WO2019167477A1 - Two-dimensional spectroscopy method and two-dimensional spectroscopy device - Google Patents

Abstract

In this two-dimensional spectroscopy method, divided optical pulse trains are obtained by dividing an optical pulse train in which a plurality of optical pulses having a predetermined frequency distribution are arranged chronologically, each of a plurality of optical pulse trains to be received after one of the divided optical pulse trains among the divided optical pulse trains acts on each of measurement areas of an object to be measured is made to interfere with another of the divided optical pulse trains among the plurality of divided optical pulse trains obtained by diving the optical pulse train, and wavelength information for each of the measurement areas of the object to be measured is obtained from the generated interference signals.

Description

2D spectroscopy and 2D spectrometer

The present invention relates to a two-dimensional spectroscopy method and a two-dimensional spectroscopy apparatus. This application claims priority on March 2, 2018 based on Japanese Patent Application No. 2018-0308102 filed in Japan, 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 acquired data, and for example, an expanded 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, in the conventional two-dimensional spectroscopy, since time sweeping takes time, there are problems such as being affected by air fluctuations on the measurement optical path and problems such as being unable to measure a dynamic object. On the other hand, if two-dimensional spectroscopic information can be acquired at once, it is possible to accurately perform spectroscopic measurement of various dynamic objects without being affected by air fluctuations.

As a two-dimensional spectroscopy method, two-dimensional spatial information and one-dimensional wavelength information are acquired at once using, for example, a diffraction grating, or acquired while sweeping a wavelength band transmitted through a variable bandpass filter. The method etc. are mentioned. Non-Patent Document 1 discloses an image slicer type surface spectroscopic unit that is called a slicer and includes an optical element in which a plurality of elongated mirrors are arranged. Non-Patent Document 2 and Non-Patent Document 3 disclose a variable bandpass filter applicable to a technique for acquiring two-dimensional spatial information and one-dimensional wavelength information while sweeping a wavelength band transmitted by a variable bandpass filter. Is disclosed.

However, when the image slicer type surface spectroscopic unit disclosed in Non-Patent Document 1 is used, the resolution of the spatial information depends on the number of divisions of the captured image, and the number of divisions of the spatial information is suppressed to about 24 at the maximum. However, the half width of the wavelength information can be reduced to about 1 nm. On the other hand, 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 2, the spatial resolution is substantially equal to that of the image element. To improve. In the imaging apparatus disclosed in Non-Patent Document 2 and Non-Patent Document 3, as described in Non-Patent Document 3, for example, a temperature stability of ± 0.1 ° C. is used to suppress thermal expansion of a Fabry-Perot filter. Is required. That is, the conventional two-dimensional spectroscopy has a problem that it is difficult to achieve both high resolution and high resolution.

The present invention has been made to solve the above-described problems, and provides a two-dimensional spectroscopy method and a two-dimensional spectroscopy apparatus that can achieve both high resolution and high resolution.

In the two-dimensional spectroscopy of the present invention, the first optical pulse train generating step for generating the first optical pulse train and the second optical pulse train having different relative chirp amounts and the first optical pulse train are different from each other in the object to be measured. An optical pulse train irradiating step for irradiating a measurement region; each of a plurality of light receiving target optical pulse trains after the first optical pulse train has acted on each of the measurement regions of the object to be measured; and the second optical pulse train; An interference signal measurement step of measuring an interference signal generated by causing interference with the signal, and a wavelength information acquisition step of acquiring wavelength information for each measurement region of the object to be measured from the interference signal.

In the above-described two-dimensional spectroscopy, in the optical pulse train irradiation step, the wavelength information acquisition step acquires the chirp amount of at least one optical pulse train of the first optical pulse train and the second optical pulse train. The resolution of the wavelength information to be changed may be changed.

In the above-described two-dimensional spectroscopy, the interference signals may have interference fringes that are different from each other and indicate a wavelength having the lowest interference fringe frequency. In the wavelength information acquisition step, the wavelength having the lowest interference fringe frequency may be acquired as wavelength information for each measurement region of the object to be measured.

In the above-described two-dimensional spectroscopy, in the wavelength information acquisition step, the interference signal is obtained by adding a predetermined delay time to the light receiving target optical pulse train, and the wavelength dependence of the transmittance of the interference signal is reversed to each other. The transmission intensity transmitted through the filter may be acquired, and the spectrum information for each measurement region of the object to be measured may be acquired based on the acquired transmission intensity ratio.

