JPH0320705B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a quantitative analysis method and apparatus using Kerse spectroscopy.

Kerse spectroscopy is a type of nonlinear Raman spectroscopy that has progressed with the development of high-power lasers and dye lasers, and compared to conventional Raman spectroscopy,
Since it has a detection sensitivity of about 10 ⁵ times, there are many expectations for its application.

The principle of this Kerse spectroscopy can be briefly explained as follows. As shown in Figure 1, an excitation laser beam with a frequency ω ₁ is applied to the material (Raman active material) RM, and the same frequency (Stokes frequency) as the Stokes light of the material RM ω ₂ (=ω ₁ −Ω, where Ω is _the natural frequency of the molecules of the material RM) _.
+Ω) is generated resonantly and extremely strongly in the form of a beam. This phenomenon can be understood as a four-photon process, as shown in the energy diagram of Figure 2. Also, the intensity of the anti-Stokes light at this time
I ₃ is I ₃ ∝I ₁ ²・I ₂・N ² ……(1) (where, N is the density of the material RM, I ₁ is the intensity of the laser beam with frequency ω ₁ , and I ₂ is the frequency ω ₂ laser beam intensity). Therefore, by detecting the intensity _I3 of the anti-Stokes light, the concentration of the substance RM can be detected. Kerse spectroscopy is based on the above principle, and the concentration of the substance to be measured is determined by detecting the intensity I ₃ of the anti-Stokes light.

By the way, detection by this Kerse spectroscopy actually varies greatly depending on fluctuations in the intensity of the excitation laser beam, optical system conditions, etc., so there are no known quantitative analyzers (concentration measuring devices) using conventional Kerse spectroscopy. The signal intensity from the system to be measured is corrected based on the signal from the reference cell containing the reference substance, and the concentration is thereby measured.

FIG. 3 shows a conventional quantitative analysis apparatus using Kerse spectroscopy, in which cell A is filled with a substance to be measured, and cell B is filled with a reference substance at a predetermined concentration. The excitation laser beam with the frequency ω ₁ is reflected by the mirror 1 and guided to the dichroic mirror 2, and the laser beam with the frequency ω ₂ is applied to the dichroic mirror 2. dichroic mirror 2
combines an excitation laser beam with a frequency of ω ₁ and a laser beam with a frequency of ω ₂ , splits this combined light into two by a beam splitter 2', and sends one of the beams to the lens 4, cell A,
In addition to the spectrometer 7 via the lens 5 and prism 6,
The other side is mirror 3, lens 8, cell B, lens 9,
It is applied to a spectrometer 11 via a prism 10. Detectors 7a and 11a are provided in the spectrometers 7 and 11, respectively, and the intensity of light applied to the spectrometers 7 and 11 is detected as an electrical signal.

However, the conventional method described above requires two signal detection systems: a first signal detection system including a spectrometer 7 and a detector 7a, and a second signal detection system including a spectrometer 11 and a detector 11a. Since the adjustment had to be performed in two systems, the cost was high and the adjustment operation was time-consuming.

This invention was made in view of the above points,
It is an object of the present invention to provide a quantitative analysis method and apparatus using Curse spectroscopy that has a simple configuration and reduces the number of adjustment points by half.

Therefore, in this invention, together with the excitation laser beam of frequency ω ₁ , the laser beam of frequency ω ₂ applied to the substance to be measured has a wide linewidth (broadband) of oscillation frequency, and the same as the substance to be measured is used as a reference material. A cell with a similar Raman frequency (one that can be covered by the wide laser beam described above) is used, and the first cell filled with the substance to be measured and the second cell filled with the reference substance are connected to the input laser beam. and the first
In addition to the multi-channel detector that simultaneously detects the laser light that has passed through the cell and the second cell in different channels for each wavelength, the signal output corresponding to the substance to be measured generated in each different channel of the multi-channel detector and the The concentration of the substance to be measured is detected from the intensity ratio with the signal output corresponding to the reference substance, so that the concentration can be accurately detected with one detection system.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 4 shows an embodiment of the present invention, and parts that perform the same functions as the device shown in FIG. 3 are given the same reference numbers for convenience of explanation. That is, cell A is a cell for filling the substance to be measured, and cell B is a cell for filling the substance to be measured.
is a cell for filling the reference material. In this example, YAG laser light (wavelength
532nm) using YAG, this excitation laser beam YAG
In addition, a broadband dye laser beam Dye is used as another laser beam added to the measurement system. The YAG laser beam YAG is reflected by the mirror 12 and guided to the dichroic mirror 13, and the dye laser beam Dye
The YAG laser beam is applied to the dichroic mirror 13.
It is added from the direction perpendicular to YAG. The dichroic mirror 13 reflects the YAG laser beam YAG and transmits the dye laser beam Dye, and the YAG laser beam YAG and the dye laser beam Dye are combined by the dichroic mirror 13.
This combined light is transmitted through lens 14, cell A, lens 15,
Lens 16, cell B, lens 17, prism 18
is applied to the spectrometer 19 via the detector 19a.
detected by. Here, the detector 19a is a so-called multi-channel detector that simultaneously detects the light received by the spectroscope 19 in different channels for each wavelength. Note that the lenses 14, 15, 16, and 17 are lenses for converging or refocusing the laser beam, and are not necessarily necessary as long as the convergence of the laser beam is maintained.

