Spectrometer

Abstract

The purpose of the present invention is to suppress accuracy deterioration resulting from the influence of noise light.　A spectroscopic device (1) comprises: a light source (2); a quantum optical system (4) that has one or more nonlinear optical elements (12) for generating a photon pair of idler light and signal light from pump light by an entangled photon pair generation process and that comprises a sample placement tool (35) for placing a sample (SP) on an optical path of the idler light; and a detection unit (6) that is for detecting the light intensity of light output from the quantum optical system (4); and an analysis device (8). The quantum optical system (4) is configured to emit first and second signal light (s1, s2) through differing optical paths. The detection unit (6) comprises a beam splitter (40) for receiving the first and second signal light (s1, s2) from the quantum optical system (4) and detects the respective light intensities of two light beams emitted from the beam splitter (40). The analysis device (8) acquires an interferogram from the two light beams which have been detected by the detection unit (6).

Description

[Technical Field]

[0001] This invention relates to a spectroscopic apparatus. [Background technology]

[0002] In infrared spectroscopy, a technique has been proposed that eliminates the need for infrared detection and enables spectroscopic analysis using only visible light by employing quantum mechanically correlated photon pairs (see, for example, Non-Patent Documents 1, 2, and 3). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Anna Paterova, Hongzhi Yang, Chengwu An, Dmitry Kalashnikov and Leonid Krivitsky, "Measurement of infrared optical constants with visible photons", New Journal of Physics, April 2018, Volume 20 043015 [Non-Patent Document 2] Chiara Lindner, Sebastian Wolf, Jens Kiessling, and Drunk kuhnemann, “Fourier transform infrared spectroscopy with visible light”, Optics Express, Vol. 28, Issue 4, pp. 4426-4432 (2020) [Non-Patent Document 3] Y. Mukai, M. Arahata, T. Tashima, R. Okamoto, and S. Takeuchi, “Quantum Fourier-Transform Infrared Spectroscopy for Complex Transmittance Measurements”, PHYSICAL REVIEW APPLIED, Vol. 15, Issue 3, March 2021 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] However, if stray light, ambient light, or fluorescence from optical elements generates noise in the optical system used for generating photon pairs, there is a problem in that the accuracy of the spectroscopic analysis deteriorates due to the influence of this noise.

[0005] The present invention aims to provide a spectroscopic apparatus that can suppress the decrease in accuracy caused by the influence of noise light. [Means for solving the problem]

[0006] This specification contains all the contents of Japanese Patent Application No. 2022-035693, filed on March 8, 2022. One aspect of the present invention is a spectrometer comprising: a light source that emits pump light; a quantum optical system having one or more nonlinear optical elements that receive the pump light and generate idler light and signal light photon pairs from the pump light through an entangled photon pair generation process, and a sample placement device that places a sample on the optical path of the idler light; a detection unit that detects the light intensity of the light output from the quantum optical system; and an analysis device that acquires an interferogram based on the light intensity, wherein the quantum optical system is configured to emit first and second signal light through different optical paths; the detection unit comprises a beam splitter that receives first and second signal light from the quantum optical system and detects the light intensity of each of the two lights emitted from the beam splitter; and the analysis device acquires the interferogram from the two lights detected by the detection unit. [Effects of the Invention]

[0007] According to one aspect of the present invention, it is possible to suppress the decrease in accuracy due to the influence of noise light. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic diagram showing the configuration of an infrared spectrometer according to an embodiment of the present invention. [Figure 2] Figure 2 is a schematic diagram of an interferogram obtained by the infrared spectrometer of this embodiment. [Figure 3] Figure 3 is an explanatory diagram of the synthesis of the signal rays s1 and s2 in the beam splitter. [Figure 4] Figure 4 is a schematic diagram showing the configuration of the reference setup. [Figure 5] Figure 5 is a schematic diagram of the interferogram obtained with the reference configuration. [Figure 6] Figure 6 is a schematic diagram showing the configuration of an infrared spectrometer according to Modification Example 1. [Figure 7] Figure 7 is a schematic diagram showing the configuration of an infrared spectrometer according to Modification Example 2. [Figure 8]FIG. 8 is a diagram schematically showing the configuration of the infrared spectroscopic apparatus according to Modification 3. [Figure 9] FIG. 9 is a diagram schematically showing the configuration of the infrared spectroscopic apparatus according to Modification 4. [Figure 10] FIG. 10 is a diagram schematically showing the configuration of the infrared spectroscopic apparatus according to the second embodiment. [Figure 11] FIG. 11 is a diagram schematically showing the configuration of the infrared spectroscopic apparatus according to the third embodiment. MODE FOR CARRYING OUT THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings. [First Embodiment] FIG. 1 is a diagram schematically showing the configuration of an infrared spectroscopic apparatus 1 according to the first embodiment. In FIG. 1, optical paths that overlap each other are drawn separately for convenience of explanation. The infrared spectroscopic apparatus 1 of the present embodiment is a measuring apparatus using infrared spectroscopy. Infrared spectroscopy is an analytical technique for performing structural analysis and quantification of a sample SP based on an absorption spectrum obtained by irradiating the sample SP with infrared rays. Measuring apparatuses using infrared spectroscopy are classified into a dispersive type and a Fourier transform type, and the infrared spectroscopic apparatus 1 of the present embodiment is a Fourier transform type apparatus, and the sample SP is spectroscopically analyzed by performing Fourier transform analysis on an interferogram obtained by optical interference.

[0010] In addition, the infrared spectroscopic apparatus 1 of the present embodiment uses, as light for irradiating the sample SP, an idler photon in the infrared region, which is a pair of photons that are quantum mechanically correlated, and a signal photon in the visible region, and by using quantum interference between pairs of photons that are quantum mechanically correlated, it is possible to obtain an interferogram by detecting signal photons in the visible region. Note that "pairs of photons that are quantum mechanically correlated" are also called "entangled photon pairs" or "entangled photon pairs", and in this specification, they will be referred to as "entangled photon pairs".

[0011] In addition, the infrared spectrometer 1 of this embodiment acquires an interferogram that removes the influence of noise light, such as ambient light, stray light, and fluorescence from optical elements, even when noise light is included in the signal photons, enabling highly accurate spectroscopic analysis.

[0012] As shown in Figure 1, the infrared spectrometer 1 comprises a light source 2, a quantum optical system 4, a detection unit 6, and an analysis device 8.

[0013] Light source 2 is a laser device that incidents continuous wave laser light in the visible wavelength range onto the quantum optical system 4. This laser light is used as a pump light p to excite the nonlinear crystal 12, which will be described later, in the quantum optical system 4, and in this embodiment, light with a wavelength of 532 nm is used.

[0014] The quantum optical system 4 is an optical system having at least an entangled photon pair generation function, a quantum interference function, a sample action function, a variable optical path length function, and a signal light separation output function.

[0015] [Entangled Photon Pair Generation Function] The entangled photon pair generation function generates entangled photon pairs of idler photons with wavelengths in the infrared region and signal photons with wavelengths in the visible region through an entangled photon pair generation process. In this embodiment, the wavelength of the idler photon is 1.5 μm, and the wavelength of the signal photon is 0.824 μm. Furthermore, both these idler photons and signal photons are continuous waves, and hereafter, the continuous wave idler photon will be referred to as "idler photon i," and the continuous wave signal photon will be referred to as "signal photon s."

[0016] Furthermore, spontaneous parametric down-conversion (SPDC), a nonlinear optical process, is used in the entangled photon pair generation process. That is, as shown in Figure 1, the quantum optical system 4 includes a nonlinear crystal 12, which is an example of a nonlinear optical element that generates spontaneous parametric down-conversion upon incidence of pump light p. The nonlinear crystal 12 converts the pump light p incident via the focusing lens 10 and the first dichroic mirror 11 into entangled photon pairs (idler light i and signal light s) by spontaneous parametric down-conversion, and outputs the entangled photon pairs. The phase matching conditions of the nonlinear crystal 12 are appropriately adjusted so that signal light s with a wavelength of 1 μm or less and infrared idler light i can be obtained from visible light pump light p. In this embodiment, as described above, the wavelength of signal light s is 0.824 μm and the wavelength of idler light i is 1.5 μm. The focusing lens 10 has its focal point located at the nonlinear crystal 12 and is a lens that focuses the pump light p with the nonlinear crystal 12. The first dichroic mirror 11 transmits the signal light s and reflects the pump light p.

