JP2011007669A - Terahertz spectroscopic system and substance identification method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a terahertz spectroscopic system which is low cost, as well as, being simple in configuration.SOLUTION: Terahertz signals used for measurement are irradiated to a measuring object 100 at a plurality of limited single frequencies; the intensity ratio of transmitted wave or reflected wave at each frequency is calculated and is compared with the intensity ratios of candidate substances; and a candidate substance where the error of the intensity ratio is to lie within a predetermined range is specified. Thus, a candidate substance contained in the measuring object 100 is specified at low cost.

Description

  The present invention relates to a terahertz spectroscopy system that identifies a substance using terahertz waves and a substance identification method using the system.

  In recent years, the use of terahertz waves in a region exceeding 100 GHz has been attracting attention in the fields of medical care, food, and security. This is because various substances exhibit characteristic absorption spectra (fingerprint spectra) in the terahertz region. For example, as shown in FIG. 9, it has been shown that terahertz waves are effective for nondestructive identification of drugs (see Non-Patent Document 1). For spectrum measurement of terahertz waves, for example, terahertz time domain spectroscopy (THz-TDS) using the apparatus shown in FIG. 10 is generally used (see Non-Patent Document 2). In the identification of a substance using a conventional terahertz wave, a spectrum curve is measured over a wide frequency range, and a person is identified qualitatively from a characteristic peak position of a continuous spectrum (see Patent Document 1). ).

JP 2008-151760 A

K. Kawase, Y. Ogawa, Y. Watanabe, and H. Inoue, "Non-destructive terahertz imaging of illicit drugs using spectral fingerprints", Opt. Exp., 2003, Vol. 11, No. 20, p.2549- 2554 Katsuhiro Ajido, Yuko Ueno, Tsuneyuki Haga, Naoya Kyutsu, "Terahertz Spectroscopy", NTT Technical Journal, 2008, Vol. 20, No. 12, p.33-36 M. Izutsu, S. Shikama, and T. Sueta, "Integrated Optical SSB Modulator / Frequency Shifter", IEEE JOURNAL OF QUANTUM ELECTRONICS, November 1981, Vol.QE-17, No. 11, p.2225-2227

  However, THz-TDS has a drawback that the system is increased in size and cost, such as a femtosecond laser and a mechanical stage with high accuracy for performing time delay scanning.

  In THz-TDS, a pulse signal including a wide frequency component is used for measurement. Currently, radio waves above 275 GHz are not regulated as radio waves, but if the use of these frequency bands expands as technology advances in the future, radiation of terahertz radio waves is also regulated by law, and inspection and measurement Only limited frequency bands may be allowed for the purpose.

  The present invention has been made in view of the above, and an object thereof is to provide an inexpensive terahertz spectroscopy system.

  The terahertz spectroscopy system according to the first aspect of the present invention measures terahertz wave irradiating means for irradiating a plurality of terahertz waves having different frequencies, and the intensity of a transmitted wave or a reflected wave when each of the plurality of terahertz waves is irradiated to a measurement object. Measuring means, and for each of the intensities measured by irradiating each of the plurality of terahertz waves to the candidate substance, a ratio of the other intensity to the reference when one of the intensities is used as a reference is set as the candidate substance intensity ratio The stored storage means and the intensity of each of the plurality of terahertz waves measured by the measurement means are received, and the ratio of the other intensity to the reference when one of the intensity is used as a reference is calculated as the measurement target intensity ratio And identifying means for identifying the measurement object by comparing the measurement object intensity ratio with the candidate substance intensity ratio stored in the storage means. And features.

  In the above terahertz spectroscopy system, the terahertz wave irradiating means includes a light source that generates a plurality of modes having a predetermined frequency interval, an extraction means that extracts two of the plurality of modes, and a plurality of signals that output signals having different frequencies. An oscillator, a switch for selecting one signal from signals output from a plurality of oscillators, and one of the two modes are input, and the frequency of the mode is changed based on the frequency of the signal selected by the switch. A modulator, an optical coupler that combines one mode whose frequency has changed and the other of the two modes, a photoelectric converter that converts an optical signal including the two combined modes into a terahertz wave, and It is characterized by having.