FIG. 5 shows an example of measurement using the apparatus shown in FIG. This graph shows wavelength on the horizontal axis and signal strength on the vertical axis. In this measurement example, silane gas SiH ₄ (Raman wave number 2190cm
^-1 ) Carbon monoxide CO (Raman wavenumber
2143cm ^-1 ) is used. In the graph shown in FIG. 5, the peak (A) is due to silane gas SiH ₄ and appears at a wavelength of 602.2 nm. peak again
(B) is due to carbon monoxide CO, wavelength 600.4nm
appears at the position of The concentration of the substance to be measured (in this case, silane gas SiH ₄ ) can be determined from the intensity ratio of peaks (A) and (B). Note that the absolute concentration is calibrated by measuring the ratio of the substance to a reference substance using a substance to be measured whose concentration is known and measured by another method, and using this ratio as a reference.

Figure 6 shows silane gas generated by plasma discharge.
This figure shows an example in which the present invention is applied to an apparatus for measuring changes in the concentration of SiH ₄ . Plasma chamber 20 is filled with silane gas SiH ₄ via valve 21 . Then, the absolute pressure of the silane gas SiH ₄ at this time is measured by the pressure gauge 22. Note that the electrodes 23a and 23b are plasma electrodes, and the valve 24 is a valve for discharging gas within the plasma chamber 20. Also, in reference cell 25
Carbon monoxide CO is filled from the CO cylinder 26 via valves 27 and 28.

In this state, the laser beam (combination of YAG laser beam YAG and dye laser beam Dye) w ₁ + w ₂ is connected to lens 2.
The light that has passed through the plasma chamber 20 is refocused by the lens 30 and is irradiated onto the reference cell 25.
Of the light converged by 1, the anti-Stokes light is converted into a laser beam w ₁ by a dichroic mirror 32.
+w ₂ and guided to a spectrometer (not shown).
The spectrometer uses a multi-channel detector to measure the received light intensity for each wavelength, thereby obtaining a graph as shown in FIG. The peak ratio of the measured substance (SiH ₄ ) to the reference substance (CO) at this time becomes the standard for the following silane gas concentration measurement.

Next, the electrodes 23a, 2 of the plasma chamber 20
3b, and the peak ratio of the measured substance (SiH ₄ ) to the reference substance (CO) at this time is measured.
By the way, the silane gas concentration in the plasma chamber changes due to discharge, but the monoxide gas concentration in the reference cell does not change. Therefore, the change in the concentration of silane gas can be measured from the peak ratio.

Although the above example shows the case where the present invention is applied to the measurement of changes in silane gas concentration during plasma discharge, this is just one example, and the present invention can be applied to various quantitative analysis fields. You should understand. For example, the present invention is also effective for quantitative analysis of the combustion process within an engine.

In addition, in the embodiments shown in FIGS. 4 and 6, both the measured material system (cell A or plasma chamber 20) and the reference material system (cell B or reference cell 25) are connected to the input laser beam. Although they are arranged in this order, they may be arranged in the reverse order. That is, the input laser beam may be configured to first pass through the reference material system and then input into the measured material system.

Further, as the reference material used in this invention, any material can be used as long as the Raman frequency is sufficiently close to that of the reference material (it can be covered by other laser light added together with the excitation laser light).

As explained above, according to the present invention, accurate quantitative analysis can be performed using one measurement system, and the cost can be reduced, and the number of adjustable parts is reduced, making the operation easier.

[Brief explanation of the drawing]

Figures 1 and 2 are diagrams explaining the principle of Kerse spectroscopy used in this invention, Figure 3 is a diagram explaining a conventional example of this invention, and Figure 4 is a diagram explaining an embodiment of this invention. , FIG. 5 is a graph showing a measurement example according to the present invention, and FIG. 6 is a diagram showing another embodiment of the present invention. 1, 3, 12... Mirror, 2... Dichroic mirror, 2'... Beam splitter, 7, 11, 1
9... Spectrometer, 13, 32... Dichroic mirror, 20... Plasma chamber, 25... Reference cell, A, B... Cell.

Claims (1)

[Claims] 1. A second system filled with a reference substance is arranged in series with a first system filled with a substance to be measured, and a first laser beam for excitation and the substance to be measured and the second system filled with a reference substance are arranged in series. A second laser beam that both has the Stokes frequency of the reference material is added to the first and second systems, and the laser beam that has passed through the first system and second system is incident on a spectroscope. The concentration of the substance to be measured is determined from the intensity ratio between the signal output corresponding to the substance to be measured and the signal output corresponding to the reference substance generated in different channels of the multi-channel detector. A quantitative analysis method using Curse spectroscopy that detects 2. The quantitative analysis method using Kerse spectroscopy according to claim 1, wherein the substance to be measured is silane gas or disilane gas, and the reference substance is carbon monoxide. 3. A first means for oscillating a first laser beam for excitation, and a second means for oscillating a second laser beam that includes both the Stokes frequency of the substance to be measured and the reference substance.
a third means for combining the first laser beam and the second laser beam to form an input laser beam; a first chamber filled with the substance to be measured; On the other hand, a second chamber is arranged in series with the first chamber and filled with the reference substance at a predetermined concentration, and a laser beam that has passed through the first chamber and the second chamber is divided into different wavelengths. a spectrometer having a multi-channel detector for detection in channels, and from the intensity ratio of the signal output corresponding to the measured substance and the signal output corresponding to the reference substance occurring in different channels of the multi-channel detector. A quantitative analysis device using Curse spectroscopy, which detects the concentration of the substance to be measured.