[0017] Lithium niobate (LiNbO3) crystals are used for the nonlinear crystal 12, but other nonlinear crystals such as silver gallium sulfide (AgGaS2) crystals can also be used. Furthermore, the nonlinear optical element can be replaced with a pseudo-phase matching element in which the polarization is periodically reversed, a silicon resonator, or an optical waveguide formed from silicon (Si) and / or silicon nitride (SiN), etc., instead of the nonlinear crystal 12.

[0018] [Quantum Interference Function] The quantum interference function is a function that generates quantum interference between multiple entangled photon pair generation processes. In the quantum optical system 4 of this embodiment, the number of times the entangled photon pair generation process can occur is two. Hereinafter, the first entangled photon pair generation process will be referred to as the "first entangled photon pair generation process," and the second entangled photon pair generation process will be referred to as the "second entangled photon pair generation process." Furthermore, the idler light i and signal light s generated in the first entangled photon pair generation process will be denoted with the symbols "i1" and "s1," respectively, and the idler light i and signal light s generated in the second entangled photon pair generation process will be denoted with the symbols "i2" and "s2," respectively. The symbol "i1" may be referred to as the first idler light i1, the symbol "i2" as the second idler light i2, "s1" as the first signal light s1, and the symbol "s2" as the second signal light s2.

[0019] In quantum optics, both the first and second entangled photon pair generation processes are described by probability amplitudes. In quantum interference, when the probability amplitudes of the first and second entangled photon pair generation processes interfere while they are in phase, the probability amplitudes are amplified (so-called "constructive interference"). Conversely, when the probability amplitudes of the first and second entangled photon pair generation processes interfere while they are out of phase, the probability amplitudes cancel each other out (so-called "destructive interference").

[0020] According to quantum optics, when these "constructive interferences" and "destructive interferences" occur, the probability of detecting photons constituting an entangled photon pair increases or decreases. Conversely, when these quantum interferences do not occur (i.e., when the state vectors corresponding to the first photon generation process and the state vectors corresponding to the second photon generation process are independent and distinguishable, these quantum interferences do not occur), the above increase or decrease in detection probability does not occur.

[0021] The quantum optical system 4 of this embodiment is configured to generate quantum interference between the first entangled photon generation process and the second entangled photon generation process. More specifically, the quantum optical system 4, as shown in Figure 1, includes a fixed mirror 14 that reflects the pump light p emitted from the nonlinear crystal 12. The fixed mirror 14 reflects the pump light p incident on it so that it travels through the same optical path to the nonlinear crystal 12 and is incident on the nonlinear crystal 12 again. As a result, the pump light p passes through the nonlinear crystal 12 twice in opposite directions (i.e., round trip), generating a first entangled photon pair generation process on the outward path and a second entangled photon pair generation process on the return path. In other words, in this embodiment 1, there is one nonlinear crystal 12, and the quantum optical system 4 emits a first signal light s1 and a second signal light s2 through an optical path (optical path) of pump light p that travels back and forth through the single nonlinear crystal 12.

[0022] Furthermore, in this embodiment, the conversion efficiency of the spontaneous parametric downconversion in the nonlinear crystal 12 is low, and only a very small portion of the pump light p is converted into entangled photon pairs. Therefore, the amount of pump light p traveling back and forth through the nonlinear crystal 12 is approximately the same in the forward and return paths of the same optical path, and the amount of entangled photon pairs generated in the first entangled photon pair generation process and the second entangled photon pair generation process are also approximately the same. When the sample SP is not placed, quantum interference occurs between these two photon pair generation processes. Furthermore, a collimating lens 70 is positioned in front of the fixed mirror 14 to align the pump light p and the signal light s1.

[0023] [Sample function] The sample action function involves passing idler light i1, separated from the entangled photon pair generated in the first entangled photon pair generation process, through the sample SP to be analyzed, thereby causing absorption or reflection (absorption in this embodiment) by the sample SP. The absorption or reflection effect of the sample SP on the idler light i1 weakens the quantum interference intensity compared to when the sample SP is not present. This weakening of intensity is reflected in the detection probabilities of the signal lights s1 and s2.

[0024] In this embodiment, in order to realize the sample handling function, the quantum optical system 4 comprises a second dichroic mirror 32, a movable mirror 34, and a sample holder 35, with the sample holder 35 and a collimating lens 72 positioned between the second dichroic mirror 32 and the movable mirror 34. The sample holder 35 is a device for holding a sample SP, and includes, for example, a sample holder such as a sample case or sample stage that is transparent to idler light i, and the sample holder holds the sample SP on the optical path of idler light i1. The second dichroic mirror 32 is an optical component that separates idler light i1 from light emitted from the nonlinear crystal 12 (pump light p, signal light s1, and idler light i1). The movable mirror 34 is a reflecting mirror that receives idler light i1 separated by the second dichroic mirror 32 and reflects it back to the second dichroic mirror 32 through the same optical path it took to enter it. The collimating lens 72 is a lens that aligns the idler light i1 into parallel light. By positioning the sample SP in the optical path between the second dichroic mirror 32 and the movable mirror 34, the sample SP acts on the idler light i1 that travels back and forth between the second dichroic mirror 32 and the movable mirror 34, weakening the intensity of quantum interference. This weakening of intensity is reflected in the detection probability of signal lights s1 and s2. Since signal light s1 is entangled with idler light i1, which is acted upon by the sample SP, and signal light s2 is entangled with idler light i2, which is not acted upon by the sample SP, spectroscopic analysis of the sample SP becomes possible based on these signal lights s1 and s2.

[0025] Furthermore, by providing a sealed sample chamber for containing the sample SP in the optical path and installing the sample placement device 35 inside the sample chamber, it may be possible to perform spectroscopic analysis of the sample SP while adjusting the atmospheric pressure inside the sample chamber.

[0026] [Variable optical path length function] The variable optical path length function is a function that changes the optical path length from the second dichroic mirror 32 to the movable mirror 34. To realize this function, the quantum optical system 4 is equipped with an actuator 36 that changes the optical path length by moving the movable mirror 34 at a constant speed in the same axial direction as the optical path.

[0027] [Signal light separation output function] The signal light separation output function is a function that outputs the signal light s1 and signal light s2, which have become observable by the sample interaction function, from separate optical paths. To realize this function, the quantum optical system 4 includes a bandpass filter 38 and the fixed mirror 14. Both the bandpass filter 38 and the fixed mirror 14 are optical components that have optical properties that transmit light of the desired wavelength. The fixed mirror 14 is used as a first output component that outputs signal light s1, and the bandpass filter 38 is used as a second output component that outputs signal light s2. More specifically, the bandpass filter 38 is an optical filter that transmits the signal light s2 and blocks the other light (pump light p and idler light i2) from the light (pump light p and entangled photon pairs (signal light s2 and idler light i2)) that has passed through the second dichroic mirror 32 from the side of the nonlinear crystal 12. As a result, the signal light s2 is output from the quantum optical system 4 through the bandpass filter 38. A collimating lens 74 is placed on the output side of this bandpass filter 38, and the signal light s2 is parallelized by the collimating lens 74 and output. The fixed mirror 14 is a reflecting mirror with optical properties that reflect the pump light p and transmit the signal light s1. As a result, of the light (pump light p and signal light s1) incident on the fixed mirror 14 from the second dichroic mirror 32, the signal light s1 is output from the quantum optical system 4 through the fixed mirror 14. This signal light s1 is made into parallel light by the collimating lens 70 described above, similar to the signal light s2.

[0028] Furthermore, Non-Patent Documents 1 to 3 described above show a configuration in which the signal light s1 is superimposed on the pump light p and re-incidentated to the nonlinear crystal 12 through the same optical path, thereby outputting the signal light s1 and signal light s2 in a superimposed state. However, as in this embodiment, even if the signal light s1 is not re-incident to the nonlinear crystal 12 due to transmission through the fixed mirror 14, quantum interference occurs by combining the two signal lights s1 and s2 with the beam splitter 40 described later (see, for example, XYZou, LJWang, L.Mandel, "Induced coherence and indistinguishability in optical interference", Physical Review Letters, Volume 67, Issue 3, July 15, 1991, pp.318-321).

[0029] In this embodiment, the quantum optical system 4 has a configuration similar to that of a Michelson interferometer, with the second dichroic mirror 32, the fixed mirror 14, and the movable mirror 34. However, this configuration can be replaced with one similar to that of other interferometers, such as a Mach-Zehnder interferometer, as long as a path difference is created between the optical path between the second dichroic mirror 32 and the fixed mirror 14 and the optical path between the second dichroic mirror 32 and the movable mirror 34.

