measuring the third-order nonlinear susceptibility χ ⁽³⁾ (−ω; ω, ω, −ω), including degenerate four wave mixing (DFWM), Z scan, and optical Kerr effect ( Methods such as Optical Kerr Effect (OKE) and optical interference measurement are known, and are disclosed, for example, in Patent Documents 1 to 3 below. In each of these cases, the measurement of the ^third- order nonlinear susceptibility に 対 す る⁽³⁾ for light of a predetermined wavelength (frequency) is repeated while changing the wavelength of light, so that the third-order nonlinear susceptibility χ ⁽ This is a method to obtain the spectrum of ³⁾ .
[0006]
Non-Patent Document 1 below discloses that a third-order nonlinear susceptibility χ ⁽³⁾ in a frequency band of an optical pulse is obtained by using a femtosecond optical pulse and decomposing a frequency component included in the optical pulse by a prism. ⁾ Is disclosed.
[0007]
[Patent Document 1]
JP-A-5-107569
[Patent Document 2]
JP-A-5-149825
[Patent Document 3]
JP-A-10-115573
[Non-patent document 1]
Guan S. Guang S. He, et al., “New technique for degenerate two-photon absorption spectral measurements using femtosecond continuum generation”, [online], June 1, 2002 (1 July 2002), OPTICS EXPRESS, Vol. 10, No. 13, p. 566-574, Optical Society of America, [2002 November 19 search], Internet <URL: http://www.opticsexpress.org/issue.cfm? issue_id = 145>
[0011]
[Problems to be solved by the invention]
The conventional measurement method described above is a measurement at a predetermined wavelength, and in order to obtain the spectrum data of the ^third- order nonlinear susceptibility χ ⁽³⁾ , it is necessary to repeat the measurement while changing the wavelength, which takes a very long time. It was hanging. If the number of measurements is large, it may take several days to several weeks. For this reason, there have not been many reports of spectrum measurement so far, and the reported spectrum data is spectrum data having at most about 10 to 30 measurement points, and has low accuracy and reproducibility. And it was difficult.
[0012]
In the above Non-Patent Document 1, although it is possible to measure the frequency spectrum of the ^third- order nonlinear susceptibility χ ^{(3) at} a time, it is measured because the transmitted light intensity of a single light beam is measured. The third-order nonlinear susceptibility χ ⁽³⁾ relates to absorption and does not include refraction effects. That is, with the measurement method according to Non-Patent Document 1, the spectrum of the ^third- order nonlinear susceptibility χ ^{(3) including} the effect of the light intensity-dependent refractive index cannot be measured at once.
[0013]
In order to solve the above problems, the present invention provides a third-order nonlinear susceptibility だ⁽³⁾ spectrum including an effect of a light-intensity-dependent refractive index by a single irradiation of a sample to be measured with a chirped light pulse. It is an object of the present invention to provide a measuring device and a measuring method of a third-order nonlinear optical characteristic capable of measuring the optical characteristics.
[0014]
[Means for Solving the Problems]
The object of the present invention is achieved by the following means.
[0015]
That is, the measuring device (1) of the third-order nonlinear optical characteristic according to the present invention includes: a positive chirp irradiating unit that irradiates a sample to be measured with a positive chirp pulse; a negative chirp irradiating unit that irradiates a negative chirp pulse to the sample; Light receiving means for receiving diffracted light from diffracted photons induced in the sample through the third-order nonlinear optical characteristics of the sample by the positive chirp pulse and the negative chirp pulse, wherein the wavelength in the positive chirp pulse is The wavelength in the negative chirped pulse monotonically decreases from the beginning to the end of the pulse, and the wavelength in the negative chirped pulse monotonically increases from the beginning to the end of the pulse, at least a part of the wavelength band of the positive chirped pulse, and the negative chirped pulse. At least a part of the wavelength band overlaps, the incident direction of the positive chirp pulse and the negative chirp pulse forms a predetermined angle, At the same time in the sample, a part of the positive chirp pulse and a part of the negative chirp pulse are superimposed, and the light receiving means uses the sample as a position reference and is twice the wave vector of the positive chirp pulse. By subtracting the wave vector of the positive chirp pulse from the direction of the first vector obtained by subtracting the wave vector of the negative chirp pulse from the wave vector, or the wave vector of twice the wave vector of the negative chirp pulse It is characterized by being arranged in the direction of the obtained second vector.
