JPWO2019167478A1 - Two-dimensional spectroscopic measurement method and two-dimensional spectroscopic measurement device - Google Patents

Abstract

In the two-dimensional spectroscopic measurement method of the present invention, the first optical frequency comb having a repetition frequency four times the offset frequency is generated, the first optical frequency comb is divided into the second to fifth optical frequency combs, and 4 The phases of the fifth and fifth optical frequency combs on the time axis are shifted by 90 ° from each other. In the two-dimensional spectroscopic measurement method of the present invention, the interference signal of the third and fourth optical frequency combs containing the optical information of the sample in any one and the third and fifth optical frequency combs containing the optical information of the sample in any one of them The envelope strength with the interference signal of is acquired, and the optical information of the sample is extracted based on the envelope strength.

Description

The present invention relates to a two-dimensional spectroscopic measurement method and a two-dimensional spectroscopic measurement device. The present application claims priority based on Japanese Patent Application No. 2018-038101 filed in Japan on March 2, 2018, the contents of which are incorporated herein by reference.

Conventionally, many methods such as imaging method, Fourier Transform Infrared Spectroscopy (FT-IR), and distributed infrared spectroscopy have been used as methods for obtaining spectral information. With these methods, it was difficult to obtain two-dimensional spatial information and one-dimensional wavelength information at the same time. Hereinafter, two-dimensional spatial information and one-dimensional wavelength information may be collectively referred to as two-dimensional spectroscopic information.

In recent years, in academic fields such as astronomy, earth science, and physical properties, there are increasing expectations for two-dimensional spectroscopy that can simultaneously acquire each information contained in two-dimensional spectroscopy information in real time. Two-dimensional spectroscopy is also called surface spectroscopy or hyperspectral imaging. If two-dimensional spectroscopic information is obtained, for example, an image of an arbitrary wavelength can be extracted from the acquired data, and an expanded celestial body such as a galaxy can be analyzed in detail. In the conventional two-dimensional spectroscopy, for example, while scanning each point (a plurality of measurement regions) on a two-dimensional plane, FT-IR can be performed on each point to acquire two-dimensional spectral information. However, the conventional two-dimensional spectroscopy has a problem that it is difficult to measure a dynamic object because it takes time to sweep the space. On the other hand, if two-dimensional spectroscopic information can be acquired at one time, spectroscopic measurement of various dynamic objects can be performed accurately.

Examples of the two-dimensional spectroscopy method include a method of acquiring while sweeping a wavelength band transmitted by a variable bandpass filter. Non-Patent Document 1 discloses a variable bandpass filter applicable to a method of acquiring two-dimensional spatial information and one-dimensional wavelength information while sweeping the wavelength band transmitted by the variable bandpass filter. ..

H. R. Morris, C. C. Hoyt, P. Miller and P. J. Treado, “Liquid Crystal Tunable Filter Raman Chemical Imaging,” Appl. Spectrosc. Vol. 50, no. 6, pp. 805-811 (1996).

However, when the variable band pass filter disclosed in Non-Patent Document 1 transmits light of different wavelength bands to acquire two-dimensional spatial information and one-dimensional wavelength information, it is necessary to sweep the wavelength band. Therefore, there is a problem that it takes a long time to sweep and it is difficult to instantly obtain high-resolution wavelength information and spectral information such as spectral distribution. Therefore, two-dimensional spectroscopy in which the wavelength band is swept using the above-mentioned variable bandpass filter is not suitable for measuring dynamic phenomena.

The present invention has been made to solve the above-mentioned problems, and is a two-dimensional spectroscopic measurement method and two-dimensional spectroscopic measurement that can instantly acquire high-resolution spectroscopic information and enable two-dimensional spectroscopic measurement in real time. Provide the device.

The two-dimensional spectroscopic measurement method of the present invention is an integral multiple of a predetermined repetition frequency with respect to a first frequency mode having a predetermined offset frequency with respect to zero on the frequency axis and the first frequency mode on the frequency axis. An optical frequency comb generation step of generating a first optical frequency comb having a plurality of second frequency modes arranged at intervals and having the repetition frequency four times the offset frequency, and the first light The frequency comb is divided into a second optical frequency comb and a third optical frequency comb, the second optical frequency comb is divided into a fourth optical frequency comb and a fifth optical frequency comb, and the fourth optical frequency comb is divided. A phase difference imparting step of shifting the phase on the time axis of the fifth optical frequency comb by 90 ° with respect to the phase on the time axis of the fifth optical frequency comb, and the third optical frequency comb or the fourth optical frequency comb and the third. A sample irradiation step of irradiating a sample with 5 optical frequency combs to obtain the 3rd optical frequency comb or the 4th optical frequency comb and the 5th optical frequency comb that are emitted from the sample and contain optical information. , The fourth optical frequency comb containing the optical information in any of them interferes with the third optical frequency comb to generate a first interference signal, and the fifth optical frequency comb containing the optical information in any of them. An interference signal generation step of interfering an optical frequency comb with the third optical frequency comb to generate a second interference signal, and acquiring an envelope strength from the first interference signal and the second interference signal. It includes an wrapping line strength acquisition step and an optical information extraction step of extracting optical information of the sample based on the wrapping line strength.

The above-mentioned two-dimensional spectroscopic measurement method further includes a repeating frequency adjusting step of adjusting the repeating frequency according to a phase shift between the fourth optical frequency comb and the fifth optical frequency comb on the time axis. You may.

Further, in the above-mentioned two-dimensional spectroscopic measurement method, in the envelope strength acquisition step, the transmission strength when the envelope strength passes through each of the two filters having opposite wavelength dependence of the transmittance is acquired. Then, in the optical information extraction step, the optical information may be calculated based on the ratio of the transmittance.

Further, in the above-mentioned two-dimensional spectroscopic measurement method, in the optical information extraction step, a predetermined delay time is added to the second optical frequency comb or the third optical frequency comb, and the intensity spectrum including the optical information and the intensity spectrum The phase spectrum may be acquired.