[0030] The detection unit 6 interferes with the signal light s1 and s2 output from the quantum optical system 4 by combining them, and detects the combined light. It comprises a beam splitter 40, a first detector 41, and a second detector 42.

[0031] The beam splitter 40 is an optical element that interferes by combining signal lights s1 and s2, and has two input ports 40A1 and 40A2 and two output ports 40B1 and 40B2. The signal lights s1 and s2 are incident on the beam splitter 40 from different input ports 40A1 and 40A2. Specifically, signal light s1 is incident on input port 40A1 guided from the quantum optical system 4 by a reflector 51, and signal light s2 is incident on the other input port 40A2 guided from the quantum optical system 4 by a reflector 52. These signal lights s1 and s2 are combined inside the beam splitter 40, and the combined light is branched and output to the two output ports 40B1 and 40B2, respectively.

[0032] As described above, signal light s1 is entangled with idler light i1, which is affected by sample SP, and signal light s2 is entangled with idler light i2, which is not affected by sample SP. Therefore, the light output from each of the output ports 40B1 and 40B2 is light resulting from the interference of signal light s1, which contains information about the interaction with sample SP, and signal light s2, which does not contain information about the interaction with sample SP.

[0033] In this embodiment, the beam splitter 40 has a reflectance-to-transmittance ratio of 1:1, and the amount of light output from the two output ports 40B1 and B2 is approximately equal. However, the reflectance-to-transmittance ratio of the beam splitter 40 is not limited to 1:1. Furthermore, in the following explanation, the light output from the two output ports 40B1 and 40B2 will be referred to as signal light s1' and signal light s2', respectively. However, as stated above, both signal light s1' and signal light s2' are light after the interference of signal lights s1 and s2, and signal light s1' does not originate solely from signal light s1, nor does signal light s2' originate solely from signal light s2.

[0034] The first detector 41 is a photodetector that detects signal light s1' and outputs a first detection signal to the analysis device 8, and the second detector 42 is a photodetector that detects signal light s2' and outputs a second detection signal to the analysis device 8. These first detector 41 and second detector 42 use silicon-based photodetectors with optical properties capable of detecting visible light, such as image sensors made of solid semiconductor elements like CCDs (Charged-Coupled Devices) or CMOSs ​​(Complementary Metal-Oxide-Semiconductors). Alternatively, a standalone PD (photodiode) can be used instead of an image sensor. The first detection signal and the second detection signal are signals that indicate an intensity (i.e., light intensity) corresponding to (more precisely, directly proportional to) the number of photons detected in the signal lights s1' and s2'.

[0035] The analysis device 8 acquires an interferogram based on the difference between the first detection signal of the first detector 41 and the second detection signal of the second detector 42 while the moving mirror 34 is moving at a constant speed, and performs spectroscopic analysis of the sample SP by performing Fourier transform analysis of the interferogram. The analysis device 8 of this embodiment is equipped with a computer that realizes these functions. The computer is equipped with a processor such as a CPU (Central Processing Unit) or MPU (Micro-Processing Unit), a memory device such as a ROM (Read Only Memory) or RAM (Random Access Memory) (also called main memory), a storage device such as an HDD (Hard Disk Drive) or SSD (Solid State Drive) (also called secondary memory), and an interface circuit for connecting the light source 2, quantum optical system 4 and detection unit 6 so that signals can be sent and received. The processor executes a program stored in the memory device or storage device to realize each of the functions shown in Figure 1. In other words, as shown in Figure 1, the analysis device 8 includes a moving mirror control unit 60, an interferogram acquisition unit 62, and a spectrum creation unit 64. The movable mirror control unit 60 transmits a control signal to the actuator 36 to move the movable mirror 34, thereby controlling the movement of the movable mirror 34.

[0036] The interferogram acquisition unit 62 acquires an interferogram by calculating the difference between the first detection signal of the first detector 41 and the second detection signal of the second detector 42 while the moving mirror 34 is moving at a constant speed.

[0037] The spectrum generation unit 54 generates a wavelength or wavenumber spectrum by performing a Fourier transform (e.g., Fast Fourier Transform) on the interferogram. Qualitative and quantitative analysis of the sample SP is then performed based on the peak wavenumber (wavelength) and peak intensity of this spectrum.

[0038] Furthermore, the analysis device 8 may not be limited to the functions described above, but may also control various parts of the infrared spectrometer 1, such as turning the light source 2 on and off.

[0039] Figure 2 is a schematic diagram of the interferogram acquired by the analysis device 8. An interferogram is a signal that shows the relationship between the combined signal light s1 and s2 (signal light s1', s2') and the amount of movement ΔL of the moving mirror 34 (i.e., the change in the optical path length of idler light i). In this embodiment, the combined signal light s1 and s2 is equally distributed from the beam splitter 40 into two signal light s1' and s2'. The interferogram acquisition unit 62 of the analysis device 8 then acquires the difference (P2s-P1s) between the respective light intensities P1s and P2s of these signal light s1' and s2' as an interferogram.

[0040] Figure 3 is an explanatory diagram of the synthesis of the signal rays s1 and s2 in the beam splitter 40. In the infrared spectrometer 1, as shown in Figure 3, suppose that noise (stray light, fluorescence, etc.) is mixed into the path of the signal light s2, resulting in the signal light s2 containing a noise component sx (stray light, fluorescence, etc.). In this case, when the signal light s2 is incident on the beam splitter 40, the noise component sx is evenly distributed to the paths of the signal light s1' and signal light s2'. As a result, signal light s1' and signal light s2' containing a noise component sx' with half the height of the noise component sx are output from the beam splitter 40. Here, since the signal lights s1 and s2, which originate from the crystal, undergo quantum interference, the intensities of signals s1' and s2' oscillate in opposite phases. Therefore, if we take the difference (P2s-P1s) between the respective light intensities P1s and P2s of these signal lights s1' and s2', as shown in Figure 2 above, the noise component sx' of the signal lights s1' and s2' disappears, leaving only the interference signal. Furthermore, by taking the difference between light intensities P1s and P2s (P2s-P1s), the waveform of the interferogram becomes a waveform with the difference (P2s-P1s) = 0 (zero) axis as the reference axis, that is, a waveform with an offset of "zero," as shown in Figure 2 above.

[0041] Thus, in the infrared spectrometer 1, even if noise light is generated before the detection unit 6 and this noise light mixes with the signal lights s1 and s2, the difference between the signal lights s1' and s2' cancels out the effect of the noise light, and an interferogram free from the influence of noise light is obtained. In particular, if the conversion efficiency of the nonlinear crystal 12 is poor and the light intensity of the signal lights s1, s2, s1', and s2' is weak, even a small amount of noise light can significantly reduce the accuracy of the analysis results. In contrast, with the infrared spectrometer 1 of this embodiment, an interferogram free from the influence of noise light can be obtained, thus suppressing the reduction in accuracy due to noise light and enabling highly accurate spectroscopic analysis.

[0042] Next, quantum interference and interferograms in infrared spectrometer 1 will be described in more detail from the perspective of quantum optics. To facilitate understanding these concepts, quantum interference and interferograms in a sample configuration will be explained first.

[0043] [Reference configuration] Figure 4 is a schematic diagram showing the configuration of reference configuration 1R for the infrared spectrometer 1 of this embodiment. In this figure, the same reference numerals are used for the same components as those shown in Figure 1, and their descriptions are omitted. Reference Configuration 1R, as shown in Figure 4, comprises a light source 2R, a quantum optical system 4R, a detection unit 6R, and an analysis device 8R, corresponding to the light source 2, quantum optical system 4, detection unit 6, and analysis device 8 of the infrared spectrometer 1, respectively. However, there are the following main differences between the infrared spectrometer 1 and Reference Configuration 1R. In other words, the first difference is that the quantum optical system 4 of the infrared spectrometer 1 outputs the signal light s1 and s2 separately, whereas the quantum optical system 4R of reference configuration 1R outputs them superimposed. That is, in the quantum optical system 4 of the infrared spectrometer 1, the fixed mirror 14 transmits the signal light s1, but in the quantum optical system 4R of reference configuration 1R, the fixed mirror 14R reflects the signal light s1 without transmitting it. The second difference is that the detection unit 6 of the infrared spectrometer 1 combines two signal beams s1 and s2 using a beam splitter 40, whereas the quantum optical system 4R of reference configuration 1R combines and outputs the two signal beams s1 and s2 by superimposing them through the same optical path. The third difference is that the detection unit 6 of the infrared spectrometer 1 splits the combined light into two signal lights s1' and s2' using the beam splitter 40 and outputs them, and the analysis device 8 obtains an interferogram from the difference in light intensities P1s and P2s of the signal lights s1' and s2', whereas in reference configuration 1R, the light intensity Ps of the light from which the two signal lights s1 and s2 are combined is detected by a single detector 41R, and the analysis device 8R obtains an interferogram based on the light intensity Ps.

