JP7194437B2 - Interference signal strength acquisition method and interference signal strength acquisition device - Google Patents

Description

The present invention relates to an interference signal strength acquisition method and an interference signal strength acquisition apparatus. This application claims priority based on Japanese Patent Application No. 2018-038103 filed in Japan on March 2, 2018, the content of which is incorporated herein.

Conventionally, many techniques such as imaging, Fourier Transform Infrared Spectroscopy (FT-IR), and dispersive infrared spectroscopy have been used as techniques for obtaining spectral information. With these methods, it is 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 spectral information.

In recent years, in academic fields such as astronomy, earth science, and physical physics, there are increasing expectations for two-dimensional spectroscopy that can simultaneously acquire each piece of information included in two-dimensional spectroscopic information in real time. Two-dimensional spectroscopy is also called area spectroscopy or hyperspectral imaging. If two-dimensional spectral information can be obtained, for example, an image of an arbitrary wavelength can be extracted from the acquired data, and an extended 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 areas) on a two-dimensional plane, FT-IR is performed for each point, thereby acquiring two-dimensional spectral information. However, the conventional two-dimensional spectroscopic method 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 to be transmitted by a variable bandpass 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 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 acquiring two-dimensional spatial information and one-dimensional wavelength information by transmitting light in 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 long time to sweep, and it is difficult to instantaneously obtain high-resolution wavelength information and spectral distribution. Therefore, two-dimensional spectroscopy that sweeps the wavelength band using the variable bandpass filter described above is not suitable for measuring dynamic phenomena. In order to solve such problems, there has been a demand for a technology that enables direct acquisition of wavelength information without sweeping the wavelength band or delay time.

As one method for directly obtaining wavelength information of a sample to be measured, spectral interference between an optical pulse train that does not contain optical information of the sample and an optical pulse train that contains optical information of the sample is used to generate a wavelength-dependent interference signal. A method of measuring the envelope strength is included. Also, as means for measuring the envelope intensity of the wavelength-dependent interference signal, for example, a method based on the Hilbert transform can be used. However, since the Hilbert transform performs Fast Fourier Transform (FFT), a series of interference waveforms to be transformed must be acquired in advance. Therefore, the two-dimensional spectroscopic method based on the Hilbert transform has a problem that the envelope intensity at a certain moment cannot be calculated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and provides an interference signal strength acquisition method and an interference signal strength acquisition apparatus capable of instantaneously acquiring the envelope curve strength of an interference signal.

The interference signal strength acquisition 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 integral multiple of a predetermined repetition frequency for the first frequency mode on the frequency axis. an optical frequency comb generating step for generating a first optical frequency comb having a plurality of spaced apart second frequency modes, wherein the repetition frequency is four times the offset frequency; dividing the 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, and dividing the fourth optical frequency comb A phase difference providing 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, the third optical frequency comb, or the fourth optical frequency comb and the a fifth optical frequency comb containing arbitrary optical information, causing interference between the fourth optical frequency comb and the third optical frequency comb to generate a first interference signal, and the fifth optical frequency comb An interference signal generation step of generating a second interference signal by interfering with the third optical frequency comb, and an envelope strength of obtaining an envelope strength from the first interference signal and the second interference signal and an obtaining step.

The interference signal intensity acquisition method described above 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

The interference signal strength acquisition apparatus of the present invention includes 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 for the first frequency mode on the frequency axis. an optical frequency comb output unit for outputting a first optical frequency comb having a plurality of spaced second frequency modes, the repetition frequency being four times the offset frequency; and the first light. A first branching section that divides the frequency comb into a second optical frequency comb and a third optical frequency comb, and a second branching section that divides the second optical frequency comb into a fourth optical frequency comb and a fifth optical frequency comb. a branching unit, 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 The comb, or the fourth optical frequency comb and the fifth optical frequency comb contain arbitrary optical information, and the fourth optical frequency comb and the third optical frequency comb are caused to interfere to generate a first interference an interference signal generator that generates a signal and causes the fifth optical frequency comb and the third optical frequency comb to interfere with each other to generate a second interference signal; and an envelope strength obtaining unit that obtains the strength of the envelope with respect to the interference signal.

In the interference signal strength acquisition device described above, a part of the fourth optical frequency comb and the fifth optical frequency comb emitted from the phase difference applying unit is acquired, and feedback is provided to the optical frequency comb output unit A mechanism may be further provided.

