Quantum absorption spectroscopic system and quantum absorption spectroscopic method

Abstract

The quantum absorption spectroscopic system (100) comprises a laser source (1), a quantum optical system (201), a light detector (31) and a controller (4). The laser source (1) emits pumping light. The quantum optical system (201) comprises a nonlinear optical crystal (23) for generating quantum entangled photon pairs of signal photons and idle photons by irradiation with pumping light, and a movable reflector (25) configured to change the phase of the idle photons, and configured to generate quantum interference between multiple physical processes for generating quantum entangled photon pairs. The light detector (31) idly detects signal photons when the phase of the idle photons is changed by the nonlinear optical crystal (23) when the sample is arranged in the optical path of the idle photons, and outputs a quantum interference signal corresponding to the number of detected photons. The controller (4) calculates the absorption spectroscopic characteristics of the sample by Fourier transforming the quantum interference signal.

Description

Technical Field

[0001] The present disclosure relates to a quantum absorption spectroscopic system and a quantum absorption spectroscopic method. Background Art

[0002] Generally speaking, in infrared absorption spectroscopy, infrared light is irradiated on a sample. Then, the change in the intensity of the infrared light accompanying the absorption of the sample is obtained as the infrared absorption spectrum of the sample. Among infrared absorption spectroscopy, Fourier transform infrared spectroscopy (FTIR) is particularly widely used in the fields of chemistry, biology, and pharmacy to determine the molecular structure (type of functional group or three-dimensional structure, etc.).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: U.S. Patent No. 10,648,908

[0006] Non-patent literature

[0007] Non-patent literature 1: Anna Paterova, Hongzhi Yang, Chengwu An, Dmitry Kalashnikov and Leonid Krivitsky, "Measurement of infrared optical constants with visible photons", New Journal of Physics 20 (2018) 043015

[0008] Non-patent document 2: Masayuki Okano, Hwan Hong Lim, Ryo Okamoto, Norihiko Nishizawa, Sunao Kurimura and Shigeki Takeuchi, "0.54 μm resolution two-photon interference with dispersion cancellation for quantum optical coherence tomography", Scientific Reports volume 5, Article number: 18042 (2015) Summary of the invention

[0009] In recent years, in the field of quantum technology such as quantum measurement, quantum communication and quantum computing, research on using two photons to generate photon pairs with "quantum entanglement" related to quantum mechanics to achieve new functions is developing. Hereinafter, such photon pairs are also referred to as "quantum entangled photon pairs". The inventors of the present invention are concerned with the application of quantum entangled photon pairs to spectroscopic systems and spectroscopic methods. In addition, the inventors have found that by performing appropriate computational processing on the detection signal from the photodetector, the wavelength band that can be spectroscopically divided can be widened.

[0010] The present disclosure is made to solve the above-mentioned problems, and an object of the present disclosure is to provide a technology capable of performing spectroscopy over a wide wavelength band in a spectroscopy system or spectroscopy method (quantum absorption spectroscopy system or quantum absorption spectroscopy method) using quantum entangled photon pairs.

[0011] (1) The quantum absorption spectroscopic system of the first aspect of the present disclosure comprises a light source, a quantum optical system, a light detector and a computing device. The light source emits pumping light. The quantum optical system includes: a nonlinear optical element that generates a quantum entangled photon pair of a signal photon and an idle photon by irradiating the pumping light; and a phase shifter that is configured to change the phase of one of the signal photon and the idle photon. The quantum optical system is configured to cause quantum interference between multiple physical processes that generate quantum entangled photon pairs. The light detector outputs a quantum interference signal corresponding to the number of signal photons detected when the phase shifter changes the phase of one of the photons when the sample is configured in the optical path of the idle photon. The computing device calculates the absorption spectroscopic characteristics of the sample by Fourier transforming the quantum interference signal.

[0012] (2) In a certain embodiment, the computing device may calculate a reference Fourier spectrum by Fourier transforming a quantum interference signal when the sample is not arranged in the optical path of the idle photon, in addition to calculating the Fourier spectrum by Fourier transforming the quantum interference signal when the sample is arranged in the optical path of the idle photon. The computing device may also calculate the complex transmittance spectrum of the sample based on the ratio of the Fourier spectrum to the reference Fourier spectrum.

[0013] (3) In one embodiment, the computing device may calculate the absorption spectrum of the sample by squaring the absolute value of the complex transmittance spectrum of the sample.

[0014] (4) In a certain embodiment, the computing device may calculate the absorption spectral characteristics of the sample by performing Fourier transform on the quantum interference signal obtained in the quantum optical system without performing wavelength scanning on the quantum entangled photon pair or wavelength decomposing the signal photon.

[0015] (5) In a certain embodiment, the nonlinear optical element may be a chirped or fan-shaped quasi-phase matching element.

[0016] (6) In other embodiments, the nonlinear optical element may also be a quasi-phase matching element including a nonlinear optical crystal. The quasi-phase matching element may also be configured such that, when quantum entangled photon pairs are generated multiple times, the wavelengths of the idle photon group including the idle photons are distributed over the entire wide band determined by the material of the nonlinear optical crystal and the polarization inversion period.

[0017] (7) In one embodiment, the material of the nonlinear optical crystal may include lithium niobate. The polarization inversion period of the nonlinear optical crystal may be determined so that the idle photon group includes a plurality of photons having different wavelengths within a wavelength band of 0.4 μm to 5.2 μm.

[0018] (8) In other embodiments, the material of the nonlinear optical crystal may include gallium phosphide. The polarization inversion period of the nonlinear optical crystal may be determined so that the idle photon group includes a plurality of photons having different wavelengths within the wavelength range of 0.7 μm to 12 μm.

[0019] (9) In another embodiment, the material of the nonlinear optical crystal may include gallium arsenide. The polarization inversion period of the nonlinear optical crystal may be determined so that the idle photon group includes a plurality of photons having different wavelengths within a wavelength range of 1 μm to 18 μm.

[0020] (10) In another embodiment, the material of the nonlinear optical crystal may include lithium tantalate. The polarization inversion period of the nonlinear optical crystal may be determined so that the idle photon group includes a plurality of photons having different wavelengths in the wavelength band of 0.3 μm to 5.5 μm.

[0021] (11) In another embodiment, the material of the nonlinear optical crystal may include zinc selenide. The polarization inversion period of the nonlinear optical crystal may be determined so that the idle photon group includes a plurality of photons having different wavelengths within a wavelength range of 0.4 μm to 22 μm.

[0022] (12) In one embodiment, the photodetector may be a single-pixel photodetector.

[0023] (13) In one embodiment, the signal photon is a photon in the visible light frequency domain. The photodetector may also be a silicon-based photodetector.

[0024] (14) In one embodiment, the quantum optical system may further include a total reflection measurement device configured to perform total reflection measurement of a sample.

[0025] (15) In one embodiment, the phase shifter may include: a first movable reflector configured to be movable along the propagation direction of the signal photon; and a second movable reflector configured to be movable along the propagation direction of the idle photon. The quantum absorption spectroscopic system further includes a control device. The control device may also be configured to selectively move one of the first movable reflector and the second movable reflector.

[0026] (16) In one embodiment, the phase shifter may include a movable mirror configured to be movable along a propagation direction of the signal photon.

[0027] (17) In one embodiment, the nonlinear optical element may be configured to generate idle photons in the ultraviolet frequency domain. The computing device may also calculate the ultraviolet absorption spectral characteristics of the sample.

[0028] (18) The second aspect of the present disclosure includes the first to third steps of the quantum absorption spectroscopic method (QAS). The first step is to irradiate a nonlinear optical element with pump light in a quantum optical system configured to generate quantum entangled photon pairs of signal photons and idle photons by causing quantum interference between multiple physical processes. This generates quantum entangled photon pairs. The second step is to detect the signal photons when the phase of one of the signal photons and the idle photons is changed by a phase shifter in a state where the sample is arranged in the optical path of the idle photons by idling the photodetector, thereby acquiring a quantum interference signal corresponding to the number of detected photons. The third step is to calculate the absorption spectroscopic characteristics of the sample by Fourier transforming the quantum interference signal of the photodetector.

[0029] According to the present disclosure, it is possible to perform spectroscopy over a wide wavelength band in a quantum absorption spectroscopy system or a quantum absorption spectroscopy method. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a diagram showing the overall configuration of a quantum absorption spectroscopic system according to Embodiment 1 of the present disclosure.

[0031] Figure 2 This is a conceptual diagram for explaining the principle of quantum absorption spectroscopy.

[0032] Figure 3 This is a functional block diagram for schematically explaining the calculation processing performed by the calculation device.

[0033] Figure 4 This is a flowchart showing the processing procedure of quantum absorption spectroscopy in the first embodiment.

[0034] Figure 5 This is a diagram showing the overall configuration of a quantum absorption spectroscopic system according to a modified example of the first embodiment.

[0035] Figure 6 This is a diagram showing the overall structure of a quantum absorption spectroscopic system according to the second embodiment.

[0036] Figure 7 It is a diagram showing a configuration example of a quasi-phase matching device.

[0037] Figure 8 This is a diagram showing the overall configuration of a quantum absorption spectroscopic system according to the third embodiment.

[0038] Fig. 9 This is a diagram showing the overall configuration of a quantum absorption spectroscopic system according to Modification 1 of Embodiment 3.

[0039] Fig.10 This is a conceptual diagram for explaining the difference in detection principles depending on the type of photodetector.

[0040] Fig.11 This is a diagram showing the overall configuration of a quantum absorption spectroscopic system according to a second variation of the third embodiment.

[0041] Fig.12 This is a diagram showing the overall configuration of a quantum absorption spectroscopic system according to a fourth embodiment.

[0042] Fig.13 This is a diagram showing the overall configuration of a quantum absorption spectroscopic system according to a modified example of the fourth embodiment.

[0043] Fig.14 It is a diagram showing a configuration example of a total reflection measurement method unit.

[0044] Fig.15 This is a diagram showing an example of the measurement result of the quantum interference signal.

[0045] Fig.16 It is shown by Fig.15 The diagram shows the Fourier spectrum obtained by Fourier transforming the quantum interference signal shown.

[0046] Fig.17 This is a diagram showing the difference in the signal photon spectrum due to the quantum interference effect.

[0047] Fig.18 This is a diagram showing an example of the measurement results of a quantum interference signal related to quartz glass.

[0048] Fig.19 It is shown by Fig.18 The Fourier spectrum obtained by Fourier transforming the quantum interference signal shown is shown.

[0049] Fig. 20 It is a graph showing the absolute value of transmittance and phase difference obtained by measuring quartz glass.

[0050] Fig.21 : is a diagram showing the polarization inversion period at each position of the nonlinear optical crystal.

[0051] Fig. 22 FIG. 1 is a diagram showing an example of a simulation result of a spectrum of a quantum entangled photon pair generated using a quasi-phase matching device.

[0052] Fig.23 It shows that when using Fig. 22 The spectrum shown is a diagram of the simulation results of the quantum interference signal obtained in the case of a quantum entangled photon pair.

[0053] Fig.24 : is a diagram showing the relationship between the polarization inversion period of each material of the nonlinear optical crystal and the generation wavelength band of idler light.

[0054] Fig.25 This diagram summarizes the characteristics of various materials that can be used for nonlinear optical crystals.

[0055] Fig.26 This is a diagram showing an example of a simulation result of obtaining a complex transmittance spectrum over a wide wavelength band.

[0056] Fig. 27 It is shown from Fig.26 The complex transmittance spectrum shown is a diagram of the simulation results for obtaining the complex refractive index of the sample.

[0057] Fig.28 This is a diagram showing an example of the measurement results of quantum interference signals over a wide wavelength band.

[0058] Fig.29 It is shown from Fig.28 The graph shown is a result of calculating the complex transmittance spectrum of the sample using the quantum interference signal.

[0059] Fig.30 It is a diagram showing a quantum interference signal obtained by simulation of scanning an idle optical path or a signal optical path.

[0060] Fig.31 It is shown by Fig.30 The Fourier spectrum obtained by Fourier transforming the quantum interference signal shown is shown.

[0061] Fig.32This is a diagram showing a Fourier spectrum obtained by simulation of scanning the idle light path or the signal light path in a state where a sample as an infrared absorber is arranged in the idle light path.

[0062] Fig.33 This is a diagram showing a quantum interference signal obtained by simulation of scanning an idle optical path or a signal optical path in a quantum absorption spectroscopic system for measuring absorption spectroscopic characteristics in the ultraviolet light frequency domain.

[0063] Fig.34 FIG. 4 is a diagram showing a Fourier spectrum obtained when the signal optical path is scanned.