[0044] The quantum interference and interferogram in the reference configuration 1R are described using quantum optics as follows. The meanings of symbols, variables, operators, etc., in the following explanation are shown in Table 1.

[0045] [Table 1]

[0046] First, in classical optics, light is described by an electric field described by a complex number. On the other hand, in quantum optics, the state of a system is described by a state vector, which is an element of a complex Hilbert space, and the physical quantities (operators on the Hilbert space) that act on that state vector. In reference configuration 1R, assuming for convenience that idler light i1 and idler light i2 can be distinguished, and that signal light s1 and signal light s2 can be distinguished, the state vector of quantum optical system 4R is expressed by the following equation (1).

[0047]

number

[0048] However, in the quantum optical system 4R of the reference configuration 1R, in reality, signal light s1 and signal light s2 are superimposed coaxially and have the same polarization and angular frequency, so they cannot be distinguished, and the annihilation operators of signal light s1 and signal light s2 are related by the following equation (2). Idler light i1 and idler light i2 are similarly indistinguishable. However, since idler light i1 passes through the sample SP twice, using the so-called beam splitter model, the annihilation operators of idler light i1 and idler light i2 are related by the following equation (3) (for equation (3), see, for example, Non-Patent Literature 1).

[0049]

number

[0050]

number

[0051] Therefore, when signal light s1 and signal light s2 are coupled by equation (2), and idler light i1 and idler light i2 are coupled by equation (3), the state vector of the quantum optical system 4R is given by equation (4) from equations (1) to (3).

[0052]

number

[0053] Next, in reference configuration 1R, the positive frequency electric field at time t measured by detector 41R is expressed by the following equation (5).

[0054]

number

[0055] Then, when the positive frequency electric field from equation (5) is applied to equation (4), which represents the state vector of the quantum optical system 4R, the following equation (6) is obtained.

[0056]

number

[0057] Next, the square of the norm of equation (6) is obtained by taking the dot product of the state vector in equation (6) and its conjugate vector (equation (6A)). Using this obtained equation, the time average of the signal light intensity Ps measured by detector 41R in reference configuration 1R is expressed by the following equation (7). However, in equation (7), the "t" in the lower right of "< >" means time average, and "cc" means the complex conjugate of the preceding term. The range of the time average should be at least longer than the response time of the infrared detector.

[0058]

number

[0059]

number

[0060] Here, let the wavelength center of the signal light s be ω 0s and the wavelength center of the idler light i be ω 0i . Then, in spontaneous parametric down - conversion, since ω s +ω i =ω p = constant holds, ω s and ω i in Equation (7) can be expressed respectively using one angular frequency Ω as ω s =ω 0s -Ω, ω i =ω 0i +Ω. Using this, F(ω s , ω i ) = F(Ω), and Equation (7) is expressed as the following Equation (8).

[0061]

Equation

[0062] And, in the reference configuration 1R, when the displacement amount ΔL of the moving mirror 34R is "0" and the origin of the displacement amount ΔL is set so that t 0i = t 0s , Equation (8) becomes the following Equation (9).

[0063]

Equation

[0064] Here, in order to facilitate comparison with the infrared spectrometer 1 of this embodiment, we determine the light intensity when there is no loss of signal light s and the quantum efficiency of the detector 41R is "1". The constant "2" on the right-hand side of equation (9) corresponds to the average power, and if I0 is the power of the signal light s generated when the pump light p passes through the nonlinear crystal 12 in only one direction, then it is reasonable to assume that the average power is 2I0. Therefore, in this case, equation (9) becomes equation (10), and in reference configuration 1R, an interferogram corresponding to this equation (10) is obtained.

[0065]

number

[0066] Next, the quantum interference and interferogram in infrared spectrometer 1 are described using quantum optics as follows. The meanings of symbols, variables, operators, etc., in the following explanation are shown in Table 2.

[0067] [Table 2]

[0068] Unlike in reference configuration 1R, in infrared spectrometer 1, signal light s1 and signal light s2 travel through completely different paths and are clearly distinguishable, so equation (2) above does not hold, and the annihilation operators of signal light s1 and signal light s2 are independent. On the other hand, idler light i1 and idler light i2 in infrared spectrometer 1 overlap as in reference configuration 1R, so equation (3) above holds as is. Therefore, the state vector of the quantum optical system 4 of infrared spectrometer 1 can be expressed as equation (11) using equations (1) and (3).

[0069]

number

[0070] Furthermore, in the detection unit 6 of the infrared spectrometer 1, the conversion of light in the beam splitter 40 with a transmittance-to-reflectance ratio of 1:1 is expressed by the following equation (12), using the annihilation operators of signal light s1 and signal light s2 input to different incident ports 40A1 and 40A2, and the annihilation operators of signal light s1' and signal light s2' output from different exit ports 40B1 and 40B2. In equation (12), the 2x2 matrix portion represents the conversion operation of the beam splitter 40, and each component of this matrix portion is determined based on the transmittance and reflectance of the beam splitter 40. Note that there are several ways to display the matrix related to the beam splitter 40 depending on how the phase component is handled, and here equation (12) is adopted. For example, there is also a display method in which the matrix related to the beam splitter 40 is represented by equation (12A), but the final result is essentially the same as the display method of equation (12), only with the addition of a phase constant.

[0071]

number

[0072]

number

[0073] In the infrared spectrometer 1, the positive frequency electric field at time t of the signal light s1' measured by the first detector 41 is expressed by equation (13), and similarly, the positive frequency electric field at time t of the signal light s2' measured by the second detector 42 is expressed by equation (14).

[0074]

number

[0075]

number

[0076] Then, applying equation (13) to equation (11), which represents the state vector of the quantum optical system 4, we obtain equation (15), and similarly, applying equation (14) to equation (11) yields equation (16).

[0077]

number

[0078]

number

[0079] Next, the square of the norm of equation (15) is obtained by taking the dot product of the state vector in equation (15) and its conjugate vector (equation (16A)). Using this obtained equation, the time average of the light intensity P1s of the signal light s1' measured by the first detector 41 of the infrared spectrometer 1 is expressed by the following equation (17). However, in equation (17), the "t" in the lower right of "< >" means time average, and "cc" means the complex conjugate of the preceding term. The range of the time average is set to exceed at least the response time of the infrared detector. Similarly, the square of the norm of equation (16) is obtained by taking the dot product of the state vector of equation (16) and its conjugate vector (equation (17A)). Using this obtained equation, the time average of the light intensity P2s of the signal light s2' measured by the second detector 42 of the infrared spectrometer 1 is expressed by the following equation (18). However, in equation (18), the "t" in the lower right of "< >" means time average, and "cc" means the complex conjugate of the preceding term. The range of the time average is set to exceed at least the response time of the infrared detector.

[0080]

number

[0081]

number

[0082]

number

[0083]

number

[0084] In equations (17) and (18), the constant "1" on the right-hand side is thought to represent the average power at each output port 40B1 and 40B2. In the beam splitter 40, the power is split evenly at a 1:1 ratio, so the average power at each output port 40B1 and 40B2 is equal. Therefore, in both equations (17) and (18), the ratio of the right-hand side to the left-hand side is considered to be equal, and the difference between light intensity P1s and light intensity P2s can be calculated as shown in equation (19) by simply calculating the difference between equations (17) and (18).

[0085]

number

[0086] Equation (19), like equation (8), can be expressed as equation (20) using one angular frequency Ω.

[0087]

number

[0088] Furthermore, in the infrared spectrometer 1, when the movement amount ΔL of the moving mirror 34 is "0", t 0i =t 1s -t 2s If the origin of the displacement ΔL is set such that equation (20) becomes equation (21).

[0089]

number

[0090] Here, if we determine the light intensity when there is no loss of signal light s1, s2, s1', s2' and the quantum efficiency of the first detector 41 and the second detector 42 is "1", then equations (17) and (18) become equations (22) and (23), respectively.

[0091]

number

[0092]

number

[0093] Then, equation (21) can be expressed using equations (22) and (23) as shown in equations (24) and (25). The analysis device 8 of the infrared spectrometer 1 will then produce an interferogram corresponding to equations (24) and (25).

