Fourier transform infrared spectrophotometer

Abstract

To provide a Fourier transform infrared spectrophotometer (FTIR) that can smoothly and accurately perform wave number correction of a measured spectrum.SOLUTION: A Fourier transform infrared spectrophotometer (FTIR) 100 includes: an infrared light source 10; an interferometer 12; a semiconductor laser 30 for position reference of a movable mirror 24 of the interferometer; and a computer 16 that calculates a spectrum by Fourier transforming a detection signal of infrared interference waves from a sample based on a stored wavelength value of the semiconductor laser 30 and a detected value of laser interference wave by a laser detector 32. The computer 16 calculates a spectrum of a solid reference sample, performs interpolation processing of a wave number region of a unique peak in the spectrum of the reference sample, reads the wave number of the unique peak based on data after the interpolation processing, and updates a wavelength value of the semiconductor laser 30 used in the Fourier transform processing so that a read value of the wave number falls within a predetermined range based on an original wave number of the unique peak.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a Fourier transform infrared spectrophotometer (FTIR) equipped with a wavenumber correction function. [Background technology]

[0002] A Fourier transform infrared spectrophotometer uses an interferometer to detect the interference wave of the measurement light in a non-dispersive manner, and then performs a Fourier transform on a computer to obtain spectral data of the measurement light. By forming an interference wave, each wavenumber component can be calculated from the intensity signal consisting of all wavenumber components by Fourier transform. Fourier transform spectroscopy is suitable for high-speed measurements and is the mainstream method for infrared spectrophotometers.

[0003] The interferometer used in this device is generally a Michelson interferometer, consisting of a semi-transparent mirror (such as a beam splitter) and two reflecting mirrors (a fixed mirror and a movable mirror). The movable mirror changes the optical path difference of the interferometer, and there is a one-to-one relationship between the position of the movable mirror and the optical path difference. The interferometer generates an interference wave of the measurement light corresponding to this optical path difference. By detecting the intensity of this interference wave, an interferogram (interference curve) can be obtained, with the optical path difference on the horizontal axis and the intensity signal on the vertical axis. A computer performs a Fourier transform on the interferogram data to calculate spectral data.

[0004] The interference wave is generally detected when the moving distance of the movable mirror reaches a position corresponding to the wavelength of the position reference laser, based on the position where the optical path difference is zero. When laser light is shone on the movable mirror, a laser interference wave is formed from the reflected light. The interference wave of the measurement light is usually detected when the intensity signal of the laser interference wave reaches zero. In other words, the detection timing depends on the wavelength λ of the position reference laser. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-112364 Summary of the Invention [Problem to be solved by the invention]

[0006] As mentioned above, because the detection timing of the infrared interference wave depends on the wavelength λ of the position reference laser, it was common to use a He-Ne laser, which is a gas laser with a stable wavelength λ, as a rangefinder in the past, but recently there have been cases where small, inexpensive semiconductor lasers are used as rangefinders. Unlike gas lasers, semiconductor lasers do not have a stable wavelength λ, so wavenumber correction is required to improve the reliability of the wavenumber.

[0007] For example, Patent Document 1 discloses an FTIR using a semiconductor laser as a position reference laser and describes a method for correcting the wavelength of the semiconductor laser. Specifically, in a first step, the absorption peak of atmospheric carbon dioxide in the interferometer is measured based on the wavelength before correction, and the wavenumber is compared with the wavenumber of the carbon dioxide's inherent absorption peak to correct the wavelength of the semiconductor laser. In a second step, the absorption peak of atmospheric water vapor is measured based on the corrected wavelength, and the wavenumber is compared with the wavenumber of the water vapor's inherent absorption peak to correct the wavelength of the semiconductor laser again. Thus, in Patent Document 1, the wavelength of the semiconductor laser is corrected in stages by first using the carbon dioxide absorption peak and then using the water vapor absorption peak.

[0008] In Patent Document 1, a gas (air) such as carbon dioxide or water vapor is used as a sample (also called a reference sample) for wavenumber correction in FTIR. This appears to have the advantage of being able to target absorption peaks that are closer to linear than solid reference samples. However, FTIR instruments often use nitrogen purging or a vacuum inside the sample chamber or housing, which weakens (or even eliminates) the detected absorption peaks of atmospheric carbon dioxide or water vapor, potentially making it impossible to correct the wavelength of the semiconductor laser. However, once purged with nitrogen or evacuated, opening the sample chamber or housing to the atmosphere just for wavenumber correction is a significant hassle. Furthermore, even for wavenumber correction, introducing air into the instrument, which can interfere with the actual measurement, is a disadvantage. For example, this is a significant disadvantage when the FTIR is operated continuously 24 hours a day, 365 days a year.

[0009] Furthermore, the peak heights of the absorption spectra of atmospheric carbon dioxide and water vapor vary widely and are indefinite depending on the measurement environment. This change in peak height causes the S / N ratio to change each time (in other words, the measurement time is not fixed), making it difficult to ensure the accuracy of wavenumber correction.