  In the terahertz spectroscopy system, the terahertz wave irradiation means includes a continuous light source that outputs an optical signal continuously including a wide frequency region, a first optical coupler that branches an optical signal output from the continuous light source, and one branched A first filter that cuts out an optical signal of a predetermined frequency from the optical signal of the first, a plurality of second filters that cut out optical signals of a plurality of different frequencies, and the other branched optical signal. An optical switch that selects one of the two filters and inputs the other optical signal to the selected second filter; and a second optical coupler that combines the optical signals output by the first and second filters. And a photoelectric converter that converts the combined optical signal into a terahertz wave.

  In the terahertz spectroscopy system, the terahertz wave irradiation means includes a first single mode laser that outputs a mode having a predetermined frequency, a plurality of second single mode lasers that output modes having different frequencies, and a plurality of second modes. An optical switch that selects one of the outputs of the single-mode laser, and an optical coupler that combines the output of the first single-mode laser and the output of the second single-mode laser selected by the optical switch And a photoelectric converter that converts an optical signal including two modes into a terahertz wave.

  In the terahertz spectroscopy system, the terahertz wave irradiation means includes a plurality of oscillators that output signals having different frequencies, a switch that selects one of the signals output from the plurality of oscillators, and a frequency multiplication of the signal selected by the switch. And a frequency multiplier that radiates a terahertz wave.

  In the above terahertz spectroscopy system, the terahertz wave irradiation means outputs a first oscillator that outputs a signal of a predetermined frequency, a plurality of second oscillators that output signals of different frequencies, and a plurality of second oscillators that output A switch that selects one of the signals to be transmitted, and a harmonic mixer that multiplies the signal output by the first oscillator and radiates a terahertz wave by up-converting the signal at the frequency of the signal selected by the switch. Features.

  The substance identification method according to the second aspect of the present invention includes a step of irradiating a plurality of terahertz waves having different frequencies, a step of measuring the intensity of a transmitted wave or a reflected wave when each of the plurality of terahertz waves is irradiated to a measurement object, A step of receiving the intensity of each of the plurality of terahertz waves measured in the measurement step, and a step of calculating a ratio of another intensity with respect to the reference when one of the received intensity is used as a reference as a measurement target intensity ratio And for each of the intensities measured by irradiating the candidate substance with each of a plurality of terahertz waves, the ratio of the other intensity with respect to the reference when one of the intensities is used as a reference is stored as a candidate substance intensity ratio. Reading from the means, and identifying the measurement object by comparing the read candidate substance intensity ratio and the measurement object intensity ratio; Characterized in that it has.

  According to the present invention, an inexpensive terahertz spectroscopy system can be provided.

It is a block diagram which shows the structure of the terahertz spectroscopy system in 1st Embodiment. It is a figure which shows the optical spectrum of each part in the said terahertz spectroscopy system. It is a figure which shows the measurement result of the measurement result of the terahertz spectroscopy spectrum of three types of chemical | medical agents, and the absorption characteristic at five single frequencies. It is a figure which shows the intensity ratio of the transmitted wave in the terahertz wave of each frequency of three types of chemical | medical agents. It is a block diagram which shows the structure of the terahertz spectroscopy system in 2nd Embodiment. It is a block diagram which shows the structure of the terahertz spectroscopy system in 3rd Embodiment. It is a block diagram which shows the structure of the terahertz spectroscopy system in 4th Embodiment. It is a block diagram which shows the structure of the terahertz spectroscopy system in 5th Embodiment. It is a graph which shows the measurement result of the terahertz spectrum of three types of chemical | medical agents. It is a figure which shows the structure of the conventional apparatus used for a terahertz time domain spectroscopy.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[First Embodiment]
FIG. 1 is a block diagram illustrating a configuration of the terahertz spectroscopy system according to the first embodiment. A terahertz spectroscopy system 1 shown in FIG. 1 includes a supercontinuum (SC) light source 11, an arrayed waveguide grating (AWG) 12, an optical single sideband (SSB) modulator 13, a millimeter wave. Wave switch 14, fixed oscillators 15 </ b> A to 15 </ b> E that oscillate millimeter-wave signals having different frequencies, optical switch 16, optical coupler 17, photoelectric converter 18 that converts an optical signal into a terahertz wave, and transmitted wave intensity (absorption characteristics) A terahertz detector 19 for measurement and a determination device 20 are provided. The terahertz spectroscopy system shown in FIG. 1 irradiates a device under test 100 with a plurality of single-frequency terahertz waves, measures the intensity of transmitted waves in the terahertz waves of each frequency, and one of the intensities of these transmitted waves. Find the value obtained by dividing the intensity of the other transmitted wave by this reference intensity (the intensity ratio of the transmitted wave), and compare it with the intensity ratio of the transmitted wave in the candidate substance measured in advance by the terahertz wave of the same frequency. Then, it is determined whether the candidate substance is included in the object to be measured.