[0064] (Explanation of symbols)

[0065] 1: laser source; 201-205: quantum optical system; 211-214: lens; 221-223: dichroic mirror; 23: nonlinear optical crystal; 231: first crystal; 232: second crystal; 24: sample holder; 25, 28: movable reflector; 250, 280: drive device; 271: Faraday rotator; 272: λ / 4 wavelength plate; 26, 29: fixed reflector; 31, 32: photodetector; 4: controller; 41: processor; 42: memory; 43: input / output port; 5: monitor; 401: light source control unit; 402: reflector Control unit; 403: Count rate calculation unit; 404: Fourier transform unit; 405: First storage unit; 406: Second storage unit; 407: Transmittance calculation unit; 408: Absorption spectrum calculation unit; 409: Monitor control unit; 6: Dispersed optical element; 7: QPM device; 71, 74: Lens; 72: Nonlinear optical crystal; 73: Long pass filter; 75: Sharp cutoff filter; 8: ATR unit; 81, 83: Lens; 82: Prism; 100, 100A, 200, 300, 300A, 300B, 400, 400A: Quantum absorption spectroscopic system. DETAILED DESCRIPTION

[0066] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In addition, the same reference numerals are attached to the same or corresponding parts in the drawings, and their description will not be repeated.

[0067] In the present disclosure and its embodiments, the ultraviolet light frequency domain means the band of 10nm to 360nm. The visible light frequency domain means the band of 360nm to 1050nm. The near-infrared light frequency domain means the band of 1050nm to 2μm. The mid-infrared light frequency domain means the band of 2μm to 5μm. The far-infrared light frequency domain means the band of 5μm to 20μm. The ultra-far-infrared light frequency domain (terahertz frequency domain) means the band of 20μm to 1mm. The infrared light frequency domain can include all of the near-infrared light frequency domain, the mid-infrared light frequency domain, the far-infrared light frequency domain and the ultra-far-infrared light frequency domain.

[0068] [Implementation Method 1]

[0069] In Embodiment 1 (and Embodiments 2 to 4 described later), the quantum absorption spectrometer of the present disclosure measures the absorption spectroscopic characteristics of the sample in the infrared frequency domain. However, as described in detail later, the wavelength band that can be measured by the quantum absorption spectrometer of the present disclosure is not limited to the infrared frequency domain.

[0070] <System Structure>

[0071] Figure 1 1 is a diagram showing the overall structure of a quantum absorption spectroscopic system according to Embodiment 1 of the present disclosure. The quantum absorption spectroscopic system 100 is configured to measure infrared absorption spectroscopic characteristics (infrared absorption spectrum, etc.) of a sample by applying quantum entangled photon pairs to infrared absorption spectroscopy. The quantum absorption spectroscopic system 100 includes a laser source 1, a quantum optical system 201, a photodetector 31, a controller 4, and a monitor 5.

[0072] The laser source 1 emits pumping light for exciting a nonlinear optical crystal 23 (described later). In the figure, the pumping light is represented by Lp. In the first embodiment, the laser source 1 emits a continuous wave (CW: Continuous wave) laser light included in the visible light frequency domain. Specifically, for example, a semiconductor laser that emits green laser light with a wavelength of 532nm can be used as the laser source 1.

[0073] The quantum optical system 201 is configured to generate quantum interference between multiple physical processes that generate quantum entangled photon pairs of signal photons and idle photons. Figure 2 As described in detail in , quantum interference is different from ordinary light interference, so it is necessary to pay attention. In the figure, Ls represents the optical path of signal light (light containing signal photons), and Li represents the optical path of idle light (light containing idle photons). In addition, hereinafter, the optical path of signal light is sometimes referred to as "signal optical path", and the optical path of idle light is sometimes referred to as "idle optical path".

[0074] In this embodiment, the quantum optical system 201 is an optical system using a structure similar to that of a Michelson interferometer and includes lenses 211 to 214 , dichroic mirrors 221 and 222 , a nonlinear optical crystal 23 , a sample holder 24 , a movable mirror 25 , and a fixed mirror 26 .

[0075] The lens 211 is disposed between the laser light source 1 and the dichroic mirror 221 . The lens 211 is configured to collect the pumping light from the laser light source 1 , and to focus the collected pumping light on the nonlinear optical crystal 23 .

[0076] The dichroic mirror 221 is disposed between the lens 211 and the nonlinear optical crystal 23. The dichroic mirror 221 transmits light in a wavelength band including the wavelength of the signal light, and reflects light outside the wavelength band.

[0077] In this example, the wavelength of the pumping light is 532 nm. The wavelength of the signal light is, for example, included in the band of 603 nm to 725 nm. The wavelength of the idle light is, for example, included in the band of 2 μm to 4.5 μm. Therefore, the dichroic mirror 221 transmits the signal light, and on the other hand, reflects the pumping light and the idle light. The pumping light is reflected by the dichroic mirror 221 and irradiates the nonlinear optical crystal 23.

[0078] The nonlinear optical crystal 23 generates signal light and idle light from the pump light focused by the lens 211. In more detail, the nonlinear optical crystal 23 uses the spontaneous parametric down conversion (SPDC) of the pump light to generate a photon pair of a signal photon and an idle photon. The nonlinear optical crystal 23 is, for example, a lithium niobate (LiNbO3) crystal. In this case, the signal light is visible light, and the idle light is infrared light (in more detail, near-infrared light or mid-infrared light). However, the type of the nonlinear optical crystal 23 is not particularly limited. Other types of nonlinear optical crystals such as silver gallium sulfide (AgGaS2) crystals may also be used. Figure 2 The principle of quantum absorption spectroscopy using the nonlinear optical crystal 23 will be described.

[0079] In addition, when a compound is expressed by a stoichiometric composition formula in this specification, the stoichiometric composition formula is only a representative example. The composition ratio may also be non-stoichiometric. For example, when lithium niobate is expressed as "LiNbO3", unless otherwise specified, lithium niobate is not limited to the composition ratio of "Li / Nb / O=1 / 1 / 3" and may contain Li, Nb and O in any composition ratio. The same applies to the other compounds exemplified below.

[0080] The dichroic mirror 222 is disposed between the nonlinear optical crystal 23 and the movable reflector 25 and between the nonlinear optical crystal 23 and the fixed reflector 26. In the present embodiment, the dichroic mirror 222 transmits visible light and reflects infrared light. The signal light in the visible light frequency domain transmits the dichroic mirror 222 together with the pump light and is directed toward the fixed reflector 26. On the other hand, the idle light in the infrared light frequency domain is reflected by the dichroic mirror 222 and is directed toward the movable reflector 25. In addition, the dichroic mirror 222 can also transmit infrared light and reflect visible light.

[0081] The lens 212 is disposed between the dichroic mirror 222 and the sample holder 24. The lens 212 parallelizes the idle light reflected by the dichroic mirror 222. The lens 213 is disposed between the dichroic mirror 222 and the fixed reflection mirror 26. The lens 213 parallelizes the pump light and the signal light transmitted through the dichroic mirror 222.

[0082] The sample holder 24 is disposed between the nonlinear optical crystal 23 and the movable reflector 25. The sample holder 24 holds the sample (indicated by SP in the figure). A material transparent to the idle light (in this example, infrared light) is used as the material of the sample holder 24. The idle light is irradiated to the sample, and the transmitted light is directed toward the movable reflector 25.

[0083] The movable reflector 25 is configured to be movable along the propagation direction of the idle light. Specifically, a driving device 250 is provided in the movable reflector 25. The driving device 250 is an electric actuator controlled by the controller 4, for example, a motor driving device (servo motor, stepping motor, etc.) that mechanically displaces according to a control instruction from the controller 4. The driving device 250 may also be a piezoelectric element (piezoelectric element) that displaces according to an applied voltage from the controller 4. By using the driving device 250 to periodically change the position of the movable reflector 25 (to make the movable reflector 25 move back and forth), the idle light path can be scanned (in the figure, the scanning situation is represented by ΔX).

[0084] The movable reflector 25 is preferably a plane mirror, and reflects the idle light after passing through the sample. The reflected idle light is further reflected by the dichroic mirror 222 and returns to the nonlinear optical crystal 23. The idle light passes through the nonlinear optical crystal 23, but is reflected by the dichroic mirror 221, so it does not reach the photodetector 31.

[0085] In addition, the movable reflector 25 is an example of the phase conversion unit of the present disclosure. The phase conversion unit of the present disclosure may also include a phase modulator (not shown) such as an electro-optical modulator (EOM) instead of the movable reflector 25 or in addition thereto. For example, it is possible to use a phase modulator to achieve a slight change in the optical path length on the basis of using the movable reflector 25 provided with the drive device 250 to make a relatively rough change in the optical path length.

[0086] The fixed reflector 26 is, for example, a plane mirror, and reflects the pump light and the signal light after passing through the dichroic mirror 222. The reflected light of the pump light and the reflected light of the signal light pass through the dichroic mirror 222 again and return to the nonlinear optical crystal 23. The pump light passes through the nonlinear optical crystal 23, but is reflected by the dichroic mirror 221. On the other hand, the signal light passes through the nonlinear optical crystal 23 and also passes through the dichroic mirror 221. In addition, the fixed reflector 26 may also be a concave reflector. In this case, the lens 213 can be omitted.

[0087] The lens 214 is disposed between the dichroic mirror 221 and the photodetector 31 . The lens 214 collects the signal light transmitted through the dichroic mirror 221 , and outputs the collected signal light to the photodetector 31 .

[0088] The photodetector 31 is a silicon-based photodetector having an optical property capable of splitting visible light (and a portion of near-infrared light). In Embodiment 1, the photodetector 31 is a multi-pixel photodetector including a plurality of pixels arranged in a two-dimensional array. Specifically, the photodetector 31 is a CCD (Charged-Coupled Device) image sensor or a CMOS (Complementary Metal-Oxide-Semiconductor) image sensor, etc. The photodetector 31 detects the signal light in response to a control instruction from the controller 4, and outputs its detection signal to the controller 4. In addition, the intensity of the detection signal of the signal light is an intensity corresponding to the number of signal photons detected by the photodetector 31 (in more detail, a signal intensity that is proportional to the number of photons). Therefore, the photodetector 31 can be said to output a detection signal corresponding to the number of detected photons (a quantum interference signal described later).

[0089] The controller 4 is, for example, a microcomputer. The controller 4 includes a processor 41 such as a CPU (Central Processing Unit), a memory 42 such as a ROM (Read Only Memory) and a RAM (Random Access Memory), and an input / output port 43. The controller 4 controls the devices (the laser source 1 and the driving device 250) in the quantum absorption spectroscopic system 100.

[0090] In addition, the controller 4 performs various calculations for realizing quantum absorption spectroscopy. More specifically, the controller 4 calculates the infrared absorption spectral characteristics of the sample based on the detection signal from the light detector 31. The infrared absorption spectral characteristics of the sample may include the Fourier spectrum, complex transmittance spectrum and infrared absorption spectrum of the sample. The calculations performed by the controller 4 will be described in detail later. The controller 4 first calculates the Fourier spectrum of the sample. Then, the controller 4 calculates the complex transmittance spectrum and infrared absorption spectrum of the sample by performing predetermined calculations using the Fourier spectrum. In addition, the controller 4 is an example of a calculation device and a control device disclosed in the present invention. The calculation device and the control device disclosed in the present invention may also be constructed separately.

[0091] The monitor 5 is, for example, a liquid crystal display, and displays the result of the calculation process performed by the controller 4. Thus, the measurer can confirm the infrared absorption spectral characteristics of the sample, such as the Fourier spectrum.

[0092] In addition, the dichroic mirror 221 can also transmit light of the wavelength of the idle light (or a wavelength longer than the idle light). In this case, a short-pass filter (not shown) can also be provided between the dichroic mirror 221 and the lens 214. The short-pass filter transmits the signal light, and on the other hand reflects (or absorbs) the idle light. Thus, it is possible to suppress the idle light from reaching the photodetector 31. However, in the case where the photodetector 31 has a low sensitivity in the wavelength band of the idle light, the short-pass filter can be omitted, allowing the idle light to reach the photodetector 31.

[0093] The nonlinear optical crystal 23 is an example of the nonlinear optical element of the present disclosure. The nonlinear optical element of the present disclosure is not limited thereto, and may be, for example, a ring resonator or an optical waveguide formed of silicon (Si) and / or silicon nitride (SiN) or the like (both not shown).

[0094] In addition, Figure 1 In the quantum optical system 201 shown, a quantum interferometer similar to the Michelson interferometer is used. However, the quantum optical system of the present disclosure may also have a structure similar to a Mach-Zehnder interferometer including a plurality of nonlinear optical elements.

[0095] In a typical existing quantum absorption spectroscopic system, a light source that emits infrared light is combined with a photodetector that is highly sensitive to infrared light, and there may be room for performance improvement in the light source and the photodetector. To give a specific example to illustrate, most light sources that emit infrared light (tungsten lamps, etc.) use blackbody radiation, so the energy conversion efficiency is low. In addition, in general, the sensitivity of infrared light detectors based on compound semiconductors such as indium gallium arsenide (InGaAs) is lower than the sensitivity of visible light detectors (silicon-based photodetectors, etc.). On the other hand, in recent years, the miniaturization and low price of visible light laser sources such as semiconductor lasers are developing. In addition, the popularity of digital cameras and smart phones is developing, and the sensitivity of silicon-based photodetectors is increasing and the price is decreasing. By adopting such a laser source and photodetector, the high sensitivity and low price of the quantum absorption spectroscopic system 100 can be achieved.