ADVANTAGE OF THE INVENTION According to this invention, the interference signal strength acquisition method and interference signal strength acquisition apparatus which can acquire the envelope curve strength of an interference signal instantaneously are provided.

It is a figure for demonstrating the two-dimensional spectroscopy measurement method of this invention, and is a schematic diagram of the electric field distribution on a time-axis (upper stage) and intensity distribution (lower stage) on a frequency-axis of an optical frequency comb. FIG. 4 is a schematic diagram showing the electric field distribution on the time axis of an optical frequency comb controlled so as to maintain the relationship that the repetition frequency is four times the carrier envelope offset. 1 is a schematic diagram of a pulse generating optical system for generating optical frequency combs (optical pulse trains) that are 90° out of phase with each other; FIG. FIG. 4 is a schematic diagram for explaining the time interval between the first optical pulse and the second optical pulse on the time axis in the optical frequency comb; FIG. 4 is a schematic diagram showing an example of an optical system for stabilizing fluctuations occurring in the optical path of an optical frequency comb; It is a schematic diagram showing the configuration of an interference signal intensity acquisition device that can be applied to the two-dimensional spectroscopic measurement device of the present invention. 11. It is a schematic diagram which shows the structure of the delay mechanism of the interference signal intensity|strength acquisition apparatus shown in FIG. 6, and the two-dimensional spectroscopy measurement apparatus shown in FIG. FIG. 7 is a perspective view showing transmission and reflection of an optical frequency comb on a half mirror of the interference signal intensity acquisition device shown in FIG. 6 ; FIG. 7 is a perspective view showing how an optical frequency comb is transmitted and reflected by another half mirror of the interference signal intensity acquisition device shown in FIG. 6 ; FIG. 7 is a perspective view showing how an optical frequency comb is transmitted and reflected by still another half mirror of the interference signal intensity acquisition device shown in FIG. 6 ; FIG. 4 is a schematic diagram showing envelope intensity distributions of interference signals that are out of phase with each other by 90°; 1 is a schematic diagram showing the configuration of a two-dimensional spectrometer of the present invention; FIG. 13 is a graph showing the wavelength dependence of the transmittance of the filter of the two-dimensional spectrometer shown in FIG. 12;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of an interference signal strength acquisition method and an interference signal strength acquisition device of the present invention will be described with reference to the drawings.

<Explanation of principle>
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 an 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 Equation (1) holds between the repetition time T _rep and the frequency interval f _rep of the optical pulse train that is oscillated with constant repetition.

Each optical pulse train consists of a superposition of many longitudinal modes propagating inside the cavity of the light source. An optical pulse train is composed of a carrier wave, which is a superposed wave of these longitudinal modes, and a wave packet that constitutes the envelope of the carrier wave. A carrier wave is also called a carrier. A carrier envelope 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 a phase difference occurs over time. A laser cavity is composed of a dispersive 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 phase shift φ _CEO is one cycle at time T _CEO .

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. 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 ) f ₀ and a plurality of frequency modes (second frequency modes) f _m arranged on the frequency axis at intervals of integral multiples of a predetermined repetition frequency f _rep with respect to the frequency mode f ₀ . The carrier envelope offset f _CEO of the optical frequency comb corresponds to the reciprocal of the time T _CEO . The relationship shown in Equation (2) holds among the carrier envelope offset f _CEO , phase shift φ _CEO , and time T _CEO .

The frequency of the n-th spectrum of the optical frequency comb is represented by Equation (3) using the repetition frequency f _rep and the carrier envelope offset f _CEO as parameters.

Based on the interrelationship described above, the carrier wave and envelope can be controlled by controlling the parameters of the multiple frequency modes of the optical frequency comb. In this embodiment, the parameters for multiple 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 equation (4). do.

FIG. 2 is a schematic diagram showing the 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 to maintain the relationship of formula (4). As shown in FIG. 2, the phase shift between optical pulses adjacent to each other on the time axis is (π/2)=90°. The same phase and waveform pattern as those of the reference optical pulse appear in the optical pulse that is four ahead on the time axis from the reference optical pulse. The relationship of equation (5) holds 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 output unit 103, a half mirror (second branch unit) 112, a half mirror 118, total reflection mirrors 114 and 116, and a delay imparting unit (phase difference provision unit) 123. The optical frequency comb output unit 103 includes a function generator (not shown) and the like. The optical frequency comb output unit 103 mainly controls the carrier envelope offset f _CEO so that the repetition frequency f _rep and the carrier envelope offset f _CEO maintain the relationship of formula (4) by operating the function generator, A carrier-envelope offset f _CEO controlled optical frequency comb C1 is launched.