[0094]

number

[0095]

number

[0096] Comparing equation (10) for reference configuration 1R with equation (25) for infrared spectrometer 1, equation (10) includes the term "2I0" which corresponds to the power of the signal lights s1 and s2, whereas equation (25) does not. In the quantum optical system 4R of reference configuration 1R, noise light (stray light, fluorescence, etc.), which is not entangled photon pairs generated in the nonlinear crystal 12 but rather light due to contamination, reaches the infrared detector 41R and is added to the interferogram. As a result, as shown in Figure 5, an interferogram with a waveform where the center of the power amplitude is far from zero is obtained. In contrast, in infrared spectrometer 1, noise light (stray light, fluorescence, etc.), which is not entangled photon pairs generated in the nonlinear crystal 12 but rather light due to contamination of the quantum optical system 4, is not related to quantum interference and is therefore equally distributed to the two output ports 40B1 and 40B2. As a result, in the interferogram obtained by taking the difference, such noise is removed, as shown in Figure 2.

[0097] Incidentally, as mentioned in the explanation of equation (12), the signal light s1' and signal light s2' emitted from the beam splitter 40 are inverted in phase with respect to each other. This can be explained as follows.

[0098] In other words, when measuring the light intensity of signal light s1 on the incident side of the beam splitter 40, it is clear that the source of this signal light s1 is the first entangled photon pair generation process, so quantum interference does not occur, and no fluctuation in light intensity occurs even when the movable mirror 34 is moved. Similarly, when measuring the light intensity of signal light s2 on the incident side of the beam splitter 40, no fluctuation in light intensity occurs due to the movable mirror 34 for the same reason. Furthermore, the sum of the light intensities of the two signal rays s1 and s2 incident on the beam splitter 40 is equal to the sum of the light intensities of the two signal rays s1' and s2' emitted from the beam splitter 40. Also, as mentioned above, since the light intensities of the signal rays s1 and s2 do not change even when the movable mirror 34 is moved, the sum of the light intensities of the signal rays s1' and s2' also does not change even when the movable mirror 34 is moved. Furthermore, when the light intensity of the signal light s1' is measured on the output side of the beam splitter 40, quantum interference occurs because the source of this signal light s1' is unknown, and an interferogram is observed when the movable mirror 34 is moved. The same is true when the light intensity of the signal light s2' is measured on the output side of the beam splitter 40. However, as mentioned above, the sum of the light intensities of the signal rays s1' and s2' does not change even when the movable mirror 34 is moved, so the two interferograms observed on the output side of the beam splitter 40 are in opposite phase.

[0099] The embodiments described above represent only one aspect of the present invention and can be modified and applied as needed without departing from the spirit of the invention.

[0100] For example, in the embodiment described above, an example was explained in which an interferogram is obtained from the difference (P2s-P1s) between the respective light intensities P1s and P2s of the signal lights s1' and s2'. However, the interferogram may also be obtained from the difference (αP2s-βP1s) obtained by multiplying at least one of the differences in light intensities P1s and P2s by a constant (α and β are constants, one of which may be 1). This makes it possible to cancel noise by adjusting α and β, for example, when the ratio of reflectance to transmittance of the beam splitter deviates from 1:1 and noise cannot be completely canceled by a simple difference. Furthermore, although the offset of the interferogram obtained by such an operation may not be 0 as shown in Figure 2, noise cancellation may be prioritized. Further modifications of embodiments of the present invention will be described below.

[0101] (Variation 1) In the infrared spectrometer 1 described above, the quantum optical system 4 is equipped with a variable optical path length function that changes the optical path length from the second dichroic mirror 32 to the movable mirror 34, and the configuration described above changes the optical path length of the idler light i using this optical path length changing function. However, the quantum optical system 4 may also change the optical path length of the signal light s1 instead of the optical path length of the idler light i.

[0102] Figure 6 is a schematic diagram showing the configuration of the infrared spectrometer 100 according to this modified example. In this figure, the same reference numerals are used for the components shown in Figure 1, and their descriptions are omitted. In the infrared spectrometer 100 according to this modified example, the quantum optical system 104 uses a fixed mirror 114 as a reflector that reflects the idler light i1, thereby fixing the optical path length of the idler light i1. The quantum optical system 104 also includes an optical path length variable mechanism 180 in front of the detection unit 6 for varying the optical path length of the signal light s1. The optical path length variable mechanism 180 includes a movable mirror 34 that is moved at a constant speed by an actuator 36, a first reflector 181 that reflects the signal light s1 that has passed through the fixed mirror 14 toward the movable mirror 34, and a second reflector 182 that reflects the signal light s1 reflected by the movable mirror 34 toward the detection unit 6. The optical path length of the signal light s1 (the optical path length between the second dichroic mirror 32 and the movable mirror 34) is varied by the movement of the movable mirror 34. As described above, the signal light s1 is entangled with the idler light i1 passing through the sample SP and contains information about its interaction with the sample SP. Therefore, by varying the optical path length of the signal light s1 and interfering it with the signal light s2, which does not contain information about the sample SP, an interferogram can be obtained.

[0103] According to this modification, it is not necessary to extend the optical path length of the idler light i in which the sample SP is placed, and it can be fixed to the minimum required length. This allows the dimensions of the sample chamber containing the sample SP to be limited to the minimum required length. Therefore, even when it is necessary to introduce air into the sample chamber for analysis, the amount of air can be limited, and the decrease in analytical accuracy due to absorption by moisture in the air can be suppressed.

[0104] (Modification 2) In the infrared spectrometer 1 described above, the quantum optical system 4 is equipped with a fixed mirror 14 that reflects the pump light p emitted from the nonlinear crystal 12 and re-enters the nonlinear crystal 12 in order to realize a quantum interference function that generates quantum interference between multiple entangled photon pair generation processes. By causing the pump light p to move back and forth across the nonlinear crystal 12, multiple entangled photon pair generation processes are generated in the same nonlinear crystal 12. However, the quantum optical system 4 may also generate entangled photon pair generation processes in different nonlinear crystals 12.

[0105] Figure 7 is a schematic diagram showing the configuration of the infrared spectrometer 200 according to this modified example. In this figure, the same reference numerals are used for the components shown in Figure 1, and their descriptions are omitted. The quantum optical system 204 of the infrared spectrometer 200 includes a first nonlinear crystal 12A and a second nonlinear crystal 12B that can be considered identical to each other, instead of a single nonlinear crystal 12, and is configured such that the pump light p emitted from the light source 2 passes through these first nonlinear crystal 12A and second nonlinear crystal 12B in sequence, thereby generating a first entangled photon pair generation process and a second entangled photon pair generation process. That is, in the modified example 2, the system includes a first nonlinear crystal 12A and a second nonlinear crystal 12B, and the quantum optical system 204 emits a first signal light s1 in the optical path of the pump light p incident on the first nonlinear crystal 12A, and emits a second signal light s2 in the optical path of the pump light p incident on the second nonlinear crystal 12B.

[0106] In this configuration, a variable optical path length mechanism 280 for varying the optical path length of idler light i1 is positioned between the first nonlinear crystal 12A and the second nonlinear crystal 12B. The variable optical path length mechanism 280 has substantially the same configuration as the variable optical path length mechanism 180 provided in the infrared spectrometer 100, and comprises a movable mirror 34, a first reflecting mirror 281 that reflects the idler light i1 emitted from the first nonlinear crystal 12A toward the movable mirror 34, and a second reflecting mirror 282 that reflects the idler light i1 reflected by the movable mirror 34 toward the sample SP. The optical path length of the idler light i1 is varied by moving the movable mirror 34 at a constant speed by an actuator 36.

[0107] Meanwhile, the pump light p and signal light s1 emitted from the first nonlinear crystal 12A are reflected by the reflector 221 toward the fixed mirror 14, and the signal light s1 passes through the fixed mirror 14 and is output to the detection unit 6. The pump light p is reflected by the fixed mirror 14 and incident on the second nonlinear crystal 12B via the focusing lens 276 and the third dichroic mirror 236. Furthermore, the idler light i1 that passes through the sample SP is incident on the second nonlinear crystal 12B in an overlapping state with the pump light p, passing through the focusing lens 277 and the third dichroic mirror 236. As a result, the second entangled photon pair generation process and the first entangled photon pair generation process in the second nonlinear crystal 12B cause quantum interference. In this case, since the idler light i1 passes through the sample SP only once, the equation corresponding to equation (3) becomes equation (25A), and the equations corresponding to equations (10) and (25), etc., are expressed as follows in their respective equations: *2 " to "τ * This will be replaced with ".