The two-dimensional spectroscopic device of the present invention includes a light source unit that generates a first optical pulse train and a second optical pulse train having different relative chirp amounts, and a first optical pulse train emitted from the light source unit. An optical pulse train irradiating unit for irradiating different measurement regions of the measurement object, each of the plurality of light receiving target optical pulse trains after the first optical pulse train acts on each of the measurement regions of the measurement object, and the second An interference signal generation unit that generates an interference signal with the optical pulse train, and a wavelength information acquisition unit that acquires wavelength information for each measurement region of the object to be measured based on the interference signal generated by the interference signal generation unit And comprising.

In the above-described two-dimensional spectroscopic device, the interference signals may have interference fringes which are different from each other and indicate a wavelength having the lowest interference fringe frequency. In the wavelength information acquisition unit, the wavelength having the lowest interference fringe frequency may be acquired as wavelength information for each measurement region of the object to be measured.

In the above-described two-dimensional spectroscopic device, the interference signal generation unit includes a delay time adjustment mechanism that adds a predetermined delay time to the light reception target optical pulse train, and the wavelength information acquisition unit has the wavelength dependence of the transmittances opposite to each other. A pair filter may be provided.

According to the present invention, a two-dimensional spectroscopic method and a two-dimensional spectroscopic device capable of achieving both high resolution and high resolution are provided.

It is a figure for demonstrating the two-dimensional spectroscopy of this invention, and is a schematic diagram of a chirped light pulse train. It is a schematic diagram for demonstrating the electric field distribution (upper stage) and the intensity distribution (lower stage) on a frequency axis on the time axis of an optical frequency comb. It is a top view which shows the structure of the two-dimensional spectrometer of 1st Embodiment of this invention. It is a top view which shows the structure of the modification of the two-dimensional spectroscopy apparatus shown in FIG. FIG. 4 is a schematic diagram for explaining the principle that an interference signal is generated in the two-dimensional spectroscopic device shown in FIG. 3 and wavelength information of one measurement region of an object to be measured. It is a top view which shows an example of the specific structure of the wavelength information acquisition part of the two-dimensional spectrometer shown in FIG. It is a schematic diagram which shows the structure of a part of interference signal generation part of the two-dimensional spectroscopy apparatus shown in FIG. It is a graph which shows the wavelength dependence of the transmittance | permeability of the pair filter applicable to the two-dimensional spectrometer shown in FIG. It is a schematic diagram which shows the delay time dependence of the transmission intensity of a pair filter applicable to the two-dimensional spectrometer shown in FIG. 6, and is a figure which shows the delay time dependence of the transmission intensity of one filter (F1) of a pair filter. is there. It is a schematic diagram which shows the delay time dependence of the transmission intensity of the pair filter applicable to the two-dimensional spectrometer shown in FIG. 6, and is a figure which shows the delay time dependence of the transmission intensity of the other filter (F2) of the pair filter. is there. It is a schematic diagram which shows the delay time dependence of the transmission intensity of a pair filter applicable to the two-dimensional spectrometer shown in FIG. 6, and is a figure which shows the delay time dependence of the ratio of the transmission intensity of a pair filter.

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

[Principle explanation]
First, the principle of the two-dimensional spectroscopy of the present invention will be described. The two-dimensional spectroscopy of the present invention includes an optical pulse train generation step, an optical pulse train irradiation step, an interference signal measurement step, and a wavelength information acquisition step. In the optical pulse train generation step, a first optical pulse train and a second optical pulse train having different relative chirp amounts are generated. In the optical pulse train irradiation step, the first optical pulse train is applied to different measurement regions of the object to be measured. In the interference signal measuring step, the first optical pulse train is caused to interfere with each of the plurality of light receiving target optical pulse trains after the first optical pulse train has acted on each of the measurement regions of the object to be measured, and the interference generated by the interference. Measure the signal. In the wavelength information acquisition step, wavelength information for each measurement region of the object to be measured is acquired from the interference signal.

In the two-dimensional spectroscopy of one embodiment of the present invention, in the optical pulse train irradiating step, at least one of the two optical pulse trains is optically pulsed with a predetermined frequency distribution with respect to the time axis in time series. A plurality of optical pulse trains (so-called chirp optical pulse trains) are used. That is, at least one of the two optical pulse trains is chirped.

FIG. 1 is a schematic diagram of an optical pulse train (chirped optical pulse train) AP in which a plurality of optical pulses CP (k) having a predetermined frequency distribution with respect to the time axis are arranged in time series. k is an arbitrary natural number and represents a number on the time axis of the optical pulse. In each optical pulse CP (k), the frequency continuously changes on the time axis. Hereinafter, the optical pulse train AP may be referred to as a chirped optical pulse train AP. The method for generating the chirped optical pulse train AP is not particularly limited. In the present embodiment, a technique for obtaining a chirped optical pulse train AP by passing an optical frequency comb through a dispersion medium will be described as an example of a technique for generating a chirped optical pulse train AP.

