WO2019167478A1

WO2019167478A1 - Two-dimensional spectroscopic measurement method and two-dimensional spectroscopic measurement device

Info

Publication number: WO2019167478A1
Application number: PCT/JP2019/001898
Authority: WO
Inventors: 薫美濃島; 峰士加藤
Original assignee: 国立大学法人電気通信大学
Priority date: 2018-03-02
Filing date: 2019-01-22
Publication date: 2019-09-06
Also published as: JPWO2019167478A1; JP7194438B2

Abstract

In this two-dimensional spectroscopic measurement method, a first optical frequency comb in which a repetition frequency is four times an offset frequency is generated, the first optical frequency comb is divided into second to fifth optical frequency combs, and the phases of the fourth optical frequency comb and the fifth optical frequency comb on a time axis are offset from each other by 90°. In the two-dimensional spectroscopic measurement method, the envelope strength of the following is acquired: an interference signal of the third and fourth optical frequency combs in which either of said optical frequency combs includes optical information regarding a sample; and an interference signal of the third and fifth optical frequency combs in which either of said optical frequency combs includes optical information regarding a sample. The optical information regarding the sample is then extracted on the basis of the envelope strength.

Description

Two-dimensional spectroscopic measurement method and two-dimensional spectroscopic measurement device

The present invention relates to a two-dimensional spectroscopic measurement method and a two-dimensional spectroscopic measurement apparatus. This 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, as a technique for obtaining spectroscopic information, many techniques such as an imaging method, Fourier transform infrared spectroscopy (FT-IR), and a dispersive infrared spectroscopic method are used. In these methods, it is difficult to obtain two-dimensional spatial information and one-dimensional wavelength information at the same time. Hereinafter, the two-dimensional spatial information and the one-dimensional wavelength information may be collectively referred to as two-dimensional spectral information.

In recent years, in the academic fields such as astronomy, earth science, and physical properties, there is an increasing expectation for two-dimensional spectroscopy that can simultaneously acquire each information included in the 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 a celestial body such as a galaxy can be analyzed in detail. In the conventional two-dimensional spectroscopy, for example, two-dimensional spectroscopic information can be acquired by performing FT-IR for each point while scanning each point (a plurality of measurement regions) on the two-dimensional plane. 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 once, spectroscopic measurement of various dynamic objects can be accurately performed.

As a method of two-dimensional spectroscopy, for example, there is a method of acquiring while sweeping a wavelength band transmitted through a variable band pass filter. Non-Patent Document 1 discloses a variable bandpass filter that can be applied to a method of acquiring two-dimensional spatial information and one-dimensional wavelength information while sweeping a wavelength band transmitted by a variable bandpass filter. .

However, when two-dimensional spatial information and one-dimensional wavelength information are acquired by transmitting light of different wavelength bands with the variable bandpass filter disclosed in Non-Patent Document 1, it is necessary to sweep the wavelength band. Therefore, there is a problem that it takes a sweep time and it is difficult to obtain spectral information such as high-resolution wavelength information and spectral distribution instantaneously. Therefore, two-dimensional spectroscopy that sweeps the wavelength band using the above-described variable bandpass filter is not suitable for measurement of dynamic phenomena.

The present invention has been made to solve the above-described problem, and is a two-dimensional spectroscopic measurement method and a two-dimensional spectroscopic measurement that can instantaneously acquire high-resolution spectroscopic information and perform two-dimensional spectroscopic measurement in real time. Providing equipment.

The two-dimensional spectroscopic measurement method of the present invention includes a first frequency mode having a predetermined offset frequency with respect to zero on the frequency axis and an integer multiple of a predetermined repetition frequency with respect to the first frequency mode on the frequency axis. An optical frequency comb generating step of generating a first optical frequency comb having a plurality of second frequency modes arranged at intervals, wherein the repetition frequency is 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 A phase difference providing step of shifting the phase on the time axis of the second 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 first optical frequency comb Test 5 optical frequency combs And irradiating the sample to obtain the third optical frequency comb or the fourth optical frequency comb and the fifth optical frequency comb that are emitted from the sample and include optical information, The fourth optical frequency comb including the third optical frequency comb is caused to interfere with the third optical frequency comb to generate a first interference signal, and the fifth optical frequency comb including the optical information is included in the third optical frequency comb and the third optical frequency comb. An interference signal generating step of generating a second interference signal by causing interference with the optical frequency comb, and an envelope strength acquisition step of acquiring an envelope strength from the first interference signal and the second interference signal; An optical information extraction step of extracting optical information of the sample based on the envelope intensity.

