JPS6381228A - Optical analysis instrument - Google Patents

Abstract

PURPOSE:To eliminate the dependency on wavelength at the time of analysis and to facilitate qualitative and quantitative analyses by projecting the exit light spectrally split by a spectroscopic prism to a prism for internal reflection at the incident angle corresponding to the wavelength thereof. CONSTITUTION:The dependency of the depth of penetration of the electric field from the base of the prism 1 for internal reflection on the wavelength is eliminated if the incident light 3 on the prism 1 for internal reflection is dispersively projected thereto at the incident angle 5 corresponding to the wavelength thereof. The detection depth from the front surface of a sample 2 in an internal reflection method is therefore, maintained nearly constant in a wide wavelength region of light. The qualitative and quantitative analyses are thereby facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an improvement in an optical analysis device used, for example, for structural analysis of thin films.

(Prior Art) The internal reflection method (ATR method) using a prism is a method used to measure the absorption spectrum of a sample that is difficult to measure using a normal transmission method. This ATR method, as shown in Figure 4,
The sample 2 is brought into close contact with the bottom of the high refractive index (n) prism 1, and the light 3 is totally reflected from the prism side at the interface (θC
The reflected light 4 is made incident at <90°, θC: critical angle), and the resulting reflected light 4 is separated into spectra, and changes in reflectance are recorded with respect to wavelength.

If the sample does not absorb any light, the light will be totally reflected at the interface; however, if the sample absorbs light, the reflectance will decrease according to the degree of absorption, so the obtained spectrum will be similar to that of normal transmission. It looks very similar to a spectrum. This is because light enters when reflected at the interface, and it is thought that the absorption of the sample during that time is related to the reflectance.

As can be seen from the above, the total reflection spectrum is related only to the thin layer on the sample surface that is in close contact with the optical plane of the high refractive index medium of the sample, so it is a method that is very suitable for studying thin films and surface layers. be. Therefore, in recent years, the human TR method has been widely used for structural analysis of monomolecular films and cumulative films using infrared/visible/ultraviolet spectroscopy.

However, in this ATR method, the penetration depth of the electric field of light during internal reflection largely depends on the wavelength of the incident light. has become a major obstacle. For example, if the sample is a thin film with a layered structure, in a certain wavelength range of light, only a spectrum from a single layer can be obtained, but in other wavelength ranges, spectra from multiple layers can be obtained. It is completely impossible to analyze the structure of a film from a spectrum in a wide range of wavenumbers.

(Problems to be solved by the invention) As mentioned above, the optical analyzer using the conventional ATR method has
The downside is that the depth of penetration of the electric field of light into the sample largely depends on the wavelength of the light, making it difficult to perform qualitative/quantitative analysis or structural analysis of the sample. The present invention
It is an object of the present invention to provide an optical analysis device that improves this drawback.

[Structure of the invention]

(Means for Solving the Problems) The present invention includes a prism for internal reflection, a spectroscopic prism, an optical system that guides all the emitted light from the spectroscopic prism to the prism for internal reflection, and a prism for internal reflection. In a spectrometer equipped with an optical system that guides the emitted light from a prism to a photodetector, an optical arrangement is adopted in which the emitted light separated by the spectroscopic prism is incident on the internal reflection prism at an incident angle corresponding to its wavelength. The present invention relates to an optical analysis device comprising:

The present invention will be explained in more detail below.

In the ATR method, the electric field penetration depth (dp) of internally reflected light toward the sample side is determined by the internal reflection prism (ATR
The refractive index of the prism) and the sample are each “1 e”*
The angle between the incident light and the normal to the bottom of the human TR prism is θ,
If the wavelength of the incident light is human, then λ dp= ・・・・・・・・・
...-ti>2π(nlsin"θ-nl).

When the incident angle θ of light is fixed as shown in equation (1), when the wavelength λ changes, the electric field penetration depth (dp) changes in proportion to it. Therefore, in order to keep the electric field penetration depth (dp) constant, both the wavelength λ and the incident angle θ of the incident light may be changed according to the following equation (2).