The two-dimensional spectroscopic measuring apparatus of the present invention has a first frequency mode having a predetermined offset frequency with respect to zero on the frequency axis and an integral multiple of a predetermined repetition frequency with respect to the first frequency mode on the frequency axis. An optical frequency comb emitting unit that has a plurality of second frequency modes arranged at intervals and emits a first optical frequency comb whose repetition frequency is four times the offset frequency, and the first light A first branch that divides a frequency comb into a second optical frequency comb and a third optical frequency comb, and a second that divides the second optical frequency comb into a fourth optical frequency comb and a fifth optical frequency comb. A phase difference imparting portion that shifts the phase on the time axis of the fourth optical frequency comb by 90 ° with respect to the phase on the time axis of the fifth optical frequency comb, and the third optical frequency. The comb or the fourth optical frequency comb and the fifth optical frequency comb include arbitrary optical information and cause the fourth optical frequency comb and the third optical frequency comb to interfere with each other to cause a first interference signal. To generate a second interference signal by interfering the fifth optical frequency comb with the third optical frequency comb to generate a second interference signal, the first interference signal and the second interference. The frequency comb strength acquisition unit for acquiring the frequency comb strength with the signal and the optical information extraction unit for extracting the optical information based on the frequency comb strength are provided.

In the above-mentioned two-dimensional spectroscopic measuring device, feedback that acquires a part of the fourth optical frequency comb and the fifth optical frequency comb emitted from the phase difference imparting unit and feeds them back to the optical frequency comb emitting unit. Further mechanisms may be provided.

In the above-mentioned two-dimensional spectroscopic measurement device, the envelope intensity acquisition unit includes two filters having opposite wavelength dependence of transmittance, and the envelope intensity passes through each of the two filters. The optical information extraction unit may calculate the optical information based on the ratio of the transmitted intensity.

The above-mentioned two-dimensional spectroscopic measurement device further includes a delay mechanism for adding a predetermined delay time to the second optical frequency comb or the third optical frequency comb, and the optical information extraction unit includes the optical information. The intensity / phase spectrum may be acquired.

In the two-dimensional spectroscopic measurement method and the two-dimensional spectroscopic measurement apparatus described above, the optical information is the optical frequency of any one of the third optical frequency comb, the fourth optical frequency comb, and the fifth optical frequency comb. The distribution of the refractive index on the optical path of the comb, the fluctuation of the refractive index, was arranged on the path of the third optical frequency comb, or on the path of the fourth optical frequency comb and the fifth optical frequency comb. Includes any of the sample shapes.

According to the present invention, there is provided a two-dimensional spectroscopic measurement method and a two-dimensional spectroscopic measurement apparatus that can instantly acquire high-resolution spectroscopic information and enable two-dimensional spectroscopic measurement in real time.

It is a figure for demonstrating the two-dimensional spectroscopic measurement method of this invention, and is the schematic diagram of the electric field distribution (upper) and the intensity distribution (lower) on the time axis of an optical frequency comb. FIG. 5 is a schematic diagram showing an electric field distribution on the time axis of an optical frequency comb controlled so as to maintain a relationship in which the repetition frequency is four times the carrier envelope offset. It is the schematic of the pulse generation optical system which generates the optical frequency comb (optical pulse train) which is 90 ° out of phase with each other. It is a schematic diagram for demonstrating the time interval between the 1st optical pulse and the 2nd optical pulse on the time axis in an optical frequency comb. It is the schematic which shows an example of the optical system which stabilizes the fluctuation generated in the optical path of the optical frequency comb. It is the schematic which shows the structure of the interference signal strength acquisition apparatus applicable to the 2D spectroscopic measurement apparatus of this invention. It is a schematic diagram which shows the structure of the delay mechanism of the interference signal strength acquisition apparatus shown in FIG. 6 and the two-dimensional spectroscopic measurement apparatus shown in FIG. It is a perspective view which shows the state of transmission / reflection of an optical frequency comb in the half mirror of the interference signal intensity acquisition apparatus shown in FIG. It is a perspective view which shows the state of transmission / reflection of an optical frequency comb in another half mirror of the interference signal intensity acquisition apparatus shown in FIG. It is a perspective view which shows the state of transmission / reflection of an optical frequency comb in still another half mirror of the interference signal intensity acquisition apparatus shown in FIG. It is a schematic diagram which shows the envelope intensity distribution of the interference signal which is 90 ° out of phase with each other. It is a schematic diagram which shows the structure of the 2D spectroscopic measurement apparatus of this invention. It is a graph which shows the wavelength dependence of the transmittance of the filter of the 2D spectroscopic measuring apparatus shown in FIG.

Hereinafter, the two-dimensional spectroscopic measurement method and the embodiment of the two-dimensional spectroscopic measurement apparatus of the present invention will be described with reference to the drawings.

<Principle explanation>
FIG. 1 is a schematic diagram showing an electric field distribution (upper row) on the time axis and an intensity distribution (lower row) on the frequency axis of the optical frequency comb. The intensity distribution on the frequency axis represents the spectral distribution. As shown in the upper part of FIG. 1, the relationship shown in Eq. (1) holds between the repetition time _Trep of the optical pulse train oscillated at a constant repetition and the frequency interval _frep .

Each optical pulse train consists of a superposition of many longitudinal modes that propagate inside the resonator of the light source or the like. The optical pulse train is composed of a carrier wave that is a superposition wave of these longitudinal modes and a wave packet that constitutes an envelope of the carrier wave. Carrier waves are also called carriers. The envelope of a carrier wave is also called an envelope. In such an optical pulse train, the velocity of the carrier wave and the velocity of the wave packet are different from each other, so that a phase difference occurs with the passage of time. The laser cavity is composed of a dispersion medium. In an optical pulse train that is repeatedly emitted at intervals of a predetermined repetition time _trep on the time axis, a phase shift φ _CEO occurs between adjacent pulses. The period of the phase shift φ _CEO is one cycle at the time _TCEO .

When the above-mentioned ultrashort pulse train on the time axis is Fourier transformed and observed on the frequency axis, as shown in the lower part of FIG. 1, they are arranged at intervals of the repetition frequency _rep corresponding to the reciprocal of the repetition time _tre. However, many frequency modes are observed.