[0096] <Measurement Principle>

[0097] Figure 2 This is a conceptual diagram used to explain the principle of quantum absorption spectroscopy. Figure 1 In the embodiment, a structure in which only one nonlinear optical crystal 23 is arranged in the optical path of the pumping light is described. Figure 2 In order to facilitate understanding of the measurement principle, a configuration in which two nonlinear optical crystals are arranged in the optical path of pump light is described as an example. The two nonlinear optical crystals are described as a first crystal 231 and a second crystal 232.

[0098] When the pumping light from the laser source 1 is irradiated to the first crystal 231, the SPDC in the first crystal 231 causes one photon with relatively large energy to be split into two photons with smaller energy in accordance with the law of conservation of energy. Figure 2 In the example shown, a quantum entangled photon pair of one visible photon (signal photon) and one infrared photon (idle photon) is generated from one visible photon (pump photon). A quantum entangled photon pair of one visible photon and one infrared photon is also generated by irradiating the second crystal 232 with pump light. In this example, a photodetector 31 is arranged in the traveling direction of the visible photon in the quantum entangled photon pair.

[0099] Quantum interference occurs between a state in which a quantum entangled photon pair is generated by the first crystal 231 (hereinafter referred to as the "first physical process") and a state in which a quantum entangled photon pair is generated by the second crystal 232 (hereinafter referred to as the "second physical process"). In more detail, when the probability amplitude representing the first physical process is added to the probability amplitude representing the second physical process, if the two probability amplitudes are of the same phase, the first physical process and the second physical process reinforce each other. On the other hand, if the two probability amplitudes are of opposite phases, the first physical process and the second physical process cancel each other out (quantum interference effect). The following is an example of interference (destructive interference) in which the first physical process and the second physical process cancel each other out. However, the quantum optical system 201 can also be configured to cause interference (constructive interference) in which the first physical process and the second physical process reinforce each other.

[0100] When the sample as an infrared absorber is not arranged in the idle optical path, the first physical process and the second physical process cannot be distinguished, and the first physical process and the second physical process cause quantum interference (in this example, cancel each other out). In this case, it is observed that no quantum entangled photon pair is generated in the subsequent stage of the second crystal 232. In other words, the signal light (visible photon) is not detected by the photodetector 31.

[0101] On the other hand, when the sample is arranged in the idle light path, the idle light is absorbed by the sample. Then, the first physical process and the second physical process are distinguished, and the quantum interference between the first physical process and the second physical process becomes incomplete. As a result, the signal light is detected by the photodetector 31 .

[0102] Thus, in quantum absorption spectroscopy, by detecting one visible photon (signal photon) of the quantum entangled photon pair by the photodetector 31, it can be determined that the other infrared photon (idle photon) is absorbed by the sample.

[0103] also, Figure 1 The structure of the quantum optical system 201 shown is a structure in which the nonlinear optical crystal 23 has both the first crystal 231 and the second crystal 232. By making the pumping light go back and forth in the nonlinear optical crystal 23, the number of nonlinear optical crystals to be installed can be reduced.

[0104] In addition, Figure 2 The conceptual diagram shown in FIG. 2 illustrates an example in which quantum interference occurs between two physical processes (the first and second physical processes) in the quantum optical system 201. However, the quantum optical system of the present disclosure may also cause quantum interference between three or more physical processes. In other words, the quantum optical system of the present disclosure may be configured to cause quantum interference between at least two physical processes.

[0105] <Calculation Processing by Controller>

[0106] Figure 3 1 is a functional block diagram for schematically explaining the calculation processing performed by the controller 4. The controller 4 includes a light source control unit 401, a mirror control unit 402, a count rate calculation unit 403, a Fourier transform unit 404, a first storage unit 405, a second storage unit 406, a transmittance calculation unit 407, an absorption spectrum calculation unit 408, and a monitor control unit 409. First, an overview of the function of each block is explained.

[0107] The light source control unit 401 controls the light output (laser power) of the laser light source 1. The laser power during measurement by the quantum absorption spectroscopic system 100 is basically maintained constant.

[0108] The mirror control unit 402 controls the movement (reciprocating motion) of the movable mirror 25. When the position of the movable mirror 25 changes, the idle optical path length changes, so the idle light propagation time (hereinafter referred to as "idle propagation time") t0 changes. Therefore, by making the movable mirror 25 reciprocate, the detection signal of the signal light from the light detector 31 is acquired as a time waveform of the idle propagation time t0.

[0109] The counting rate calculation unit 403 calculates the “signal photon counting rate P” based on the detection signal of the signal light from the photodetector 31. s " as a function of the idle propagation time t0. The signal photon count rate P s (t0) refers to the number of signal photons counted per unit time. Signal photon counting rate P s The calculation result of (t0) is output to the Fourier transform unit 404.

[0110] The Fourier transform unit 404 calculates the signal photon counting rate P s In the quantum absorption spectroscopic system 100, the signal photon count rate P is obtained in both the state where the sample is arranged in the sample holder 24 and the state where the sample is not arranged in the sample holder 24. s (t0) The signal photon count rate P acquired when the sample is arranged in the sample holder 24 is s The Fourier spectrum obtained by Fourier transform of (t0) is recorded as “A s (ω)”. On the other hand, the signal photon count rate P obtained in the state where the sample is not arranged in the sample holder 24 is s The Fourier spectrum obtained by Fourier transform of (t0) is recorded as “A s 0 (ω)”. The Fourier transform unit 404 transforms the Fourier spectrum A s(ω) is output to the first storage unit 405 and the monitor control unit 409, and the Fourier spectrum A s 0 (ω) is output to the second storage unit 406. In addition, the Fourier spectrum A s 0 (ω) corresponds to the “reference Fourier spectrum” of the present disclosure.

[0111] The first storage unit 405 stores the Fourier spectrum A in a state where the sample is arranged in the sample holder 24 in a nonvolatile manner. s The second storage unit 406 stores the Fourier spectrum A in a nonvolatile manner when the sample is not arranged on the sample holder 24. s 0 (ω). The stored Fourier spectrum (A s (ω) or A s 0 (ω)) is appropriately read by the transmittance calculation unit 407.

[0112] The transmittance calculation unit 407 calculates the transmittance according to the Fourier spectrum A s (ω) and the Fourier spectrum A s 0 The transmittance calculation unit 407 outputs the calculation result of the complex transmittance spectrum τ(ω) to the absorption spectrum calculation unit 408 and the monitor control unit 409.

[0113] The absorption spectrum calculation unit 408 calculates the infrared absorption spectrum of the sample based on the complex transmittance spectrum τ(ω) of the sample and outputs the calculation result of the infrared absorption spectrum to the monitor control unit 409 .

[0114] The monitor control unit 409 makes the calculation result (Fourier spectrum A of the sample) of the controller 4 s (ω), complex transmittance spectrum τ(ω) and infrared absorption spectrum) are displayed on monitor 5.

[0115] <Computation Processing Details>

[0116] Next, the functions of some blocks are described in detail. In the following, the parameters appended with "signal" are parameters related to signal photons. The parameters appended with "idle" are parameters related to idle photons.

[0117] First, the calculation process performed by the count rate calculation unit 403 is described. The state vector |Ψ>, which is a superposition of two states (the first and second physical processes described above) in which quantum entangled photon pairs are generated by the nonlinear optical crystal 23, is expressed as the following equation (1).

[0118] [Formula 1]

[0119]

[0120]

[0121] In formula (1), |vac> represents the state vector of vacuum. η represents the SPDC generation efficiency. ω represents s Represents the signal frequency, using ω i Indicates the idle frequency. s ,ω i ) represents the two-photon field amplitude. + s1 and a + s2 denote the signal generation operators in the first and second physical processes respectively. + i1,in or a + i1,out Indicates the idle generation operator in the first physical process. The idle light generated in the first physical process transmits the sample arranged on the idle light path. The generation operator corresponding to the idle light before transmitting the sample is added with the subscript in, and the generation operator corresponding to the idle light after transmitting the sample is added with the subscript out, thereby distinguishing before and after the transmission of the sample. + i2 Indicates the idle generation operator in the second physical process. This indicates that the phase delay of the pumping light is obtained according to the optical path difference of the pumping light between the first physical process and the second physical process.

[0122] When the optical loss caused by a sample placed in the idle optical path is evaluated according to the beam splitter model, the idle elimination operator a after the sample is transmitted is i1,out It is represented by the following formula (2).

[0123] [Formula 2]

[0124] a i1，out =τ 2 a i1，in +rτa v1 +ra v2 …(2)

[0125] In equation (2), τ represents the complex transmittance (complex transmission amplitude) of the sample, and r represents the complex reflectance (complex reflection amplitude) of the sample. In the beam splitter model representing the transmission of the j-th (j=1, 2) sample, a vj represents the vacuum field incident from a port different from the port into which the idler photon is input.

[0126] The pattern of the signal light generated in the first physical process is adjusted so as to be spatially consistent with the pattern of the signal light generated in the second physical process. In addition, the pattern of the idle light generated in the first physical process is adjusted so as to be spatially consistent with the pattern of the idle light generated in the second physical process. As shown in the following equations (3) and (4), if the phase change caused by propagation is removed, these patterns can be expressed by the same generation and elimination operator.

[0127] [Formula 3]

[0128]

[0129]

[0130] In equations (3) and (4), t1 represents the propagation time until the signal light generated in the first physical process reaches the nonlinear optical crystal 23 again. Similarly, t0 represents the propagation time until the idle light generated in the first physical process reaches the nonlinear optical crystal 23 again when the sample is not arranged in the idle optical path.

[0131] Next, the electric field E of the signal light in the photodetector 31 s (+) (t) is represented by the following formula (5).

[0132] [Formula 4]

[0133]

[0134] The signal photon count rate P is expressed as follows using the state vector |Ψ> shown in equation (1): s .

[0135] [Formula 5]

[0136]

[0137] By substituting equations (1) to (4) into equation (5), the following equation (7) is derived: Equation (7) represents the time waveform of quantum interference (quantum beat frequency) between the first and second physical processes that generate quantum entangled photon pairs.

[0138] [Formula 6]

[0139]

[0140] Here, the distance from the center frequency ω is used s0 The detuning Ω is used to redefine the signal frequency ω s That is, it is expressed as ω s =ω s0 -Ω. About idle frequency ωi Similarly, we use the distance from the center frequency ω i0 The detuning Ω is expressed as ω i =ω i0 +Ω. Therefore, according to the above equations (6) and (7), the signal photon count rate P s It is transformed as shown in the following formula (8).

[0141] [Formula 7]

[0142]

[0143] In the experimental device disclosed in Non-Patent Document 1, a spectrometer (monochromator) is arranged in the front stage of an avalanche photodiode (APD) (see Non-Patent Document 1). Figure 2 ). The setting of the spectrometer limits the signal photons reaching the APD to narrow-band photons, which means that the infrared absorption spectrum is narrowed. This is because in Non-Patent Document 1, the wavelength of the signal photon is limited to a narrow band of the resolution of the spectrometer, and the light intensity of each band of the signal photon is measured under this limitation, thereby inferring the absorption of the idle photon at the wavelength corresponding to the signal photon.

[0144] Thus, in non-patent document 1, it is essential to use a spectrometer to split the signal light (wavelength measurement) and measure the light intensity of the signal light for each wavelength after the splitting. Generally speaking, the device including the spectrometer may be large or expensive. In addition, it takes time to scan the wavelength of the spectrometer, which may also be an obstacle to shortening the measurement time.

[0145] In the optical system disclosed in Patent Document 1, the filter system 524 is also arranged in the front stage of the photodetector 510 (see Patent Document 1). Figure 5 A and the second paragraph from the 11th line). In addition to removing unnecessary pump light, the filter system 524 also performs wavelength selection for the signal light. Thus, Patent Document 1 also preliminarily limits only signal photons in a specific narrow wavelength band to reach the photodetector 510, and only considers measuring signal photons under this limitation.

[0146] In contrast, in this embodiment, the signal photons of the entire frequency range generated by the nonlinear optical crystal 23 are detected by the photodetector 31 without passing through a spectrometer or unnecessary filters. This is based on the idea that the frequency (signal frequency) ω of the signal photons detected by the photodetector 31 is not limited. s In which frequency domain is the signal photon count rate P contained? s This idea is expressed as integrating the frequency component (detuning Ω) in the above equation (8).

[0147] Furthermore, in this embodiment, the frequency dependence of the complex transmittance τ and the complex reflectance r of the sample is considered, and the complex transmittance τ and the complex reflectance r are both set to the idle frequency ω i Function (τ→τ(ω i ), r→r(ω i )). In this case, the following formula (9) can be obtained from formula (8).

[0148] [Formula 8]

[0149]

[0150]

[0151] In equation (9), the first term (the constant term of 2) represents the signal photon count rate P s The second term (integral term) and the third term (complex conjugate term) represent the signal photon count rate P s The quantum interference component. The optical path length of the signal light in the secondary physical process of generating quantum entangled photon pairs is constant, so the propagation time t1 is a fixed value. In addition, the following equation (10) representing the standardization condition of the two-photon field amplitude holds. Therefore, from equation (9), it can be seen that the signal photon count rate P s Therefore, by moving the reflector 25 back and forth to periodically change the idle optical path length (scan the idle optical path), the signal photon count rate P for various idle propagation times t0 can be measured. s (t0). In this way, the measured signal photon count rate P s The correlated signal is also called a "quantum interference signal" (or quantum interference waveform).