  The SC light source 11 generates a plurality of longitudinal modes (optical signals) with a frequency interval f0. A plurality of modes generated by the SC light source 11 are input to the AWG 12, and two modes are selected by the AWG 12 and the optical switch 16.

  The optical SSB modulator 13 converts the frequency of the optical signal according to the frequency of the input millimeter wave signal. The millimeter wave signal input to the optical SSB modulator 13 is switched by the millimeter wave switch 14 to change the frequency conversion amount. In the present embodiment, one of the selected two modes is frequency-converted by the optical SSB modulator 13. Details of the optical SSB modulator 13 are described in Non-Patent Document 3.

  The determination device 20 includes a calculation unit 21 and a storage unit 22. The calculation unit 21 obtains the intensity ratio of the transmitted wave in the DUT 100 from the result of the intensity of the transmitted wave measured by each single frequency terahertz wave, and transmits the plurality of candidate substances stored in the accumulation unit 22. When the difference between the intensity ratio of the transmitted wave of the object to be measured 100 and the intensity ratio of the transmitted wave of the candidate substance in the terahertz wave of each frequency is within a predetermined range as compared with the intensity ratio of the wave, the object to be measured 100 Is determined to contain the candidate substance.

  Next, the operation flow of the terahertz spectroscopy system 1 will be described with reference to the drawings. FIG. 2 is a diagram showing the optical spectrum of each part in the terahertz spectroscopy system 1, and shows the optical spectrum at points A to E in FIG.

  First, as shown in FIG. 2A, the SC light source 11 generates a plurality of modes at a frequency interval of f0. Then, the AWG 12 and the optical switch 16 select two modes in which the frequency interval is N × f0 (N is an integer) from a plurality of modes, as shown in FIGS. The frequency interval f0 of the plurality of modes generated by the SC light source 11 uses a microwave to millimeter wave frequency region of about 10 to 50 GHz that is relatively easy to generate due to the band performance of optical components and electronic components. This is because it is necessary to extract two modes apart from each other in order to select two modes of the frequency interval of the region.

  One of the two selected modes is frequency-converted by Δfmk (k = 1, 2, 3, 4, 5) by the optical SSB modulator 13. The amount of frequency conversion depends on the frequency of the millimeter wave signal input to the optical SSB modulator 13. That is, the frequency conversion amount is changed by selecting the outputs of the plurality of fixed oscillators 15A to 15E by the millimeter wave switch 14 (D in FIG. 2).

  Then, the frequency-converted mode and the other mode are multiplexed by the optical coupler 17. The combined optical signal includes two modes having a frequency interval of N × f0 + Δfmk (k = 1, 2, 3, 4, 5), as indicated by E in FIG. This optical signal is converted into a terahertz wave having a frequency of N × f 0 + Δfmk (k = 1, 2, 3, 4, 5) by the photoelectric converter 18 and irradiated on the object 100 to be measured. The frequency of each terahertz signal to be irradiated is f1 = N × f0 + Δfm1, f2 = N × f0 + Δfm2, f3 = N × f0 + Δfm3, f4 = N × f0 + Δfm4, f5 = N × f0 + Δfm5, and by setting Δfmk, for example, f1 = 1 .21 THz, f2 = 1.39 THz, f3 = 1.56 THz, f4 = 1.70 THz, f5 = 1.83 THz can be generated as a terahertz signal.

