US-12625068-B2 - Optical device, spectroscopic device, and spectroscopic method

US12625068B2US 12625068 B2US12625068 B2US 12625068B2US-12625068-B2

Abstract

An optical device includes: an analysis optical system; and a length measurement optical system. The analysis optical system includes a moving mirror configured to reflect analysis light to add a first modulation signal to the analysis light, a gas cell with a gas that absorbs light of a predetermined wavelength sealed therein and configured to add a light absorption signal to the analysis light, and a first light receiving element configured to receive the analysis light including a sample-derived signal, the first modulation signal, and the light absorption signal. The length measurement optical system includes a second light source and obtains a displacement signal corresponding to a position of the moving mirror using laser light.

Inventors

Kohei Yamada

Assignees

SEIKO EPSON CORPORATION

Dates

Publication Date: 20260512
Application Date: 20240321
Priority Date: 20230322

Claims (11)

1 . An optical device comprising: an analysis optical system; and a length measurement optical system, wherein the analysis optical system includes a moving mirror configured to reflect analysis light emitted from a first light source to add a first modulation signal to the analysis light, a gas cell with a gas that absorbs light of a predetermined wavelength sealed therein and configured to add a light absorption signal to the analysis light, and a first light receiving element configured to receive the analysis light including a sample-derived signal generated by a sample, the first modulation signal, and the light absorption signal, and output a first light receiving signal, and the length measurement optical system includes a second light source configured to emit laser light and obtains a displacement signal corresponding to a position of the moving mirror using the laser light.
2 . The optical device according to claim 1 , wherein the analysis optical system includes the first light source.
3 . The optical device according to claim 1 , wherein the analysis optical system includes an incidence switching unit configured to switch between a first state in which the analysis light is incident on the gas cell and is not incident on the sample and a second state in which the analysis light is incident on the sample and is not incident on the gas cell.
4 . The optical device according to claim 3 , wherein the incidence switching unit is configured to switch between the first state and the second state by inserting and removing the gas cell.
5 . The optical device according to claim 3 , wherein the incidence switching unit includes a light shield configured to switch between the first state and the second state by shielding the analysis light.
6 . The optical device according to claim 1 , wherein the analysis optical system includes a wavelength conversion element configured to convert a wavelength of the analysis light emitted therefrom with respect to the analysis light incident thereon.
7 . The optical device according to claim 1 , wherein the length measurement unit includes an optical modulator configured to add a second modulation signal to the laser light.
8 . The optical device according to claim 1 , wherein the second light source is a semiconductor laser element.
9 . A spectroscopic device comprising: the optical device according to claim 1 ; a moving mirror position calculation unit configured to generate a moving mirror position signal based on the displacement signal; a light intensity calculation unit configured to generate, based on the first light receiving signal and the moving mirror position signal, a waveform representing an intensity of the first light receiving signal at the position of the moving mirror; a Fourier transform unit configured to perform Fourier transform on the waveform to generate a spectral pattern including a peak that is based on the light absorption signal; and a moving mirror position correction unit configured to calculate, based on a position of the peak, a correction value for correcting the moving mirror position signal.
10 . A spectroscopic method of performing spectroscopy on a sample comprising: measuring a position of the moving mirror based on the displacement signal obtained by the optical device according to claim 1 ; disposing the gas cell and the sample on an optical path of the analysis light, causing the analysis light to be incident on the gas cell and the sample while changing the position of the moving mirror, causing the first light receiver to receive the analysis light emitted from the gas cell and the sample, and outputting the first light receiving signal; generating, based on the first light receiving signal and a measurement value of the position of the moving mirror, a waveform indicating an intensity of the first light receiving signal at the position of the moving mirror; performing Fourier transform on the waveform to generate a spectral pattern including a peak, that is based on the light absorption signal, and information derived from the sample; calculating, based on a difference between a wavelength of the peak and a fundamental wavelength of the gas cell, a correction value for correcting the measurement value of the position of the moving mirror; and correcting the spectral pattern based on the correction value.
11 . A spectroscopic method of performing spectroscopy on a sample comprising: disposing the gas cell in the optical device according to claim 1 on an optical path of the analysis light; measuring a position of the moving mirror based on the displacement signal obtained by the optical device; causing the analysis light to be incident on the gas cell while changing the position of the moving mirror, causing the first light receiving element to receive the analysis light emitted from the gas cell, and outputting the first light receiving signal derived from the gas cell; generating, based on the first light receiving signal derived from the gas cell and a measurement value of the position of the moving mirror, a waveform indicating an intensity of the first light receiving signal derived from the gas cell at the position of the moving mirror; performing Fourier transform on the waveform derived from the gas cell to generate a spectral pattern including a peak that is based on the light absorption signal; calculating, based on a difference between a wavelength of the peak and a fundamental wavelength of the gas cell, a correction value for correcting the measurement value of the position of the moving mirror; disposing the sample on the optical path of the analysis light; measuring the position of the moving mirror using the displacement signal obtained by the optical device; causing the analysis light to be incident on the sample while changing the position of the moving mirror, causing the first light receiving element to receive the analysis light emitted from the sample, and outputting the first light receiving signal derived from the sample; generating, based on the first light receiving signal derived from the sample, the measurement value of the position of the moving mirror, and the correction value, a waveform indicating an intensity of the first light receiving signal derived from the sample at the position of the moving mirror; and performing Fourier transform on the waveform derived from the sample to generate a spectral pattern including information derived from the sample.