After the white light is spectrally dispersed by a spectroscopic optical element such as a prism or a diffraction grating, this light is transferred to the ATR prism as described above (2).
If the light is incident at an angle of incidence that satisfies the equation ), it becomes possible to perform analysis using the ATR method in which the depth of electric field penetration (dp) is constant with respect to the wavelength (λ) of the incident light.

(Function) By distributing the incident light to the ATR prism at an incident angle according to its wavelength, the wavelength (λ) dependence of the electric field penetration depth (dp) from the bottom of the ATR prism is eliminated. As a result, the detection depth from the sample surface in the ATR method can be made almost constant over a wide wavelength range of light, and qualitative and quantitative analysis can be easily performed from the spectrum obtained by the optical analyzer of the present invention. become.

(Example) Hereinafter, an example will be described based on FIGS. 1, 2, and 3.

When the refractive index of the TR prism used is n1==3 and the refractive index of the sample is n,=l,5, the change in the depth of penetration of the electric field of light (dp) with respect to the wavelength of light (λ) is The illustrations are shown in FIG. 1 at various angles of incidence (θ).

The wavelength range of light in this figure is the wavelength range generally used for infrared spectroscopy.

θ is the critical angle θc (= s !n' (-”) = 39
') to 90°, so 2.5~2
Although it is not possible to obtain a completely constant ctp in a wide wavelength range of 5 μm, it is possible to keep dp within a very narrow range, as shown by the thick solid line in the figure, and to make it almost constant. Furthermore, it is clear from FIG. 1 that it is possible to keep dp completely constant in a narrower wavelength range.

By the way, when a regular triangular prism KBr prism is used as the spectroscopy prism, the deflection angle δ of light of 2.5 to 25 μm by the prism is as shown by the broken line in FIG.

In FIG. 2, the change in θ on the thick solid line in FIG. 1 is also shown by a solid line. Although the scales of the δ and θ axes are different, they are in a proportional relationship, and since the two curves of θ and δ change in almost the same way on this graph, the light is emitted from the spectroscopic prism in the relationship shown by the broken line. It is possible to make the light incident on the ATR prism in a relationship very close to that of θ. An example of an optical system that implements this is shown in FIG.

The white light 13 incident on the KBr prism (spectral prism) 7 exits the prism at a deflection angle shown by the broken line in FIG. The separated light has a focus of 0. ．． 0.
and 0. ．． 0. With two spheroidal mirrors 8 and 9 held in
The light is made incident on the ATR prism 1 at an incident angle as indicated by the solid line in FIG. The light emitted from the ATR prism has a focal point of 0. ．． 0
The light is condensed by a spheroidal mirror 10 held at 4, and then enters a photodetector 12 through a concave fill.

[Efficacy of invention]

According to the present invention, since there is no wavelength dependence during analysis, qualitative and quantitative analysis becomes easy.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the wavelength of light (λ) and the depth of electric field penetration (dp) in the ATR prism, and Figure 2 is a graph showing the relationship between the wavelength of light (λ) and the deflection angle by the KBr prism. FIG. 2 is a schematic diagram showing the relationship between the two and the system for the ATR prism. 1... Prism for internal reflection (ATR prism) 2.
...sample, 3...incident light, 4...outgoing light, 5...
Incident angle, 6...Critical angle, 7...Spectroscopy prism, 8
, 9.10...Spheroidal mirror, 11...Concave mirror, 1
2...Photodetector, 13...White light. Agent Patent Attorney Noriyuki Ken Yudo Takehana Kikuo's Mu Nagairi (,'Jm) Figure 1 Yumeranami Omoteiri (Aim) Figure 2 Figure 4

Claims (1)

[Claims] An internal reflection prism, a spectroscopic prism, an optical system that guides all the light emitted from the spectroscopic prism to the internal reflection prism, and an optical system that guides the emitted light from the internal reflection prism to the internal reflection prism. The device is equipped with an optical system that guides the light to the detector, and is characterized by comprising an optical arrangement that causes the emitted light separated by the spectroscopy prism to enter the internal reflection prism at an incident angle corresponding to the wavelength thereof. Optical analysis device.