[0010] Another possible method is to fill a gas cell with a standard sample of a gas other than carbon dioxide or water vapor, such as hydrochloric acid gas, at a specified concentration and uniquely determine the peak height from the cell length and concentration. However, this method is difficult to maintain for long periods of time (the concentration changes) and is not easy to handle (the size and weight of the cell make it difficult to place the cell in the optical path). Placing the cell under vacuum creates negative pressure outside the cell, so maintaining the cell in a sealed state and establishing safety measures in case of gas leakage are issues that arise depending on the sample). Therefore, standard samples such as hydrochloric acid gas may not be suitable as reference samples for calibration.

[0011] Thus, one aspect of the air being unsuitable as a reference sample for wavelength correction is that the inventors have been working diligently to develop a Fourier transform infrared spectrophotometer that can smoothly and accurately perform wavenumber correction of measured spectra using an easy-to-handle solid reference sample such as a polystyrene film (e.g., 0.04 mm thick).

[0012] An object of the present invention is to provide a Fourier transform infrared spectrophotometer that uses a semiconductor laser to reference the position of a movable mirror, and that can smoothly and accurately perform wavenumber correction of a measured spectrum using a solid reference sample. [Means for solving the problem]

[0013] That is, the Fourier transform infrared spectrophotometer according to the present invention has the following features: an infrared light source; an interferometer having a beam splitter, a fixed mirror, and a movable mirror, which generates an infrared interference wave using the infrared light from the infrared light source; an infrared detector that detects the intensity of the infrared interference wave transmitted through or reflected by the sample; a revolver-type switching device including a plurality of apertures; a semiconductor laser that irradiates the interferometer with laser light; a laser detector that detects the intensity of a laser interference wave generated by the interferometer based on the laser light; a memory for storing the wavelength value of the semiconductor laser; a computer that calculates a spectrum of a sample by Fourier transforming the detection signal of the infrared detector using the wavelength value in the memory and the detection signal of the laser detector; A Fourier transform infrared spectrophotometer comprising: The computer executes a program that calculates a spectrum of a solid reference sample, interpolates the wavenumber range of at least one peak specific to the reference sample with respect to the calculated spectrum of the reference sample, reads the wavenumber of the at least one peak based on the data after the interpolation process, and updates the wavelength value in the memory so that the read value of the wavenumber falls within a predetermined range based on the original wavenumber of the specific peak. It is configured as follows: the solid reference sample is provided in at least one of the plurality of apertures; It is characterized by:

[0014] Furthermore, the Fourier transform infrared spectrophotometer according to the present invention comprises: an infrared light source; an interferometer having a beam splitter, a fixed mirror, and a movable mirror, which generates an infrared interference wave using the infrared light from the infrared light source; an infrared detector that detects the intensity of the infrared interference wave transmitted through or reflected by the sample; a revolver-type switching device including a plurality of apertures; a semiconductor laser that irradiates the interferometer with laser light; a laser detector that detects the intensity of a laser interference wave generated by the interferometer based on the laser light; a memory for storing the wavelength value of the semiconductor laser; a computer that calculates a spectrum of a sample by Fourier transforming the detection signal of the infrared detector using the wavelength value in the memory and the detection signal of the laser detector; a Peltier element for adjusting the temperature of the semiconductor laser; a temperature controller for the Peltier element; A Fourier transform infrared spectrophotometer comprising: The computer executes a program that calculates a spectrum of a solid reference sample, interpolates the wavenumber range of at least one peak specific to the reference sample with respect to the calculated spectrum of the reference sample, reads the wavenumber of the at least one peak based on the data after the interpolation, and operates the temperature controller of the Peltier element to adjust the temperature of the semiconductor laser so that the read value of the wavenumber falls within a predetermined range based on the original wavenumber of the specific peak. It is configured as follows: the solid reference sample is provided in at least one of the plurality of apertures; It is characterized by:

[0015] Furthermore, the Fourier transform infrared spectrophotometer according to the present invention comprises: an infrared light source; an interferometer having a beam splitter, a fixed mirror, and a movable mirror, which generates an infrared interference wave using the infrared light from the infrared light source; an infrared detector that detects the intensity of the infrared interference wave transmitted through or reflected by the sample; a revolver-type switching device including a plurality of apertures; a semiconductor laser that irradiates the interferometer with laser light; a laser detector that detects the intensity of a laser interference wave generated by the interferometer based on the laser light; a memory for storing the wavelength value of the semiconductor laser; a computer that calculates a spectrum of a sample by Fourier transforming the detection signal of the infrared detector using the wavelength value in the memory and the detection signal of the laser detector; an applied current controller for adjusting the applied current to the semiconductor laser; A Fourier transform infrared spectrophotometer comprising: The computer executes a program that calculates a spectrum of a solid reference sample, interpolates the wavenumber range of at least one peak specific to the reference sample with respect to the calculated spectrum of the reference sample, reads the wavenumber of the at least one peak based on the data after the interpolation, and operates the applied current controller to adjust the applied current to the semiconductor laser so that the read value of the wavenumber falls within a predetermined range based on the original wavenumber of the specific peak. It is configured as follows: the solid reference sample is provided in at least one of the plurality of apertures; It is characterized by:

[0016] Here, in each invention, the distinctive peak may be one or more. For example, when referring to multiple distinctive peaks, the deviation (wavenumber deviation) between the read value of each peak wavenumber and the original wavenumber (reference wavenumber) may be calculated, and based on these multiple wavenumber deviations, processing such as (1) updating the wavelength value in memory, (2) adjusting the temperature of the semiconductor laser using a Peltier element, or (3) adjusting the current applied to the semiconductor laser may be performed.

