JPH0629856B2 - Fiber-optical probe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Field The present invention relates to fiber-optical probes useful for both light scattering and luminescence.

Prior Art The use of light to measure certain physical and chemical properties has been known in the laboratory for quite some time. For example, both qualitative and quantitative analyzes are often performed using spectroscopic techniques. The advent of lasers and optical fibers has greatly increased activity in this area.
In particular, optical fibers allow the placement of sensitive and expensive equipment at locations remote from the harsh reactor environment, making optical analysis techniques suitable for commercial production process applications.

One of the analytical methods that is useful in commercial production applications is Raman spectroscopy (Raman spectroscopy). When light of a single wavelength interacts with a molecule, the light scattered by the molecule contains a small amount of light having a different wavelength than the incident light. This is known as the Raman effect. The wavelengths present in the scattered light are unique to the structure of the molecules, and the intensity of this light depends on the concentration of these molecules. Therefore, the identity and concentration of various molecules in a substance can be determined by illuminating the substance with a single wavelength of light (monochromatic light) and then measuring the individual wavelengths in the scattered light and their intensities. You can ask for it. Details of Raman spectroscopy are discussed in US Pat. No. 3,556,659, in which additional references are cited regarding the theory of Raman effects.

The main difficulty with Raman spectroscopy is the small intensity of scattered light compared to excitation light. An elaborate spectrometer with high light collection and (light) dispersion, high stray light rejection, and sensitive detector is needed to isolate and measure Raman scattered light of low intensity. These devices are expensive, vulnerable, and therefore not well suited for use in commercial production or process equipment. As a result, they are rarely used outside the laboratory environment. A simplified fiber-optic probe that can be placed at a point remote from the light source and from the spectrometer makes Raman spectroscopy available for analysis of commercial production processes.

In optical measurements, the detection probe is usually the area illuminated by the light-transmitting (light-transmitting) fibers to the sample and the area seen by the light-collecting (light-collecting) fibers from the sample. The structure is designed to maximize the overlap between them. So ideally, according to Hirschfeld, his paper “Remote Fiber Fluorimetric Analysis”,
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A single fiber should be used for both light transmission and collection, as discussed on page 7. However, Raman spectroscopy cannot be realized due to the low intensity of scattered light. The light propagating through the fiber excites the molecules of the fiber itself, thus causing scattering in the fiber, which interferes with the scattered light collected by the fiber from the sample. Therefore, it is necessary to use multi-fiber probes with fibers that perform independent functions of light propagation and light collection.

A probe having two fibers is disclosed in JP-A-55-12549.
No. However, that reference teaches the need for a lens to focus the laser (excitation) light at the fiber ends and to collect the Raman (scattered) light. A suitable linear array of these focusing lenses is necessarily critical to achieving a common image point, but due to the very small diameter of the fibers (typically 100 microns or less). Alignment is difficult to achieve. As a result, the focusing lens adds significant cost and complexity to the probe, making it less attractive for commercial production processes.

<Object and Structure of the Invention> The present invention provides a relatively simple probe that is useful for Raman analysis and can be easily retrofitted to many different purposes.

The present invention provides a fiber-optical probe for sensitive Raman analysis, which is effective for light scattering or luminescence measurement.
It has the advantage of not requiring a focusing lens, and (a) at least one optical fiber for propagating light into the sample; and (b) at least two for collecting light from the sample for Raman analysis. Optical fibers, the collecting fibers are closely spaced to the propagating fibers, and the longitudinal axis of the collecting fibers is converging on the longitudinal axis of the propagating fibers. And a convergence angle of less than 45 °, which is a fiber-optical probe.

The present invention also provides a fiber-optical probe for sensitive Raman analysis, useful for light scattering or luminescence measurements, which generally has the advantage of not requiring a focusing lens, and (a) At least one optical fiber for propagating light; and (b) at least two optical fibers for collecting light from the sample for Raman analysis, the collecting fiber being in close proximity to the propagating fiber. A fiber-optical probe which is related and in which the longitudinal axis of the collecting fiber is converging on the longitudinal axis of the propagating fiber, and thus the convergence angle is less than 45 °. Raman spectroscopic analysis characterized in that laser light is made incident on a propagating fiber to propagate to a sample, and light scattered in the sample is collected by a collecting fiber and propagated to a Raman spectrometer. Is the way. In the present invention, convergence means that both axes are arranged so that the axes of the fibers for collection and propagation in the longitudinal direction are intersected, and the convergence angle is the intersection of the above axes. The angle formed by the thing.