The above-described two-dimensional spectroscopic measurement method further includes a repetition frequency adjustment step of adjusting the repetition frequency according to a phase shift between the fourth optical frequency comb and the fifth optical frequency comb on the time axis. May be.

Further, in the above-described two-dimensional spectroscopic measurement method, in the envelope intensity acquisition step, the transmission intensity when the envelope intensity passes through each of the two filters whose wavelength dependences are opposite to each other is acquired. In the optical information extraction step, the optical information may be calculated based on the transmission intensity ratio.

In the above 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 an intensity spectrum including the optical information and A phase spectrum may be acquired.

The two-dimensional spectroscopic measurement apparatus according to the present invention includes a first frequency mode having a predetermined offset frequency with respect to zero on the frequency axis and an integer multiple of a predetermined repetition frequency with respect to the first frequency mode on the frequency axis. A first optical frequency comb emitting unit configured to emit a first optical frequency comb having a plurality of second frequency modes arranged at intervals, the repetition frequency being four times the offset frequency, and the first light A first branching unit that divides the frequency comb into a second optical frequency comb and a third optical frequency comb, and a second branching unit that divides the second optical frequency comb into a fourth optical frequency comb and a fifth optical frequency comb. A phase difference providing 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, and the third optical frequency Comb or the fourth optical frequency comb and The fifth optical frequency comb includes arbitrary optical information, causes the fourth optical frequency comb and the third optical frequency comb to interfere with each other to generate a first interference signal, and the fifth optical frequency comb. An interference signal generator for generating a second interference signal by causing a comb to interfere with the third optical frequency comb; and an envelope for acquiring an envelope strength of the first interference signal and the second interference signal A line intensity acquisition unit; and an optical information extraction unit that extracts the optical information based on the envelope intensity.

In the above-described two-dimensional spectroscopic measurement apparatus, feedback that obtains a part of the fourth optical frequency comb and the fifth optical frequency comb emitted from the phase difference applying unit and feeds back to the optical frequency comb emitting unit. A mechanism may be further provided.

In the above-described two-dimensional spectroscopic measurement apparatus, the envelope intensity acquisition unit includes two filters whose transmittance wavelength dependence is opposite to each other, and the envelope intensity passes through each of the two filters. And the optical information extraction unit may calculate the optical information based on the transmission intensity ratio.

The above-described two-dimensional spectroscopic measurement apparatus further includes a delay mechanism that adds 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 above-described two-dimensional spectroscopic measurement method and two-dimensional spectroscopic measurement apparatus, the optical information is an optical frequency of any one of the third optical frequency comb, the fourth optical frequency comb, and the fifth optical frequency comb. The refractive index distribution on the optical path of the comb, the fluctuation of the refractive index, the path of the third optical frequency comb, or 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 are provided a two-dimensional spectroscopic measurement method and a two-dimensional spectroscopic measurement device that instantaneously 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 a schematic diagram of the electric field distribution (upper stage) on the time axis of an optical frequency comb, and the intensity distribution (lower stage) on a frequency axis. It is a schematic diagram which shows the electric field distribution on the time-axis of the optical frequency comb controlled so that the repetition frequency may maintain the relationship which is 4 times the carrier envelope offset. FIG. 3 is a schematic diagram of a pulse generation optical system that generates optical frequency combs (optical pulse trains) that are 90 ° out of phase with each other. It is a schematic diagram for demonstrating the time interval of 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 | variation which arose in the optical path of an optical frequency comb. It is the schematic which shows the structure of the interference signal strength acquisition apparatus applicable to the two-dimensional 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 mode of permeation | transmission / reflection of the optical frequency comb in the half mirror of the interference signal strength acquisition apparatus shown in FIG. It is a perspective view which shows the mode of transmission / reflection of the optical frequency comb in another half mirror of the interference signal strength acquisition apparatus shown in FIG. It is a perspective view which shows the mode of permeation | transmission / reflection of the optical frequency comb in another half mirror of the interference signal strength acquisition apparatus shown in FIG. It is a schematic diagram which shows the envelope intensity distribution of the interference signal which the phase mutually shifted 90 degrees. It is the schematic which shows the structure of the two-dimensional spectroscopy measuring device of this invention. It is a graph which shows the wavelength dependence of the transmittance | permeability of the filter of the two-dimensional spectrometry apparatus shown in FIG.