  Then, the terahertz detector 19 measures the intensities (absorption characteristics) of transmitted waves of the terahertz signals having the frequencies f1 to f5 irradiated on the object 100 to be measured. The measured transmitted wave intensity is transmitted to the determination device 20.

  The determination device 20 transmits the transmitted wave intensity ratio Rk () of the terahertz signal having the other frequency fk (k = 2, 3, 4, 5) to the intensity (reference intensity) of the transmitted wave of the terahertz signal having the frequency f1 (reference frequency). k = 2, 3, 4, 5) for each of the transmitted wave intensities (reference intensities) in the terahertz signal of the frequency f1 of the plurality of candidate substances (a, b, c,...) stored in the storage unit 22. Compared with the transmitted wave intensity ratio Sik (k = 2, 3, 4, 5, i = a, b, c,...) In the terahertz signal of frequency fk (k = 2, 3, 4, 5). The candidate substance i having the transmitted wave intensity ratio is determined to be a substance contained in the measurement object 100.

  FIG. 3 shows measurement results of terahertz spectrum of aspirin, stimulant (methamphetamine), narcotic (MDMA: dl-methylindioxymethamphetamine), f1 = 1.21 THz, f2 = 1.39 THz, f3 = 1.56 THz, The result of having measured the intensity | strength of the transmitted wave with each of the five single frequency terahertz signals of f4 = 1.70 THz and f5 = 1.83 THz is shown. The upper table in FIG. 4 shows the case where each candidate substance (here, aspirin, stimulant (methamphetamine), narcotic (MDMA)) is based on the intensity of the transmitted wave with a terahertz signal having a frequency f1 = 1.21 THz. The transmitted wave intensity ratio in terahertz signals of other frequencies f2 to f5 is shown. Assuming that aspirin, stimulant and narcotic are candidate substances a, b and c, respectively, for example, the intensity ratio of transmitted waves in aspirin (candidate substance a) is Sa2 = 1.6, Sa3 = 1.1, Sa4 = 1. .9, Sa5 = 2.9.

  As shown in FIG. 4, when the intensity ratio of the transmitted wave between the frequencies is compared, it is understood that the intensity ratio of the transmitted wave between the frequencies is different among the three substances. Accordingly, the intensity ratio of the transmitted wave in the terahertz signal of each frequency is measured in advance for each candidate substance (based on the intensity of the transmitted wave in the terahertz signal of a certain frequency). By comparing with the result of the transmitted wave intensity ratio, it becomes possible to identify candidate substances included in the DUT 100. That is, the transmitted wave intensity ratio data Sik (k = 2, 3, 4, 5, i = a, b, c,...) In the candidate substance i calculated in advance using terahertz signals of a plurality of frequencies. And the intensity ratio Rk (k = 2, 3, 4, 5) of the transmitted wave in the DUT 100 actually measured and calculated, k of Sik (i = a, b, c,...) = 2, 3, 4 and 5 are identified by determining that the substance i is included in the DUT 100 by specifying Sik in which the error from Rk is within a predetermined value (for example, 10%). Note that the error range when comparing and identifying the intensity ratio may be set as appropriate.

  In this way, by limiting the frequency used for measurement to a plurality of single frequencies and calculating the intensity ratio of transmitted waves at each frequency to identify the substance, it is not necessary to measure the spectrum curve over a wide frequency range Therefore, the terahertz spectroscopy system can be configured at low cost and simply.

[Second Embodiment]
Next, a terahertz spectroscopy system in the second embodiment will be described.

  FIG. 5 is a block diagram illustrating a configuration of the terahertz spectroscopy system according to the second embodiment. The terahertz spectroscopy system 3 shown in the figure includes a continuous light source 31 that outputs an optical signal continuously including a wide frequency region, an optical coupler 32, an optical switch 33, optical filters 34A to 34F, an optical coupler 35, a photoelectric converter 36, A terahertz detector 37 and a determination device 38 are provided.

