JP2001304964A - Fourier spectroscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Fourier spectroscope for improved S/N even if the amount of measurement light decreases. SOLUTION: An interferometer is made to scan for measuring the interference light of measured light, and the measuring result is Fourier-transformed with a calculation controlling circuit for the spectrum of the measured light. Here, there are provided a first light receiving means for detecting the interference light transmitting an object as measurement light, a second light receiving means for detecting the interference light as reference light, a first low-gain processing channel and a first high-gain processing channel where the output of the first light receiving means is converted into a digital signal and is held, a second low-gain processing channel and a second high-gain processing channel where the output of the second light receiving means is converted into a digital signal and is held, and a calculation control circuit where, if any one of first and second high-gain processing channels saturates, the output in saturation range of the high-gain processing channel on saturated side is replaced with the output of low-gain processing channel on saturated side which is reduced for the output of the high-gain processing channel on saturated side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Fourier spectrometer, and more particularly, to an S / S spectrometer even when the amount of measurement light decreases.
The present invention relates to a Fourier spectrometer capable of improving N.

[0002]

2. Description of the Related Art A conventional Fourier spectrometer scans an interferometer to measure interference light of measurement light, and obtains a spectrum of the measurement light by performing a Fourier transform on the measurement result by an arithmetic control means such as a computer.

[0003] A steep peak called a center burst exists in the center of the interferogram as a measurement result. For this reason, in the conventional Fourier spectrometer, since the full span of the A / D converter is set so as not to saturate the center burst, the quantization voltage increases and S / S
There was a problem that N decreased.

[0004] To solve such a problem, there is Japanese Patent Application No. 11-126761 filed by the present applicant.
In the above-mentioned application, two processing channels, a high gain processing channel and a low gain processing channel, are provided, and a saturated portion of the measurement result in the high gain processing channel is replaced with the measurement result in the low gain processing channel, thereby obtaining a high S signal. / N Fourier spectrometer is realized.

FIG. 4 is a block diagram showing an example of such a conventional double-beam Fourier spectrometer.

In FIG. 4, reference numerals 1a and 1b denote light receiving means composed of a photodiode serving as a light receiving element and a current-voltage conversion circuit, and 2a and 2b denote 1/1 of the sampling frequency.
Filter circuit for attenuating two or more high frequency signals, 3a
And 3b are low gain amplifiers, 4a, 4b, 7a and 7b are A / D converters, 5a, 5b, 8a and 8b are storage circuits,
6a and 6b are high gain amplifiers, 9 is an operation control circuit, 10
Reference numerals 0 and 101 denote measurement light and reference light from an interferometer (not shown).

Further, reference numerals 1a to 8a denote processing means 50a on the side of measurement light 100, 1b to 8b denote processing means 50b on the side of reference light 101, and 3a to 5a denote low-gain processing channels 51a.
3b to 5b are the low gain processing channels 51b, 6a
8a constitute a high gain processing channel 52a, and 6b-8b constitute a high gain processing channel 52b.

The measuring light 100 detected by the light receiving means 1a is converted into an electric signal, and a high frequency signal having a frequency equal to or more than 1/2 of the sampling frequency is attenuated by the filter circuit 2a. The output signal of the filter circuit 2a is amplified by the low gain amplifier 3a and the high gain amplifier 6a, respectively, and the A / D converter 4a
Storage circuit 5a after being converted into a digital signal at 7a and 7a
And 8a.

Similarly, the reference light 101 detected by the light receiving means 1b is converted into an electric signal, and a high-frequency signal of 1/2 or more of the sampling frequency is attenuated by the filter circuit 2b. The output signal of this filter circuit 2b is a low gain amplifier 3
b and a high-gain amplifier 6b, respectively, are converted into digital signals by A / D converters 4b and 7b, and then stored in storage circuits 5b and 8b.

The arithmetic control circuit 9 performs a synthesizing process of each interferogram stored in the storage circuits 5a and 8a. The spectrum of the measurement light is obtained by performing a Fourier transform on the interferogram of the synthesized measurement light.

The arithmetic and control circuit 9 performs a synthesizing process of each interferogram stored in the storage circuits 5b and 8b. The spectrum of the reference light is obtained by Fourier transforming the interferogram of the synthesized reference light.

Here, the operation of the conventional example shown in FIG. 4 will be described with reference to FIG. FIG. 5 is a flowchart illustrating the operation of the arithmetic control circuit 9.