Hereinafter, embodiments of the two-dimensional spectroscopic measurement method and 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 on the time axis (upper stage) and an intensity distribution on the frequency axis (lower stage) of the optical frequency comb. The intensity distribution on the frequency axis represents a spectral distribution. As shown in the upper part of FIG. 1, the relationship shown in the equation (1) is established between the repetition time T _rep of the optical pulse train oscillated at a constant repetition and the frequency interval f _rep .

Each optical pulse train is composed of a superposition of many longitudinal modes propagating inside a resonator of the light source. The optical pulse train is composed of a carrier wave, which is a superposition wave of these longitudinal modes, and a wave packet constituting an envelope of the carrier wave. A carrier wave is also called a carrier. The envelope of the 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 time. The laser resonator is constituted by a dispersion medium. In an optical pulse train that is repeatedly emitted at intervals of a predetermined repetition time T _rep on the time axis, a phase shift φ _CEO occurs between adjacent pulses. The period of the phase shift φ _CEO is one period at time T _CEO .

When the above 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 f _rep corresponding to the reciprocal of the repetition time T _rep. Many frequency modes are observed.

As shown in the lower part of FIG. 1, the optical frequency comb is 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. ) F ₀ and a plurality of frequency modes (second frequency modes) f _m arranged at intervals of an integer multiple of a predetermined repetition frequency f _rep with respect to the frequency mode f _{0 on} the frequency axis. Carrier envelope offset _{f CEO} of the optical frequency comb is equivalent to the reciprocal of the time _{T CEO.} The carrier envelope offset _{f CEO,} shift phi _CEO phase, between the time _{T CEO,} holds the relationship shown in equation (2).

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

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 based on the above-described correlation. In this embodiment, two parameters of the optical frequency comb, that is, parameters related to a plurality of frequency modes of the optical frequency comb are controlled so that the repetition frequency f _rep and the carrier envelope offset f _CEO maintain the relationship of the expression (4). To do.

FIG. 2 is a schematic diagram showing the electric field distribution on the time axis of the 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 expression (4). As shown in FIG. 2, the phase shift between adjacent optical pulses on the time axis is (π / 2) = 90 °. The same phase and waveform pattern as the reference optical pulse appear in the four optical pulses ahead on the time axis from the reference optical pulse. The relationship of the formula (5) is established between the time T _CEO and the carrier envelope offset f _CEO .

FIG. 3 is a schematic diagram 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 applying unit (phase difference). Granting part) 123. The optical frequency comb emitting unit 103 includes a function generator (not shown). The optical frequency comb emitting unit 103 mainly controls the carrier envelope offset f _CEO so that the repetition frequency f _rep and the carrier envelope offset f _CEO keep the relationship of the expression (4) by the operation of the function generator. The envelope offset f _CEO is emitted from the controlled optical frequency comb C1.

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 enters 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 applying unit 123, and enters the half mirror 118. The delay imparting unit 123 is composed of two total reflection mirrors 121 and 122 with their respective reflecting surfaces facing each other. The optical frequency comb C5 reflected by the total reflection mirror 114 enters the delay applying unit 123, reciprocates a predetermined number of times between the reflection surfaces of the total reflection mirrors 121 and 122 while shifting the optical path, toward the half mirror 118. Exit. The positions and the 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 is delayed by an amount corresponding to 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 T _rep .

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 varies due to vibrations of various mirrors, air fluctuations, and the like. Based on this, the fluctuation of the optical path difference between the optical frequency combs C4 and C5 is absorbed by controlling the repetition frequency f _rep of the optical frequency comb C1 and finely adjusting the repetition time T _rep of the optical pulse of the optical frequency comb C1. In addition, the optical frequency combs C4 and C5 can be stabilized. FIG. 4 shows the first optical pulse <1st optical pulse shown in FIG. 3 and FIG. 4> and the second optical pulse <shown in FIG. 3 and FIG. It is a schematic diagram for demonstrating the time interval with "2nd" optical pulse>. The repetition times T _rep1 , T _rep2 , and T _rep3 between the first optical pulse and the second optical pulse adjacent on the time axis are _expressed by the following equations (6) to (8) according to 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 FIGS. 4 and (6) to (8), the repetition frequency f _rep of the optical frequency comb C1 is controlled.