[0152] [Formula 9]

[0153] ∫dΩ|F(Ω)| 2 =1 …(10)

[0154] Next, the calculation processing performed by the Fourier transform unit 404 is described. The Fourier transform unit 404 performs Fourier transform on the measured quantum interference signal (refer to the above equation (9)) while changing the idle optical path length. Thus, the Fourier spectrum A is obtained as shown in the following equation (11): s (ω) reproduces the information of each wavelength of infrared light absorbed by the sample. In the Fourier integral shown in equation (11), the constant integral term providing the DC component and the complex conjugate term providing the -ω component are omitted.

[0155] [Formula 10]

[0156]

[0157]

[0158] Next, the calculation process performed by the transmittance calculation unit 407 will be described. As described above, the Fourier spectrum when the sample is arranged in the idle optical path is recorded as A s (ω), the Fourier spectrum when the sample is not placed in the idle optical path is recorded as A s 0 (ω), thus distinguishing the two. Fourier spectrum A s 0 (ω) is equivalent to setting the complex transmittance of the sample τ = 1 in the above equation (11). Therefore, when the difference in the Fourier spectrum due to the presence or absence of the sample is calculated, more specifically, the Fourier spectrum A s (ω) relative to the Fourier spectrum A s 0 When the amplitude ratio of (ω) is 1, the following equation (12) is derived.

[0159] [Formula 11]

[0160]

[0161] As can be seen from equation (12), two measurements are performed depending on the presence / absence of the sample, and the ratio of the two Fourier spectra is taken to determine the frequency dependence of the complex transmittance τ of the sample (ie, the complex transmittance spectrum τ(ω)).

[0162] Finally, the calculation process performed by the absorption spectrum calculation unit 408 will be described. The absorption spectrum calculation unit 408 calculates the (intensity) absorption spectrum of the sample in the infrared light frequency domain by calculating the square of the absolute value of the complex transmittance spectrum τ(ω).

[0163] Thus, the quantum interference signal in the present embodiment is not generated based on light of a specific wavelength band obtained by wavelength decomposing the signal light using a spectrometer. The quantum interference signal in the present embodiment is generated based on signal light of all wavelength bands generated by the nonlinear optical crystal 23 and incident on the light detector 31 after passing through the quantum optical system 201. Therefore, according to the present embodiment, infrared absorption spectrometry in a wide wavelength band can be achieved compared to the case of using a spectrometer. In other words, according to the present embodiment, in principle, light detection of each wavelength band is not required (more specifically, neither wavelength scanning of quantum entangled photon pairs using wavelength-variable resonators based on MEMS (Micro Electro Mechanical Systems) nor wavelength decomposition of signal light using a spectrometer is required), and the complex transmittance spectrum of the sample in a wide wavelength band can be obtained through a single light detection.

[0164] In addition, by scanning the idle optical path, the signal photon count rate P s The (quantum interference signal) is calculated as a function of the idle propagation time t0 (see the above formula (9)). Then, the Fourier spectrum A can be obtained by Fourier transforming the quantum interference signal in the time domain into the frequency domain. s (ω) (refer to the above equation (11)). By analyzing the Fourier spectrum A s (ω) is analyzed, and the absolute value of the transmittance of the sample can be calculated based on the intensity change of the transmitted light of the sample. In addition, in this embodiment, how the phase of the transmitted light is shifted is determined based on the presence or absence of the sample. More specifically, the Fourier spectrum A is calculated when the sample is arranged in the idle optical path. s (ω) and the Fourier spectrum A when no sample is placed in the idle optical path s 0 (ω) (refer to the above formula (11)). The complex transmittance spectrum τ(ω) of the sample in a wide wavelength band can also be calculated by this operation. Furthermore, the infrared absorption spectrum of the sample in a wide wavelength band can also be calculated based on the complex transmittance spectrum τ(ω) of the sample.

[0165] <Measurement process>

[0166] Figure 4 1 is a flowchart showing the processing sequence of quantum absorption spectroscopy in Embodiment 1. This flowchart is called from the main routine and executed when, for example, an input device such as an operation button (not shown) accepts an operation by a measurer. Each step is basically implemented by software processing performed by the controller 4, but can also be implemented by hardware processing performed by a circuit made in the controller 4. Hereinafter, the step is abbreviated as "S".

[0167] In S1, a sample is placed in a sample holder 24 disposed in an idle optical path. The sample is usually placed by a person performing measurement. However, it is also possible to automate the process by providing a delivery device (not shown) for conveying the sample.

[0168] In S2 , the controller 4 controls the laser light source 1 to start outputting pumping light.

[0169] In S3, the controller 4 controls the driving device 250 provided on the movable reflector 25 to start or continue the high-speed reciprocating motion. Generally speaking, by accumulating the light detection results, the signal-to-noise ratio of the infrared absorption spectrum can be improved. Therefore, in S3, the movable reflector 25 moves back and forth about several tens of times per second in the range of sub-mm (e.g., tens of μm) to several cm (e.g., maximum 5 cm). However, in the case where accumulation is not required or high speed is required such as obtaining the time change of the infrared absorption spectrum, only one reciprocating motion may be performed.

[0170] In addition, in order to calculate the complex transmittance spectrum of the sample with high accuracy, it is required to measure the phase change of the transmitted light corresponding to the presence or absence of the sample with high accuracy. For this purpose, it is preferable to stabilize the optical path length of the signal light and the pump light, for example, according to a sub-wavelength scale below 25nm. In addition, it is also preferable for the drive device 250 for driving the movable reflector 25 to have a positioning accuracy of a sub-wavelength scale. However, the accuracy of the optical path length and the positioning accuracy of the drive device 250 can be appropriately determined according to the performance (resolution and / or stability) required by the quantum absorption spectroscopic system 100.

[0171] In S4, the controller 4 calculates the signal photon count rate P according to the detection signal from the light detector 31. s (t0).

[0172] In S5, the controller 4 determines whether a condition (termination condition) for terminating the reciprocating motion of the movable reflector 25 is satisfied. The controller 4 may, for example, reciprocate the movable reflector 25 for a predetermined number of times or for a predetermined time while calculating the signal photon count rate P. s (t0), it is determined that the end condition is met. If the end condition is not met (No in S5), the controller 4 returns the process to S3. Thus, the processes of S3 and S4 are repeated until data of a predetermined number of times or a predetermined time is acquired. When the end condition is met (Yes in S5), the controller 4 enters the process into S6.

[0173] In S6, the controller 4 controls the laser light source 1 to stop the output of the pumping light. In addition, the controller 4 controls the driving device 250 of the movable mirror 25 to stop the reciprocating motion of the movable mirror 25.

[0174] In S7, the controller 4 calculates the signal photon count rate P when the sample is arranged in the idle optical path. s (t0) (quantum interference signal) is Fourier transformed to calculate the Fourier spectrum A s (ω).

[0175] Although not shown, before the execution of the series of processes from S1 to S7, the Fourier spectrum A is acquired by the same process (so-called background measurement) in a state where the sample is not arranged in the idle optical path. s 0 In S8, the controller 4 calculates the Fourier spectrum A based on the series of processing. s (ω) and the Fourier spectrum A obtained in advance s 0(ω), the complex transmittance spectrum τ(ω) of the sample is calculated. In addition, when the background measurement is not performed, the sample is not arranged, and the same processing as the processing of S1 to S7 is performed to obtain the Fourier spectrum A s 0 (ω).

[0176] In S8, the controller 4 calculates the Fourier spectrum A when the sample is not arranged in the idle optical path. s 0 (ω) (reference Fourier spectrum) and Fourier spectrum A when the sample is placed in the idle optical path s The complex transmittance spectrum τ(ω) of the sample is calculated by the ratio of τ(ω) to τ(ω).

[0177] In S9 , the controller 4 calculates the infrared absorption spectrum of the sample by calculating the square of the absolute value of the complex transmittance spectrum τ(ω) of the sample.

[0178] In S10, the controller 4 controls the monitor 5 to display the measurement result of the infrared absorption spectral characteristics of the sample based on the processing of S1 to S9. Specifically, the controller 4 outputs the result of the processing of S7 so that the Fourier spectrum A of the sample in the state where the sample is arranged in the idle optical path is displayed. s (ω) is displayed on the monitor 5. In addition, the controller 4 outputs the result of the process in S8 and displays the complex transmittance spectrum τ(ω) of the sample on the monitor 5. Furthermore, the controller 4 outputs the result of the process in S9 and displays the infrared absorption spectrum of the sample on the monitor 5.

[0179] As described above, in Embodiment 1, all signal lights that have passed through the quantum optical system 201 are not separated by the spectrometer (wavelength separation or frequency separation) or removed by the filter, but are detected by the photodetector 31. Then, the Fourier spectrum A is calculated by Fourier transform of the quantum interference signal. s (ω). The information of all bands is reflected in the Fourier spectrum A s (ω), so compared with the structure of the spectrometer that only reflects information in a specific wavelength band (see non-patent document 1), it is possible to perform infrared absorption spectroscopy in a wide wavelength band. Furthermore, the phase information of the sample can be obtained by the difference in the Fourier spectrum caused by the presence or absence of the sample configuration on the idle optical path.

[0180] In general Fourier transform infrared spectroscopy (FTIR) using an existing optical system, the light intensity incident on the sample is relatively large, so the temperature of the sample may increase. In contrast, in Embodiment 1 using a quantum optical system, the light intensity incident on the sample is greatly reduced. To illustrate, in the first embodiment described below, the intensity of the idle light is 100fW (=1×10 －13This means that the light intensity is 10 times smaller than that of ordinary FTIR. 9 Therefore, according to the first embodiment, the infrared absorption spectral characteristics of the sample can be measured while suppressing the characteristic changes of the sample (which may include the deterioration and damage of the sample) associated with heating due to infrared light irradiation.

[0181] In addition, in Embodiment 1, a laser source 1 in the visible light frequency domain and a photodetector 31 in the visible light frequency domain are used instead of the conventional light source in the infrared light frequency domain and the photodetector in the infrared light frequency domain. By using a light source in the visible light frequency domain, thermal countermeasures become easier and the system can be miniaturized. In addition, by using a highly sensitive photodetector in the visible light frequency domain, cooling by liquid nitrogen for reducing thermal noise is not required, thereby also miniaturizing the system. As a result, according to Embodiment 1, it is possible to realize on-site measurement of sample extraction (so-called on-site measurement).

[0182] In addition, in Embodiment 1, infrared absorption spectroscopy in the near-infrared light frequency domain is used as an example for explanation, but the infrared light used for infrared absorption spectroscopy is not limited to near-infrared light. The quantum absorption spectroscopy disclosed in the present invention can also be applied to mid-infrared light, far-infrared light or terahertz light. When the infrared light frequency domain is used as the measurement object, the quantum absorption spectroscopy (QAS) disclosed in the present invention can be referred to as quantum Fourier transform infrared spectroscopy (Q-FTIR: Quantum Fourier Transform InfraRed spectroscopy). In addition, the light irradiated to the nonlinear optical crystal 23 is not limited to visible light, and can be either ultraviolet light or infrared light.

[0183] Furthermore, SPDC using pump light to generate quantum entangled photon pairs is described, but a four-wave mixing process can also be used instead of SPDC. When the four-wave mixing process is used, signal photons and / or idle photons having a wavelength shorter than that of the pump light can be generated. Therefore, the absorption spectroscopic characteristics of a sample in the ultraviolet light frequency domain or the visible light frequency domain can also be measured by the quantum absorption spectroscopic system disclosed in the present invention (refer to the eighth embodiment described later).

[0184] Various modifications of the quantum absorption spectroscopic system of the present disclosure will be described below. For the sake of organization, the features of each embodiment and modification are briefly summarized and shown below.

[0185] Implementation 1: Basic structure

[0186] Variation of Embodiment 1: Basic Structure + Dispersion Elements

[0187] Implementation 2: Quasi-Phase Matching Device

[0188] Embodiment 3: Single-pixel photodetector

[0189] Variation 1 of Embodiment 3: Single-pixel photodetector + quasi-phase matching device

[0190] Modification 2 of Embodiment 3: Single-pixel photodetector + circular polarization measurement

[0191] Implementation method 4: Idle optical path scanning + signal optical path scanning

[0192] Variation of Implementation 4: Signal Light Path Scanning + Total Reflection Measurement

[0193] [Variation of Embodiment 1]

[0194] Figure 5 1 is a diagram showing the overall structure of a quantum absorption spectroscopic system according to a modified example of the first embodiment. The quantum absorption spectroscopic system 100A is different from the quantum absorption spectroscopic system 100 according to the first embodiment (see Figure 1 )different.

[0195] The dispersion optical element 6 is, for example, a diffraction grating or a prism, which disperses the signal light output from the quantum optical system 201 in different directions according to the wavelength. Thus, the multi-pixel photodetector 31 is configured to measure the light intensity of the signal light of different wavelengths for each of the plurality of pixels arranged in an array. Fig.10 Description of the Fourier spectrum A in the quantum absorption spectroscopic system 100A s Characteristics of the calculation method of (ω).