In "S001" in FIG. 5, the arithmetic and control circuit 9 detects the saturation start point, the saturation end point and the saturation range from the high gain data of the measurement light stored in the storage circuit 8a.
In the middle “S002”, the arithmetic control circuit 9 stores the memory circuit 8b.
, A saturation start point, a saturation end point, and a saturation range are detected from the high gain data of the reference light stored in.

In the case where the arithmetic and control circuit 9 cannot detect the saturation from both the high-gain data of the measurement light and the reference light in "S003" in FIG. 5, do not replace the low-gain data in "S004" in FIG. "S009" in FIG.
Is performed.

On the other hand, if "S003" in FIG. 5 indicates that the arithmetic and control circuit 9 has detected saturation from both or one of the high gain data of the measurement light and the reference light, the operation shown in FIG.
In step S005 ", the arithmetic and control circuit 9 obtains a range that includes both the detected measurement light saturation range and the reference light saturation range, and sets this range as the total saturation range.

In FIG. 5, in "S006", the arithmetic and control circuit 9 obtains a range including both the saturation range and a preset setting range, and sets this range as a low gain data use range. Further, in "S007" in FIG. 5, the arithmetic control circuit 9 expands the low-gain data use range by a preset value.

In "S008" in FIG. 9, the arithmetic and control circuit 9 replaces the high gain data in the previously set low gain data use range with the low gain data obtained by converting the value of the high gain data output into the measurement light. And an interferogram of the reference light is synthesized.

Finally, in "S009" in FIG. 5, the arithmetic and control circuit 9 Fourier-transforms the combined interferogram to obtain the spectrum of the measurement light and the reference light.

As described above, by making the use range of the low gain data of the measurement light and the reference light the same, the error curve between the measurement light and the reference light after the Fourier transform tends to be the same. Calculating the ratio reduces noise and reduces S /
N will be improved.

As a result, in the case of a double beam Fourier spectrometer, by making the use range of low gain data the same for the measurement light and the reference light, it is possible to reduce the interferogram synthesis error, S / N is improved.

[0021]

However, in the conventional example shown in FIG. 5, when measuring the transmission and absorption of the object to be measured, the amount of the measuring light decreases. For this reason, saturation does not occur in the high gain amplifier on the measurement light side, but as can be seen from the flowchart shown in FIG. 5, as long as saturation occurs in the high gain amplifier on the reference light side, low saturation occurs even on the measurement light side. Since the gain data is used, there is a problem that the S / N is reduced due to the influence of noise on the low gain side.

For example, FIG. 6 shows high gain amplifiers 6a and 6b
And the gains of the low-gain amplifiers 3a and 3b are 1
It is a characteristic curve figure which shows the change of S / N with respect to the light absorbency of a measurement object at the time of doubling.

The characteristic curves indicated by "CH01" and "CH02" in FIG. 6 are the characteristics when 1-times and 16-times data are used, respectively. "CH03" in FIG. 6 is the characteristic curve of the conventional example shown in FIG. It shows the characteristics. (However, in FIG. 6)
In the characteristic shown in CH02 ", if the absorbance of the measurement object is small, the data of 16 times is saturated and cannot be used because it is saturated.) As can be seen from" CH03 "in FIG. Therefore, the problem to be solved by the present invention is to realize a Fourier spectrometer capable of improving the S / N even when the amount of measurement light is reduced.

[0024]

In order to achieve the above object, according to the first aspect of the present invention, the interferometer is scanned to measure the interference light of the measurement light, and the measurement result is obtained. In a Fourier spectrometer that obtains a spectrum of the measurement light by performing a Fourier transform by an arithmetic control circuit, a first light receiving unit that receives the interference light transmitted through the measurement target as the measurement light, and receives the interference light as the reference light A second light receiving means, a first low gain processing channel and a first high gain processing channel for converting an output of the first light receiving means into a digital signal and holding the digital signal, and an output of the second light receiving means. A second low-gain processing channel and a second high-gain processing channel for converting and holding a digital signal;
And when one of the second high-gain processing channels is saturated, the output of the high-gain processing channel on the saturated side is converted to the output of the high-gain processing channel on the saturated side. And an arithmetic control circuit for replacing with the output of the low-gain processing channel on the side of the S / N ratio even when the amount of measurement light is reduced.
Can be improved.