[0017] The interpolation process can employ well-known methods such as cubic spline interpolation and Lagrange interpolation, etc. Alternatively, a zero-filling method (a method that adds zero data to the outer range away from the center burst of interferogram data, allowing for easy acquisition of spectrum data with dense wavenumber intervals after Fourier transform) may be employed.

[0018] Furthermore, in each of the above inventions, it is preferable that the computer, instead of performing the interpolation process on the calculated spectrum of the reference sample, fits known peak shape data of a peak specific to the reference sample, and uses the wavenumber of the peak top after fitting as the wavenumber readout value.

[0019] In addition, in the Fourier transform infrared spectrophotometer according to the present invention, The computer When the Fourier transform infrared spectrophotometer is not performing a measurement and there is no input related to the operation of the Fourier transform infrared spectrophotometer for a certain period of time or more, The program is automatically executed to correct the wavenumber, Measure the background under normal sample measurement conditions, It is preferable to implement a waiting state for the input of the next measurement.

[0020] In this configuration, when the computer determines that the conditions for the Fourier transform infrared spectrophotometer to be in an unoperated state (when no input related to the operation of the Fourier transform infrared spectrophotometer continues for a certain period of time or more) are met, the wavenumber correction program is automatically executed, followed by automatically executing background measurement at the corrected wavenumber. Furthermore, once these processes are completed, the computer automatically enters a standby state for the next measurement. Therefore, even if the user is not aware that wavenumber correction is being executed, the wavenumber is always maintained in a corrected state, allowing the next measurement to start smoothly.

[0021] In addition, in the Fourier transform infrared spectrophotometer according to the present invention, When an input related to the execution of the program is received while the Fourier transform infrared spectrophotometer is not performing a measurement, or when a reservation for execution of the program is set and the reserved time arrives, the computer: Execute the program to correct the wavenumber, Measure the background under normal sample measurement conditions, It is preferable to implement a waiting state for the input of the next measurement.

[0022] With this configuration, wavenumber correction is limited to the timing intended by the user, so the Fourier transform infrared spectrophotometer will not perform wavenumber correction without the user's knowledge. For example, in FTIR applications where measurements are performed continuously 24 hours a day, 365 days a year, this can accommodate operations where wavenumber correction is desired to be performed at a fixed time, such as "a certain time late at night every Monday." [Effects of the Invention]

[0023] All of these FTIR configurations have in common the function of measuring the spectrum of a solid reference sample, reading the wavenumber of the absorption peak specific to the reference sample, and comparing it with the original wavenumber to correct the wavenumber of the measured spectrum. First, in an FTIR under nitrogen purging or vacuum conditions, using the absorption peak of a solid reference sample rather than the absorption peak of the atmosphere (carbon dioxide or water vapor) provides a greater detection intensity, making it easier to compare the wavenumber readings of the measured spectrum with the actual wavenumbers.

[0024] Furthermore, a solid reference sample provides spectral data with a more stable S / N ratio than the spectrum of air (carbon dioxide or water vapor), whose peak heights vary depending on the measurement environment. This allows the reference measurement time to be fixed, making it easier to ensure the accuracy of wavenumber correction.

[0025] In addition, even if the half-width of the characteristic peak of the solid reference sample is much larger than the wavenumber accuracy desired to be obtained by correction, by adding interpolated data to the wavenumber range of the characteristic peak of the reference sample in the spectrum calculated by FTIR, it becomes possible to read the wavenumber of the characteristic peak with high accuracy, thereby improving the reliability of the wavenumber correction of the measured spectrum.

[0026] As described above, according to the configuration of the present invention, wavenumber correction of a measured spectrum can be performed smoothly and accurately using a solid reference sample. In addition, by adjusting the temperature or applied current of the semiconductor laser and driving the semiconductor laser at a constant temperature or applied current, it is possible to obtain the effect of easily suppressing instability of the semiconductor laser. [Brief explanation of the drawings]

[0027] [Figure 1] FIG. 1 is a schematic diagram of an FTIR according to an embodiment. [Figure 2]FIG. 1 is a diagram of the FTIR aperture validation wheel. [Figure 3] FIG. 2 is a flow chart of the wave number correction of the FTIR. [Figure 4] FIG. 10 is an explanatory diagram of a method for interpolating measurement data in the flow of wave number correction. DETAILED DESCRIPTION OF THE INVENTION

[0028] A preferred embodiment of the present invention will be described below with reference to the drawings. The present invention is applicable to a Fourier transform infrared spectrophotometer (FTIR) and an infrared microscope. Here, the present invention is particularly applied to an FTIR 100 as shown in FIG. 1. The FTIR 100 includes an infrared light source 10, an interferometer 12 that generates an infrared interference wave, a sample holder 26 that holds a sample, an infrared detector 14 that detects the intensity of the interference wave obtained by irradiating the sample with the infrared interference wave, and a computer 16 that calculates spectral information of the sample based on the detection signal from the infrared detector 14. The computer 16 may be a microcomputer built into the main body of the FTIR 100, or may be a personal computer separate from the main body.