[0108]

number

[0109] In this modified infrared spectrometer 200, when absorption by the sample SP is large, the amplitude of the resulting interferogram increases, making it possible to measure even larger absorbances. For example, power transmittance 10 -4 When the sample SP is the target of measurement, the amplitude of the resulting interferogram is 100 times (=√10 -4 ) / (10 -4 )) Furthermore, with the infrared spectrometer 200 according to this modified example, there is no need to return the pump light p to the same nonlinear crystal 12 (Figure 1), thus improving the degree of freedom in the layout of the quantum optical system 204.

[0110] (Variation 3) In the infrared spectrometer 200 according to Modification 2, the quantum optical system 204 is configured to vary the optical path length of the idler light i1, but similar to Modification 1, it may also be configured to vary the optical path length of the signal light s1. Figure 8 is a schematic diagram showing the configuration of the infrared spectrometer 300 according to this modified example. In this figure, the same reference numerals are used for the components shown in Figure 7, and their descriptions are omitted. In the quantum optical system 304 of the infrared spectrometer 300, instead of the variable optical path length mechanism 280 that varies the optical path length of idler light i1, a variable optical path length mechanism 380 that varies the optical path length of signal light s1 is provided. The variable optical path length mechanism 380 has substantially the same configuration as the variable optical path length mechanism 180 provided in the infrared spectrometer 100, and comprises a movable mirror 34, a first reflecting mirror 381 that reflects the signal light s1 emitted from the nonlinear crystal 12A and passed through the fixed mirror 14 toward the movable mirror 34, and a second reflecting mirror 382 that reflects the signal light s1 reflected by the movable mirror 34 toward the detection unit 6. The optical path length of the signal light s1 is varied by moving the movable mirror 34 at a constant speed by the actuator 36.

[0111] (Modification 4) In the infrared spectrometer 100 according to Modification 1 and the infrared spectrometer 300 according to Modification 3, a configuration was described in which the optical path length of the signal light s1 is varied. When the optical path length of the signal light s1 is varied in this way, it is preferable that the optical path length of the pump light p is also varied by the same amount as the optical path length of the signal light s1.

[0112] More specifically, the interferogram based on the difference in light intensities P1s and P2s of the two signal lights s1' and s2' output from the beam splitter 40 is a waveform corresponding to equation (21) above. Equation (21) is the product of the integral calculation part shown in equation (26) and the variation factor part shown in equation (27).

[0113]

number

[0114]

number

[0115] The integral part is a factor of the envelope that changes slowly, and the fluctuation factor is a factor that oscillates violently in the phase shown in equation (27).

[0116] In the infrared spectrometer 1 according to the embodiment and the infrared spectrometer 200 according to the modified example 2, when the optical path length of idler light i1 is moved by ΔL, t 0i Since it moves with a coefficient of 2ΔL / c, the phase change is given by equation (28) below.

[0117]

number

[0118] Here, .'' oi Since λ is the central wavelength of idler light i, the interferogram is the idler central wavelength λ. oi This results in oscillations with half the period, and by processing the interferogram, the transmittance of the sample SP with respect to the idler wavelength can be determined.

[0119] In contrast, in the infrared spectrometer 100 according to Modification 1 and the infrared spectrometer 300 according to Modification 3, the optical path length of the signal light s1 is varied. However, using the same explanation as when the optical path length of the idler light i1 is varied, the interferogram in this case oscillates at half the central wavelength of the signal light s1. Therefore, processing this interferogram directly yields the relationship between the "signal wavelength" and the "transmittance for the idler wavelength corresponding to that signal wavelength." In this case, when the wavelength of the pump light p can be considered constant, the relationship between the idler wavelength and the transmittance corresponding to that idler wavelength can be derived from this. However, when the wavelength of the pump light p drifts or otherwise cannot be considered constant, it becomes necessary to measure the wavelength of the pump light p separately.

[0120] Therefore, when the optical path lengths of both the signal light s1 and the pump light p are varied by the same amount, the phase is given by the following equation (29).

[0121]

number

[0122] In this case, when the moving mirror 34 is moved by a displacement ΔL, the interferogram oscillates with a period of half the wavelength of the idler light i1, similar to the infrared spectrometer 1 according to the embodiment and the infrared spectrometer 300 according to Modification 3. Therefore, even when the wavelength of the pump light p is fluctuating, it is possible to directly determine the spectral characteristics (such as transmittance) of the sample SP with respect to the wavelength of the idler light based on the interferogram.

[0123] Figure 9 is a schematic diagram showing the configuration of the infrared spectrometer 400 according to this modified example. In this figure, the same reference numerals are used for the components shown in Figure 8, and their descriptions are omitted. As shown in the figure, in the quantum optical system 404 of the infrared spectrometer 400, the optical path length variable mechanism 380 (Figure 8) described above, which varies the optical path length of the signal light s1, is placed between the nonlinear crystal 12A and the fixed mirror 14, so that the path lengths of the signal light s1 and the pump light p are varied by the same amount.

[0124] Those skilled in the art will understand that the exemplary embodiments described above, and each of their modifications, are specific examples of the following embodiments.

[0125] A spectroscopic apparatus according to one embodiment comprises a light source that emits pump light, a quantum optical system into which the pump light is incident, a detection unit that detects the light intensity of the light output from the quantum optical system, and an analysis device that acquires an interferogram based on the light intensity, wherein the quantum optical system comprises a nonlinear optical element that generates photon pairs of idler light and signal light by causing a first entangled photon pair generation process upon incidence of pump light from the light source, a movable mirror that varies the optical path length of the idler light or the signal light, and a fixed mirror that reflects the pump light emitted from the nonlinear optical element and causes it to incident again on the nonlinear optical element, thereby causing a second entangled photon pair generation process in the nonlinear optical element that produces quantum interference with the first entangled photon pair generation process, A spectrometer comprising: a sample placement device for placing a sample on the optical path of idler light generated in either the first entangled photon pair generation process or the second entangled photon pair generation process; a first output member for outputting signal light generated in the first entangled photon pair generation process; and a second output member for outputting signal light generated in the second entangled photon pair generation process, wherein the detection unit comprises a beam splitter into which the signal light output from the first output member and the second output member of the quantum optical system is incident, and two detectors for detecting the light intensity of each of the two beams emitted from the beam splitter, and the analysis device for acquiring the interferogram by the difference in the light intensity detected by each of the two detectors.

[0126] According to the spectroscopic apparatus of the above embodiment, an interferogram free from the effects of noise light can be obtained.

[0127] A spectroscopic apparatus according to one embodiment comprises a light source that emits pump light, a quantum optical system into which the pump light is incident, a detection unit that detects the light intensity of the light output from the quantum optical system, and an analysis device that acquires an interferogram based on the light intensity, wherein the quantum optical system includes a first nonlinear optical element that generates photon pairs of idler light and signal light by causing a first entangled photon pair generation process upon incidence of pump light from the light source, a movable mirror that varies the optical path length of the idler light or the signal light, a fixed mirror that reflects the pump light emitted from the first nonlinear optical element, and a second nonlinear optical element that causes a second entangled photon pair generation process that causes quantum interference with the first entangled photon pair generation process upon incidence of the pump light reflected by the fixed mirror A spectrometer comprising a linear optical element, a sample placement device for placing a sample on the optical path of the idler light generated in either the first entangled photon pair generation process or the second entangled photon pair generation process, a first output member for outputting signal light generated in the first entangled photon pair generation process, and a second output member for outputting signal light generated in the second entangled photon pair generation process, wherein the detection unit comprises a beam splitter into which the signal light output from the first output member and the second output member of the quantum optical system is incident, and two detectors for detecting the light intensity of each of the two beams emitted from the beam splitter, and the analysis device acquires the interferogram by the difference in the light intensity detected by each of the two detectors.

[0128] According to the spectroscopic apparatus of the above embodiment, an interferogram free from the effects of noise light can be obtained. Furthermore, since it is not necessary to return the pump light to the same nonlinear optical element, the degree of freedom in the layout of the quantum optical system is improved.

[0129] In the spectroscopic apparatus according to each of the above embodiments, the quantum optical system may be configured such that the signal light and the pump light are incident on the movable mirror, and the optical path lengths of the signal light and the pump light are varied by the movement of the movable mirror by the same amount.

[0130] This spectrometer allows for the direct determination of the sample's spectral characteristics against the idler light wavelength based on the interferogram, even when the pump light wavelength is fluctuating.