FIG. 2 is a schematic diagram showing an electric field distribution on the time axis (upper stage) and an intensity distribution on the frequency axis (that is, spectral distribution, lower stage) of the optical frequency comb. As shown in FIG. 2, the relationship shown in the equation (1) is established between the time width τ of the pulse of the optical frequency comb and the frequency spread Δν.

As shown in the upper part of FIG. 2, the optical pulse train oscillated at a constant repetition time _Trep has a constant frequency interval _frep when viewed on the frequency axis. Between the repetition time T _rep and the frequency interval f _rep , the relationship shown in the equation (2) is established.

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. Since the velocity of the carrier wave and the velocity of the wave packet are different from each other, 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 time intervals of a predetermined 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 . The relationship shown in the equation (3) is established among the repetition time T _rep , the time T _CEO and the phase shift φ _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. 2, they are arranged at intervals of the repetition frequency f _rep corresponding to the reciprocal of the time interval T _rep. Many frequency modes are observed. The overall spectral width of the optical frequency comb corresponds to the reciprocal (1 / τ) of the time width of the ultrashort optical pulse.

As shown in the lower part of FIG. 2, the optical frequency comb of the carrier envelope offset _{(Carrier Envelope Offset: CEO) f} CEO 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 (4).

The frequency of the m-th spectrum of the optical comb is expressed as in equation (5) using the repetition frequency f _rep and the carrier envelope offset f _CEO as parameters.

Based on the above-mentioned interrelationship, the carrier wave and the envelope can be controlled by controlling the parameters related to the plurality of frequency modes forming the optical frequency comb. Further, by providing appropriate dispersion to the generated optical frequency comb, a chirped optical pulse train AP having a desired chirp amount can be obtained.

[Two-dimensional spectrometer]
FIG. 3 is a top view showing the configuration of the two-dimensional spectroscopic apparatus 1A of the present invention. As shown in FIG. 3, the two-dimensional spectroscopic device 1A includes a light source 3 that emits an optical pulse train AP, a half mirror 12, an optical pulse train irradiation unit 4, an interference signal generation unit 6, a wavelength information acquisition unit 8, Is provided. The half mirror 12 divides the optical pulse train AP emitted from the light source 3 into a plurality (two in FIG. 3) of divided optical pulse trains DP1 and DP2. The light pulse train irradiation unit 4 irradiates the measurement regions of the measurement object S different from each other with the divided light pulse train (first light pulse train) DP1. The interference signal generation unit 6 interferes with each of the plurality of light receiving target optical pulse trains EP after the split optical pulse train DP1 has acted on each of the measurement regions of the measured object S and the split optical pulse train (second optical pulse train) DP2. A signal IMG is generated. The wavelength information acquisition unit 8 acquires wavelength information for each measurement region of the measured object S based on the interference signal IMG. The light source 3 and the half mirror 12 function as a light source unit that generates the divided optical pulse trains DP1 and DP2 having different relative chirp amounts.

The light source 3 emits the optical pulse train AP controlled with a desired amount of chirp as described above.
The optical pulse train irradiation unit 4 includes half mirrors 12 and 14 and a total reflection mirror 16.

In the configuration shown in FIG. 3, the optical pulse train AP emitted from the light source 3 is divided by the half mirror 12 into the divided optical pulse trains DP1 and DP2. The divided optical pulse train DP1 is reflected by the half mirror 12 and the total reflection mirror 16, passes through the half mirror 14, and is applied to the object S to be measured. The divided light pulse train D1 is reflected from the object to be measured S and includes spectral information of the object to be measured S, becomes a light receiving object light pulse train EP, is reflected by the half mirror 14, and enters the interference signal generator 6. On the other hand, the divided optical pulse train DP2 out of the divided optical pulse trains DP1 and DP2 divided by the half mirror 12 is incident on the interference signal generator 6 as it is.

It should be noted that the spectral information of the measured object S may be included in the light reception target light pulse train EP. Therefore, when the divided optical pulse train DP1 acts on each of the measurement regions of the measured object S, the divided optical pulse train DP1 may be reflected from the measured object S after entering the measured object S as described above. 4 may pass (transmit) the measured object S as shown in FIG. FIG. 4 is a top view showing a configuration of a two-dimensional spectroscopic apparatus 1B which is a modification of the two-dimensional spectroscopic apparatus 1A of the present embodiment. In the configuration of FIG. 4, the measured object S is disposed between the total reflection mirror 16 and the total reflection mirror 15.

3 and 4, only the optical axes of the optical pulse train AP, the divided optical pulse trains DP1 and DP2, and the light receiving target optical pulse train EP are illustrated. These optical pulse trains are diffused and collected by an optical system (not shown). Light and collimated.