According to a second aspect of the present invention, there is provided a Fourier spectroscope which scans an interferometer to measure interference light of measurement light, and Fourier-transforms the measurement result by an arithmetic and control circuit to obtain a spectrum of the measurement light. First light receiving means for receiving the interference light transmitted through the measurement target as measurement light, second light receiving means for receiving the interference light as reference light, and converting the output of the first light receiving means into a digital signal A first low-gain processing channel and a first high-gain processing channel for holding the output, and a second low-gain processing channel and a second high-gain channel for converting and holding the output of the second light receiving means to a digital signal. If one of the gain processing channel and one of the first and second high gain processing channels is saturated, the output of the low gain processing channel on the saturated side is saturated. And an arithmetic control circuit that replaces the output of the high gain processing channel in the saturation range with the output of the low gain processing channel on the saturated side. N can be improved.

According to a third aspect of the present invention, there is provided a Fourier spectrometer which scans an interferometer to measure interference light of measurement light, and Fourier-transforms the measurement result by an arithmetic and control circuit to obtain a spectrum of the measurement light. First light receiving means for receiving the interference light reflected by the measurement target as measurement light, second light receiving means for receiving the interference light as reference light, and converting the output of the first light receiving means into a digital signal A first low-gain processing channel and a first high-gain processing channel for holding the output, and a second low-gain processing channel and a second high-gain channel for converting and holding the output of the second light receiving means to a digital signal. When the gain processing channel and either one of the first and second high gain processing channels are saturated, the output of the saturated range of the high gain processing channel on the saturated side is placed before the saturated side. And an arithmetic control circuit that replaces the output of the high gain processing channel with the output of the low gain processing channel on the saturated side, which is converted to the value of S / S even when the amount of measurement light decreases. N can be improved.

According to a fourth aspect of the present invention, there is provided a Fourier spectrometer for measuring an interference light of a measuring light by scanning an interferometer, and performing a Fourier transform of the measurement result by an arithmetic and control circuit to obtain a spectrum of the measuring light. First light receiving means for receiving the interference light reflected by the measurement target as measurement light, second light receiving means for receiving the interference light as reference light, and converting the output of the first light receiving means into a digital signal A first low-gain processing channel and a first high-gain processing channel for holding the output, and a second low-gain processing channel and a second high-gain channel for converting and holding the output of the second light receiving means to a digital signal. If one of the gain processing channel and one of the first and second high gain processing channels is saturated, the output of the low gain processing channel on the saturated side is saturated. And an arithmetic control circuit that replaces the output of the high gain processing channel in the saturation range with the output of the low gain processing channel on the saturated side. N can be improved.

According to a fifth aspect of the present invention, in the Fourier spectrometer according to the first to fourth aspects of the present invention, the arithmetic and control circuit expands the saturation range by a predetermined value. S / N can be improved even when the amount of measurement light is reduced.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration block diagram showing one embodiment of a Fourier spectrometer according to the present invention. 1a to 8 in FIG.
a, 1b to 8b, 50a, 50b, 51a, 51b, 5
Reference numerals 2a, 52b, 100, and 101 denote the same reference numerals as in FIG. 4, 10 denotes an arithmetic control circuit, 11 denotes a spectroscope, 12 denotes an optical branching element, and 13 denotes a measurement target. Reference numeral 102 denotes interference light output from the spectroscope 10.

The connection inside the processing means 50a and 50b is the same as that of the conventional example shown in FIG. Interference light 1 output from spectroscope 11
02 is split into two by an optical branching element 12, and one of the lights is transmitted through the measurement target 13 and is converted into a measurement light 100 by a processing unit 50.
a. The other light is directly incident on the processing means 50b as reference light.

Here, the operation of the embodiment shown in FIG. 1 will be described with reference to FIG. FIG. 2 is a flowchart illustrating the operation of the arithmetic control circuit 10.

In "S101" in FIG. 2, the arithmetic and control circuit 10 detects the saturation start point, the saturation end point and the saturation range from the high gain data of the measurement light stored in the storage circuit 8a, and in "S102" in FIG. The arithmetic control circuit 10 detects a saturation start point, a saturation end point, and a saturation range from the high gain data of the reference light stored in the storage circuit 8b.

When the arithmetic and control circuit 10 detects saturation from both the high gain data of the measurement light and the reference light in "S103" in FIG. 2, the arithmetic and control circuit 10 performs the detected measurement in "S104" in FIG. A range that includes both the light saturation range and the reference light saturation range is determined, and is defined as a total saturation range.