[0016]
The measuring device (2) for a third-order nonlinear optical characteristic according to the present invention is the measuring device (1) for the third-order nonlinear optical characteristic described above, wherein the wavelength in the positive chirped pulse linearly decreases from the beginning to the end of the pulse. The wavelength in the negative chirped pulse linearly increases from the beginning to the end of the pulse.
[0017]
The third-order nonlinear optical characteristic measuring device (3) according to the present invention is the above-mentioned third-order nonlinear optical characteristic measuring device (1) or (2), wherein the wavelength band of the positive chirp pulse and the wavelength of the negative chirp pulse are different from each other. It is characterized in that the band is the same.
[0018]
The measuring device (4) for the third-order nonlinear optical characteristic according to the present invention is the same as the measuring device (1) to (3) for the third-order nonlinear optical characteristic, wherein the pulse width of the positive chirp pulse and the negative chirp are used. The pulse width of the pulse is the same.
[0019]
Further, in the third-order nonlinear optical characteristic measuring device (5) according to the present invention, in any one of the third-order nonlinear optical characteristic measuring devices (1) to (4), the light receiving means is a two-dimensional CCD. The output signal of the two-dimensional CCD is added in a direction perpendicular to the incident vector of the positive chirp pulse and the incident vector of the negative chirp pulse.
[0020]
The method (1) for measuring a third-order nonlinear optical characteristic according to the present invention includes a step of generating a positive chirp pulse for generating a positive chirp pulse whose wavelength monotonously decreases from an ultrashort pulse having a constant wavelength from the beginning to the end of the pulse. A positive chirp pulse irradiating the sample to be measured with the positive chirp pulse, and a negative chirp pulse generating step of generating a negative chirp pulse whose wavelength monotonically increases from the beginning to the end of the pulse from the ultrashort pulse. Negative chirp pulse irradiation for irradiating the negative chirp pulse in an incident direction forming a predetermined angle with the incident direction of the positive chirp pulse to the sample so that the sample reaches the sample at the same time as the positive chirp pulse. And a wave vector that is twice as large as the wave vector of the positive chirped pulse, using the sample as a position reference. The direction of the first vector obtained by subtracting the wave vector of the negative chirp pulse from the above, or the wave vector of the positive chirp pulse is subtracted from the wave vector of twice the wave vector of the negative chirp pulse. Light-receiving means arranged in the direction of the second vector, receiving light diffracted by the positive chirp pulse and the negative chirp pulse from within the sample, including at least a wavelength band of the positive chirp pulse. A part of the wavelength band overlaps with at least a part of the wavelength band of the negative chirp pulse.
[0021]
The method (2) for measuring the third-order nonlinear optical characteristic according to the present invention is the method for measuring the third-order nonlinear optical characteristic (1), wherein the wavelength in the positive chirped pulse decreases linearly from the beginning to the end of the pulse. The wavelength in the negative chirped pulse linearly increases from the beginning to the end of the pulse.
[0022]
The method (3) for measuring the third-order nonlinear optical characteristic according to the present invention is the method for measuring the third-order nonlinear optical characteristic (1) or (2), wherein the wavelength band of the positive chirped pulse and the wavelength of the negative chirped pulse are different. It is characterized in that the band is the same.
[0023]
The third-order nonlinear optical characteristic measuring method (4) according to the present invention is the method according to any of the third-order nonlinear optical characteristic measuring methods (1) to (3), wherein the pulse width of the positive chirp pulse and the negative chirp are The pulse width of the pulse is the same.
[0024]
Also, in the method (5) for measuring the third-order nonlinear optical characteristic according to the present invention, in any one of the methods (1) to (4) for measuring the third-order nonlinear optical characteristic, the light receiving means is a two-dimensional CCD. It is characterized by including an adding step of adding an output signal of the two-dimensional CCD in a direction perpendicular to the incident vector of the positive chirp pulse and the incident vector of the negative chirp pulse.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a block diagram showing a schematic configuration of an apparatus for measuring third-order nonlinear optical characteristics according to an embodiment of the present invention. The measuring device of the third-order nonlinear optical characteristic according to the present embodiment includes an optical pulse generator 1, a splitter 2, a positive chirp generator 3, a negative chirp generator 4, and a detector 5.
