JPH03279825A - Fourier transforming spectral method using pulse light source - Google Patents

Abstract

PURPOSE:To expand a light source and a measurement object range by using the pulse light source as a light source, emitting pulses whose period is shorter than a sampling period and extracting an interferogram of a low-frequency component from the output of a detector, and sampling and processing it by Fourier transformation. CONSTITUTION:The period t' of the pulse light emitted by the period pulse light source 1 is shorter than the period (t) of a trigger signal generated by an interferometer according to a sampling rule, so the output of an interferometer, i.e. detector 5 is obtained by sampling a conventional interferogram at the period t'. Further, a low-pass filter 7 obtains an interferometer which is the envelope of the output of the detector 5. Then the light source 1 and filter 7 are combined to sample the interferogram by an AD converter 8 with the trigger signal which has the period (t) and this is processed by Fourier transformation to obtain a target analyzed spectrum.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to Fourier transform spectroscopy using a pulsed light source to extract an interferogram using an interferometer and perform Fourier transform to obtain an analytical spectrum of a sample.

[Conventional technology]

FIG. 3 is a diagram for explaining a conventional example of Fourier transform optical spectroscopy, and FIG. 4 is a diagram showing signal waveforms of the circuit shown in FIG. 3.

In the rapid scan Fourier transform optical spectroscopy represented by the Michelson interferometer, as shown in FIG. A detector 5 is used. Then, the light from the light source 1' is divided into two beams by the semi-transparent mirror 2 of the two-light East interferometer, and one is guided to the fixed mirror 3 side and the other to the movable mirror 4 side that moves at a constant speed. The interferogram (Fig. 4 Q)) is detected due to the optical path difference. This interferogram is generated by using a trigger signal with a period t generated by an interferometer as shown in FIG. 2(C) in the AD converter 8.
) is sampled as shown in FIG. 9, and is subjected to Fourier transformation by the CPU 9 to obtain an analysis spectrum. Note that the sample is not directly relevant here, so it will be omitted.

[Problem to be solved by the invention]

In the above-mentioned rapid scan method, the Fourier transform light distribution is based on the condition that the intensity of the light source is constant and the light is continuous in time. That is, the light source 1' emits temporally continuous light with constant intensity as shown in FIG. 2(a),
The light incident on the interferometer is modulated into a frequency proportional to the wave number of the light by moving the movable mirror 4 at a constant speed, and is received by the detector.

In this case, there is a problem that the light source to be used is restricted, and since the light is continuously irradiated, the sample is limited to those that are not affected by continuous irradiation.

The present invention solves the above-mentioned problems, and aims to provide a Fourier transform spectroscopy method using a pulsed light source that can expand the range of light sources and measurement targets.

[Means to solve the problem]

To this end, the present invention uses a pulsed light source as a light source and emits pulsed light with a period shorter than the sampling period in Fourier transform spectroscopy in which an interferogram is taken out using an interferometer and subjected to Fourier transformation to obtain an analysis spectrum of the sample. This method is characterized by obtaining the analysis spectrum of the sample by extracting the interferogram of low frequency components from the detector output, sampling it, and Fourier transforming it.

(Function) In the Fourier transform spectroscopy using the pulsed light source of the present invention,
Since a pulsed light source is used as the light source and emits pulsed light with a period shorter than the sampling period, an interferogram of low frequency components can be extracted from the detector output by passing it through a low-pass filter. Similarly, an analysis spectrum of a sample can be obtained by sampling and Fourier transform.

〔Example〕

Examples will be described below with reference to the drawings.

FIG. 1 is a diagram for explaining one embodiment of Fourier transform spectroscopy using a pulsed light source according to the present invention, and FIG. 2 is a diagram showing signal waveforms of the main parts in FIG. 1. In the figure, 1 is a periodic pulse light source, 2 is a semi-transparent mirror, 3 is a fixed mirror, 4 is a movable mirror, 5 is a detector, 6 is an amplifier, 7 is a low-pass filter, 8
indicates an AD converter.

The periodic pulse light source 1 emits pulsed light of equal intensity with a period t', and the period t' is as shown in FIG. 2(a), (
As shown in d), it is shorter than the period t of the trigger produced by the interferometer according to the sampling law. Therefore, the output of the interferometer, that is, the output of the detector 5 is the 21K(b
), the conventional interferogram is sampled at a period t'. The low-pass filter 7 obtains an interferogram, which is an envelope of the output of the detector 5, as shown in FIG. 2(C). By combining the periodic pulse light source 1 and the low-pass filter 7 in this way, the AD converter 8 can convert the interferogram to the 21st one using the trigger signal with the period t shown in FIG.
1K(e) can be sampled as shown in
By Fourier transforming this, a target analysis spectrum can be obtained.

Note that as a periodic pulse light source, SOR (S ync
hrotron Orbital Radiati
(on) A light source, a laser-excited Raman sample, etc. may be used. Furthermore, if the intensity of the light source fluctuates, the intensity may be monitored to standardize the detector output.