FIG. 5 is a schematic diagram for explaining the principle of generating an interference signal and the wavelength information of one measurement region of the object S to be measured. As shown in FIG. 5, in the interference signal generation unit 6, the split optical pulse train DP2 and the light receiving target optical pulse train EP are incident on the beam splitter 22 from different directions and are combined. As an example, the interference signal generation unit 6 generates an interference signal IMG between the split optical pulse DP2 of the positive chirp and the light receiving target optical pulse train EP of the negative chirp. “Negative chirp” represents a chirp opposite to a positive chirp on the wavelength axis (frequency axis). If the split optical pulse train DP2 and the light receiving target optical pulse train EP are combined by the beam splitter 22, and the generated interference signal IMG is wavelength-separated by the diffraction grating 24, <A>, <B>, <C> shown in FIG. Each distribution is obtained. The graph <A> in FIG. 5 shows the relationship between the wavelength and the delay time converted into distance. The graph <B> in FIG. 5 shows the relationship between the wavelength and the intensity of the interference signal IMG and the envelope EV. The graph <C> in FIG. 5 shows the relationship between the delay time and the intensity of the envelope EV.

The wavelength information acquisition unit 8 according to the present embodiment is connected to the interference signal generation unit 6 and includes, for example, a light receiving element capable of detecting the interference signal IMG for each of a plurality of pixels and a program incorporated in a computer. .

[Two-dimensional spectroscopy]
The two-dimensional spectroscopy of the present invention includes an optical pulse train irradiation step, an interference signal measurement step, and a wavelength information acquisition step. In the optical pulse train irradiation step, one of the divided optical pulse trains DP1 and DP2 in which a plurality of optical pulse trains AP in which a plurality of optical pulses having a predetermined frequency distribution with respect to the time axis are arranged in time series is divided into a plurality of divided optical pulse trains DP1. Irradiate different measurement areas of the object S to be measured. In the interference signal measurement step, an interference signal IMG generated by causing the divided optical pulse train DP2 to interfere with each of the plurality of light receiving target optical pulse trains EP after the divided optical pulse train DP1 has acted on each of the measurement regions of the object S to be measured. Measure. In the wavelength information acquisition step, wavelength information for each measurement region of the measured object S is acquired from the interference signal IMG. Using the two-dimensional spectroscopic apparatus 1A shown in FIG.

In the optical pulse train irradiation step, the optical pulse train AP emitted from the light source 3 is divided into at least two divided optical pulse trains DP1 and DP2 by the half mirror 12, and one of the split optical pulse trains DP1 is reflected by the total reflection mirror 16 and then the half mirror. 14 is transmitted and irradiated to different measurement areas of the object S to be measured. The divided optical pulse train DP1 reflects from the measured object S and holds the spectral information of the measured object S as wavelength information. In the optical pulse train irradiation step, the divided optical pulse train DP1 is reflected by the half mirror 14 as the light receiving target optical pulse train EP and is incident on the interference signal generator 6.

In the two-dimensional spectroscopy of the present embodiment, the divided optical pulse train DP2 of the two divided optical pulse trains DP1 and DP2 is transmitted through the half mirror 12 and is incident on the interference signal generation unit 6. In the present embodiment, the divided optical pulse train DP2 is chirp-free with respect to the light receiving target optical pulse train EP that is a chirped optical pulse train. However, instead of the split optical pulse train DP2 being chirp-free with respect to the light reception target optical pulse train EP, the split optical pulse train DP2 may be chirped in the opposite direction on the time axis with respect to the light reception target optical pulse train EP.

In the interference signal measuring step, the light reception target optical pulse train EP and the split optical pulse train DP2 incident on the interference signal generator 6 from different directions are combined to generate an interference signal IMG. The interference signal IMG has interference fringes which are different from each other and indicate a wavelength having the lowest interference fringe frequency. As shown in the graph of <B> in FIG. 5, a plurality of interference fringes with nonuniform intervals on the wavelength axis appear in the interference signal IMG. “Lowest” means that the interference fringe frequency included in the interference signal IMG is relatively lowest, and means that the interval on the wavelength axis is the widest.

In the wavelength information acquisition step, the wavelength having the lowest interference fringe frequency is acquired as wavelength information for each measurement region of the object to be measured. Specifically, the interference signal IMG is detected by the light receiving element. For example, if the target wavelength band for spectroscopic measurement is near-infrared, an array sensor or an image sensor of the order of InGaAs VGA can be applied as the light receiving element. If the wavelength band at the time of spectroscopic measurement is visible light, an 8K image element made of Si can be used as the light receiving element. Other examples of the light receiving element include a far-infrared bolometer, an X-ray scintillator method, and an ultraviolet CCD image element.