In "S105" in FIG. 2, the arithmetic and control circuit 10 obtains a range that includes both the saturation range and a preset setting range, and sets this range as a low gain data use range. Further, in "S106" in FIG. 2, the arithmetic control circuit 10 expands the low-gain data use range by a predetermined value, and synthesizes the interferograms of the measurement light and the reference light in "S107" in FIG. "S1" in FIG.
Move to step 18 ".

If both the high-gain data of the measurement light and the reference light are not saturated at "S103" in FIG. 2, the arithmetic control circuit 10 determines whether the measurement light is saturated at "S108" in FIG. If it is determined that the measurement light is saturated, the arithmetic and control circuit 10 obtains a range including both the saturation range and the set range of the measurement light in "S109" in FIG. And

At "S110" in FIG. 2, the arithmetic control circuit 10 enlarges the low gain data use range by a predetermined value, and synthesizes an interferogram of the measurement light at "S111" in FIG. It moves to the step of "S113" in FIG.

On the other hand, if the measurement light is not saturated in "S108" in FIG. 2, the arithmetic and control circuit 10 uses all the high gain data without using the low gain data of the measurement light in "S112" in FIG. Range.

In step S113 in FIG. 2, it is determined whether the reference light is saturated. If the reference light is saturated, the operation control circuit 10 determines the reference light saturation range in step S114 in FIG. And a range that includes both the set range and the low gain data use range.

In "S115" in FIG. 2, the arithmetic control circuit 10 enlarges the low gain data use range by a predetermined value, and synthesizes the interferogram of the measurement light in "S116" in FIG. It moves to the step of "S118" in FIG.

On the other hand, if the reference light is not saturated in "S113" in FIG. 2, the operation control circuit 10 does not use the low gain data of the reference light but uses all of the high gain data in "S117" in FIG. Range.

Finally, at "S118" in FIG. 2, the arithmetic and control circuit 10 Fourier-transforms the combined interferogram to obtain the spectrum of the measurement light and the reference light.

For example, FIG. 3 shows high gain amplifiers 6a and 6b
And the gains of the low-gain amplifiers 3a and 3b are 1
FIG. 4 is a characteristic curve diagram showing a change in S / N with respect to the absorbance of the measurement object when the measurement is doubled, and “CH01” and “CH” in FIG.
02 "and" CH03 "are given the same reference numerals as in FIG.

If it is assumed that the saturation of high gain data of the measurement light occurs when the absorbance is smaller than the absorbance indicated by "AB11" in FIG. 3, the embodiment shown in FIG. 1 has the characteristic shown by "CH11" in FIG. In a region where the high gain data of the measurement light indicated by “AR11” in FIG. 3 is not saturated, the S / N is “CH0” in FIG.
2 ”, and the S / N is higher than that of“ CH03 ”in FIG.
It can be seen that is improved.

As a result, when the high gain data of either the measurement light or the reference light is saturated, the low gain data is used only on the saturated side and the high gain data is used on all the non-saturated sides. In addition, even when the amount of the measurement light decreases when measuring the transmission and absorption of the measurement target, the S / N can be improved.

Although the embodiment shown in FIG. 1 is configured to measure the amount of transmitted light, it may measure the amount of reflected light.

Also, the high gain data of the measurement light does not saturate,
The present invention can be applied even when the high gain data of the reference light is saturated.

Further, when synthesizing the interferogram, even if the value of the low gain data is converted to the value of the high gain data and synthesized, the value of the high gain data is converted to the value of the low gain data and synthesized. Or any of them.

[0048]

As is apparent from the above description,
According to the present invention, the following effects can be obtained. According to the first to fifth aspects of the present invention, when the high gain data of one of the measurement light and the reference light is saturated, the low gain data is used only on the saturated side, and the non-saturation side is all high. By using the gain data, it is possible to improve the S / N even when the amount of the measurement light decreases when measuring the transmission and absorption of the measurement target.

[Brief description of the drawings]

FIG. 1 is a configuration block diagram showing one embodiment of a Fourier spectroscope according to the present invention.

FIG. 2 is a flowchart illustrating an operation of an arithmetic control circuit.

FIG. 3 is a characteristic curve diagram showing a change in S / N with respect to the absorbance of a measurement object.