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. Optical frequency comb C4 is reflected by total reflection mirror 116 and enters 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. FIG. The delay imparting section 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 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, and is directed toward the half mirror 118. emit. The positions and separation distances of the total reflection mirrors 121 and 122 are adjusted so that the phase of one of the optical frequency combs C4 and C5 incident on the half mirror 118 is shifted by 90° from the phase of the other. That is, in the optical system 120, the optical frequency comb is branched, and one is delayed with respect to the other by the time difference between a certain optical pulse and the optical pulse one after 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 between the optical frequency combs C4 and C5 fluctuates due to vibrations of various mirrors, air fluctuations, and the like. Based on this, the repetition frequency f _rep of the optical frequency comb C1 is controlled, and the optical pulse repetition time T _rep of the optical frequency comb C1 is finely adjusted to absorb the variation in the optical path difference of the optical frequency combs C4 and C5. and the optical frequency combs C4 and C5 can be stabilized. FIG. 4 shows the first optical pulse <the “1st” optical pulse shown in FIGS. 3 and 4> and the second optical pulse <shown in FIGS. "2nd" light pulse> is a schematic diagram for explaining the time interval. 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 given by equations (6) to (8) using the repetition frequencies f _rep1 , f _rep2 , and f _rep3 . is expressed as

Based on the relative relationship between T _rep and f _rep shown in FIG. 4 and equations (6) to (8), the repetition frequency f _rep of the optical frequency comb C1 is controlled.

As can be seen from FIG. 4 and equations (6) to (8), the _repetition time T _rep 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 that are 90° out of phase with each other, the fluctuations occurring in the optical paths of the optical frequency combs C4 and C5. The time difference δ is further added or reduced by . FIG. 5 is a schematic diagram showing an example of an optical system 124 capable of stabilizing fluctuations occurring 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 . The half mirror 126 is arranged ahead 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 arranged on the paths of the optical frequency combs C4 and C5 different from the optical frequency combs C4 and C5 passing 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 split 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 is reflected by the half mirror 126, enters the feedback mechanism 128, and enters the optical frequency comb output section 103. feedback to This adjusts the repetition frequency f _rep of the optical frequency comb C1. As shown in FIG. 5, the repetition time T _rep of the optical frequency comb C1 output from the optical frequency comb output 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 again becomes 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 which is an interference signal intensity acquisition apparatus of the present invention and which instantaneously acquires interference intensity signals with a phase difference of 90°. The interference intensity signal acquisition optical system 130 includes an optical frequency comb output unit 103, a partial optical system 124P, a branch unit 150, a delay mechanism 206, and an imaging camera (envelope intensity acquisition unit) 161. A partial optical system 124P shown in FIG. 6 shows a configuration of the optical system 124 shown in FIG. The branching unit 150 extracts the optical frequency combs C6 and C7 from the optical frequency comb C3. The splitter 150 includes a half mirror (interference signal generator) 152 , half mirrors (first splitter) 153 , 155 and 158 , and total reflection mirrors 154 , 156 and 157 .

The optical frequency comb output unit 103 outputs 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 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 applying unit 106 shifts the phase of the optical frequency comb C4 on the time axis from the phase of the optical frequency comb C5 on the time axis by 90°. The interference signal generation unit 107 generates an interference signal (first interference signal) IM1 by causing the optical frequency comb C4 and an optical frequency comb (third optical frequency comb) C6 containing arbitrary optical information to interfere with each other. An interference signal (second interference signal) IM2 is generated by causing interference between the frequency comb C5 and an optical frequency comb (third optical frequency comb) C7 containing optical information.

The optical information in this specification refers to the optical characteristics of each optical frequency comb itself, the distribution and fluctuation of the refractive index on the optical path of each optical frequency comb, and the sample added by passing through the sample placed on the optical path. including all the shapes of For example, when the sample S is not installed as in the interference intensity signal acquisition optical system 130 shown in FIG. means the distribution and fluctuation of the refractive index of On the other hand, when a sample S to be measured is arranged as in the two-dimensional spectroscopic measurement device 200 described later, optical characteristics including the shape of the sample S are the main optical information. As shown in FIG. 11, the envelope strength obtaining unit 108 obtains 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 portion 103 is separated by the half mirror 153 into optical frequency combs C2 and C3. The optical frequency comb C2 enters the partial optical system 124P and exits as optical frequency combs C4 and C5 that 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 enters the splitter 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 that adds 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 with their reflecting surfaces 207r facing each other. By moving the delay mechanism 206 along the arrow M, the optical path length of the optical frequency comb C3 is changed and a predetermined delay time is added.