[0029] Housing 60 houses infrared light source 10 and interferometer 12. Interferometer 12 includes a beam splitter 20 that splits the infrared light, fixed mirror 22 that reflects each of the split beams, and movable mirror 24, and combines two beams of light with different optical path lengths to generate an infrared interference wave. Movable mirror 24 is provided so as to be movable in both directions, toward and away from beam splitter 20.

[0030] The infrared interference wave emitted from the exit window is irradiated onto a sample in a sample holder 26 located between the exit window and the infrared detector 14. The infrared detector 14 receives the infrared interference wave from the sample and outputs an intensity signal. The detection signal from the infrared detector 14 is input to a computer 16 via an amplifier 14a and an A / D converter 14b.

[0031] Housing 60 also contains a semiconductor laser 30 for position reference, which obtains position information of movable mirror 24 using laser light, and a laser detector 32 for detecting laser interference waves. In this embodiment, interferometer 12 also functions as a laser interferometer, and laser light (monochromatic light) from semiconductor laser 30 is guided along the same optical path as infrared light and enters beam splitter 20. Interferometer 12 also generates laser interference waves as movable mirror 24 moves, and laser detector 32 detects the laser interference waves from beam splitter 20 and outputs an intensity signal thereof to computer 16. Note that a separate, dedicated laser rangefinder may be provided in the same housing as interferometer 12 to form a separate rangefinder for measuring the position of movable mirror 24, for example, using a laser optical path that does not pass through beam splitter 20.

[0032] In this embodiment, a vertical cavity surface emitting laser (VCSEL), which is smaller and has a longer life than a normal semiconductor laser, is disposed as the semiconductor laser 30 within the housing 60, thereby achieving a smaller size and a longer life for the FTIR 100. The semiconductor laser 30 is provided with an applied current controller 68 for adjusting the current applied to the semiconductor laser 30. The semiconductor laser 30 is also provided with a Peltier element 70 for temperature adjustment, together with a temperature control controller 72 that controls the Peltier element.

[0033] Additionally, a revolver-type switching device (aperture validation wheel) 74 is located in front of the exit window in the housing 60, automatically switching between the aperture and the reference sample. Figure 2 shows the disc-shaped switching device 74 with a central hole 74c for the motor drive shaft. Multiple apertures AP1 to AP8 are formed along the periphery of the disc of the switching device 74. The apertures AP1 to AP6 are of different sizes, enabling automatic switching to the aperture size corresponding to the set wavenumber resolution. Figure 2 shows the state in which aperture AP6 is positioned exactly on the optical path of the interference wave from the beam splitter 20. Apertures AP7 and AP8 are used for reference samples. In this embodiment, a reference sample 74a (e.g., a polystyrene film) is fixed so as to cover aperture AP8. Another reference sample 74b, such as glass, may be attached to aperture AP7. The sizes of apertures AP7 and AP8 correspond to the wavenumber resolution that is expected to be set when measuring reference samples 74a and 74b, and are the same size as aperture AP5 in this example. Note that by aligning the portion of the disk where no aperture is formed with the optical path of the interference wave, the switching device 74 functions as a shielding plate.

[0034] Use of such a switching device 74 eliminates the need to set a reference sample holder in the sample chamber of the FTIR 100 each time, facilitating routine wavenumber correction. The wavenumber correction process is performed automatically by a computer running a wavenumber correction program. The reference sample 74a is positioned within the housing 60 far enough from the infrared light source 10, the largest heat source of the FTIR 100, and is thus positioned within a sealed space and far from the heat source. This ensures that the reference sample 74a is always in a state close to thermal equilibrium, thereby stabilizing its temperature. Therefore, wavenumber shifts due to temperature changes in the solid sample do not occur, and wavenumber correction can be performed consistently in the same way.

[0035] A temperature and humidity sensor 76 is also disposed in the housing 60. This temperature and humidity sensor 76 constantly detects the temperature and humidity inside the housing 60, making it possible to monitor the temperature and humidity on the display device 46 of the FTIR 100, etc.

[0036] If distortion occurs in the interferometer 12 itself due to temperature fluctuations, a corresponding drift in the measured wave number may occur. Therefore, the temperature fluctuation of the interferometer 12 may be read from the temperature detected by the temperature and humidity sensor 76, and the wave number drift may be corrected.