Description

The present application is based on, and claims priority from JP Application Serial Number 2023-045063, filed Mar. 22, 2023, the disclosure of which is hereby incorporated by reference herein in its entirety. BACKGROUND 1. Technical Field The present disclosure relates to an optical device, a spectroscopic device, and a spectroscopic method. 2. Related Art WO 2019/009404 discloses an optical module used for spectroscopy for obtaining spectrum information of light emitted or absorbed by a sample and analyzing components in the sample based on the spectrum information. The optical module includes a mirror unit, a beam splitter unit, a light incident unit, a first photodetector, a second light source, and a second photodetector. The mirror unit includes a movable mirror that moves in a predetermined direction and a fixed mirror whose position is fixed. In such an optical module, an interference optical system into which measurement light and laser light are incident is implemented by the beam splitter unit, the movable mirror, and the fixed mirror. The measurement light incident from a first light source through a measurement target passes through the light incident unit and is split in the beam splitter unit. A part of the split measurement light is reflected by the movable mirror and is returned to the beam splitter unit. A remaining part of the split measurement light is reflected by the fixed mirror and is returned to the beam splitter unit. The part of measurement light and the remaining part returned to the beam splitter unit are detected by the first photodetector as interference light. Further, laser light emitted from the second light source is split by the beam splitter unit. A part of the split laser light is reflected by the movable mirror and is returned to the beam splitter unit. A remaining part of the split laser light is reflected by the fixed mirror and is returned to the beam splitter unit. The part of laser light and the remaining part returned to the beam splitter unit are detected by the second photodetector as interference light. In such an optical module, a position of the movable mirror is measured based on a detection result of the interference light of the laser light. Further, based on a measurement result of the position of the movable mirror and the detection result of the interference light of the measurement light, the spectroscopy of the measurement target is possible. Specifically, a waveform called an interferogram is obtained by determining an intensity of the measurement light at each position of the movable mirror. By performing Fourier transform on the interferogram, spectrum information about the measurement target can be determined. Therefore, the optical module described in WO 2019/009404 is used for a Fourier transform infrared spectrometer (FTIR). WO 2019/009404 is an example of the related art. SUMMARY In a Fourier transform spectrometer, measurement accuracy of the position of the movable mirror (moving mirror) is directly linked to accuracy on a wavenumber axis (wavelength axis) of a spectral pattern. In the optical module disclosed in WO 2019/009404, the second light source that emits the laser light is required to have sufficiently high wavelength stability. The second light source disclosed in WO 2019/009404 has semiconductor laser such as a VCSEL, whereas the semiconductor laser generally has low wavelength stability. Therefore, when the optical module disclosed in WO 2019/009404 is applied to a Fourier transform spectrometer, there is room for improvement in accuracy on the wavenumber axis (wavelength axis) of the obtained spectral pattern. Meanwhile, in order to stabilize the wavelength of the semiconductor laser, there is also a method of providing additional equipment such as a light source thermostatic system. However, such additional equipment increases a size and power consumption of the optical module. Therefore, an object is to provide an optical device capable of accurately measuring a position of a moving mirror and achieving size reduction and low power consumption. An optical device according to an application example of the present disclosure includes: an analysis optical system; anda length measurement optical system,the analysis optical system includes a moving mirror configured to reflect analysis light emitted from a first light source to add a first modulation signal to the analysis light,a gas cell with a gas that absorbs light of a predetermined wavelength sealed therein and configured to add a light absorption signal to the analysis light when the analysis light is incident thereon, anda first light receiving element configured to receive the analysis light including a sample-derived signal generated by an action between the analysis light and a sample, the first modulation signal, and the light absorption signal, and output a first light receiving signal, and the length measurement optical system includes a second