  The optical signal output from the continuous light source 31 is branched by the optical coupler 32, and the frequency interval is fk = fa−fbi (i = 1, 2, 3, 4, 5, fa>) by the optical switch 33 and the optical filters 34A to 34F. Two modes (optical signals) to be fbi) are selected. Specifically, one optical signal branched by the optical coupler 32 is input to the optical filter 34A to cut out the mode of the frequency fa, and the other optical signal is selected from the optical filters 34B to 34F by the optical switch 33. Is input, and the mode of the frequency fbi (i = 1, 2, 3, 4, 5) is cut out. As shown in FIG. 3, in terahertz band spectrum spectroscopy, accuracy of 10 GHz or less is not necessary in most cases. Therefore, transmission characteristics of an FBG filter (Fiber Bragg Grating Filter) in which a pass band of 10 GHz or less is realized. The necessary frequency resolution can be obtained by using.

  The two selected modes are combined by the optical coupler 35, converted into a terahertz wave by the photoelectric converter 36, and irradiated on the object 100 to be measured.

  Then, similarly to the first embodiment, the intensity of the transmitted wave of the terahertz signal of each frequency irradiated to the device under test 100 is measured by the terahertz detector 37, and the intensity ratio of the transmitted wave is determined by the determination device 38. The substance contained in the DUT 100 is identified by calculating and comparing it with the intensity ratio data of the candidate substance.

[Third Embodiment]
Next, a terahertz spectroscopy system in the third embodiment will be described.

  FIG. 6 is a block diagram illustrating a configuration of the terahertz spectroscopy system according to the third embodiment. The terahertz spectroscopy system 4 shown in the figure includes a plurality of single mode lasers 41A to 41F that output modes having different frequencies, an optical switch 42, an optical coupler 43, a photoelectric converter 44, a terahertz detector 45, and a determination device 46. Prepare.

  Each of the single mode lasers 41A to 41F outputs modes (optical signals) of frequencies fa and fb1 to fb5. The frequency interval is fk = fa−fbi (i = 1, 2, 3, 4, 5, by one selected by the optical switch 42 from the output of the single mode laser 41A and the output of the single mode lasers 41B to 41F. Two modes are obtained, fa> fbi). The frequency of the output signals of the single mode lasers 41A to 41F can be adjusted with a resolution of 10 GHz depending on the current and temperature. As shown in FIG. 3, in terahertz band spectrum spectroscopy, accuracy of 10 GHz or less is not necessary in most cases, so that the required frequency resolution can be obtained with this configuration.

  The mode selected by the optical switch 42 is combined with the mode output by the single mode laser 41 </ b> A by the optical coupler 43, converted into a terahertz wave by the photoelectric converter 44, and irradiated on the object 100 to be measured.

  Then, similarly to the first embodiment, the intensity of the transmitted wave of the terahertz signal of each frequency irradiated to the device under test 100 is measured by the terahertz detector 45, and the intensity ratio of the transmitted wave is determined by the determination device 46. The substance contained in the DUT 100 is identified by calculating and comparing it with the intensity ratio data of the candidate substance.

[Fourth Embodiment]
Up to now, optical technology has been used as a light source for terahertz spectroscopy, but in the fourth and fifth embodiments, the optical technology is used.

  FIG. 7 is a block diagram illustrating a configuration of a terahertz spectroscopy system according to the fourth embodiment. The terahertz spectroscopy system 5 shown in the figure includes a plurality of fixed oscillators 51A to 51E that generate signals having different frequencies, a millimeter wave switch 52, a frequency multiplier 53, a terahertz detector 54, and a determination device 55.

  One signal of the frequency Δfmk (k = 1, 2, 3, 4, 5) generated by each of the fixed oscillators 51A to 51E is selected by the millimeter wave switch 52, and the frequency multiplier 53 performs frequency multiplication (N times, N Is an integer). As a result, the device under test 100 is irradiated with a terahertz signal having a frequency N × Δfmk (k = 1, 2, 3, 4, 5). Δfmk (k = 1, 2, 3, 4, 5) is selected so that the frequency of the irradiated terahertz signal becomes the frequency fk (k = 1, 2, 3, 4, 5) desired to be measured.