As can be seen from FIGS. 4 and (6) to (8), the repetition time T _rep is controlled by controlling the repetition frequency f _rep of the optical frequency comb C 1 by operating the function generator of the optical frequency comb emission unit 103. Can be controlled.

As shown in FIG. 3, with respect to the shift of one optical pulse on the time axis of the optical frequency combs C4 and C5 whose phases are shifted from each other by 90 °, fluctuations generated in the respective optical paths of the optical frequency combs C4 and C5. Thus, the time difference δ is further added or the time difference δ is reduced. FIG. 5 is a schematic diagram showing an example of an optical system 124 that can stabilize fluctuations that occur in the optical paths 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. Half mirror 126 is arranged ahead of half mirror 118 in the direction of travel of optical frequency combs C4 and C5. The feedback mechanism 128 is arranged on the path of optical frequency combs C4 and C5 that are separated by the half mirror 126 and different from the optical frequency combs C4 and C5 that pass through the half mirror 126. The optical frequency combs C4 and C5 combined by the half mirror 118 and including the time difference δ are separated into two by the half mirror 126. One of the separated optical frequency combs (parts 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 output unit 103 Feedback. As a result, the repetition frequency f _rep of the optical frequency comb C1 is adjusted. As shown in FIG. 5, the repetition time T _rep of the optical frequency comb C1 emitted from the optical frequency comb emission unit 103 is increased or decreased by the time difference δ. By adjusting the repetition time T _rep with the time difference δ, the phase shift between the optical frequency combs C4 and C5 incident on the half mirror 118 is again 90 °, that is, one optical pulse.

<Interference signal intensity acquisition device>
FIG. 6 is a schematic diagram showing the 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, which is an interference signal intensity acquisition apparatus of the present invention. The interference intensity signal acquisition optical system 130 includes an optical frequency comb emission unit 103, a partial optical system 124P, a branching unit 150, a delay mechanism 206, and an imaging camera (envelope intensity acquisition unit) 161. A partial optical system 124P illustrated in FIG. 6 has a configuration in which the optical frequency comb emitting unit 103 is excluded from the optical system 124 illustrated in FIG. The branching unit 150 takes out the optical frequency combs C6 and C7 from the optical frequency comb C3. The branching unit 150 includes a half mirror (interference signal generating unit) 152, half mirrors (first branching units) 153, 155, and 158, and total reflection mirrors 154, 156, and 157.

The optical frequency comb emitting unit 103 emits an optical frequency comb (first optical frequency comb) C1 in which the repetition frequency f _rep is four times the carrier envelope offset f _CEO . The first branching unit 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 branching unit 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 providing 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 generates an interference signal (first interference signal) IM1 by causing the optical frequency comb C4 and the optical frequency comb (third optical frequency comb) C6 including arbitrary optical information to interfere with each other. The frequency comb C5 and an optical frequency comb (third optical frequency comb) C7 including optical information are caused to interfere with each other to generate an interference signal (second interference signal) IM2.

The optical information in this specification is added by passing through a sample placed on the optical path, optical characteristics of each optical frequency comb itself, refractive index distribution / fluctuation on the optical path of each optical frequency comb, and so on. This includes all sample shapes. Further, the shape of the sample includes an uneven shape on 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, it is possible to acquire shape information such as the surface of the sample or the internal structure. 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 the optical characteristics of the optical frequency comb C3 itself and the optical path of the optical frequency combs C3, C6, C7. This means the refractive index distribution and fluctuation. On the other hand, when the sample S to be measured is arranged as in a two-dimensional spectroscopic measurement apparatus 200 described later, the optical information mainly includes optical characteristics including the shape of the sample S. As illustrated 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 emission unit 103 is separated into optical frequency combs C2 and C3 by a half mirror 153. The optical frequency comb C2 enters the partial optical system 124P and exits as optical frequency combs C4 and C5 whose phases are shifted by 90 ° as described above. On the other hand, the optical frequency comb C3 reflected by the half mirror 153 enters the branching unit 150, is reflected by the total reflection mirror 154, and is separated by the half mirror 155 into optical frequency combs C6 and C7.