[0196] [Implementation Method 2]

[0197] In Embodiment 2, a structure is described in which the wavelength band of idle light is widened to achieve infrared absorption spectroscopy in a wider wavelength band.

[0198] Figure 6 2 is a diagram showing the overall structure of a quantum absorption spectroscopic system according to Embodiment 2. The quantum absorption spectroscopic system 200 is different from the quantum absorption spectroscopic system 100 according to Embodiment 1 (see Figure 1 The quantum optical system 202 includes a quasi-phase-matched (QPM) device 7 instead of the nonlinear optical crystal 23 .

[0199] Figure 7is a diagram showing a configuration example of a QPM device 7. The QPM device 7 includes a lens 71, a nonlinear optical crystal 72, a long pass filter 73, a lens 74, and a sharp cutoff filter 75.

[0200] The nonlinear optical crystal 72 has a periodic polarization inversion structure. The arrow in the figure indicates the spontaneous polarization direction. The material of the nonlinear optical crystal 72 is, for example, Mg doped stoichiometric lithium tantalate, which is also recorded as Mg:SLT. The nonlinear optical crystal 72 has a rectangular parallelepiped shape. When pump light is incident on one end (first end) 721 of the opposite end faces of the nonlinear optical crystal 72, signal photons and idle photons are emitted from the other end (second end) 722. The nonlinear optical crystal 72 has, for example, 5 polarization inversion structures (also referred to as segments or segments) between the first end 721 and the second end 722. The number of divisions of a typical segment provided in the nonlinear optical crystal 72 is about several tens. The width of the segment (polarization inversion period Λ) is as follows Figure 7 As shown, it gradually increases from the first end 721 to the second end 722. By appropriately designing the number of segment divisions and the polarization reversal period Λ, quantum entangled photon pairs can be generated over a wide band (for details, refer to Fig.21 as well as Fig. 22 ).

[0201] The nonlinear optical crystal 72 can be manufactured using nanofabrication polarization technology. In the nanofabrication polarization technology, first, a resist pattern is drawn by electron beam lithography. Then, the resist pattern is transferred to aluminum by dry etching. After that, a strong electric field is applied to the aluminum electrode in a vacuum. For details on the structure and manufacturing method of the QPM device 7, refer to non-patent document 2.

[0202] The long pass filter 73 and the sharp cut filter 75 cut off light having a wavelength shorter than a specific wavelength in the pumping light, respectively. However, the long pass filter 73 and the sharp cut filter 75 may be omitted.

[0203] The QPM device 7 is equivalent to the “quasi-phase matching element” of the present disclosure. Figure 7 The QPM device 7 shown is a chirped element in which the polarization inversion period varies along the optical path. However, the quasi-phase matching element of the present disclosure may also be a fan-shaped (fanout structure) element in which the polarization inversion period varies in a fan-shaped manner.

[0204] As described above, in the second embodiment, the QPM device 7 disposed in the optical path of the pumping light is used to generate idle photons. Figure 21 to Figure 23To explain in detail, by selecting a suitable material for the nonlinear optical crystal 72 and appropriately designing the polarization inversion period Λ, it is possible to generate idle light having a flat intensity distribution in the entire frequency domain of the entire wide band. Therefore, according to the second embodiment, compared with the first embodiment, the band in which infrared absorption spectroscopy can be performed can be further widened.

[0205] In addition, in the present disclosure, the method of widening the wavelength band in which infrared absorption spectroscopy can be performed is not limited to the method of using a "quasi-phase matching element". Even in the case of using a bulk-type nonlinear optical crystal 23 as in Embodiment 1, the wavelength band in which infrared absorption spectroscopy can be widened. Specifically, the sample holder 24 holding the nonlinear optical crystal 23 can be arranged on a rotating table (not shown), and the rotating table is rotated by a predetermined angle each time the signal photon count rate Ps is measured. The rotation of the rotating table changes the orientation of the nonlinear optical crystal 23 (the inclination of the optical axis of the nonlinear optical crystal 23 with respect to the incident direction of the pumping light), thereby generating idle photons of various wavelengths.

[0206] However, in the above case, the order of rotating the rotating table to measure the signal photon count rate Ps must be repeated, so the measurement time may be prolonged. In addition, the calculation process for calculating the complex transmittance spectrum of the sample may become complicated. That is, the complex transmittance is calculated using the measurement result of the signal photon count rate Ps for each angle of the rotating table, and the frequency dependence of the calculated complex transmittance is plotted to obtain the complex transmittance spectrum for the first time. In contrast, when a "quasi-phase matching element" is used, the complex transmittance spectrum can be calculated based on only the measurement result of the signal photon count rate Ps once.

[0207] [Implementation Example 3 (+ Modification Example 1)]

[0208] In Embodiments 1 and 2, the structure of a multi-pixel photodetector 31 in which a plurality of pixels are arranged in a two-dimensional array is described. However, in the case of using the computational processing of quantum absorption spectroscopy disclosed in the present invention, a multi-pixel photodetector (multi-channel detector) is not necessarily required. In Embodiment 3 (and variations), the structure of a single-pixel photodetector (single-channel detector) is described.

[0209] Figure 8 3 is a diagram showing the overall structure of a quantum absorption spectroscopic system according to Embodiment 3. The quantum absorption spectroscopic system 300 is different from the quantum absorption spectroscopic system 100 according to Embodiment 1 (see Figure 1 )different.

[0210] Fig. 9 300A is a diagram showing the overall configuration of a quantum absorption spectroscopic system according to a first variation of the third embodiment. The quantum absorption spectroscopic system 300A includes a single-pixel photodetector 32 and a QPM device 7 (see FIG. 200A ) instead of the quantum optical system 201. Figure 7 ) is different from the quantum absorption spectroscopic system 100 of the first embodiment (see Figure 1 )different.

[0211] Reference Figure 8 as well as Fig. 9 The single-pixel photodetector 32 is, for example, a PIN photodiode or an APD or other photodiode. However, a phototube or a photomultiplier tube may be used instead of a photodiode. In addition, in order to obtain a high signal-to-noise ratio, a superconducting photon detector (SSPD: Superconducting Single Photon Detector) may also be used. The photodetector 32 detects the signal light in response to a control instruction from the controller 4, and outputs its detection signal to the controller 4.

[0212] The structure of the quantum absorption spectroscopic system 300A other than the photodetector 32 is the same as the corresponding structure of the quantum absorption spectroscopic system 100 of the first embodiment. Figure 6 Furthermore, the processing order of the quantum absorption spectroscopy in the third embodiment and its variant is also the same as the processing order of the quantum absorption spectroscopy in the first embodiment (refer to Figure 4 Therefore, the detailed description will not be repeated.

[0213] Fig.10 This is a conceptual diagram for explaining the difference in detection principles according to the type of photodetector. Here, two structures are compared for explanation. The first structure (see above) is a structure in which a typical nonlinear optical crystal 23 and a multi-pixel photodetector 31 are combined. Fig.10 Although not shown in the figure, a dispersive optical element 6 may be arranged between the nonlinear optical crystal 23 and the photodetector 31 (see Figure 5 ). The second structure (see below) is a structure in which the QPM device 7 and the single-pixel type photodetector 32 are combined.

[0214] First, referring to the first configuration, the emission direction of the signal photon generated by the SPDC in the nonlinear optical crystal 23 has wavelength dependence. Therefore, when a multi-pixel photodetector 31 is used, a signal light of a different frequency is detected for each pixel. In other words, in each pixel of the photodetector 31, a signal light divided into a single color is detected. Therefore, in order to realize the wide-band infrared absorption spectroscopy, it is also considered to control the signal photon count rate P for each pixel. s (t0) Perform Fourier transform to calculate the Fourier spectrum A s However, in order to realize infrared absorption spectroscopy in a wide wavelength band, it is necessary to obtain the Fourier spectrum A from each pixel. s (ω) for synthesis.

[0215] In contrast, in the second configuration, the signal photons generated by the SPDC in the QPM device 7 are not spatially divided but guided to the single-pixel photodetector 32. Thus, the signal light that may contain all frequency components is detected by the single single-pixel photodetector 32. Therefore, the signal light can be detected by only counting the single signal photon count rate P obtained by the photodetector 32. s (t0) (quantum interference signal) is Fourier transformed to calculate the Fourier spectrum A s (ω), it is possible to achieve infrared absorption spectroscopy in a wide band.

[0216] As described above, in the third embodiment, the signal photon count rate P is calculated using the single-pixel photodetector 32. s (t0), based on which the Fourier spectrum A is calculated s (ω). In the first configuration, the signal light divided into a single color must be aligned for each pixel of the multi-pixel photodetector 31. In contrast, in the third embodiment corresponding to the second configuration, the signal light can be input into the single-pixel photodetector 32, so it is easy to adjust the optical system. In addition, in the third embodiment, the Fourier spectrum A of each pixel is not required. s Furthermore, there is no need to calculate the Fourier spectrum A of multiple pixels. s (ω) synthesis. Therefore, it is also possible to reduce the calculation load of the controller 4. These effects are as follows Fig.10 This becomes particularly noticeable in the case of the broadband QPM device 7 shown below.

[0217] [Variation 2 of Implementation Example 3]

[0218] The idle photons irradiated to the sample are linearly polarized. In this case, when the sample has optical activity and / or circular dichroism, the idle photons are transmitted through the sample, thereby changing the polarization state of the idle photons, and the idle photons after the sample is transmitted become elliptically polarized. In addition, optical activity means the property of rotating the polarization axis of the photons. Circular dichroism means the property of different absorbance between left-handed circular polarization and right-handed circular polarization. Such changes in the polarization state of idle photons reduce the clarity of quantum interference, so the measurement accuracy of the infrared absorption spectroscopic characteristics of the sample may decrease.

[0219] Fig.11 3 is a diagram showing the overall structure of a quantum absorption spectroscopic system according to a second variation of the third embodiment. The quantum absorption spectroscopic system 300B is different from the quantum absorption spectroscopic system 100 according to the first embodiment (see FIG. 3 ) in that it includes a single-pixel photodetector 32 and a quantum optical system 203 instead of the quantum optical system 201. Figure 1 The quantum optical system 203 is different from the quantum optical system 201 in that it further includes a Faraday rotator 271 and a λ / 4 wavelength plate 272 .

[0220] The Faraday rotator 271 is disposed between the lens 212 and the λ / 4 wavelength plate 272 . The Faraday rotator 271 compensates for the rotation of the polarization axis of the idle photons caused by the λ / 4 wavelength plate 272 .

[0221] The λ / 4 wavelength plate 272 is disposed between the λ / 4 wavelength plate 272 and the sample holder 24. The λ / 4 wavelength plate 272 converts the idle photons from the dichroic mirror 222 toward the sample from linear polarization to circular polarization. In addition, the λ / 4 wavelength plate 272 converts the idle photons that pass through the sample from the moving reflector 25 and return to the dichroic mirror 222 from circular polarization to linear polarization.

[0222] As described above, in the second variation of the third embodiment, the Faraday rotator 271 and the λ / 4 wavelength plate 272 are added to the front stage of the sample, and the idle photons irradiated to the sample are converted into circularly polarized light. In the case where the incident light is circularly polarized light, the polarization state of the incident light is not disturbed. Therefore, according to the second variation of the third embodiment, the clarity of quantum interference caused by the optical rotation and / or circular dichroism of the sample can be suppressed. As a result, the infrared absorption spectral characteristics of the sample can be measured with high precision.

[0223] [Implementation Method 4]

[0224] In the quantum optical systems 201 to 203 described above, the movable reflector 25 is arranged in the idle optical path. However, in order to cause quantum interference between the signal photon and the idle photon, the phase (more specifically, the effective optical path length) of one of the signal photon and the idle photon can be changed relative to the phase of the other photon. Therefore, the movable reflector can also be arranged in the signal optical path.

[0225] Fig.12 4 is a diagram showing the overall structure of a quantum absorption spectroscopic system according to a fourth embodiment. The quantum absorption spectroscopic system 400 is different from the quantum absorption spectroscopic system 100 according to the first embodiment (see Figure 1 The quantum optical system 204 is different from the quantum optical system 201 in that it includes a movable mirror 28 disposed in the signal optical path in addition to the movable mirror 25 disposed in the idle optical path. A driving device 280 is provided for the movable mirror 28.

[0226] The controller 4 is configured to scan the idle optical path by reciprocating the movable reflection mirror 25 and scan the signal optical path by reciprocating the movable reflection mirror 28. The idle optical path and the signal optical path are selectively scanned.

[0227] In this example, a dichroic mirror 223 is added between the lens 213 and the movable reflector 28. The signal light of the pumping light and the signal light transmitted through the dichroic mirror 222 passes through the dichroic mirror 223 and travels toward the movable reflector 28. On the other hand, the pumping light is reflected by the dichroic mirror 223. Although not essential, it is preferable to separate the signal light from the pumping light in this way.

[0228] In addition, Fig.12 In the example shown, a single-pixel photodetector 32 is used as in the second embodiment, but a multi-pixel photodetector 31 may be used (see Figure 1 ). In addition, a QPM device 7 may be used instead of the nonlinear optical crystal 23 (see Figure 6 ).