  Then, similarly to the first embodiment, the intensity of the transmitted wave of the terahertz signal of each frequency irradiated to the device under test 100 is measured by the terahertz detector 54, and the intensity ratio of the transmitted wave is determined by the determination device 55. The substance contained in the DUT 100 is identified by calculating and comparing it with the intensity ratio data of the candidate substance.

[Fifth Embodiment]
FIG. 8 is a block diagram illustrating a configuration of a terahertz spectroscopy system according to the fifth embodiment. The terahertz spectroscopy system 6 shown in the figure includes a plurality of fixed oscillators 61A to 61E that generate signals of different frequencies, a millimeter wave switch 62, a harmonic mixer 63, a fixed oscillator 64 that generates a signal of frequency f0, and a terahertz detector 65. And a determination device 66.

  The fifth embodiment differs from the fourth embodiment in that a harmonic mixer 63 is used to generate a terahertz signal. In the harmonic mixer 63, the frequency of the input LO signal is multiplied (N times), and further up-converted with the frequency of the IF signal input from another IF port. In the present embodiment, a signal having a frequency f0 generated by the fixed oscillator 64 is input to the harmonic mixer 63 as an LO signal, and the frequency Δfmk (k = 1, 2,) generated by the fixed oscillators 61A to 61E by the millimeter wave switch 62 is input. One of the signals 3, 4, 5) is selected and input to the IF port of the harmonic mixer 63. As a result, the output frequency of the harmonic mixer 63 becomes fk = N × f0 + Δfmk (k = 1, 2, 3, 4, 5). Δfmk (k = 1, 2, 3, 4, 5) is selected so that the frequency of the irradiated terahertz signal becomes the frequency fk (k = 1, 2, 3, 4, 5) desired to be measured.

  Then, similarly to the first embodiment, the intensity of the transmitted wave of the terahertz signal of each frequency irradiated to the device under test 100 is measured by the terahertz detector 65, and the intensity ratio of the transmitted wave is determined by the determination device 66. The substance contained in the DUT 100 is identified by calculating and comparing it with the intensity ratio data of the candidate substance.

  However, since the frequency multiplier 53 and the harmonic mixer 63 are limited in the wide band, there is a disadvantage that they cannot be used when it is necessary to measure a wide frequency region.

  In each of the above embodiments, five single-frequency terahertz waves (signals) are used. However, the present invention is not limited to this. In order to calculate the intensity ratio, it is necessary to use at least two single-frequency terahertz waves.

  Further, in each of the above embodiments, the intensity ratio is calculated by measuring the intensity of the transmitted wave of the terahertz wave (signal) irradiated to the object 100 to be measured, but the intensity ratio is calculated by measuring the intensity of the reflected wave. You may do it.

  As described above, the frequency of the terahertz signal used for measurement is limited to a plurality of single frequencies, and the device under test 100 is irradiated, and the intensity ratio of the transmitted wave or reflected wave at each frequency is calculated to calculate the candidate substance. By identifying candidate substances that have an intensity ratio error within a predetermined range as compared with the intensity ratio, the candidate substances included in the DUT 100 can be identified with an inexpensive and simple configuration.

  In the future, it is possible to cope with the case where the emission of terahertz radio waves is regulated by law.

DESCRIPTION OF SYMBOLS 1, 3, 4, 5, 6 ... Terahertz spectroscopy system 11 ... SC light source 31 ... Continuous light source 41A-41F ... Single mode laser 12 ... AWG
DESCRIPTION OF SYMBOLS 13 ... Optical SSB modulator 14, 52, 62 ... Millimeter wave switch 15A-15E, 51A-51E, 61A-61E, 64 ... Fixed oscillator 16, 33, 42 ... Optical switch 17, 32, 35, 43 ... Optical coupler 34A 34F ... Optical filter 18, 36, 44 ... Photoelectric converter 53 ... Frequency multiplier 63 ... Harmonic mixer 19, 37, 45, 54, 65 ... Terahertz detector 20, 38, 46, 55, 66 ... Determination device 21 ... Calculation unit 22 ... Accumulation unit 100 ... DUT