[0037] Next, the computer 16 includes a control unit 40 that controls each component of the computer 16, a calculation unit 42 that calculates spectral information of the sample based on the detection signal from the infrared detector 14 and performs spectral analysis of the sample, and a memory 44 that stores the data processing program executed by the calculation unit 42, the calculated spectral information, analysis results, background information, etc. Also connected to the computer 16 are a display device 46 and a user interface 48.

[0038] Furthermore, a movable mirror control device (movable mirror controller) 34 is connected to computer 16. A calculation unit 42 calculates position information of movable mirror 24 by counting changes in the intensity of the laser interference wave that accompany the movement of movable mirror 24, based on the intensity signal of the laser interference wave from laser detector 32. Movable mirror control device 34 receives the position information of movable mirror 24 and information on the target position, and controls the speed of movable mirror 24, particularly its constant speed control.

[0039] The calculation unit 42 receives the intensity signal of the infrared interference wave for one scan while the movable mirror control device 34 moves the movable mirror 24 by one stroke, and calculates an interferogram (interference curve) based on the intensity signal of the infrared interference wave and the position information of the movable mirror 24.

[0040] The calculation unit 42, for example, adds up interferograms for multiple scans and performs Fourier transform to calculate a single beam spectrum (SB spectrum), but may also perform calculations using other procedures, such as adding up SB spectra after Fourier transform instead of interferograms. Furthermore, the SB spectrum may be divided by background information to calculate a transmission spectrum.

[0041] A communication device 50 may be connected to the computer 16 as needed. The communication device 50 is, for example, a wireless communication device using Wi-Fi or Bluetooth, capable of communicating with a remote mobile device 52 and displaying the same information displayed on the display device 46 on the monitor of the mobile device 52. The mobile device 52 may also be a mobile terminal such as a smartphone, which may transmit the measured spectral data via encrypted email to an external server computer (not shown). The server computer may then perform spectral analysis of the measured spectral data, and the analysis results may be sent via email to the mobile device and displayed on its monitor. By providing the communication device 50 and configuring a remote server computer to perform spectral analysis via the mobile device 52, it is no longer necessary to carry a personal computer or other device for spectral analysis together with the FTIR 100, thereby improving portability. Since the computer 16 of the FTIR 100 only needs to be equipped with the minimum necessary functions, the computer 16 can be configured as a built-in microcomputer alone, further reducing the size of the FTIR 100.

[0042] <About the wavenumber correction program> The spectral wavenumber correction program is a program for correcting the wavenumber measured by FTIR based on the spectral data of a reference sample.

[0043] The wave number correction program causes the computer 16 to execute the following process flows S1 to S5. As shown in Fig. 3, after the wave number correction process of this embodiment, process flows S6 and S7 may be executed successively in some cases.

[0044] The FTIR 100 first drives the switching device 74 to select an aperture AP5 of the same size as the aperture AP8 at the location where the reference sample 74a is attached, and then performs background measurement (process flow S1). This background information is also used in calculating the spectrum of the reference sample 74a measured during wavenumber correction.

[0045] The process flow S2 (spectrum measurement of a reference sample) in FIG. 3 will now be described. First, the computer 16 drives the switching device 74 to select a reference sample 74a and measure its spectral data. The wavenumber resolution (number of spectral data points on the wavenumber axis) of the FTIR 100 is set according to the type of reference sample 74a and the shape of the peak (reference wavenumber) specific to that reference sample 74a. If this wavenumber resolution is set too high, the aperture diameter selected will become smaller, the light intensity (signal S) will decrease, and the S / N ratio will deteriorate, making it difficult to distinguish the peak tops. Therefore, for example, the wavenumber resolution may be set so that the wavenumber interval of the calculated spectrum is roughly one to three orders of magnitude larger than the required correction accuracy.

[0046] Next, the process flow S3 (interpolation of measurement data) will be described. The acquired measurement data is automatically interpolated into high-density data. Here, smoothing processing using a cubic spline is performed, but this is not limiting. In this embodiment, the amount of calculation by the computer 16 is significantly reduced by performing two steps: applying interpolation processing to the spectrum data after Fourier transformation, and extracting only the data in the wavenumber range required for peak formation and then applying interpolation processing to that data.

[0047] Then, the peak position (measured wavenumber) is obtained from the minimum value (when the vertical axis is transmittance %T) or maximum value (when the vertical axis is absorbance Abs) within the wavenumber range. Figure 4 shows the measured wavenumber of the peak when the vertical axis is transmittance %T. If the measured wavenumber of the peak of the measurement data is, for example, "3059.51 cm -1 ", but the interpolated data shows the more accurate measured wave number of the peak. Here, the measured wave number of the peak based on the interpolated data is, for example, "3059.60 cm -1 " became.

[0048] Next, the process flow S4 (comparison with reference wavenumber / calculation of wavenumber deviation) will be described. The computer 16 calculates, for example, "3059.7 cm" as the reference wavenumber of the characteristic peak of the reference sample 74a. -1 In this example, the wavenumber deviation is "-0.1cm" which is calculated by subtracting the reference wavenumber from the measured wavenumber of the peak based on the interpolated data. -1 " becomes.