<Detailed Description of Embodiment> The probe of the present invention uses at least one optical fiber for propagating light into a sample, while at least two optical fibers arranged at an angle to the propagating fiber. Consists of optical fibers bundled into a bundle, characterized in that they are also used for collecting light from the sample. The probe may also have a shield that hides the bundle and protects the bundle from the hostile environment in which it is inserted.

The expression of bundling optical fibers into a "bundle" implies that a close packing arrangement is desired for the fiber axes that are substantially parallel and for the minimum spacing between the fiber ends. This means that the fiber ends are preferably in contact with each other.

The terms "optical fiber" and "fiber-optical" are used interchangeably herein to refer to a fiber capable of light propagation. The term "fiber" is intended to include both single or mono and multifilament optical fibers.

A single optical fiber for light propagation into the sample is sufficient for typical applications. In order to maximize the overlap between the area illuminated by the single fibers and the area visible to all of the collecting fibers, it is preferred to place the single propagating fibers in the center of the fiber bundle. The collecting fibers can then be placed around the propagating fibers. FIG. 1 shows a probe 10 having a propagating fiber 11 surrounded by six collecting fibers 12.

The intensity of the Raman signal that can be generated using the probe of the present invention decreases dramatically as the spacing between individual fibers within the probe itself increases. Therefore, it is preferable to minimize the distance between the fibers in the bundle. Most preferably, the ends of the fibers are in direct (contact) contact with each other. To achieve this minimum distance in the above arrangement where a single central propagating fiber is surrounded by multiple collecting fibers, the propagating fiber diameter must not be greater than the collecting fiber diameter. Is.

The greater the number of collecting fibers in the probe, the greater the amount of Raman scattered light that can be collected, and thus the greater the Raman signal generated. In the probe of the present invention, two collecting fibers work well, but preferably there are 3 to 7 collecting fibers arranged around the propagating fiber. The highly preferred arrangement of FIG. 1 is a probe with one central propagating fiber surrounded by six collecting fibers 12.

The fibers of the probe of the present invention are preferably single filament fibers. Each fiber has a transparent core 13, usually made of glass or fused silica, which is encased in a transparent cladding 14 having a lower index of refraction than the core. Each fiber is covered by an opaque jacket 15. These fibers have a diameter of 50 microns to 1,000
Available on the market with core dimensions in the micron range. To facilitate effective collection of Raman scattered light and construction of the probe, it is preferable to use optical fibers having a core diameter in the range of 200 to 700 microns. In this range, optical fibers having a core diameter of about 600 microns are most preferred.

In addition to minimizing the distance between the fibers in the bundle, changing the angle 16 between the central longitudinal axis 17 of the propagating fibers and the central longitudinal axis 18 of the collecting fibers changes the probe. It has been found that the performance of the is improved. The performance of the probe is improved if the end of the collecting fiber is slightly inclined toward the center of the probe, and thus the axis of the collecting fiber and the axis of the propagating fiber are slightly converged at the fiber end. . The performance improvement increases as the convergence angle increases from 0 ° to angles between 10 ° and 20 °. Performance decreases as the convergence angle increases beyond this range, resulting in about 4
The performance at a 5 ° convergence angle is almost the same as when the fibers are parallel (0 ° convergence angle).

The desired convergence angle is only a certain length from the end of the fiber when the probe is made, for example 5 mm,
This is accomplished by removing the protective jacket 15 from the fiber and clinching the fiber ends (for a minimum distance) to produce the desired angle. Keeping the fibers in place by trapping them in heat shrink tubing 19. Alternatively, the convergence angle of the fibers can be adjusted by placing small shims between the fibers at a distance from the ends of the fiber bundle.

The present invention is directed to optical fiber-probes that can be used in a variety of different industrial applications. In these applications, the probe may be exposed to different environments, some of which may be harmful to the fiber itself. Under these circumstances, it is necessary to protect the environment from the environment by wrapping the fiber bundles in protective shells. The structure of such shells, including shell materials, will vary depending on the particular environment. The shell will need to have a structure suitable for insertion and connection to a process vessel such as a reactor.