FIG. 8 is a schematic diagram showing 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. 8, of the optical frequency combs C4 and C5, the optical frequency comb C4 is incident on the reflecting surface 118a of the half mirror 118 and reflected substantially perpendicularly 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 is transmitted through the reflecting surface 118b and the reflecting surface 118a of the half mirror 118 opposite to the reflecting surface 118a, and overlaps the course of the optical frequency comb C4 in top view. It 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 deviated from each other.

FIG. 9 is a schematic diagram showing reflection of the optical frequency comb C6 and transmission of the optical frequency comb C7 at the half mirror 158 of the splitter 150. As shown in FIG. As shown in FIG. 9, of 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 reflected substantially perpendicularly to the incident direction when viewed from above. On the other hand, among the optical frequency combs C6 and C7, the optical frequency comb C7 is transmitted through the surface 158b opposite to the reflecting surface 158a of the half mirror 158 and the reflecting surface 158a, and overlaps with the path of the optical frequency comb C6 when viewed from above. It 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 deviated from each other. The height of the course 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 transmission of the optical frequency combs C4 and C5 and reflection of the optical frequency combs C6 and C7 at the half mirror 152 of the splitter 150. FIG. As shown in FIG. 10, the optical frequency combs C4 and C5 emitted from the half mirror 118 pass through the surface 152b of the half mirror 152 opposite to the reflecting surface 152a. 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 to the incident direction in a top view, and the optical frequency combs C4 and C5 transmitted through the surface 152b. and generate interference signals IM1 and IM2. 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 on the half mirror 118 are different from each other, and the irradiation positions of the optical frequency combs C5 and C7 on the half mirror 158 are mutually different. make different. As a result, the position where the optical frequency combs C4 and C6 overlap to generate the interference signal IM1 is different from the position where the optical frequency combs C5 and C7 overlap to generate the interference signal IM2.

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

The envelope intensity EV is detected by the imaging camera 161 as described above. 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 installed in a computer connected to the imaging camera 161 . The interference intensity signal acquisition optical system 130 instantaneously obtains the envelope intensity EV of the interference signals IM1 and IM2 that are out of phase with each other by 90°.

<Interference signal intensity acquisition method>
The interference signal intensity acquisition method of the present invention is a method that can acquire the envelope intensity EV of the interference signals IM1 and IM2 using the interference signal intensity acquisition optical system 130, and includes an optical frequency comb generation step and a phase difference provision step. , an interference signal generation step, and an envelope strength acquisition step.

In the optical frequency comb generating step, an optical frequency comb C1 is generated (see FIG. 1). The optical frequency comb C1 has a frequency mode f 0 with a predetermined carrier envelope offset f _CEO with respect to _zero on the frequency axis, and an integer multiple of a predetermined repetition frequency f _rep with respect to the frequency mode f ₀ on the frequency axis. and a plurality of spaced apart frequency modes _fm . In the optical frequency comb C1, the relationship f _rep =4×f _CEO holds. In order to establish the above relationship, the function generator of the optical frequency comb output unit 103 is used to control the carrier envelope offset f _CEO and the repetition frequency f _rep .

Next, in the phase difference providing 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 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.

In this embodiment, optical information is included in optical frequency comb C3 or optical frequency combs C4 and C5. In the interference signal generating step, the optical frequency comb C4 and the optical frequency comb C6, which contain optical information, are combined and caused to interfere with each other to generate the interference signal IM1. In the interference signal generating step, the optical frequency comb C5 and the optical frequency comb C7, which contain optical information, are combined and interfered to generate the 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. The interference signal strength acquisition method of the present embodiment further includes a frequency adjustment step in addition to the steps described above. In the frequency adjustment step, 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 (time difference δ, see FIG. 3) with the optical frequency combs C4 and C5 is adjusted. to adjust the repetition frequency f _rep .

<Two-dimensional spectrometer>
FIG. 12 is a schematic diagram showing the configuration of the two-dimensional spectrometer 200. As shown in FIG. As shown in FIG. 12, the two-dimensional spectrometer 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 spectrometer 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 (time difference δ, see FIG. 3) with the optical frequency combs C4 and C5 The repetition frequency f _rep 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 and 242 having the same number of pixels, and an image processing unit (optical information extraction unit) 250. And prepare. The total reflection mirror 154 of the interference intensity signal acquisition optical system 130 is replaced with a half mirror 159 . A sample S to be spectroscopically measured is placed on the path of the optical frequency comb C3 passing through the half mirror 159 .