[0229] First, regarding the state where the sample is not arranged in the idle optical path, the case where the idle optical path is scanned by moving the movable reflector 25 back and forth and the case where the signal optical path is scanned by moving the movable reflector 28 back and forth are compared. The scanning width of the idle optical path (the moving distance of the movable reflector 25) is recorded as ΔL idl , the scanning width of the signal light path (the moving distance of the moving reflector 28) is recorded as ΔL sig .

[0230] In Embodiment 1, the expression (9) has been used to explain this. However, the signal photon count rate P when scanning the idle optical path is s Depends on the idle propagation time t0. For convenience, equation (9) is recorded again below.

[0231] [Formula 12]

[0232]

[0233] When observing equation (9), it can be seen that equation (9) shows the signal photon count rate P s In addition to the idle propagation time t0, the signal propagation time t1 is also determined. The signal propagation time t1 is the time until the signal light generated by the nonlinear optical crystal 23 is reflected by the moving mirror 28 and returns to the nonlinear optical crystal 23.

[0234] Here, it is assumed that the spectrum shape of the two-photon field amplitude F(Ω) is a Gaussian function as shown in the following equation (13): In equation (13), the spectrum width of the idle photon generated by the nonlinear optical crystal 23 is expressed as σ.

[0235] [Formula 13]

[0236]

[0237] Furthermore, for simplification, the optical loss inside the quantum optical system 204 is neglected, and the complex transmittance of the sample not provided on the idle optical path is approximated as τ = 1. Therefore, the above equation (9) can be transformed as shown in the following equation (14).

[0238] [Formula 14]

[0239]

[0240] Formula (14) represents the signal photon count rate P s The formula for the dependence of the idle propagation time t0 and the signal propagation time t1. By converting the time in equation (14) into distance, equation (14) can be transformed into a formula that represents the signal photon count rate P s For idle distance L idl And the signal distance L sig Specifically, according to the dependence of L idl = ct0 and L sig = ct1, converting the idle propagation time t0 into the idle distance L idl , and transform the signal propagation time t1 into the signal distance L sig In addition, use the same i0 =ck i0 The dispersion relation will be the center frequency ω of the idle photoni0 Transformed into the central wave number k i0 , and use the same s0 =ck s0 The dispersion relation converts the central frequency ω of the signal photon into s0 Transformed into the central wave number k s0 Therefore, the following equation (15) is derived from equation (14). By using equation (15), it is possible to simulate what kind of quantum interference signal is obtained when scanning the idle optical path or the signal optical path.

[0241] [Formula 15]

[0242]

[0243] Next, the Fourier spectrum obtained when a sample as an infrared absorber is arranged in an idle optical path is described. For the purpose of distinction, the Fourier spectrum obtained by scanning the idle optical path is recorded as A s idl , the Fourier spectrum obtained by scanning the signal optical path is recorded as A s sig Fourier spectrum A when scanning the idle optical path s idl According to the above formula (11), it is derived as the following formula (16).

[0244] [Formula 16]

[0245]

[0246] The following formula (17) can be obtained from formula (16).

[0247] [Formula 17]

[0248]

[0249] Idle frequencyω i Using idle photons from the center frequency ω i0 The detuning Ω is expressed as ω i =ω i0 +Ω. When this relational expression is substituted into equation (17), equation (17) can also be expressed as equation (18). From equation (18), it can be seen that the amplitude of the Fourier spectrum distributed in the frequency domain (infrared light frequency domain) of the idle photon |A s idl (ω i0 +Ω)| and the square of the two-photon field amplitude F(Ω) and the complex transmittance τ(ω) of the sample in the infrared light frequency domain i0 +Ω) squared.

[0250] [Formula 18]

[0251]

[0252] Similarly, the Fourier spectrum A of the case where the signal optical path is scanned s sig It is derived as shown in the following formula (19).

[0253] [Formula 19]

[0254]

[0255] According to formula (19), the following formula (20) is obtained.

[0256] [Formula 20]

[0257]

[0258] Signal frequencyω s Using the center frequency ω of the signal photon s0 The detuning Ω is expressed as ω s =ω s0 -Ω. Therefore, equation (20) is expressed as equation (21) below. Equation (21) represents the amplitude |A of the Fourier spectrum of the signal photon distributed in the frequency domain, which is the visible light frequency domain, in this example. s sig (ω s0 +Ω)| and the square of the two-photon field amplitude F(-Ω) The complex transmittance τ(ω) of the sample in the infrared light frequency domain i0 -Ω) squared.

[0259] [Formula 21]

[0260]

[0261] As described above, in Embodiment 4, the quantum absorption spectroscopic system 400 is configured to scan both the idle optical path and the signal optical path. Then, as shown in the seventh embodiment below, the same wave number resolution can be achieved in both the case of scanning the idle optical path and the case of scanning the signal optical path. Therefore, depending on the absorption spectroscopic characteristics of the sample, any feasible optical path in the idle optical path and the signal optical path can be scanned.

[0262] Furthermore, when the idle optical path is scanned by moving the movable reflector 25 back and forth, the movable reflector 25 corresponds to the phase shifter of the present disclosure, and the idle photon corresponds to the “one photon” of the present disclosure. On the other hand, when the signal optical path is scanned by moving the movable reflector 28 back and forth, the movable reflector 28 corresponds to the phase shifter of the present disclosure, and the signal photon corresponds to the “one photon” of the present disclosure.

[0263] In Embodiment 4, a structure capable of scanning both the idle optical path and the signal optical path is described. However, a system structure capable of scanning only the signal optical path may also be adopted. This is because by using the scanned optical path as the signal optical path, an advantage in the installation of the quantum absorption spectroscopic system can be generated as in the following modified example.

[0264] [Variation of Implementation Example 4]

[0265] Instead of the transmission method in which a photodetector detects transmitted light from a sample, a reflection method may be used. For example, the total reflection measurement method (ATR: Attenuated Total Reflection) may be applied to the quantum absorption spectroscopic system of the present disclosure.

[0266] Fig.13 4 is a diagram showing the overall structure of a quantum absorption spectroscopic system according to a modified example of the fourth embodiment. The quantum absorption spectroscopic system 400A is different from the quantum absorption spectroscopic system 400 according to the fourth embodiment (see Fig.12 The quantum optical system 205 is different from the quantum optical system 204 in that it includes an ATR unit 8 instead of the sample holder 24 and includes a fixed mirror 29 instead of the movable mirror 25 and the drive device 250 in the idle optical path.

[0267] Fig.14 : is a diagram showing a configuration example of the ATR unit 8. The ATR unit 8 includes a lens 81, a prism 82, and a lens 83. The lens 81, the prism 82, and the lens 83 are arranged in this order along the propagation direction of the idle photons. The ATR unit 8 may also include a reflector for adjusting the optical axis instead of the lenses 81 and 83, or in addition thereto.

[0268] The prism 82 is configured to have a high refractive index and to be in contact with the sample surface. Idle photons incident from the lens 81 into the prism 82 are totally reflected at the interface between the prism 82 and the sample. At this time, idle photons (evanescent waves) that have leaked out to the sample side are absorbed by the sample surface, so by detecting the totally reflected light, the infrared absorption spectral characteristics of the sample surface can be measured.

[0269] In ATR, it is necessary to make the idle light incident on one end of the prism and reflected from the other end of the prism to the rear stage reflector (in Fig.14 In the case where the idle light path is scanned by the reciprocating movement of the movable reflector 25 arranged in the idle light path as described in the first embodiment (see Figure 1), the optical axis of the idle light can change periodically along with the reciprocating movement of the movable reflector 25. Therefore, the quantum optical system 201 must be constructed in such a way that the optical axis of the idle light is always maintained at an appropriate position during the scanning process of the idle light path. However, it is difficult to adjust such an optical system.

[0270] In addition, the ATR unit 8 and the prism 82 (and the optical system such as the lenses 81 and 82 before and after it) are larger than the sample holder 24 used in the transmission method or other reflection methods. It is also considered that when the size of the device is limited, it may be difficult to avoid mechanical contact between the sample and the movable mirror 25 while ensuring a space for the reciprocating motion of the movable mirror 25 at the stage after the sample.

[0271] In contrast, in a modification of the fourth embodiment, the signal optical path is scanned by moving the movable reflector 28 disposed in the signal optical path back and forth. In this way, the optical axis of the idle light does not change in time with the back and forth movement of the movable reflector 28. Therefore, according to the modification of the fourth embodiment, the difficulty of constructing the quantum optical system 205 can be reduced. In addition, there is no mechanical contact between the sample and the movable reflector, so the problem of ensuring space can also be avoided. Therefore, the installation of the quantum absorption spectroscopic system can be easily achieved.

[0272] In addition, there are cases where tiny bumps exist on the sample surface, in other words, the sample surface is not smooth at the microscopic level. In this case, in a typical transmission method, idle photons are scattered and / or reflected on the sample surface, which may produce multiple modes. As a result, the measurement accuracy of the infrared absorption spectroscopic characteristics of the sample may decrease due to the reduction in signal intensity and the increase in noise. On the other hand, in ATR, the prism 82 is configured to contact the sample surface, so even if tiny bumps exist on the sample surface, the above-mentioned problems will not occur. Therefore, the infrared absorption spectroscopic characteristics of the sample can be measured with high accuracy.

[0273] Embodiments 1 to 4 and variations of each embodiment can be combined appropriately. For example, the following structure can be adopted: Embodiments 2, 3, and 4 are combined, a QPM device 7 is adopted, and a single-pixel photodetector 32 is adopted, and both the idle light path and the signal light path can be scanned. The following structure can also be adopted: a variation of Embodiment 1 is combined with Embodiment 4, a dispersed optical element 6 is arranged in the front stage of a multi-pixel photodetector 31, and both the idle light path and the signal light path can be scanned. In addition, Embodiment 2 can be combined with a variation of Embodiment 4, a QPM device 7 can be adopted, and a measurement based on the total reflection measurement method can be implemented.

[0274] [Example]

[0275] Hereinafter, the results of simulating or measuring the Fourier spectrum and the absorption spectral characteristics of a sample using the quantum absorption spectroscopy system of any of Embodiments 1 to 4 (and modifications) will be described.

[0276] <First Embodiment>

[0277] In the first embodiment, the Fourier spectrum A is calculated by performing Fourier transform on the quantum interference signal obtained without placing the sample in the idle optical path. s 0 (refer to the Fourier spectrum). This measurement is the so-called background measurement, which can also be said to be a measurement of the absorption spectral characteristics of air in the idle optical path. This measurement uses the quantum absorption spectroscopic system 200 of embodiment 2 (refer to Figure 6 ) system structure. In addition, as the nonlinear optical crystal 23, a single crystal of LiNbO 3 was used (the same also applies to the second and third embodiments described later).

[0278] Fig.15 This is a diagram showing an example of the measurement result of the quantum interference signal. Fig.15 The horizontal axis represents the scan width ΔL of the idle light path. idl , the vertical axis represents the signal photon count rate P s . Fig.16 It is shown by Fig.15 The Fourier spectrum A obtained by Fourier transform of the quantum interference signal shown s 0 . Fig.16 The horizontal axis represents wavelength, and the vertical axis represents light intensity.

[0279] The central wavelength λ of the signal photon generated by the nonlinear optical crystal 23 s is 816nm, the central wavelength of the idle photon is λ i This measurement confirmed that a Fourier spectrum A having a peak near the design wavelength of idle light, 1530 nm, was obtained. s 0. Fourier spectrum A s 0 The bandwidth (full width at half maximum) is about 30nm. s The Fourier transform of the Fourier spectrum A is obtained s 0 .

[0280] <Second Embodiment>

[0281] In the second embodiment, the results of an experiment to confirm how the quantum interference effect is reflected in the spectrum of signal photons are described. This measurement uses a quantum absorption spectroscopic system 100A (see FIG. 1 ) of a modified example of the first embodiment. Figure 5 ) system structure. The central wavelength λ of the signal photon s is 810nm, the central wavelength of the idle photon is λ i The wavelength is 1550 nm. The sample is not placed in the idle light path.

[0282] Fig.17 This is a diagram showing the difference in the spectrum of signal photons due to the quantum interference effect. The horizontal axis represents the wavelength, and the vertical axis represents the light intensity of the signal photons.

[0283] exist Fig.17 The figure shows the signal photon spectrum under the constructive interference of the two processes (the first and second physical processes mentioned above) that generate quantum entangled photon pairs in the nonlinear optical crystal 23, and the signal photon spectrum under the destructive interference of the two processes that cancel each other out. Furthermore, for comparison, the signal photon spectrum is also shown when the quantum interference effect is completely eliminated by blocking idle light. Fig.17 It was confirmed that, based on the case where no quantum interference effect occurs, the intensity of the signal photon spectrum increases due to constructive interference, while the intensity of the signal photon spectrum decreases due to destructive interference.

[0284] <Third Embodiment>

[0285] In the third embodiment, the sample is placed in an idle optical path, and the refractive index of the sample is calculated from the complex transmittance spectrum of the sample. This measurement uses the quantum absorption spectroscopic system 200 of the second embodiment (see Figure 6 ) system structure to implement.