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 includes two total reflection prisms 207 in which respective reflection surfaces 207 r are arranged to face each other. As 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 diagram showing the state of reflection of the optical frequency comb C4 and transmission of the optical frequency comb C5 at the half mirror 118 of the partial optical system 124P (that is, the optical system 124). As shown in FIG. 7, out 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 when viewed from above. On the other hand, of the optical frequency combs C4 and C5, the optical frequency comb C5 transmits the surface 118b and the reflective surface 118a opposite to the reflective surface 118a of the half mirror 118, and overlaps the path of the optical frequency comb C4 in top view. The light is emitted from the half mirror 118 along the course. In the height direction, the paths of the optical frequency combs C4 and C5 are shifted from each other.

FIG. 9 is a schematic diagram showing a state of reflection of the optical frequency comb C6 and transmission of the optical frequency comb C7 in the half mirror 158 of the branching unit 150. As shown in FIG. 9, among the optical frequency combs C6 and C7, the optical frequency comb C6 is incident on the reflecting surface 158a of the half mirror 158 and is reflected substantially at right angles to the incident direction in a top view. On the other hand, of the optical frequency combs C6 and C7, the optical frequency comb C7 transmits the surface 158b and the reflective surface 158a opposite to the reflective surface 158a of the half mirror 158, and overlaps the path of the optical frequency comb C6 in top view. The light is emitted from the half mirror 158 along the course. In the height direction, the paths of the optical frequency combs C6 and C7 are shifted from each other. The height of the path of the optical frequency comb C6 matches the height of the optical frequency comb C4, and the height of the optical frequency comb C7 matches the height of the optical frequency comb C5.

FIG. 10 is a schematic diagram showing a state of transmission of the optical frequency combs C4 and C5 and reflection of the optical frequency combs C6 and C7 in the half mirror 152 of the branching unit 150. As shown in FIG. 10, the optical frequency combs C <b> 4 and C <b> 5 emitted from the half mirror 118 pass through the surface 152 b on the opposite side of the reflection surface 152 a 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 at a substantially right angle with respect to the incident direction in a top view and transmitted through the surface 152b. Interference signals IM1 and IM2 are generated. The interference signal IM1 is an interference signal between the optical frequency combs C4 and C6, and the interference signal IM2 is an interference signal between the optical frequency combs C5 and C7. In this 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 made different from each other, and the irradiation positions of the optical frequency combs C5 and C7 in the half mirror 158 are mutually different. Make it different. Accordingly, the position where the optical frequency combs C4 and C6 are overlapped to generate the interference signal IM1 is different from the position where the optical frequency combs C5 and C7 are overlapped to generate the interference signal IM2.

Since the phases of the optical frequency combs C4 and C5 are shifted from each other by 90 °, the phases of the interference signals IM1 and IM2 are shifted from each other by 90 °. FIG. 11 is a graph showing an example of the envelope intensity 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 intensity EV is detected by the imaging camera 161. The envelope intensity EV detected by the imaging camera 161 is appropriately processed by a processing unit (not shown) attached to the imaging camera 161. The processing unit is, for example, a program built in a computer connected to the imaging camera 161. In the interference intensity signal acquisition optical system 130, the envelope intensity EV of the interference signals IM1 and IM2 whose phases are shifted from each other by 90 ° can be instantaneously obtained.

<Two-dimensional spectroscopic measurement device>
FIG. 12 is a schematic diagram showing the configuration of the two-dimensional spectroscopic measurement apparatus 200 of the present invention. As illustrated in FIG. 12, the two-dimensional spectroscopic measurement apparatus 200 includes a wavelength information acquisition unit 208 in place of the single imaging 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 apparatus 200, the optical frequency combs C4 and C5 are fed back to the optical frequency comb output 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). Accordingly, the repetition frequency f _rep is adjusted.

The wavelength information acquisition unit 208 includes a half mirror 231, a total reflection mirror 232, filters F1 and F2, two

imaging cameras

241 and 242 having the same number of pixels, and an image processing unit (optical information extraction unit) 250. With. The total reflection mirror 154 of the interference intensity signal acquisition optical system 130 is replaced with a half mirror 159. The sample S that 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 is irradiated onto the sample S. The optical frequency comb C3 reflected from the sample S includes optical information including all the spectral information and phase / shape information of the sample S. The optical information of the sample S is also included in the optical frequency combs C6 and C7 divided into two by the half mirror 155 from the optical frequency comb C3. The optical information of the sample S is reflected in the interference signals IM1 and IM2. The envelope strength EV of the interference signals IM1 and IM2 is 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 dependences of the transmittances of the filters F1 and F2 are 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. As described above, the wavelength dependency of the transmittance of the filters F1 and F2 is opposite to each other, so that there is a one-to-one correspondence between the light intensity ratio and the wavelength for the envelope intensities EV1 and EV2 that have passed through the 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 and 242 through the filters F1 and F2. Based on the ratio of the transmission intensity of the envelope intensity EV1 and EV2 calculated for each pixel of the