[0026]
The optical pulse generation unit 1 generates a wide-band ultrashort pulse whose phase is controlled for each wavelength at fixed time intervals. The light pulse generation unit 1 may be a laser device itself that generates an ultrashort pulse of 5 femtoseconds to 100 picoseconds such as a titanium sapphire laser, but in order to expand its wavelength band without losing its short pulse property. The laser output light is passed through a transparent medium such as glass, water, heavy water, or an organic solvent, and a white light pulse containing a wide range of wavelength components is generated by self-phase modulation to output a wavelength range. It is desirable to provide an enlarging means inside the optical pulse generation unit 1. The optical path of the white light pulse output from the light pulse generation unit 1 is split by the splitter 2 in two directions (L1, L2). For the splitter 2, a half mirror, a prism, or the like can be used.
[0027]
The separated optical pulse L1 in the optical path in one direction becomes a positive chirp pulse L3 that is positively chirped by the positive chirp generation unit 3 as described later. In addition, the light pulse L2 in another light path becomes a negative chirp pulse L4 that is negatively chirped by the negative chirp generator 4 as described later. The positive and negative chirp pulses L3 and L4 are adjusted in timing, are simultaneously irradiated on the sample 6 to be measured, interfere with each other in the sample 6 to be measured, and have a diffracted photon having an intensity corresponding to the third-order nonlinear optical characteristic of the sample 6 to be measured. Is temporarily generated in the sample to be measured, and the diffracted photons emit diffracted lights L5 and L6 in predetermined directions according to the incident directions of the two pulses L3 and L4.
[0028]
The diffracted lights L5 and L6 are white light, that is, light containing a wide wavelength component, and the diffracted light L5 in a predetermined direction is detected by the detection unit 5 having a two-dimensional CCD. Here, the simultaneous arrival of the positive and negative chirped pulses L3 and L4 to the sample 6 is achieved by an optical system including a mirror, a prism, and the like for adjusting the length of the optical path of the positive and negative chirped pulses L3 and L4. This is possible by arranging a system (not shown) on the optical path (L1 to L4) after being separated by the splitter 2.
[0029]
The optical pulse generation unit 1 generates a single-wavelength laser beam of a femtosecond pulse having a pulse width of about 10 to 500 fs (femtosecond), for example, as a broadband ultrashort pulse. The time interval for generating the pulse is set to be sufficiently longer than the pulse width, for example, 1 ms (millisecond) so as not to cause interference between adjacently generated pulses. If the wavelength of the laser light of the femtosecond pulse of 10 to 500 fs is from several nm (nanometers) to several tens of nanometers, the laser light is self-phased when the optical pulse generation unit 1 is provided with a wavelength range expanding unit. The modulation results in a white pulse having a wavelength band of several hundred nm. That is, at the center of the pulsed light, the refractive index changes rapidly with time due to the optical Kerr effect, and the pulse shape of the incident laser light changes sharply to generate a frequency component different from the original wavelength. . As a result, a white pulse having a frequency spread by several hundred nm around the wavelength of the original laser light is obtained.
[0030]
The positive chirp generating unit 3 and the negative chirp generating unit 4 are an optical system including a diffraction grating pair, a prism pair, and the like. The positive chirp generating unit 3 and the negative chirp generating unit 4 change the waveforms of the input light pulses L1 and L2, respectively. A chirp pulse L4 is generated. The positive chirp pulse is an optical pulse whose wavelength is shortened inside the pulse as shown by a solid line in FIG. While the wavelength λ of the incident laser light without chirp indicated by the broken line is constant within the pulse, the positive chirped pulse has a longer leading wavelength λ ′ and a shorter leading wavelength. Conversely, the negative chirp pulse L4 is a pulse obtained by inverting the time axis of the positive chirp pulse L3, that is, a light pulse whose wavelength becomes longer inside the pulse. A component having a long wavelength (red) is located at the end of the pulse.
[0031]
For example, the optical system shown in FIG. 3 can be used for the positive chirp generation unit 3 and the negative chirp generation unit 4. FIG. 3 is constituted by a combination of a plurality of triangular prisms. In FIG. 3, by changing the number of prisms used and their arrangement, a positive or negative chirped pulse in the required wavelength band is generated.
[0032]
Next, the incidence and diffraction of the positive and negative chirped pulses L3 and L4 to the sample will be described with reference to FIG. FIG. 4 is a cross-sectional view schematically showing a diffraction phenomenon caused by the incidence of the positive and negative chirped pulses L3 and L4 on the sample 6 to be measured in the third-order nonlinear optical characteristic measuring apparatus according to the embodiment of the present invention.