[0049] Next, the process flow S5 (calculation / storage of wavenumber correction value) will be described. The wavenumber data interval after the Fourier transform of FTIR is proportional to "1 / λ: λ is the wavelength of the semiconductor laser." Using this relationship, in this embodiment, the wavelength (maximum wavenumber) assumed in the calculation during the Fourier transform is corrected based on the wavenumber deviation. For example, the FTIR100 acquires an interferogram at the wavelength interval of the reference laser (≈850 nm), performs a Fourier transform (FFT) on it, and calculates a wavenumber correction value of 11765 cm. -1 Assume that the data is expanded at equal intervals in the wavenumber space (≒1 / 850 nm).

[0050] For simplicity, the design value of the laser wavelength is 850 nm. -1 ) has a peak wavenumber axis of 3059.7 cm -1 The computer 16 calculates the Fourier transform output value as "3059.6 cm" when the laser wavelength is 850 nm. -1 ", the output value of the Fourier transform is "3059.7 cm -1Calculate the laser wavelength so that

[0051] In other words, assuming the laser wavelength is 850 nm, the computer 16 calculates the wavelength as (1 / 850 nm) cm -1 ~0cm -1 The spectral data is expanded at equal intervals in the wavenumber space of 3059.6 cm. -1 " is "3059.7cm -1 " In other words, if the coefficient A is set as "A = 3059.7 ÷ 3059.6", the wave number space after correction will be (A / 850nm)cm -1 ~0cm -1 Therefore, the computer 16 can calculate the laser wavelength to be used in the Fourier transform calculation as 850÷A≈849.97 nm.

[0052] Alternatively, the corrected laser wavelength may be calculated from each of the multiple characteristic peaks of the reference sample 74a in the same manner, and the calculated values ​​from all the peaks (such as the above "850 nm ÷ A") may be averaged to be used as the corrected laser wavelength. Alternatively, the calculated values ​​for each peak may be weighted to be averaged to be used as the corrected laser wavelength.

[0053] The computer 16 can calculate a wavenumber-corrected spectrum by Fourier transforming the measured interferogram using this corrected laser wavelength. The corrected laser wavelength value is stored in the memory 44 of the FTIR or control PC and used for subsequent Fourier transforms.

[0054] In the above description, the reference wave number of the characteristic peak of the reference sample 74a stored in the memory 44 is, for example, “3059.7 cm -1 ", but this reference wave number is "3059.68 cm -1 ~3059.72cm -1 " may be saved as a predetermined range.

[0055] For example, when wavenumber correction is performed based on a plurality of peaks of the reference sample 74a, instead of determining the wavenumber values ​​of the spectrum by the average value of the corrected laser wavelengths calculated respectively as described above, it is possible to determine the wavenumber values ​​of all peak positions of the reference sample 74a based on the corrected laser wavelengths within a predetermined range of the above-mentioned reference wavenumbers (for example, "3059.68 cm"). -1 ~3059.72cm -1 The final corrected laser wavelength may be determined based on whether the wavelength falls within the range of 0.01 to 0.01. This allows for a larger amount of information to be used for correction based on multiple peaks than correction based on a single peak, thereby improving the accuracy of the correction.

[0056] Furthermore, an operation system may be constructed in which the results of the wave number correction are automatically sent to a server computer via a network and recorded as medium- to long-term maintenance information. The method of communication between the FTIR 100 and a remote server computer is not limited to email via a mobile terminal (mobile device 52) such as the above-mentioned smartphone. For example, if a mobile device receives wavenumber correction results from the FTIR 100 and has access rights to the server computer, the mobile device can automatically upload the data directly to the server computer's storage area. Alternatively, the user can manually perform file operations. The server computer manages the received wavenumber correction result files for each uploaded device and can provide them to the user at any time in response to a request from the mobile device via the network.

[0057] In addition to file sharing, information can also be shared by writing to a database file on a cloud or server computer. In this case, the mobile device and the server computer each access the database file on the cloud or server computer, and exchange information in a single file. In this case, the mobile device can acquire and use a user interface for viewing the contents of the database file in the form of a dedicated program or browser application.

[0058] In addition, solid reference sample 74a was used to measure the specific wavenumber range (e.g., 3060 cm -1 To measure a peak in the vicinity of ≈ ...

[0059] In process flow S2, measuring the solid reference sample 74a at a relatively low wavenumber resolution means that when a baseline is drawn at a specific peak to set the half-width, the number of spectral data points in the wavenumber range of that half-width will be approximately "10 to 100 points," preferably "15 to 50 points." If the measurement time for the interferogram data is the same, obtaining the peak wavenumber by interpolating the spectrum data (high S / N) obtained under low-resolution conditions will result in better reproducibility of the peak position (wavenumber reading) than obtaining the peak wavenumber by least-squares approximation of the spectrum data (low S / N) obtained under high-resolution conditions.

[0060] In this embodiment, interpolated data is added when reading the peak specific to the reference sample 74a, but instead, the peak top (measured wavenumber) may be read by fitting a known peak shape of the peak specific to the reference sample 74a.