[0131] [Second Embodiment] Figure 10 is a schematic diagram showing the configuration of the infrared spectrometer 500 according to the second embodiment. 504 represents the quantum optical system. In this figure, the same reference numerals are used for components that are the same as those shown in Figure 1, and their descriptions are omitted. Also, in Figure 10, overlapping optical paths are depicted separately for the sake of clarity. The quantum optical system 504 of the second embodiment, like the modified examples 2 to 4 shown in Figures 7 to 9, includes a first nonlinear crystal 12A and a second nonlinear crystal 12B, which can be considered identical to each other, instead of a single nonlinear crystal 12. Here, the first nonlinear crystal 12A and the second nonlinear crystal 12B have equivalent properties.

[0132] In the second embodiment, unlike modifications 2 to 4, a pump light beam splitter (pump light branching member) 210 is provided in front of the first nonlinear crystal 12A, with a transmittance-to-reflectance ratio of 1:1. The pump light p is split into two pump lights p1 and p2 by the pump light beam splitter 210. One pump light p1 is incident on the first nonlinear crystal 12A, causing a first entangled photon pair generation process, and the other pump light p2 is incident on the second nonlinear crystal 12B, causing a second entangled photon pair generation process. In addition, the second embodiment is provided with a movable mirror (signal light reflection mirror for signal light path length adjustment) 134 which constitutes a variable optical path length mechanism for varying the optical path length of the signal light s1.

[0133] To elaborate on the quantum optical system 504, one pump light p1 passes through the focusing lens 10 and is incident on the first nonlinear crystal 12A, where a very small portion of the pump light p1 is converted into a first signal light s1 and a first idler light i1 by spontaneous parametric downconversion. The pump light p1, the partially converted first signal light s1, and the first idler light i1 pass through the collimating lens 76 and enter the first idler light reflection mirror 150. The pump light p1 and the first signal light s1 pass through the first idler light reflection mirror 150, while the first idler light i1 is reflected by the first idler light reflection mirror 150.

[0134] The pump light p1 and the first signal light s1 transmitted through the first idler light reflection mirror 150 are incident on a bandpass filter (BPS) 151. The first signal light s1 separated by the bandpass filter 151 is reflected in the order of the first signal light reflection mirror 153, the movable mirror (signal light reflection mirror for adjusting the signal light path length) 34, and the second signal light reflection mirror 154, and introduced into the first input port of a signal light mixing beam splitter 240 where the ratio of transmittance to reflectance is 1:1. A first detector 41 is connected to the first input port, and the first signal light s1' is measured by the first detector 41. Furthermore, the first idler light i1 reflected by the first idler light reflection mirror 150 described above is incident on the sample placement device 35.

[0135] The other pump light p2, which has been split by the pump light beam splitter 210, is reflected by the pump reflection mirror 155 and transmitted through the second idler light reflection mirror 156. At the second idler light reflection mirror 156, the first idler light i1 described above, which has been transmitted through the sample holder 35, is reflected, and the other pump light p2 and the first idler light i1 are incident on the second nonlinear crystal 12B via the focusing lens 10.

[0136] In the second nonlinear crystal 12B, a very small portion of the pump light p2 is converted into the second signal light s2 and the second idler light i2 by spontaneous parametric downconversion. Since the conversion efficiency is small, the power of the pump light p2 can be considered equal before and after incidence.

[0137] The second signal light s2, pump light p2, first idler light i1, and second idler light i2 emitted from the second nonlinear crystal 12B pass through the collimating lens 78 and are incident on the signal light reflection mirror 157. At this time, the optical paths of the first idler light i1 and the second idler light i2 overlap precisely. The pump light p2, the first idler light i1, and the second idler light i2 are transmitted through the signal light reflection mirror 157, and the second signal light s2 is reflected by the signal light reflection mirror 157. This reflected second signal light s2 is introduced into the second input port of the signal light mixing beam splitter 240. A second detector 42 is connected to the second input port, and the second signal light s2' is measured by the second detector 42.

[0138] In the analysis device 8, the difference between the signal light intensity of the first signal light s1' measured by the first detector 41 and the signal light intensity of the second signal light s2' measured by the second detector 42 is recorded, and an interferogram is obtained by moving the movable mirror (signal light reflection mirror for adjusting the signal light path length) 34, and the sample SP is spectrally analyzed by performing a Fourier transform analysis of the interferogram.

[0139] In other words, according to the second embodiment, a beam splitter 210 for branching pump light is provided in front of the nonlinear crystal 12, and the nonlinear crystal 12 consists of two nonlinear crystals, a first and a second nonlinear crystal 12A and 12B. The quantum optical system 504 is configured to direct one of the pump light beams p1, branched by the beam splitter 210, into the first nonlinear crystal 12A, and the other pump light beam p2, into the second nonlinear crystal 12B. This increases the design flexibility of the quantum optical system 504.

[0140] According to the second embodiment, since a movable mirror 34 is provided that can change the optical path length of the signal light s1, an interferogram can be obtained from the difference between the light intensity of the first signal light s1' measured by the first detector 41 and the light intensity of the second signal light s2' measured by the second detector 42 while the movable mirror 34 is moving at a constant speed, and the sample SP can be spectroscopically analyzed by performing Fourier transform analysis of the interferogram.

[0141] [Third Embodiment] Figure 11 is a schematic diagram showing the configuration of the infrared spectrometer 600 according to the third embodiment. 604 represents the quantum optical system. In this figure, the same reference numerals are used for the components shown in Figures 1 and 10, and their descriptions are omitted. Also, in Figure 11, overlapping optical paths are depicted separately for the sake of clarity. In the second embodiment, the signal optical path length is adjusted using a movable mirror (signal optical path length adjustment signal light reflection mirror) 34, but in the third embodiment, the idler optical path length is adjusted using a movable mirror (idler optical path length adjustment idler reflection mirror) 34 that constitutes an optical path length variable mechanism for varying the optical path length of the idler light i1.

[0142] One of the pump beams p1, split by the beam splitter 210 for splitting the pump beam, passes through the focusing lens 10 and is incident on the first nonlinear crystal 12A, where a very small portion of the pump beam p1 is converted into the first signal beam s1 and the first idler beam i1. The pump light p1, the partially converted first signal light s1, and the first idler light i1 pass through the collimating lens 76 and enter the first idler light reflection mirror 150. The pump light p1 and the first signal light s1 pass through the first idler light reflection mirror 150, while the first idler light i1 is reflected by the first idler light reflection mirror 150.

[0143] The pump light p1 and the first signal light s1 transmitted through the first idler light reflection mirror 150 are incident on the bandpass filter 151. The first signal light s1 separated by the bandpass filter 151 is reflected by the first signal light reflection mirror 161 and the second signal light reflection mirror 162, and introduced into the first input port of the signal light mixing beam splitter 240, where the ratio of transmittance to reflectance is 1:1. A first detector 41 is connected to the first input port, and the first signal light s1' is measured by the first detector 41. Furthermore, the first idler light i1 reflected by the first idler light reflection mirror 150 described above is incident on the sample placement device 35.

[0144] The other pump light p2, which is branched by the pump light beam splitter 210, is reflected by the pump reflection mirror 155 and transmitted through the second idler light reflection mirror 156. The first idler light i1 described above, which has been transmitted through the sample holder 35, is reflected in the order of the third idler light reflection mirror 163, the movable mirror (idler light reflection mirror for adjusting the idler light path length) 34, and the fourth idler light reflection mirror 164, and is reflected by the second idler light reflection mirror 156. The other pump light p2 and the first idler light i1 emitted from the second idler light reflection mirror 156 pass through the focusing lens 10 and are incident on the second nonlinear crystal 12B.

[0145] In the second nonlinear crystal 12B, a very small portion of the pump light p2 is converted into the second signal light s2 and the second idler light i2. Since the conversion efficiency is small, the power of the pump light p2 can be considered equal before and after incidence.

[0146] The second signal light s2, pump light p2, first idler light i1, and second idler light i2 emitted from the second nonlinear crystal 12B pass through the second collimating lens 78 and are incident on the signal light reflection mirror 157. The pump light p2, the first idler light i1, and the second idler light i2 are transmitted through the signal light reflection mirror 157, and the second signal light s2 is reflected by the signal light reflection mirror 157. This reflected second signal light s2 is introduced into the second input port of the signal light mixing beam splitter 240. A second detector 42 is connected to the second input port, and the second signal light s2' is measured by the second detector 42.

[0147] In the analysis device 8, the difference between the signal light intensity of the first signal light s1' measured by the first detector 41 and the signal light intensity of the second signal light s2' measured by the second detector 42 is recorded, and an interferogram is obtained by moving the movable mirror (idler light reflection mirror for adjusting the idler optical path length) 34, and the sample SP is spectrally analyzed by performing a Fourier transform analysis of the interferogram.