[0033]
The positive and negative chirped pulses L3 and L4 are incident on the measured sample 6 at a fixed angle θ by adjusting the timing, and are superposed in the measured sample 6. Here, particularly, a case will be described in which the positive chirp pulse L3 and the negative chirp pulse L4 are formed such that the wavelengths within the pulse change linearly as shown in FIG. That is, the wavelength of the positive chirp pulse L3 decreases linearly from λ2 to λ1 (λ2> λ1) from the head (time t1) to the end (time t2) of the pulse, and the negative chirp pulse L4 changes from the head of the pulse (time t1). ) To the end (time t2), the wavelength is formed to increase linearly from λ1 to λ2.
[0034]
The positive chirped pulse L3 and the negative chirped pulse L4 superimposed in the measured sample 6 have different wavelength portions of the respective pulses overlapping in most places in the measured sample 6, but in a specific spatial region. The same frequency of each pulse overlaps. At each point on the line segment connecting the two points A1 and A2 on the horizontal broken line shown in FIG. 4 (actually on the plane indicated by the broken line), the wavelength of the overlapping positive chirp pulse L3 is The wavelength of the negative chirp pulse L4 becomes the same. Further, the wavelength changes from the long wavelength (λ2) to the short wavelength (λ1) from the point A1 to the point A2 on the broken line in FIG.
[0035]
In this case, as is known with respect to the two-beam DFWM method, assuming that the wave vectors of two incident lights are k ₁ and k ₂ , the diffracted light has the wave vectors 2k ₁ -k ₂ and 2k ₂ -k ₁ . Occurs in the direction. Therefore, diffracted light from the point where the absolute values of the wave vectors of the two incident lights have the same value (| k ₁ | = | k ₂ |), that is, the two points A1 and A2 shown in FIG. Are diffracted in the same two directions (directions of wave vectors 2k ₁ -k ₂ and 2k ₂ -k ₁ ). Further, as described above, the distribution of the wavelength of the diffracted light is linearly (eg, from a long wavelength to a short wavelength) in a direction perpendicular to the diffraction direction in a plane including the two wave number vectors k ₁ and k _2. Change.
[0036]
The diffracted light L5 in _one of two directions (directions of the wave vectors 2k ₁ -k ₂ and 2k ₂ -k ₁ ) is separated from the sample 6 by a predetermined distance using the optical system (lens) 8. If the image is formed on the two-dimensional CCD 9 arranged in this manner, the diffracted light spatially spread for each wavelength as described above can be received corresponding to each pixel of the CCD 9. As described above, since the wavelength distribution of the diffracted light L5 linearly changes in a direction perpendicular to the diffraction direction, the diffracted light L5 incident on each pixel of the CCD 9 has two wave number vectors k ₁ and k _2. , The diffracted light L5 of the same wavelength enters. Accordingly, by adding the output signals of the pixels of the CCD 9 in the direction perpendicular to the _two wave vectors k ₁ and k ₂ , a one-dimensional spectrum of the diffracted light intensity with improved S / N can be obtained. From the one-dimensional spectrum of the diffracted light intensity, a frequency spectrum of the ^third- order nonlinear susceptibility χ ⁽³⁾ can be obtained.
[0037]
Here, diffracted light (for example, L7 and L8 shown in FIG. 4) due to superposition of light having different wavelengths is generated from a portion other than the plane where the same wavelengths overlap in the sample 6 to be measured. It is considered that the diffracted light enters the CCD 9 and becomes noise. However, since the diffracted light due to the superposition of light of different wavelengths has a different diffraction angle from the diffracted light due to the superposition of light of the same wavelength, the CCD 9 is set to receive the diffracted light due to the superposition of light of the same wavelength. 6 can be prevented from entering the CCD 9 by diffracted light due to superposition of light of different wavelengths. It is desirable that the distance between the CCD 9 and the sample 6 to be measured is determined within a range in which the output signal of the CCD 9 can be reduced. If the distance between the CCD 9 and the sample 6 to be measured cannot be sufficiently ensured, it is desirable to provide an optical system such as a slit so as to block the diffracted light resulting from the superposition of light having different wavelengths from entering the CCD 9. .