[0061] A modified example of the wavenumber correction program will now be described. In the program processing flow S3, the computer 16 calculates the peak position “3059.6 cm” based on the interpolated data. -1 " is calculated, and the peak position "3059.6 cm" based on the above interpolated data is -1 " is the reference wavenumber of reference sample 74a, "3059.7 cm -1 " (e.g., 3059.7±1.5cm -1 1 may adjust the current applied to the semiconductor laser 30 so that the measured wavenumber of the spectrum or the laser oscillation wavelength is within the range of 1 / 2000. In this case, it is advisable to obtain in advance the correlation between the applied current and the measured wavenumber of the spectrum or the laser oscillation wavelength.

[0062] Next, another modified example of the wavenumber correction program will be described. In the processing flow S3 of the program, the computer 16 calculates the peak position “3059.6 cm ” based on the interpolated data. -1 " is calculated, and the peak position "3059.6 cm" based on the above interpolated data is -1 " is the reference wavenumber of reference sample 74a, "3059.7 cm -1 1 may control the Peltier element 70 so that the laser temperature falls within an allowable range centered on "." In this case, it is advisable to obtain in advance the correlation between the laser temperature and the measured wavenumber of the spectrum or the laser oscillation wavelength.

[0063] Here, the computer 16 is configured to have at least one or more execution patterns of the following plurality of wave number correction programs. When the user manually executes the wavenumber correction program during daily inspection of the FTIR 100, the computer 16 executes the wavenumber correction program. The computer 16 is configured so that the user can set an execution schedule for the wavenumber correction program, and the wavenumber correction program is automatically executed at the set date and time. When aging after power-on is complete and the FTIR 100 has stabilized, or when the computer 16 starts a measurement program (for example, when a measurement menu or the like is displayed on the monitor), the computer 16 automatically executes the wavenumber correction program. If there is no input related to the operation of the FTIR, such as a user operation, for a certain period of time, the computer 16 determines that the FTIR is in an unoperated state and automatically executes the wavenumber correction program.

[0064] In any of the above execution patterns, after the wavenumber correction is completed by executing the wavenumber correction program, background measurement may be automatically performed using the parameters that were set immediately before the wavenumber correction (for example, parameters that represent various measurement conditions for a normal sample, such as the selection of an aperture and the stroke length of the movable mirror), and then the system may enter a waiting state (standby state) for input related to the next measurement (see processing flow S6 and S7 in FIG. 3 described later).

[0065] In particular, when the computer 16 determines the activation state of the FTIR and executes wavenumber correction, if the computer 16 also automatically executes background measurement following the series of wavenumber correction operations, the user will not need to remeasure the background the next time he or she performs a measurement, thereby improving user convenience.

[0066] According to the configuration of the FTIR 100 of this embodiment described above, first, by using a solid reference sample 74a such as a polystyrene film, a greater detection intensity can be obtained than when air (carbon dioxide or water vapor) is used as a reference sample, which is easily affected by nitrogen purging or a vacuum state in the FTIR 100, and the wavenumber readout value of the measured spectrum can be easily compared with the actual wavenumber. Furthermore, with a solid reference sample 74a, the measurement time is more likely to be constant and the accuracy of wavenumber correction of the measured spectrum can be more easily ensured than with a spectrum of air (carbon dioxide or water vapor), whose peak heights vary depending on the measurement environment and whose S / N ratio changes each time.

[0067] In addition, by adding interpolated data to the wavenumber range of the peak specific to the reference sample 74a for the spectrum calculated by the FTIR 100, even if the peak specific to the solid reference sample 74a has a half-width much larger than the wavenumber accuracy desired to be obtained by correction, the wavenumber of the peak can be read with high accuracy, thereby improving the reliability of the wavenumber correction of the measured spectrum.

[0068] According to the configuration of the FTIR 100 of this embodiment, even if there is instability in the oscillation wavenumber specific to the semiconductor laser 30, by executing the wavenumber correction function of the FTIR 100, it is possible to obtain the same wavenumber accuracy (reproducibility) of the measurement spectrum as when a He-Ne laser is used.

[0069] Furthermore, as FTIR instruments have become easier to miniaturize, there is an increasing need for portability of FTIR instruments. In other words, compared to conventional FTIR instruments, which were premised on constant stable use in a stationary state, there is an increasing need for confirmation of the reliability of the instrument (daily inspection) and calibration. By adopting this embodiment, it is possible to improve reliability, particularly with regard to wavenumber precision / reproducibility, or wavenumber accuracy. [Explanation of symbols]

[0070] 10 Infrared light source 12 Interferometer 14 Infrared detector 16 Computer 20 Beam splitter (light beam dividing part) 22 Fixed mirror 24 Movable mirror 30 Semiconductor laser 32 Laser detector 34 Movable mirror control device 44 Memory 46 Display device 48 User Interface 50 Communication equipment 52 Mobile devices 60 cabinets 68 Applied Current Controller 70 Peltier element 72 Temperature controller 74 Switching Device 74a Reference sample 76 Temperature and humidity sensor 100 Fourier transform infrared spectrophotometer (FTIR)