As shown in the lower part of FIG. 1, the optical frequency comb has a frequency mode (first frequency mode) having a predetermined carrier envelope offset (CEO, offset frequency) f _CEO with respect to zero on the frequency axis. ) having a f _0, and a plurality of frequency modes (second frequency mode) f _m arranged at an integral multiple spacing of the predetermined repetition frequency f _rep with respect to the frequency mode f ₀ the frequency axis. Carrier envelope offset _{f CEO} of the optical frequency comb is equivalent to the reciprocal of the time _{T CEO.} Then, the relationship shown in Eq. (2) is established between the carrier development offset f _CEO , the phase shift φ _CEO , and the time T _CEO .

The frequency of the nth spectrum of the optical frequency comb is expressed as in Eq. (3) with the repetition frequency f _rep and the carrier envelope offset f _CEO as parameters.

Based on the above-mentioned interrelationship, the carrier wave and the envelope can be controlled by controlling the parameters related to the plurality of frequency modes of the optical frequency comb. In the present embodiment, the parameters related to the plurality of frequency modes of the optical frequency comb are controlled so that the two parameters of the optical frequency comb, that is, the repetition frequency f _rep and the carrier envelope offset f _CEO maintain the relationship of the equation (4). To do.

FIG. 2 is a schematic diagram showing an electric field distribution on the time axis of an optical frequency comb in which the repetition frequency f _rep and the carrier envelope offset f _CEO are controlled so as to maintain the relationship of the equation (4). As shown in FIG. 2, the phase shift of adjacent optical pulses on the time axis is (π / 2) = 90 °. The optical pulse four ahead of the reference optical pulse on the time axis has the same phase and waveform pattern as the reference optical pulse. The relationship of Eq. (5) holds between the time T _CEO and the carrier development offset f _CEO .

FIG. 3 is a schematic view showing an example of an optical system 120 that generates optical pulse trains that are 90 ° out of phase with each other. As shown in FIG. 3, the optical system 120 includes an optical frequency comb emitting unit 103, a half mirror (second branching unit) 112, a half mirror 118, total reflection mirrors 114 and 116, and a delay imparting unit (phase difference). (Granting unit) 123 and. The optical frequency comb emitting unit 103 includes a function generator (not shown) and the like. The optical frequency comb emitting unit 103 mainly controls the carrier envelope offset f _CEO so that the repeating frequency f _rep and the carrier envelope offset f _CEO maintain the relationship of the equation (4) by operating the function generator, and the carrier -Emit the optical frequency comb C1 with the envelope offset f _CEO controlled.

The optical frequency comb C1 passes through the half mirror 112 and is separated into an optical frequency comb C4 and an optical frequency comb C5. The optical frequency comb C4 is reflected by the total reflection mirror 116 and is incident on the half mirror 118. The optical frequency comb C5 is reflected by the half mirror 112 and the total reflection mirror 114, passes through the delay imparting unit 123, and is incident on the half mirror 118. The delay imparting unit 123 is composed of two total reflection mirrors 121 and 122 with their reflection surfaces facing each other. The optical frequency comb C5 reflected by the total reflection mirror 114 is incident on the delay imparting portion 123, reciprocates between the reflection surfaces of the total reflection mirrors 121 and 122 a predetermined number of times while shifting the optical path, and is directed toward the half mirror 118. Exit. The positions and separation distances of the total reflection mirrors 121 and 122 are adjusted so that one phase of the optical frequency combs C4 and C5 incident on the half mirror 118 is shifted by 90 ° with respect to the other phase. That is, in the optical system 120, the optical frequency comb is branched, and one of them is delayed by the time difference between a certain optical pulse and the next optical pulse on the time axis. The time difference between adjacent optical pulses on the time axis corresponds to the repetition time _Trep .

As shown in FIG. 3, in the optical system 120, the optical path length difference of each of the optical frequency combs C4 and C5 fluctuates due to vibration of various mirrors, air fluctuation, and the like. Based on this, by controlling the repetition frequency _prep of the optical frequency comb C1 and finely adjusting the repetition time _rep of the optical pulse of the optical frequency comb C1, the fluctuation of the optical path difference of the optical frequency combs C4 and C5 is absorbed. However, the optical frequency combs C4 and C5 can be stabilized. FIG. 4 shows the first optical pulse <“1st” optical pulse shown in FIGS. 3 and 4> and the second optical pulse (shown in FIGS. 3 and 4) of the optical frequency comb C1 as a reference on the time axis. It is a schematic diagram for demonstrating the time interval with "2nd" light pulse>. The repetition times of the first optical pulse and the second optical pulse adjacent to each other on the time axis are T _rep1 , T _rep2 , and T _rep3 , _depending on the repetition frequencies f _rep1 , f _rep2 , and f _rep3 . It is expressed as an expression.

Based on the relative relationship between _{T rep} and _{f rep} shown in FIG. 4 and (6) to (8), for controlling the repetition frequency _{f rep} of the optical frequency comb C1.

4 and (6) as can be seen from the equation - (8), such as the operation function generator of the optical frequency comb emitting unit 103, by controlling the repetition frequency _{f rep} of the optical frequency comb C1, repetition time _{T rep} Can be controlled.