As shown in FIG. 12, the optical frequency comb C3 reflected by the half mirror 153 is transmitted through the half mirror 159 and irradiated onto the sample S. As shown in FIG. The optical frequency comb C3 reflected from the sample S contains optical information including all 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 from the optical frequency comb C3 by the half mirror 155 . Optical information of the sample S is reflected in the interference signals IM1 and IM2. The envelope intensities EV of the interference signals IM1 and IM2 are divided into two by the half mirror 231, and the two divided envelope intensities EV1 and EV2 pass through the filters F1 and F2, respectively.

FIG. 13 is a graph showing the wavelength dependence of transmittance of filters F1 and F2. As shown in FIG. 13, the wavelength dependencies of the transmittances of the filters F1 and F2 are opposite to each other. The transmittance of filter F1 generally decreases as the wavelength increases. On the other hand, the transmittance of filter F2 generally increases as the wavelength increases. Since the wavelength dependencies of the transmittances of the filters F1 and F2 are thus opposite to each other, a one-to-one correspondence is established between the light intensity ratio and the wavelength regarding the envelope intensities EV1 and EV2 that have passed through the filters F1 and F2. .

The image processing unit 50 calculates the transmission intensity ratio of the envelope intensities 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 transmission intensity ratio of the envelope intensities 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 that expresses each intensity within the distribution of the envelope intensity EV is determined. determined instantly. By instantaneously obtaining wavelength information, phase information of the optical frequency comb C3 reflected from the sample S at each spatial position (measurement area) 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 this embodiment, it is assumed that the phase spectrum of the optical frequency comb C6 reflected from the sample S is essentially unchanged when the physical position is acquired instantaneously.

<Two-dimensional spectroscopic measurement method>
The two-dimensional spectroscopic measurement method using the two-dimensional spectroscopic measurement device 200 described above uses the two-dimensional spectroscopic measurement device 200 to instantaneously acquire the envelope strength EV of the interference signals IM1 and IM2, and the obtained envelope strength EV is It is a method capable of obtaining optical information of the sample S based on the above. A two-dimensional spectroscopic measurement method using the two-dimensional spectroscopic measurement device 200 includes an optical frequency comb generation process, a phase difference application process, an interference signal generation process, an envelope intensity acquisition process, and an optical information extraction process. . The optical frequency comb generation step, the phase difference provision step, the interference signal generation step, and the envelope intensity acquisition step in the two-dimensional spectroscopic measurement method using the two-dimensional spectroscopic measurement device 200 are each step of the interference signal intensity acquisition method described above. , redundant description of each step is omitted.

In the optical information extraction step, optical information of the sample S is extracted based on the envelope intensity 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 intensities when the envelope strengths EV1 and EV2 pass through the filters F1 and F2, respectively, are captured. Acquired by cameras 241 and 242 . In the optical information extraction step, wavelength information about the sample S is instantaneously acquired based on the transmission intensity ratio of the envelope intensities EV1 and EV2 acquired in the envelope intensity acquisition step. Calculate the optical information of S. Specifically, the two-dimensional spectral information and 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.

Also in the two-dimensional spectrometer 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 (time difference δ, see FIG. 3) with the optical frequency combs C4 and C5 is corrected. Adjust the repetition frequency f _rep accordingly.

As described above, the interference signal intensity acquisition method of this embodiment includes the above-described optical frequency comb generation step, phase difference provision step, interference signal generation step, and envelope intensity acquisition step. The interference intensity signal acquisition optical system 130 of the present embodiment includes the optical frequency comb output unit 103, the first branch unit 104, the second branch unit 105, the phase difference applying unit 106, and the interference signal generation unit. 107 and an envelope strength acquisition unit 108 . In the interference signal intensity acquisition method and the interference intensity signal acquisition optical system 130 of the present embodiment, the repetition frequency f _rep of the optical frequency comb and the carrier envelope offset f _CEO are controlled to set f _rep =4×f _CEO , and the repetition frequency The optical frequency comb whose f _rep is adjusted is divided into two to generate optical frequency combs that are 90° out of phase with each other. 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 is interfered with an optical frequency comb containing arbitrary optical information to optically generate a 90° out-of-phase interference signal 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 intensity of the interference signal can be obtained instantaneously in real time during measurement. By using an optical frequency comb, the repetition frequency f _rep and carrier envelope offset f _CEO can be controlled with stability and accuracy comparable to an atomic clock. By controlling the carrier-envelope offset _fCEO , the phase difference between adjacent optical pulses on the time axis can be utilized, and in principle, the phase difference can be accurately aligned in the entire target wavelength range during measurement. . Therefore, according to the interference signal intensity acquisition method and the interference intensity signal acquisition optical system 130 of the present embodiment, it is possible to generate reference beams whose phases are accurately shifted by 90° from each other, and to stably control the reference beam and the probe beam. , the envelope strength of the interference signal can be obtained with high accuracy.