Claims

1. an infrared light source; an interferometer having a beam splitter, a fixed mirror, and a movable mirror, which generates an infrared interference wave using the infrared light from the infrared light source; an infrared detector that detects the intensity of the infrared interference wave transmitted through or reflected by the sample; a revolver-type switching device including a plurality of apertures; a semiconductor laser that irradiates the interferometer with laser light; a laser detector that detects the intensity of a laser interference wave generated by the interferometer based on the laser light; a memory for storing the wavelength value of the semiconductor laser; a computer that calculates a spectrum of a sample by Fourier transforming the detection signal of the infrared detector using the wavelength value in the memory and the detection signal of the laser detector; A Fourier transform infrared spectrophotometer comprising: the computer is configured to execute a program that calculates a spectrum of a solid reference sample, interpolates a wavenumber range of at least one peak specific to the reference sample with respect to the calculated spectrum of the reference sample, reads the wavenumber of the at least one peak based on the data after the interpolation process, and updates the wavelength value in the memory so that the read value of the wavenumber falls within a predetermined range based on the original wavenumber of the specific peak; A Fourier transform infrared spectrophotometer, characterized in that the solid reference sample is provided in at least one of the plurality of apertures.

2. an infrared light source; an interferometer having a beam splitter, a fixed mirror, and a movable mirror, which generates an infrared interference wave using the infrared light from the infrared light source; an infrared detector that detects the intensity of the infrared interference wave transmitted through or reflected by the sample; a revolver-type switching device including a plurality of apertures; a semiconductor laser that irradiates the interferometer with laser light; a laser detector that detects the intensity of a laser interference wave generated by the interferometer based on the laser light; a memory for storing the wavelength value of the semiconductor laser; a computer that calculates a spectrum of a sample by Fourier transforming the detection signal of the infrared detector using the wavelength value in the memory and the detection signal of the laser detector; a Peltier element for adjusting the temperature of the semiconductor laser; a temperature controller for the Peltier element; A Fourier transform infrared spectrophotometer comprising: the computer is configured to execute a program that calculates a spectrum of a solid reference sample, interpolates a wavenumber range of at least one peak specific to the reference sample with respect to the calculated spectrum of the reference sample, reads the wavenumber of the at least one peak based on the data after the interpolation, and operates the temperature control controller of the Peltier element to adjust the temperature of the semiconductor laser so that the read value of the wavenumber falls within a predetermined range based on the original wavenumber of the specific peak; A Fourier transform infrared spectrophotometer, characterized in that the solid reference sample is provided in at least one of the plurality of apertures.

3. an infrared light source; an interferometer having a beam splitter, a fixed mirror, and a movable mirror, which generates an infrared interference wave using the infrared light from the infrared light source; an infrared detector that detects the intensity of the infrared interference wave transmitted through or reflected by the sample; a revolver-type switching device including a plurality of apertures; a semiconductor laser that irradiates the interferometer with laser light; a laser detector that detects the intensity of a laser interference wave generated by the interferometer based on the laser light; a memory for storing the wavelength value of the semiconductor laser; a computer that calculates a spectrum of a sample by Fourier transforming the detection signal of the infrared detector using the wavelength value in the memory and the detection signal of the laser detector; an applied current controller for adjusting the applied current to the semiconductor laser; A Fourier transform infrared spectrophotometer comprising: the computer is configured to execute a program that calculates a spectrum of a solid reference sample, interpolates a wavenumber range of at least one peak specific to the reference sample with respect to the calculated spectrum of the reference sample, reads the wavenumber of the at least one peak based on the data after the interpolation, and operates the applied current controller to adjust the applied current to the semiconductor laser so that the read value of the wavenumber falls within a predetermined range based on the original wavenumber of the specific peak; A Fourier transform infrared spectrophotometer, characterized in that the solid reference sample is provided in at least one of the plurality of apertures.

4. The Fourier transform infrared spectrophotometer according to any one of claims 1 to 3, the computer, instead of performing the interpolation process on the calculated spectrum of the reference sample, fits known peak shape data of a peak specific to the reference sample, and uses the wavenumber of the peak top after fitting as the wavenumber readout value.

5. The Fourier transform infrared spectrophotometer according to any one of claims 1 to 4, The computer When the Fourier transform infrared spectrophotometer is not performing a measurement and there is no input related to the operation of the Fourier transform infrared spectrophotometer for a certain period of time or more, The program is automatically executed to correct the wavenumber, Measure the background under normal sample measurement conditions, A Fourier transform infrared spectrophotometer characterized by executing a waiting state for an input related to the next measurement.

6. The Fourier transform infrared spectrophotometer according to any one of claims 1 to 4, When an input related to the execution of the program is received while the Fourier transform infrared spectrophotometer is not performing a measurement, or when a reservation for execution of the program is set and the reserved time arrives, the computer: Execute the program to correct the wavenumber, Measure the background under normal sample measurement conditions, A Fourier transform infrared spectrophotometer characterized by executing a waiting state for an input related to the next measurement.

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