As shown in FIG. 3, the fluctuation generated in each optical path of the optical frequency combs C4 and C5 with respect to the deviation of one optical pulse on the time axis of the optical frequency combs C4 and C5 which are 90 ° out of phase with each other. Further, the time difference δ is added or the time difference δ is reduced. FIG. 5 is a schematic view showing an example of an optical system 124 capable of stabilizing fluctuations generated in the optical path of the optical frequency combs C4 and C5. The optical system 124 includes a half mirror 126 and a feedback mechanism 128 in addition to the configuration of the optical system 120. The half mirror 126 is arranged in front of the half mirror 118 in the traveling direction of the optical frequency combs C4 and C5. The feedback mechanism 128 is separated by the half mirror 126 and is arranged on the path of the optical frequency combs C4 and C5 different from the optical frequency combs C4 and C5 that pass through the half mirror 126. The optical frequency combs C4 and C5 that are combined by the half mirror 118 and include the time difference δ are separated into two by the half mirror 126. One of the separated optical frequency combs (a part of the fourth optical frequency comb and the fifth optical frequency comb) C4 and C5 are reflected by the half mirror 126 and input to the feedback mechanism 128, and the optical frequency comb outlet 103 Feedback to. As a result, the repetition frequency _frep of the optical frequency comb C1 is adjusted. As shown in FIG. 5, the repetition time _Trep of the optical frequency comb C1 emitted from the optical frequency comb emitting unit 103 is increased or decreased by a time difference δ. By adjusting the repetition time _Trep with the time difference δ, the phase shift between the optical frequency combs C4 and C5 incident on the half mirror 118 becomes 90 ° again, that is, one optical pulse.

<Interference signal strength acquisition device>
FIG. 6 is a schematic view showing a configuration of an interference intensity signal acquisition optical system 130 that instantaneously obtains interference intensity signals that are 90 ° out of phase with each other in the interference signal intensity acquisition device of the present invention. The interference intensity signal acquisition optical system 130 includes an optical frequency comb exit unit 103, a partial optical system 124P, a branch unit 150, a delay mechanism 206, and an imaging camera (envelope intensity acquisition unit) 161. The partial optical system 124P shown in FIG. 6 shows a configuration in which the optical frequency comb emitting unit 103 is excluded from the optical system 124 shown in FIG. The branch portion 150 takes out the optical frequency combs C6 and C7 from the optical frequency combs C3. The branch portion 150 includes a half mirror (interference signal generation unit) 152, a half mirror (first branch portion) 153,155,158, and a total reflection mirror 154,156,157.

The optical frequency comb emitting unit 103 emits an optical frequency comb (first optical frequency comb) C1 whose repetition frequency f _rep is four times the carrier envelope offset f _CEO . The first branch portion 104 divides the optical frequency comb C1 into an optical frequency comb (second optical frequency comb) C2 and an optical frequency comb (third optical frequency comb) C3. The second branch 105 divides the optical frequency comb C2 into an optical frequency comb (fourth optical frequency comb) C4 and an optical frequency comb (fifth optical frequency comb) C5 (see FIG. 5). The phase difference imparting unit 106 shifts the phase on the time axis of the optical frequency comb C4 and the phase on the time axis of the optical frequency comb C5 by 90 °. The interference signal generation unit 107 causes the optical frequency comb C4 and the optical frequency comb (third optical frequency comb) C6 containing arbitrary optical information to interfere with each other to generate an interference signal (first interference signal) IM1 to generate light. An interference signal (second interference signal) IM2 is generated by interfering the frequency comb C5 with the optical frequency comb (third optical frequency comb) C7 containing optical information.

The optical information in the present specification is added by the optical characteristics of each optical frequency comb itself, the distribution / fluctuation of the refractive index of each optical frequency comb on the optical path, and the passage of a sample arranged on the optical path. All the shapes of the samples are included. The shape of the sample includes the uneven shape of the surface of the sample, the internal structure of the sample, and the like. That is, according to the interference intensity signal acquisition optical system 130, information on the shape such as the surface or internal structure of the sample can be acquired. For example, when the sample S is not installed as in the interference intensity signal acquisition optical system 130 shown in FIG. 6, the optical information is on the optical characteristics of the optical frequency comb C3 itself or on the optical path of the optical frequency combs C3, C6, and C7. It means the distribution and fluctuation of the refractive index of. On the other hand, when the sample S to be measured is arranged as in the two-dimensional spectroscopic measurement device 200 described later, the optical information mainly includes optical characteristics including the shape of the sample S. As shown in FIG. 11, the envelope strength acquisition unit 108 acquires the envelope strength EV of the interference signal IM1 and the interference signal IM2.

As shown in FIG. 6, the optical frequency comb C1 emitted from the optical frequency comb emitting unit 103 is separated into optical frequency combs C2 and C3 by a half mirror 153. The optical frequency comb C2 is incident on the partial optical system 124P and is emitted as optical frequency combs C4 and C5 which are out of phase with each other by 90 ° as described above. On the other hand, the optical frequency comb C3 reflected by the half mirror 153 is incident on the branch portion 150, reflected by the total reflection mirror 154, and separated into the optical frequency combs C6 and C7 by the half mirror 155.

The delay mechanism 206 is a mechanism for adding a predetermined delay time to the optical frequency comb C3, and is arranged on the path of the optical frequency comb C3. As shown in FIG. 7, the delay mechanism 206 has two total reflection prisms 207 in which the reflection surfaces 207r are arranged to face each other. When the delay mechanism 206 moves along the arrow M, the optical path length of the optical frequency comb C3 changes, and a predetermined delay time is added.

FIG. 8 is a schematic view showing the state of reflection of the optical frequency comb C4 and transmission of the optical frequency comb C5 in the half mirror 118 of the partial optical system 124P (that is, the optical system 124). As shown in FIG. 7, of the optical frequency combs C4 and C5, the optical frequency comb C4 is incident on the reflection surface 118a of the half mirror 118 and is reflected substantially at right angles to the incident direction in the top view. On the other hand, of the optical frequency combs C4 and C5, the optical frequency comb C5 passes through the surface 118b and the reflecting surface 118a on the side opposite to the reflecting surface 118a of the half mirror 118, and overlaps the path of the optical frequency comb C4 in the top view. Emitted from the half mirror 118 along the path. In the height direction, the paths of the optical frequency combs C4 and C5 are deviated from each other.

FIG. 9 is a schematic view showing the state of reflection of the optical frequency comb C6 and transmission of the optical frequency comb C7 in the half mirror 158 of the branch portion 150. As shown in FIG. 9, of the optical frequency combs C6 and C7, the optical frequency comb C6 is incident on the reflection surface 158a of the half mirror 158 and is reflected substantially at right angles to the incident direction in the top view. On the other hand, of the optical frequency combs C6 and C7, the optical frequency comb C7 passes through the surface 158b and the reflecting surface 158a on the side opposite to the reflecting surface 158a of the half mirror 158, and overlaps the path of the optical frequency comb C6 in the top view. It is emitted from the half mirror 158 along the path. In the height direction, the paths of the optical frequency combs C6 and C7 are deviated from each other. The height of the path of the optical frequency comb C6 coincides with the height of the optical frequency comb C4, and the height of the optical frequency comb C7 coincides with the height of the optical frequency comb C5.