Next, an application example of the present invention will be explained.

FIG. 5 is a diagram for explaining a conventional example of time-resolved spectroscopy.

The need to periodically apply stimulation to a sample using electricity, laser, or other means and measure the reaction state of the sample during the process of recovery from the stimulation is used in a variety of fields, such as the evaluation of liquid crystal properties. The measurement method is FT-IR (Fourier transform infrared spectrophotometer).
There is a time-resolved spectroscopy method using This method can be classified into those using a rapid scan interferometer and those using a step scan interferometer, and has been widely used in the past because it can measure a wide wave number range with a high signal-to-noise ratio.

The FT-IR interferogram has a condition that it will not distort unless the characteristics such as the transmittance of the sample are constant during the measurement. Information that is different from the information that appears will appear. In addition, in time-resolved spectroscopy, the period of the applied stimulus is generally required to be longer than the time at which the reaction ends. When applying periodic stimulation, it is necessary to match the stimulation if the stimulation is applied regardless of the movement of the movable mirror. Therefore, conventionally, stimulation is applied in synchronization with a reference signal possessed by an interferometer.

With rapid scan interferometers, as mentioned above, stimulation is applied in synchronization with the reference signal of the interferometer and interferograms are taken, so the following three cases can be divided depending on the length of the target's response cycle: I can do it.

■ If the response to the stimulus is very slow, that is, the period τ of the reaction of the object to be measured or a change in a similar state is time for one measurement)
If longer (τ>T) ■ If the response to the stimulus is relatively slow, that is, the period τ of the response to be measured or a similar state change is the fifth
When the time interval (sampling interval) for measuring each point of a school of fish that forms an interferogram is longer than t (1<τ<T), as shown in Fig.
As shown in Figure 5(C), in the case of τ x t, for example, in the case of (■) above, the reaction period τ of the object is longer than the scanning time T of the moving mirror, so as shown in Figure 5(a), If the scanning speed is increased, an interferogram will be obtained at a time when the applied stimulus is delayed, so by Fourier transforming this interferogram, the spectrum of the desired state can be obtained.

However, in the case of ■, the reaction time is short, so multiple scans are performed as shown in Figure 5, etc.
Second interferometer scan, second interferometer scan,
Measurement is performed by shifting the stimulation timing by the period t of the reference signal of the interferometer, and in each scan, the data with the same delay time ■, ■, etc. are identified and edited. By creating an interferogram, we obtain the spectrum of the state a.

In the case of ■, since the reaction period T is included in the sampling period t, stimulation is repeatedly applied in synchronization with the reference signal of the interferometer as shown in FIG. 5(C), and a constant delay time Δτ The state spectrum is obtained by performing measurements at , and editing the data with the same delay time to create an interferogram.

However, especially in the case (2) above, synchronization with the reference signal of the interferometer is required, and extremely fast measurement is required. For example, if the sampling period t is 100 μs, 100
If a point is to be measured, the measurement must be repeated every 1 μs, and a very large amount of data must be captured and processed in one scan of the movable mirror. Moreover, after measurement, each data must be identified and data with the same delay time must be edited. In this case, FTIR has a high-speed sampling mechanism, data editing function, etc.
It becomes necessary to add functions that were not previously provided.

Furthermore, if the reaction period is shorter than the sampling time, there is a problem that dead time is generated until the next sampling after the reaction is completed, resulting in poor measurement efficiency.

Furthermore, in the case of the above example, 11111m is given in synchronization with the reference signal of the interferometer, but it is difficult to achieve such synchronization, and in cases where periodic stimulation is naturally excited. has the problem that it cannot be measured using the above method.

Therefore, by using the Fourier transform spectroscopy using the pulsed light source of the present invention, the above problem can be solved as follows.

FIG. 6 is a diagram showing the configuration of one embodiment of a time-resolved spectrometer to which the present invention is applied, and FIG. 7 is a waveform diagram for explaining the operation of the time-resolved spectrometer shown in FIG. 6. In the figure, 11
is a pulsed light source, 12 is an interferometer, 13 is a sample, 14 is a detector, 15 is a timer, 16 is a variable delay circuit, 17 is a power source for the light source, 18 is a stimulus generator, 19 is a preamplifier, 20 is a low-pass filter, 21 is a main amplifier, 22 is an AD converter, and 23 is a CPU.

In FIG. 6, sample 13 repeatedly shows the same response to the stimulus, and is the object of measurement for the response period τ as shown in FIG. This is shorter than the sampling interval t. As shown in FIGS. 7 and 7, the timer 15 generates a clock signal having a period t' which is asynchronous with the reference signal of the interferometer 12 shown in FIG. 7(a) and which is longer than the reaction period τ.

