US-12625071-B2 - Electromagnetic wave measuring apparatus, method, and recording medium

US12625071B2US 12625071 B2US12625071 B2US 12625071B2US-12625071-B2

Abstract

An electromagnetic wave measuring apparatus irradiates an irradiation target having a measuring target with a pre-irradiation electromagnetic wave and, based on a post-irradiation electromagnetic wave obtained, measures the measuring target. The post-irradiation electromagnetic wave has a response component from the measuring target and a background component corresponding to the pre-irradiation electromagnetic wave. The electromagnetic wave measuring apparatus includes a first frequency spectrum acquiring section, a second frequency spectrum acquiring section, and a subtracting section. The first frequency spectrum acquiring section acquires a frequency spectrum of a first signal that includes the background component and the response component of the post-irradiation electromagnetic wave. The second frequency spectrum acquiring section acquires a frequency spectrum of a second signal that includes the background component of the post-irradiation electromagnetic wave. The subtracting section subtracts the frequency spectrum of the second signal from the frequency spectrum of the first signal.

Inventors

Takao Sakurai
Nobutaka Takahashi
Yoshinori Kikuchi

Assignees

ADVANTEST CORPORATION

Dates

Publication Date: 20260512
Application Date: 20240524
Priority Date: 20230829

Claims (15)

1 . An electromagnetic wave measuring apparatus arranged to irradiate an irradiation target having a measuring target with a pre-irradiation electromagnetic wave and, based on a post-irradiation electromagnetic wave obtained, measure the measuring target, in which the post-irradiation electromagnetic wave has a response component from the measuring target and a background component corresponding to the pre-irradiation electromagnetic wave, the electromagnetic wave measuring apparatus, comprising: a first frequency spectrum acquiring section arranged to acquire a frequency spectrum of a first signal that includes the background component and the response component of the post-irradiation electromagnetic wave; a second frequency spectrum acquiring section arranged to acquire a frequency spectrum of a second signal that includes the background component of the post-irradiation electromagnetic wave; and a subtracting section arranged to subtract the frequency spectrum of the second signal from the frequency spectrum of the first signal.
2 . The electromagnetic wave measuring apparatus according to claim 1 , wherein the post-irradiation electromagnetic wave further has a non-signal component that is neither the background component nor the response component, and the second signal further includes at least a part of the non-signal component.
3 . The electromagnetic wave measuring apparatus according to claim 2 , wherein a length of time of the first signal is equal to a length of time of the second signal.
4 . The electromagnetic wave measuring apparatus according to claim 1 , wherein the post-irradiation electromagnetic wave further has a non-signal component that is neither the background component nor the response component, and the first signal further includes at least a part of the non-signal component.
5 . The electromagnetic wave measuring apparatus according to claim 1 , wherein a waveform of the post-irradiation electromagnetic wave is acquired by dual-comb spectroscopy.
6 . The electromagnetic wave measuring apparatus according to claim 1 , wherein a waveform of the post-irradiation electromagnetic wave is acquired by terahertz time domain spectroscopy.
7 . The electromagnetic wave measuring apparatus according to claim 1 , wherein a waveform of the post-irradiation electromagnetic wave is acquired by pump-probe method.
8 . The electromagnetic wave measuring apparatus according to claim 1 , wherein the response component is a free induction decay signal.
9 . The electromagnetic wave measuring apparatus according to claim 1 , wherein the irradiation target is gas.
10 . The electromagnetic wave measuring apparatus according to claim 9 , wherein the irradiation target is housed in a gas cell.
11 . The electromagnetic wave measuring apparatus according to claim 10 , wherein the electromagnetic wave measuring apparatus is arranged to measure a concentration of the measuring target.
12 . The electromagnetic wave measuring apparatus according to claim 1 , wherein the irradiation target is liquid or solid.
13 . The electromagnetic wave measuring apparatus according to claim 12 , wherein the electromagnetic wave measuring apparatus is arranged to measure a presence of the measuring target.
14 . An electromagnetic wave measuring method for irradiating an irradiation target having a measuring target with a pre-irradiation electromagnetic wave and, based on a post-irradiation electromagnetic wave obtained, measuring the measuring target, in which the post-irradiation electromagnetic wave has a response component from the measuring target and a background component corresponding to the pre-irradiation electromagnetic wave, the electromagnetic wave measuring method, comprising: acquiring a frequency spectrum of a first signal that includes the background component and the response component of the post-irradiation electromagnetic wave; acquiring a frequency spectrum of a second signal that includes the background component of the post-irradiation electromagnetic wave; and subtracting the frequency spectrum of the second signal from the frequency spectrum of the first signal.
15 . A non-transitory computer-readable medium including a program of instructions for execution by a computer to perform an electromagnetic wave measuring process for irradiating an irradiation target having a measuring target with a pre-irradiation electromagnetic wave and, based on a post-irradiation electromagnetic wave obtained, measuring the measuring target, in which the post-irradiation electromagnetic wave has a response component from the measuring target and a background component corresponding to the pre-irradiation electromagnetic wave, the electromagnetic wave measuring process, comprising: acquiring a frequency spectrum of a first signal that includes the background component and the response component of the post-irradiation electromagnetic wave; acquiring a frequency spectrum of a second signal that includes the background component of the post-irradiation electromagnetic wave; and subtracting the frequency spectrum of the second signal from the frequency spectrum of the first signal.