FIG. 10 is a schematic view showing a state of transmission of optical frequency combs C4 and C5 and reflection of optical frequency combs C6 and C7 in the half mirror 152 of the branch portion 150. As shown in FIG. 10, the optical frequency combs C4 and C5 emitted from the half mirror 118 pass through the surface 152b on the side opposite to the reflection surface 152a of the half mirror 152. On the other hand, the optical frequency combs C6 and C7 emitted from the half mirror 158 are reflected by the reflecting surface 152a of the half mirror 152 substantially at right angles to the incident direction in the top view, and the optical frequency combs C4 and C5 transmitted through the surface 152b. Interferes with each other, and interference signals IM1 and IM2 are generated. The interference signal IM1 is an interference signal between optical frequency combs C4 and C6, and the interference signal IM2 is an interference signal between optical frequency combs C5 and C7. In the present embodiment, as shown in FIGS. 8 to 10, the irradiation positions of the optical frequency combs C4 and C6 in the half mirror 118 are different from each other, and the irradiation positions of the optical frequency combs C5 and C7 in the half mirror 158 are set to each other. Make it different. As a result, the position where the optical frequency combs C4 and C6 overlap to generate the interference signal IM1 and the position where the optical frequency combs C5 and C7 overlap to generate the interference signal IM2 are different.

Since the phases of the optical frequency combs C4 and C5 are shifted by 90 ° from each other, the phases of the interference signals IM1 and IM2 are shifted by 90 ° from each other. FIG. 11 is a graph showing an example of the envelope strength EV obtained from the interference signals IM1 and IM2. If the intensity T1 of the interference signal IM1 and the intensity T2 of the interference signal IM2 at a certain moment are acquired by the imaging camera 161, the envelope intensity EV is calculated by calculating {(T1) ² + (T2) ² } ^1/2. Can be obtained instantly.

As described above, the envelope strength EV is detected by the imaging camera 161. The envelope intensity EV detected by the image pickup camera 161 is appropriately processed by a processing unit (not shown) attached to the image pickup camera 161. The processing unit is, for example, a program built in a computer connected to the image pickup camera 161. In the interference intensity signal acquisition optical system 130, the envelope intensity EVs of the interference signals IM1 and IM2, which are out of phase with each other by 90 °, can be obtained instantly.

<Two-dimensional spectroscopic measurement device>
FIG. 12 is a schematic view showing the configuration of the two-dimensional spectroscopic measuring device 200 of the present invention. As shown in FIG. 12, the two-dimensional spectroscopic measurement device 200 includes a wavelength information acquisition unit 208 in place of the single image pickup camera 161 in addition to the configuration of the interference intensity signal acquisition optical system 130 described above. Also in the two-dimensional spectroscopic measurement device 200, the optical frequency combs C4 and C5 are fed back to the optical frequency comb emitting unit 103 by the feedback mechanism 128, and the phase shift from the optical frequency combs C4 and C5 (time difference δ, see FIG. 3). The repetition frequency _feedback is adjusted accordingly.

The wavelength information acquisition unit 208 includes a half mirror 231, a total reflection mirror 232, filters F1 and F2, two imaging cameras 241,242 having the same number of pixels, and an image processing unit (optical information extraction unit) 250. And. The total reflection mirror 154 of the interference intensity signal acquisition optical system 130 has been replaced with a half mirror 159. The sample S, which is the object of spectroscopic measurement, is arranged on the path of the optical frequency comb C3 that passes through the half mirror 159.

As shown in FIG. 12, the optical frequency comb C3 reflected by the half mirror 153 passes through the half mirror 159 and irradiates the sample S. The optical frequency comb C3 reflected from the sample S includes optical information including all the spectral information and the phase / shape information of the sample S. The optical frequency combs C6 and C7 divided into two by the half mirror 155 from the optical frequency comb C3 also include the optical information of the sample S. The optical information of the sample S is reflected in the interference signals IM1 and IM2. The envelope strength EVs of the interference signals IM1 and IM2 are divided into two by the half mirror 231 and the two divided envelope strengths EV1 and EV2 pass through the filters F1 and F2, respectively.

FIG. 13 is a graph showing the wavelength dependence of the transmittance of the filters F1 and F2. As shown in FIG. 13, the wavelength dependence of the transmittance of the filters F1 and F2 is opposite to each other. The transmittance of the filter F1 generally decreases as the wavelength increases. On the other hand, the transmittance of the filter F2 generally increases as the wavelength increases. Since the wavelength dependence of the transmittance of the filters F1 and F2 is opposite to each other in this way, there is a one-to-one correspondence between the light intensity ratio and the wavelength with respect to the envelope strengths EV1 and EV2 that have passed through these filters F1 and F2. Is established.

The image processing unit 50 calculates the ratio of the transmission intensities of the envelope strengths EV1 and EV2 for each measurement region of the sample S acquired by the imaging cameras 241,242 through the filters F1 and F2. The signal intensity ratio of each pixel is obtained based on the ratio of the transmission intensities of the envelope strengths EV1 and EV2 calculated for each pixel of the imaging cameras 241,242, and the wavelength at which each intensity is expressed in the distribution of the envelope strength EV is determined. It is decided instantly. By obtaining the wavelength information instantly, the phase information of the optical frequency comb C3 reflected from the sample S in each spatial position (measurement region) is measured. The phase information of the optical frequency comb C3 is a time difference, and indicates a difference in physical position and a difference in refractive index. In the present embodiment, it is assumed that the phase spectrum of the optical frequency comb C6 reflected from the sample S basically does not change when the physical position is acquired instantaneously.