imaging cameras

241 and 242, the signal intensity ratio of each pixel is obtained, and the wavelength expressing each intensity in the distribution of the envelope intensity EV is Determined instantly. By obtaining the wavelength information instantaneously, the phase information of the optical frequency comb C3 reflected from the sample S at each spatial position (measurement region) is measured. The phase information of the optical frequency comb C3 is a time difference and indicates a physical position difference and a refractive index difference. In this embodiment, when the physical position is acquired instantaneously, it is assumed that the phase spectrum of the optical frequency comb C6 reflected from the sample S basically does not change.

<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 providing step, a sample irradiation step, an interference signal generation step, an envelope intensity acquisition step, and an optical information extraction step. In the two-dimensional spectroscopic measurement method according to an embodiment of the present invention, the envelope intensity EV of the interference signals IM1 and IM2 is instantaneously acquired 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.

In the optical frequency comb generation step, an 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 A plurality of frequency modes f _m arranged at intervals. In the optical frequency comb C1, a relationship of f _rep = 4 × f _CEO is established. In order to establish the above-mentioned relationship, the carrier envelope envelope offset f _CEO and the repetition frequency f _rep are controlled using a function generator of the optical frequency comb emitting unit 103 or the like.

Next, in the phase difference providing step, the optical frequency comb C1 is divided into the optical frequency comb C2 and the optical frequency comb C3 by the half mirror 153, and the optical frequency comb C2 is further divided into the optical frequency comb C4 by the half mirror 112 (see FIG. 3). Divide into optical frequency comb C5. Subsequently, the delay applying 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 comb C3 or the optical frequency combs C4 and C5, and the optical frequency comb C3 or the optical frequency combs C4 and C5 which are emitted from the sample S and include optical information are obtained.

In this embodiment, the optical frequency comb C3 or the optical frequency combs C4 and C5 includes arbitrary optical information. In the interference signal generation step, the optical frequency comb C4 and the optical frequency comb C6 including optical information in any one of them are caused to interfere with each other to generate an interference signal IM1. In the interference signal generating step, the optical frequency comb C5 and the optical frequency comb C7 including optical information in any one of them are caused to interfere with each other to generate an interference signal IM2.

Next, in the envelope strength acquisition step, the interference signals IM1 and IM2 are simultaneously detected by the imaging 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 intensity EV. In this 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, respectively, is imaged. Obtained by the

cameras

241 and 242. Thereafter, wavelength information regarding the sample S is acquired instantaneously based on the ratio of the transmission intensities of the envelope strengths EV1 and EV2 acquired in the envelope intensity acquisition step, and the optical information of the sample S is obtained from the wavelength information described above by the image processing unit 250. Is calculated. Specifically, the two-dimensional spectroscopic information or the three-dimensional shape of the sample S can be calculated by comparing with the relationship between the wavelength information obtained from the intensity ratio measured in advance and the delay distance.

The two-dimensional spectroscopic measurement method of this embodiment further includes a frequency adjustment step in addition to the above-described steps. In the frequency adjustment step, a part of the optical frequency combs C4 and C5 is fed back to the optical frequency comb output 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) To adjust the repetition frequency f _rep .

As described above, the two-dimensional spectroscopic measurement method of the present embodiment includes the above-described optical frequency comb generation step, phase difference application step, interference signal generation step, envelope intensity acquisition step, and optical information extraction step. . The two-dimensional spectroscopic measurement apparatus 200 of this embodiment includes the above-described optical frequency comb emitting unit 103, the first branching unit 104, the second branching unit 105, the phase difference providing unit 106, and the interference signal generating unit 107. And an envelope strength acquisition unit 108 and an image processing unit 250. In the two-dimensional spectroscopic measurement method and the two-dimensional spectroscopic measurement apparatus 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 be f _rep = 4 × f _CEO , and the repetition frequency f _The optical frequency comb whose _rep is controlled is divided into two to generate optical frequency combs whose phases are shifted from each other by 90 °. 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 including arbitrary optical information, and an interference signal whose phase is shifted by 90 ° is optically generated in real time. The optical frequency comb including 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 acquired instantaneously and in real time during measurement. By using the optical frequency comb, the repetition frequency f _rep and the carrier envelope offset f _CEO are controlled with the same degree of stability and accuracy as the atomic clock. By controlling the carrier envelope offset f _CEO , the phase difference between the adjacent optical pulses on the time axis can be utilized, and in principle, the phase difference can be accurately aligned in the entire wavelength range to be measured. . Therefore, according to the two-dimensional spectroscopic measurement method and the two-dimensional spectroscopic measurement apparatus 200 of the present embodiment, high-resolution spectroscopic information can be acquired instantaneously, and two-dimensional spectroscopic measurement can be performed in real time.