[0038]
In the above, the case where the wavelengths of the positive chirp pulse L3 and the negative chirp pulse L4 both linearly change and the positive chirp pulse L3 and the negative chirp pulse L4 are symmetrical with respect to the time axis has been described. As described above, the relationship may be such that the wavelength band of the negative chirp pulse L4 includes the wavelength band of the positive chirp pulse L3. In FIG. 6, the wavelength of the positive chirped pulse L3 changes from λ4 to λ3 (λ4> λ3) from the beginning (t = t1) to the end (t = t2) of the pulse. The wavelength of the negative chirp pulse L4 changes from λ5 to λ6 (λ5 <λ6) from the beginning (t = t1) to the end (t = t2) of the pulse, and from t3 to t4, from λ3 to λ4 (positive). (The wavelength band of the chirp pulse L3). Also in this case, the wavelength of the positive chirped pulse L3 and the wavelength of the negative chirped pulse L4 are the same in a specific plane in the sample 6 to be measured, and the diffracted light from that plane is in the same two directions (wave number vector) as described above. 2k ₁ -k ₂ and 2k ₂ -k ₁ directions).
[0039]
In the above description, the relationship between the positive chirp pulse L3 and the negative chirp pulse L4 may be exchanged, and the wavelength band of the positive chirp pulse L3 may include the wavelength band of the negative chirp pulse L4.
[0040]
Further, a part of the wavelength band of the positive chirped pulse L3 may coincide with a part of the wavelength band of the negative chirped pulse L4. For example, FIG. 7 shows a state in which the wavelength bands λ4 to λ5 (λ4> λ5) are included in the positive chirp pulse L3 and the negative chirp pulse L4. Are diffracted in the same two directions (directions of wave vectors 2k ₁ -k ₂ and 2k ₂ -k ₁ ) in the same manner as described above.
[0041]
Further, the wavelength of each of the positive chirp pulse L3 and the negative chirp pulse L4 is not limited to the case where the wavelength changes linearly, and the wavelength change of the positive chirp pulse L3 increases monotonously from the beginning to the end of the pulse. It is sufficient that the wavelength change of the chirp pulse L4 monotonically decreases from the beginning to the end of the pulse. An example is shown in FIG. In this case, the wavelength of the positive chirp pulse L3 and the wavelength of the negative chirp pulse L4 are the same on a specific curved surface in the sample 6 to be measured, and the diffracted light from the curved surface is in the same two directions ( (In the directions of the wave vectors 2k ₁ -k ₂ and 2k ₂ -k ₁ ).
[0042]
The light receiving means is not limited to a two-dimensional CCD, but may be another two-dimensional light sensor, a one-dimensional line sensor, or the like.
[0043]
【The invention's effect】
According to the measuring device and measuring method of the third-order nonlinear optical characteristic according to the present invention, the spectrum of the ^third- order nonlinear susceptibility に お け る⁽³⁾ in a predetermined frequency band can be measured at once by irradiating one ultrashort pulse. As a result, the spectrum measurement of the ^third- order nonlinear susceptibility χ ⁽³⁾ , which conventionally took several days to several weeks, can be reduced to, for example, more than ten minutes.
[0044]
In addition, since the diffraction phenomenon is used, the spectrum of the ^third- order nonlinear susceptibility χ ⁽³⁾ due to the effect of refraction and the effect of absorption can be measured by irradiation of one ultrashort pulse.
[0045]
In addition, the ability to efficiently measure the spectrum of the ^third- order nonlinear susceptibility χ ⁽³⁾ accelerates the elucidation of the relationship between unclear nonlinear optical properties and the electronic structure of materials, and increases the light-intensity-dependent refractive index. It will be possible to promote applications to ultra-high-speed switches and applications to light-limiting materials for two-photon absorption and optical microfabrication.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic configuration of a measuring device of a third-order nonlinear optical characteristic according to an embodiment of the present invention.
FIG. 2 is a diagram showing a change in wavelength within a positive chirp pulse.
FIG. 3 is a diagram illustrating an example of an optical system that generates chirp.
FIG. 4 is a cross-sectional view schematically showing a diffraction phenomenon due to the incidence of chirp light on a sample to be measured in the measuring device for third-order nonlinear optical characteristics according to the embodiment of the present invention.
FIG. 5 is a diagram showing an example of a graph in which the wavelengths of positive and negative chirped pulses having the same wavelength band linearly change.
FIG. 6 is a diagram showing an example of a graph in which the wavelength band of a positive chirped pulse is included in the wavelength band of a negative chirped pulse and the wavelength changes linearly.