<Two-dimensional spectroscopic measurement method>
The two-dimensional spectroscopic measurement method of the present invention includes an optical frequency comb generation step, a phase difference imparting step, a sample irradiation step, an interference signal generation step, an envelope strength acquisition step, and an optical information extraction step. In the two-dimensional spectroscopic measurement method of the embodiment of the present invention, the envelope intensity EV of the interference signals IM1 and IM2 is instantaneously acquired by using the two-dimensional spectroscopic measurement apparatus 200, and the sample S is based on the acquired envelope intensity EV. It is a method that can obtain the optical information of.

In the optical frequency comb generation step, the optical frequency comb C1 is generated (see FIG. 1). Optical frequency comb C1 is a frequency mode f ₀ having a predetermined carrier envelope offset f _CEO against zero on the frequency axis, of the predetermined relative frequency mode f ₀ the frequency axis repetition frequency f _rep integral multiple of the has a plurality of frequency modes f _m arranged at intervals, the. In the optical frequency comb C1, the relationship of f _rep = 4 × f _CEO is established. In order to establish the above-mentioned relationship, the carrier development offset f _CEO and the repetition frequency f _rep are controlled by using a function generator of the optical frequency comb emitting unit 103 or the like.

Next, in the phase difference imparting step, the optical frequency comb C1 is divided into an optical frequency comb C2 and an optical frequency comb C3 by a half mirror 153, and the optical frequency comb C2 is further divided into an optical frequency comb C4 by a half mirror 112 (see FIG. 3). Divide into optical frequency comb C5. Subsequently, the delay imparting unit 123 shifts the phase of the optical frequency comb C5 on the time axis by 90 ° with respect to the phase of the optical frequency comb C4 on the time axis.

Next, in the sample irradiation step, the sample S is irradiated with the optical frequency combs C3 or the optical frequency combs C4 and C5, and the optical frequency combs C3 or the optical frequency combs C4 and C5 emitted from the sample S and containing the optical information are obtained.

In the present embodiment, the optical frequency comb C3 or the optical frequency combs C4 and C5 include arbitrary optical information. In the interference signal generation step, the optical frequency comb C4 containing the optical information and the optical frequency comb C6 are made to interfere with each other to generate the interference signal IM1. In the interference signal generation step, the optical frequency comb C5 containing the optical information and the optical frequency comb C7 are made to interfere with each other to generate the interference signal IM2.

Next, in the envelope strength acquisition step, the interference signals IM1 and IM2 are simultaneously detected by the image pickup camera 161 to obtain the envelope strength EV.

Next, in the optical information extraction step, the optical information of the sample S is extracted based on the envelope strength EV. In the present embodiment, in the envelope strength acquisition step, the envelope strength EV is divided into two envelope strengths EV1 and EV2, and the transmission strength when the envelope strengths EV1 and EV2 pass through the filters F1 and F2 is imaged. Acquired by cameras 241,242. After that, the wavelength information about the sample S is instantly acquired based on the ratio of the transmission intensities of the envelope strengths EV1 and EV2 acquired in the envelope strength acquisition step, and the image processing unit 250 instantly acquires the wavelength information of the sample S from the above-mentioned wavelength information. Is calculated. Specifically, the two-dimensional spectral information or the three-dimensional shape of the sample S can be calculated by comparing the relationship between the wavelength information and the delay distance obtained from the ratio of the intensities measured in advance.

The two-dimensional spectroscopic measurement method of the present embodiment further includes a frequency adjustment step in addition to the above-mentioned steps. In the frequency adjustment step, a part of the optical frequency combs C4 and C5 is fed back to the optical frequency comb emitting unit 103 by the feedback mechanism 128, and according to the phase shift from the optical frequency combs C4 and C5 (time difference δ, see FIG. 3). And adjust the repetition frequency _feedback .

As described above, the two-dimensional spectroscopic measurement method of the present embodiment includes the above-mentioned optical frequency comb generation step, phase difference imparting step, interference signal generation step, envelope strength acquisition step, and optical information extraction step. , Equipped with. The two-dimensional spectroscopic measurement device 200 of the present embodiment includes the above-mentioned optical frequency comb emission unit 103, a first branch unit 104, a second branch unit 105, a phase difference imparting unit 106, and an interference signal generation unit 107. The envelope strength acquisition unit 108 and the image processing unit 250 are provided. In the two-dimensional spectroscopic measurement method and the two-dimensional spectroscopic measurement device 200 of the present embodiment, the repetition frequency f _rep and the carrier envelope offset f _CEO of the optical frequency comb are controlled to set f _rep = 4 × f _CEO , and the repetition frequency f. _The optical frequency comb whose _rep is controlled is divided into two to generate an optical frequency comb whose phase is 90 ° out of phase with each other. The two optical frequency combs that are 90 ° out of phase with each other are optical pulse trains that function as reference light. Each of these two optical frequency combs interferes with an optical frequency comb containing arbitrary optical information, and an interference signal that is 90 ° out of phase is optically generated in real time. An optical frequency comb containing arbitrary optical information is an optical pulse train that functions as probe light. As a result, the envelope strength of the interference signal can be obtained instantly and in real time at the time of measurement. By using an optical frequency comb, the repetition frequency f _rep and the carrier envelope offset f _CEO are controlled with the same level of stability and accuracy as an atomic clock. By controlling the carrier development offset f _CEO , it is possible to take advantage of the phase difference between adjacent optical pulses on the time axis and, in principle, accurately align the phase difference in the entire target wavelength range during measurement. .. Therefore, according to the two-dimensional spectroscopic measurement method and the two-dimensional spectroscopic measurement device 200 of the present embodiment, high-resolution spectroscopic information can be obtained instantly, and two-dimensional spectroscopic measurement can be performed in real time.