Description

BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to measuring frequency spectrum. Description of the Related Art There has conventionally been known acquiring a signal including free induction decay (FID) that is generated after pulse excitation of gas and, based on its frequency spectrum, measuring the concentration of a predetermined gas component (see Patent Literature 2, for example). In this frequency spectrum, absorption is observed at a predetermined frequency that corresponds to the predetermined gas component. In order to obtain the depth of the absorption, it is necessary to obtain a component in the frequency spectrum that does not depend on the predetermined gas to be measured (this may hereinafter be referred to as “baseline”). In order to obtain a baseline, there has been known designating a path through which a pulse passes (which shall not pass through a gas cell with gas housed therein) as a reference path (the reference path may be designated by removing the gas cell from a signal path to be described hereinafter), and measuring the frequency spectrum of the pulse that has passed through the reference path for designation as a baseline (see Patent Literature 1, Patent Literature 3, and Non-Patent Literature 1, for example). However, since the reference path is different from the signal path, through which the pulse passes (which shall pass through the gas cell), it is not always possible to obtain the baseline accurately due to difference in the condition such as pulse reflection in the paths. In order to obtain a baseline, there has alternatively been known designating a path through which a pulse passes (which shall pass through a gas cell with gas removed therefrom (or an empty cell with no gas housed therein)) as a reference path, and measuring the frequency spectrum of the pulse that has passed through the reference path for designation as a baseline (see Non-Patent Literature 2, for example). However, it is time consuming to remove gas from the gas cell, and the baseline may fluctuate due to such a lapse of time. In order to obtain a baseline, there has further been known approximating a baseline by a polynomial for each narrower frequency range in view of the fact that the baseline fluctuates slowly in a narrower frequency range (see Non-Patent Literature 3, for example). CITATION LIST [Patent Literature 1] WO2021/261240[Patent Literature 2] Japanese Patent Application Publication No. 2016-521859[Patent Literature 3] U.S. Pat. No. 9,557,219[Non-Patent Literature 1] Albert Schliesser, et. al. “Frequency-comb infrared spectrometer for rapid, remote chemical sensing”, Optics Express, 2005, Vol. 13, Issue 22 p. 9029-9038[Non-Patent Literature 2]S. Okubo, et. al., “Ultra-broadband dual-comb spectroscopy across 1.0-1.9 m”, Applied Physics Express, 2015, 8, 082402[Non-Patent Literature 3]G. B. Rieker, F. R. Giorgetta, W. C. Swann, et. al., “Frequency-comb-based remote sensing of greenhouse gases over kilometer air paths”, Optica, 2014, Vol. 1, Issue 5, p. 290-298 SUMMARY OF THE INVENTION However, in order to approximate a baseline by a polynomial, it is necessary to repeatedly approximate the baseline for each narrower frequency range many times, which may be a cumbersome approach. It is hence an object of the present invention to make it easy to obtain a component (a so-called baseline) in the frequency spectrum that does not depend on a measuring target. According to the present invention, an electromagnetic wave measuring apparatus arranged to irradiate an irradiation target having a measuring target with a pre-irradiation electromagnetic wave and, based on a post-irradiation electromagnetic wave obtained, measure the measuring target, in which the post-irradiation electromagnetic wave has a response component from the measuring target and a background component corresponding to the pre-irradiation electromagnetic wave, includes: a first frequency spectrum acquiring section arranged to acquire a frequency spectrum of a first signal that includes the background component and the response component of the post-irradiation electromagnetic wave; a second frequency spectrum acquiring section arranged to acquire a frequency spectrum of a second signal that includes the background component of the post-irradiation electromagnetic wave; and a subtracting section arranged to subtract the frequency spectrum of the second signal from the frequency spectrum of the first signal. According to the thus constructed electromagnetic wave measuring apparatus, the electromagnetic wave measuring apparatus is arranged to irradiate an irradiation target having a measuring target with a pre-irradiation electromagnetic wave and, based on a post-irradiation electromagnetic wave obtained, measure the measuring target. The post-irradiation electromagnetic wave has a response component from the measuring target and a background component corresponding to the pre-irradiation electroma