FIG. 2 shows an example of the shell structure required. A tube 20 encloses the fiber bundle (not shown) and has a window 21 extending across the end of the tube adjacent the end of the fiber. The window should have sufficient optical clarity so as not to interfere or alter the propagation of light from and to the fiber ends. Suitable materials for windows are eg fused silica,
Alternatively, it is a crystal of sapphire and diamond. Window 21
Is sealed across the tube 20 by a gasket 22 placed in a shell cap 23, the gasket forming a pressure (or interference) fit with the tube. Other methods for sealing the cap 23 to the tube may also be applied, for example a threaded fit. The cap is shown as having a convex aperture 24 that is illuminated by the fibers and is sloped away from the window so that it does not interfere with the visible area.

The substances used as components of the protective shell must withstand the environment for which the probe is intended. In many applications,
Monel steel is a suitable material for shell tube 20 and shell cap 23, and nickel is a suitable material for gasket 22. Another type of protective shell that has been found to be effective is one made entirely of glass with optically polished ends adjacent the ends of the (optical-fiber) bundle. This completely eliminates the need for a separate window and sealing gasket.

Operation When the fiber-optical probe of the present invention is used for the purpose of Raman spectroscopy, it is necessary to use light generated by a laser as excitation light. A suitable light source is an argon ion laser.

At a distance from the probe, the central propagating fiber is separated from the other fibers of the bundle and optically connected to the laser using methods well known to those skilled in the art. The end of the remaining collecting fiber that emerged from the probe is the structure connected to the Raman spectrometer. For such connections the fiber ends are preferably arranged linearly. With proper connection to the laser and Raman spectrometer, the probe is inserted into the medium to be analyzed. The laser light is then incident on the propagating fiber to propagate the light into the medium. The collecting fiber collects the light scattered in the medium and propagates the light back to the spectrometer for analysis.

The optical fiber probe of the present invention is also effective for other light scattering and luminescence measurements, such as fluorescence. For such applications, it would be possible to use light sources other than lasers, including light emitting diodes. The present invention is directed to all such applications of this optical fiber probe.

[Brief description of drawings]

FIG. 1 is a perspective view of a preferred embodiment of an array of fibers within a probe, showing a partial cross section. FIG. 2 is a side view showing a cross section of an embodiment of a protective shell for a probe.

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Claims (8)

[Claims] 1. A fiber-optical probe for high-sensitivity Raman analysis and effective for light scattering or luminescence measurement, which has the advantage of generally not requiring a focusing lens, and At least one optical fiber for propagating light; and (b) at least two optical fibers for collecting light from the sample for Raman analysis, the collecting fiber being in close proximity to the propagating fiber. A fiber-optical probe which is related and in which the longitudinal axis of the collecting fiber is converging on the longitudinal axis of the propagating fiber, and thus the convergence angle is less than 45 °. . 2. The invention as set forth in claim 1, wherein the fiber ends are gathered in a bundle and the propagating fibers are arranged in the center of the bundle.
The probe according to item. 3. The probe according to claim 1, wherein the fiber is a monofilament fiber, and the core diameter of the propagating fiber is not larger than the core diameter of the collecting fiber. 4. The probe according to claim 1, 2 or 3 having a convergence angle of 10 ° to 20 °. 5. The probe according to any one of claims 1 to 4, wherein one probe fiber and three to seven collecting fibers are provided. 6. The probe according to any one of claims 1 to 5, wherein the fiber core diameter is 200 to 700 microns. 7. The probe of claim 6 wherein each fiber core has a diameter of about 600 microns. 8. A fiber-optical probe for high-sensitivity Raman analysis and effective for light scattering or luminescence measurement, which has the advantage of generally not requiring a focusing lens, and (a) At least one optical fiber for propagating light; and (b) at least two optical fibers for collecting light from the sample for Raman analysis, the collecting fiber being in close proximity to the propagating fiber. A fiber-optical probe which is related and in which the longitudinal axis of the collecting fiber is converging on the longitudinal axis of the propagating fiber, and thus the convergence angle is less than 45 °. Raman spectroscopic analysis method, wherein laser light is incident on a propagation fiber to propagate to a sample, and light scattered in the sample is collected by a collection fiber and propagated to a Raman spectrometer.