In the wavelength information acquisition step, the delay time (Delay) is changed to obtain an interference signal IMG having an envelope EV substantially the same as the spectrum shape of the optical pulse train AP. The peak value of the intensity of the envelope EV depends on the intensity of the optical pulse train AP emitted from the light source 3.

FIG. 6 is a top view of the two-dimensional spectrometer 1C showing an example of a specific configuration of the wavelength information acquisition unit 8 of the two-dimensional spectrometer 1A shown in FIG. A two-dimensional spectroscopic device 1C shown in FIG. 6 includes a half mirror 31, a total reflection mirror 32, a pair filter PF, 2 as a wavelength information acquisition unit 8 in addition to the basic configuration of the two-dimensional spectroscopic device 1A shown in FIG. Imaging cameras (imaging units) 41 and 42 and an image processing unit 50 are provided. The imaging cameras 41 and 42 have the same number of pixels.

In the two-dimensional spectroscopic device 1C, the half mirror 14 is disposed in front of the total reflection mirror 16 on the path of the divided optical pulse train DP1. The object to be measured S is disposed on the path of the divided optical pulse train DP1 that passes through the half mirror 14. Wavelength information (spectral information) of each measurement region of the measured object S is added to the divided light pulse train DP1 incident on the measured object S. The divided optical pulse train DP1 is reflected toward the half mirror 14 as a light receiving target optical pulse train EP including wavelength information of each measurement region. The light receiving target optical pulse train EP is reflected by the half mirror 14 and the total reflection mirror 16 and enters the interference signal generation unit 6 as in the two-dimensional spectroscopic devices 1A and 1B.

FIG. 7 is a schematic diagram showing a partial configuration of the interference signal generation unit 6 in the two-dimensional spectroscopic apparatus 1C. As shown in FIG. 7, a predetermined delay time is added to the light reception target optical pulse train EP incident on the interference signal generation unit 6 by, for example, the delay time adjustment mechanism 26. The delay time adjustment mechanism 26 has two total reflection prisms 27 arranged so that the respective reflection surfaces 27r face each other. When the delay time adjusting mechanism 26 is moved along the arrow M by a control unit (not shown), the optical path length of the light receiving target optical pulse train EP is changed. A delay time corresponding to the amount of movement of the delay time adjusting mechanism 26 is added to the light receiving target optical pulse train EP.

Although not shown, the two- dimensional spectrometers 1A, 1B, and 1C have a configuration for acquiring the interference signal IMG having a phase difference from each other. In such a configuration, for example, the divided optical pulse train DP2 is further divided into two, and the phase of one of the divided optical pulse trains DP2 is shifted by a predetermined amount (preferably 90 °) with respect to the other divided optical pulse train DP2. The optical pulse train DP2 and the light receiving target optical pulse train EP are caused to interfere with each other, and the envelope intensity of each generated interference signal is acquired. The acquired envelope intensity enters the wavelength information acquisition unit 8.

The split optical pulse train DP2 incident on the interference signal generator 6 and a predetermined delay time are added to the light receiving target optical pulse train EP. The light reception target optical pulse train EP is combined by, for example, the beam splitter 22 to generate an interference signal IMG. As shown in FIG. 6, the interference signal IMG (the combined optical pulse train MP) enters the half mirror 31 from the interference signal generation unit 6. The interference signal IMG is divided into two by the half mirror 31, and one interference signal IMG1 is reflected by the total reflection mirror 32 and enters the filter F1 of the pair filter PF. The other interference signal IMG2 enters the filter F2 from the half mirror 31. The filters F1 and F2 may be integrated with the incident portions of the imaging cameras 41 and 42.

FIG. 8 is a graph showing an example of the wavelength dependence of the transmittance of the filters F1 and F2 constituting the pair filter PF. As shown in FIG. 8, it is preferable that the wavelength dependence of the transmittance of the pair filters F1 and F2 is opposite to each other. The transmittance of the filter F1 generally decreases as the wavelength increases. On the other hand, the transmittance of the filter F2 generally increases as the wavelength increases. Thus, since the wavelength dependence of the transmittance of the pair filters F1 and F2 is opposite to each other, a pair of the light intensity ratio and the wavelength relating to the intensity of the envelope EV (hereinafter sometimes referred to as envelope intensity EL). One correspondence is established.

As shown in FIG. 6, the combined optical pulse trains MP1 and MP2 that have passed through the filters F1 and F2 are incident on the light receiving portions (not shown) of the imaging cameras 41 and 42. Input information of each light receiving unit of the imaging cameras 41 and 42 is transmitted to the image processing unit 50. The image processing unit 50 is a computer, for example. The image processing unit 50 incorporates a program such as an image processing program. The image processing unit 50 appropriately processes input information from the imaging cameras 41 and 42 using a program.