In the two-dimensional spectroscopic measurement method and the two-dimensional spectroscopic measurement device 200 of the present embodiment, the fourth optical frequency comb and the fifth optical frequency comb are fed back to the optical frequency comb emitting unit 103, and the fourth optical frequency comb and the fifth optical frequency comb are fed back. The repetition frequency _frep is adjusted according to the phase shift (time difference δ) from the optical frequency comb of 5. This makes it possible to eliminate the phase shift between the optical frequency combs of the reference light. According to the two-dimensional spectroscopic measurement method and the two-dimensional spectroscopic measurement device 200 of the present embodiment, when an optical element such as a mirror constituting the two-dimensional spectroscopic measurement device 200 vibrates and the optical path of the optical frequency comb fluctuates. Even if there is, it is possible to optically compensate for the fluctuation of the optical path of the optical frequency comb without adding a mechanically driven configuration such as a piezo element to the optical system as in the conventional case.

In the two-dimensional spectroscopic measurement method and the two-dimensional spectroscopic measurement device 200 of the present embodiment, the transmission strength when the envelope strengths EV1 and EV2 pass through two filters F1 and F2 whose transmittances have opposite wavelength dependences. Is obtained, and the optical information of the sample S is calculated based on the ratio of the transmitted intensity of the acquired envelope strengths EV1 and EV2. By such a detection method, the wavelength information of the sample S included in the envelope intensity EV can be instantly acquired, and the optical information of the sample S can be acquired in real time with high resolution from the acquired wavelength information.

In the two-dimensional spectroscopic measurement method and the two-dimensional spectroscopic measurement device 200 of the present embodiment, the intensity / phase spectrum including the optical information can be acquired by adding a predetermined delay time to the optical frequency comb C3 by the delay mechanism 206.

The optical information obtained by the two-dimensional spectroscopic measurement method and the two-dimensional spectroscopic measurement device 200 of the present embodiment is the distribution / fluctuation of the refractive index on the optical path of the optical frequency comb C3 or the optical frequency combs C4 and C5, and the shape of the sample S. Any of these is included, and in the above configuration, the three-dimensional shape of the sample S is included. According to the two-dimensional spectroscopic measurement method and the two-dimensional spectroscopic measurement device 200 of the present embodiment, the three-dimensional shape of the sample S can be acquired based on the envelope strength EV, so that the three-dimensional shape measurement can be realized instantaneously and in real time. It can be applied to a wide range of fields including the astronomical field and the physical property field.

Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments. The present invention may be modified within the scope of the gist of the invention described within the claims.

For example, in the above-described embodiment, the optical frequency comb C3 is given the optical information of the sample S by passing through the sample S, but the optical information of the sample S is replaced with the optical frequency comb C3. It may be applied to the optical frequency combs C4 and C5. In that case, the polarized light of the optical frequency combs C4 and C5 are orthogonal to each other, combined, passed through the sample S, and then demultiplexed. Obtaining interference signals (first interference signal, second interference signal) between each of the optical frequency combs C4 and C5 including the optical information of the sample S and the optical frequency combs C6 and C7 not including the optical information of the sample S. Therefore, the same effect as that of the above-described embodiment can be obtained. However, it is assumed that the optical information of the sample S does not have polarization dependence and can be acquired without considering the polarization dependence.

In the two-dimensional spectroscopic measuring apparatus 200 shown in FIG. 12, the optical frequency comb C3 reflected from the sample S is acquired, but the optical frequency comb C3 transmitted from the sample S by irradiating the sample S with the optical frequency comb C3 is obtained. You may get it. In that case, the half mirror 159 may be replaced with a total reflection mirror, and the sample S may be arranged between the total reflection mirror and the half mirror 155 replaced as described above on the path of the optical frequency comb C3.

When measuring the phase spectrum with respect to the sample S in the two-dimensional spectroscopic measuring apparatus 200 of the above-described embodiment, the phase spectrum of the optical frequency comb C3 reflected from the sample S may change with respect to the wavelength. However, the change in the phase spectrum of the optical frequency comb C3 in that case must be uniquely determined with respect to the wavelength. The phase spectrum with respect to the sample S can be obtained by adding a time delay to the optical frequency comb C3 or the optical frequency comb C1 and measuring the delay time dependence of the intensities of the interference signals IM1 and IM2.

In the above embodiment, if the delay mechanism 206 is arranged either on the path of the optical frequency comb C3 between the half mirrors 153 and 159 and on the path of the optical frequency comb C2 between the half mirrors 153 and 112. Good. The configuration of the delay mechanism 206 is not particularly limited as long as a predetermined delay time can be added to the predetermined optical frequency comb. In the two-dimensional spectroscopic measuring apparatus 200 of the above-described embodiment, when the three-dimensional shape of the sample S is instantaneously measured, it is not necessary to sweep the time with the delay mechanism 206. The optical frequency comb C3 is given a delay time derived from the shape of the sample S when the sample S is transmitted or reflected. In the case of instantaneously measuring the three-dimensional shape of the sample S, the optical frequency comb C3 to which the delay time is given is measured by the two-dimensional spectroscopic measuring device 200 of the above-described embodiment excluding the delay mechanism 206 to measure the sample. The delay time derived from the shape of S can be instantly acquired as wavelength information. Acquiring such wavelength information is the same as performing instantaneous three-dimensional shape measurement of the sample S.

In the above-described embodiment, depth information, that is, a three-dimensional shape is obtained as typical optical information of the sample S while maintaining accuracy and stability due to the optical characteristics of the optical frequency comb. However, the optical information of the sample S obtained by the two-dimensional spectroscopic measurement method and the two-dimensional spectroscopic measurement device of the present invention has a three-dimensional shape as long as the time for the optical pulse train of the optical frequency comb to reach the interference signal generation unit is staggered. Not limited to. The optical information of the sample S obtained by the two-dimensional spectroscopic measurement method and the two-dimensional spectroscopic measurement apparatus of the present invention includes, for example, fluctuation of the refractive index. Depending on the type of optical information of the sample S to be acquired, the configuration of the wavelength information acquisition unit and the optical information extraction unit, and the processing content by the program of the processing unit can be appropriately changed.

In the above-described embodiment, the optical frequency combs C4, C5, C6, and C7 may be chirped. When chirping the optical frequency combs C4, C5, C6, and C7, an appropriate dispersion medium is installed on each optical path of the optical frequency combs C2 and C3, which are the sources of these optical frequency combs, and light is applied to the dispersion medium. The frequency combs C2 and C3 may be passed. When the optical frequency combs C4, C5, C6, and C7 are chirped through the dispersion medium in this way, the interference signals IM1 and IM2 do not change, so that the same effects as those in the above-described embodiment can be obtained.