Claims (7)

Terahertz wave irradiation means for irradiating a plurality of terahertz waves having different frequencies;
Measuring means for measuring the intensity of the transmitted wave or reflected wave when the measurement object is irradiated with each of the plurality of terahertz waves;
For each of the intensities measured by irradiating a candidate substance with each of the plurality of terahertz waves, a ratio of the other intensity to the reference when one of the intensities is used as a reference is stored as a candidate substance intensity ratio Storage means;
Receiving the intensity in each of the plurality of terahertz waves measured by the measuring means, and calculating a ratio of the other intensity to the reference when one of the intensity is used as a reference as a measurement target intensity ratio; Identifying means for identifying the measurement object by comparing the measurement object intensity ratio with the candidate substance intensity ratio stored in the storage means;
A terahertz spectroscopy system characterized by comprising: The terahertz wave irradiation means is
A light source that generates a plurality of modes at predetermined frequency intervals;
Take-out means for taking out two modes out of the plurality of modes;
A plurality of oscillators that output signals of different frequencies;
A switch for selecting one signal from signals output from the plurality of oscillators;
A modulator that inputs one of the two modes and changes the frequency of the mode based on the frequency of the signal selected by the switch;
An optical coupler for combining the one mode whose frequency has changed and the other of the two modes;
A photoelectric converter that converts an optical signal including two combined modes into a terahertz wave;
The terahertz spectroscopy system according to claim 1, comprising: The terahertz wave irradiation means is
A continuous light source that outputs an optical signal continuously including a wide frequency range;
A first optical coupler for branching an optical signal output from the continuous light source;
A first filter that cuts out an optical signal having a predetermined frequency from one of the branched optical signals;
A plurality of second filters that cut out optical signals having a plurality of different frequencies;
An optical switch that receives the other branched optical signal, selects one of the plurality of second filters, and inputs the other optical signal to the selected second filter;
A second optical coupler for combining optical signals output from the first and second filters;
A photoelectric converter that converts the combined optical signal into a terahertz wave;
The terahertz spectroscopy system according to claim 1, comprising: The terahertz wave irradiation means is
A first single mode laser that outputs a mode of a predetermined frequency;
A plurality of second single mode lasers that output modes of different frequencies;
An optical switch for selecting one of the outputs of the plurality of second single mode lasers;
An optical coupler for combining the output of the first single mode laser and the output of the second single mode laser selected by the optical switch;
A photoelectric converter that converts an optical signal including two combined modes into a terahertz wave;
The terahertz spectroscopy system according to claim 1, comprising: The terahertz wave irradiation means is
A plurality of oscillators that output signals of different frequencies;
A switch for selecting one of signals output from the plurality of oscillators;
A frequency multiplier that radiates a terahertz wave by frequency multiplying the signal selected by the switch;
The terahertz spectroscopy system according to claim 1, comprising: The terahertz wave irradiation means is
A first oscillator that outputs a signal of a predetermined frequency;
A plurality of second oscillators that output signals of different frequencies;
A switch for selecting one of signals output from the plurality of second oscillators;
A harmonic mixer that multiplies the signal output by the first oscillator and radiates a terahertz wave by up-converting the signal at a frequency selected by the switch;
The terahertz spectroscopy system according to claim 1, comprising: Irradiating a plurality of terahertz waves having different frequencies;
Measuring the intensity of a transmitted wave or a reflected wave when each of the plurality of terahertz waves is irradiated to a measurement object;
Receiving the intensity in each of the plurality of terahertz waves measured in the measuring step;
Calculating a ratio of the other received intensity with respect to the reference when one of the received intensity is set as a reference as a measurement target intensity ratio;
For each of the intensities measured by irradiating a candidate substance with each of the plurality of terahertz waves, a ratio of the other intensity to the reference when one of the intensities is used as a reference is stored as a candidate substance intensity ratio. Reading from the storage means, and identifying the measurement object by comparing the read candidate substance intensity ratio and the measurement object intensity ratio;
A substance identification method characterized by comprising:

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