The two-dimensional spectroscopy using the two-dimensional spectrometer 1C includes an optical pulse train irradiation step, an interference signal measurement step, and a wavelength information acquisition step similar to those described above.

In the interference signal measurement step, each of the plurality of light receiving target light pulse trains EP after acting on each of the measurement regions of the object S to be measured is combined with the divided light pulse train DP2 by using the beam splitter 22 or the like to interfere with each other. . In order to acquire spectrum information (wavelength information) for each measurement region of the object S to be measured, the combined optical pulse train MP is sent to the wavelength information acquisition unit 8.

FIG. 9A, FIG. 9B, and FIG. 9C are schematic diagrams showing the delay time dependence of the transmission intensity of the filters F1 and F2. In the wavelength information acquisition step, the combined optical pulse trains MP1 and MP2 generated by branching the combined optical pulse train MP subjected to time sweep using the delay time adjusting mechanism 26 have the wavelength dependency of the transmittance shown in FIG. Passes through each of the filters F1, F2. As a result, the transmission intensity changes with the delay time as shown in FIGS. 9A and 9B. Using the imaging cameras 41 and 42, the transmission intensities of the combined optical pulse trains MP1 and MP2 associated with the delay time can be acquired as described above. A broken line in each of FIGS. 9A and 9B represents the transmitted light intensity of the multiplexed light pulse trains MP1 and MP2 when the light does not pass through the filter F1 or the filter F2.

Each measurement area of the object S to be measured corresponds to each pixel of the imaging cameras 41 and 42. As shown in FIG. 9C, when the ratio of the transmission intensity in the filters F1 and F2 is taken, a value equal to the transmittance ratio of each of the filters F1 and F2 appears. Based on these facts, in the wavelength information acquisition step, by using the pair filters F1 and F2, the ratio of the envelope intensity EL for each measurement region of the object S to be measured acquired by the imaging cameras 41 and 42 is determined by the image processing unit 50. Calculate with Based on the ratio of the envelope intensity EL calculated for each pixel of the imaging cameras 41 and 42, the signal intensity ratio of each pixel is obtained, and the wavelength that expresses each intensity in the distribution of the envelope intensity EL is determined. Based on the correspondence relationship between the determined wavelength and the envelope intensity EL, the spectral distribution (wavelength information) of each pixel of the imaging cameras 41, 42, that is, each measurement region of the measured object S is acquired.

The wavelength information of each delay time when the delay time is changed is acquired using the delay time adjustment mechanism 26, and compared with the wavelength change with respect to the original delay time. Thus, it can be seen how much the phase of each wavelength in the measurement object has changed, and the phase spectrum can be measured. However, the change in the phase spectrum in that case is limited to a change that becomes a phase spectrum uniquely determined with respect to the wavelength.

As described above, the two-dimensional spectroscopy of this embodiment includes the above-described optical pulse train irradiation step, interference signal measurement step, and wavelength information acquisition step. According to the two-dimensional spectroscopy of this embodiment, by adjusting the wavelength width (that is, the chirp amount) of each optical pulse CP (k) of the optical pulse train A0 emitted from the light source 3 in the optical pulse train irradiation step. The resolution of the wavelength information acquired in the wavelength information acquisition step can be changed. In the two-dimensional spectroscopy of the present embodiment, the wavelength resolution is determined by the peak wavelength width of the interference signal IMG in the low frequency region. Based on this, the carrier wave and the envelope can be controlled by controlling the parameters (repetition frequency f _rep , carrier envelope offset f _CEO, etc.) relating to a plurality of frequency modes forming the optical frequency comb. By using an appropriate dispersion element, the chirp amount of each optical pulse CP (k) of the chirped optical pulse train AP can be adjusted to a desired amount. As described above, by increasing the chirp amount of the optical pulse CP (k) of the chirped optical pulse train AP, the wavelength width of the peak in the low frequency region of the interference signal IMG is narrowed, and the wavelength resolution of the two-dimensional spectroscopy is increased. can do. That is, the two-dimensional spectroscopy of the present embodiment can achieve both high resolution and high resolution in spectroscopic measurement.

As a method for adjusting the chirp amount of each optical pulse CP (k) of the chirped optical pulse train AP, for example, a dispersion medium is arranged between the half mirror 12 and the total reflection mirror 16, and the divided light is dispersed in the dispersion medium. There is a method of passing the pulse train DP1. Instead of the dispersion medium, for example, a glass rod having a predetermined length, a single mode fiber, a diffraction grating pair, or a prism pair may be used. As described above, in the two-dimensional spectroscopy of the present embodiment, the resolution at the time of spectroscopic measurement can be changed by adjusting the chirp amount of the optical pulse train that is a carrier for spectroscopic measurement. Increase in size can be suppressed.