The stimulus generator 18 gives a trigger (stimulus) to the sample 13 as shown in FIG.
It is asynchronous with the reference signal of No.2. Variable delay circuit 1
6 generates a trigger delayed by a certain time Δτ' from the tarok signal of the timer 15, and the light source power supply 1
Reference numeral 7 is for driving the pulse light source 11 at the timing shown in FIG. 7 [d] using this trigger.

Since the pulsed light source 11 is driven at the timing shown in FIG. 7(d) as described above, the detector 14 has the timing shown in FIG.
A comb-shaped signal is obtained as shown in . In other words, this is the same as applying a gate with a certain delay time from the stimulus to a repeated stimulus and sampling only the signal with a certain delay time relative to the stimulus, and a comb-shaped interferogram is obtained. The low-pass filter 20 is used to remove harmonics obtained from the output of the detector 14 to obtain an envelope as shown in FIG. 7(f).
The comb-shaped interferogram is converted into a normal analog signal by a low-pass filter 20.

According to the above configuration, the output of the detector 14 when the sample 13 does not change is (σ; wave number - 1/λ) (1), but when the sample 13 is stimulated and a constant delay △τ′
Since the output of the detector 16 is sampled at equal intervals, the output of the detector 16 when gated at , includes the comb function ■, · which is a delta function at equal intervals, and (1+cos2πσx)dσ...
...(2). Here, if the speed of the movable mirror of the interferometer is V, then x=2vt, but there is no phase relationship because the periodic stimulation is asynchronous with the movement of the movable mirror.

In (1'-, C092πσX) of the above formula (2),
Only the term multiplied by cos 2πσX can be converted into a spectrum, so if only this term is extracted, the output will be F″fX) −LIJ j・(t−△τ°). Therefore, this signal is low-pass In order to see the output obtained when passing through the filter 20, we perform a Fourier transform on IP, ・(t-△τ゛) at t, and we get = e −'"f'" (1/ t') [14ry
t・(f) ”・・”(3)=1/l' [δ(O
+δ(f-1/l') e-"'te+...+
δ(f+1/l') e">7"+,.

, which is also a comb function. Furthermore, the data is output at an interval that is the reciprocal of the sampling interval. Therefore, low pass filter 2
When 0 is passed through, ...(4) is obtained, and this is obtained as the output. Comparing this equation (4) with the above [1] equation, the equation F''(X) shows that we have obtained an interferogram of the state of the sample when there is a delay of △τ'' after applying the stimulus. Therefore, at the sampling interval determined by the ?J!i number band of the signal,
All you need to do is D conversion.

The above example uses a clock signal generated by a timer)
The pulsed light source is configured to control the stimulus generator using the oscillator and to drive the pulsed light source by delaying the stimulus generator by the time Δτ' using a variable delay circuit. When using a pulsed laser,
Monitor the light source, then ill with a delay of t'-△τ'
It may also be configured to give a powerful effect.

When a pulsed light source is used as described above, time-resolved spectroscopic measurements can be performed with a conventional system by using a low-pass filter.

Note that the present invention is not limited to the above embodiments, and various modifications are possible. For example, in the above embodiments, the present invention was applied to time-resolved spectroscopy, but it can be similarly applied to other Fourier transform optical spectroscopy.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, since a pulsed light source is used as a light source, an SOR light source, a pulsed laser-excited Raman sample, or the like can be used as a light source. Moreover, since the time to irradiate the measurement target with light can be shortened and the amount of light irradiated can be reduced, Fourier transform spectroscopy can be used even for measurement targets that are affected by light irradiation or for which continuous irradiation is undesirable. It can be applied and the range of applications is expanded.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining one embodiment of Fourier transform spectroscopy using a pulsed light source according to the present invention, FIG. 2 is a diagram showing the signal waveform of the main part in FIG. 1, and FIG. 4 is a diagram for explaining a conventional example of converted light spectroscopy. FIG. 4 is a diagram showing a signal waveform of the circuit shown in FIG. 3. FIG. FIG. 6 is a diagram showing the configuration of one embodiment of a time-resolved spectrometer to which the present invention is applied, and FIG. 7 is a waveform diagram for explaining the operation of the time-resolved spectrometer shown in FIG. 6. DESCRIPTION OF SYMBOLS 1... Periodic pulse light source, 2... Half-transparent mirror, 3... Fixed mirror, 4... Moving mirror, 5... Detector, 6... Tomb, 7... Low pass filter, 8...A/D converter. Applicant: JEOL Ltd.

Claims (1)

[Claims] (1) In Fourier transform spectroscopy, an interferogram is taken out using an interferometer and Fourier transformed to obtain the analysis spectrum of the sample, a pulsed light source is used as the light source and pulsed light with a period shorter than the sampling period is emitted and output from the detector. A Fourier transform spectroscopy method using a pulsed light source that is characterized by obtaining an analytical spectrum of a sample by extracting, sampling and Fourier transforming an interferogram of low frequency components from a sample.