In the two-dimensional spectroscopic measurement method and the two-dimensional spectroscopic measurement apparatus 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 second optical frequency comb are combined. The repetition frequency f _rep is adjusted according to the phase shift (time difference δ) with respect to the optical frequency comb 5. As a result, the phase shift between the optical frequency combs of the reference light can be eliminated. According to the two-dimensional spectroscopic measurement method and the two-dimensional spectroscopic measurement apparatus 200 of the present embodiment, when an optical element such as a mirror constituting the two-dimensional spectroscopic measurement apparatus 200 vibrates and the optical path of the optical frequency comb changes. Even in such a case, the optical path variation of the optical frequency comb can be optically compensated without adding a mechanically driven configuration such as a piezo element to the optical system.

In the two-dimensional spectroscopic measurement method and the two-dimensional spectroscopic measurement apparatus 200 according to the present embodiment, the transmission intensities when the envelope intensities EV1 and EV2 pass through two filters F1 and F2 whose transmittances have wavelength dependencies opposite to each other. And the optical information of the sample S is calculated based on the ratio of the transmission intensity of the acquired envelope intensities EV1 and EV2. By such a detection method, the wavelength information of the sample S included in the envelope intensity EV can be acquired instantaneously, 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 apparatus 200 according to the present embodiment, an intensity / phase spectrum including 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 apparatus 200 of the present embodiment includes the distribution and 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. In any of the above-described configurations, the three-dimensional shape of the sample S is included. According to the two-dimensional spectroscopic measurement method and the two-dimensional spectroscopic measurement apparatus 200 of the present embodiment, since the three-dimensional shape of the sample S can be acquired based on the envelope strength EV, instantaneous and real-time three-dimensional shape measurement is realized, It can be applied to a wide range of fields including astronomy and physical properties.

As mentioned above, although the preferable embodiment of this invention was explained in full detail, this invention is not limited to the above-mentioned embodiment. The present invention can be modified within the scope of the gist of the present invention described in the claims.

For example, in the above-described embodiment, when the optical frequency comb C3 passes through the sample S, the optical information of the sample S is given to the optical frequency comb C3. However, the optical information of the sample S is changed to the optical frequency comb C3. May be given to the optical frequency combs C4 and C5. In that case, the polarizations of the optical frequency combs C4 and C5 are multiplexed so as to be orthogonal to each other, and after passing through the sample S, are demultiplexed. Obtaining interference signals (first interference signal, second interference signal) between 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 Thus, 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 dependency and can be acquired without considering the polarization dependency.

In the two-dimensional spectroscopic measurement apparatus 200 shown in FIG. 12, the optical frequency comb C3 reflected from the sample S is acquired. However, 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 this case, the half mirror 159 may be replaced with a total reflection mirror, and the sample S may be disposed between the total reflection mirror and the half mirror 155 in which the sample S is replaced as described above on the path of the optical frequency comb C3.

In the two-dimensional spectroscopic measurement apparatus 200 of the above-described embodiment, when measuring the phase spectrum related to the sample S, the phase spectrum of the optical frequency comb C3 reflected from the sample S may change with respect to the wavelength. However, the change of the phase spectrum of the optical frequency comb C3 in that case must be uniquely determined with respect to the wavelength. The phase spectrum related 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 intensity of the interference signals IM1 and IM2.