According to the two-dimensional spectroscopy of the present embodiment, spectral interference is performed using a chirped optical pulse train in which optical pulses CP (k) having different chirp amounts are arranged in time series, and measurement is performed based on the result of the spectral interference. The wavelength information of the measurement region of the object S can be acquired. If there is a light source that can emit light in the wavelength band including the target wavelength band of spectroscopic measurement, and a light receiving element or detector having sensitivity in the target wavelength band, two-dimensional spectroscopy in any target wavelength band is performed. Can do. In other words, the two-dimensional spectroscopy of this embodiment does not depend on the wavelength used. The wavelength band of the target for spectroscopic measurement can be easily adjusted by performing wavelength conversion in accordance with the wavelength band of the target or using an optical frequency comb in the wavelength band of the target. Therefore, unlike conventional spectroscopic methods and spectroscopic apparatuses, it is not necessary to replace optical components such as a filter in accordance with the change of the target wavelength band, and it is not necessary to use very expensive ultra-wideband optical components.

According to the two-dimensional spectroscopy of the present embodiment, the wavelength resolution can be determined and easily adjusted by the relative chirp amount between the split optical pulse train DP2 and the light receiving target optical pulse train EP that cause spectral interference as described above. Thus, it is possible to easily achieve both high resolution and high resolution, instead of either increasing the resolution of spatial information or increasing the resolution of wavelength information as in the prior art.

According to the two-dimensional spectroscopy of this embodiment, the resolution of the spatial information is determined by the irradiation optical system (including the objective lens, for example) used for irradiating the object S to be measured with the divided optical pulse train DP1 and the pixels of the light receiving element. It depends on the size. By adjusting the parameters in the irradiation optical system and the pixel size of the light receiving element, a high-resolution spectroscopic measurement image can be acquired at an arbitrary target wavelength. The highest resolution of the spatial information is determined by the diffraction limit of the optical pulse train AP emitted from the light source 3.

According to the two-dimensional spectroscopy of the present embodiment, a signal from the measurement region of the measurement object S is detected as an interference signal IMG by spectral interference with the divided light pulse train DP2. As a result, simultaneously with the detection of the interference signal IMG, what color signal has reacted in each of the measurement regions (corresponding to one pixel of the light receiving element) of the measured object S, that is, which wavelength signal has reacted. As a result, wavelength information can be acquired instantaneously. This makes it possible to perform two-dimensional spectroscopy without being affected by changes in the surrounding environment and improve measurement accuracy.

According to the two-dimensional spectroscopic method and the two-dimensional spectroscopic apparatus 1C of the present embodiment, since the pair filter PF is used, the intensity that changes substantially monotonously with respect to the delay time for the combined optical pulse trains MP1 and MP2 that have passed through the filters F1 and F2. A ratio is obtained. As a result, the combination of the intensity ratio of the combined optical pulse trains MP1 and MP2 and the delay time (that is, the wavelength) is uniquely determined, and the spectral spectrum in each measurement region of the measurement object S can be acquired. Such a method can be applied to a light source that emits light having an arbitrary spectrum. Further, the wavelength information of each measurement region of the measured object S can be specified based on the intensity received by each pixel of the imaging cameras 41 and 42.

That is, according to the two-dimensional spectroscopy and the two-dimensional spectrometer 1C of the present embodiment, three-dimensional information including two-dimensional spatial information and one-dimensional wavelength information can be acquired with high accuracy. According to the two-dimensional spectroscopic method and the two-dimensional spectroscopic device 1C of the present embodiment, one-dimensional wavelength information can be acquired as a spectrum, that is, an intensity distribution having wavelength dependency, instead of a single wavelength or color. Therefore, the two-dimensional spectroscopic device 1C can be operated like a hyperspectral camera that does not depend on the target wavelength range.

According to the two- dimensional spectrometers 1A, 1B, and 1C of the present embodiment, high-resolution and high-resolution two-dimensional spectroscopy is possible, and the same effect as the above-described two-dimensional spectroscopy can be obtained.

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

For example, the chirped optical pulse train used in the two-dimensional spectroscopy of the present invention is not limited to the one generated by the optical frequency comb as described in the above embodiment. In the above-described embodiment, both of the divided optical pulse trains (first optical pulse train and second optical pulse train) DP1 and DP2 are chirped and have different chirp amounts from each other. At least one of the pulse train and the second optical pulse train may be chirped. That is, only one of the first optical pulse train and the second optical pulse train may be chirp-free.