[0148] According to the third embodiment, similar to the second embodiment, the degree of freedom in designing the quantum optical system 604 is increased, and because it is equipped with a movable mirror 234 that can change the optical path length of the first idler light i1, an interferogram can be obtained from the difference between the light intensity of the first signal light s1' measured by the first detector 41 and the light intensity of the second signal light s2' measured by the second detector 42 while the movable mirror 234 is moving at a constant speed, and the sample SP can be spectroscopically analyzed by performing Fourier transform analysis of the interferogram.

[0149] (Other variations) In each of the embodiments and modifications described above, the combinations of the wavelengths of the pump light p, signal lights s1 and s2, and idler lights i1 and i2 may be arbitrarily changed depending on the spectroscopic apparatus to which the present invention is applied.

[0150] In each of the embodiments and modifications described above, the configuration of each quantum optical system 4, 104, 204, 304, 404 can be replaced with other classically equivalent configurations or other quantum optically equivalent configurations.

[0151] In the embodiments described above and in each of the modifications, the horizontal and vertical directions, various numerical values, shapes, and materials include, unless otherwise specified, a range that produces the same effects as those directions, numerical values, shapes, and materials (the so-called equivalence range).

[0152] [Pattern] Those skilled in the art will understand that the exemplary embodiments described above, and each of their modifications, are specific examples of the following embodiments.

[0153] (Section 1) A spectroscopic apparatus according to one embodiment comprises a light source that emits pump light, a quantum optical system that has one or more nonlinear optical elements into which the pump light is incident and which generate idler light and signal light photon pairs from the pump light through an entangled photon pair generation process, and a sample placement device that places a sample on the optical path of the idler light, a detection unit that detects the light intensity of the light output from the quantum optical system, and an analysis device that acquires an interferogram based on the light intensity, wherein the quantum optical system is configured to emit first and second signal light through different optical paths, the detection unit comprises a beam splitter that receives first and second signal light from the quantum optical system and detects the light intensity of each of the two lights emitted from the beam splitter, and the analysis device acquires the interferogram from the two lights detected by the detection unit.

[0154] According to the spectroscopic apparatus described in paragraph 1, an interferogram free from the effects of noise light can be obtained.

[0155] (Section 2) In the spectroscopic apparatus described in Section 1, there is one nonlinear optical element, and the quantum optical system may emit first and second signal light in the optical path of the pump light that reciprocates through the one nonlinear optical element. According to the spectroscopic apparatus described in paragraph 2, the quantum optical system is constructed using a single nonlinear optical element, thus simplifying its configuration.

[0156] (3) In the spectroscopic apparatus described in paragraph 1, the nonlinear optical element comprises a first and a second nonlinear optical element, and the quantum optical system may emit the first signal light through the optical path of the pump light incident on the first nonlinear optical element, and emit the second signal light through the pump light incident on the second nonlinear optical element. According to the spectroscopic apparatus described in Section 3, there is no need to return the pump light to the same nonlinear optical element, thus improving the flexibility of the quantum optical system layout.

[0157] (Clause 4) In the spectroscopic apparatus described in Clause 3, a pump light splitting element may be provided in front of the nonlinear optical element, and one of the pump light split by the pump light splitting element may be incident on the first nonlinear optical element, and the other pump light may be incident on the second nonlinear optical element. The spectroscopic apparatus described in Section 4 improves the degree of freedom in the layout of the quantum optical system.

[0158] (Article 5) A spectroscopic apparatus described in any one of paragraphs 1 to 4 may be provided with a variable optical path length mechanism for varying the optical path length of the signal light. According to the spectroscopic apparatus described in paragraph 5, the interferogram can be obtained from the two lights while the optical path length of the signal light is varied.

[0159] (Article 6) A spectroscopic apparatus described in any one of paragraphs 1 to 4 may be provided with a variable optical path length mechanism for varying the optical path length of the idler light. According to the spectroscopic apparatus described in paragraph 6, the interferogram can be obtained from the two lights detected by the detection unit while the optical path length of the idler light is being varied.

[0160] (Clause 7) In the spectroscopic apparatus described in paragraph 5 or 6, the optical path length variable mechanism is equipped with a movable mirror, and the analysis apparatus may acquire the interferogram from the two lights detected by the detection unit while the movable mirror is moving at a constant speed. According to the spectroscopic apparatus described in paragraph 7, the interferogram can be obtained from the two lights detected by the detection unit while the moving mirror is moving at a constant speed.

[0161] (Clause 8) In the spectroscopic apparatus described in any one of paragraphs 1 to 7, the analysis apparatus may obtain the interferogram from the difference in light intensity of the two lights detected by the detection unit. According to the spectroscopic apparatus described in paragraph 8, the acquisition of the interferogram can be performed easily and accurately.

[0162] (Clause 9) In the spectroscopic apparatus described in any one of paragraphs 1 to 7, the analysis apparatus may obtain the interferogram from the difference in the value obtained by multiplying the light intensity of at least one of the two lights detected by the detection unit by a constant. According to the spectroscopic apparatus described in paragraph 9, the acquisition of the interferogram can be performed easily and accurately. [Explanation of symbols]

[0163] 1, 100, 200, 300, 400, 500, 600 Infrared spectrometer (spectroscopy device) 2, 2R light source 4, 4R, 104, 204, 304, 404, 504, 604 Quantum optical system 6, 6R detection unit 8, 8R analysis device 12. Nonlinear crystals (nonlinear optical elements) 12A First nonlinear crystal (first nonlinear optical element) 12B Second nonlinear crystal (second nonlinear optical element) 14, 14R fixed mirror 32. Second Dichroic Mirror 34, 34R, moving mirror 35. Sample placement device 40, 240 Beam Splitter 40A1, 40A2 Injection Port 40B1, 40B2 ejection port 41 First detector 42 Second detector 62 Interferogram Acquisition Section 210 Beam splitter for pump optical distribution (pump optical distribution component) Ps, P1s, P2s light intensity SP sample i, i1, i2 iDra Light p, p1, p2 pump light s, s1, s2 signal light

Claims

1. A light source that emits pump light, A quantum optical system comprising one or more nonlinear optical elements that receive the pump light and generate idler light and signal light photon pairs from the pump light through an entangled photon pair generation process, and a sample placement device that places a sample on the optical path of the idler light, A detection unit for detecting the light intensity of light output from the quantum optical system, An analysis device that acquires an interferogram based on the aforementioned light intensity, Equipped with, The quantum optical system is configured to emit, through different optical paths, a first signal light that interacts with the sample and forms a photon pair with the idler light, and a second signal light that does not interact with the sample and forms a photon pair with the idler light. The detection unit includes a beam splitter that receives and interferes with first and second signal light from the quantum optical system, and detects the light intensity of each of the two beams emitted from the beam splitter. The analysis device acquires the interferogram based on the difference in light intensity of the two lights detected by the detection unit. Spectroscopic device.

2. The aforementioned nonlinear optical element is one, The quantum optical system emits first and second signal light in the optical path of the pump light that travels back and forth through a single nonlinear optical element. The spectroscopic apparatus according to claim 1.

3. The aforementioned nonlinear optical element comprises a first nonlinear optical element and a second nonlinear optical element. The quantum optical system emits a first signal light through the optical path of the pump light incident on the first nonlinear optical element, and emits a second signal light through the pump light incident on the second nonlinear optical element. The spectroscopic apparatus according to claim 1.

4. A pump optical branching element is provided in front of the aforementioned nonlinear optical element. One of the pump beams split by the pump beam splitting element is incident on the first nonlinear optical element, and the other pump beam is incident on the second nonlinear optical element. The spectroscopic apparatus according to claim 3.

5. It is equipped with a variable optical path length mechanism for varying the optical path length of the signal light. The spectroscopic apparatus according to claim 1.

6. The system includes a variable optical path length mechanism for varying the optical path length of the idler light. The spectroscopic apparatus according to claim 1.

7. The optical path length variable mechanism includes a movable mirror, The analysis device acquires the interferogram from the two lights detected by the detection unit while the moving mirror is moving at a constant speed. The spectroscopic apparatus according to claim 5 or 6.

8. The analysis device obtains the interferogram from the difference in light intensity of the two lights detected by the detection unit. The spectroscopic apparatus according to claim 1.

9. The analysis device obtains the interferogram from the difference in the value obtained by multiplying the light intensity of at least one of the two lights detected by the detection unit by a constant. The spectroscopic apparatus according to claim 1.

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