FIG. 4 is a configuration block diagram illustrating an example of a conventional double beam Fourier spectrometer.

FIG. 5 is a flowchart illustrating the operation of the arithmetic control circuit.

FIG. 6 is a characteristic curve diagram showing a change in S / N with respect to the absorbance of a measurement object.

[Explanation of symbols]

 1a, 1b Light receiving means 2a, 2b Filter circuit 3a, 3b Low gain amplifier 4a, 4b, 7a, 7b A / D converter 5a, 5b, 8a, 8b Storage circuit 6a, 6b High gain amplifier 9 Operation control circuit 10 Operation control Circuit 11 Spectroscope 12 Optical branching element 13 Measurement target 50a, 50b Processing means 51a, 51b Low gain processing channel 52a, 52b High gain processing channel 100 Measurement light 101 Reference light 102 Interference light

Claims (5)

[Claims] 1. A Fourier spectroscope which scans an interferometer to measure interference light of measurement light, and Fourier-transforms the measurement result by an arithmetic and control circuit to obtain a spectrum of the measurement light. A first light receiving unit that receives the interference light as the measurement light, a second light receiving unit that receives the interference light as the reference light, and a first that converts an output of the first light receiving unit into a digital signal and holds the digital signal. A low-gain processing channel and a first high-gain processing channel, a second low-gain processing channel and a second high-gain processing channel for converting an output of the second light receiving means into a digital signal and holding the digital signal; When one of the first and second high gain processing channels is saturated, the high gain processing channel on the side that saturates the output of the saturation range of the high gain processing channel on the saturated side. Fourier spectrometer characterized by comprising the conversion has been saturated side to the output of the Le a calculation control circuit to replace the output of the low gain channel. 2. A Fourier spectroscope which scans an interferometer to measure interference light of measurement light, and Fourier-transforms the measurement result by an arithmetic and control circuit to obtain a spectrum of the measurement light. A first light receiving unit that receives the interference light as the measurement light, a second light receiving unit that receives the interference light as the reference light, and a first that converts an output of the first light receiving unit into a digital signal and holds the digital signal. A low-gain processing channel and a first high-gain processing channel, a second low-gain processing channel and a second high-gain processing channel for converting an output of the second light receiving means into a digital signal and holding the digital signal; If one of the first and second high gain processing channels is saturated, the high gain processing on the saturated side is converted with respect to the output of the low gain processing channel on the saturated side. Fourier spectrometer, characterized in that it includes a calculation control circuit to replace the output of the saturation range at the output of the low gain channel of the saturated side of Yan'neru. 3. A Fourier spectrometer which scans an interferometer to measure interference light of measurement light, and Fourier-transforms the measurement result by an arithmetic and control circuit to obtain a spectrum of the measurement light. A first light receiving unit that receives the interference light as the measurement light, a second light receiving unit that receives the interference light as the reference light, and a first that converts an output of the first light receiving unit into a digital signal and holds the digital signal. A low-gain processing channel and a first high-gain processing channel, a second low-gain processing channel and a second high-gain processing channel for converting an output of the second light receiving means into a digital signal and holding the digital signal; When one of the first and second high gain processing channels is saturated, the high gain processing channel on the side that saturates the output of the saturation range of the high gain processing channel on the saturated side. Fourier spectrometer characterized by comprising the conversion has been saturated side to the output of the Le a calculation control circuit to replace the output of the low gain channel. 4. A Fourier spectroscope that scans an interferometer to measure interference light of measurement light, and Fourier-transforms the measurement result by an arithmetic and control circuit to obtain a spectrum of the measurement light. A first light receiving unit that receives the interference light as the measurement light, a second light receiving unit that receives the interference light as the reference light, and a first that converts an output of the first light receiving unit into a digital signal and holds the digital signal. A low-gain processing channel and a first high-gain processing channel, a second low-gain processing channel and a second high-gain processing channel for converting an output of the second light receiving means into a digital signal and holding the digital signal; If one of the first and second high gain processing channels is saturated, the high gain processing on the saturated side is converted with respect to the output of the low gain processing channel on the saturated side. Fourier spectrometer, characterized in that it includes a calculation control circuit to replace the output of the saturation range at the output of the low gain channel of the saturated side of Yan'neru. 5. The Fourier spectroscope according to claim 1, wherein the arithmetic control circuit expands the saturation range by a predetermined value.