In the above-described embodiment, if the delay mechanism 206 is disposed either on the path of the optical frequency comb C3 between the half mirrors 153 and 159 or 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 a predetermined optical frequency comb. In the two-dimensional spectroscopic measurement 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. When the three-dimensional shape of the sample S is instantaneously measured, the optical frequency comb C3 to which the delay time is given is measured by the two-dimensional spectroscopic measurement apparatus 200 of the above-described embodiment excluding the delay mechanism 206, whereby the sample The delay time derived from the shape of S can be instantaneously 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 apparatus of the present invention is 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 shifted. It is 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, a refractive index fluctuation. 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 the optical path of each of the optical frequency combs C2 and C3 that are the sources of these optical frequency combs, and light is transmitted 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 of the above-described embodiment can be obtained.

DESCRIPTION OF SYMBOLS 103 ... Optical frequency comb output part 104 ... 1st branch part 105 ... 2nd branch part 106 ... Phase difference providing part 107 ... Interference signal generation part 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 (fourth 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

A first frequency mode having a predetermined offset frequency with respect to zero on the frequency axis, and a plurality of second frequency lines 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 generating step of generating a first optical frequency comb having a frequency mode, wherein the repetition frequency is four times the offset frequency;
Dividing the first optical frequency comb into a second optical frequency comb and a third optical frequency comb; dividing the second optical frequency comb into a fourth optical frequency comb and a fifth optical frequency comb; A phase difference providing step of shifting 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;
Irradiating a sample with the third optical frequency comb or the fourth optical frequency comb and the fifth optical frequency comb, the third optical frequency comb emitted from the sample and including optical information, or the first A sample irradiation step for obtaining four optical frequency combs and the fifth optical frequency comb;
The fifth optical frequency comb including the optical information is generated by causing the fourth optical frequency comb including the optical information to interfere with the third optical frequency comb to generate a first interference signal. An interference signal generating step of generating a second interference signal by causing a frequency comb to interfere with the third optical frequency comb;
An envelope strength acquisition step of acquiring an envelope strength from the first interference signal and the second interference signal;
An optical information extraction step of extracting optical information of the sample based on the envelope intensity;
A two-dimensional spectroscopic measurement method comprising:
A repetition frequency adjustment step of adjusting the repetition frequency according to a 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,
Obtaining the transmission intensity when the envelope intensity passes through each of the two filters whose transmittance wavelength dependence is opposite to each other;
In the optical information extraction step,
Calculating the optical information based on the ratio of the transmitted intensity;
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, and an intensity / phase spectrum including the optical information is acquired.
The two-dimensional spectroscopic measurement method according to any one of claims 1 to 3.
The optical information includes a refractive index distribution on an optical path of any one of the third optical frequency comb, the fourth optical frequency comb, and the fifth optical frequency comb, and fluctuation of the refractive index. Including any of the sample shapes,
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 frequency lines 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 emits a first optical frequency comb having a frequency mode and the repetition frequency is four times the offset frequency;
A first branch that divides the first optical frequency comb into a second optical frequency comb and a third optical frequency comb;
A second branch that divides the second optical frequency comb into a fourth optical frequency comb and a fifth optical frequency comb;
A phase difference providing 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 contain arbitrary optical information, and cause the fourth optical frequency comb and the third optical frequency comb to interfere with each other. Generating a first interference signal, and causing the fifth optical frequency comb and the third optical frequency comb to interfere with each other to generate a second interference signal;
An envelope strength acquisition unit for acquiring an 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 intensity;
A two-dimensional spectroscopic measurement apparatus.
A feedback mechanism for acquiring a part of the fourth optical frequency comb and the fifth optical frequency comb emitted from the phase difference providing unit and feeding back to the optical frequency comb output unit;
The two-dimensional spectroscopic measurement apparatus according to claim 6.
The envelope strength acquisition unit
It has two filters whose wavelength dependency of transmittance is opposite to each other,
Obtaining the transmission intensity when the envelope intensity passes through each of the two filters;
The optical information extraction unit
Calculating the optical information based on the ratio of the transmitted intensity;
The two-dimensional spectroscopic measurement 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;
In the optical information extraction unit,
Obtaining an intensity / phase spectrum including the optical information;
The two-dimensional spectroscopic measurement apparatus according to any one of claims 6 to 8.
The optical information includes a refractive index distribution on an optical path of any one of the third optical frequency comb, the fourth optical frequency comb, and the fifth optical frequency comb, and fluctuation of the refractive index. Any of the shapes of the samples arranged on the path of the third optical frequency comb or on the paths of the fourth optical frequency comb and the fifth optical frequency comb,
The two-dimensional spectroscopic measurement apparatus according to any one of claims 6 to 9.