Further, in the above-described embodiment, only the light reception target optical pulse train EP reflected from the frontmost surface of the measured object S in the traveling direction of the divided optical pulse train DP1 is considered. Therefore, as shown in the graph <B> in FIG. 5, only one interference fringe having the widest fringe spacing on the wavelength axis appears in the interference signal IMG. That is, in the interference signal IMG, an interference fringe indicating only one wavelength having the lowest interference fringe frequency appears. However, in addition to the surface closest to the traveling direction of the divided optical pulse train DP1 in the measured object S, for example, when the received light pulse train EP is reflected also from the inside in the thickness direction of the measured object S, a plurality of interferences are caused. A signal IMG is obtained. That is, it is possible to acquire the same number of interference signals IMG as the number of positions where the light reception target optical pulse train EP is reflected in the thickness direction of the measurement object S. With the plurality of interference signals IMG, information on the wavelength having the lowest interference fringe frequency is obtained for each position where the light reception target optical pulse train EP is reflected. A tomographic image of the object S to be measured is obtained based on the plurality of wavelengths.

In order to obtain a tomographic image of the object S to be measured, an object having a part capable of transmitting at least a part of the optical pulse train AP and reflecting the optical pulse train EP to be received is arranged in the thickness direction as the object S to be measured. .
As the measurement object S in the two- dimensional spectroscopic devices 1A, 1B, and 1C of the above-described embodiment, the measurement object S having transparency in the wavelength band of the optical pulse train AP emitted from the light source 3 is disposed. The tomographic image of the object S can be measured.

1A, 1B, 1C ... Two-dimensional spectroscopic device AP ... Optical pulse train DP1, DP2 ... Divided optical pulse train EP ... Light receiving target optical pulse train MP1, MP2 ... Synthetic optical pulse train S ... Measured object

Claims (7)

1. An optical pulse train generating step for generating a first optical pulse train and a second optical pulse train having different relative chirp amounts;
   An optical pulse train irradiating step of irradiating different measurement regions of the object to be measured with the first optical pulse train;
   Measures an interference signal generated by causing each of a plurality of light receiving target optical pulse trains after the first optical pulse train to act on each of the measurement regions of the object to be measured to interfere with the second optical pulse train. Interference signal measurement process to
   A wavelength information acquisition step of acquiring wavelength information for each measurement region of the object to be measured from the interference signal;
   Two-dimensional spectroscopy.
2. In the optical pulse train irradiation step, the resolution of the wavelength information acquired in the wavelength information acquisition step is changed by adjusting a chirp amount of at least one optical pulse train of the first optical pulse train and the second optical pulse train. Let
   The two-dimensional spectroscopy according to claim 1.
3. The interference signals have interference fringes that are different from each other and indicate the wavelength having the lowest interference fringe frequency;
   In the wavelength information acquisition step,
   The wavelength having the lowest interference fringe frequency is obtained as wavelength information for each measurement region of the measured object.
   The two-dimensional spectroscopy according to claim 1 or 2.
4. In the wavelength information acquisition step,
   A predetermined delay time is added to the optical pulse train to be received to obtain the interference signal, and the transmission intensity obtained by allowing the interference signal to pass through a filter in which the wavelength dependences of the transmittances are opposite to each other is obtained, and the obtained transmission is obtained. Obtaining spectral information for each measurement region of the object to be measured based on the intensity ratio;
   The two-dimensional spectroscopy according to claim 1 or 2.
5. A light source unit that generates a first optical pulse train and a second optical pulse train having different relative chirp amounts;
   An optical pulse train irradiating unit for irradiating the first optical pulse train emitted from the light source unit to different measurement regions of the object to be measured;
   An interference signal generation unit configured to generate an interference signal between each of the plurality of light receiving target optical pulse trains after the first optical pulse train has acted on each of the measurement regions of the object to be measured and the second optical pulse train;
   A wavelength information acquisition unit that acquires wavelength information for each measurement region of the object to be measured based on the interference signal generated by the interference signal generation unit;
   A two-dimensional spectroscopic device.
6. The interference signals have interference fringes that are different from each other and indicate the wavelength having the lowest interference fringe frequency;
   In the wavelength information acquisition unit,
   The wavelength having the lowest interference fringe frequency is acquired as wavelength information for each measurement region of the measured object.
   The two-dimensional spectroscopic apparatus according to claim 5.
7. The interference signal generation unit includes a delay time adjustment mechanism that adds a predetermined delay time to the light reception target optical pulse train,
   The wavelength information acquisition unit includes a pair filter in which the wavelength dependency of transmittance is opposite to each other,
   The two-dimensional spectroscopic apparatus according to claim 5.

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