[0286] As a sample, quartz glass with a known refractive index (specifically, a quartz glass substrate with a thickness of 140 μm) was used. The literature value of the refractive index of quartz glass is 1.506 (wavelength 1550 nm). For each case where quartz glass is configured in the idle light path and the case where quartz glass is not configured, the scanning width ΔL of the idle light path is changed to idl The step width of the idle optical path was set to 100 nm, and signal photons detected for 50 milliseconds in each step were accumulated.

[0287] Fig.18 1 is a diagram showing an example of the measurement result of the quantum interference signal related to quartz glass. Due to the phase delay caused by the quartz glass, when the quartz glass is arranged, the peak of the quantum interference signal is shifted by about 150 μm compared to the case where the quartz glass is not arranged.

[0288] Fig.19 It is shown by Fig.18The Fourier spectrum A obtained by Fourier transform of the quantum interference signal shown s , A s 0 However, in order to obtain the overall measurement results of these two Fourier spectra, the scan width ΔL of the idle light path idl Expanded from 400μm to 680μm.

[0289] As described in equation (12), the Fourier spectrum A of the case where the silica glass is not arranged in the idle optical path is calculated. s 0 (ω) Fourier spectrum A when quartz glass is placed in the idle optical path s The complex transmittance spectrum τ(ω) of silica glass can be obtained by calculating the amplitude ratio of the complex transmittance spectrum τ(ω). It is difficult to plot the complex transmittance spectrum τ(ω) on a two-dimensional plane, so The complex transmittance spectrum τ(ω) is divided into the absolute value T of the transmittance and the phase difference between the two Fourier spectra. And the icon.

[0290] Fig. 20 The absolute value T of the transmittance and the phase difference obtained by measuring the quartz glass are shown in FIG. The horizontal axis represents the wavelength. The vertical axis represents the transmittance T (absolute value) at the top and the phase difference at the bottom.

[0291] According to the two Fourier spectra A s , A s 0 The amplitude ratio (|A s | / |A s 0 |) The result of calculating the complex transmittance τ is that the refractive index of silica glass is calculated to be 1.53. This value can be said to be sufficiently close to the value in the literature (about 1.51). Therefore, it is confirmed that the complex transmittance spectrum τ(ω) can be calculated with high accuracy using the quantum absorption spectroscopic system 200.

[0292] <Fourth Embodiment>

[0293] In the fourth to sixth embodiments, various results of simulating infrared absorption spectroscopy over a wide wavelength band are described. In the fourth embodiment, it is assumed that the quantum absorption spectroscopy system 300A of the first variation of the third embodiment (see Fig. 9 ) system structure.

[0294] In the following Figure 21 to Figure 23In the embodiment, the material of the nonlinear optical crystal 72 of the QPM device 7 is set to a single crystal of LiNbO3. The length of the nonlinear optical crystal 72 in the light propagation direction is set to 2 cm. The wavelength of the pumping light is set to 532 nm.

[0295] Fig.21 72 is a graph showing the polarization reversal period Λ at various positions of the nonlinear optical crystal 72. The horizontal axis represents the position in the direction from the first end 721 (incident end) to the second end 722 (exit end) of the nonlinear optical crystal 72 (refer to Figure 7 ). The vertical axis represents the polarization reversal period Λ at each position.

[0296] Assuming that the number of segments of the polarization inversion structure of the nonlinear optical crystal 72 is sufficiently large, the spatial frequency (the inverse of the polarization inversion period Λ) of the nonlinear optical crystal 72 changes linearly and continuously (chirps) between the first end 721 and the second end 722 .

[0297] In addition, the polarization reversal period Λ in the first end 721 of the nonlinear optical crystal 72 is set to 7 μm, and the polarization reversal period Λ in the second end 722 of the nonlinear optical crystal 72 is set to 11.9 μm. The polarization reversal period Λ is designed to satisfy the following two phase matching conditions regarding the two ends of the nonlinear optical crystal 72. The first phase matching condition refers to a phase matching condition related to SPDC that generates a signal photon with a wavelength of 900 nm and an idle photon with a wavelength of 1300 nm in the first end 721 of the nonlinear optical crystal 72. The second phase matching condition refers to a phase matching condition related to SPDC that generates a signal photon with a wavelength of 600 nm and an idle photon with a wavelength of 4700 nm in the second end 722 of the nonlinear optical crystal 72.

[0298] Fig. 22 1 is a diagram showing an example of simulation results of the spectrum of the quantum entangled photon pair generated using the QPM device 7. The spectrum of the signal photon is shown on the left, and the spectrum of the idler photon is shown on the right. Fig. 22 As shown, the simulation result shows that idle photons may be generated in the wide infrared light frequency range of about 1.5 μm to 4.5 μm. In addition, the absorption of the nonlinear optical crystal 72 on the side with a wavelength longer than 4.7 μm is not considered.

[0299] Fig.23 It shows that when using Fig. 22A diagram showing the simulation results of the quantum interference signal obtained in the case of a quantum entangled photon pair of the spectrum shown. The overall diagram of the quantum interference signal is shown on the left, and the enlarged diagram near the peak of the quantum interference signal is shown on the right. The top is the case where the sample is not configured, and the bottom is the case where the sample is configured. In addition, for details on the calculation method of the quantum interference signal, reference can be made to the above-mentioned formula (9), formula (14) or formula (15), etc.

[0300] In this simulation, the complex dielectric constant ε of the sample is assumed as in the following equation (22). The complex dielectric constant ε is the square of the complex refractive index N (ε = N 2 ). εb represents the background dielectric constant, Ki represents the resonance wave number, f i represents the oscillator strength, γ i Represents the line width. The influence of multiple reflections in the sample is assumed to be negligible.

[0301] [Formula 22]

[0302]

[0303] from Fig.23 It can be seen that when the quantum interference signal with the sample is compared with the quantum interference signal without the sample, the vibration period (interval between interference fringes) is the same, but a peak shift occurs due to infrared absorption by the sample.

[0304] As an example of the material of the nonlinear optical crystal 72, lithium niobate (LiNbO3) is cited and described, but other materials can also be used. For example, gallium phosphide (GaP), gallium arsenide (GaAs), lithium tantalate (LiTaO3), zinc selenide (ZnSe), etc. can be used. The material of the nonlinear optical crystal 72 can also be an organic material. The material of the nonlinear optical crystal 72 can also be, for example, DAST (4-N, N-Dimethylamino-4'-N'methylstilbazolium tosylate), DLD164, or a compound in which a functional group of a part of these compounds is replaced by other atoms or atomic groups.

[0305] Fig.24 : is a graph showing the relationship between the polarization reversal period Λ of each material of the nonlinear optical crystal 72 and the generation wavelength band of the idle light. The horizontal axis represents the polarization reversal period Λ of the nonlinear optical crystal 72, and the vertical axis represents the wavelength of the idle photon. Fig.24The simulation results for various cases where the material of the nonlinear optical crystal 72 is lithium niobate (pump light wavelength 532nm, room temperature), gallium phosphide (pump light wavelength 800nm, 55°C), gallium arsenide (pump light wavelength 1064nm, 55°C), lithium tantalate (pump light wavelength 532nm, room temperature) or zinc selenide (pump light wavelength 633nm, room temperature) are shown. In addition, for zinc selenide, it is assumed that the Mayer winding equation, which has been confirmed to be valid up to a wavelength of 16μm, can be applied up to a wavelength of 22μm.

[0306] The range of the polarization reversal period Λ is also appropriately designed in any material, so that the wavelength band of the idle photons generated by the nonlinear optical crystal 72 can be adjusted. Specifically, in lithium niobate, the polarization reversal period Λ is designed to vary in the range of 7μm to 12μm, so that the wavelength band of the idle photons can be adjusted to the range of 1μm to 5μm. In gallium phosphide, the polarization reversal period Λ is designed to vary in the range of 6.5μm to 21μm, so that the wavelength band of the idle photons can be adjusted to the range of 1.6μm to 12μm. In gallium arsenide, the polarization reversal period Λ is designed to vary in the range of 7.5μm to 27.5μm, so that the wavelength band of the idle photons can be adjusted to the range of 2μm to 18μm. In lithium tantalate, the polarization reversal period Λ is designed to vary in the range of 8μm to 13.5μm, so that the wavelength band of the idle photons can be adjusted to the range of 1μm to 5μm. In zinc selenide, the polarization reversal period Λ is designed to vary in the range of 5μm to 31.5μm, so that the wavelength band of idle photons can be adjusted to the range of 1.3μm to 22μm. The characteristics of each material that can be used for the nonlinear optical crystal 72 are sorted out and Fig.25 Shown in.

[0307] <Fifth Embodiment>

[0308] In the fifth embodiment, the simulation results of the complex transmittance spectrum when the idle photons distributed over a wide wavelength band are generated using the QPM device 7 are described. The true value of the complex refractive index of the sample is assumed to be known. More specifically, the true value of the complex refractive index of the sample is determined according to the complex dielectric constant ε of the above formula (12). Then, the simulation results and the true value are compared. In this simulation, the quantum absorption spectroscopic system 300A (refer to Fig. 9 ) system structure.

[0309] Fig.26 This is a diagram showing an example of simulation results for obtaining the complex transmittance spectrum (the spectrum of the transmittance T as an absolute value) over a wide wavelength band. As described above, by measuring the sample with or without these two configurations, two Fourier spectra A are obtained. s , As 0 The simulation result is obtained by changing the scan width ΔL of the idle light path to idl The wave number resolution of the Fourier spectrum was set to 5 cm -1 .

[0310] Fig. 27 It shows that according to Fig.26 The complex refractive index N of the sample is obtained by the complex transmittance spectrum shown in FIG. The real part Re(N) of the complex refractive index N is shown at the top, and the imaginary part Im(N) of the complex refractive index N is shown at the bottom. The simulation result of the complex refractive index is shown on the left, and the true value of the complex refractive index is shown on the right. The complex refractive index obtained by simulation is consistent with the true value to a considerable extent.

[0311] <Sixth Embodiment>

[0312] In Example 6, the measurement results of the complex transmittance of the entire wide band are described. As a sample, a bandpass filter (FBH1550-12 manufactured by Thorlabs) having a transmission band width of 12 nm near 1550 nm was used. The quantum interference signal was measured for both the case where the sample was configured in the idle light path and the case where it was not configured. The scanning width ΔL of the idle light path when the sample was configured was set to idl Set the scan width ΔL of the idle optical path when no sample is placed to 2000 μm. idl The step width of the idle light path was set to 200 μm. In any case, the step width of the idle light path was set to 100 nm, and the signal photons detected for 50 milliseconds in each step were accumulated. This measurement was performed using the quantum absorption spectroscopic system 300 of embodiment 3 (see Figure 8 ) system structure to implement.

[0313] Fig.28 This is a diagram showing an example of the measurement results of the quantum interference signal of the entire wide band. The quantum interference signal when the sample is configured is shown at the top, and the quantum interference signal when the sample is not configured is shown at the bottom. When the sample is configured, the peak of the quantum interference signal is shifted by about 2000μm compared to when the sample is not configured.

[0314] Fig.29 It shows that according to Fig.28 The quantum interference signal shown in FIG. 1 is a graph showing the result of obtaining the complex transmittance spectrum (the spectrum of transmittance T) of the sample. Specifically, the Fourier spectrum A is calculated for the presence and absence of the sample. s , A s 0The amplitude ratio of (refer to the above formula (12)). Fig.29 For comparison, the transmittance spectrum measurement results using a conventional spectrometer (UV3600-Plus manufactured by Shimadzu Corporation) are also shown. Regarding the intensity and bandwidth, it can be seen that the complex transmittance spectrum obtained from the quantum interference signal is well consistent with the complex transmittance spectrum obtained using the conventional spectrometer.

[0315] <Seventh Embodiment>

[0316] In the seventh embodiment, simulation results are described for the case where the signal optical path is scanned. Fig.12 ) system structure.

[0317] Fig.30 : is a graph showing a quantum interference signal obtained by simulation of scanning an idle optical path or a signal optical path. The horizontal axis represents the scanning width of the idle optical path (the amount of change in the idle optical path length) ΔL idl Or the scanning width of the signal light path (the change in the length of the signal light path) ΔL sig The vertical axis represents the signal photon count rate P s The entire quantum interference signal is shown on the left, and an enlarged view of the quantum interference signal near sweep width = 0 is shown on the right.

[0318] In this simulation, the irradiation wavelength is assumed to be 532 nm (wave number 18797 cm -1 ) to generate a pumping light with a wavelength of 810nm (wave number 12346cm -1 ) and the signal photon with wavelength 1550nm (wave number 6451cm -1 ) of the idle photon. The spectrum width of the idle photon is set to σ / 2πc=40cm -1 The scan width of the idle optical path is ΔL idl The maximum value of the signal light path and the scanning width ΔL sig The maximum value of is set to 500 μm. In addition, the step width (the interval between plotted points indicated by circles in the enlarged diagram) when scanning each optical path is set to 100 nm. In this case, 5000 points are plotted for each simulation.