In the interference signal intensity acquisition method and the interference intensity signal acquisition optical system 130 of the present embodiment, the optical frequency comb C4 and the optical frequency comb C5 are fed back to the optical frequency comb output unit 103, and the optical frequency comb C4 and the optical frequency comb C5 The repetition frequency f _rep is adjusted according to the phase shift (time difference δ). This can eliminate the phase shift between the optical frequency combs of the reference light. According to the interference signal intensity acquisition method and the interference intensity signal acquisition optical system 130 of the present embodiment, optical elements such as mirrors constituting the interference intensity signal acquisition optical system 130 vibrate, causing fluctuations in the optical path of the optical frequency comb. Even in this case, variations in the optical path of the optical frequency comb can be optically compensated without adding a mechanically driven configuration such as a piezo element to the optical system as in the conventional art.

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 invention can be modified within the scope of the invention described in the claims.

For example, in the above-described embodiment, the optical information of the sample S is imparted to the optical frequency comb C3 by passing the sample S through the optical frequency comb C3. The optical information of the sample S may be given to the optical frequency combs C4 and C5 instead of the optical frequency comb C3. In that case, the polarizations of the optical frequency combs C4 and C5 are made orthogonal to each other, combined, passed through the sample S, and then demultiplexed. Obtaining interference signals (first interference signal, second interference signal) between the optical frequency combs C4 and C5 containing the optical information of the sample S and the optical frequency combs C6 and C7 not containing the optical information of the sample S. , the same effect as 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 obtained without considering the polarization dependence.

In the two-dimensional spectrometer 200 shown in FIG. 12, the optical frequency comb C3 reflected from the sample S is acquired. may be obtained. In that case, the half mirror 159 may be replaced with a total reflection mirror, and the sample S may be placed between the replaced total reflection mirror and the half mirror 155 on the path of the optical frequency comb C3.

In the two-dimensional spectrometer 200 of the above-described embodiment, when measuring the phase spectrum of the sample S, the phase spectrum of the optical frequency comb C3 reflected from the sample S may change. In that case, the phase spectrum of the optical frequency comb C3 must be uniquely determined with respect to wavelength. A phase spectrum for 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.

103... Optical frequency comb emitting part 104... First branching part 105... Second branching part 106... Phase difference providing part 107... Interference signal generating part 108... Envelope intensity 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)

Claims (4)

a first frequency mode having a predetermined offset frequency with respect to zero on the frequency axis; an optical frequency comb generating step for 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 giving step of shifting the phase on the time axis of the 4 optical frequency combs 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. an interference signal generating step of generating a first interference signal by using the third optical frequency comb and causing the fifth optical frequency comb and the third optical frequency comb to interfere to generate a second interference signal;
an envelope strength obtaining step of obtaining envelope strength from the first interference signal and the second interference signal;
An interference signal strength acquisition method comprising: Further 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 interference signal intensity acquisition method according to claim 1. a first frequency mode having a predetermined offset frequency with respect to zero on the frequency axis; an optical frequency comb output unit for outputting a first optical frequency comb having a frequency mode, the repetition frequency being four times the offset frequency;
a first branching section that divides the first optical frequency comb into a second optical frequency comb and a third optical frequency comb;
a second branching section that divides the second optical frequency comb into a fourth optical frequency comb and a fifth optical frequency comb;
a phase difference applying 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. an interference signal generation unit that generates a first interference signal by using the above, and generates a second interference signal by causing the fifth optical frequency comb and the third optical frequency comb to interfere with each other;
an envelope intensity acquisition unit that acquires the envelope intensity of the first interference signal and the second interference signal;
An interference signal strength acquisition device comprising: Further 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 applying unit and feeds it back to the optical frequency comb output unit,
The interference signal strength acquisition device according to claim 3.

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