103 ... Optical frequency comb exit unit 104 ... First branch portion 105 ... Second branch portion 106 ... Phase difference imparting unit 107 ... Interference signal generation unit 108 ... Envelope strength Acquisition unit 130: Interference intensity signal acquisition optical system (interference signal intensity acquisition device)
C1 ... Optical frequency comb (first optical frequency comb)
C2 ... Optical frequency comb (second optical frequency comb)
C3 ... Optical frequency comb (third optical frequency comb)
C4 ... Optical frequency comb (4th optical frequency comb)
C5 ... Optical frequency comb (fifth optical frequency comb)
C6 ... Optical frequency comb (third optical frequency comb)
C7 ... Optical frequency comb (third optical frequency comb)
S ... Sample

Claims (10)

A first frequency mode having a predetermined offset frequency with respect to zero on the frequency axis and a plurality of second frequencies arranged at intervals of an integral multiple of a predetermined repetition frequency with respect to the first frequency mode on the frequency axis. An optical frequency comb generation step of generating a first optical frequency comb having a frequency mode and having the repetition frequency four times the offset frequency.
The first optical frequency comb is divided into a second optical frequency comb and a third optical frequency comb, and the second optical frequency comb is divided into a fourth optical frequency comb and a fifth optical frequency comb. A phase difference imparting step of shifting the phase on the time axis of the optical frequency comb of No. 4 by 90 ° with respect to the phase on the time axis of the fifth optical frequency comb, and
The third optical frequency comb or the third optical frequency comb that irradiates the sample with the third optical frequency comb or the fourth optical frequency comb and the fifth optical frequency comb and emits from the sample and contains optical information. A sample irradiation step for obtaining the optical frequency comb of 4 and the 5th optical frequency comb, and
The fourth optical frequency comb containing the optical information in any of them interferes with the third optical frequency comb to generate a first interference signal, and the fifth light containing the optical information in any of them. An interference signal generation step of generating a second interference signal by interfering the frequency comb with the third optical frequency comb,
An envelope strength acquisition step of acquiring the envelope strength from the first interference signal and the second interference signal, and
An optical information extraction step for extracting optical information of the sample based on the envelope strength, and
A two-dimensional spectroscopic measurement method comprising. Further comprising a repeating frequency adjusting step of adjusting the repeating frequency according to the phase shift between the fourth optical frequency comb and the fifth optical frequency comb on the time axis.
The two-dimensional spectroscopic measurement method according to claim 1. In the envelope strength acquisition step,
The transmission intensity when the envelope intensity passes through each of the two filters having opposite wavelength dependence of the transmittance is obtained.
In the optical information extraction step
The optical information is calculated based on the ratio of transmission intensities.
The two-dimensional spectroscopic measurement method according to claim 1 or 2. In the optical information extraction step
A predetermined delay time is added to the second optical frequency comb or the third optical frequency comb to acquire an intensity / phase spectrum including the optical information.
The two-dimensional spectroscopic measurement method according to any one of claims 1 to 3. The optical information includes the distribution of the refractive index on the optical path of any one of the third optical frequency comb, the fourth optical frequency comb, and the fifth optical frequency comb, and the fluctuation of the refractive index. , Including any of the shapes of the samples,
The two-dimensional spectroscopic measurement method according to any one of claims 1 to 4. A first frequency mode having a predetermined offset frequency with respect to zero on the frequency axis and a plurality of second frequencies arranged at intervals of an integral multiple of a predetermined repetition frequency with respect to the first frequency mode on the frequency axis. An optical frequency comb emitting unit that has a frequency mode and emits a first optical frequency comb whose repetition frequency is four times the offset frequency.
A first branch portion that divides the first optical frequency comb into a second optical frequency comb and a third optical frequency comb, and
A second branch portion that divides the second optical frequency comb into a fourth optical frequency comb and a fifth optical frequency comb, and
A phase difference imparting unit that shifts the phase on the time axis of the fourth optical frequency comb by 90 ° with respect to the phase on the time axis of the fifth optical frequency comb.
The third optical frequency comb or the fourth optical frequency comb and the fifth optical frequency comb include arbitrary optical information and cause the fourth optical frequency comb and the third optical frequency comb to interfere with each other. An interference signal generation unit that generates a first interference signal and causes the fifth optical frequency comb to interfere with the third optical frequency comb to generate a second interference signal.
An envelope strength acquisition unit that acquires the envelope strength of the first interference signal and the second interference signal,
An optical information extraction unit that extracts the optical information based on the envelope strength,
A two-dimensional spectroscopic measuring device comprising. A feedback mechanism that acquires a part of the fourth optical frequency comb and the fifth optical frequency comb emitted from the phase difference imparting unit and feeds back to the optical frequency comb emitting unit is further provided.
The two-dimensional spectroscopic measuring apparatus according to claim 6. The envelope strength acquisition unit
It has two filters with opposite wavelength dependence of transmittance.
Obtaining the transmission strength when the envelope strength passes through each of the two filters,
The optical information extraction unit
The optical information is calculated based on the ratio of transmission intensities.
The two-dimensional spectroscopic measuring apparatus according to claim 6 or 7. A delay mechanism for adding a predetermined delay time to the second optical frequency comb or the third optical frequency comb is further provided.
In the optical information extraction unit
Acquire the intensity / phase spectrum including the optical information.
The two-dimensional spectroscopic measuring apparatus according to any one of claims 6 to 8. The optical information includes the distribution of the refractive index on the optical path of any one of the third optical frequency comb, the fourth optical frequency comb, and the fifth optical frequency comb, and the fluctuation of the refractive index. Includes either the shape of a sample placed on the path of the third optical frequency comb, or on the path of the fourth optical frequency comb and the fifth optical frequency comb.
The two-dimensional spectroscopic measuring apparatus according to any one of claims 6 to 9.

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