[0319] As shown in the overall diagram on the left, the width of the quantum interference signal when scanning the idle optical path is equal to the width of the quantum interference signal when scanning the signal optical path. In addition, as shown in the enlarged diagram on the right, the quantum interference signal when scanning the idle optical path is sparse, while the quantum interference signal when scanning the signal optical path is dense. The vibration period (interval of interference fringes) of the quantum interference signal when scanning the idle optical path is read is equivalent to the wave number of the idle photons, and the vibration period of the quantum interference signal when scanning the signal optical path is equivalent to the wave number of the signal photons.

[0320] Fig.31 It is shown by Fig.30 The Fourier spectrum obtained by Fourier transforming the quantum interference signal shown in FIG. Fig.31 It can be seen that when scanning the idle optical path and the signal optical path, the same shape of Fourier spectrum can be obtained, and the wave number resolution (interval between plotted points) of the Fourier spectrum is equal. idl , ΔL sig When the scanning width of both optical paths is set to 500 μm, the wavenumber resolution of the Fourier spectrum is 20 cm -1 .

[0321] Furthermore, from Fig.31 The central wave number of each Fourier spectrum read out becomes a value corresponding to the wave number of the photon propagating in the scanned optical path. That is, the central wave number k of the Fourier spectrum when scanning the idle optical path is i0 Equivalent to the wave number of the idle photon, in this case k i0 =6452cm -1 The central wave number k of the Fourier spectrum in the case of scanning the signal optical path s0 Equivalent to the wave number of the signal photon, in this example k s0 =12346cm -1 .

[0322] Fig.32 This is a diagram showing the Fourier spectrum obtained by simulation of scanning the idle light path or the signal light path in a state where a sample as an infrared absorber is arranged in the idle light path. The horizontal axis represents the wave number, and the vertical axis represents the amplitude of the Fourier spectrum (|A s idl |、|A s sig |).

[0323] In this simulation, it is assumed that the wavelength is 532nm (wave number 18797cm -1) to generate a pumping light with a wavelength of 810nm (wave number 12346cm -1 ) and the signal photon with wavelength 1550nm (wave number 6451cm -1 ) of the idle photon. In addition, the spectrum width of the idle photon is set to σ / 2πc=1114cm -1 The absorption band of the sample was set to a wavelength of 1750nm (wave number 5714cm -1 ).

[0324] Fourier spectrum A when scanning the idle optical path s idl and Fourier spectrum A in the case of scanning the signal optical path s sig In any spectrum of , a dip indicating absorption based on the sample is confirmed. Fig.32 Read, Fourier spectrum A s idl and Fourier spectrum A s sig Symmetrical about the axis of symmetry (mirror symmetry). The wave number of the symmetry axis (indicated by a single-point dashed line) is the half-value of the wave number of the pumping light, 9396 cm -1 .

[0325] <Eighth Embodiment>

[0326] In the eighth embodiment, a structure for measuring absorption spectroscopic characteristics in the ultraviolet frequency domain is described. In this measurement, the quantum absorption spectroscopic system 400 (see Fig.12 ) is basically the same system structure. However, in the quantum absorption spectroscopic system 400, quantum entangled photon pairs of signal light in the visible light frequency domain and idle light in the infrared light frequency domain are generated, while in the quantum absorption spectroscopic system of this embodiment, quantum entangled photon pairs of signal light in the visible light frequency domain and idle light in the ultraviolet light frequency domain are generated.

[0327] In order to generate idle light in the ultraviolet frequency domain, four-wave mixing can be used as described below. Alternatively, the type of nonlinear optical crystal 23 can be changed. For example, CsB3OP5 (CBO), CsLiB6O 10 (CLBO) and other known crystals.

[0328] Fig.33 This is a diagram showing a quantum interference signal obtained by simulation of scanning an idle optical path or a signal optical path in a quantum absorption spectroscopic system for measuring absorption spectroscopic characteristics in the ultraviolet light frequency domain.

[0329] In this simulation, it is assumed that two excitation photons are converted into a photon pair of a signal photon and an idle photon, that is, the use of four-wave mixing. Specifically, it is assumed that a pump light with a wavelength of 400nm (two pump photons for excitation) is irradiated to generate a wavelength of 927nm (wave number 10788cm -1 ) and the signal photon with wavelength 255nm (wave number 392157cm -1 ) of the idle photon. In addition, the spectrum width of the idle photon is set to σ / 2πc=400cm -1 . The sample is set to non-setting.

[0330] Scan width of idle light path ΔL idl The maximum value of the signal light path and the scanning width ΔL sig The maximum value of is set to 30 μm. In addition, the step width of scanning each optical path is set to 10 nm and 125 nm. In the figure, the simulation results when the step width is 10 nm are shown on the left, and the simulation results when the step width is 125 nm are shown on the right.

[0331] When scanning the idle optical path, a normal quantum interference signal was obtained when the step width was 10nm, while distortion was confirmed in the quantum interference signal when the step width was 125nm. On the other hand, when scanning the signal optical path, a normal quantum interference signal was obtained when the step width was 10nm and when the step width was 125nm. The reason is as follows.

[0332] When the sampling theorem is applied to this embodiment, in the case of scanning the idle optical path, it is required to make the step width Δ larger than the half wavelength (λ i / 2) small (Δ<λ i / 2). When scanning the signal optical path, it is required that the step width Δ is larger than the half wavelength (λ s / 2) small (Δ<λ s / 2). More specifically, the wavelengths of the idle photons and the signal photons are distributed in a wavelength band of a predetermined width including the central wavelength. It is required to set the step width Δ to a value smaller than 1 / 2 of the lower limit value of the wavelength band.

[0333] In the present embodiment, the idle photons are ultraviolet photons. Therefore, corresponding to the amount by which the wavelength of the idle photons (central wavelength 255 nm) is shorter, it is difficult to satisfy the sampling theorem compared to the case where the idle photons are infrared photons. In this example, when the step width Δ=10 nm, 10 nm << 255 nm / 2, so the sampling theorem is satisfied. On the other hand, when the step width Δ=125 nm, 125 nm ≒ 255 / 2, so when considering that the wavelength distribution of the idle photons is typically around tens of nm, it is considered that the sampling theorem is not satisfied (undersampling).

[0334] Thus, when the idle photons are ultraviolet photons, in order to avoid undersampling when scanning the idle optical path, it is required to set the step width Δ to a very small value. Therefore, when the idle photons are ultraviolet photons, the idle optical path can be scanned without scanning the signal optical path. The signal photons are visible photons, so they are easy to satisfy the sampling theorem according to the length of their wavelength (central wavelength 927nm). In this example, when the step width Δ=10nm, the sampling theorem is of course satisfied. When the step width Δ=125nm, 125nm<<927nm / 2, so the sampling theorem is also satisfied.

[0335] Fig.34 : is a diagram showing the Fourier spectrum obtained when scanning the signal optical path. The step width is set to 125nm. When scanning the signal optical path, it is confirmed that a Fourier spectrum with a peak at an appropriate position can be obtained. On the other hand, when scanning the idle optical path, a portion of the peak of the Fourier spectrum reaches the maximum wave number of the system, 40000cm -1 Due to the limitation of system specifications, only an incomplete Fourier spectrum can be obtained. In this way, the scanning optical path can be selected according to the system specifications.

[0336] The embodiments disclosed this time should be considered in all points as illustrative and not restrictive. The scope of the present disclosure is indicated by the claims rather than the description of the embodiments above, and is intended to include all modifications within the meaning and scope equivalent to the claims.

Claims

1. A quantum absorption spectroscopic system comprising a light source, a quantum optical system, a light detector and a computing device, The light source emits pumping light, The quantum optical system is composed of: A nonlinear optical element, which generates quantum entangled photon pairs of signal photons and idle photons through the irradiation of the pumping light; as well as a phase conversion unit configured to change the phase of one of the signal photon and the idle photon, Quantum interference occurs between the multiple physical processes that produce the quantum entangled photon pairs. The photodetector outputs a quantum interference signal corresponding to the number of detected signal photons when the phase shifter changes the phase of the one photon while the sample is arranged in the optical path of the idle photon. The computing device calculates the absorption spectral characteristics of the sample by Fourier transform of the quantum interference signal, wherein the absorption spectral characteristics include phase information of the sample. In addition to calculating the Fourier spectrum by Fourier transform of the quantum interference signal when the sample is arranged in the optical path of the idle photon, the computing device also calculates a reference Fourier spectrum by Fourier transform of the quantum interference signal when the sample is not arranged in the optical path of the idle photon. The complex transmittance spectrum of the sample is calculated based on the ratio of the Fourier spectrum to the reference Fourier spectrum.

2. The quantum absorption spectroscopic system according to claim 1, wherein: The computing device calculates the absorption spectrum of the sample by squaring the absolute value of the complex transmittance spectrum of the sample.

3. The quantum absorption spectroscopic system according to claim 1 or 2, wherein: The computing device calculates the absorption spectral characteristics of the sample by performing Fourier transform on the quantum interference signal acquired in the quantum optical system without performing wavelength scanning on the quantum entangled photon pair or performing wavelength decomposition on the signal photon.

4. The quantum absorption spectroscopic system according to claim 1 or 2, wherein: The nonlinear optical element is a chirped or fan-shaped quasi-phase matching element.

5. The quantum absorption spectroscopic system according to claim 1 or 2, wherein: The nonlinear optical element is a quasi-phase matching element including a nonlinear optical crystal, The quasi-phase matching element is configured such that, when the quantum entangled photon pairs are generated multiple times, the wavelengths of the idle photon group including the idle photons are distributed over a wide band determined by the material of the nonlinear optical crystal and the polarization inversion period.

6. The quantum absorption spectroscopic system according to claim 5, wherein: The material of the nonlinear optical crystal includes lithium niobate, The polarization inversion period of the nonlinear optical crystal is determined so that the idle photon group includes a plurality of photons having mutually different wavelengths within a wavelength band of 0.4 μm to 5.2 μm.

7. The quantum absorption spectroscopic system according to claim 5, wherein: The material of the nonlinear optical crystal includes gallium phosphide, The polarization inversion period of the nonlinear optical crystal is determined so that the idle photon group includes a plurality of photons having mutually different wavelengths within a wavelength band of 0.7 μm to 12 μm.

8. The quantum absorption spectroscopic system according to claim 5, wherein: The material of the nonlinear optical crystal includes gallium arsenide, The polarization inversion period of the nonlinear optical crystal is determined so that the idle photon group includes a plurality of photons having mutually different wavelengths within a wavelength band of 1 μm to 18 μm.

9. The quantum absorption spectroscopic system according to claim 5, wherein: The material of the nonlinear optical crystal includes lithium tantalate, The polarization inversion period of the nonlinear optical crystal is determined so that the idle photon group includes a plurality of photons having mutually different wavelengths within a wavelength band of 0.3 μm to 5.5 μm.

10. The quantum absorption spectroscopic system according to claim 5, wherein: The material of the nonlinear optical crystal includes zinc selenide, The polarization inversion period of the nonlinear optical crystal is determined so that the idle photon group includes a plurality of photons having mutually different wavelengths within a wavelength band of 0.4 μm to 22 μm.

11. The quantum absorption spectroscopic system according to claim 1 or 2, wherein: The photodetector is a single-pixel type photodetector.

12. The quantum absorption spectroscopic system according to claim 1 or 2, wherein: The signal photon is a photon in the visible light frequency domain, The photodetector is a silicon based photodetector.

13. The quantum absorption spectroscopic system according to claim 1 or 2, wherein: The quantum optical system further includes a total reflection measurement device configured to be able to perform total reflection measurement of the sample.

14. The quantum absorption spectroscopic system according to claim 1 or 2, wherein: The phase conversion unit comprises: a first movable reflecting mirror configured to be movable along a propagation direction of the signal photon; and The second movable reflector is configured to be movable along the propagation direction of the idle photons. The quantum absorption spectroscopic system further comprises a control device, The control device is configured to selectively move one of the first movable reflecting mirror and the second movable reflecting mirror.

15. The quantum absorption spectroscopic system according to claim 1 or 2, wherein: The phase shifter includes a movable mirror configured to be movable along a propagation direction of the signal photon.

16. The quantum absorption spectroscopic system according to claim 1 or 2, wherein: The nonlinear optical element is configured to generate the idle photons in the ultraviolet frequency domain, The computing device calculates the ultraviolet absorption spectroscopic characteristics of the sample.

17. A quantum absorption spectroscopy method, comprising: In a quantum optical system configured to cause quantum interference between a plurality of physical processes for generating quantum entangled photon pairs of signal photons and idler photons, irradiating pump light to a nonlinear optical element, thereby generating the quantum entangled photon pairs; A step of acquiring a quantum interference signal corresponding to the number of detected photons by detecting, by a light detector, the signal photon when the phase of one of the signal photon and the idle photon is changed by a phase change unit in a state where a sample is arranged in an optical path of the idle photon, thereby; and a step of calculating the absorption spectral characteristics of the sample by Fourier transform of the quantum interference signal, wherein the absorption spectral characteristics include phase information of the sample; In addition to calculating the Fourier spectrum by Fourier transform of the quantum interference signal in a state where the sample is arranged in the optical path of the idle photon, a reference Fourier spectrum is calculated by Fourier transform of the quantum interference signal in a state where the sample is not arranged in the optical path of the idle photon. The complex transmittance spectrum of the sample is calculated based on the ratio of the Fourier spectrum to the reference Fourier spectrum.

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