FIG. 7 is a diagram illustrating an example of a graph in which the wavelength of positive and negative chirped pulses in which a part of the wavelength band overlaps changes linearly;
FIG. 8 is a diagram illustrating an example of a graph in which the wavelengths of positive and negative chirped pulses in which a part of the wavelength band overlaps change nonlinearly.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 light pulse generating unit 2 splitter 3 positive chirp generating unit 4 negative chirp generating unit 5 detecting unit 6 sample under test 7 prism 8 lens 9 CCD
L1 to L6 light pulse

Claims (10)

Positive chirp irradiating means for irradiating the sample to be measured with a positive chirp pulse,
Negative chirp irradiating means for irradiating the sample with a negative chirp pulse,
Light receiving means for receiving diffracted light generated from the diffraction grating induced in the sample by the positive chirp pulse and the negative chirp pulse,
The wavelength in the positive chirped pulse monotonically decreases from the beginning to the end of the pulse,
The wavelength in the negative chirp pulse monotonically increases from the beginning to the end of the pulse,
At least a portion of the wavelength band of the positive chirp pulse and at least a portion of the wavelength band of the negative chirp pulse overlap,
The incident direction of the positive chirp pulse and the negative chirp pulse forms a predetermined angle,
At the same time in the sample, a part of the positive chirp pulse and a part of the negative chirp pulse are superimposed,
The light receiving means, with the sample as a position reference, the direction of a first vector obtained by subtracting the wave vector of the negative chirp pulse from the wave vector of twice the wave vector of the positive chirp pulse, or An apparatus for measuring a third-order nonlinear optical characteristic, which is arranged in a direction of a second vector obtained by subtracting a wave vector of a positive chirp pulse from a wave vector twice as large as a wave vector of a negative chirp pulse. The wavelength in the positive chirped pulse decreases linearly from the beginning to the end of the pulse,
The measuring device of the third-order nonlinear optical characteristic according to claim 1, wherein the wavelength in the negative chirped pulse increases linearly from the beginning to the end of the pulse. 3. The measuring device of the third-order nonlinear optical characteristic according to claim 1, wherein a wavelength band of the positive chirp pulse and a wavelength band of the negative chirp pulse are the same. The measuring device of the third-order nonlinear optical characteristic according to any one of claims 1 to 3, wherein a pulse width of the positive chirp pulse and a pulse width of the negative chirp pulse are the same. The light receiving means is a two-dimensional CCD,
5. The tertiary order according to claim 1, wherein the output signal of the two-dimensional CCD is added in a direction perpendicular to the incidence vector of the positive chirp pulse and the incidence vector of the negative chirp pulse. Measurement device for nonlinear optical characteristics. A positive chirp pulse generating step of generating a positive chirp pulse in which the wavelength monotonically decreases from the beginning to the end of the pulse from an ultrashort pulse having a constant wavelength from the beginning to the end of the pulse,
A positive chirp pulse irradiation step of irradiating the sample to be measured with the positive chirp pulse,
From the ultrashort pulse, a negative chirp pulse generating step of generating a negative chirp pulse whose wavelength monotonically increases from the beginning to the end of the pulse,
A negative chirp pulse irradiation step of irradiating the negative chirp pulse in an incident direction forming a predetermined angle with the incident direction of the positive chirp pulse on the sample so as to reach the sample at the same time as the positive chirp pulse. ,
The direction of the first vector obtained by subtracting the wave vector of the negative chirp pulse from the wave vector twice as large as the wave vector of the positive chirp pulse, using the sample as a position reference, or the wave number of the negative chirp pulse The light-receiving means arranged in the direction of a second vector obtained by subtracting the wave vector of the positive chirp pulse from the wave vector of twice the vector, the positive chirp pulse and the negative chirp pulse cause the sample to enter the sample by the light receiving means. Receiving a diffracted light generated from the induced diffraction grating,
A method for measuring a third-order nonlinear optical characteristic, wherein at least a part of the wavelength band of the positive chirp pulse and at least a part of the wavelength band of the negative chirp pulse overlap. The wavelength in the positive chirped pulse decreases linearly from the beginning to the end of the pulse,
The method according to claim 6, wherein the wavelength in the negative chirped pulse increases linearly from the beginning to the end of the pulse. The method according to claim 6, wherein the wavelength band of the positive chirp pulse is the same as the wavelength band of the negative chirp pulse. 9. 9. The method for measuring third-order nonlinear optical characteristics according to claim 6, wherein the pulse width of the positive chirp pulse and the pulse width of the negative chirp pulse are the same. The light receiving means is a two-dimensional CCD,
10. An adding step of adding an output signal of the two-dimensional CCD in a direction perpendicular to the incident vector of the positive chirp pulse and the incident vector of the negative chirp pulse. 3. The method for measuring a third-order nonlinear optical characteristic according to 1.

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